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Nano Energy (2014) 10, 63–70

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A complete three-dimensionallynanostructured asymmetric supercapacitorwith high operating voltage window basedon PPy and MnO2

Fabian Grote1, Yong Lein,1

Ilmenau University of Technology, Institute of Physics & IMN MacroNanos (ZIK), Prof. Schmidt-Str. 26,98693 Ilmenau, Germany

Received 5 August 2014; received in revised form 26 August 2014; accepted 28 August 2014Available online 10 September 2014

KEYWORDSHybrid materials;Functional coatings;Core/shell nanotubes;Polymeric materials;Nanodevices;Supercapacitors

0.1016/j.nanoen.2lsevier Ltd. All rig

thor.ong.lei@tu-ilmena3748.

AbstractThe development of novel functional nanostructures and the implementation of an asymmetriccell design are the key challenges to increase the electrochemical performance of aqueousbased supercapacitors. In this manuscript complex three-dimensional electrode materials arenano-engineered based on free-standing open-ended core/shell nanotube arrays with tailoredfunctions. Both the negative and positive electrode materials are designed and nanostructuredindividually, using an innovative material combination of Polypyrrole (PPy) and manganeseoxide (MnO2). This asymmetric cell design increases the possible operating potential window to1.7 V, which is a major leap to enhance the specific energy of supercapacitors. The prepareddevice exhibits a high specific energy of 27.2 Wh kg�1 and a high specific power 24.8 kW kg�1.& 2014 Elsevier Ltd. All rights reserved.

Introduction

The ongoing technological advances in areas such as electricmobility, consumer electronics, wireless sensor networks,and energy harvesting set new demands for energy storage

014.08.019hts reserved.

u.de (Y. Lei).

and energy management systems [1–3]. The next generationof high performance energy and power devices requires astrongly enhanced electrochemical performance as well asoperating safety, limited environmental impact, and eco-nomical viability [4]. In order to fulfill these aims a crucialrole is addressed to supercapacitors because of the superiorpower delivery and cycling life compared to those of lithiumion batteries. Today, the main challenge is to increasethe specific energy of supercapacitors without sacrificingspecific power.

Figure 1 Schematic diagram of the fabrication and assemblyof the asymmetric three-dimensional supercapacitor. Synthe-sized well-ordered SnO2 NT arrays serve as a fundamentalsubstructure to fabricate either SnO2/PPy or SnO2/MnO2 core/shell NT arrays, which act as a negative and positive electrode,respectively. These three-dimensional arrays are separatedfrom each other by a thin separator and integrated into onesingle cell, forming an asymmetric aqueous based supercapa-citor (PPy//MnO2).

F. Grote, Y. Lei64

The specific energy of supercapacitors can be improved bymaximizing the specific capacitance (c) and/or maximizingthe operating potential window (V) according to the follow-ing equation: [5]

E ¼ 12cV2 ð1Þ

In order to achieve an enhanced specific energy, three majorstrategies can be distinguished. (i) The implementation ofnew electrode materials that possess higher specific capaci-tance compared to commercially utilized carbon basedmaterials, such as metal oxides [6–12], conductive polymers[13], and metal nitrides [14]. (ii) The development of novelfunctional nanostructures and material compositions. Thismainly includes complex core/shell nanostructures thatcombine the advantage of two materials (i.e., core andshell) [15–21]. Such designs provide a fast electron transportthrough the core and a well utilization of the activeelectrode material in the shell. (iii) The realization of high-voltage supercapacitors operating in aqueous electrolytes[22]. Previously, asymmetric supercapacitors that use differ-ent electrode materials for the negative and positive elec-trode have drawn much attention [23]. Such configurationscircumvent the main limitation of aqueous based super-capacitors and extend the operating voltage window beyondthe thermodynamic limit of �1.2 V to operating voltages ashigh as �2 V [24]. Especially the combination of variouscarbon based negative and different MnO2 based positiveelectrode structures were studied intensively [5,25–28].However, other promising materials with complementarypotential windows to MnO2, in particular conductive poly-mers, are only insufficiently investigated as negative elec-trode materials in asymmetric supercapacitors. Therebyconductive polymers possess higher specific capacitancevalues compared to carbon materials and thus offer greatpotential to further increase the specific energy of super-capacitors [29]. The combination of asymmetric supercapa-citors that utilize negative and positive electrode materialswith complementary operating potential windows and theuse of advanced functional electrode materials, such asoptimized high aspect ratio core/shell structures are highlypromising to enhance the electrochemical performance ofthe next generation of supercapacitors. However, until nowsupercapacitors with three-dimensionally nano-engineerednegative and positive electrodes based on different materialshave not been reported. In order to take full advantage ofboth the nanostructured electrode surface and the increasedoperating potential window due to the asymmetry of theelectrodes nature, innovative supercapacitor configurationsneed to be developed.

Here, we report an all new asymmetric supercapacitorbased on highly ordered free-standing three-dimensional (3D)core/shell nanotube arrays of SnO2/Polypyrrole (PPy) andSnO2/MnO2 as negative and positive electrode material,respectively (Figure 1). The utilized fabrication processallows a precise control of many structural parameters andis based on anodic aluminum oxide (AAO) nano-templates,[30] atomic layer deposition (ALD) to synthesize free-standing SnO2 nanotube (NT) arrays, and a conformal coatingof PPy and MnO2 by electrochemical deposition. Very impor-tantly, the completely new cell-configuration of the nano-engineered 3D PPy//MnO2 asymmetric supercapacitor can

operated at 1.7 V and shows an outstanding electrochemicalperformance with obtained specific energy and specificpower values that are among the highest reported.

Materials and methods

SnO2 substructure: the free-standing SnO2 NT array wasfabricated by AAO templates and ALD. The AAO templatewas synthesized using a two step-anodization process [31–33] from a 99.999% pure aluminum foil at 40 V in 0.2 Moxalic acid with a second anodization time of 15 min,including a post-etching in 5 wt% phosphoric acid for15 min at 30 1C to increase the AAO pore size to 60 nm.Such AAO templates were then coated by SnO2 nanotubes ina PicoSun ALD reactor according to the following process.The ALD cycle was based on 1 s pulse and 4 s purge for theTin(IV)chloride (SnCl4) precursor and 2 s pulse and 8 s purgefor H2O at 250 1C. This cycle was repeated for 1500 times.Afterwards, the backside of the SnO2 covered AAO wassupported by a 100 nm gold layer by physical vapor deposi-tion, the aluminum base was removed in a saturated copperchloride solution, and the remaining AAO template wasetched by a 5 wt% sodium hydroxide solution in a two-stepprocess. First, a pre-etching of 20 min was applied toliberate the SnO2 NT top parts, which were then removedby scratching the surface of the sample with a sharp scalpel.Second, the remaining AAO template was dissolved entirelyin the same etching solution for 120 min, gaining a free-standing SnO2 NT array (see supplementary video).

Supplementary material related to this article can befound online at http://dx.doi.org/10.1016/j.nanoen.2014.08.019.

Positive and negative electrode: the positive electrodewas fabricated by electrochemical deposition of MnO2 ontothe SnO2 NT array from a solution containing 0.1 M manga-nese acetate (Mn(Ac)2) and 0.1 M sodium sulfate (Na2SO4) at1 V versus a Ag/AgCl reference electrode. A Pt foil was usedas a counter electrode. The electrochemical performance ofthe fabricated SnO2/MnO2 core/shell positive electrode wasinvestigated in a three-electrode cell containing a 1 MNa2SO4 electrolyte, a Ag/AgCl reference electrode, and aPt foils as the counter electrode. The electrodes per-formance was studied in a potential window from 0–0.9 V.

65Three-dimensionally nanostructured asymmetric supercapacitor

The SnO2/PPy core/shell negative electrode material wassynthesized by electrochemical polymerization of PPy ontoSnO2 NT arrays from a solution containing 0.1 M pyrrolemonomer (98%) and 0.2 M oxalic acid at 0.8 V versusAg/AgCl. The electrochemical performance was investi-gated in an identical setup as described for the positiveelectrode in a potential window from �0.8 to 0 V versusAg/AgCl. The specific capacitances of the SnO2/PPy andSnO2/MnO2 core/shell NT arrays were calculated for variouscurrent densities from the gradient (ðΔV=ΔtÞ) of theassociated discharge curve according to the followingequation:

c�=þ ¼ IðΔV=ΔtÞ �m�=þ

ð2Þ

with m�=þ being the negative and positive active electrodemasses derived from the charge flown during the electro-chemical deposition process.

Asymmetric supercapacitor: The negative SnO2/PPy andpositive SnO2/MnO2 core/shell electrode materials wereassembled into two-electrode Swagelok-type cells formingan asymmetric supercapacitor labeled as PPy//MnO2 (nega-tive electrode//positive electrode). The electrodes wereseparated by a porous membrane and a 1 M Na2SO4 solutionwas used as an electrolyte. The cells were operated at apotential window of 1.7 V. Thereby the active electrodemasses of PPy and MnO2 (total combined mass 0.277 mg)were balanced based on the charges passed across thenegative and positive electrode (q+ =q�) according to:

mþm�

¼ c�ΔU�cþΔUþ

ð3Þ

with ðmþ =m� Þ being the ideal ratio of positive to negativeactive electrode materials, c�=þ the specific capacitance ofthe respective electrode material, and ΔU�=þ the respec-tive operating potential (0.8 V for negative and 0.9 V forpositive electrode). The specific energy is calculatedaccording to:

E ¼ 12casyV

2 ð4Þ

with V being the voltage after the potential drop and casybeing the specific capacitance of the asymmetric super-capacitor cell measured from the discharge curve gradient(ðΔV=ΔtÞ) of the charge/discharge profiles according to:

casy ¼I

ðΔV=ΔtÞ �mð5Þ

where I is the discharge current and m is mass of the activeelectrode materials. The specific power is calculated fromthe specific energy divided by the discharge time (tdischarge)according to:

Preal ¼E

tdischargeð6Þ

All electrochemical measurements were performed on aBio-Logic VSP electrochemical work station at 20 1C.

Results and discussion

The fabrication of the asymmetric PPy//MnO2 supercapa-citor is based on free-standing SnO2 nanotube arrays that

are fabricated by using AAO nano-templates and atomiclayer deposition (see supplementary video for the details ofthe fabrication process). The synthesized SnO2 nanotubearrays serve as a fundamental substructure to fabricate (viaconformal electrochemical polymerization and deposition)both 3D SnO2/PPy and SnO2/MnO2 core/shell nanotubearrays for the use as negative and positive electrodematerials, respectively (Figure 1). The implementation ofthe two different electrodes into one single supercapacitordefines the asymmetric device nature and enables thehighly desired increase in operating potential window. Wewant to emphasize that the developed fabrication processfor both electrodes is highly reproducible, which ensures awell repeatable electrochemical performance.

Negative electrode

The PPy based negative electrode is fabricated by potentio-static electrochemical polymerization of pyrrole monomerat 0.8 V vs Ag/AgCl onto a SnO2 nanotube array. Thestructure and the core/shell nature of the 3D SnO2/PPynanotube array are investigated by SEM and TEM measure-ments. Figure 2a displays a top-view and cross-sectionSEM image of a bare free-standing SnO2 nanotube array(diameter �60 nm), showing the high structural regularity,the top-opened nanotube nature, and the vertical align-ment of adjacent nanotubes (length �1.8 μm). Theseunique structural features make this high aspect ratiomaterial an ideal substructure for fabricating 3D core/shellmaterials for supercapacitor applications. A representativetop-view and cross-section view of a PPy covered SnO2

nanotube array is presented in Figure 2b, showing theconformal coating of PPy and the high porosity of thestructure. The TEM inset of a single SnO2/PPy nanotube inFigure 2c outlines the well conformal coating, which issupported by the observed morphology change duringelectrochemical polymerization of PPy on the surface ofbare SnO2 nanotubes, as compared by SEM cross-sectionimages in Figure 2d. The formation of a core/shell structureis further verified by EDX line-scans and reveals the materialdistribution across the tubular structure. Figure 2e presentsthe Sn L line scan profile across two parallel SnO2/PPynanotubes, showing signal peaks located at the wall posi-tions of the SnO2 NTs, which proves the nanotubular natureof SnO2. The C K spectrum in Figure 2f indicates anincreased carbon concentration across the nanotubes, ori-ginating most likely from the PPy shell.

The electrochemical performance of the SnO2/PPy core/shell nanotube array as a negative electrode in supercapa-citor devices is investigated by cyclic voltammetry (CV) andgalvanostatic charge/discharge measurements. The electro-chemical measurements were performed in a three-electrode configuration (platinum foil as counter electrode;Ag/AgCl reference electrode) in a water-based 1 M Na2SO4

electrolyte from �0.8 to 0 V vs Ag/AgCl. The CV curves inFigure 3a are recorded at different scan rates in the rangefrom 2–50 mV s�1. The shape of the CV profiles reassemblesthe expected shape for a pseudocapacitive material to greatextend and is of reversible nature, indicating a well capa-citive behavior. The charge/discharge curves in Figure 3b aremeasured at various current densities to investigate the

Figure 3 Electrochemical investigation of the SnO2/PPy core/shell NT array as a negative supercapacitor electrode measured in athree-electrode configuration. (a) CV curves measured at different scan rates. (b) Galvanostatic charge/discharge curves recordedat various current densities.

Figure 2 Structural investigation of the 3D SnO2/PPy NT array. (a) Top-view and cross-section view of bare SnO2 NT array. (b) Top-view SEM image of PPy covered SnO2 NT array, showing the highly porous nature of the core/shell electrode. (c) Cross-section SEMview of PPy covered NTarray and TEM image of a single PPy/SnO2 NT (inset), indicating the well conformal coating. (d) Cross-sectionSEM image of bare SnO2 compared to PPy covered NT array. (e and f) TEM images of two parallel SnO2/PPy NTs with EDX line scans,showing the material distribution across the tubular structure. (e) Sn L line scan profile shows signal peaks located at the wallpositions of the SnO2 NTs, proving the nanotubular nature. (f) C K spectrum, indicating an increased carbon concentration across theNTs, originating from the PPy shell.

F. Grote, Y. Lei66

specific capacitance and the rate capability of the core/shellstructure as a negative supercapacitor electrode. The spe-cific capacitance (c�) is calculated from the gradient of thedischarge curve according to Eq. (2) (Eqs. 2–6 are listed inthe Materials and methods section) and achieves a maximumof 260 F g�1 at 1 A g�1 and remains high 189 F g�1 at50 A g�1, assigning the core/shell structure a good ratecapability (Figure S2). Hence, this PPy based core/shellnanotube array is a promising candidate as a negativeelectrode material in supercapacitors.

Positive electrode

The positive electrode based on a SnO2/MnO2 core/shellnanotube array is fabricated by potentiostatic electroche-mical deposition of MnO2 onto a bare SnO2 nanotube arrayfrom a solution containing 0.1 M Mn(Ac)2 at 1 V vs Ag/AgCl.

Figure 4a and b presents the structural and chemicalinvestigation of the SnO2/MnO2 material by SEM, TEM, andEDX mapping. The cross-section and top-view SEM images inFigure 4a show the maintained nanotube nature afterelectrochemical deposition of MnO2 and outline the wellconformal coating, leading to highly porous core/shelltubular nanostructures. These results are approved by TEMand EDX mapping of the O K, Mn K, and Sn L spectrarecorded on a single SnO2/MnO2 core/shell nanotube, asshown in Figure 4b. Thereby confirms the elemental dis-tribution of Sn the nanotubular nature with solid nanotubewalls and the Mn spectrum proves that manganese isdistribution across the entire surface of the SnO2 nanotubes,verifying the core/shell structure. The O K signal arises fromthe oxygen present in MnO2 and SnO2 and therefore ishomogeneously distributed across the core and shell of thestructure. The electrochemical performance of the SnO2/MnO2 core/shell nanotube array as a positive electrode

Figure 4 SnO2/MnO2 core/shell nanotube array as positive electrode for supercapacitors. (a) Top-view and cross-section SEMimages. (b) TEM image and EDX mapping (O K, Mn K, and Sn L spectra) of a single core/shell nanotube, showing a well conformalcoating of MnO2 across the SnO2 nanotube. (c) CV curves of SnO2/MnO2 nanotube array measured at different scan rates in a three-electrode configuration.

Figure 5 Investigation of the operating potential window for the as-prepared 3D PPy//MnO2 asymmetric supercapacitors. (a) CVcurves of single SnO2/PPy and SnO2/MnO2 core–shell NT arrays measured at 20 mV s�1 in a three-electrode cell, showing thecomplementary voltage windows of both materials. (b) CV curves of PPy//MnO2 asymmetric supercapacitor measured at differentpotential windows from 0.9–1.7 V in a two-electrode cell configuration at 20 mV s�1, exhibiting a mirror-image current response onvoltage reversal until 1.7 V.

67Three-dimensionally nanostructured asymmetric supercapacitor

material in supercapacitors was investigated by CV andgalvanostatic charge/discharge measurements. The mea-surements were performed using a three-electrode config-uration in a potential window from 0–0.9 V vs Ag/AgCl in awater-based 1 M Na2SO4 electrolyte. Figure 4c presents theCV curves recorded at different scan rates. The profiles ofthe curves are rectangular and exhibit a mirror imagecharacteristic to the x-axis and maintain this symmetryeven at high scan rates, proving a good pseudocapacitivebehavior. The specific capacitance (c+) of the SnO2/MnO2

core/shell material is calculated according to Eq. (2) andachieves excellent 910 F g�1 at 1 A g�1 and remaining217 F g�1 at 50 A g�1 (see Figures S1 and S2 for charge/discharge curves and rate capability), making this core/shell structure an attractive material for the positiveelectrode in asymmetric supercapacitors.

Asymmetric supercapacitor device

The merge of 3D core/shell PPy based negative and MnO2

based positive electrode materials into one single deviceoffers a completely new path to enhance the electrochemical

performance of supercapacitors. The 3D nanostructuredtubular array increases the surface area of the electrodesdrastically while the asymmetric nature of the electrodematerials enables the expansion of the operating potentialwindow, leading both to an increase in specific energy.Thereby the core/shell nature provides a well utilization ofthe active electrode materials and ensures a fast chargecarrier transport through the electrode matrix, which is akey criterion to obtain high specific power, as shown byresent results [34]. Figure 5a outlines the working potentialwindows of each electrode individually and emphasizesthe ideal combination of PPy as negative and MnO2 as positiveelectrode materials. Both materials show pseudocapacitivebehavior in complementary operating potential windows sothat the integration of both electrodes into one super-capacitor is leading to the desired increase in operating cellvoltage to 1.7 V. Owing to the asymmetric device config-uration, PPy can serve as a negative electrode material,unlike in symmetric PPy systems where undoping and theformation of an isolating state of PPy under negativepotentials hinders its usage in energy storage applications,as investigated by Béguin et al. [22]. The maximum operatingpotential window of the PPy//MnO2 asymmetric configuration

F. Grote, Y. Lei68

is investigated on the basis of CV measurements in the rangefrom 0.9–1.7 V in a two-electrode cell configuration at20 mV s�1 in a 1 M Na2SO4 electrolyte, as shown inFigure 5b. The CV curves of the PPy//MnO2 supercapacitorexhibit a mirror-image current response on voltage reversaluntil 1.7 V, proving a good capacitive behavior and thesuperiority to symmetric MnO2//MnO2 configurations (i.e.,max. cell voltage 0.9 V). Thereby this configuration circum-vents the main limitation of aqueous based supercapacitors,namely the dissociation of water at potentials higher than�1.2 V, because of high over-potentials for hydrogen andoxygen evolution at the negative and positive electrodesand extends the operating voltage window beyond thethermodynamic limit to 1.7 V [22,35].

The electrochemical performance of the nanostructuredPPy//MnO2 asymmetric supercapacitor is investigated in atwo-electrode setup, using a 1 M Na2SO4 aqueous electro-lyte in a potential window of 1.7 V. Figure 6a presents theCV curves of a PPy//MnO2 device recorded at differentpotential scan rates. The shape of the curves outline thatthe charge storing characteristic of individual PPy and MnO2

based electrodes could be successfully transferred into afull asymmetric device. The CV curves exhibit a nearlysymmetric and rectangular shape, which is maintained athigh scan rates over the entire potential window of 1.7 V,proving the good capacitive behavior of this device. Thisresult is further supported by the symmetric triangular

Figure 6 Electrochemical performance of the as-prepared 3D PPy/potential window of 1.7 V. (a) CV curves recorded at different scanvarious current densities. (c) Long-time cycling stability of the PPy/showing reported specific energy (E) and specific power (Preal) valueand asymmetric supercapacitors (carbon//MnO2 [25,35,38,40–46],MnO2 [39], and PPy//MnO2) (filled symbols: this study, framed sym

shape of the galvanostatic charge/discharge profiles, asshown in Figure 6b. Thereby possesses the PPy//MnO2

asymmetric supercapacitor a high charge efficiency(496%) and exhibits a good long-time cycling stability witha capacitance retention of over 80% after 2000 consecutivecharge/discharge cycles (Figure 6c). As shown in Figure S3,the cycling stabilities of the individual PPy and MnO2 basedelectrodes, measured in a three-electrode configurationwithin their respective voltage windows, show comparablestability characteristics. Leakage current is a serious con-cern is supercapacitor applications. However, only very fewpublications report this value in their study. As shown inFigure S4. The leakage current of the reported device wasdetermined to 57 mA after 30 min potential hold at 1.7 V,which is in the range of a reported CNT/PANI supercapacitor[36]. Most importantly, the 3D PPy//MnO2 core/shell asym-metric supercapacitor obtains specific energy and specificpower values that are among the highest reported. Thedevices specific energy (E) is calculated from the associatedcharge/discharge curve in Figure 6b according to Eq. (4)while the real specific power (Preal) is derived by dividingthe specific energy by the discharge time according toEq. (6). The device exhibits a high specific energy of27.2 Wh kg�1 at 0.85 kW kg�1 and remains excellent 7.8 Whkg�1 at 24.8 kW kg�1, fulfilling the power target require-ments (15 kW kg�1 based on the active electrode mass) ofthe Partnership for a New Generation of Vehicles (PNGV).

/MnO2 supercapacitor investigated in a two-electrode setup in arates. (b) Galvanostatic charge/discharge curves measured at

/MnO2 device (inset: charge/discharge curves). (d) Ragone plot,s of symmetric (MnO2//MnO2 [38,47], carbon//carbon [48–50])Fe2O3//MnO2 [37,38], graphene//MnO2 [26,51,52], PEDOT//

bols: reported values reported in literature).

69Three-dimensionally nanostructured asymmetric supercapacitor

Thereby this device exceeds the performance reportedfor other asymmetric supercapacitor devices, such asFe2O3//MnO2 [37,38] and PEDOT//MnO2 [39] and can com-pete with the highest reported values for carbon//MnO2

[25,35,38,40–46] and graphene//MnO2 [17,31,32] asym-metric devices, as outlined in Figure 6c. Further theasymmetric PPy//MnO2 supercapacitor outnumbers theelectrochemical performance of aqueous devices based onsymmetric configurations like MnO2//MnO2 [38,47] andcarbon//carbon, [48–50] as well as a symmetric devicebased on as-prepared 3D SnO2/MnO2 electrodes. Theseresults demonstrate that the electrochemical performanceof supercapacitors can be successfully enhanced by introdu-cing three-dimensionally structured electrodes in combina-tion with an asymmetric cell design.

Conclusion

In summary, this work describes an innovative method forefficiently fabricating 3D core/shell nanotube arrays asnegative and positive electrodes for supercapacitor applica-tions. The implementation of an innovative PPy//MnO2

asymmetric aqueous based supercapacitor has shown thatthe electrochemical performance of supercapacitors can beimproved by introducing 3D core/shell nanostructures incombination with complementary energy storing materials.Considering the fact that many of the challenges that facethe field of aqueous supercapacitors are related to difficul-ties associated with compound materials and operatingpotential window, the fabrication of asymmetric super-capacitors based on 3D core/shell nanotube arrays coulddramatically accelerate the progress in this field and lead toenergy storage devices that are safe to operate and havelimited environmental impact.

Acknowledgments

Financial support from the European Research Council (ThreeD-surface: 240144), BMBF (ZIK-3DNanoDevice: 03Z1MN11),Volkswagen-Stiftung (Herstellung funktionaler Oberflächen:I/83 984) is gratefully acknowledged.

Appendix A. Supporting information

Supplementary data associated with this article can befound in the online version at http://dx.doi.org/10.1016/j.nanoen.2014.08.019.

Supplementary data and Supplementary Video are avail-able from the Wiley Online Library or from the author.

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Fabian Grote received his diploma degreeof physics in 2011 from the University ofMünster and is currently pursuing his Ph.D.at the Ilmenau University of Technology(Germany) in the 3D nanostructuring groupof Prof. Yong Lei. His research interestincludes the fabrication of 3D nanostruc-tures using nano-porous alumina templatesfor applications in high performance energystorage devices.

Yong Lei received his Bachelor degree inSun Yat-Sen University in 1991 and Ph.D.degree from Chinese Academy of Sciencesin 2001. After two years of postdoc researchin Singapore-MIT Alliance, he worked as anAlexander von Humboldt Fellow at Karls-ruhe Research Center in 2003–2006.He worked in University of Muenster as agroup leader from 2006 and was promotedto a W1 Professor in 2009. He joined

Ilmenau University of Technology in 2011 as a W2 Professor. Thecurrent research topics of his group are mainly focusing ontemplate-realized functional nanostructures, 3D nano-structuringand surface nano-patterning, energy-related and optoelectronicapplications. Prof. Lei received a few prestigious funding includingEuropean Research Council and BMBF (Federal Ministry of Educationand Research of Germany) ZIK projects.