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Letter

Visible Light-driven Z-scheme Water Splitting Using Oxysulfide H Evolution Photocatalysts 2

Guijun Ma, Shanshan Chen, Yongbo Kuang, Seiji Akiyama, Takashi Hisatomi, Mamiko Nakabayashi, Naoya Shibata, Masao Katayama, Tsutomu Minegishi, and Kazunari Domen J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.6b01802 • Publication Date (Web): 14 Sep 2016 Downloaded from http://pubs.acs.org on September 16, 2016

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The Journal of Physical Chemistry Letters

Visible Light-driven Z-scheme Water Splitting Using Oxysulfide H2 Evolution Photocatalysts Guijun Ma,†,‡ Shanshan Chen,†,‡ Yongbo Kuang,†,‡ Seiji Akiyama,§ Takashi Hisatomi,†,‡ Mamiko Nakabayashi,|| Naoya Shibata,|| Masao Katayama,†,‡ Tsutomu Minegishi,†,‡ Kazunari Domen*,† †Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyoku, Tokyo 113-8656, Japan ‡Japan Technological Research Association of Artificial Photosynthetic Chemical Process (ARPChem), 2-11-9 Iwamotocho, Chiyoda-ku, 101-0032 Tokyo, Japan §Mitsubishi Chemical Group Science and Technology Research Center Inc., 1000 Kamoshida-cho, Aoba-ku, Yokohama-shi, Kanagawa 227-8502, Japan. ||Institute of Engineering Innovation, The University of Tokyo, 2-11-16 Yayoi, Bunkyo-ku, Tokyo 113-8656, Japan. Corresponding Author Department of Chemical System Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyoku, Tokyo 113-8656, Japan Tel: (+81) -3-5841-1148, Fax: (+81) -3-5841-8838, E-mail address: [email protected] (K. Domen)

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*

To whom correspondence should be addressed


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ABSTRACT A Sm2Ti2S2O5 (STSO) oxysulfide photocatalyst prepared by a novel flux method showed a higher degree of crystallinity and greater photocatalytic activity than that prepared by conventional polymerized complex and sulfurization processes. Co-loading with both IrO2, as an oxidative cocatalyst, and Pt, as a reductive cocatalyst was found to be essential for promoting the photocatalytic activity of the STSO. Visible light-driven Z-scheme water splitting into H2 and O2 was realized by utilizing the STSO photocatalyst for H2 evolution in conjunction with a WO3 photocatalyst treated with H+ and Cs+ and loaded with PtOx for O2 evolution, and a triiodide/iodide (I3-/I-) redox couple as a shuttle electron mediator. Various other narrow band gap oxysulfide photocatalysts with H2 evolution activity, such as La5Ti2CuS5O7 and La6Ti2S8O5, were also shown to be applicable as H2 evolution photocatalysts in the present Z-scheme water splitting

system.

TOC GRAPHICS

hν hv

e− e−

Eg

I─

H2O O2

e−

Eg e− h+ H-Cs-WO3

e−

H2 H+

I3─ e−

h+ Sm2Ti2S2O5 La5Ti2CuS5O7 La6Ti2S8O5

KEYWORDS Photocatalysis; Z-scheme water splitting; Oxysulfide; Hydrogen


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Visible light-driven photocatalytic overall water splitting is an ideal approach to converting solar energy into chemical energy. Z-scheme water splitting based on the two-step excitation of H2 and O2 evolution photocatalysts (HEP and OEP) coupled with a redox shuttle electron mediator has attracted much attention in recent years, because narrow band gap photocatalysts that exhibit activity either in the H2 or O2 evolution reaction can be applied to water splitting. Since Abe and Sayama et al. reported photocatalytic Z-scheme water splitting using UV-active -

-

TiO2 photocatalysts and an IO3 /I shuttle redox mediator, various Z-scheme systems have been developed based on visible light-active photocatalysts that can produce H2 or O2 but do not suffer from backward reactions, even in the presence of a shuttle redox mediator.1-15 As a group of important visible light-responsive photocatalysts, oxysulfide materials have been studied extensively for use in water splitting reactions.16-25 However, the research concerning oxysulfides has primarily been limited to those half reactions that proceed via the consumption of sacrificial electron or hole scavengers. This is the case even if the band gap straddles the redox potentials for water splitting as the result of (i) a high density of defect sites acting as electronhole recombination centers20-25 and (ii) difficulty in simultaneously promoting both H2 and O2 evolution reactions using cocatalysts.22-24 For these reasons, it is an alternative to utilize oxysulfide photocatalysts for Z-scheme overall water splitting. In 2014, our group reported that Pt-loaded Sm2Ti2S2O5 (STSO) combined with rutile-type TiO2 and NaI showed Z-scheme water splitting activity in a basic solution under UV irradiation.25 The application of this STSO oxysulfide photocatalyst to overall water splitting was a milestone in the path toward efficient solar hydrogen production, based on the ability of this system to absorb visible light up to 590 nm. However, this system still did not function under visible light because of the use of UV-active TiO2, and so it is necessary to develop a Z-scheme


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water splitting system that works under visible light irradiation. In the present study, highly crystalline STSO was prepared by a flux method and the photocatalytic H2 evolution activity of this material was further optimized by co-loading with IrO2 and Pt to generate oxidation and reduction sites, respectively. Based on employing STSO as the HEP, we were successful in achieving visible light-induced Z-scheme water splitting, using WO3 treated with H+ and Cs+ (HCs-WO3) and loaded with PtOx as the OEP and triiodide/iodide (I3-/I-) as a redox couple. Moreover, other narrow band gap oxysulfide photocatalysts, such as La5Ti2CuS5O7 (LTCSO) and La6Ti2S8O5 (LTSO), were also found to be applicable as the HEP in this Z-scheme system.

Figure 1. UV-vis diffuse reflectance spectra (top left), XRD patterns (top right) and SEM images (bottom and insets) of STSO-flux and STSO-PC samples. The scale bars in the SEM images and insets are 5 and 1 µm, respectively. STSO was synthesized either using a novel flux-assisted method (with the product denoted as STSO-flux) or a traditional polymerized complex (PC) process followed by sulfurization (denoted as STSO-PC).21-25 The Brunauer–Emmett–Teller (BET) surface areas for STSO-flux and STSO-PC were 4.0 and 8.1 m2 g-1, respectively. Figure 1 compares UV-vis diffuse reflectance spectra (DRS), X-ray diffraction (XRD) patterns and scanning electron microscopy


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(SEM) images of these two materials. It can be seen from the DRS that both samples had similar light absorption edges while the STSO-flux had a lower absorption background than the STSOPC, implying a lower level of impurities absorbing within the band gap of the STSO-flux. The XRD patterns show that crystalline, phase-pure STSO was prepared by the flux method, since no peaks attributed to the precursors (TiO2, TiS2 and Sm2O3) are observed. It is noteworthy that the peaks associated with the (004), (006) and (008) crystal planes of the STSO-flux are relatively more intense than those of the STSO-PC, suggesting preferential two-dimensional crystal growth along the (00l) planes during the preparation of the STSO-flux. This anisotropic crystal growth was also reflected by the morphologies of the STSO particles. As is evident from the SEM images, the STSO-flux sample had a more regular particle morphology than the STSO-PC. The STSO-flux consisted of plate-like crystals with in-plane dimensions of approximately 1 µm and a thickness of around 0.2 µm, while the STSO-PC was made up of aggregates with irregular sizes and morphologies. The elemental mapping by SEM-EDS analysis (Figure S1) showed that Sm, Ti and S atoms were uniformly distributed on the STSO-flux particle and the ratios of Sm:Ti and S:Ti were close to the stoichiometric ratio of STSO. Figure 1 demonstrate that the STSO-flux had a higher degree of crystallinity and fewer crystal defects than the STSO-PC, which typically results in improved photocatalytic activity. In fact, the STSO-flux exhibited approximately twice the photocatalytic activity of the STSO-PC in the sacrificial H2 and O2 evolution reactions (Figure S2). In our previous work on Rh- or Pt-loaded STSO photocatalysts, co-loading of Ag2S to generate oxidation sites was found to effectively enhance the photocatalytic H2 evolution activity in a solution containing Na2S and Na2SO3 as hole scavengers.22,23 This result suggested that the inherent oxidation activity of the bare STSO surface was low. In the present work, we therefore


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attempted to promote both the reduction and oxidation activities of the STSO by loading IrO2 to obtain oxidation sites and then subsequently photodepositing Pt to produce reduction sites. TEM images showed that the IrO2 particles 3–5 nm in size were uniformly loaded on STSO-flux (Figure S3). Figure S4 presents the time courses of H2 evolution during photodeposition of Pt on both bare and IrO2-loaded STSO in an aqueous solution containing Na2S and Na2SO3 as hole scavengers. Photodeposition of Pt on the IrO2/STSO was evidently complete within a 1 h period while, in the case of the bare STSO, deposition was still not accomplished even after 14 h. In addition, the amount of photocatalytic H2 produced from the IrO2-loaded STSO-flux was approximately 50 times that generated by the bare STSO after a 6 h reaction time. It should be noted that the IrO2-loaded STSO-flux exhibited comparatively low H2 evolution activity than the Pt and IrO2 co-loaded sample. Clearly, coloading of the IrO2 cocatalyst facilitated the photodeposition of Pt and hence increased the photocatalytic H2 evolution activity of the STSOflux through enhancement of the oxidation activity of the photocatalyst. The apparent quantum efficiencies for the sacrificial H2 and O2 production were 0.6% over the Pt- and IrO2-loaded STSO-flux, and 1.3% over the IrO2-loaded STSO-flux, respectively, under a monochromatic light (420 nm) irradiation. Table 1. H2 and O2 evolution activities of Z-scheme water splitting systems based on various oxysulfide H2 evolution photocatalysts.a Activityb (µmol) Entry

H2 photocatalyst

O2 photocatalyst

H2

O2

1

STSO-flux

None

1.0

0.0


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2

STSO-flux

WO3

6.0

1.1

3

STSO-flux

H-Cs-WO3

40.6

16.1

4

STSO-PC

H-Cs-WO3

10.4

3.6

5

LTCSO

H-Cs-WO3

10.5

3.1

6

LTSO

H-Cs-WO3

3.1

1.1

a

Reaction conditions: photocatalyst, STSO-flux and STSO-PC: 0.05 g (Pt 1 wt%- IrO2 2 wt%); LTCSO: 0.05 g (Pt 0.5 wt%); LTSO: 0.05 g (Rh 1 wt%); WO3 and H-Cs-WO3: 0.15 g (PtOx 0.45 wt%); aqueous NaI solution (2.5 mM, 150 mL) with pH value of 6.5; light source, xenon lamp (300 W) equipped with a L-42 cutoff filter; reaction vessel, Pyrex top-irradiation type; b Estimated from the amount of gases evolved in 10 h. The synthesis of STSO by the flux method and the co-loading of Pt and IrO2 as reduction and oxidation sites, respectively, effectively enhanced the photocatalytic activity during the half reactions. Thus, a visible-light-driven Z-scheme overall water splitting reaction was carried out, using the optimized STSO-flux photocatalyst as the HEP. Table 1 summarizes the amounts of H2 and O2 evolved over 10 h with various oxysulfides as the HEP in conjunction with WO3-based photocatalysts as an OEP and NaI as an electron mediator. As shown in entry 1, a trace amount of H2 was produced in the absence of PtOx/WO3, suggesting that some small quantity of I- ions was photo-oxidized over the STSO-flux. The time profile of entry 1 (Figure S5) demonstrates that the H2 evolution activity decreased with the progress of the photocatalytic reaction and leveled off after approximately 5 h. This suppression of H2 production was likely due to the backward reduction of the photo-oxidized products of I- ions on the STSO-flux. The introduction of WO3 to this system (entry 2) led to enhanced H2-evolution activity and simultaneous O2 evolution. However, the H2/O2 ratio was on the order of 6:1, a value that is much higher than the expected stoichiometric ratio of 2. UV−vis absorption spectra indicated that I3- ions were produced in the neutral aqueous solution during this trial (Figure S6). This is in contrast to other


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Z-scheme systems based on I-, in which the IO3-/I- redox system is generated in situ and acts as a shuttle electron mediator.9-13 These results also offer a good explanation for the relatively low O2 production seen in entry 2; photocatalytic O2 evolution activity over PtOx/WO3 is known to be -

very low when I3 ions are used as the electron acceptor.26,27 On a thermodynamic basis, it is -

-

more likely that I ions in a neutral solution (pH of 7.0) will be oxidized to I3 rather than to IO3 -

-

-

-

-

because the redox potential of I3 /I (0.536 V vs. NHE) is more negative than that of IO3 /I

(0.672 V vs. NHE).5 Miseki et al. reported that the photocatalytic water oxidation activity of a WO3 photocatalyst utilizing I3 ions as an electron acceptor was remarkably improved by a

CsCO3 salt-assisted thermal treatment and a subsequent H+-exchange treatment.27 This report prompted us to apply H+ and Cs+ treated WO3 (H-Cs-WO3) to the present oxysulfide-based Zscheme water splitting system to accelerate the O2 evolution process. As shown in entry 3 of Table 1, both the H2 and O2 evolution activities were significantly improved by the use of H-CsWO3 in place of WO3. Moreover, the resulting H2/O2 molar ratio was close to 2:1 in repeated reactions following evacuation of the apparatus. Z-scheme overall water splitting was also achieved with the STSO-PC photocatalyst under visible light irradiation (entry 4), although the activity of this catalyst was lower than that of the STSO-flux.


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Figure 2. Time course of Z-scheme water splitting using Pt(1 wt%)‒IrO2(2 wt%) co-loaded STSO-flux as a H2 evolution photocatalyst, PtOx(0.45 wt%)-loaded H-Cs-WO3 as an O2 evolution photocatalyst, and I3-/I- as a shuttle electron mediator under visible light irradiation. Catalysts: 0.05 g STSO-flux and 0.15 g H-Cs-WO3; solution: 150 ml NaI aqueous solution (2.5 mM) with a pH of 4.0; light source: 300 W Xe lamp with a cutoff filter (λ > 420 nm). Because of the poor photo-stability of WO3 in basic media, the pH of the reaction solution was adjusted from neutral to acidic to optimize the photocatalytic activity. As shown in Figure S7, the photocatalytic H2 and O2 evolution rates were increased by adjusting the pH from 6.5 to 3, but both decreased at pH 2. Acidification of the reaction solution probably promotes the H2 evolution reaction on STSO-flux because the band edge potential of STSO is insensitive to the pH value of the reaction solution.20 However, excessive acidification would decompose the oxysulfide. Figure 2 presents a prolonged time course of the photocatalytic H2 and O2 production using the Z-scheme system consisting of the STSO-flux, H-Cs-WO3 and NaI in a reaction solution at pH 4. During this trial, the apparatus was evacuated every 10 h to remove the produced gases, since H2 and O2 were generated continuously. The H2/O2 ratio was evidently closer to 2 after the system, including the concentrations of I3- and I- ions, reached a steady state under light irradiation. Following a reaction time of 60 h, 70% of the initial photocatalytic activity was maintained, and the total amount of H2 generated (267 µmol) was greater than the quantity of sulfide ions originally included in the STSO-flux sample (185 µmol), thus excluding the possibility that the H2 was produced from a self-corrosion process. In addition, the total amount of H2 was more than the maximum amount (187.5 µmol) that could have been produced by the stoichiometric reaction of the I- ions introduced into the system. This is assuming that one H2 molecule is formed by consuming two I- ions, indicative of a redox regeneration of I- ions


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during the reaction. XRD patterns presented in Figure S8 showed that the sample reclaimed after the long-term reaction was a mixture of STSO-flux and WO3. This result suggests that the bulk of STSO-flux and WO3 were mostly stable during the water splitting reaction. To estimate the performance of the Z-scheme water splitting system during solar-powered fuel production, the water splitting was carried out under irradiation with a solar simulator (AM 1.5G). As shown in Figure S9, H2 and O2 were steadily produced under the simulated sunlight at a solar-to-hydrogen energy conversion efficiency (STH) of approximately 3×10-3% based on the average H2 production rate. Although this STH value is quite low, the present results demonstrate that visible light-driven water splitting can be achieved using an oxysulfide photocatalyst in conjunction with a Z-scheme process. The applicability of other oxysulfide semiconductor photocatalysts having different crystal structures to Z-scheme overall water splitting was also investigated. Here, LTCSO and LTSO were examined because they absorb wide ranges of visible light up to 650 and 630 nm, respectively, and exhibit photocatalytic activity in both water reduction and oxidation reactions in the presence of corresponding sacrificial reagents under visible light irradiation (Figures S10 and S11 ).19 Entries 5 and 6 (Table 1) provide the water splitting activities of Z-scheme systems in which LTCSO and LTSO were applied as the HEP, respectively, after loading with suitable reduction cocatalysts. Although the amounts of H2 generated were more than twice that of O2 in the case of both LTCSO and LTSO in the initial stage, and their activities were lower than that of the STSO-flux, simultaneous production of H2 and O2 was observed. These results suggest that oxysulfide photocatalysts that are active in the sacrificial H2 evolution reaction may be also applicable as HEPs in Z-scheme water splitting. The relatively higher H2 production in the present Z-scheme system is probably due to partly photo-oxidation of sulfide ions on the


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oxysulfide photocatalysts, which is usually inevitable for oxysulfide semiconductors.8,28 In addition, it is necessary to accumulate certain amount of I3- ions for the Z-scheme H2 and O2 evolution cycles to proceed smoothly in the initial reaction time. The deviation of H2/O2 ratio from two owing to the above two factors is evident when the Z-scheme water splitting activity is low as in the cases of the LTCSO and LTSO photocatalysts. We believe that a near stoichiometric H2/O2 ratio can be produced by improving the photocatalytic activity on H2evolution photocatalyst. In summary, the synthesis of STSO by the flux method and subsequent co-loading with Pt and IrO2 to generate reduction and oxidation sites, respectively, were found to be essential for enhancing the H2 evolution activity of STSO and thereby increasing the water splitting activity of the Z-scheme system. Visible light-driven Z-scheme water splitting was achieved using STSO, LTCSO or LTSO oxysulfides as the HEP, surface-treated WO3 as an OEP, and the I3-/I- ion couple as a redox mediator. This work demonstrates that narrow band gap oxysulfide photocatalysts can be applied to obtain effective visible light-driven Z-scheme water splitting through promotion of the H2 evolution activity.

Supporting Information. Electronic Supplementary Information (ESI) available: Preparation processes and characterization of STSO, LTCSO, LTSO and WO3 powders, UV-vis absorption spectra of the post-reaction solutions, data for the photocatalytic Z-scheme water splitting reaction induced by a solar light simulator (AM 1.5), photocatalytic half reactions over STSO and LTSO, and other experimental procedures.

AUTHOR INFORMATION


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Notes The authors declare no competing financial interests.

ACKNOWLEDGMENT This work was financially supported by the Artificial Photosynthesis Project of the New Energy and Industrial Technology Development Organization (NEDO) and Grants-in-Aid for Scientific Research (A) (No. 16H02417) and for Young Scientists (A) (No. 15H05494) from the Japan Society for the Promotion of Science (JSPS). Part of this work was conducted at Advanced Characterization Nanotechnology Platform of the University of Tokyo, supported by “Nanotechnology Platform” of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan.

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(13) Chen, S.; Qi, Y.; Hisatomi, T.; Ding, Q.; Asai, T.; Li, Z.; Ma, S.; Zhang, F.; Domen, K.; Li, C. Efficient Visible-light-driven Z-scheme Overall Water Splitting Using a MgTa2O6−xNy /TaON Heterostructure Photocatalyst for H2 Evolution. Angew. Chem. Int. Ed. 2015, 127, 8618-8621. (14) Chen, W.; Liu, T.; Huang, T.; Liu, X.; Zhu, J.; Duan, G.; Yang, X. In situ Fabrication of Novel Z-scheme Bi2WO6 Quantum Dots/g-C3N4 Ultrathin Nanosheets Heterostructures with Improved Photocatalytic Activity, Appl. Surf. Sci. 2015, 355, 379-387. (15) Jin, J.; Yu, J.; Guo, D.; Cui, C.; Ho, W. A Hierarchical Z-scheme CdS-WO3 Photocatalyst with Enhanced CO2 Reduction Activity, Small 2015, 11, 5262-5271. (16) Lei, Z.; Ma, G.; Liu, M.; You, W.; Yan, H.; Wu, G.; Takata, T.; Hara, M.; Domen, K.; Li, C. Sulfur-substituted and Zinc-doped In(OH)3: A New Class of Catalyst for Photocatalytic H2 Production from Water under Visible Light Illumination J. Catal. 2006, 237, 322-329. (17) Ogisu, K.; Ishikawa, A.; Teramura, K.; Toda, K.; Hara, M.; Domen, K. LanthanumIndium Oxysulfide as a Visible Light Driven Photocatalyst for Water Splitting. Chem. Lett. 2007, 36, 854-855. (18) Goto, Y.; Seo, J.; Kumamoto, K.; Hisatomi, T.; Mizuguchi, Y.; Kamihara, Y.; Katayama, M.; Minegishi, T.; Domen, K. Crystal Structure, Electronic Structure, and Photocatalytic Activity of Oxysulfides: La2Ta2ZrS2O8, La2Ta2TiS2O8, and La2Nb2TiS2O8. Inorg. Chem. 2016, 55, 3674-3679. (19) Suzuki, T.; Hisatomi, T.; Teramura, K.; Shimodaira, Y.; Kobayashi, H.; Domen, K. A Titanium-based Oxysulfide Photocatalyst: La5Ti2MS5O7 (M = Ag, Cu) for Water Reduction and Oxidation. Phys. Chem. Chem. Phys. 2012, 14, 15475-15481.


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(20) Ishikawa, A.; Takata, T.; Kondo, J.; Hara, M.; Kobayashi, H.; Domen, K. Oxysulfide Sm2Ti2S2O5 as a Stable Photocatalyst for Water Oxidation and Reduction under Visible Light Irradiation (λ < 650 nm). J. Am. Chem. Soc. 2002, 124, 13547-13553. (21) Ishikawa, A.; Yamada, Y.; Takata, T.; Kondo, J.; Hara, M.; Kobayashi, H.; Domen, K. Novel Synthesis and Photocatalytic Activity of Oxysulfide Sm2Ti2S2O5. Chem. Mater. 2003, 15, 4442-4446. (22) Zhang, F.; Maeda, K.; Takata, T.; Domen, K. Modification of Oxysulfides with Two Nanoparticulate Cocatalysts to Achieve Enhanced Hydrogen Production from Water with Visible Light. Chem. Commun. 2010, 7313-7315. (23) Zhang, F.; Maeda, K.; Takata, T.; Domen, K. Improvement of the Photocatalytic Hydrogen Evolution Activity of Sm2Ti2S2O5 under Visible Light by Metal Ion Additives. J. Catal. 2011, 280, 1-7. (24) Li, R.; Chen, Z.; Zhao, W.; Zhang, F.; Maeda, K.; Huang, B.; Shen, S.; Domen, K.; Li, C. Sulfurization-assisted Cobalt Deposition on Sm2Ti2S2O5 Photocatalyst for Water Oxidation under Visible Light Irradiation. J. Phys. Chem. C 2013, 117, 376-382. (25) Zhao, W.; Maeda, K.; Zhang, F.; Hisatomi, T.; Domen, K. Effect of Post-treatments on the Photocatalytic Activity of Sm2Ti2S2O5 for the Hydrogen Evolution Reaction. Phys. Chem. Chem. Phys. 2014, 16, 12051-12056. (26) Abe, R.; Sayama, K.; Sugihara, H. Development of New Photocatalytic Water Splitting into H2 and O2 using Two Different Semiconductor Photocatalysts and a Shuttle Redox Mediator IO3-/I-. J. Phys. Chem. B 2005, 109, 16052-16061. (27) Miseki, Y.; Fujiyoshi, S.; Gunji, T.; Sayama, K. Photocatalytic Water Splitting under Visible Light Utilizing I3−/I− and IO3−/I− Redox Mediators by Z-scheme System Using


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Surface Treated PtOx/WO3 as O2 Evolution Photocatalyst. Catal. Sci. Technol. 2013, 3, 1750-1756. (28) Ma, G.; Suzuki, Y.; Singh, R. B.; Iwanaga, A.; Moriya, Y.; Minegishi, T.; Liu, J.; Hisatomi, T.; Nishiyama, H.; Katayama, M. et al. Photoanodic and Photocathodic Behaviour of La5Ti2CuS5O7 Electrodes in the Water Splitting Reaction. Chem. Sci. 2015, 6, 4513-4518.


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STSO-flux

(107)

(008) (110)

(006) (103)

STSO-PC

Intensity / a.u.

K. M. / a.u.

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(004)


STSO-flux STSO-PC

Ref. 300

400

500

600

700

10

20

2 / degree

Wavelength / nm

STSO-flux

30

STSO-PC


40

50

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50

Amount of H2 and O2 / mol

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58


H2

40 30

O2

20 10 0 0

10

20

30

40

Reaction time / h


50

60


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58

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hν e−

hv e−

I─

H2O

O2

e−

Eg e− h+ H-Cs-WO3

I3─

Eg e−

h+ Sm2Ti2S2O5

La5Ti2CuS5O7 La6Ti2S8O5


e−

H2 H+

Visible Light-Driven Z-Scheme Water Splitting ... - ACS Publications

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