Continuous Electrochemical Carbon Capture via Redox-Mediated pH Swing─Experimental Performance and Process Modeling

Abstract

We investigate a continuous electrochemical pH-swing method to capture CO2 from a gas phase. The electrochemical cell consists of a single cation-exchange membrane (CEM) and a recirculation of a mixture of salt and phenazine-based redox-active molecules. In the absorption compartment, this solution is saturated by CO2 from a mixed gas phase at high pH. In the electrochemical cell, pH is reduced, and CO2 is selectively released in a desorption step. We investigate the influence of redox molecule concentration on the charge storage capacity of the solution, as well as the impact of current density and solution recirculation rate on process performance. A theoretical framework, based on a minimal set of assumptions, is established. This framework describes the data very accurately and can be used for system design and optimization. We evaluate the trade-off between energy consumption and CO2 capture rate and compare with published reports. We report a low energy consumption of 32 kJ/mol of CO2 at a capture rate of 39 mmol/m2/min.