Low energy carbon capture via electrochemically induced pH swing with electrochemical rebalancing

This work demonstrates a safe and scalable electrochemical CO2 separation method that allows promisingly low (62 kJ/mol(CO2)) energetic cost at a high current density, and it can be used for direct air capture when a suitable molecule is used. We demonstrate a carbon capture system based on pH swing cycles driven through proton-coupled electron transfer of sodium (3,3 '-(phenazine-2,3-diylbis(oxy))bis(propane-1-sulfonate)) (DSPZ) molecules. Electrochemical reduction of DSPZ causes an increase of hydroxide concentration, which absorbs CO2; subsequent electrochemical oxidation of the reduced DSPZ consumes the hydroxide, causing CO2 outgassing. The measured electrical work of separating CO2 from a binary mixture with N-2, at CO2 inlet partial pressures ranging from 0.1 to 0.5 bar, and releasing to a pure CO2 exit stream at 1.0 bar, was measured for electrical current densities of 20-150 mA cm(-2). The work for separating CO2 from a 0.1 bar inlet and concentrating into a 1 bar exit is 61.3 kJ mol(CO2)(-1) at a current density of 20 mA cm(-2). Depending on the initial composition of the electrolyte, the molar cycle work for capture from 0.4 mbar extrapolates to 121-237 kJ mol(CO2)(-1) at 20 mA cm(-2). We also introduce an electrochemical rebalancing method that extends cell lifetime by recovering the initial electrolyte composition after it is perturbed by side reactions. We discuss the implications of these results for future low-energy electrochemical carbon capture devices.

Automated summary

This work presents a safe and scalable electrochemical method for CO2 separation with low energy cost. By utilizing proton-coupled electron transfer of DSPZ molecules, CO2 absorption and release can be achieved effectively. The results show promising potential for practical application in the future.