The use of renewable electricity to power electrochemical CO2 removal and concentration from point
sources, air, and seawater is receiving considerable interest as one strategy for mitigating climate change.
Two common embodiments of this idea involve CO2 separation using electrochemically reversible binding
of CO2 to a nucleophilic redox mediator [1], or a pH swing/gradient in aqueous solution [2]. For either
embodiment to be feasible, the energetic cost of regenerating the sorbent should be low at practical
separation throughputs. Consequently, there have been a number of efforts to understand how the
thermodynamic minimum work input for a given separation cycle varies under different conditions using
modeling. In this talk, we demonstrate that the thermodynamic minimum work input for electrochemical
CO2 separation is the sum of exergy losses incurred from differences between the partial pressure of CO2
within the CO2 source/exit streams and the partial pressure of CO2 in the sorbent. This framework
rationalizes minimum work inputs for pH-swing and redox-mediator-based CO2 separation cycles, and
motivates the measurement or estimation of the aforementioned CO2 partial pressures in experimental
studies. We will discuss other experimental implications of this result, and introduce a design for pHswing-based electrochemical CO2 capture inspired by it.
References:
[1] Clarke L., Leonard M., Hatton A., Brushett F., Thermodynamic Modeling of CO2 Separation Systems
with Soluble, Redox-Active Capture Species
[2] Jin. S, Wu M., Gordon R., Aziz M., Kwabi D., pH Swing Cycle for CO2 Capture Electrochemically Driven
through Proton-Coupled Electron Transfer