Electrochemical CO2 capture with pH-independent redox chemistry

TL;DR

This paper presents a novel pH-independent redox chemistry using TEMPO molecules that significantly reduces the energy cost of electrochemical CO2 capture, offering a more practical and cost-effective solution for climate change mitigation.

Contribution

It introduces a pH-independent redox method that lowers thermodynamic energy costs for CO2 capture, supported by molecular modeling and simulations.

Findings

Energy cost as low as 2.6 kJ/mol of CO2

pH can be decreased by 7.6 without high entropic costs

Potential for practical, cost-effective CO2 capture

Abstract

Capture of anthropogenic CO2 is critical for mitigating climate change, and reducing the energy cost is essential for wide-scale deployment. Solubility of inorganic carbon in aqueous solutions depends on the pH, and electrochemical modulation of the pH has been investigated as a means of CO2 capture and release. However, reported methods incur unavoidable energy costs due to thermodynamic penalties. In this study, we introduce a pH-independent redox chemistry that greatly lowers the thermodynamic energy costs by changing the pH without directly changing the [H+]. We show that the redox reaction of TEMPO molecules modulates the pH for capture and release of CO2 in a flow cell with an energy cost as low as 2.6 kJ/mol of CO2 corresponding to 0.027 eV/molecule. A molecular model, supported by MD and DFT simulations, is proposed of how the pH is decreased by 7.6 while largely avoiding the entropic energy cost associated with increasing the [H+]. We believe that this work showcases the potential of pH-independent redox chemistries for practical and cost-effective CO2 capture.