Reduced-Order Model of Multicomponent Electrolyte Transport in Bipolar Membranes

Recent advancements in water-dissociation catalysis and affordable renewable electricity have led to a growing interest in the application of bipolar membranes (BPMs) in electrodialysis, electrochemical carbon dioxide reduction, and other electrochemical processes. Modeling tools for BPMs commonly use direct-numerical simulations (DNS) to predict performance, which are computationally expensive and make insights into the key physics of the cells difficult to discern. As a result, a mechanistic understanding of BPMs remains unclear, which is a requisite to optimize their performance and durability for their independent technology applications. In this work, we present a reduced-order, steady-state model of a general multicomponent-electrolyte-BPM system. We systematically simplify Poisson-Nernst-Planck equations for a BPM system that consists of two bulk regions, a cation-exchange membrane, an anion-exchange membrane, and a BPM junction. DNS is used to validate the results from our model. We examine the effects of membrane-length asymmetry and pH gradients on the characteristic polarization curve for various fixed-charged groups. These findings are obtained with better numerical stability and faster computational speed than DNS without compromising the essential physics of the system.