(682h) Modeling Reactive Carbon Species in Bipolar Membranes for Carbon Capture and Conversion

CO₂ reduction chemistry in pilot-scale electrolyzers has become a very active field. The community now recognizes that one of the main roadblocks to commercialization is remedying (bi)carbonates formation at the cathode and the subsequent crossover of those (bi)carbonate anions. One potential solution to this challenge is to use an electrolyzer that employs a reverse-biased bipolar membrane (BPM) that contains a water dissociation catalyst at the interface between the anion-exchange layer (AEL) and cation-exchange layer (CEL) that forms H⁺ and OH^-. This configuration minimizes (bi)carbonate crossover via Donnan exclusion, and any (bi)carbonate anions that do cross over can be neutralized by the internally generated H⁺, thereby liberating CO₂ that can diffuse back to the cathode. The internal generation of CO₂ also facilitates the usage of aqueous carbon capture feedstocks as opposed to costly gaseous CO₂ feedstocks (currently >50$/ton CO₂). Unfortunately, the local pH environments and the transport of carbon species within BPMs are poorly understood. Better understanding of reactive carbon transport in BPMs is necessary to design materials for carbon capture and conversion.

In this talk, we demonstrate a continuum model of a BPM immersed in a (bi)carbonate feedstock to determine the local pH and carbon species concentrations in BPMs applied in carbon capture and conversion applications. Furthermore, the work demonstrates that in-situ generation of CO₂ occurs at the interface of the CEL and the aqueous electrolyte. Lastly, sensitivity analysis is employed to determine optimal BPM properties that optimize transport (enhanced CO₂ regeneration and mitigated (bi)carbonate crossover) for application in CO₂ reduction. Ultimately, the study provides improved understanding of the reactions of dissolved inorganic carbon species in an electrochemical system enabled by BPM, presenting theory and knowledge relevant for a wide range of electrochemical carbon capture and conversion technologies.