Cocatalyst engineering of a narrow bandgap Ga-La5Ti2Cu0.9Ag0.1O7S5 photocatalyst towards effectively enhanced water splitting

Abstract

Ga-La₅Ti₂Cu_0.9Ag_0.1O₇S₅ (Ga-LTCA), an oxysulfide photocatalyst, can act as a hydrogen evolution photocatalyst in Z-scheme water splitting systems in conjunction with an oxygen evolution photocatalyst (OEP) under visible light irradiation up to 700 nm. However, the overall efficiency is strongly limited by the low activity of Ga-LTCA. The present work demonstrates a drastic improvement in the H₂ evolution activity of Ga-LTCA after loading small Rh cocatalyst particles exhibiting uniform dispersion and intimate contact with the photocatalyst. Using this system, an apparent quantum yield (AQY) of 11.2 ± 0.9% at 420 nm was obtained for H₂ evolution from an aqueous Na₂S–Na₂SO₃ solution, this being the highest value yet reported for a sacrificial H₂ evolution reaction using an oxysulfide photocatalyst. Following modification with a Cr₂O₃ layer, efficient Z-scheme water splitting was also accomplished using the cocatalyst-loaded Ga-LTCA in combination with H⁺/Cs⁺/PtO_x/WO₃ as the OEP, with an improved AQY of 2.4% at 420 nm.