Identifying the Role of the Local Charge Density on the Hydrogen Evolution Reaction of the Photoelectrode.

Understanding the role of surface charges in the catalytic reaction is of great importance to fundamental science in photoelectrochemistry (PEC). However, spatial heterogeneities of charge transfer sites and catalytic sites at the electrode/electrolyte interface obscures the surface reaction process. Herein, we quantified the relationship between the local catalytic current of the hydrogen evolution reaction (HER) and the surface charge density using spatially resolved photovoltage microscopy on the Pt/Ti array on the p-Si photoelectrode. We found that the Pt/Ti islands on the p-Si surface worked as the main charge collect areas but as the sole catalytic sites to drive the PEC hydrogen evolution. Based on the achievements of identifying the local photocurrent and photovoltage on a single Pt/Ti island, we found that the local HER current can be linearly regulated by the charge density at reactive sites by concurrently adjusting the bias potential and the spacings of the Pt/Ti islands. These results emphasize the significant impact of the surface charge density on the catalytic activity in photoelectrochemistry.