Addressing the Origin of Photocurrents and Fuel Production Activities in Catalyst-Modified Semiconductor Electrodes

The direct integration of electrocatalysts with photovoltaic materials provides a strategy to photoelectrochemically power chemical transformations and store intermittent solar energy as fuels. However, many electrocatalytic components used or proposed for use in such assemblies also absorb visible light. This prompts the questions: To what extent does a selected electrocatalytic coating screen photons from reaching the underlying photovoltaic, do excited-state species associated with coating layers contribute to photocurrent production via mechanisms involving dye-sensitization processes, and are relatively high or low loadings of catalytic sites advantageous. Herein, we highlight how optical and electrochemical characterization techniques can be coupled with structural information to address these questions. The experiments described in this work make use of a p-Type gallium phosphide semiconductor that is interfaced with cobalt porphyrin hydrogen evolution reaction catalysts. However, the experimental techniques and discussions presented in this work can likely be applied to other materials and chemical transformations, providing a general yet useful strategy for better understanding the origin of photocurrents and fuel production activities in catalyst-modified semiconductor electrodes.