Sol-gel synthesis of highly reproducible WO₃ photoanodes for solar water oxidation = 溶胶-凝胶法制备高重复性的WO₃光阳极用于太 阳能水氧化反应

Abstract

Although monoclinic WO₃ is widely studied as a prototypical photoanode material for solar water splitting, limited success, hitherto, in fabricating WO₃ photoanodes that simultaneously demonstrate high efficiency and reproducibility has been realized. The difficulty in controlling both the efficiency and reproducibility is derived from the ever-changing structures/compositions and chemical environments of the precursors, such as peroxytungstic acid and freshly prepared tungstic acid, which render the fabrication processes of the WO₃ photoanodes particularly uncontrollable. Herein, a highly reproducible sol-gel process was developed to establish efficient and translucent WO₃ photoanodes using a chemically stable ammonium metatungstate precursor. Under standard simulated sunlight of air mass 1.5 G, 100 mW cm−2, the WO₃ photoanode delivered photocurrent densities of ca. 2.05 and 2.25 mA cm−2 at 1.23 V versus the reversible hydrogen electrode (RHE), when tested in 1 mol L−1 H₂SO₄ and CH₃SO₃H, respectively. Hence, the WO₃ photoanodes fabricated herein are one of the WO₃ photoanodes with the highest performance ever reported. The reproducibility of the fabrication scheme was evaluated by testing 50 randomly selected WO₃ samples in 1 mol L−1 H2SO4, which yielded an average photocurrent density of 1.8 mA cm−2 at 1.23 VRHE with a small standard deviation. Additionally, the effectiveness of the ammonium metatungstate precursor solution was maintained for at least 3 weeks, when compared with the associated upper-limit values of peroxytungstic and tungstic acid based precursors after 3 d. This study presents a key step to the future development of WO₃ photoanodes for efficient solar water splitting.