Influence of the Electrostatic Interaction between a Molecular Catalyst and Semiconductor on Photocatalytic Hydrogen Evolution Activity in Cobaloxime/CdS Hybrid Systems

The influence of the electrostatic interaction on photocatalytic H₂ evolution activity in cobaloxime/cadmium sulfide (CdS) hybrid systems was studied by measuring the charges of the cobaloximes and the zeta potentials of CdS under different pH conditions (pHs 4-7). Cobaloxime/CdS hybrid systems may have potential as a valid model for the investigation of the electrostatic interaction between a molecular catalyst and semiconductor because the kinetics of methanol oxidation and the driving force of electron transfer from photoirradiated CdS to cobaloxime have little effect on the pH-dependent photocatalytic H₂ evolution activity. Our experimental results suggest that electrostatic repulsion between cobaloxime and CdS disfavors the electron transfer from CdS to cobaloxime and hence lowers the photocatalytic H₂ evolution activity. Whereas, electrostatic attraction favors the electron transfer process and enhances the photocatalytic H₂ evolution activity. However, an electrostatic attraction interaction that is too strong may accelerate both forward and backward electron transfer processes, which would reduce charge separation efficiency and lower photocatalytic H₂ evolution activity.