Integrating Charge Carrier Dynamics and Interface Reactions: A Continuum Model for Oxygen Evolution at Photoanodes

In the process of electrochemical water splitting, the oxygen evolution reaction (OER) presents a challenge due to its complex mechanism. Continuum modeling of the OER interface can give insight into the mechanism by providing interface parameters that cannot be measured experimentally, such as the coverages of intermediate species. In photoelectrochemical cells, the illumination of the semiconductor and the related charge carrier dynamics present additional challenges to continuum modeling. Previous modeling efforts focused on either the electrochemical reactions or the spatial charge carrier dynamics in the semiconductor. This work integrates these two components, enabling the investigation of how charge carrier transport, stimulated by the electric field, illumination, and recombination, affects the OER and its intermediate species. The capabilities of the model are shown under a variety of conditions, such as different illumination and charge carrier trap state densities. Furthermore, this work shows that the common assumption of a linear electric field in the semiconductor does not accurately describe the steady-state current density, but that a full coupling of the charge carrier dynamics and the potential through the Poisson equation is necessary. As such, the continuum OER model developed in this work marks a significant step in analyzing oxygen evolution and uncovering the limitations of the OER mechanism.