Surface Property Modulates the Proton Transport Dynamics in Porous Oxygen Evolving Electrodes

Three dimensional porous electrodes, such as those in membrane electrode assemblies (MEA), are widely employed in electrochemical devices due to their high surface area and achievable current density. The highly heterogeneous internal structure and microenvironments make it challenging for experimental mechanistic investigation and effectively managing mass transport in porous electrodes. Here, we developed an operando method employing polymer bound fluorescent sensors (PFS) to directly quantify the internal proton gradient in a porous electrode for oxygen evolution reaction (OER). The results revealed notable pH gradients within OER electrodes in unbuffered electrolyte. Proton transport dynamics was found to be significantly influenced by the proton adsorption properties of the support. This property also increases the stable operation time for an electrodeposited cobalt oxide OER catalyst. The PFS method can be extended to study other variables that contribute to the microenvironments within porous electrodes, and the role of catalyst support in modulating mass transport may be applicable to many other electrochemical devices including fuel cells and CO₂ electrolyzers.