(575e) Elucidating the Mechanisms of Catalytic Water Dissociation in Bipolar Membranes: The Roles of the Electric Field and Nano-Confinement

Bipolar membranes (BPMs) are emerging as transformative tools for electrically driven separation processes in a range of applications including the decarbonization of the chemical industry, critical materials recovery, and water treatment. Their unique capability to generate and separate H⁺ and OH^- from water in the presence of an electric field enables energy-efficient production of acids and alkaline using saline brines, chemical-free pH adjustment in electrochemical reactions such as water electrolysis, electrosynthesis of organic compounds, and fuel cells, as well as chemical reactions such as CO₂ capture. However, practical applications of BPMs are still in their infancy. There is a critical research need for developing high-performing BPMs to fulfill their potential in advancing green synthesis and decarbonization of industrial processes. Existing BPMs suffer from deficiencies in water dissociation rate, ion selectivity, ionic conductivity, and operating stability, presenting a significant barrier to their broader application. In particular, the low water dissociation rate is considered a major limiting factor that hinders the overall BPM performance.

Although several studies have evaluated various catalysts for water dissociation rate, and identified metal oxide catalysts as highly active in catalyzing water dissociation, the molecular level mechanisms of the water dissociation reaction and the role of local conditions near the catalytic surfaces, such as the electric field and nanoconfinement effects, remains poorly understood, limiting the rational design of novel catalysts of higher catalytic activity.

This work employs density functional theory (DFT) to study the atomic-scale behaviors of the catalytic water dissociation reaction under special physical and electrochemical environments at the interfacial layer of BPMs. The hydrolyzed (001) facet of anatase TiO₂ nanoparticles is constructed and used as the model system for its demonstrated experimental efficacy. We first examine various possible pathways, including the widely hypothesized protonation-deprotonation mechanism, to identify the leading ones responsible for water dissociation. Then, we explore the influence of the local electric field on the dissociation rate of water molecules. The role of local nanoconfinement near the catalytic surface will also be discussed. Facets other than (001), such as (101), will be investigated as well to provide further insights. By quantifying these effects, we aim to identify design principles for optimizing water dissociation catalysts, enabling the development of next-generation BPMs to tackle the pressing challenges in electrifying separation processes, which aligns with global efforts to transition chemical manufacturing toward renewable energy-driven processes.