Corporation. Ti mesh was provided by Hongshan District, Wuhan Instrument Surgical

Transcription

1 Supporting Information Mn Doping of CoP Nanosheets Array: An Efficient Electrocatalyst for Hydrogen Evolution Reaction with Enhanced Activity at All ph Values Tingting Liu, Xiao Ma, Danni Liu, Shuai Hao, Gu Du, Yongjun Ma, Abdullah M. Asiri, ǁ Xuping Sun,, * and Liang Chen ʃ, * College of Chemistry, Sichuan University, Chengdu , China, Chengdu Institute of Geology and Mineral Resources, Chengdu , China, Analytical and Test Center, Southwest University of Science and Technology, Mianyang , China, ǁChemistry Department, King Abdulaziz University, Jeddah 21589, Saudi Arabia, and ʃningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo , China * sunxp@scu.edu.cn (X.S.); chenliang@nimte.ac.cn (L.C.) Experimental Section Materials: Co(NO 3 ) 2 4H 2 O, KOH, KCl, and NaH 2 PO 2 were purchased from Aladdin Ltd. (Shanghai, China). H 2 SO 4, ethanol, NaH 2 PO 4, and Na 2 HPO 4 were purchased from Beijing Chemical Corp. MnSO 4 H 2 O was purchased from Tianjin Chemical Corporation. Ti mesh was provided by Hongshan District, Wuhan Instrument Surgical Instruments business. Pt/C (10 wt% Pt) was purchased from Alfa Aesar (China) Chemicals Co. Ltd. Nafion (5 wt%) were purchased from Sigma-Aldrich Chemical Reagent Co., Ltd. All chemicals were used as received without further purification. The water used throughout all experiments was purified through a Millipore system. Preparation of hydroxide precursor/ti: Before electrodeposition, Ti mesh was firstly cleaned by HCl, ethanol and water several times to remove the surface impurities. To synthesize hydroxide precursor/ti, MnSO 4 H 2 O ( mol), Co(NO 3 ) 2 4H 2 O (0.02 mol), and KCl (0.01 mol) were dissolved in 100 ml deionized water and stirred for 30 min at room temperature. The three-electrode cell consists of the cleaned Ti mesh (1 cm 2 cm) as the working electrode, Ag/AgCl as the reference electrode and graphite plate as the counter electrode by a CHI 660E electrochemical analyzer (CH Instruments, Inc. Shanghai). Electrodeposition was 1

2 carried out by potentiostatically at a potential of -1.1 V vs. the Ag/AgCl reference electrode for 6 min at 343 K. After deposition, the Ti mesh was removed from the compression cell and rinsed first with ethanol, H 2 O and then dried at 60 C for 6 h. Preparation of Mn-Co-P/Ti: The hydroxide precursor/ti and NaH 2 PO 2 (0.05 g) were placed at two separate positions in a porcelain boat with NaH 2 PO 2 at the upstream side of the furnace. Subsequently, the sample was heated at 300 C for 120 min in Ar atmosphere, and then cooled to ambient temperature under Ar. After that, a black film was observed on Ti mesh. CoP/Ti was also made from its hydroxide precursor grown on Ti mesh without the presence of Mn salt. Characterizations: XRD measurements were performed using a RigakuD/MAX 2550 diffractometer with Cu Kα radiation (λ= Å). ICP-AES analysis was performed on Model ARCOS FHS12 (SPECTRO Analytical Instruments Inc., Germany). SEM images were taken on a XL30 ESEM. TEM images were collected on a Zeiss Libra 200FE transmission electron microscope operated at 200 kv. XPS measurements were performed using an ESCALABMK II X-ray photoelectron spectrometer with the exciting source of Mg. Electrochemical measurements: Electrochemical measurements were performed with CHI 660E potentiostat (CH Instruments, China). A conventional one-component three-electrode cell was used. The Mn-Co-P/Ti, Pt/C on Ti mesh and bare Ti mesh used as the working electrode, a saturated calomel electrode (SCE) used as the reference electrode, and graphite plate used as the counter electrode. The geometric surface area of the tested working electrode is 0.5 cm 0.5 cm. In all measurements, SCE was calibrated with respect to RHE. In 0.5 M H 2 SO 4, E (RHE) = E (SCE) V. In 1.0 M KOH, E (RHE) = E (SCE) V. In 1.0 M PBS, E (RHE) = E (SCE) V. Polarization curves were obtained using linear sweep voltammetry (LSV) curves conducted in acid with a scan rate of 5 mv s -1 and then corrected by the ir loss accoding to the following equation: E corr = E mea - ir. The potentials reported in our work were expressed vs. RHE. Computational details: Spin-polarized density functional theory calculations were performed using the Vienna ab initio simulation package (VASP). 1-3 We used the 2

3 PBE functional for the exchange-correlation energy 4 and projector augmented wave (PAW) potentials. 5,6 The kinetic energy cutoff was set to 450 ev. The ionic relaxation was performed until the force on each atom is less than 0.01 ev/å. The k-points meshes were with Monkhorst-Pack method. 7 DFT-D 2 method was used to calculate the adsorption energy, which is an efficient method to approximately account for the long-range vdw interactions. 8 To minimize the undesired interactions between images, a vacuum of at least 15 Å was considered along the z axis. A supercell containing one six-layered (2 2) CoP(101) slab and at least 15 Å vacuum space was used to evaluate the activity of HER. For H adsorption, we have examined four possible sites with high symmetry Co-top site, P-top site, hollow site, and Co-bridge site. The H coverage considered in the calculations is The free energy change for H* adsorption on CoP(101) surface ( G H* ) was calculated as follows, which is proposed by Norskov and oworkers: 9 G H* = E total - E surf - E H 2 /2 + E ZPE - T S where E total is the total energy for the adsorption state, E surf is the energy of pure surface, E H 2 is the energy of H 2 in gas phase, E ZPE is the zero-point energy change and S is the entropy change. 3

4 Scheme S1. Schematic diagram to illustrate the fabrication process of Mn-Co-P/Ti. 4

5 Figure S1. Optical photograph of (from up to down) bare Ti mesh, hydroxide precursor/ti and Mn-Co-P/Ti. 5

6 Figure S2. XRD pattern for the hydroxide precursor. 6

7 Figure S3. (a) XRD pattern and (b) SEM images of CoP/Ti. 7

8 Table S1. Comparison of HER performance in 0.5 M H 2 SO 4 for Mn-Co-P/Ti with other Co-based phosphides catalysts. Catalyst Tafel slope (mv dec -1 ) η at 10 ma cm -2 (mv) Ref. Mn-Co-P/Ti This work CoP nanowire/cc CoP 2 /RGO CoP/Ti 50 ~75 12 np-cop NWs/Ti CoP NA/Ti Co 2 P/Ti urchin-like CoP nanocrystals 46 ~95 16 Co 2 P NWs 45 ~ CoP/rGO CoP NWs Co 2 P branched nanostructures CoP/G CoP/CNT

9 CoP NTs CoP CPHs Co 2 P nanorods CoP hollow polyhedron Co 0.59 Fe 0.41 P nanocubes 52 ~72 27 Fe 0.5 Co 0.5 P ~ C@NiCoP Figure S4. CVs for (a) Mn-Co-P/Ti and (b) CoP/Ti. 9

10 Figure S5. The multi-potential process of Mn-Co-P/Ti for HER in 0.5 M H 2 SO 4. 10

11 Figure S6. SEM images of Mn-Co-P/Ti after HER electrolysis. 11

12 Figure S7. (a) XPS survey spectrum for Mn-Co-P after HER electrolysis. XPS spectra for the post-her Mn-Co-P in the (b) Mn 2p, (c) Co 2p, and (d) P 2p regions. 12

13 Figure S8. XRD pattern of post-her Mn-Co-P/Ti. 13

14 Table S2. Comparison of HER performance in 1.0 M KOH for Mn-Co-P/Ti with other Co-based phosphides catalysts. Catalyst Tafel slope (mv dec -1 ) η at 10 ma cm -2 (mv) Ref. Mn-Co-P/Ti This work CoP nanowire/cc CoP 2 /RGO np-cop NWs/Ti Co 2 P NWs - ~ CoP/rGO Co 2 P nanorods - ~ Co 0.59 Fe 0.41 P nanocubes CoP nanoarrays/cc

15 Table S3. Comparison of HER performance in 1.0 M PBS for Mn-Co-P/Ti with other non-noble-metal HER catalysts. Catalyst Tafel slope (mv dec -1 ) η at 10 ma cm -2 (mv) Ref. Mn-Co-P/Ti This work CoP nanowire/cc np-cop NWs/Ti MoP 2 NS/CC NiS 2 /CC WP/CC Co 9 S 8 /CC MoS 2 /Ti plate Ni 3 S 2 /Ni foam

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