Oxide layer coating enabling oxysulfide-based photocatalyst sheet to drive Z-scheme water splitting at atmospheric pressure

Abstract

•Photocatalyst sheets made of La5Ti2Cu0.9Ag0.1O7S5 (LTCA) and BiVO4 split water •Backward reactions on LTCA suppress the STH at elevated pressure •SiO2 coating allows the photocatalyst sheet to maintain an STH of 0.41% at 90 kPa •Pathways to activate photocatalyst sheets under realistic conditions are identified A photocatalyst sheet consisting of doped La5Ti2Cu0.9Ag0.1O7S5 as a hydrogen evolution photocatalyst (HEP), BiVO4 as an oxygen evolution photocatalyst (OEP), and Au as a conductor layer exhibits a solar-to-hydrogen energy conversion efficiency (STH) of 0.67% at 4 kPa in Z-scheme overall water splitting (ZOWS). However, the photocatalyst sheet loses its activity at elevated pressure due to backward reactions. Here, we show that this loss of activity can be suppressed by coating the sheet with amorphous SiO2 layer. In addition, the SiO2 coating maintained its performance at elevated temperatures, unlike the widely used amorphous TiO2 coating, and exhibited an STH of 0.41% at 90 kPa and 333 K. The results of the present study demonstrate the ability to functionalize photocatalyst sheets of narrow-band-gap materials prone to backward reactions, allowing their use in outdoor environments, and paves the way for practical solar hydrogen production. A photocatalyst sheet consisting of doped La5Ti2Cu0.9Ag0.1O7S5 as a hydrogen evolution photocatalyst (HEP), BiVO4 as an oxygen evolution photocatalyst (OEP), and Au as a conductor layer exhibits a solar-to-hydrogen energy conversion efficiency (STH) of 0.67% at 4 kPa in Z-scheme overall water splitting (ZOWS). However, the photocatalyst sheet loses its activity at elevated pressure due to backward reactions. Here, we show that this loss of activity can be suppressed by coating the sheet with amorphous SiO2 layer. In addition, the SiO2 coating maintained its performance at elevated temperatures, unlike the widely used amorphous TiO2 coating, and exhibited an STH of 0.41% at 90 kPa and 333 K. The results of the present study demonstrate the ability to functionalize photocatalyst sheets of narrow-band-gap materials prone to backward reactions, allowing their use in outdoor environments, and paves the way for practical solar hydrogen production.