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

Shijian Jin; Min Wu; Yan Jing; Roy G Gordon; Michael J Aziz

doi:10.1038/s41467-022-29791-7

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

Nat Commun. 2022 Apr 19;13(1):2140. doi: 10.1038/s41467-022-29791-7.

Authors

Shijian Jin¹, Min Wu¹, Yan Jing², Roy G Gordon^{1

2}, Michael J Aziz³

Affiliations

¹ John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA.
² Department of Chemistry and Chemical Biology, Harvard University, Cambridge, MA, 02138, USA.
³ John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, 02138, USA. maziz@harvard.edu.

Abstract

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 N₂, 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.