Measurement and adjustment of proton activity in solid polymer electrolytes

Abstract : Technological progress in electrochemical energy conversion devices requires new solid polymer electrolyte membrane (PEM) materials with particular properties. The strongly acidic nature of Nafion® is not always desirable; for instance, CO2 electroreduction requires a low proton activity to avoid excess hydrogen evolution. This communication presents a novel measurement technique for determining the acidity of a PEM, using a pH-sensitive electrode half-cell attached to the membrane sample, connected to a reference electrode via a salt bridge. A dynamic hydrogen electrode on platinized‑platinum surface (DHE) was found to give repeatable results within 5% uncertainty. Several membranes based on Nafion® impregnated with various basic species were tested, as well as an anion-exchange membrane and a poly-phosphonic acid membrane. The technique is expected to have wider reaching applications in PEM fuel cell and redox flow battery development, as well as in the electrolysis and electrodialysis industries.