Determining the sequence of charge transport events and their roles on the limit of quantum efficiency of photocatalytic hydrogen production

Quantum efficiency (QE) is a defining parameter to rank the efficiency of a photocatalyst. The QE is governed by the kinetics of recombination and transfer processes of photogenerated charge carriers along with the sequence in which these events occur. However, there are no experimental techniques able to determine the sequence (i.e., series, parallel, or combination of both) of these charge transport events and directly determine the QE from charge transport information and vice versa. To address these gaps, here we report a semi-empirical circuit model to determine the sequence of charge transport events and propose a set of hypotheses to discriminate the deciding role of recombination and charge transfer in predicting the QE in a photocatalytic process. By testing with literature data for photocatalytic water splitting, we demonstrate that this model is able to predict QE when the percentage of recombination is known and the sequence of charge transport events when QE is known.