A systematic analysis and optimization of bicarbonate electrolysis based on a bipolar membrane through multiscale simulation

Bicarbonate electrolysis facilitated by bipolar membrane has emerged as a compelling alternative to gaseous CO₂ electrolysis, primarily because of its enhanced product concentration and streamlined processes. However, despite increasing attention, a comprehensive understanding of bicarbonate electrolysis has been eclipsed by the complexity of the intertwined electrode reactions and water dissociation promotion mechanisms of bipolar membranes. A physics-based modeling approach has substantial potential to untangle the impact of intertwined physicochemical processes and expedite the optimization of bicarbonate electrolysis. In this study, a multiscale model coupled with a 1D bipolar membrane and a 2D cathode model is presented to explore the effects of bipolar membranes on cathode reactions and performance optimization using H⁺ flux as a bridge. For a bipolar membrane, the attenuation mechanism of water dissociation involving ohmic and concentration losses is presented and described using mathematical eqs. A quantification metric, the water dissociation efficiency of a bipolar membrane, is proposed to denote the degree of promoted water dissociation. Two noteworthy parameters related to the fixed functional group concentration are determined and detailed: the onset current density required to stimulate water dissociation and the limited water dissociation efficiency caused by attenuation. For the cathode, a synergistic enhancement mechanism among the operating parameters, membrane properties, and cathode properties is identified. The combined effect of these parameters on the electrolytic performance surpasses the sum of their individual enhancements. Following parameter optimization, there is a notable increase in the current density and Faraday efficiency of bicarbonate electrolysis by 68.6 mA/cm² and 18.3%, respectively. This study provides a holistic understanding of bicarbonate electrolysis and substantial guidance for its future design.