Cocatalyst effects on hydrogen evolution in a plasmon-induced water-splitting system

We explored the performance of hydrogen (H₂) evolution using noble metals or their metal oxides as cocatalysts in the plasmon-induced water-splitting system. Although many studies have employed n-type semiconductor particle systems to investigate cocatalyst effects, evaluating only the catalytic activity of H₂ and oxygen (O₂) evolution has been limited by (1) the difficulty of transferring an electron injected into the conduction band of a semiconductor to a cocatalyst due to the formation of a Schottky barrier when a metallic cocatalyst for H₂ evolution contacts the n-type semiconductor and (2) the potential for a reverse water-splitting reaction, which occurs due to the promotion of the reduction of the evolved O₂ by the cocatalyst. To overcome these limitations, in the present study, we eliminated the adverse effect of the Schottky barrier by obtaining ohmic contact between the semiconductor and the metal or metal oxide cocatalysts, and we used two separate reaction chambers for H₂ and O₂ evolution to avoid reverse water-splitting reactions such as H₂-O₂ recombination or the photoreduction of O₂. A 2-3 nm thick rhodium layer deposited on a platinum board exhibited relatively high performance, a 3-fold increase compared with the absence of a metal or metal oxide cocatalyst thin layer.