Supporting Information

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1 Supporting Information Uniformly Sized (112) Facet Co 2 P on Graphene for Highly Effective Photocatalytic Hydrogen Evolution Bin Tian, a, b Zhen Li, a, b Wenlong Zhen c and Gongxuan Lu *a a State Key Laboratory for Oxo Synthesis and Selective Oxidation, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou , P. R. China. b University of Chinese Academy of Science, Beijing , China c State Key Laboratory of Applied Organic Chemistry, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou, China. *Corresponding author: gxlu@lzb.ac.cn. Tel.: Fax:

2 Theoretical Calculation In general, the process of HER usually occurred according to three steps, H + adsorption, H + reduction and H 2 desorption in sequence. 1 Specifically, excited electron occupied in the highest molecular orbit (HOMO) of cocatalyst transfers to the lowest unoccupied molecular orbit (LUMO) of H 2 O, reduced H + to H atom on cocatalyst surface, and the adsorbed-h formed hydrogen molecule. In this process, the initial adsorption of a proton to form adsorbed-h, the Volmer reaction, H + + e - H ad, is usually considered to be fast. 2 Therefore, the strength of adsorption H atom on the catalysts is the significant factor for the HER, and we could use the hydrogen adsorption free energy ( G H ) to describe the catalytic ability of catalysts since the rate of hydrogen evolution is proportional to the exponential of the hydrogen adsorption free energy ( G H ). 3-4 In addition, the molecular hydrogen formation reaction is possible under the HOMO-LUMO gap ( E) is less than a.u. (579 kj mol -1, and the LUMO energy of free H 2 O is about 66 kj mol -1 ). 5 The smaller of HOMO-LUMO energy difference, the easier of electrons transfer with the frontier molecular orbital theory (FMO). The constructions of H atoms adsorption models were based on the periodic crystal structure of materials, and we conservatively estimate materials for H atom adsorption model, including both the transition metal and P atoms as possible active sites and optimized to obtain the optimum structure. The theoretical value and experimental value of Co 2 P, Co and P lattice parameter was in Table S1. The configuration of all 2

3 units was optimized by the B3LYP method of the plane-wave density functional theory (DFT), 6 The B3LYP when used with the LANL2DZ polar basis set would obtained excellent results when applied to metallic atoms. 7 All structures and electronic energies calculation were completed by programs of Gaussian 03 and used LANL2DZ polar basis set for Co, 6-311(d) basis set for P and H atoms. Figure S7 and Table S1 showed the geometry optimization and computational results of Co 2 P, Co, P and their H atom adsorption state, respectively. As shown in Figure S7a and b, they showed that crystal structure, calculation models of H adsorption and the charge density distribution of HOMO on Co 2 P-H. 3

4 Figure S1. XRD patterns for Co 2 P/RGO (a) and Co 2 P (b). 4

5 Figure S2. Size statistical analysis of catalyst. 5

6 Figure S3. Energy dispersive X-ray spectroscopy (EDX) of 2 P/RGO. 6

7 Figure S4 XPS spectra in the (a) O 1s in catalyst and (b) C 1s in catalyst and (c) survey spectrum for Co 2 P/RGO. 7

8 Figure S5. The photocatalytic activity of Co 2 P/RGO with different weight ratio of Co 2 P to RGO (6 mg) for the hydrogen evolution photosensitized by EY ( mol L -1 ) in 10% (v/v) TEOA aqueous solution (ph 11) under visible light irradiation (λ 420 nm) in 1.5 h. Co 2 P/RGO=2/0, 1/6, 1/3, 1/2, 2/3, 5/6 and 1, respectively. 8

9 Figure S6. UV-Vis absorption spectra of EY ( mol L -1 ), EY photosensitized Co 2 P/ RGO, Co 2 P in TEOA (10%) aqueous solution. 9

10 10

11 Figure S8. LSV curves of bare ITO glass, Co 2 P, Co 2 P/RGO coated ITO electrodes in mixed solution of 10% (v/v) TEOA and 0.1 M Na 2 SO 4 at ph 11. The scan rate was 1 mv s 1. 11

12 Table S1. Structures of Co 2 P, Co and P, and their lattice parameters: theoretical and experimental value. Materials Space Group Lattice parameters [Å] Theoretical Experimental a b c a b c ICSD NO. Co 2 P Pnma Co P P Pm-3m

13 Table S2. Calculation results of catalysts by programs of Gaussian 03 Catalysts HOMO of catalysts (kj mol -1 ) LUMO of H 2 O (kj mol -1 ) E (kj mol -1 ) G H (kj mol -1 ) Co 2 P Co P Co 2 P-H Co-H P-H

14 Table S3. Decay parameter of EY ( mol L -1 ) in Co 2 P/RGO and Co 2 P system a. Systems Lifetime(ns) Pre-exponential factors A/% Average lifetime<τ>/ns χ 2 EY τ=1.17 A= Co 2 P/EY τ 1 =0.81; τ 2 =1.43 A 1 =42.0;A 2 = Co 2 P/RGO/EY τ 1 =1.18; τ 2 =1.99 A 1 =63.2 ;A 2 = a the concentration of cocatalysts was about 0.17 mg/ml. EY used single-exponential fitted, double-exponential fit for Co 2 P/RGO and Co 2 P system. The method of calculated average lifetime <τ> has been reported. 8 14

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