Electrostatic Contributions of the Extended Environment and Local Catalytic Effects in Bipolar Membranes

Abstract

Catalyst layers are widely used to accelerate water dissociation in bipolar membranes (BPMs), yet their role in defining junction electrostatics and reversible reaction kinetics remains unclear. Here, we probe the electrochemical response of catalyst-containing BPM junctions using open-circuit voltage measurements, polarization analysis, and electrochemical impedance spectroscopy. We show that catalyst nanoparticles influence both the recovery of the membrane potential and the voltage losses associated with water dissociation and formation at the catalyst layer. These changes reflect coupled effects of catalyst surface chemistry, junction electrostatics, and proton-transfer kinetics. Notably, catalysts that recover the membrane potential do not necessarily reduce overvoltage under applied bias, highlighting that membrane-potential recovery alone is insufficient to predict BPM performance. By combining improvements in membrane-potential recovery and reaction kinetics, catalyst–ionomer interface engineering reduces water-formation losses by up to 65% and increases peak power density for energy storage by more than an order of magnitude.