Introducing an Electrochemically Driven Proton Concentration Process for CO2 Capture

Abstract

An electrochemically driven proton concentration process was developed for the capture of carbon dioxide (CO2) that was based on modulation of the proton concentration in an electrochemical cell by a proton intercalating MnO2 electrode. The pH sensitivity of CO2 hydration was leveraged such that CO2 was absorbed as bicarbonate and carbonate ions at high pH values and desorbed as gas at low pH values. A comprehensive thermodynamic model developed to determine the speciation, electrochemical performance, and energetics required to desorb CO2 captured from a flue gas was validated by chemical and electrochemical measurements, with very good agreement between simulated and experimental results. The electrochemical work requirement for the proposed proton concentration process to desorb CO2 captured from a flue gas stream was estimated to be 33.2 kJe/molCO2, suggesting that this process is competitive with other electrochemical-based approaches (with energetics ranging from 31.3 to 49 kJe/molCO2). The MnO2 electrode was successfully synthesized using a coprecipitation method followed by casting on either carbon cloth or carbon felt substrate. The fabricated electrodes were characterized using X-ray photoelectron spectroscopy to assess their chemical state, and the formation of MnO2 was confirmed. The capacitance behavior of the electrodes, which is proportional to their electrochemical performance, was evaluated using cyclic voltammetry (CV). The fabricated electrodes were also tested in a symmetrical electrochemical cell with a constant potential applied across the cell. The generated current was effectively translated into proton intercalation/deintercalation reactions through reversible cycles, resulting in modulated proton concentrations in the anode and cathode chambers. The demonstrated model and experimental data suggest that this proton concentration process could be an attractive electrochemical-based route for CO2 capture.