laser irradiation of electrode materials for energy
TRANSCRIPT
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Review
Laser Irradiation of Electrode Materialsfor Energy Storage and Conversion
Han Hu,1,* Qiang Li,2 Linqing Li,1 Xiaoling Teng,1 Zhaoxuan Feng,1 Yunlong Zhang,1 Mingbo Wu,1,*
and Jieshan Qiu3,4,*
Progress and Potential
Electrode materials capable of
electrochemical energy storage
and conversion are of paramount
importance in promoting the
application of new energy
technologies and have attracted
tremendous research efforts in the
past decades. The efficient
technologies that can elaborately
regulate the structure of electrode
materials at atomic-, nano-, micro-
, and even macroscales are thus
actively pursued with remarkable
progress. Among all the available
technologies, laser irradiation
stands out because of its
advantage of rapid, selective, and
programmable materials
processing at low thermal
budgets. Here, the recent efforts
on regulating energy storage and
conversion materials using laser
irradiation are comprehensively
summarized. The uniqueness of
laser irradiation, such as rapid
heating and cooling, excellent
controllability, and low thermal
budget, is highlighted to shed
some light on the further
development of this emerging
field.
In addition to its traditional use, laser irradiation has found extendedapplication in controlled manipulation of electrode materials forelectrochemical energy storage and conversion, which are primarilyenabled by the laser-driven rapid, selective, and programmable ma-terials processing at low thermal budgets. In this Review, we summa-rize the recent progress of laser-mediated engineering of electrodematerials, with special emphases on its capability of controlled intro-duction of structural defects, precise fabrication of heterostructures,and elaborate construction of integrated electrode architectures—all of which are highly desired for many electrochemical processes,yet difficult to be precisely synthesized via conventional technolo-gies. After a brief introduction of the fundamental mechanismof laser processing, its practical use for structural regulation of elec-trode materials is discussed in detail. The application of these laser-enabled materials for supercapacitors, rechargeable batteries, andsome fundamental electrocatalytic reactions enabling energy con-version is then summarized. Finally, we highlight the challengesfaced at the current stage, aiming to shed some light on the futuredevelopment of this prosperous field.
INTRODUCTION
The imminent shortage of fossil fuels, along with the soaring concerns about envi-
ronmental pollution, calls for revolutionizing the manner of our energy utiliza-
tion.1–4 In this regard, renewable energy sources, such as solar, wind, and hydro,
have been widely explored to promote the sustainable development of our soci-
ety.5–7 Because of the intermittency and geographical dispersion of these resources,
electrochemical energy storage and conversion systems are of paramount impor-
tance for their efficient utilization.8 In a reliable sustainable system, electricity gener-
ated from these renewable sources can either be directly stored in rechargeable
batteries and supercapacitors as power supplies or be first converted into clean fuels
via electrolyzers and then reproduced as electricity through fuel cells on demand.5,8
Although these devices operate using different mechanisms, they employ similar
device configurations whereby two separated electrodes are ionically connected
by electrolytes.5 The aforementioned electrochemical processes mainly take place
at the electrode, thus making the exploration of advanced electrode materials a
primary task for the further development of these electrochemical technologies. In
the past decades, tremendous research efforts have been devoted to maneuvering
the structures of electrode materials to boost performance, with remarkable prog-
ress being achieved.9,10 With reasonably designed synthesis and manipulation
strategies, electrode materials with diverse compositions, morphologies, dimen-
sions, and sizes have been controllably synthesized, contributing to a well-estab-
lished structure-performance relationship. The recent advance in characterization
Matter 3, 95–126, July 1, 2020 ª 2020 Elsevier Inc. 95
1State Key Lab of Heavy Oil Processing, Instituteof New Energy, College of ChemicalEngineering, China University of Petroleum (EastChina), Qingdao 266580, China
2College of Physics, Qingdao University,Qingdao 266071, China
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technologies reveals that the structural defects within electrode materials hold great
promise to boost the performance of energy storage and conversion devices
because of the structural defect-induced electronic reconfiguration facilitating the
favorable adsorption of active species.11,12 Heterostructures are also capable of
serving as highly active sites due to the synergistic effects arising from the interaction
of different components.13 Nevertheless, traditional technologies employ tedious
procedures at high thermal budgets to produce these structures but with unsatisfac-
tory controllability.14 In addition to these atomic-scale and nanoscale structural fea-
tures, the real performances also largely depend on the electrode architectures
assembled by the electrode materials, while the easy and cost-effective fabrication
of electrode architecture capable of rapid mass and/or charge transfer remains a
formidable challenge.15
Recently, laser irradiation has been demonstrated as a powerful tool for controllably
endowing the electrode materials with the aforementioned structural merits yet at
low thermal budgets.16–18 In contrast to the conventional reaction environments
created by traditional methods, a soaring temperature is generally observed with
a focused laser beam irradiating the desired location, which is then accompanied
by a rapid cooling after the irradiation.19,20 This rapid heating and cooling can create
a unique reaction condition that benefits the direct preservation of structural defects
in the final products, for example the incorporation of pentagons and heptagons
within the hexagon lattice of graphene.21 Besides, the irradiation processes can
be precisely controlled allowing the site-specific heating to drive reactions at de-
manded positions, thus producing the heterostructures in a highly controlled
manner.22 Moreover, the laser irradiation technology can be digitally controlled
via computer-aided design and be compatible with a myriad of emerging materials
processing technologies, such as three-dimensional (3D) printing and, roll-to-roll
fabrication, holding promising potential to elaborately manipulate the electrode
architectures for enhanced performance.19
The past decade has witnessed the immense progress of laser-mediated manipulation
of electrode materials at atomic-, nano-, and macroscales. Despite these achievements,
this field still remains in its infancy and continues to require the extensive attention of re-
searchers with different backgrounds. Thus, we focus here on the role of laser irradiation
on structural regulation of electrode materials for energy storage and conversion. After
an initial discussion of the fundamental mechanism of laser processing, we then concen-
trate on the uniqueness of laser processing technology, such as controlled introduction
of structural defects, precise fabrication of heterostructures, and elaborate construction
of integrated electrode architectures, all of which are extremely helpful in facilitating the
electrochemical energy storage and conversion processes, as illustrated in Fig-
ure 1.2,11,21–26 Next, the capability of these structural merits for boosting the electro-
chemical performance is reviewed. Finally, we discuss briefly the existing challenges
and opportunities of this emerging field.
3State Key Lab of Fine Chemicals, School ofChemical Engineering, Liaoning Key Lab forEnergy Materials and Chemical Engineering,Dalian University of Technology, Dalian 116024,China
4College of Chemical Engineering, BeijingUniversity of Chemical Technology, Beijing100029, China
*Correspondence: [email protected] (H.H.),[email protected] (M.W.),[email protected] (J.Q.)
https://doi.org/10.1016/j.matt.2020.05.001
LASER-MATERIALS INTERACTION
Theoretically, laser results from stimulated radiation. In particular, an incident
photon will cause the decay of an excited electron of a material to the ground state
if they possess the identical energy, as shown in Figure 2A, accompanied by the
emission of another photon possessing frequency and phase identical to those of
the incident one.27 These two photons will then propagate in a constructive interfer-
ence manner and trigger the decay of another excited electron with similar energy.
By repeating this process, light with significantly increased intensity and a well-
96 Matter 3, 95–126, July 1, 2020
Figure 1. Laser-Mediated Structural Regulation of Electrode Materials
(A) Intrinsic defects-rich graphene by laser scribing polymer. Reproduced with permission from Lin
et al.21 Copyright 2014, Springer Nature.
(B) Ultra-fine Co3O4 nanoparticles with oxygen vacancies synthesized by lasing Co metal in liquid.
Reproduced with permission from Li et al.24 Copyright 2019, Wiley-VCH.
(C) Air-stable p-n junction directly constructed on graphene by laser scanning. Reproduced with
permission from Seo et al.22 Copyright 2014, American Chemistry Society.
(D) Laser-mediated synthesis of NiO/NiFe LDH heterostructures. Reproduced with permission from
Gao et al.23 Copyright 2019, Wiley-VCH.
(E) An innovative water-splitting device enabled by laser processing. Reproduced with permission
from Zhang et al.25 Copyright 2014, American Chemical Society.
(F) Patterned supercapacitor arrays fabricated by laser scribing GO membrane. Reproduced with
permission from El-Kady et al.26 Copyright 2015, National Academy of Sciences.
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defined frequency will be produced, which is termed laser. Up to now a broad spec-
trum of active materials has been employed to produce laser, enabling highly
tunable wavelengths from UV to infrared (Figure 2B).28 The thus-generated laser fea-
tures high directionality, coherence, andmonochromaticity.20 The directionality and
coherence enable superheating at localized regions while the monochromaticity
permits selective processing.29 Because of these features, laser stands out as an
emerging technology while developing remarkable progress in a myriad of applica-
tions including materials synthesis, modification, and processing.
Laser-Induced Effects
Light illumination can drive a number of electron and molecule motions. Because of
its high intensity, laser irradiation is capable of fundamentally intensifying these mo-
tions, giving rise to a sequence of unique effects.29,31 For example, an extremely
Matter 3, 95–126, July 1, 2020 97
Figure 2. Generation and Types of Lasers as well as Laser-Induced Effects
(A) Illustration of the stimulated emission. Reproduced with permission from Wang and Gao.27 Copyright 2019, Elsevier.
(B) The wavelengths of laser from different active media. Reproduced with permission from Li.28 Copyright 2020, AIP Publishing.
(C) Illustration of different types of laser-induced effects. Reproduced with permission from Palneedi et al.20 Copyright 2019, Wiley-VCH.
(D) Time-resolved shadowgraph images of ejected Si species under laser irradiation. Reproduced with permission from Russo et al.30 Copyright 1999,
Springer Nature.
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strong excitation of free electrons and/or vibrations, depending on the photores-
ponse of the irradiated materials, could be induced, which will be dissipated as
strong heat in well-defined localized regions. Del Pino et al. reported a stimulated
temperature profile showing a rapid rise to almost 1,200 K within a timescale of
10�8 s on a laser-irradiated NiO-coated carbon nanotubes (CNTs) array.32 This tem-
perature is sufficient to drive the synthesis of a wide range of nanomaterials (Fig-
ure 2C).20,29 Moreover, the recrystallization and phase transformation of many
materials are also possible under this laser-incurred condition via which metastable
materials with high performance for energy-related applications can be pro-
duced.20,33,34 At higher intensity, the irradiated materials will melt because of
more intense energy absorbed at the irradiated areas, contributing to the welding
of individual subunits to form a continuous and highly conductive network.35 The
liquid front at the surface of the melted materials will then vaporize and eject species
into the surrounding environment at continuously increased laser intensity. Russo
et al. observed the fierce ejection of particles from the surface of melted Si under
laser irradiation, as shown in Figure 2D.30 These ejected species strongly interact
with the incident laser beams and become ionized to produce plasma at irradiance
above a threshold while the plasma can accelerate the ejection of the irradiated
species. These ejected species can either be directly collected as ultra-fine
nanomaterials for subsequent use or be confined in reactive media to produce other
nanostructured compounds.16,36,37 Such flexibility of modulating the reaction envi-
ronments further endows the laser-mediated materials synthesis with a highly
tunable and versatile feature. For irradiated materials under extremely strong
laser irradiance ablation will occur, thus making it capable of producing designable
patterns.38 The ablation effect has been widely used to directly construct
microenergy storage andconversion devices for on-chip electronics and/or wear-
able devices.39–41
98 Matter 3, 95–126, July 1, 2020
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Factors Influencing the Laser-Mediated Materials Processing
The extent of the aforementioned processes, such as heating, melting, vaporization,
plasma, and ablation, is primarily dependent on the intensity of the incident laser. As
a result, the fluence of laser plays a pivotal role in determining their occurrence. Fig-
ure 2C depicts the parameter regimes of different laser-induced effects.20,29 As
shown, a threshold power density is required to be overcome between each region.
For example, the laser welding (melt region) generally requires a power density of
105 W cm�2 while the fragmentation (vapor region) is usually performed at a power
density larger than 107 W cm�2.
Laser can be operated either continuously or in a pulsed manner. The continuous
wave (CW) laser features good coherence, which permits a stable beam profile
and energy output.29 The long duration allows the in situ generated heat to be effec-
tively conducted for uniform thermal distribution. For the pulsed laser, the irradia-
tion lasts in the timescale of microseconds (ms), nanoseconds (ns), picoseconds
(ps), and even femtoseconds (fs) in each pulse, resulting in extremely high transient
powers capable of generating a well-defined localized superheating and subse-
quent rapid self-quenching. In this regard, structural defects and metastable phases
are essentially frozen in the final products.16,29 Moreover, the high transient powers
make the pulsed laser more energy efficient compared with the CW laser.
One key advantage of laser processing is the selectivity, which is realized by ratio-
nally matching laser of a certain wavelength with the irradiated materials.37,42 As a
result, the wavelength represents another key parameter that needs to be carefully
considered in liberating the advantage of laser processing.43 A typical example is to
selectively burn off the amorphous carbon impurity covered nanodiamonds (NDs)
using an infrared laser of 1,064 nm.43 Specifically, amorphous carbon offers a strong
absorption of infrared radiation while NDs are transparent to it. Thus, the amorphous
carbon covering the NDs can be selectively burned off under infrared laser irradia-
tion, purifying the NDs. In another attempt, large particles were fragmented into
small ones under the infrared laser to produce monodisperse quantum dots.42 Basi-
cally, the band gap of nanoparticles, for example PbS nanoparticles, is related to
their size, whereby the larger ones possess narrower band gaps. As a result, the
exclusive excitation and fragmentation of larger particles are feasible under incident
laser with a long wavelength (Figures 3A and 3B), contributing to a monodispersed
colloidal dispersion shown in Figure 3C.16,42
Laser irradiation can be carried out in different media, such as vacuum conditions,
ambient atmosphere, inert conditions, and liquids.16,21,36,44,47 Thesemedia strongly
affect the laser-induced effects as well as the materials thus obtained. Figures 3D
and 3E compare the scanning electron microscopy (SEM) images of laser-induced
graphene (LIG) synthesized under different conditions. Specifically, the products
synthesized in an ambient atmosphere (Figure 3D) are super-hydrophilic while the
LIGs (Figure 3E) produced in an inert atmosphere are super-hydrophobic.44 Besides,
the composition of laser-irradiated materials can either remain the same as the irra-
diated targets if the media are inert or be converted into other compounds by intro-
ducing reactive environments.24,48 Moreover, the progressive structural evolution,
for example from nanospherical, to yolk-shelled, hollow, and nanocubic morphol-
ogies with tunable compositions, is achieved by gradually increasing the reactivity
of the reaction medium, as illustrated in Figure 3F.45 Meanwhile, the repeating
time of laser irradiation (frequency) also significantly affects the morphology and
size of the obtained materials. This is mainly due to the different possibilities of
exposing the as-formed products to the subsequent lasing. At lower repeating rates,
Matter 3, 95–126, July 1, 2020 99
Figure 3. Analysis of the Influence of Lasing Parameters on Final Products
(A) Scheme of laser fragmentation of large particles in liquid. Reproduced with permission from
Zhang et al.16 Copyright 2017, American Chemical Society.
(B and C) Electron microscopy observation of PbS nanoparticles before (B) and after (C) laser
irradiation. Reproduced with permission from Yang et al.42 Copyright 2013, Springer Nature.
(D and E) SEM images of LIG synthesized in air with super-hydrophilicity (D) and LIG in argon with
super-hydrophobicity (E). Reproduced with permission from Li et al.44 Copyright 2017, Wiley-VCH.
(F) Morphology evolution of laser-induced materials with liquid reactivity and repeating time of
laser irradiation. Reproduced with permission from Niu et al.45 Copyright 2010, American Chemical
Society.
(G) Illustration of influence of the working distance on the heated area. Reproduced with
permission from Chyan et al.46 Copyright 2018, American Chemical Society.
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the as-formed particles will move away while a secondary pulse of these particles is
highly possible at higher rates. Thus, the gradual evolution of size andmorphology is
observed along with the increased repeating rates. In addition, the working distance
also influences the structural features of the as-formed products.46 As shown in Fig-
ure 3G, the spot size of the laser beam will be enlarged at defocused positions, thus
producing a decreased power density. In this case, the thermal effect will then be
changed, resulting in final products with different structural features.
Due to the broad spectrum of laser sources and highly tunable operations, a large
number of laser-mediated materials synthesis technologies have been proposed,
such as pulsed laser deposition (PLD), direct laser writing (DLW), laser fragmentation
in liquid (LFL), laser-assisted pyrolysis (LAP), and selective laser sintering, to name a
few.16,36,49,50 These approaches only represent a minor portion of the newly devel-
oped laser-mediated technologies in recent years, which reveal a prosperous filed
100 Matter 3, 95–126, July 1, 2020
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deserving worldwide attention. Of particular note is their intrinsic capability of
precisely regulating materials at low thermal budgets, essentially opening up an
alternative avenue to developing new materials for energy storage and conversion.
LASER-MEDIATED STRUCTURAL REGULATION OF ENERGYMATERIALS
Energy storage and conversion involve electrochemical processes that are directly
driven by electrons at the electrode materials, such as nanocarbons, transition metal
compounds, and metal nanocrystals.8 As a result, the local electronic configurations
of electrode materials play a pivotal role in determining their performance.51–53
Recent advances have revealed that structural defects and heterostructures are of
paramount importance in regulating the electronic configurations.13,52 From the
viewpoint of real application, the diffusion path of the active species within the elec-
trode architectures also strongly affects the overall electrochemical performance.2
As an emerging and highly efficient materials processing technology, laser irradia-
tion has been widely used to precisely modulate the aforementioned structures,
and its remarkable progress is summarized here and its advantages highlighted by
comparing it with traditional strategies. Moreover, the key parameters of lasing,
such as wavelength, operational mode, and power density, are described to gain
an insightful view of different laser irradiation processes.
Laser-Mediated Defects Engineering
The defects in nanocarbons primarily exist in the form of non-metal heteroatoms,
intrinsic defects, and metal single-atom sites while the defects in transition metal
compounds are mainly heteroatoms and anion vacancies, for example oxygen va-
cancies.11 The defects of metal nanocrystals, especially noble metal nanocrystals,
are primarily found at stacking faults, grain boundaries, and metal single-atom sites.
Because of these apparent differences, the defects engineering for nanocarbon,
transition metal compounds, and metal nanocrystals is discussed separately.
Defects Engineering of Nanocarbons
The non-metal heteroatoms are mainly introduced by substituting carbon atoms in
carbon materials with other non-metal elements, such as N, B, S, and P.54 Because of
the difference in electronegativity, the density of states and charge population of the
non-polar C–C bonds will be essentially changed after heteroatoms doping, which
could provide favorable pathways for many electrochemical reactions.55 The current
technologies for this purpose involve the carbonization of the dopant-containing
precursors in an inert atmosphere and thermal annealing of carbon materials in
the presence of heteroatom precursors, both of which are energy intensive and
time consuming and require sophisticated apparatus.56–58 In contrast, the direct
lasing of heteroatom-containing precursors has been demonstrated as a viable
means to produce heteroatom-doped carbon materials at much higher efficiency
and lower thermal budget.59–61 A convincing example is the direct growth of nitro-
gen-doped graphene (NG) on the surface of N-SiC using an excimer laser with a
wavelength of 308 nm (pulse duration: 30 ns).62 As shown in Figures 4A–4D, the
pulsed laser irradiation (power density: 3.73 107W cm�2) can induce a superheating
as high as 3,000 K within 100 ns, which is sufficient to evaporate Si atoms and reor-
ganize the remaining C and N atoms, giving rise to NG directly on the surface of
N-SiC as revealed from the transmission electron microscopy (TEM) image (Fig-
ure 4C) and X-ray photoelectron spectroscopy (XPS) profile (Figure 4D). The time
required for producing NG by laser-mediated epitaxial growth is only 60 s, whereas
many hours are needed to complete this process via traditional annealing processes.
Thus, nitrogen-containing polymers, for example polyimide (PI), have been
Matter 3, 95–126, July 1, 2020 101
Figure 4. Engineering Defects in Nanocarbons by Laser Irradiation
(A–D) Illustration of in situ growth of NG on N-SiC by pulsed laser irradiation (A) and the stimulated temperature profiles under laser irradiation (B). TEM
image (C) and XPS analysis (D) of the as-produced NG. Reproduced with permission from Choi et al.62 Copyright 2014, American Chemical Society.
(E–G) Illustration of synthesis procedure of B-LIG (E), and structural characterizations including SEM image (F) and XPS profiles (G). Reproduced with
permission from Peng et al.60 Copyright 2015, American Chemical Society.
(H–J) TEM image of the laser-irradiated graphene nanosheets (H), their nitrogen sorption isotherms (I), and evolution of N configuration at different
laser irradiations (J). Reproduced with permission from Wang et al.64 Copyright 2018, Wiley-VCH.
(K and L) TEM (K) and AC-STEM (L) images of LIG. Reproduced with permission from Lin et al.21 Copyright 2014, Springer Nature.
(M–Q) Illustration of laser-mediated modulation of metal single-atom sites. SEM image (M) and AC-STEM image (N) of Co single-atom site catalysts
before laser treatment. SEM image (O) and AC-STEM image (P) of them after laser irradiation. (Q) Co K-edge XANES spectra revealing the existence of
Co single-atom sites. Reproduced with permission from Gong et al.65 Copyright 2019, Wiley-VCH.
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irradiated by laser to produce NG rapidly. The Nd:YAG laser with a wavelength of
1,064 nm is employed to directly scan over a PI film in an ambient condition to
generate porous graphene with a suitable N content of 5 wt %.63 Nevertheless,
only a minor amount of N will be detected in the final carbon materials if the Nd:YAG
laser is replaced with a CO2 one (wavelength: 10.6 mm; pulse duration: 14 ms; power
density:�105 W cm�2).21 The reason may be associated with the distinct heating be-
haviors of PI incurred by laser irradiations of different wavelengths.12,63 These results
strongly suggest the influence of laser’s wavelength on the final products, indicative
of the powerful capability of highly controlled structural regulation. Other hetero-
atoms, such as B, S, and F, have also been doped into carbon materials under laser
irradiance.33,60,61 In such an attempt, the mixed solution of poly(amic acid) and
H3BO3 was polymerized into a PI/H3BO3 composite film and then converted into bo-
ron-doped LIG (B-LIG) driven by a CO2 laser, as illustrated in Figures 4E–4G.60 A
large pattern made of B-LIG of several centimeters was realized within seconds,
revealing the extremely high efficiency of this technology. The dual-doped carbon
102 Matter 3, 95–126, July 1, 2020
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materials were also realized under laser irradiation by simply formulating their pre-
cursors.59 A dimethyl sulfoxide-dispersed polybenzimidazole ink was irradiated
under an UV laser of 355 nm for this purpose. The energy of the UV laser is larger
than the bond energy of C–S and C–N bonds, which would lead to their activation
and cleavage, generating the active S and N species to produce N, S-codoped gra-
phene. Apart from its high efficiency, another paramount advantage of laser-medi-
ated doping of carbon materials is the high controllability whereby the configura-
tions of heteroatoms within carbon materials can be precisely modulated. Wang
et al. reported that the type and content of N configurations could be accurately
manipulated by a laser-mediated process.64 Specifically, a pulsed laser (wavelength:
1,064 nm; pulse: 7 ns; power density: �107 W cm�2) irradiation with gradually
increased energy inputs illuminated on graphene oxide (GO), leading to a mono-
tonic increase of the amount and density of in-planemesopores on these nanosheets
(Figures 4H and 4I). Interestingly, these mesoporous sites favored the formation of
pyridinic N configuration in the subsequent treatment (Figure 4J), allowing the pro-
duction of pyridinic N-dominated graphene nanosheets. Such a highly controlled
yet facile manipulation of heteroatom configurations in carbon materials has seldom
been realized using other technologies. As a result, the laser-induced heteroatom-
doped carbon may serve as an excellent platform to unravel the structure-perfor-
mance relationship at the atomic-scale.
The latest advances have unveiled the powerful capability of non-hexagonal rings
within graphene domains, namely intrinsic carbon defects, in boostingmany electro-
chemical processes, which rekindles strong interest in this type of structural fea-
tures.51,66 Specifically, these defects could contribute to local surface charges that
serve as the adsorption, activation, or storage sites for foreign species during the
electrochemical processes. The nitrogen-removal procedure fromN-doped carbons
at around 1,000�C has been suggested as a reliable method to controllably intro-
duce these defects.51,66 Another widely used technology is the carbonization of pre-
cursors in the presence of high surface tension introduced by hard templates.67
Laser-mediated materials processing features a high self-quenching rate that can
directly freeze defects in the final products, offering an alternative means to produce
intrinsic defects-enriched carbon materials.68 In particular, the CO2 laser (wave-
length: 10.6 mm; pulse duration: 14 ms; power density: �105 W cm�2) was employed
to irradiate PI film to cause a rapid temperature rise, promoting the liberation of un-
stable functional groups and reorganization of the remaining carbon atoms.21 Rapid
cooling then follows the irradiation, which prevents the achievement of full equilib-
rium condition for all carbon atoms. The thus-generated graphene nanosheets offer
rich wrinkles at the edge (Figure 4K) and ultra-polycrystallinity on the plane where
the crystalline cores are surrounded by pentagon-heptagon pairs, as revealed by
the aberration-corrected scanning TEM (AC-STEM) images shown in Figures 1A
and 4L. The amount and density of the intrinsic defects in carbon materials have
been systematically modulated through carrying out the syntheses at different con-
ditions. The pulsed laser with a shorter wavelength irradiation permits a higher heat-
ing and cooling rate, whereby more intrinsic defects would be preserved in the final
products. As a result, a larger ID/IG ratio is observed from the 1,064-nm infrared
laser-derived graphene.21,63 Guan et al. reported the laser-mediated reduction of
GO (wavelength: 1,064 nm; pulse duration: 10 ps; power density: �107 W cm�2)
in distinct reaction media, namely nitrogen atmosphere and liquid nitrogen, to
modulate the intrinsic defects. The extremely cold environment provided by liquid
nitrogen may retard the temperature rise, finally resulting in a product with fewer de-
fects.69 In addition, the density of the defects can be maneuvered by multiple
lasing.46,70 After the first laser-mediated carbonization of PI, the energy input
Matter 3, 95–126, July 1, 2020 103
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from the subsequent lasing is capable of driving the graphitization of the as-synthe-
sized carbon materials, thus leading to gradual decrease in the density of the
intrinsic defects.46 As a result, the content of intrinsic defects in the final carbon ma-
terials can be modulated.
Another type of emerging structural defects in carbonmaterials drawing close atten-
tion is metal single-atom sites.11,71 The most well-known site affords a metal
porphyrin-like structure with one metal atom coordinated by four N atoms on the
carbon substrate. Such a structure features the unsaturated coordination that favors
activation of the reactants.71 Moreover, this type of structure is extremely stable and
can be used in strong acid and alkaline conditions applicable for a wide range of
electrochemical processes. In a recent study, Gong et al. demonstrated laser-medi-
ated regulation of metal single-atom sites (Figures 4M–4Q).65 First, the carbon nano-
polyhedrons made of CNTs (Figures 4M and 4N) with abundant Co single-atom sites
were prepared by a facile pyrolysis method,72 via which a large number of these sites
were deeply confined within the CNTs. The existence of Co single-atom sites is
confirmed by the AC-STEM observation (Figure 4N) and Co K-edge X-ray absorption
near-edge structure (XANES) spectra (Figure 4Q). Laser irradiation (wavelength:
355 nm; pulse width: 6 ns; power density:�107 W cm�2) in water was then employed
to selectively destroy the polyhedrons as well as break the CNT structure, liberating
the Co single-atom sites, as shown in Figures 4O–4Q.
The defects in carbon materials are mainly formed through the conversion pro-
cesses. As shown in Figure 2C, a relatively low power density is needed to drive
these processes. To freeze the defects in the final product a rapid self-quenching
is usually required, which makes pulsed laser irradiation the preferable choice of
technologies. The most widely used laser for producing defective carbon is the
CO2 laser with microsecond pulse durations.15,21 To produce defects by partially de-
stroying the as-formed carbon materials, the required power density is much higher
when laser irradiation with shorter pulse duration is generally chosen.64,65
Defects Engineering of Transition Metal Compounds
Similar to the doping treatments of carbon materials, the heteroatoms can also be
incorporated into lattices of transition metal compounds through either laser-medi-
ated in situ processes, whereby the heteroatoms are introduced during the synthesis
of transition metal compounds, or post-treatment by lasing the as-synthesized tran-
sition metal compounds in the presence of dopants. A typical apparatus enabling
mass production of the in situ doped transition metal compounds is schematically
illustrated in Figure 5A.73 The reactants including the precursor of the metal com-
pounds and dopants are evaporated and brought into the reaction chamber by
the carrying gases. Meanwhile, an incident laser beam is irradiated on the aerosol
of the reactants, triggering the chemical reactions to produce heteroatom-doped
transition metal compounds, for example N-SnO2 (Figure 5B). Whereas the tradi-
tional technologies, such as sputtering and wet chemical processes, either offer a
low yield or require tedious procedures. The N content in the final products can
be modulated by simply varying the formulation of the reactants, as shown in Fig-
ure 5C. In addition, cations have been doped into transition metal compounds in
a highly tunable manner by lasing the precursors with intentionally introduced
doping cations. Through this process, a widely used electrocatalyst for oxygen evo-
lution reaction (OER), namely NiFe layered double hydroxide (LDH), was doped with
Ti4+ and La3+ ions with tunable contents (wavelength: 355 nm, pulse duration: 8 ns;
pulse energy: �107 W cm�2).74 In contrast to the in situ strategy enabling bulk
doping, the post-lasing treatment allows site-specific doping with an accurately
104 Matter 3, 95–126, July 1, 2020
Figure 5. Typical Examples of Defects Engineering of Nanostructured Transition Metal Compounds
(A–C) Illustration of the LAP apparatus for mass production of heteroatom-doped transition metal compounds (A). TEM image (B) and XPS profiles (C) of
the as-produced N-SnO2. Reproduced with permission from Wang et al.73 Copyright 2017, Wiley-VCH.
(D and E) Illustration of the site-specific doping of MoS2 nanosheets with phosphorus (D) and the PL mapping of the P-MoS2 nanosheet revealing the
site-specific doping (E). Reproduced with permission from Kim et al.75 Copyright 2016, Wiley-VCH.
(F and G) Schematic illustration of the oxygen-vacancy Co3O4 nanoparticles (F) and TEM image of oxygen-vacancy Co3O4 nanoparticles with ultra-small
size and high uniformity (G). Reproduced with permission from Li et al.24 Copyright 2019, Wiley-VCH.
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controlled doping degree and position, benefiting from the site-specific laser
heating.75 In this process, laser first induces heating of the target materials,
leading to the creation of vacancies. The dopant molecules will be activated and
then fill the vacancies, giving rise to the doped transition metal compounds. Grigor-
opoulos’ group suggested the first example of the site-specific phosphorus doping
of MoS2 nanosheets by irradiating them (wavelength: 532 nm; CW; power density:
�106W cm�2) in the presence of PH3, which was verified by enhanced photolumines-
cence (PL) intensity in the doped area (Figures 5D and 5E).
Anion vacancies represent another intriguing structural defect of transition metal
compounds with rising interest for energy-related applications.24,76 The vacancies
can decrease the valence state of the metal ions, thus contributing to an increased
donor density. In this regard, the kinetics of redox reactions would be essentially
improved, consequently boosting the electrochemical performance.76 Traditionally,
these vacancies are introduced by reducing the compounds at elevated tempera-
tures that require a high thermal budget and long processing time.14 Moreover,
the controllability of these processes is generally poor. LFL technology intrinsically
holds the potential to endow the final products with anion vacancies.16 In general,
Matter 3, 95–126, July 1, 2020 105
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LFL features rapid heating andcooling, which essentially favors the formation of
these defects.14 These defects can substantially provide surface charges to stabilize
the as-formed particles without surfactants in solutions. As a result, the laser-
enabled anion vacancies-enriched nanomaterials benefit the exploration of the
intrinsic electrochemical performance of the defective materials.16 Fundamentally,
LFL is a physically top-down process whereby the anion vacancies are mainly distrib-
uted on the exterior surface. To introduce interior vacancies favoring electrical con-
ductivity, the further combination of this physical process with in situ chemical reac-
tions has been proposed.24 For example, the pulsed laser (wavelength: 1,064 nm;
pulse duration: 7 ns; pulse energy: �109 W cm�2) vaporized Co target, generating
the Co vapors that further reacted with dissolved oxygen in water to produce ul-
tra-small Co3O4 nanoparticles possessing both exterior and interior oxygen va-
cancies, is shown in Figures 5F and 5G.24 Despite these remarkable advantages,
LFL technology offers a very low efficiency. As a result, innovative strategies capable
of mass production, for example lasing the target in flowing liquids,77 are actively
pursued to surmount this deficiency.
Defects Engineering of Metal Nanocrystals
Stacking faults within metal nanocrystals are generated by altering the stacking se-
quences of metal atoms, which could introduce multiple step sites as shown in Fig-
ure 6A.78 Because of the broken periodic crystallinity at these sites, the coordination
number of surface atoms and the electronic structures of these crystals are changed.
As a result, adsorption and interaction with the reactants and intermediates can be
essentially modulated, thus leading to improved catalytic performance.79 Surpris-
ingly, the intrinsically non-active metal nanocrystals, for example Ag nanoparticles,
could bemodulated into powerfully electrocatalysts for hydrogen evolution reaction
(HER) after introducing stacking faults. The ablation of an Ag target immersed in
water with pulsed laser (wavelength: 1,064 nm, pulse duration: 7 ns, pulse energy:
�109 W cm�2) could cause the vaporization of the metal while the surrounding water
immediately cools down the hot Ag nanodroplets. The extremely fast quenching
effect causes the collapse of the close-packed Ag(111) plane, giving rise to abundant
stacking faults as revealed from the AC high-angle-annular-dark-field STEM
(AC-HAADF-STEM) image in Figure 6B.78
Grain boundaries are found at the joint regions of different crystalline orientations
within nanocrystals.79 The lattices along these boundaries are largely distorted,
via which local strain is induced at these sites. In this regard, modified d-band cen-
ters with improved adsorption capabilities toward the active species are produced
for favorable catalytic processes. Pd nanocrystals with largely distorted lattices (Fig-
ure 6C) were produced through lasing a Pd foil (wavelength: 1,064 nm, pulse dura-
tion: 7 ns; pulse energy: �108 W cm�2) in a diluted NaCl solution where the concen-
tration of NaCl plays a key role in determining the content of the grain boundaries.80
Recently, metal nanocrystals have been demonstrated as an excellent substrate to
load metal single-atom sites. The electron transfer between the metal single atoms
and substrate elements can modulate the adsorption energy toward the reactants
and/or intermediates. In contrast to multi-step processes via traditional syntheses,82
a facile one-pot lasing process has been proposed. Specifically, a Ru plate immersed
in an aqueous solution of HAuCl4 was irradiated by a nanosecond laser with a wave-
length of 1,064 nm for 30 min. Because of the high temperature, the fragmented Ru
particles could induce the thermal decomposition of the HAuCl4 and then be
quenched to produce the Au single-atom sites supported by Ru nanoparticles cata-
lysts (Figures 6D–6F).81
106 Matter 3, 95–126, July 1, 2020
Figure 6. Typical Defects in Metal Nanocrystals
(A and B) Illustration of stacking fault (A) and AC-HAADF-STEM image (B) of stacking faults in Ag
nanocrystal. Reproduced with the permission from Li et al.78 Copyright 2019, Springer Nature.
(C) AC-HAADF-STEM image of a polycrystalline Pd nanoparticle with obvious grain boundaries.
Reproduced with the permission from Lin et al.80 Copyright 2019, Royal Society of Chemistry.
(D–F) Element mapping (D) of an individual Ru nanoparticle supported Au single atoms and its AC-
HAADF-STEM images (E and F). The Au atoms are marked by red circles. Reproduced with
permission from Chen et al.81 Copyright 2019, Wiley-VCH.
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In contrast to the defects in carbon materials, the intrinsic defects within transition
metal compounds and metal nanocrystals are mainly formed through physical frag-
mentation of the irradiated metal and/or metal compound targets. Compared with
the formation of defects within carbon materials, the fragmentation processes
require higher transient power densities. As a result, the short-pulsed laser is gener-
ally used for this purpose. Moreover, the confining liquids that contribute to a reac-
tion environment with higher densities of activated species, higher temperatures,
and higher pressures are usually employed to facilitate formation of defects-rich
structures.83 As a result, LFL represents the preferable choice of technology for intro-
ducing defects, especially intrinsic defects within metal and metal compounds.
Laser-Assisted Fabrication of Heterostructures
Heterostructures refer to a type of structure made of intimately coupled multiple
components with different compositions, phases, or other properties.84–87 In
contrast to the single-component electrode materials, synergistic effects can gener-
ally be reaped at the interface where the advantages of different components are
cooperatively harnessed. The one-step direct conversion of the mixed precursors
via which different components are simultaneously generated and hybridized in
situ represents the most straightforward and effective means to harvest heterostruc-
tures.88 Recently, laser has been used to irradiate the mixed precursors for the con-
struction of such structures (Figure 7A).89 Compared with the traditionally used
methods, a laser-mediated process can significantly reduce the reaction time from
many hours to several minutes and even seconds, suggesting an essentially
improved efficiency. Currently the most widely reported heterostructures from
laser-mediated processes mainly consist of nanocarbons and transition metals as
well as their compounds. The successfully fabricated structures include but are not
Matter 3, 95–126, July 1, 2020 107
Figure 7. Laser-Mediated Fabrication of Heterostructures
(A) Typical process of one-step laser-mediated synthesis of heterostructures. Reproduced with permission from Ye et al.89 Copyright 2015, American
Chemical Society.
(B and C) TEM images of MoO2 (B) and Fe3O4 (C) embedded in carbon matrix by one-step lasing. Reproduced with the permission from Ye et al.89
Copyright 2015, American Chemical Society.
(D) TEM image of the Pt-Co alloy-carbon composition synthesized by LAP. Reproduced with permission fromMartinez et al.91 Copyright 2018, Martinez,
Malumbres, Lopez, Mallada, Hueso, and Santamaria.
(E) TEM images of MOF nanorods-decorated graphene nanosheets. Reproduced with permission from Wu et al.97 Copyright 2019, Wiley-VCH.
(F) TEM image of the Ni nanoparticles-supported NiFe LDH interfaces. Reproduced with permission from Gao et al.23 Copyright 2019, Wiley-VCH.
(G) Illustration of construction of metal/semiconductor heterostructures by lasing their mixture. Reproduced with permission from Yu et al.98 Copyright
2017, Royal Society of Chemistry.
(H and I) Schematic of construction of the rGO-GO heterostructure (H) and its optical image (I). Reproduced with permission from Cheng et al.99
Copyright 2013, Wiley-VCH.
(J–L) Illustration of creation of arbitrarily shaped p-n junction on graphene nanosheets. Resistance versus gate voltage curves (J) and Raman patterns (K)
of organic matter-coated graphene before and after laser irradiation. Schematic of creation of arbitrary shaped p-n junctions on graphene through DLW
(L). Reproduced with permission from Seo et al.22 Copyright 2014, American Chemical Society.
llReview
limited to Fe3O4/LIG, Co3O4/graphene, MoO2/LIG, Ni/carbon, NiFe/LIG, MoS2/car-
bon, crystallized TiO2/porous carbon, MoC/graphene, and Pt-Co alloy/carbon,
where the ultra-small particles of transition metals and/or their compounds are uni-
formly and intimately embedded in the highly conductive carbon frameworks as
shown in Figures 7B–7D.89–94 In addition to these achievements, the highly
controlled heating enabled by laser irradiation permits intriguing heterostructures
108 Matter 3, 95–126, July 1, 2020
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that have rarely been realized by other methods. A scalable graphene membrane
with different carbonization degrees along the vertical direction made by elabo-
rately controlling the lasing process (wavelength: 1,064 nm; CW) contributes to a
Janus super-hydrophobic/super-hydrophilic structure.95 In another attempt, Jiang
et al. reported a free-standingmembranemade of Cu nanoparticles-embedded gra-
phene nanosheets by simply lasing (wavelength: 1,064 nm, pulse duration: 80 ns;
power density: �106–107 W cm�2) metal-organic frameworks (MOF) particles where
the formation of metal-graphene composite nanoparticles are accompanied by
simultaneously stitching these particles at their boundaries.96 The one-step laser-
mediated fabrication of these novel materials has essentially enlarged the scope
of heterostructures, allowing diverse possibilities of intriguingly constructing energy
storage and conversion materials with desired performance.
Despite these remarkable achievements, the success of the one-step fabrication of
heterostructures is limited to only a few types of materials featuring high thermal sta-
bility, and the structures thus obtainedmainly exist in the form of nanoparticles firmly
embedded in the carbon frameworks. In this regard, the multi-step construction of
such structures has been proposed for delicate controls over the compositions
and morphologies. In this technology, laser irradiation is used to produce compo-
nents and intermediates of heterostructures as well as to help efficiently bond mul-
tiple components together. LIG has served as an outstanding substrate to uniformly
load a wealth of less stable components. For example, conductive polymers, ferro-
cene nanoparticles, MOF nanorods (Figure 7E), and ultrathinMnO2 nanosheets have
been incorporated with the graphene nanosheets via the subsequent vapor deposi-
tion, solvothermal growth, and electrodeposition.26,97,100,101 In another attempt,
laser has been employed to trigger the domino-like self-propagating reactions
in graphene oxide decorated with metal salts, generating reduced GO and metal/
metal oxide composites.102,103 These components, if thermally stable, can also be
introduced via a subsequent lasing process.104 Instead of being firmly embedded
in the matrix framework, the subsequently introduced nanostructured metal and/
or metal compounds are uniformly dispersed on the surface of the matrix.105 As a
result, the synthesis strategies should be carefully considered based on the require-
ments of final applications. The laser-induced intermediate was observed in the
construction of NiO/NiFe LDHs. First, the Ni and Fe targets were immersed in a
urea-containing solution.23 The ultra-fine particles isolated from the targets by the
pulsed laser irradiation (wavelength: 1,064 nm, pulse duration: 7 ns; power density:
�108 W cm�2) reacted with urea derivatives in the solution to produce ultra-large
NiFe LDH nanosheets with uniformly decorated Ni nanoparticles, as revealed in Fig-
ure 7F. These metal particles were then converted into NiO strongly bonded with
NiFe LDH, giving a well-defined interface as illustrated in Figure 1D. Another possi-
bility of multi-step construction of heterostructures mediated by laser is to induce
chemical bonding between different components. The physically mixed multiple
components undergo laser irradiation, via which chemical reactions occur at their
interfaces to give heterostructures, as illustrated from the construction of metal/
semiconductor heterostructures shown in Figure 7G (wavelength: 1,064 nm, pulse
duration: 8 ns; power density: �107 W cm�2).98 The ultrafast heating process allevi-
ates the possibility of structural damage to different components generally
observed during long annealing.
The highly controlled heating of laser irradiation further leads to the fabrication of
novel site-specific heterostructures, which has seldom been cost-efficiently realized
through other technologies.22,106 In such an attempt, the conductive and hydropho-
bic reduced graphene oxide (rGO) patterns were directly created on the insulating
Matter 3, 95–126, July 1, 2020 109
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and hydrophilic GO fiber via a one-step lasing process using a 458-nm argon-
ion laser, generating GO-rGO heterostructures capable of moisture-triggered
actuation and direct energy storage (Figures 7H and 7I).99,107 In addition, a DLW
process (wavelength: 532 nm, CW; power density: �106 W cm�2) was applied
on a 6,13-bis(triisopropylsilylethynyl)pentacene coated initially p-type graphene
film, via which n-type regions of arbitrary shapes were created, as shown in
Figures 7J–7L and 1C.22,106 Moreover, the doping degree can be continuously regu-
lated by gradually changing the intensity and duration of lasing. Traditionally the
construction of this type of heterostructure requires sophisticated equipment and
laborious processes, whereas the laser-mediated technology allows their simple
yet reliable generation.
Laser-Mediated Construction of Electrodes
In real devices for energy storage and conversion, the electrodematerials function in
aggregated forms where the materials, polymer binder, and conductive additives
are glued together to produce an electrode with a thickness of several tens, and
even hundreds of micrometers.108 The active species in the electrolytes are trans-
ferred to the surfaces of materials through the pores of the electrode architectures,
engaging in the electron-driven electrochemical processes. As a result, the perfor-
mance is highly dependent on the architecture of the electrodes, triggering exten-
sive interest in their rational design.109 Among them, the integrated electrode
architectures have attracted increasing attention because they can eliminate the
polymer binders and conductive additives that usually cause undesired interfaces.
Moreover, the integrated design affords delicate control of the porosity that facili-
tates the transfer of the active species, benefiting the overall energy storage and
conversion. Kaner’s group pioneered the research of laser-mediated construction
of electrodes. The whole electrode construction process was conducted within a
cheap and commercially available LightScribe CD/DVD optical drive.110 The drop-
cast GO film was reduced under infrared laser irradiation (wavelength: 788 nm,
optimal energy input: 5 mW), where the liberation of gases drove the formation of
an integrated porous structure made of interconnected graphene nanosheets, as
illustrated in Figure 8A. The graphene-based electrode thus obtained affords a
large specific surface area, high conductivity, and mechanical robustness. The en-
ergy intensity of the laser plays a key role in determining the uniformity of the
thus-obtained electrodes, as a higher energy intensity usually introduces cracks on
the electrodes.111
In addition to GO, other precursors including carbon quantum dots and polymer
have also been converted into integrated electrodes under laser irradiation. The hi-
erarchical control of the porosity at micro-, meso-, and macroscales was reported by
lasing (wavelength: 10.6 mm) the polymer precursor of ordered mesoporous carbon
coated on a substrate.116 Regarding the carbon dots precursor, the closely packed
carbon dots will undergo the removal of surface functional groups and reconstruc-
tion under laser irradiation (wavelength: 10.6 mm), leading to a 3D interconnected
porous network possessing a large surface area and high conductivity.117 This pro-
cess may have to be carried out in an inert atmosphere to eliminate the influence of
oxygen in the ambient atmosphere for better capacitive performance.47 In contrast,
the rationally selected polymer precursors can be directly converted into conductive
networks without the protection of inert gases enabled by lasing, significantly simpli-
fying the electrode construction process.21 The intensive laser-mediated heating of
the polymer could lead to a strong gas evolution, protecting the rearrangement of
the carbon atoms from being oxidized. On the other hand, the released gases
may help the orientation of the as-formed graphene nanosheets. As shown in
110 Matter 3, 95–126, July 1, 2020
Figure 8. Direct Engineering of Electrodes by Laser Processing
(A) Direct construction of an integrated electrode by lasing a free-standing GO. Reproduced with permission from El-Kady et al.110 Copyright 2012,
American Association for the Advancement of Science.
(B) SEM image of the LIG (top view). Reproduced with permission from Lin et al.21 Copyright 2014, Springer Nature.
(C) Typical SEM image of the LIG (side view). Reproduced with permission from Duy et al.112 Copyright 2018, Elsevier.
(D) Illustration of creation of microchannels on the blade-cast AC electrodes. Reproduced with permission from Hwang et al.113 Copyright 2017,
Wiley-VCH.
(E) Scheme of construction of complex structures by combining laser irradiation and laminated object manufacturing technology. Reproduced with
permission from Luong et al.114 Copyright 2018, Wiley-VCH.
(F) Digital image of a large graphene electrode (1,400 cm2) enabled by laser irradiation. Reproduced with permission from Wang et al.115 Copyright
2018, Wiley-VCH.
(G) Illustration of arbitrarily shaped electrodes and devices directly fabricated on GO films. Reproduced with permission from Gao et al.107 Copyright
2011, Springer Nature.
(H) Scheme of series and parallel connected devices. Reproduced with permission from El-Kady et al.26 Copyright 2015, National Academy of Sciences.
(I) Typical process of fabricating a device via the laser ablation process. Reproduced with permission from Peng et al.41 Copyright 2016, Royal Society
of Chemistry.
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Figures 8B and 8C, the as-formed nanosheets are prone to be perpendicular to the
substrate, allowing efficient charge transfer over a long distance.21,112 The thickness
of the patterned integrated electrode is tunable by varying the power of laser, and
an ultra-thick electrode of around 100 mm is produced at an average laser power of
7.5 W.118 Laser irradiation (wavelength: 10.6 mm) has also been employed to modu-
late the common blade-cast activated carbon electrode, via which microchannels
connecting the internal pores of activated carbon are formed.113 As a result, a better
means of electrolyte storage is available, as illustrated in Figure 8D, facilitating the
improved rate performance. Meanwhile, the precursors of the electrode materials
have been directly coated on current collectors and converted into highly porous
and conductive architecture.119 Such innovative research reveals that the laser-
mediated structural regulation is compatible with the current industrial technologies
Matter 3, 95–126, July 1, 2020 111
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and holds prospective potential for real applications. Another promising aspect for
laser-mediated construction of electrodes is its applicability on almost arbitrary sub-
strates.46 As such, the tedious processes of embedding energy storage and conver-
sion devices on textile fabric will be essentially predigested, providing simple yet
efficient strategies for the emerging application of wearable electronics.
Laser-mediated materials processing has been rationally combined with a myriad of
advanced manufacturing technologies for more precise control over the electrode
architectures and promoting their mass production. By repeating the precursor
loading and lasing process, a 3D graphene foam was generated capable of energy
storage and conversion at highmass loadings.120 Figure 8E exhibits the combination
of laser irradiation with the rising laminated object manufacturing, a newly devel-
oped additive-manufacturing technology to fabricate desired objectives through
consecutively layering, bonding, and tailoring the laminated building units to pre-
cisely modulate the morphology and porosity of a 3D graphene foam.114 First the
laminated structure with an LIG layer on top of a PI film is prepared through laser
scribing, then one LIG layer adheres to another LIG layer while the extra PI layer is
removed through laser ablation. Repeating these processes can then lead to an
ultra-thick graphene foam. By rationally combining different lasers, the graphene
foams can be modulated into arbitrary shapes, as shown in Figure 8E. For the scal-
able production, a large-size (1,400 cm2) free-standing electrode, shown in Fig-
ure 8F,115 was produced through DLW (wavelength: 10.6 mm, pulse duration:
14 ms, power density: �106 W cm�2). The continuous production will be possible
through combination with a subsequent roll-to-roll process.115
Laser irradiation can be digitized by computer-aided design, permitting a program-
mable construction of patterned electrodes with arbitrary shapes and sizes (Fig-
ure 8G).107 Pairing the adjacent two electrodes results in a device ready for capaci-
tive energy harvest. Figure 8H illustrates that the series and parallel connections of
devices are also feasible, offering a flexible energy output.26 The strategies for direct
construction of these devices by laser irradiation can be categorized into the conver-
sion route and ablation means. For the conversion process, laser irradiation is used
to directly convert the intrinsically insulated substrate into conductive electrode pat-
terns for devices (Figure 8G).107 The possible substrates include GO, polymers,
fabrics, and biomass, among others, capable of being carbonized under laser irradi-
ation.46,110,121,122 Regarding ablation fabrication, the electrode materials are firstly
coated on the substrates decorated with thin layers of noble metals as current col-
lectors and the devices are then craved by laser ablation. In this regard, the desired
devices with a vast extended spectrum of materials such as carbon, metal com-
pounds, and MXenes have been successfully fabricated by this means.39,41,123 Of
particular note is that the use of MXenes, as shown in Figure 8I, can avoid the
employment of noble metal as current collectors because of their metallic
conductivity.41
APPLICATIONS OF LASER-ENABLED MATERIALS FOR ENERGYSTORAGE AND CONVERSION
Supercapacitors
Supercapacitors, capable of rapid charge and discharge, have found applications in
fields where high power densities are needed.124 Basically they use a symmetrical
configuration whereby the two electrodes are identical porous carbon-based elec-
trodes with high porosity as the electrolyte reservoir and large specific surface areas
for ion adsorption.125 The surface-dominated energy storage processes render
112 Matter 3, 95–126, July 1, 2020
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supercapacitors a super-long calendar life. Despite these advantages, the low en-
ergy densities largely impede their wide applications.1 To overcome this drawback
three main strategies, namely regulation of carbon’s microstructures, integration
of pseudocapacitive materials, and construction of hybrid devices, have been
proposed.126
The advantages of laser irradiation in facile yet elaborate structural regulation of elec-
trode materials enable an excellent platform from which to explore the structure-per-
formance relationship.40,127,128 The optimal laser-irradiated GO membrane offers a
highly porous network with a large specific surface area of 1,520 m2 g�1 and a record
conductivity of 1,738 S m�1 among the rGO network (Figure 8A).110 These structural
merits endow the device based on the as-prepared electrodes with outstanding
electrochemical performance. As shown in Figure 9A, its energy density and power
density are far superior to that of the traditional AC-based supercapacitors and
lithium-metal film batteries. The in situ generated and/or modified electrodes on cur-
rent collectors by laser irradiation, such as carbon nanodots-derived 3D graphene,
carbon spheres-based 3D carbon networks, and activated carbon electrodes with
laser-etched microchannels, also afford superior performance in terms of large spe-
cific capacitances, high rate capability, and long-term stability.113,117,129 LIG, rich in
intrinsic defects (Figure 4L), features ultra-polycrystalline structures endowing abun-
dant grain boundaries (Figures 9B–9E).21 These intrinsic defects produce an
enhanced metallic behavior and are supposed to induce an excellent capacitance
capability. As shown in Figures 9F–9H, a rectangle-shaped cyclic voltammetry curve
can be maintained even at a scan rate as high as 10 V s�1, and the calculated specific
capacitance at this rate is as high as 120 F g�1. A further improved performance is
observed after the introduction of B heteroatoms. As reflected from the galvanostatic
charge and discharge profiles of LIGs with different B doping, the specific capaci-
tance gradually ascends at first and then descends with the continuous increase of
the B content.60 The optimal B doping gives a specific capacitance 4-fold higher
than the undoped one. The authors suggested that the hole charge density, which
is responsible for the improved capacitive performance, increases proportionally
with the B content at lower doping degrees while more scattering sites are incorpo-
rated at higher B doping contents, resulting in deteriorated performance.
Besides directly serving as powerful electrodes for capacitive energy harvesting,
these laser-enabled porous carbons are also excellent platforms for loading pseudo-
capacitive materials because of their highly tunable surface chemistry for further
enhanced performance. Up to now, nanostructured MnO2, FeOOH, and conductive
polymer, for example, have been hybridized with the laser-derived porous carbon
skeleton to effectively harness pseudocapacitive energy.100,101,130 One promising
feature of this type of electrode is the retention of outstanding performance even
with ultra-thick electrodes. For example, the carbon-loaded MnO2 electrodes as
thick as 110 mm could still deliver an extremely large specific capacitance.100 The
perpendicularly oriented graphene nanosheets, which allow a long electron transfer
path along vertical direction, are primarily responsible for this extraordinary perfor-
mance.15 Another recent promising example was the solvothermal growth of
conductive MOF nanorods on LIG substrates (Figure 9I), which offered rapid redox
activity in both positive and negative potential ranges (Figure 9J).97 As a result, a
symmetric pseudocapacitive capacitor with a large voltage window was constructed
on these electrodes, as revealed in Figure 9K.
Appealing results were also found in laser-mediated supercapacitor devices with
in-plane configurations, sandwich geometries, fiber shapes, and even arbitrary
Matter 3, 95–126, July 1, 2020 113
Figure 9. Performance of Supercapacitors Based on Laser-Mediated Materials and/or Devices
(A) Ragone plot of supercapacitors based on laser-scribed GO electrodes and other typical devices. Reproduced with permission from El-Kady et al.110
Copyright 2012, American Association for the Advancement of Science.
(B–E) Theoretical calculation on the charge density of graphene after introducing intrinsic defects. Reproduced with permission from Lin et al.21
Copyright 2014, Springer Nature.
(F–H) Electrochemical performance of LIGs with intrinsic defects. Reproduced with permission from Lin et al.21 Copyright 2014, Springer Nature.
(I–K) Electrochemical performance of conductive MOF nanorods on graphene for capacitive energy harvest. Reproduced with permission from Wu
et al.97 Copyright 2019, Wiley-VCH.
(L–R) Illustration of customer-designed supercapacitors enabled by laser irradiation and their performance. Reproduced with permission from Gao
et al.38 Copyright 2019, American Chemical Society.
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morphologies.122,131 The programmable processing allows flexible series and paral-
lel connections of multiple devices, rendering dynamic energy output.127,132 An
elaborately modularized device array offers a large voltage of 10.8 V even at a
scan rate as high as 100 V s�1 and gives almost 100% capacitance retention after
100,000 charge/discharge cycles.133 In addition to carbon materials, a wealth of
pseudocapacitive materials have also been directly carved into supercapacitor de-
vices.134 Moreover, the rational combination of laser-mediated devices with other
114 Matter 3, 95–126, July 1, 2020
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materials deposition technology, for example electrochemical deposition, has led
to the on-chip hybrid devices with remarkably extended voltage windows thus
significantly enhancing energy densities.26,100,135 By selective deposition of MnO2
nanosheets on one of the porous carbon electrodes of the interdigitated micro-
supercapacitor, an asymmetric supercapacitor was built with an operating voltage
window of 2 V, which compares favorably to 1 V for the symmetric device. In this
regard, a 4-fold increase of the energy density for one device is realized.26 In addi-
tion to the essentially improved performance, the precise structural modulation
of devices by laser enables highly configuration-editable supercapacitors workable
in mechanically harsh conditions, for example in a greatly stretched condition.
Enlightened by the stereo paper cutting idea, the large planar graphene-based
supercapacitors were precisely cut into multi-dimensional configurations by laser
irradiation (wavelength: 355 nm) while the garland configuration allowed the
supercapacitors to be stably operated even at a 5-fold stretching, suggesting an
alternative approach to constructing flexible energy storage devices, as shown in
Figures 9L–9R.38
Rechargeable Batteries
Rechargeable batteries use different materials capable of reversible redox reac-
tions at distinct potentials to produce stable energy output. Abundant theoretical
possibilities of pairing materials possessing different potentials produce a broad
window of rechargeable batteries. Among them, lithium-ion batteries (LIBs), so-
dium-ion batteries (SIBs), lithium-sulfur batteries, and the newly emerging metal-
air batteries and lithium-metal batteries have aroused focused attention from
both scientific and industrial communities.136–138 In contrast to supercapacitors,
the bulk phase of batteries’ electrode materials is involved in energy storage, which
leads to higher energy densities. Nevertheless, this working mechanism inevitably
results in large volume expansion and sluggish reaction kinetics, both of which are
severely detrimental to their performance. As a result, the rational modulation of
electrode materials to mitigate the volume variation and accelerate the bulk-
phase-involved reactions represents one of the foremost topics in batteries
research.9
PLD has been widely used tomanipulate the electrodes for LIBs and SIBs.36,48,139–141
In a typical process, the target materials are fragmented into ultra-fine and amor-
phous particles by pulsed laser under a vacuum condition, and the ultra-fine frag-
mented particles are then directly collected by the current collectors ready for en-
ergy storage. The PLD-derived electrodes are in fact aggregations of small-sized
amorphous particles via which the active sites are essentially exposed and the diffu-
sion distance for metal ions is fundamentally shortened. Figure 10A exhibits the
typical structure of PLD-derived electrodes made of Fe2O3 nanoparticles, where
the particles are assembled into a highly porous film.36 Because of the small size
of individual particles, the diffusion kinetics of Li+ ions is significantly enhanced.
Moreover, the void among these particles is capable of effectively accommodating
the volume variation and improving the structure stability, as shown in Figure 10B.
The PLD technology shows wide applicability, and a vast spectrum of materials
have been successfully regulated into high-performance electrodes, such as
Fe2O3 (Figure 10C), Co3O4, MnO2, and SnO2. In addition, the PLD process is highly
flexible where electrodes with multiple components are also realized.141 Such a
tunable electrode construction may provide an alternative way to harvest synergistic
effects of different materials, thus offering a novel design rationale for further
improved performance. The major drawback of this technology is the low efficiency
and high requirement of a sophisticated vacuum system. This deficiency could be
Matter 3, 95–126, July 1, 2020 115
Figure 10. Laser-Enabled Materials and Devices for Rechargeable Batteries
(A and B) TEM (A) and SEM (B) images of the PLD-derived Fe2O3 electrode. Reproduced with permission from Teng et al.36 Copyright 2018, Springer
Nature.
(C) Electrochemical performance of PLD-derived Fe2O3 electrode for reversible lithium storage. Reproduced with permission from Teng et al.36
Copyright 2018, Springer Nature.
(D) Rate capabilities of N-SnO2 with different N content for lithium storage. Reproduced with permission fromWang et al.73 Copyright 2017, Wiley-VCH.
(E and F) Kinetics analysis of lithium storage in N-SnO2 with optimal N content. Reproduced with permission from Wang et al.73 Copyright 2017,
Wiley-VCH.
(G and I) Schematic illustration of fabrication Zn-ion batteries by laser ablation. Reproduced with permission from Shi et al.142 Copyright 2017,
Wiley-VCH.
(J) Comparison of electrochemical performance of laser-enabled Zn-ion batteries with typical energy storage devices. Reproduced with permission
from Shi et al.142 Copyright 2017, Wiley-VCH.
llReview
surmounted by novel equipment design; thus, knowledge from engineering and
physics is urgently required.
LAP and DLW represent two emerging laser-mediated materials processing tech-
nologies with high efficiency and have been successfully used to produce elec-
trode materials for rechargeable batteries.73,119 LAP is a continuous process
116 Matter 3, 95–126, July 1, 2020
llReview
and the industrial pilot apparatus has already realized a large production rate of
1 kg h�1.143 The key features of many electrode materials from LAP are their small
particle sizes and high surface areas, which are desirable for alleviating volume
variation and enhancing kinetic capability. A wide range of materials, including
metal oxides, metal carbides, and element nanostructures, have been success-
fully produced by LAP technology.73,144 Besides, this technology imposes easy
requirements on the precursors if only they can be excited by laser. For the laser
inactive precursors, the photosensitizer is added to trigger the synthesis reactions
of the electrode materials. In this regard, the applicability of LAP is almost infin-
ite. Not only the single-component materials but also the composites as well as
heteroatom-doped materials have been produced. Wang et al. reported the
N-SnO2 nanoparticles for reversible lithium storage.73 The thus-obtained SnO2
with the optimal N content affords a significantly improved performance in terms
of a large specific capacity, improved rate capability, and long-term stability,
shown in Figure 10D. Figures 10E and 10F unveil a surface controlled process
for lithium storage, which is responsible for the improved rate performance of
the N-SnO2 electrode materials. For a typical DLW-mediated electrode fabrica-
tion, the precursors of the electrode materials are loaded on the current collec-
tors, which are then directly converted into the active materials for Li+/Na+ up-
take and release. The key advantage is that the in situ heating process could
contribute to enhanced adherence between the active species and current collec-
tors for boosted stability. Zhang et al. reported an N-doped porous carbon elec-
trode as the anode for SIBs prepared by the DLW process (wavelength: 10.6 mm,
pulse duration: 14 ms, laser power: �106 W cm�2).119 The pure carbon-based
electrodes show a specific capacity of 425 mAh g�1 after 100 cycles at a current
density of 0.1 A g�1.
In addition to the synthesis of electrode materials, laser has also been demonstrated
as a powerful tool to directly regulate the as-prepared electrode for improved per-
formance. A pulsed laser is used to scan the surface of the electrode to create
patterned microchannels capable of further alleviating the volume expansion.
The effectiveness of this approach has been widely demonstrated in alloy anodes
for LIBs, which possess a formidable volume expansion.145 In comparison, the
laser porosificated anode (wavelength: 532 nm, pulse duration: 63 ns; pulse energy:
�107 W cm�2) made of nanosilicon offers a specific capacity 5-fold higher than its
counterpart without laser treatment. Since this laser structuring can be directly
applied to industrial-grade electrodes, it may find an easy pathway toward real ap-
plications in the near future.
Because of the employment of different materials on anode and cathode, the fabri-
cation of a rechargeable battery device through laser-mediated processes would be
difficult. In contrast to the flourishing development of laser-enabled supercapacitor
devices, laser-enabled battery devices have seldom been reported. Recently, a
multi-step laser-mediated process was developed to construct a rechargeable bat-
tery, as illustrated in Figures 10G–10I.142 The CNTs and VO2(B) hybrid film was
engraved into a finger-like electrode as the cathode. Zn deposited CNTs film was
then carved into a similar configuration as the anode. Thereafter, these two elec-
trodes were placed at preassigned positions on a flexible substrate before coating
with a layer of gel electrolyte. Such a device can operate in a voltage window of
2 V, delivering an energy density of 188.8 mWh cm�2 and a power density of
0.61 mW cm�2 (Figure 10J). The series and parallel connection of batteries have
also been achieved, which may pave the way for flexible construction of in-plane
rechargeable batteries.
Matter 3, 95–126, July 1, 2020 117
llReview
Electrocatalysis
Electrocatalysis refers to the heterogeneous catalysis directly driven by external
electrons, involving oxygen reduction reaction (ORR), OER, and HER.146 These reac-
tions are the fundamental processes for many energy conversion devices, including
water electrolyzers and fuel cells.5 As multiple-electron transfer is involved in these
reactions, they are generally kinetically sluggish. Suitable electrocatalysts that can
essentially boost these reactions are thus actively pursued. The past few years
have witnessed the significantly boosted performance of electrocatalysts enabled
by structural defects, heterostructures, and innovative electrode design, and all of
the three structural features can be easily regulated by laser technologies.16,23,90
To engineer structural defects in electrocatalysts, the chemical reduction of the as-
synthesized catalysts in a reduced atmosphere at elevated temperatures is generally
required and the fabrication process is usually tedious and time consuming. By using
LFL this obstacle can be essentially avoided, as the fragmented particles are rich in
defects because of their unique formation process. In an example, Zhou et al. irradi-
ated (wavelength: 1,064 nm, pulse duration: 7 ns; power density: �107 W cm�2)
commercially available Co3O4 particles into monodispersed Co3O4 quantum dots
of 5.8 G 1.1 nm (Figure 11A).14 The transient high-power-induced fragmentation
and subsequent rapid cooling certainly endowed the as-prepared nanoparticles
with sufficient surface defects. When evaluated as electrocatalysts for OER, these
monodispersed nanoparticles offer a lower overpotential of 294mV at a current den-
sity of 10 mA cm�2, outperforming the benchmark RuO2 catalysts as shown in Fig-
ure 11B. By replacing Co3O4 particles with a Co target, the pulsed laser results in va-
porization of Cometal, which is then oxidized by the dissolved oxygen in the solution
to produce ultra-fine and more defective Co3O4 nanoparticles.24 In addition to the
surficial oxygen vacancies, abundant interior vacancies were also detected. The va-
cancies at different locations synergetically contribute to the outstanding perfor-
mance of ORR where the defect-rich Co3O4 nanoparticles (Figures 5F and 5G) afford
a half-wave potential of 0.878 V versus reversible hydrogen electrode, superior to
the commercially available Pt/C electrocatalysts (Figure 11C). Besides the vacancy
defects, heteroatom defects have also been controllably introduced into electroca-
talysts through the laser-mediated process. Not only the content of heteroatoms but
also their configuration can be precisely modulated.64 As a result, the laser-induced
defects engineering of electrocatalysts can serve as a reliable platform to investigate
the structure-performance relationship. In a typical example, the nitrogen configura-
tions in graphene have been accurately modulated, via which the pyridine Ns are
found to play a pivotal role in the reconstruction of favorable electronic structures
by connecting with the subsequently introduced NiCo2O4 nanoparticles to facilitate
oxygen electrocatalysis.64 These results may provide fundamental design rationales
for preparing advanced electrocatalysts.
Regarding the heterostructures used for electrocatalysis, their synergistic effects are
mainly harvested in two manners. First, the optimization of different active materials
with distinct electronic structures contributes to favorable active sites at the inter-
faces.16 Such a heterostructure was synthesized by lasing the NiFe alloy in a urea so-
lution and subsequent electrochemical oxidation whereby the well-defined inter-
faces could be observed between the loaded NiO nanoparticles and the
supported NiFe LDH nanosheets (Figure 1D).23 As shown in Figures 11D and 11E,
the heterostructures thus produced offer a record overpotential of 205 mV at a cur-
rent density of 30 mA cm�2 and a Tafel slope of 30 mV dec�1 for OER. The Ni4+ ions
are believed to be active for OER. The soft X-ray absorption spectroscopy (SXAS)
profiles (Figure 11F) show the absence of Ni4+ ions in both NiFe LDH and NiO. As
118 Matter 3, 95–126, July 1, 2020
Figure 11. Application of Laser-Regulated Materials for Enhanced Electrocatalysis
(A and B) Synthesis of Co3O4 nanoparticles with oxygen vacancies for OER. Reproduced with permission from Zhou et al.14 Copyright 2016, American
Chemical Society.
(C) ORR performance of Co3O4 nanoparticles synthesized by LFL of Co target in water. Reproduced with permission from Li et al.24 Copyright 2019,
Wiley-VCH.
(D and E) OER performance of NiO/NiFe LDH. Reproduced with permission from Gao et al.23 Copyright 2019, Wiley-VCH.
(F) SXAS profiles of Ni cation in NiO, NiFe LDH, and NiO/NiFe LDH. Reproduced with permission from Gao et al.23 Copyright 2019, Wiley-VCH.
(G–I) A full water-splitting device made by laser irradiation and its performance. Scheme of the integrated water-splitting device (G), and
electrocatalytic performance of cathode and anode (H) as well as the full device (I). Reproduced with permission from Zhang et al.25 Copyright 2017,
American Chemical Society.
llReview
a result, the detected Ni4+ ions in the heterostructures primarily exist at the inter-
faces arising from the synergistic effect of different components. The loading of
active species on porous networks, for example porous carbon, has been suggested
as an alternative route to harness the potential of heterostructures. The carbon net-
works primarily facilitate the electron transfer via which the electrochemical reac-
tions can be accelerated at the active materials loaded on the conductive substrates.
Since DLW technology can elaborately modulate the porous carbon network in
Matter 3, 95–126, July 1, 2020 119
llReview
terms of porosity, composition, and conductivity, a vast range of electrocatalysts
were successfully hybridized with the elegant carbon networks. The loaded active
species include Co3O4, NiFe LDH, Pt, and CoP, among others.90,105,147 Because
of the improved electron transfer, most of these structures afford significantly
improved performance.
The configurations of energy conversion devices are much more complex than those
of energy storage systems. The devices normally employ an open system because
gas-involved reactions take place at the electrodes.148 As a result, the design ratio-
nales for energy conversion devices are totally different from those for supercapaci-
tors and batteries, and the related research remains at the very early stage. Recently,
a novel and simple design, as illustrated in Figure 11G, has been proposed to
produce a water electrolyzer in which a single piece of film can electrocatalytically
produce hydrogen and oxygen on its opposite sides (Figure 1E).25 Patterned gra-
phene was scribed on both sides of one piece of polymer film for depositing
NiFe LDH and Co-P electrocatalysts separately. The NiFe LDH can facilitate OER
while the Co-P is responsible for the accelerated HER (Figure 11H). The connection
of the two electrodes with an external power source within an O-ring setup results in
the generation of H2 and O2 at opposite sides, which can be separately collected.
The full water splitting can be driven by a voltage of 1.66 V while a significantly
enhanced current density of 400 mA cm�2 at a voltage of 1.9 V (Figure 11I) is
observed. The laser-mediated construction of water-splitting devices may provide
a straightforward means for clean fuel production.
SUMMARY AND PROSPECTS
The rising interest in new energy materials and laser processing has led to tremen-
dous efforts devoted to laser-mediated synthesis and modulation of electrode ma-
terials for energy storage and conversion. Recent investigations revealed that struc-
tural defects, heterostructures, and integrated electrode and/or device design hold
promising potential to boost the performance of electrode materials for energy-
related applications. With the capability of inducing controllably site-specific ther-
mal effects, laser processing is advantageous for manipulating these structural
features. As a result, the rational combination of these two booming fields will essen-
tially contribute to an emerging discipline for addressing real-world issues. Up to
now, a vast spectrum of materials including carbons, metal oxides, and metal car-
bides have been precisely modulated at atomic-, nano-, and/or macroscales into
the desired structures using different types of lasers (Table 1), with fundamentally
improved capability for energy storage and conversion. In addition, laser-mediated
structural regulation is compatible with many industrial processes, endowing this
technology with promising potential for rapid application in the near future.
Despite the remarkable progress, the research in this rising field is still in its infancy
and some formidable challenges remain to be addressed. The feasibilities of laser-
mediated precise structural modulation of materials are mainly based on their inter-
action while the exact mechanisms are still under debate as both photothermal
effects and photochemical effects as well as their combination are proposed to
explain the unique materials processing. This strong disagreement has largely
impeded the regulation of materials in a rationally designed manner, and some of
the amazing results are actually found by accident. The successful elaborate struc-
tural manipulations at the current stage focus on limited precursors that retard
the exploration of promising laser processing. Besides, the dynamic materials syn-
thesis processes, which could provide an insightful view into laser processing, are
120 Matter 3, 95–126, July 1, 2020
Table 1. Comparison of Different Laser Processing Technologies
Strategy OperationalMode
Wavelength Precursor Product Application Reference, Year
DLW pulsed laser (ms) 10.6 mm PI graphene planar supercapacitordevice
Lin et al.21 2014
pulsed laser (ms) 10.6 mm H3BO3/PI composite B-doped graphene planar supercapacitordevice
Peng et al.60
2015
CW 532 nm graphene graphene-based p-njunctions
– Seo et al.22 2014
pulsed laser (ns) 355 nm graphene-based planersupercapacitor
graphene-basedstretchablesupercapacitor
stretchablesupercapacitor device
Gao et al.38 2019
pulsed laser (ms) 10.6 mm MXenes MXenes-based in-planesupercapacitor
planar pseudocapacitordevice
Kurra et al.39
2016
pulsed laser (ns) 355 nm GO film RGO pattern planar supercapacitordevice
Xie et al.40 2016
pulsed laser (ps) 355 nm dimethyl sulfoxide-dispersedpolybenzimidazole ink
N, S-codoped graphene conductive substrate Huang et al.59
2018
pulsed laser (ps) 1,064 nm GO film RGO pattern – Guan et al.69
2016
pulsed laser (ms) 10.6 mm metal complex-containing PI sheet
metal oxide nanocrystals-embedded graphene
electrocatalyst for ORR Ye et al.89 2015
pulsed laser (ms) 10.6 mm polymer N-doped graphene anode for SIBs Zhang et al.119
2018
pulsed laser (ms) 10.6 mm slurry made of ammoniummolybdate, sodiumsulfide, and citric acid
MoS2/carbon hybrids electrocatalyst for ORR Deng et al.92
2016
CW 1,064 nm PI film Janus graphene film – Li et al.95 2018
pulsed laser (ns) 1,064 nm MOF metal-graphenecomposite
– Jiang et al.96
2020
LFL pulsed laser (ns) 1,064 nm Co3O4 powder defective Co3O4 quantumdots
electrocatalyst for OER Zhou et al.14
2016
pulsed laser (ns) 1,064 nm Co target defects-rich Co3O4
quantum dotsbifunctionalelectrocatalyst for ORRand OER
Li et al.24 2019
pulsed laser (ns) 1,064 nm NiFe target NiO/NiFe LDH electrocatalyst for ORR Gao et al.23 2019
pulsed laser (ms) 1,064 nm polydispersed PbSnanocrystals
monodisperse colloidalPbS quantum dots
– Yang et al.42
2013
pulsed laser (ns) 355 nm CNTs intertwinedpolyhedrons
broken CNTs particles – Gong et al.65
2019
pulsed laser (ns) 355 nm Fe and Ni powders inLa3+-containing solution
La3+ doped NiFe LDH electrocatalyst for OER Hunter et al.74
2014
pulsed laser (ps) 532 nm aqueous suspensions withcobalt oxide powders
defects-rich cobalt oxide electrocatalyst for OER Yu et al.77 2020
pulsed laser (ns) 1,064 nm Ag target Ag nanoparticles with richstacking faults
electrocatalyst for HER Li et al.78 2019
PLD pulsed laser (ns) 248 nm Fe2O3 target nanoporous Fe2O3 film anode for LIBs Teng et al.36
2018
pulsed laser (ns) 248 nm Li3N andLi6.25Al0.25La3Zr2O12
target
garnet solid-state batteryfilms
solid electrolyte forlithium batteries
Pfenningeret al.139 2019
pulsed laser (ns) 248 nm Co target nanoporous Co-CoO film anode for LIBs Qin et al.48 2017
LAP pulsed laser (ms) 10.6 mm Sn(OH)4 precursorsolution
N-SnO2 particles anode for LIBs Wang et al.73
2017
(Continued on next page)
ll
Matter 3, 95–126, July 1, 2020 121
Review
Table 1. Continued
Strategy OperationalMode
Wavelength Precursor Product Application Reference, Year
pulsed laser (ms) 10.6 mm toluene solutioncontaining Pt(acac)2 andCo(acac)3
PtxCoy/carbon composite – Martinez et al.91
2018
CW 10.6 mm SiH4 Si nanoparticles anode for LIBs Kim et al.144
2014
Nanowelding pulsed laser (ns) 1,064 nm metal and metal oxidenanoparticles
metal/metal oxideheterostructures
– Yu et al.98 2017
CW 532 nm Cu nanowires films welded Cu nanowiresnetwork
conductive substrate Han et al.149
2014
pulsed laser (fs) 800 nm Ag nanoparticles solution Ag nanoparticles-assembled patterns
conductive substrate Wang et al.150
2015
llReview
insufficiently investigated. It is obvious that knowledge from multiple disciplines is
required to address the aforementioned issues, with joint research among re-
searchers from different backgrounds urgently needed.
Laser processing is highly sensitive, and a minor deviation in operation conditions
can incur distinctive heating of the target materials. To secure reliable results and
high reproducibility, the experimental processes and the related parameters
should be introduced as explicitly as possible. In addition, the advantages of
laser-mediated processing are investigated by comparing results from different
works while systematically conducting materials synthesis by using laser-mediated
methods and traditional technologies are still lacking. Such investigations are of
paramount importance for an insightful understanding of the advantages of laser
processing. Not only the final products but also the processing details of different
methods should be systematically compared. Only in this way can the gap be-
tween laser processing research and the practical applications be well understood,
which will be helpful for building the roadmap of laser processing in new energy
technology.
Although the history of the laser irradiation of electrode materials is very short, an
explosive growth of this field has taken place in the past few years. One possible
reason for this is that this technology has kept up with the pace of the booming
new energy field. Specifically, the structural defects, heterostructures, and inte-
grated electrode architectures, all of which have been actively pursued for energy
storage and conversion in recent years, can be facilely, efficiently, and controllably
modulated by laser processing. Despite the aforementioned challenges, the
continuing boom of this field is still expected. With a more in-depth understanding
of the fundamental science and technology issues within this field, it is we firmly
believe that an increasing amount of advanced electrode materials with essentially
enhanced performance for energy storage and conversion will be produced based
on precise design rationales.
ACKNOWLEDGMENTS
The authors thank the editor for the kind invitation. This work was financially sup-
ported by the National Natural Science Foundation of China (21975287), the start-
up grant for young talent of China University of Petroleum (East China), Taishan
Scholar Project (no. ts201712020), Technological Leading Scholar of 10000 Talent
Project (no. W03020508), and Shandong Provincial Natural Science Foundation
(ZR2018ZC1458).
122 Matter 3, 95–126, July 1, 2020
llReview
AUTHOR CONTRIBUTIONS
H.H., M.W., and J.Q. proposed the project. H.H. andQ.L. wrote themanuscript. L.L.,
X.T., and Y.Z. revised the figures. L.L. and Z.F. helped to revise the manuscript.
DECLARATION OF INTERESTS
The authors declare no competing interests.
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