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Electronic Supplementary Information

Ternary Ni-Co-P Nanoparticles and Their Hybrids with Graphene as

noble-metal-free Catalysts to Boost the Hydrolytic Dehydrogenation of

Ammonia-Borane

Chun-Chao Hou, Qiang Li, Chuan-Jun Wang, Cheng-Yun Peng, Qian-Qian Chen, Hui-Fang Ye, Wen-Fu Fu,* Chi-Ming Che, Núria López,* and Yong Chen*

Key Laboratory of Photochemical Conversion and Optoelectronic Materials and HKU-CAS Joint Laboratory on New Materials, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing, 100190, P. R. China

Institute of Chemical Research of Catalonia, ICIQ, The Barcelona Institute of Science and Technology, Av. Països Catalans, 16, 43007, Tarragona, Spain

University of Chinese Academy of Sciences, Beijing 100049, P. R. China

College of Chemistry and Engineering, Yunnan Normal University, Kunming 650092, P. R. China

Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, P. R. China

Electronic Supplementary Material (ESI) for Energy & Environmental Science.This journal is © The Royal Society of Chemistry 2017

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Experimental SectionMaterials: All chemicals and solvents were of analytical grade and used as

received without further purification. Borane ammonia complex (NH3BH3, 97%) was purchased from Sigma-Aldrich. Nickle (II) nitrate hexahydrate (Ni(NO3)26H2O, 98.0%) were obtained from Xilong Chemical Co., Ltd. Cobalt(II) nitrate hexahydrate (Co(NO3)26H2O, 99.0%) were obtained from Guangzhou Sci-Tech Co., Ltd. Sodium hypophosphite (NaH2PO2, 99.0%) was bought from Aladdin Ltd (Shanghai, China). Sodium citrate (C6H5Na3O76H2O, 99.0%) was obtained from Beijing Chemical works. HCl, NaOH and all solvent were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China).

Material synthesis: Synthesis of Ni1-0.5xCo0.5x(OH)2 and Ni0.35Co0.65(OH)2/GO precursors. The Ni1-0.5xCo0.5x(OH)2 precursors were synthesized through a modified co-precipitation method.1,2 In a typical synthesis of Ni1-0.5xCo0.5x(OH)2, 250 mg sodium citrate and 2 g of NaOH were firstly dissolved in 80 mL of deionized water, and then the mixture was ultrasonicated at room temperature for at least 20 min to generate a homogeneous solution. After that, desired amount of Ni(NO3)26H2O and Co(NO3)26H2O dissolved in 20 mL of deionized water was slowly dropwise injected into the above aqueous solution and the total concentration of Ni2+ and Co2+ was controlled at 3.44 mmol. After aging under continuous stirring for 1 h, a colloidal dispersion was formed. The gel was collected by centrifugation, washed subsequently with deionized water and ethanol for three times and then dried under vacuum at 60 oC overnight. The Ni0.35Co0.65(OH)2/GO precursors were prepared by the similar process and details are as follows: 125 mg sodium citrate,1 g of NaOH and 30 mg GO were firstly dissolved in 80 mL of deionized water, and then the mixture was ultrasonicated at room temperature for up to 5 h to generate a homogeneous solution. After that, 175 mg Ni(NO3)2·6H2O and 325 mg Co(NO3)2·6H2O dissolved in 20 mL of deionized water was slowly dropwise injected into the above aqueous solution. After aging under continuous stirring for 1 h, a uniform dispersion was formed. Then, the precipitate was centrifuged and washed several times with pure water and ethanol. The precipitates were dried at 60 oC in a reduced-pressure oven overnight at room temperature.

Synthesis of the Ni2-xCoxP nanoparticles and Ni0.7Co1.3P/GO nanohybrid. Ni2-xCoxP nanoparticles were synthesized through a simple solid state reaction by reacting the Ni1-0.5xCo0.5x(OH)2 precursors with NaH2PO2 at high temperature.3,4 In a typical process, 200 mg Ni1-0.5xCo0.5x(OH)2 precursors and 1 g NaH2PO2 were mechanically blended and grounded down into a fine powder and kept at 300 °C for 2 h in a quartz tube with a heating rate of 5 °C min-1 under the protection of an Ar flow. After cooling to room temperature in continued Ar flow, the obtained products were thoroughly washed with 1 M HCl, deionized water and ethanol several times, respectively. Then the obtained Ni2-xCoxP catalysts were dried under vacuum overnight at 60 °C. The Ni0.7Co1.3P/GO nanohybrid was prepared through the same

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process by starting from the as-prepared Ni0.35Co0.65(OH)2/GO precursor. The weight percentage was 63.2%, measured by ICP-OES.

Structural Characterization: Powder X-ray diffraction patterns (XRD) were carried out on a Bruker AXS D8 X-ray diffractometer (Cu K, = 1.5406 Å, 100 mA, and 40 kV). X-ray photoelectron spectroscopy (XPS) spectra were firstly deoxygenated under Ar for 1 h and then investigated on a ThermoScientific ESCALAB 250XI spectroscopy equipped with an Al K X-ray source and a power of 250 W was used. The charge effect was calibrated using the binding energy of C (1s) (284.8 eV). Scanning electron microscope (SEM) images, corresponding energy-dispersion X-ray spectroscopy measurements and their corresponding energy dispersive X-ray mapping were conducted on a Hitachi S-4800 field emission scanning electron microscope. Samples for transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM) and energy-dispersion X-ray (EDX) spectroscopy measurements were analyzed by using a transmission electron microscope (JEM 2100F) with an accelerating voltage of 200 kV. For all TEM, HRTEM, SEM, SAED, and corresponding EDX measurements, the samples were firstly dispersed in ethanol and sonicated for at least 30 min, then dropped on an ultrathin carbon film copper mesh and allowed to dry in air at room temperature prior to these measurements. Elemental analysis data for samples were obtained using ICP-OES (Varian 710-OES, USA). Surface areas were estimated from the amount of N2 adsorbed by using the BET equilibrium equation at 77 K. The absorption spectra of Ni and Co K-edge were collected in transmission mode at the X-ray absorption fine structure (XAFS) station of the 1W1B beamline of the Beijing Synchrotron Radiation Facility (BSRF).

Catalytic Activity Measurement: The hydrolytic dehydrogenation experiments were performed in a 10 mL two-necked round-bottom flask, in which one neck was sealed with a rubber cap, while the other was connected to a gas burette. We use a constant-temperature bath to maintain the reaction system’s temperature, which was further confirmed by a thermometer. A certain amount of catalysts were placed in the two-necked round-bottomed flask, and then AB in 0.5 M NaOH aqueous solution (5 mL) was quickly injected using a syringe. The generated H2 in the system was identified though a gas chromatograph (GC-14C, Shimadzu) equipped with a 5 Å molecular sieve column (3 m 2 mm), thermal conductivity detector and the carrier gas is Ar. The amount of gas was measured quantitatively using a gas burette with an accuracy of 0.5 mL.

The reusability of the Ni0.7Co1.3P and Ni0.7Co1.3P/GO catalysts was carefully performed at room temperature. At an early stage, various parallel experiments were carried out at the same time. After that, the catalysts in these experiments were collected, combined together, and washed with deionized water and ethanol, respectively. Then, the restored catalysts were dried in a vacuum over at 343 K for the next use. Similar process was repeated for the several another cycles according to the above experimental process.

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Computational Details: To further illustrate the enhancing effect of Cobalt on Ni2P, Density Functional Theory (DFT) calculations were performed by using Vienna ab initio simulation package (VASP). The exchange and correlation energies were obtained through the PBE functional. The inner electrons were represented by projector augmented wave (PAW) pseudopotentials with kinetic cut-off energies of 600 and 450 eV for bulk and surface calculations. Gama centred 7×7×13 and 3×3×1 Monkhorst-Pack mesh k-points were sampled for bulk relaxation and surface optimization. Surface with a p(2×2) supercell configuration and five atomic layers were used to simulate the catalysts of Ni2P and Ni0.7Co1.3P. The first two layers were fully relaxed to mimic the surface and the rest were fixed to their bulk parameters. A vacuum of 15 Å was used to avoid the interaction between two slabs and dipole correction was also introduced to eliminate the spurious contributions arising from the asymmetry of the system along the z direction. Upon relaxation, surfaces were then fixed during the adsorption and transition state calculations. Gas phase molecules such as Ammonia Bromine, water and hydrogen were optimized in a box of 20 Å side cubic box and cut-off energy of 450 eV. Zero point energies (ZPE) for the molecular units have been corrected for all the energies of structures in this paper.

Calculated lattice parameters of hexagonal Ni2P bulk structure are a = b = 5.871, and c = 3.377 Å, in good agreement with experiment values of a = b = 5.859 and c = 3.382 Å and previous DFT results. For Co doped model, four Ni atoms were replaced by Co (Ni : Co = 1 : 2 ) to simulate the catalyst with stoichiometry of Ni0.7Co1.3P. The reoptimized bulk parameters are a = b = 5.766 and c = 3.368 Å. For Co-only bulk structure (Co2P), six Ni atoms were replaced by Co atoms in Ni2P bulk. Optimized parameters within considering spin polarization are a = b = 5.723 and c = 3.401 Å. For Ni2P (0001) surface, there are two terminations structures with stoichiometry of N3P2 and Ni3P. In this work, all reactions were studied on Ni3P2 terminated as it is widely accepted as the most stable one. For the Co containing material, the NiCoP2 terminated surface was used. Spin polarization were not considered for adsorption and transition state calculations on Ni3P2 and NiCo2P2 surfaces because the magnetizations of each atom are almost zero in the population results. Climbing-image Nudged Elastic Band (CI-NEB) method and the improved dimer method (IDM) were applied to locate the transition states. All transition states were verified with only one imaginary value from frequency calculations obtained by diagonalization of the Hessian matrix constructed by the displacement of all atoms by 0.02 Å. Visualization of transition states was displayed by using Molden package.5 Calculated solvation energy of AB in the liquid phase is 0.65 eV by using the MGCM methodology6. All structures have been uploaded to our open database iochem-BD7

and are available (http://dx.doi.org/10.19061/iochem-bd-1-34).

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NMR Measurement: NMR spectra were recorded on a BRUKER AVANCE 400 MHz spectrometer (400.1 MHz for 1H NMR; 128.3 MHz for 11B NMR). Liquid samples of the filtrates, in which D2O was included as solvent or a lock, were contained in sample tubes of 5 mm o. d., in which coaxial inserts of BF3·(C2H5)2O as an external reference were placed. NH3BH3 was dissolved in water or 0.5 M NaOH to form colorless solution, which exhibits a quadruplet peak centered at = -23.9 ppm with 1JB–H = 91Hz in the 11B NMR spectrum, in agreement with previous reports (See Figure S7-S10).8,9 After catalytic reaction, the acquired product exhibits a singlet peak centered at = 4.71 ppm ( = 4.72 ppm in 0.5 M NaOH) in the 1H NMR spectrum, which confirms the existence of NH4

+. In water, the 11B NMR spectrum of the acquired product shows a broad resonance at = 8.78 ppm. However, in 0.5 M NaOH, the 11B NMR spectrum shows a resonance at = 1.55 ppm. This observed low field-shifted single 11B resonance and its pH dependence behavior can be attributed to an equilibrium process between BO2

−, H3BO3 and other borate species, which undergo rapid change between each other in the solution on the NMR time scale.10 Due to the existence of equilibrium process, the final borate species (such as BO2

–, B(OH)3, B(OH)4

– etc.) obtained is complicated and disputable. Recently, Chen and co-workers confirmed that B-containing byproducts are mainly in the form of an NH4B(OH)4-B(OH)3 mixture rather than NH4BO2 as reported previously, which was corroborated by a combination of thermodynamic analysis and FTIR measurement.11 It was believed the existence of an acid-base equilibrium B(OH)4

– ⇋ B(OH)3 + OH– (pKa = 9.2) for the B-containing byproducts in the reaction solution. In view of the strong alkali condition in our experiments (0.5 M NaOH), we propose the B(OH)4

– as main product. Therefore, the main reaction in our system is tentatively described as follows:

H3NBH3 + 4H2ONH4+ + B(OH)4

– + 3H2

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10 20 30 40 50 60 70 80

Ni0.35Co0.65(OH)2

Ni0.5Co0.5(OH)2

Ni0.25Co0.75(OH)2

Inte

nsity

(a. u

.)

2-Theta (degree)

Ni(OH)2

JCPDF: 14-0117

Figure S1. Powder XRD patterns of the Ni1-0.5xCo0.5x(OH)2 colloidal precursors.

20 40 60 80

Ni0.5Co1.5P

Ni0.7Co1.3P

NiCoP

PDF #65-3544 (Ni2P)Inte

nsity

(a. u

.)

2-Theta (degree)

Ni2P

Figure S2. Powder XRD patterns of the as-prepared Ni2−xCoxP catalysts.

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36 38 40 42 44

Ni0.5Co1.5P

Ni0.7Co1.3P

NiCoPIn

tens

ity (a

. u.)

2-Theta (degree)

Ni2P

Figure S3. Zoom-in part of XRD patterns for the Ni2-xCoxP NPs.

Figure S4. EDX results corresponding to a selected scanning electron microscope image of the Ni0.7Co1.3P NPs.

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Table S1. The radio of Ni and Co in various Ni-Co-P nanocatalysts.

Samples Added value of Ni : Co

Measured value of Ni : Co by ICP-OES

Ni2P 2:0 2:0NiCoP 1:1 1:0.998

Ni0.7Co1.3P 0.7:1.3 0.7:1.270Ni0.5Co1.5P 0.5:1.5 0.5:1.505

Ni0.7Co1.3P/GO 0.7:1.3 0.76:1.3

Figure S5. (a) XPS survey data and XPS spectra of the (b) Ni 2p, c) Co 2p, and d) P 2p of the as-prepared Ni0.7Co1.3P NPs.

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0.5 1.0 1.5 2.0

0

1x105

2x105

3x105

O2 N2

Pe

ak a

reas

Time (min)

H2

Figure S6. Recorded peak area of iso-volumetric gases corresponding to labeled H2 produced in reaction systems. Note: the GC column for H2 detection is not suitable for NH3. Instead, the generated gas was bubbled into a dilute H2SO4 solution through a home-made device and the resulting solution was carefully analyzed by classic Nessler method and ion chromatography. Trace amount of NH3 was confirmed in our experimental conditions.

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Figure S7. 1H NMR spectra of NH3BH3 solution in D2O, (a) before and (b) after reaction at 298 K.

Figure S8. 11B NMR spectra of NH3BH3 solution in D2O, (a) before and (b) after reaction at 298 K.

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Figure S9. 1H NMR spectra of NH3BH3 solution in D2O containing 0.5 M NaOH, (a) before and (b) after reaction at 298 K.

Figure S10. 11B NMR spectra of NH3BH3 solution in D2O containing 0.5 M NaOH, (a) before and (b) after reaction at 298 K.

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1.8 2.1 2.4 2.7 3.0 3.3

3.6

3.9

4.2

4.5

4.8

ln ra

te

ln[Cat]

ln rate = 0.903 ln [Cat] + 1.829 R2 = 0.997

Figure S11. Logarithmic plot of H2 generation rate versus [Ni0.7Co1.3P].

0 1 2 3 40

50

100

150

200

H 2 evo

lutio

n (m

L)

ncat/nAB

0.042 0.035 0.030 0.026

Time (min)Figure S12. Relationship between hydrogen-generating rate and AB concentration at fixed amount (0.0674 mmol) of Ni0.7Co1.3P catalyst in 0.5 M NaOH aqueous solution at 298K.

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5.8 5.9 6.0 6.1 6.2

4.3

4.4

4.5ln rate = 0.51 ln [AB] + 1.35 R2 = 0.994

ln ra

te

ln [AB]Figure S13. Logarithmic plot of H2 generation rate versus [AB].

3.0 3.2 3.4 3.62

3

4

5

ln T

OF

1/T (10-3 K-1)

ln TOF = 21.06 - 5194.19 / T R2 = 0.992

Activation EnergyEa = 43.2 KJ/mol

Figure S14. Arrhenius plot of ln TOF versus 1/T. The activation energy is calculated to be 43.2 kJ/mol for the Ni0.7Co1.3P sample in the catalytic hydrolysis of AB.

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Figure S15. (a) TEM, (b) magnified TEM and (c) HRTEM images of the reclaimed Ni0.7Co1.3P NPs after 10 cycles; (d) XRD patterns and (e) XPS spectra of the Ni 2p of the initial Ni0.7Co1.3P NPs and reclaimed Ni0.7Co1.3P NPs after 10 cycles. Scale bar: (a) 50 nm; (b) 20 nm; (c) 5 nm.

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Figure S16. XPS spectra of a) Ni 2p, b) Co 2p, and c) P 2p of the as-prepared Ni2-

xCoxP NPs.

Figure S17. (a) Co K-edge and (b) magnified XANES spectra for NiCoP, Ni0.7Co1.3P, and Ni0.5Co1.5P nanocatalysts. (c) Co K-edge EXAFS k3 (k) oscillation functions of NiCoP, Ni0.7Co1.3P, Ni0.5Co1.5P NPs and Co foil. (d) The corresponding FT curves of NiCoP, Ni0.7Co1.3P, and Ni0.5Co1.5P NPs.

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Table S2. Bader charge analysis (in e-) of two layers in bulk Ni2P and Ni2/3Co3/4P.12

Ni2P Ni2/3Co4/3PAtoms Ni3P(0001) Ni3P2(0001) NiCo2P(0001) NiCo2P2(0001)

Ni 0.29, 0.29, 0.29 0.11, 0.11, 0.11 0.26 0.07Co 0.30, 0.30 0.10, 0.10P -0.42 -0.38, -0.38 -0.42 -0.35, -0.35

Scheme S1：Proposed AB hydrolytic dehydrogenation mechanism

Table S3. Adsorption energies (Eads, eV) of closed shell molecules on Ni3P2 and NiCo2P2, and their solvation energies (Esolvation, eV) in water by using VASP-MGCM method6 are also listed.

Species Eads on Ni3P2 Eads on NiCo2P2 Esolvation

H -0.48 -0.66 0.008NH3 -0.59 -0.76 -0.184BH3 -1.21 -1.65 -0.126

BH2OH -0.88 -1.72 -0.214H2O -0.21 -0.29 -0.295, -0.273a

BH3-NH3 -1.03 -1.45 -0.650HOBH2-NH3 -1.04 -1.46 0.732

a: from Ref.13

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Table S4. DFT calculated adsorption energies, reaction barriers and energies in the H2 production from AB.

Activation Energy / eV Reaction Energy / eVReactions

Ni3P2 NiCo2P2 Ni3P2 NiCo2P2

H3B-NH3(g) + * → H3B-NH3* 0.00 0.00 -1.02 -1.46H2O(g) + * → H2O* 0.00 0.00 -0.21 -0.29H3B-NH3 + OH* → HOBH3* + NH3* 1.08 0.87 -0.20 -0.62HOBH3* → HOBH2* + H* 0.36 0.32 0.10 0.27HOBH3*+OH*→BH2 (OH)2* + H* / 1.01 / -0.49BH2OH* → BHOH* + H* / 1.06 / -0.45H2O*+BH2OH*→ BHOH* + H2*+OH* / 1.38 / -0.34

BH2OH*+ OH*→ BH2(OH)2* / 0.89 / -0.74HOBH2* + NH3* → HOBH2-NH3* 0.04 0.12 -0.51 -0.06

OH* + HOBH2NH3→ BH2(OH)2* + NH3* / 0.69 / -0.51H2O* + H* → OH* + H2* 0.83 0.87 -0.59 -0.76H2* → H2(g) 0.22 0.50 -0.22 -0.50

Table S5. Bader charge analysis (in e-) of the related species in the proposed mechanism.

BH3gas + NH3gas ABgas ABads HOBH3* +NH3* HOBH2* + NH3* HOBH2-NH3*

B 2.80 1.69 1.50 1.63 1.26 1.75N -1.18 -1.25 -1.31 -1.22 -1.20 -1.40

Table S6. d-band centers (ɛd in eV) of Ni and Co in bulk of Ni2P, Ni2/3Co4/3P and Co2P.

Ni2P Ni2/3Co4/3P Co2P

Ni -2.38 -1.86 /Co / -1.52 -1.49

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Figure S18. TEM images of the NiCoP NPs. Scale bar: (a) 200 nm; (b) 20 nm; (c) 10 nm; (d) 5 nm.

Figure S19. TEM images of the Ni2P, NiCoP and Ni0.5Co1.5P NPs. Scale bar: (a) 50 nm; (b, c) 20 nm.

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Figure S20. TEM images of the Ni0.7Co1.3P/GO. Scale bar: (a) 50 nm; (b) 20 nm; (c, d) 10 nm.

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Figure S21. XPS spectra of the (a) Ni 2p, (b) Co 2p, and (c) P 2p of the as-prepared Ni0.7Co1.3P NPs and Ni0.7Co1.3P/GO nanohybrid.

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0.0 0.2 0.4 0.6 0.8 1.0

0

100

200

300

Ni2P NiCoP Ni0.7Co1.3P Ni0.5Co1.5P Ni0.7Co1.3P/GO

Va /

cm

3 g-1(S

TP)

P/P0

Figure S22. Nitrogen adsorption desorption isotherms of the Ni2-xCoxP NPs NPs and Ni0.7Co1.3P/GO nanohybrid.

Table S7. The specific surface areas of different samples calculated through the Brunauer-Emmett-Teller (BET) method.

Samples Ni2P NiCoP Ni0.7Co1.3P Ni0.5Co1.5P Ni0.7Co1.3P/GO

SBET

(m2/g) 28.97 49.90 69.26 41.80 80.0

0 10 20 30 40 50 60

0

50

100

150

200

H 2 evo

lutio

n (m

L)

1st

2nd

3rd

4th

5th

6th

Time (min)Figure S23. Reusable Ni0.7Co1.3P/GO (5 mg) catalyst with AB (2.592 mmol) in 0.5 M NaOH aqueous solution (5 mL) at 298K.

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Table S8. TOF values reported in the literatures.

Catalyst Highest gained TOF (H2) mol /molCat·min T(K) Ref

Ni0.7Co1.3P/GO 153.9a

109.4b 298 This work

Co NPs (in-situ) 49.8 298 14

Ni2P 40.4 298 15

CuCo@MIL-101 19.8 298 16

Ni@ZIF-8 14.2 298 17

Cu0.8Co0.2O-GO 70.0 298 18

CoP 72 298 19

Cu NPs@SCF 40.0 298 20

CuO-NiO 60.0 298 21

Cu0.5Ni0.5/CMK-1 54.8 298 22

Ni NPs@3D-(N)GFs 41.7 298 23

Co@PEI-GO 39.9 298 24

Cu0.49Co0.51/C 28.7 298 25

Ni NPs/CNT 23.5 298 26

Ni NPs/C 8.8 298 27

Co/graphene 13.8 298 28

Cu0.2Co0.8@MCM-41 15.0 298 29Cu0.1@Co0.45Ni0.45

/graphene 15.46 298 30

Ni@MCS-30 30.7 298 31

Ni@CNT 26.2 298 32

CoP NA/Ti 42.8 298 33

Co/CTF 42.3 298 34

CuCo/MIL-101-1-U 51.7 298 35

Co/NPCNW 7.29 298 36

Pt-CoCu@SiO2 272.8 (based on Pt) 303 37

Pt/C 111.0 298 38

Pt black 14.0 298 38a TOF was based on the total mole number of Ni2-xCoxP; b TOF was based on the total mole number of metal.

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References1. X. Zhou, Z. Xia, Z. Zhang, Y. Ma, Y. Qu, J. Mater. Chem. A, 2014, 2, 11799.2. J. Y. Li, M. Yan, X. M. Zhou, Z. Q. Huang, Z. M. Xia, C. R. Chang, Y. Y. Ma, Y. Q. Qu, Adv. Funct. Mater., 2016, 26, 6785.3. C. C. Hou, S. Cao, W. F. Fu, Y. Chen, ACS Appl. Mater. Interfaces, 2015, 7, 28412. 4. C. C. Hou, Q. Q. Chen, C. J. Wang, F. Liang, Z. S. Lin, W. F. Fu, Y. Chen, ACS Appl. Mater. Interfaces, 2016, 8, 23037.5. G. Schaftenaar , J. H. Noordik. J. Comput.-Aided Mol. Design, 2000, 14, 123.6. M. Garcia-Ratés, N. López, J. Chem. Theory Comput., 2016, 12, 1331.7. M. Álvarez-Moreno, C. de Graaf, N. López, F. Maseras, J. M. Poblet, C. Bo, J. Chem. Inf. Model., 2015, 55, 95.8. D.F. Gaines, R. Schaeffer, J. Am. Chem. Soc., 1964, 86, 1505.9. B.F. Spielvogel, J.M. Purser, J. Am. Chem. Soc., 1967, 89, 5294.10. M. Chandra, Q. Xu, Journal of Power Sources, 2006, 156, 190.11. W. Y. Chen, D. Li, Z. J. Wang, G. Qian, Z. J. Sui, X. Z. Duan, X. G. Zhou, I. Yeboah, D. Chen, AIChE J., 2017, 1, 60.12. G. Henkelman, A. Arnaldsson, H. Jónsson, Comput. Mater. Sci., 2006, 36, 254.13. D. J. Tannor, B. Marten, R. Murphy, R. A. Friesner, D. Sitkoff, A. Nicholls, B. Honig, M. Ringnalda, W. A. GoddardIII, J. Am. Chem. Soc., 1994, 116, 11875.14. J. M. Yan, X. B. Zhang, H. Shioyama, Q. Xu, J. Power Sources, 2010, 195, 1091.15. C. Y. Peng, L. Kang, S. Cao, Y. Chen, Z. S. Lin, W. F. Fu, Angew. Chem. Int. Ed., 2015, 54, 15725.16. J. Li, Q. L. Zhu, Q. Xu, Catal. Sci. Technol., 2015, 5, 525.17. P. Z. Li, K. Aranishiab, Q. Xu, Chem. Commun., 2012, 48, 3173.18. K. Feng, J. Zhong, B. H. Zhao, H. Zhang, L. Xu, X. H. Sun, S. -T. Lee, Angew. Chem. Int. Ed., 2016, 55, 11950.19. Z. -C. Fu, Y. Xu, S. Chan, W. Wang, F. Li, F. Liang, Y. Chen, Z. Lin, W. F. Fu, C. -M. Che, Chem. Commun., 2017, 53, 705.20. M. Kaya, M. Zahmakiran, S. Özkar, M. Volkan, ACS Appl. Mater. Interfaces, 2012, 4, 3866.21. H. Yen, F. Kleitz, J. Mater. Chem. A, 2013, 1, 14790.22. H. Yen, Y. Seo, S. Kaliaguine, F. Kleitz, ACS Catal., 2015, 5, 5505.23. M. Mahyari, A. Shaabani, J. Mater. Chem. A, 2014, 2, 16652.24. J. T. Hu, Z. X. Chen, M. X. Li, X. H. Zhou, H. B. Lu, ACS Appl. Mater. Interfaces, 2014, 6, 13191.25. A. Bulut, M. Yurderi, I. E. Ertas, M. Celebi, M. Kaya, M. Zahmakiran, Appl Catal B-Environ, 2016, 180, 121.26. G. Q. Zhao, J. Zhong, J. Wang, T. K. Sham, X. H. Sun, S. T. Lee, Nanoscale, 2015, 7, 9715.27. Ö. Metin, V. Mazumder, S. Özkar, S. H. Sun, J. Am. Chem. Soc., 2010, 132, 1468.28. L. Yang, N. Cao, C. Du, H. M. Dai, K. Hu, W. Luo, Cheng, G. Z. Mater. Lett., 2014, 115, 113.29. Z. H. Lu, J. P. Li, G. Feng, Q. L. Yao, F. Zhang, R. Y. Zhou, D. J. Tao, X. S. Chen, Z. Q. Yu, Int. J. Hydrogen Energy, 2014, 39, 13389.

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30. X. Y. Meng, L. Yang, N. Cao, C. Du, K. Hu, J. Su, W. Luo, G. Z. Cheng, ChemPlusChem, 2014, 79, 325.31. P. Z. Li, A. Aijaz, Q. Xu, Angew. Chem. Int. Ed., 2012, 51, 6753.32. J. K. Zhang, C. Q. Chen, W. J. Yan, F. F. Duan, B. Zhang, Z. Gao, Y. Qin, Catal. Sci. Technol., 2016, 6, 2112.33. C. Tang, F. Qu, A. M. Asiri, Y. Luo, X. P. Sun, Inorg. Chem. Front., 2017, 4, 659.34. Z. Li, T. He, L. Liu, W. Chen, M. Zhang, G. Wu, P. Chen, Chem. Sci., 2017, 8, 781.35. P. Liu, X. Gu, K. Kang, H. Zhang, J. Chen, H. Su, ACS Appl. Mater. Interfaces, 2017, 9, 10759.36. L. Zhou, J. Meng, P. Li, Z. Tao, L. Mai, J. Chen, Mater. Horiz., 2017, 4, 268.37. Y. Ge, Z. H. Shah, X. -J. Lin, R. Lu, Z. Liao, S. Zhang, ACS Sustainable Chem. Eng., 2017, 5, 1675.38. Q. Xu, M. Chandra,;J. Alloy Compd., 2007, 446-447, 729-732.