Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1%

Transcription

1 SUPPLEMENTARY INFORMATION DOI: /NMAT4589 Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1% Qian WANG, 1,2 Takashi HISATOMI, 1,2 Qingxin JIA, 1,2 Hiromasa TOKUDOME, 2,3 Miao ZHONG, 1,2 Chizhong WANG, 1 Zhenhua PAN, 1 Tsuyoshi TAKATA, 4 Mamiko NAKABAYASHI, 5 Naoya SHIBATA, 5 Yanbo LI, 6 Ian D. SHARP, 6 Akihiko KUDO, 7 Taro YAMADA, 1,2 Kazunari DOMEN 1,2,* Affiliation and full postal address 1 Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo , Japan 2 Japan Technological Research Association of Artificial Photosynthetic Chemical Process (ARPChem), Kashiwanoha, Kashiwa-shi, Chiba , Japan 3 Research Institute, TOTO Ltd., Honson, Chigasaki, Kanagawa , Japan 4 Global Research Center for Environment and Energy Based on Nanomaterials Science (GREEN), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba-shi, Ibaraki , Japan NATURE MATERIALS 1

2 5 Institute of Engineering Innovation, The University of Tokyo, Yayoi, Bunkyo-ku, Tokyo , Japan 6 Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, United States 7 Department of Applied Chemistry, Tokyo University of Science, 1-3 Kagurazaka, Shinjuku-ku, Tokyo , Japan *Corresponding author Professor Kazunari DOMEN Department of Chemical System Engineering, School of Engineering, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo , Japan Tel: Fax: domen@chemsys.t.u-tokyo.ac.jp 2

3 Supplementary Figure S1 SEM images for (a) SrTiO3:La,Rh photocatalyst powder, (b) BiVO4:Mo photocatalyst powder, and (c) Ru-modified SrTiO3:La,Rh/Au/BiVO4:Mo sheet (top-view). SrTiO3:La,Rh consisted of particles μm in size and BiVO4:Mo consisted of plate-like particles with the clear crystal habit reflecting the high crystallinity. 3

4 Supplementary Figure S2 Ru 3p3/2 XPS spectra for SrTiO3:La,Rh powder, BiVO4:Mo powder, and SrTiO3:La,Rh/Au/BiVO4:Mo sheet. The Ru species were photodeposited on SrTiO3:La,Rh powder (100 mg) and BiVO4:Mo powder (100 mg) in aqueous methanol (10 vol%) and NaIO3 (4 mm) 1 solutions, respectively, containing 10 μmol of RuCl3 3H2O under Xe lamp (λ > 420 nm). The SrTiO3:La,Rh/Au/BiVO4:Mo sheet was irradiated using the same light source in a distilled water containing 0.4 μmol RuCl3 3H2O. The XPS signal of the Ru species deposited on SrTiO3:La,Rh was deconvoluted into a major peak at ev and a small peak at ev. These peaks were attributable to metallic Ru and tetravalent RuO2, respectively. 2 The XPS signal of the Ru species deposited on BiVO4:Mo was deconvoluted into a major peak of tetravalent RuO2 at ev and two peaks at ev and ev attributable to metallic Ru and hydrous ruthenium oxide (RuOxHy), respectively. 2 The peak deconvolution suggests that the Ru species deposited on the SrTiO3:La,Rh/Au/BiVO4:Mo sheet were likely attributable to metallic Ru on SrTiO3:La,Rh and RuOx on BiVO4:Mo although the difference in the deposition conditions of the Ru species on the photocatalyst sheet and powders needs to be taken into account. 4

5 Supplementary Figure S3 Dependence of overall water splitting activity of Ru-modified SrTiO3:La,Rh/Au/BiVO4:Mo photocatalyst sheets on annealing duration. All samples were annealed at 573 K. w/o stands for the pristine sample. The error bars show the standard deviations. The reactions were carried out under Xe lamp (300 W) illumination (λ > 420 nm) at 288 K and 5 kpa. 5

6 Supplementary Figure S4 Time courses for overall water splitting on Ru-modified SrTiO3:La,Rh/Au/BiVO4:Mo sheets without heat treatment (red circles), with pre-annealing (blue squares), and with annealing at 573 K for 20 min (green triangles). The reactions were carried out under Xe lamp (300 W) illumination (λ > 420 nm) at 288 K and 5 kpa. 6

7 Supplementary Figure S5 Effect of annealing on the PEC properties. a,b, Current-potential curves for (a) SrTiO3:La,Rh/Au and (b) BiVO4:Mo/Au photoelectrodes before and after annealing at 573 K for 20 min acquired under Xe lamp (300 W) illumination (λ > 420 nm). SrTiO3:La,Rh/Au electrodes showed a cathodic photocurrent with an onset potential at +1.2 V vs. reversible hydrogen electrode (RHE). Compared with the unannealed SrTiO3:La,Rh/Au electrode, the sample annealed at 573 K for 20 min generated almost twice the photocurrent at the water reduction potential (0 V vs. RHE). On the other hand, BiVO4:Mo/Au electrodes showed an anodic photocurrent. The magnitude of the photocurrent of the BiVO4:Mo/Au electrode is not comparable to that of previously reported BiVO4 electrodes 3,4 because gold has a large work function and will not form an ohmic contact with n-type semiconductors. 5 Note that the current-potential profiles of SrTiO3:La,Rh/Au and BiVO4:Mo/Au photoelectrodes were dependent on the scan directions to some extent presumably because of redox reactions involving the dopants. 7

8 Supplementary Figure S6 Appearance of gold-deposited SrTiO3:La,Rh and BiVO4:Mo after annealing. a,b, Photographs of gold-deposited SrTiO3:La,Rh and BiVO4:Mo after annealing (a) at various temperatures for 20 min and (b) at 573 K for different times. w/o stands for the pristine sample. 8

9 Supplementary Figure S7 Dependence of overall water splitting activity of SrTiO3:La,Rh/Au/BiVO4:Mo sheets upon the amounts of RuCl3. The reactions were carried out under Xe lamp (300 W) illumination (λ > 420 nm) at 288 K and 5 kpa. 9

10 Supplementary Figure S8 Time course of the water spitting reaction on a Ru-modified SrTiO3:La,Rh/Au/BiVO4:Mo sheet under simulated sunlight (AM 1.5G). The reaction was carried out at 288 K and 5 kpa. 10

11 Supplementary Figure S9 Effect of background pressure on photocatalytic water splitting rate of the SrTiO3:La,Rh/Au/BiVO4:Mo sheets. a-c, Dependence of gas evolution rates on (a) Ru-loaded, (b) Cr2O3/Ru-loaded, and (c) a-tio2/cr2o3/ru-loaded SrTiO3:La,Rh/Au/BiVO4:Mo sheets upon the background pressure in the reaction system. Photodeposition from RuCl3 3H2O (0.2 μmol), K2CrO4 (0.2 μmol), Ti peroxide (1.3 μmol) and the overall water splitting reaction were carried out under Xe lamp (300 W) illumination (λ > 420 nm) at 288 K. 11

12 Supplementary Figure S10 Dependence of overall water splitting activity of Ru-modified SrTiO3:La,Rh/Au/BiVO4:Mo sheets upon the amounts of K2CrO4 added. The reactions were carried out under Xe lamp (300 W) illumination (λ > 420 nm) at 288 K and 5 kpa. 12

13 Supplementary Figure S11 A top-view SEM image of a printed SrTiO3:La,Rh/Au colloid (10 wt%)/bivo4:mo photocatalyst sheet. 13

14 Supplementary Figure S12 Structure of a printed SrTiO3:La,Rh/Au colloid (40 wt%)/bivo4:mo photocatalyst sheet. a-e, Top-view SEM-EDX elemental mapping images showing (a) an SEM image with back-scattered electrons, (b) Sr distribution, (c) Bi distribution, (d) Au distribution, and (e) superimposition of (b-d). 14

15 Supplementary Figure S13 Dependence of overall water splitting activity of SrTiO3:La,Rh/Au colloid/bivo4:mo printed photocatalyst sheets (6.25 cm 2 ) upon the weight fraction of gold colloid. The reactions were carried out under Xe lamp (300 W) illumination (λ > 420 nm) at 288 K and 5 kpa. 15

16 Supplementary Figure S14 XRD patterns for photocatalyst powders. a, SrTiO3:La,Rh and the reference SrTiO3. b, BiVO4:Mo and the reference BiVO4. Production of single-phase SrTiO3:La,Rh in the SrTiO3-type structure (JCPDS-ICDD: ) and BiVO4:Mo in the monoclinic BiVO4 phase (JCPDS-ICDD: ) was confirmed. 16

17 Supplementary Figure S15 Diffuse-reflectance spectra for SrTiO3:La,Rh and BiVO4:Mo powders. SrTiO3:La,Rh had a steep absorption edge intrinsic to SrTiO3 at around 390 nm and shoulder absorption extending to the visible light region owing to the impurity levels of trivalent Rh species, 6 whilst BiVO4:Mo had a steep absorption edge typical to monoclinic BiVO4 at 520 nm. 7 17

18 Supplementary Figure S16 Dependence of overall water splitting activity of SrTiO3:La,Rh/Au/BiVO4:Mo upon the mass ratio of SrTiO3:La,Rh to BiVO4:Mo. The reactions were carried out under Xe lamp (300 W) illumination (λ > 420 nm) at 288 K and 5 kpa. 18

19 Supplementary Figure S17 Spatial distribution of the power spectra of the Xe lamp used. a,b, A 300 W Xe lamp equipped with (a) a cut-off filter ( > 420 nm) and (b) a band-pass filter ( = nm, full width half maximum = 9.5 nm). The spectra were acquired with the spatial interval of 2 mm from the centre of illumination. 19

20 Supplementary Figure S18 Power spectra of the standard AM 1.5G (ASTMG 173) and the solar simulator used. 20

21 Supplementary Table S1 EDX analysis of BiVO4:Mo with and without annealing. Samples Molar ratio of Bi/V Pristine 1.0 Annealed (773 K, 20 min) 1.2 Annealed (573 K, 30 min) 1.1 The turnover number (TON) of the water splitting reaction using a Cr2O3/Ru-modified SrTiO3:La,Rh/Au/BiVO4:Mo sheet (this discussion refers to Figure 2 in the main text) The TON of the water splitting reaction was estimated by the following equation: TON = the number of reacted electrons in 10 h / the number of chosen atom in the materials Assuming that the amount of the SrTiO3:La,Rh and BiVO4:Mo powders on the photocatalyst sheet is 10 mg each, the TONs for SrTiO3:La,Rh, BiVO4:Mo, Cr, Ru, Rh and Mo are calculated to be 54, 96, , , and at 331 K, by far higher than unity, which attests the stability of the photocatalyst sheet. The TONs estimated here are the lower bounds because not all of the atoms are exposed to the reaction solution and not all of the photocatalyst particles remain on the photocatalyst sheet. References 1. Tabata, M. et al. Modified Ta3N5 powder as a photocatalyst for O2 evolution in a two-step water splitting system with an iodate/iodide shuttle redox mediator under visible light. Langmuir 26, (2010). 2. Park, K. C. et al. Carbon-supported Pt-Ru nanoparticles prepared in 21

22 glyoxylate-reduction system promoting precursor-support interaction. J. Mater. Chem. 20, (2010). 3. Kim, T. W. & Choi, K.-S. Nanoporous BiVO4 photoanodes with dual-layer oxygen evolution catalysts for solar water splitting. Science 343, (2014). 4. Zhong, M. et al. Surface modification of CoOx loaded BiVO4 photoanodes with ultrathin p-type NiO layers for improved solar water oxidation. J. Am. Chem. Soc. 137, (2015). 5. Wang, Q. et al. Z-scheme water splitting using particulate semiconductors immobilized onto metal layers for efficient electron relay. J. Catal. 328, (2015). 6. Wang, Q., Hisatomi, T., Ma, S. S. K., Li, Y. & Domen, K. Core/shell structured La- and Rh-codoped SrTiO3 as a hydrogen evolution photocatalyst in Z-scheme overall water splitting under visible light irradiation. Chem. Mater. 26, (2014). 7. Kudo, A., Omori, K. & Kato, H. A novel aqueous process for preparation of crystal form-controlled and highly crystalline BiVO4 powder from layered vanadates at room temperature and its photocatalytic and photophysical properties. J. Am. Chem. Soc. 121, (1999). 22