Supporting Information

Transcription

1 Supporting Information Utilization of Metal Sulfide Material of (CuGa) 1 x Zn 2x S 2 Solid Solution with Visible Light Response in Photocatalytic and Photoelectrochemical Solar Water Splitting Systems Takaaki Kato, a Yuichiro Hakari, a Satoru Ikeda, a Qingxin Jia, a Akihide Iwase, a,b Akihiko Kudo *a,b a Department of Applied Chemistry, Faculty of Science, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo , Japan b Photocatalysis International Research Center, Research Institute for Science and Technology, Tokyo University of Science, 2641 Noda-shi, Yamazaki, Chiba-ken , Japan Experimental section Characterization The phases of obtained photocatalysts were confirmed by X-ray diffraction (Rigaku, MiniFlex). Diffuse reflectance spectra were obtained with a UV-vis-NIR spectrometer (Jasco, U-570) equipped with an integrating sphere and were converted from reflection to absorbance by the Kubelka-Munk method. Photocatalytic reactions Photocatalytic reactions were carried out using a gas-closed circulation system and an Ar-gas flow system. In sacrificial H 2 evolution, the (CuGa) 1 x Zn 2x S 2 powder (0.3 g) was dispersed in an aqueous solution (150 ml) containing K 2 SO 3 and Na 2 S of electron donors in a top-irradiation cell with a Pyrex window using a gas-closed circulation system. In Z-schematic water splitting, the (CuGa) 1 x Zn 2x S 2 of a H 2 -evolving photocatalyst (0.05 g) and BiVO 4 of an O 2 -evolving photocatalyst (0.05 g) were dispersed in an aqueous Co-complex solution (120 ml) in an Ar flow system. The suspensions were irradiated with visible light (λ>420 nm) through a cut-off filter (HOYA, L42) from a 300-W Xe lamp (Perkin-Elmer, CERMAX-PE300F). A solar simulator with an AM-1.5 filter (YAMASHITA DENSO, YSS-80QA, 100 mw cm 2 ) was also used. Turnover numbers (TONs) for a Co-complex and S atoms at the surface of (CuGa) 0.8 Zn 0.4 S 2 and solar energy conversion efficiency were calculated from the following equations; [TON for Co-complex]=[The number of electrons (holes) consumed for water splitting]/[the number of Co-complexes in the reactant solution] S1

2 [TON for S atoms at the surface]= [The number of electrons (holes) consumed for water splitting]/[the number of S atoms at the surface of (CuGa) 0.8 Zn 0.4 S 2 ] where we assume that (112) face with high S atom concentration is exposed at the surface. [Solar energy conversion efficiency %] =100x([ΔG 0 (H 2 O)/J mol 1 ]x[rate of H 2 evolution/mol h 1 ])/(3600x[Solar energy AM-1.5/W cm 2 ]x[irradiation area/cm 2 ]) Photoelectrochemical measurements Photoelectrochemical properties of (CuGa) 1 x Zn 2x S 2 were evaluated using a potentiostat (HOKUTO DENKO; HZ-3000 and HSV-100) with an H-type cell consisting of the (CuGa) 1 x Zn 2x S 2 photoelectrode, a Pt electrode, and a Ag/AgCl/saturated KCl electrode as working, counter, and reference electrodes, respectively. A mixed aqueous solution (ph 6.8) of 0.1 mol L 1 of K 2 SO 4, mol L 1 of Na 2 HPO 4, and mol L 1 of KH 2 PO 4 was used as an electrolyte. Photoelectrochemical water splitting was carried out using the (CuGa) 1 x Zn 2x S 2 and the BiVO 4 photoelectrodes in a one-pot cell. A mixed aqueous solution (ph 8) of mol L 1 of Na 2 HPO 4 and mol L 1 of KH 2 PO 4 was used as an electrolyte. Photoelectrodes were irradiated from the substrate side with visible-light through a cutoff filter (L42) from a 300-W Xe lamp. A 100-W Xe lamp (ASAHI SPECTRA, LAX 102) with band-pass filters was employed for IPCE measurement. The photon flux of the monochromatic light was measured by a silicon photodiode (OPHIR, PD300-UV SH head and NOVA display). A solar simulator with an AM-1.5 filter (Peccell Technologies, PRC-L11, 100 mw cm 2 ) was also used. IPCE and a solar energy conversion efficiency were calculated from the following equations; [IPCE %]=(1240x[Photocurrent density/µa cm 2 ])/([Wavelength/nm]x[Photon flux/w m 2 ]) [Solar energy conversion efficiency %] =100x([Photocurrent density/ma cm 2 ])x(1.23 E apply /V)/[Solar energy AM-1.5/mW cm 2 ] S2

3 Figure S1 (a) 2-photon excitation (Z-scheme) powdered system and (b) photoelectrode system for water splitting. S3

4 Figure S2 X-ray diffraction patterns of (CuGa) 1 x Zn 2x S 2 prepared at 1073 K by a solid-state reaction; the values of x were (a) 0, (b) 0.2, and (c) % of excess Ga 2 S 3 was added in the starting materials for all samples in the synthesis. S4

5 315 Cell volume / Å x in (CuGa) 1 x Zn 2x S 2 Figure S3 Cell volumes of (CuGa) 1 x Zn 2x S 2 prepared at 1073 K by a solid-state reaction. 10% of excess Ga 2 S 3 was added in the starting materials for all samples in the synthesis. S5

6 Absorbance / arb. units (d) (a) (c) (b) Wavelength / nm Figure S4 Diffuse reflectance spectra of (CuGa) 1 x Zn 2x S 2 prepared at 1073 K by a solid-state reaction; the values of x were (a) 0, (b) 0.2, (c) 0.5, and (d) 1. 10% of excess Ga 2 S 3 was added in the starting materials for all samples in the synthesis. S6

7 IPCE % Non-loaded (x 10) Ru-loaded Absorbance / arb. units Wavelength / nm Figure S5 Action spectra of Ru-loaded (CuGa) 0.8 Zn 0.4 S 2 electrode for IPCE measured at 0.6 V vs. Ag/AgCl and a diffuse reflectance spectrum of (CuGa) 0.8 Zn 0.4 S 2. (CuGa) 0.8 Zn 0.4 S 2 powder was prepared by a solid-state reaction (at 1073 K for 10 h, 20 atm% excess of Ga 2 S 3 and ZnS). Electrolyte: 0.1 mol L 1 of K 2 SO 4, mol L 1 of Na 2 HPO 4, and mol L 1 of KH 2 PO 4 (ph 6.8), light source: 300-W Xe-arc lamp with a band-pass filter. S7

8 Solar energy conversion efficiency % Applied bias voltage / V vs. a counter electrode Figure S6 Solar energy conversion efficiency of the photoelectrochemical cell consisting of Ru-loaded (CuGa) 0.5 ZnS 2 photocathode and CoOx-loaded BiVO 4 photoanode. Electrolyte: mol L 1 of Na 2 HPO 3 and mol L 1 of KH 2 PO 4 (ph 8), light source: solar simulator (AM 1.5, 100 mw cm 2 ). (CuGa) 0.8 Zn 0.4 S 2 powder was prepared by a solid-state reaction at 1073 K for 10 h, 20 atm% excess of Ga 2 S 3 and ZnS. S8