Electrochemical CO2 capture with pH-independent redox chemistry

Sang Cheol Kim; Marco Gigantino; John Holoubek; Jesse E. Matthews; Junjie Chen; Yaereen Dho; Thomas F. Jaramillo; Yi Cui; Arun Majumdar; Yan-Kai Tzeng; Steven Chu

arXiv · 2502.01028

Electrochemical CO2 capture with pH-independent redox chemistry

Sang Cheol Kim·Marco Gigantino·John Holoubek·Jesse E. Matthews·Junjie Chen·Yaereen Dho·Thomas F. Jaramillo·Yi Cui·Arun Majumdar·Yan-Kai Tzeng·Steven Chu

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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.

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Sang Cheol Kim, Marco Gigantino, John Holoubek, Jesse E. Matthews, Junjie Chen, Yaereen Dho, Thomas F. Jaramillo, Yi Cui, Arun Majumdar, Yan-Kai Tzeng, Steven Chu. 2025-02-03. Electrochemical CO2 capture with pH-independent redox chemistry. https://arxiv.org/abs/2502.01028

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