Open circuit potential decay transients quantify interfacial pH swings during high current density hydrogen electrocatalysis

Many energy conversion technologies comprise proton-coupled electron transfer reactions that consume/produce protons at electrode surfaces, thereby generating interfacial pH environments that differ substantially from the bulk. Quantification of these interfacial pH swings is a prerequisite for designing efficient energy conversion systems. Herein, we develop a methodology for quantifying interfacial pH using open circuit potential (OCP) transients. Using a model system of hydrogen evolution on Pt, we quantify polarization-induced pH swings under a wide variety of conditions relevant for functional devices. We find that even strongly buffered solutions experience pH swings of >2 pH units at modest current densities of −30 mA cm−2. The interfacial pH swings are augmented by the addition of supporting electrolyte and the presence of Nafion polymer overlayers—resulting in swings >12 pH units. Analytical transport modeling validates the developed methodology and enables quantitative prediction of both steady-state and transient interfacial pH swings.