Water-Dissociation Catalysis and Voltage-Driven Proton Transfer with Metal Oxides: Fundamentals and Applications in Bipolar Membranes

Reactions of water typically involve breaking H-O bonds and are ubiquitous in biological, industrial, and environmental processes. The simplest reaction is heterolytic water dissociation (WD), H2O ??' H+ + OH-, the understanding of which has been a focus of experiment and theory for decades. We use a bipolar-membrane (BPM) electrolyzer, where WD is driven in the region between a hydroxide-exchange and proton-exchange membrane by an applied voltage, to study WD kinetics. We apply various electrochemical platforms to study the basic factors and mechanisms that control the kinetics of WD, discovering how tuned metal-oxide nanoparticles provide surfaces with (controllable) proton-absorption sites that catalyze WD while also focusing the interfacial electric field across the BPM junction to speed the WD rate (e.g. Science 2020, Nature Comm. 2022). Temperature-dependent measurements show the WD catalysts do not primarily lower the activation energy for WD, but instead dramatically increase the number of water configurational microstates poised for the proton-transfer elementary steps in WD (Joule, 2023). These discoveries enabled the design of new WD catalysts for BPMs that operate with 40-times better voltage efficiency than the commercial state of the art (Nature Materials, 2024), and at current-densities of up to 4 A/cm2, driving commercialization efforts for advanced bipolar membranes and new applications.

Speaker: Shannon Boettcher, UC Berkeley