关键词: 氧化铜, 光电化学分解水, 电化学阻抗谱, 速率方程, 光生载流子动力学

Abstract:

Photocatalytic splitting of water over p-type semiconductors is a promising strategy for production of hydrogen. However, the determination of rate law is rarely reported. To this purpose, copper oxide (CuO) is selected as a model photocathode in this study, and the photogenerated surface charge density, interfacial charge transfer rate constant and their relation to the water reduction rate (in terms of photocurrent) were investigated by a combination of (photo)electrochemical techniques. The results showed that the charge transfer rate constant is exponential-dependent on the surface charge density, and that the photocurrent equals to the product of the charge transfer rate constant and surface charge density. The reaction is first-order in terms of surface charge density. Such an unconventional rate law contrasts with the reports in literature. The charge density-dependent rate constant results from the Fermi level pinning (i.e., Galvani potential is the main driving force for the reaction) due to accumulation of charge in the surface states and/or Frumkin behavior (i.e., chemical potential is the main driving force). This study, therefore, may be helpful for further investigation on the mechanism of hydrogen evolution over a CuO photocathode and for designing more efficient CuO-based photocatalysts.

Key words: CuO, Photoelectrochemical water splitting, Electrochemical impedance spectroscopy, Rate law, Kinetics of photogenerated carriers