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. 2022 Aug 12;8(32):eadc9115.
doi: 10.1126/sciadv.adc9115. Epub 2022 Aug 10.

Surface-modified, dye-sensitized niobate nanosheets enabling an efficient solar-driven Z-scheme for overall water splitting

Shunta Nishioka  1 , Koya Hojo  1 , Langqiu Xiao  2 , Tianyue Gao  2 , Yugo Miseki  3 , Shuhei Yasuda  4 , Toshiyuki Yokoi  4 , Kazuhiro Sayama  3 , Thomas E Mallouk  2   5 , Kazuhiko Maeda  1
Affiliations

Surface-modified, dye-sensitized niobate nanosheets enabling an efficient solar-driven Z-scheme for overall water splitting

Shunta Nishioka et al. Sci Adv. .

Abstract

While dye-sensitized metal oxides are good candidates as H2 evolution photocatalysts for solar-driven Z-scheme water splitting, their solar-to-hydrogen (STH) energy conversion efficiencies remain low because of uncontrolled charge recombination reactions. Here, we show that modification of Ru dye-sensitized, Pt-intercalated HCa2Nb3O10 nanosheets (Ru/Pt/HCa2Nb3O10) with both amorphous Al2O3 and poly(styrenesulfonate) (PSS) improves the STH efficiency of Z-scheme overall water splitting by a factor of ~100, when the nanosheets are used in combination with a WO3-based O2 evolution photocatalyst and an I3-/I- redox mediator, relative to an analogous system that uses unmodified Ru/Pt/HCa2Nb3O10. By using the optimized photocatalyst, PSS/Ru/Al2O3/Pt/HCa2Nb3O10, a maximum STH of 0.12% and an apparent quantum yield of 4.1% at 420 nm were obtained, by far the highest among dye-sensitized water splitting systems and comparable to conventional semiconductor-based suspended particulate photocatalyst systems.

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Figures

Fig. 1.
Fig. 1.. Electron transfer mechanism.
Schematic electron transfer mechanism and energy level diagram of the Ru/Pt/HCa2Nb3O10 nanosheets for H2 evolution and PtOx/H-Cs-WO3 for O2 evolution. C.B., conduction band; V.B., valence band.
Fig. 2.
Fig. 2.. Half-cell H2 evolution reactions.
Time courses of H2 evolution from an aqueous NaI solution over Ru/Pt/HCa2Nb3O10 nanosheets with different modifications. Reaction conditions: catalyst, 20 mg; solution, aqueous NaI (10 mM, 100 ml, pH 3.8 to 4.0); light source, xenon lamp (300 W) fitted with CM-1 cold mirror and L42 cutoff filter (λ > 400 nm). Irradiation area, 44 cm2. (A and B) Data taken under higher-intensity (80 mW cm−2) and lower-intensity (8.0 mW cm−2) irradiation, respectively. Experimental error in the H2 amount was ~20%.
Fig. 3.
Fig. 3.. Transient diffuse reflectance decay.
Time-dependent absorbance change in transient diffuse reflectance measurements of Ru-sensitized HCa2Nb3O10 nanosheets with and without surface modification recorded in aqueous NaI solutions (pH 4.0) monitored at (A) 475 nm (10 mM NaI) and (B) 380 nm (100 mM NaI).
Fig. 4.
Fig. 4.. Solar-driven Z-scheme overall water splitting.
(A) STH energy conversion efficiencies of Ru/Pt/HCa2Nb3O10 nanosheets with different modifications for Z-scheme water splitting. (B) Time courses of H2 and O2 evolution from a mixture of PSS/Ru/Al2O3/Pt/HCa2Nb3O10 and PtOx/H-Cs-WO3 under simulated sunlight (50 mW cm−2). Reaction conditions: catalyst, modified Ru/Pt/HCa2Nb3O10, 20 mg; PtOx/H-Cs-WO3, 50 mg; reactant solution, 5 mM aqueous NaI (100 ml, pH 4); light source, solar simulator with an irradiation area of 9 cm2. Closed and open symbols indicate data based on H2 and O2 evolution, respectively.
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