Hofmann-Like Metal-Organic-Framework-Derived PtxFe/C/N-GC Composites as Efficient Electrocatalysts for Methanol Oxidation

Jia Zhao, Hui Huang, Ming Liu, Jin-Hua Wang, Kai Liu, and Zhao-Yang Li*

School of Materials Science and Engineering, Nankai University, 38 Tongyan Road, Haihe

Educational Park, Tianjin 300350, P.R. China

Tel&Fax: +86-22-85358786, +86-22-85358158

E-mail: zhaoyang@nankai.edu.cn

Experimental Section

No further purification is required for all commercially available reagents.

1.1 Preparation

1.1.1. Synthesis of Pt/Fe-MOFs

The new Pt/Fe-MOFs were prepared via a facial hydrothermal method. Typically, a

mixture of Fe(ClO4)·xH2O (0.025 mmol, 6.4 mg), K2[Pt(CN)4] (0.0125 mmol, 5.4 mg),

dipyridyl-naphthalenediimide (DPNDI) (0.025 mmol, 3.0 mg), methanol (CH3OH, 5 ml)

and deionized water (5 ml) was placed in a glass vial. After ultrasonic dispersion, heated

at 80 °C under autogenous pressure for 10 h. The yellow needle bar crystals were

collected by filtration and washed with CH3OH.

1.1.2 Synthesis of Pt/Fe-MOFs@GO composites

10 mg of GO uniformly dispersed in the 5 ml H2O, then 6.4 mg (0.025 mmol)

Fe(ClO4)·xH2O was added to the GO aqueous suspension, after sonicating for 2 h, 5.4

mg (0.0125 mmol) K2[Pt(CN)4], 3.0 mg (0.025 mmol) DPNDI and 5 ml CH3OH were

added to the solution for sonicating 2 h, following this, the mixture was heated at 60 °C

with a shaking table at an astonishing 150 revolutions per minute. After 10 h, the

precipitates were obtained via filtration and soaked with deionized water several times

Electronic Supplementary Material (ESI) for RSC Advances.This journal is © The Royal Society of Chemistry 2019

and dried for characterization.

1.1.3 Synthesis of PtxFe/C/N-GC bimetallic electrocatalysts at different

temperature

The obtained Pt/Fe-MOFs@GO composites were thermally treated at 600, 700 and 800

°C inside a tube furnace under a stream of N2 atmosphere respectively. The temperature

was raised to aim temperature at a ramping rate of 5 °C min−1, and then stabilized for 2

h. Then cooling down to room temperature naturally, the resulting PtxFe/C/N-GC

products were obtained.

1.1.4 Construction of electrocatalysts modified electrodes

1 mg PtxFe/C/N-GC-600, PtxFe/C/N-GC-700, PtxFe/C/N-GC-800, Pt/C (20%) catalysts

was added to the mixture solution of H2O (100 μL) and Nafion (20 μL) respectively.

After continuous sonicated for 0.5 h, 8 μL of the prepared catalyst slurry was slowly

drop casted on the glassy-carbon electrode (diameter = 4 mm) for MOR.

1.2 Characterizations

A Rigaku XtalAB PRO MM007 DW diffractometer has been employed to measure X-

ray single-crystal diffraction data for Pt/Fe-MOFs, which was carried out at 77 K with

Cu-Kα radiation (λ = 1.54 Å) in multi-scan mode. A Rigaku MiniFlex600

diffractometer (60 kV, 300 mA, with a Cu-target tube and a graphite monochromator)

was employed to perform the room-temperature PXRD of all as-prepared products.

Scanning electron microscopy (SEM) images were obtained by a field emission SEM

(JSM-7800F, Japan). Energy dispersive spectroscopy mapping and a high-resolution

TEM was employed on JEM-2800 (Japan). The Raman spectrum was investigated by a

Renishaw in Via Raman spectrometer (laser wavelength was 532 nm). A Thermo

Scientific ESCALAB 250Xi (Thermo, USA) X-ray photoelectron spectrometer was

used to examine the oxidation state of transition metals, and the containment carbon

peak was used to calibrate the binding energies. The Brunauer-Emmett-Teller (BET)

specific surface area of materials were measured at 77 K by ASAP 2460. The ICP-OES

(IRIS Intrepid Ⅱ XSP) was used to measure the content of Pt and Fe in catalysts. The

ICP-OES (Agilent ICP-OES-730) was used to measure the content of Pt and Fe in

electrolyte and mother liquid. The elemental analysis was investigated by element

analyzer (USA, LECO-TCH600).

1.3 Electrochemical Measurements

A three-electrode cell was used to perform the electrochemical measurements. For

MOR, platinum plate electrode was used as a counter electrode and Ag /AgCl electrode

was used as a reference electrode. The working electrode was a glassy-carbon electrode.

The voltage range was −0.2 to 1.2 V (vs. Ag / AgCl) for CV in nitrogen-saturated 0.5 M

H2SO4 and the mixture of 0.5 M H2SO4 +1 M CH3OH solutions with a sweep rate of 50

mV s−1 respectively. The data was collected by CHI760E electrochemical workstation

(Shanghai Chenhua). The electrochemically active surface area (ECSA) was obtained

from the charge of hydrogen desorption between −0.2 and 1.2 V (vs. Ag / AgCl) and

corrected with the Pt capacity of 210 μC cm−2. i-t curves were obtained at the fixed

potential 0.62 V in 0.5 M H2SO4 +1 M CH3OH electrolyte. All the electrochemical

measurements were executed on room temperature.

Figure S1. The PXRD patterns of Pt/Fe-MOFs.

Figure S2. The asymmetric unit of Pt/Fe-MOFs (H atoms are omitted for clarity).

Table S1. Crystal data and structure refinement for Pt/Fe-MOFs.

Complex Pt/Fe-MOFsChemical formula C17H12FeN6O4PtFormula Mass 615.27Crystal system Orthorhombica/Å 15.1120(4)b/Å 21.1317(4)c/Å 29.3846(8)α/° 90β/° 90γ/° 90Volume/Å3 9383.7(4)T/K 293(2)Space group IbcaZ 16Radiation type CuKαμ/mm−1 16.231Reflections measured 14819Independent reflections 4640Rint 0.0240R1

a (I> 2σ(I)) 0.0324wR2

b(F2) (I> 2σ(I)) 0.1084R1 (all data) 0.0376wR(F2) (all data) 0.1127Goodness of fit on F2

CCDC number1.1361892853

aR1= Fo-Fc/Fo. bwR2=[[w(Fo2-Fc

2)2]/[w(Fo2)2]]1/2.

Table S2. Selected bond lengths (Å) and angles (°) for Pt/Fe-MOFs.

Bond Angle

Pt(1)—C(1) 1.994(7) C(1)—Pt(1)—C(2) 180.0Pt(1)—C(2) 2.003(6) C(1)—Pt(1)—C(3) 91.86(13)Pt(1)—C(3) 1.999(7) C(1)—Pt(1)—C(3) 91.86(13)Pt(2)—C(4) 1.993(5) C(3)—Pt(1)—C(2) 88.14(13)Pt(2)—C(5) 1.980(6) C(3)—Pt(1)—C(3) 176.3(3)Fe(1)—O(3) 2.125(5) C(4)—Pt(2)—C(4) 89.9(3)Fe(1)—N(1) 2.157(6) C(5)—Pt(2)—C(4) 177.89(16)Fe(1)—N(3) 2.161(5) C(5)—Pt(2)—C(4) 90.5(3)Fe(1)—N(4) 2.172(4) C(5)—Pt(2)—C(5) 89.2(3)Fe(2)—O1(W) 2.126(4) O(3)—Fe(1)—O(3) 171.5(2)Fe(2)—N(5) 2.134(5) O(3)—Fe(1)—N(1) 85.76(12)Fe(2)—N(6) 2.192(4) O(3)—Fe(1)—N(3) 94.24(12)

O(3)—Fe(1)—N(4) 92.2(2)O(3)—Fe(1)—N(4) 87.9(2)N(1)—Fe(1)—N(3) 180.0N(1)—Fe(1)—N(4) 90.84(8)N(3)—Fe(1)—N(4) 89.16(8)N(4)—Fe(10—N(4) 178.32(16)O(1)W—Fe(2)—O1(W) 180.0O(1)W—Fe(2)—N(50) 91.2(2)O(1)W—Fe(2)—N(5) 88.8(2)O(1)W—Fe(2)—N(6) 91.4(2)O(1)W—Fe(2)—N(6) 88.6(2)N(5)—Fe(20)—N(5) 180.0N(5)—Fe(2)—N(6) 88.83(16)N(5)—Fe(2)—N(6) 91.17(16)N(6)—Fe(2)—N(6) 180.00(18)Fe(2)—O(1)W—H(1)WA 111.7Fe(2)—O(1)W—H(1)WB 111.0H(1)WA—O(1)W—H(1)WB 102.3Fe(1)—O(3)—H(3) 125.8(15)C(18)—O(3)—Fe(1) 125.5(4)C(18)—O(3)—H(3) 108.5(15)C(2)—N(1)—Fe(1) 180.0C(1)—N(3)—Fe(1) 180.0C(4)—N(4)—Fe(1) 175.0(5)C(5)—N(5)—Fe(2) 171.7(4)C(6)—N(6)—Fe(2) 122.9(4)C(10)—N(6)—Fe(2) 120.5(3)

Figure S3. PXRD patterns of Pt/Fe-MOFs, Pt/Fe-MOFs@GO and GO.

Table S3. Elemental analysis data of GO and as-prepared catalysts.

C (%) N (%) O (%) C : N C : O

GO 39.0 0.282 29.2 138.30 1.37

PtxFe/C/N-GC-600 58.8 1.87 9.87 31.44 5.96

PtxFe/C/N-GC-700 58.9 1.34 8.11 43.96 7.26

PtxFe/C/N-GC-800 50.3 1.0 11.5 50.3 4.37

From the elemental analysis data, we can find that after thermal annealing treatment, the

ratio of C to N decrease and C to O increase obviously, indicating the content of N has

increased and the content of O species has decreased, which can prove GO has

converted into reduced graphene oxide, and the N atoms were successfully doped in

graphitized carbon directly.

Figure S4. SEM images of (a) PtxFe/C/N-GC-600; (b) PtxFe/C/N-GC-800.

Figure S5. (a) TEM and (b) HRTEM images of PtxFe/C/N-GC-600.

Figure S6. (a) TEM and (b) HRTEM images of PtxFe/C/N-GC-800.

Figure S7. Raman spectra of PtxFe/C/N-GC-600, PtxFe/C/N-GC-700, PtxFe/C/N-GC-

800.

Figure S8. XPS survey spectra of Pt/Fe-MOFs@GO, PtxFe/C/N-GC-600, PtxFe/C/N-

GC-700, and PtxFe/C/N-GC-800.

Figure S9. High-resolution N 1s XPS spectrum of Pt/Fe-MOFs.

Table S4. ICP-OES data of samples annealed at different temperatures.

Sample Fe (wt%) Pt (wt%)

PtxFe/C/N-GC-600 6.89 7.92

PtxFe/C/N-GC-700 6.44 16.5

PtxFe/C/N-GC-800 8.18 17.2

404 402 400 398 396

Inte

nsity

(a.u

.)

Binding Energy (eV)

Pyridinic N Pyridinic N Graphitic N

398.88 eV

400.09 eV401.16 eV

PtxFe/C/N-GC-600

Figure S10. High-resolution N 1s XPS spectrum of PtxFe/C/N-GC-600.

406 404 402 400 398 396

Inte

nsity

(a.u

.)

Binding Energy (eV)

Graphitic N Pyrrolic N Pyridinic N

PtxFe/C/N-GC-800

401.59 eV 399.85 eV 398.64 eV

Figure S11. High-resolution N 1s XPS spectrum of PtxFe/C/N-GC-800.

Table S5. The percentage of three nitrogen species in PtxFe/C/N-GC-600, PtxFe/C/N-

GC-700 and PtxFe/C/N-GC-800, respectively.

PtxFe/C/N-GC-600 PtxFe/C/N-GC-700 PtxFe/C/N-GC-800

Graphitic N 26.61% 49.21% 43.81%

Pyrrolic N 31.92% 26.68% 30.99%

Pyridinic N 41.47% 24.11% 25.20%

Table S6. ICP-OES data of the electrolyte of t-PtxFe/C/N-GC-800.

Fe 0.0943 mg/ L

Pt 0.0659 mg/ L

Table S7. The comparison of the MOR of PtxFe/C/N-GC-700 with other reported Pt-

based electrocatalysts which tested under similar conditions.

Material ECSA of

Pt/C (20%)

ECSA Specific/ mass

activity

Long-term

stability

PtxFe/C/N-GC-700 0.9 m2g-1Pt 26.36 m2 g-1

Pt 295.63 mA mg-1Pt 4000 s

Pt0.33Bi0.67 /POSS 1 67.6 m2g-1Pt 78.7 m2 g-1

Pt 0.826 A mg-1Pt 4000 s

PtCu3 nanocage 2 48.6 m2g-1 35.7 m2 g-1 14.1 mA cm-2 800 s

Pt2Ru3 3 — — 1.4 mA mg-1

Pt —

Pt-CeO2/C-O 4 55.5 m2g-1Pt 38.6 m2 g-1

Pt 0.83 A mg-1Pt 3500 s

Pt-CeO2/C-S 4 55.5 m2g-1Pt 52.3 m2 g-1

Pt 1.45 A mg-1Pt 3500 s

Pt-CeO2/C-C 4 55.5 m2g-1Pt 47.1 m2 g-1

Pt 1.07 A mg-1Pt 3500 s

VT-PtRhNWs

without INSAFs 5

68.51 m2/gPt 79.20 m2/gPt 455 A g-1 1000 s

RGO/Pt-Pd 6 — 0.91 cm2 59.60 mA cm-2 3000 s

Pt–Ni NCs 7 43.3 m2g-1Pt 29.5 m2 g-1

Pt 1.26 A mg-1Pt —

Pt–Ni–P MNCs 8 — 2.28 mA cm-2 3600 s

Ru@Pt/C-TiO2 9 60.0 m2/gPt 69.6 m2/gPt 1.08 mA cm-2 8000 s

PtRu-RGO 10 — 18.70 m2 g-1 23.1 mA cm-2 1500 s

Pt/NiCo/GCE 11 — — 66.1 mA cm-2 500 s

Pt3Fe 12 — 9.2 m2 g-1Pt 0.32 A mg-1

Pt —

NP-PtCo 13 — 23.0 m2 g-1 Pt — —

Pt-Cu BANCs 14 57.1 m2g-1 73.9 m2 g-1 3.36 mA cm-2 3000 s

Pt66 Ni27 Ru7 15 — 19.9 m2 g-1 805.2 mA mg-1 3600 s

Pt@HfSx/CNT 16 — — 4.98 mA cm-2 5000 s

PtAu/C 17 — 28.8 m2 g-1Pt 36.2 mA mg-1

Pt —

Pt/ATO-C-90 18 — 66.0 m2 g-1Pt 0.737 A g-1 4000 s

PtPdCu nanowires 19 37.6 m2g-1Pt 58.8 m2g-1

Pt 535.3 mA mg-1Pt 2000 s

PtCu nanowires 19 37.6 m2g-1Pt 27.9 m2g-1

Pt 366.64 mA mg-1Pt 2000 s

PtPd nanowires 19 37.6 m2g-1Pt 29.0 m2g-1 294.12 mA mg-1

Pt 2000 s

Pt/Lg-CDs-800 20 — 40.6 m2g-1Pt 0.76 mA cm-2 1000 s

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