Photocatalyst Design Principles for Photocatalytic Hydrogen Production and Benzyl Alcohol Oxidation with CdS Nanosheets

To produce hydrogen using photocatalysts while maintaining environmentally friendly characteristics, research has focused on using benzyl alcohol (BzOH) as a hole scavenger to convert it into the valuable compound benzaldehyde (BA). However, due to the relatively slow oxidation rate of BzOH compared to conventional hole scavengers, tailored photocatalyst designs are necessary. In this study, we prepared CdS nanosheets (NSs) and introduced Na₂SO₄–Na₂SO₃ and BzOH as hole scavengers to adjust the oxidation half-reaction rate (OHR) during the photocatalytic reaction. Various co-catalysts were introduced to examine how changes in the reduction half-reaction (RHR) and OHR rates influence hydrogen production. The results reveal that the selection of co-catalyst and hole scavenger significantly influences the rate-determining step (RDS) in the photocatalytic reaction. For bare CdS NSs, the slow RHR results in the RDS being the RHR, leading to similar hydrogen production rate regardless of the scavenger type. However, with Pt as a co-catalyst, the RDS shifts to the OHR due to the accelerated RHR, inducing hydrogen production rate highly sensitive to the type of scavenger. Consequently, hydrogen production is significantly reduced when using BzOH, which has a slower oxidation rate. These findings suggest that achieving high hydrogen yields is fundamentally challenging with BzOH due to its slow oxidation rate, even with the introduction of excellent co-catalysts. Therefore, it is imperative to develop photocatalyst materials with lower valence band level for high oxidation power.