Oxygen-tolerant electrochemical CO2 separation using N-heterocyclic imines with superstoichiometric release per electron

Electrochemically mediated CO₂ capture (EMCC) offers a promising alternative to thermochemical capture, but benchmark sorbents possess an undesired trade-off: strong CO2 binding necessitates a highly negative reduction potential, driving reduction into a region competitive with undesirable oxygen reduction. Meanwhile, more positive potentials compromise binding. Here, we circumvent this tradeoff using N-heterocyclic imines (NHI), which exhibit a tailorable CO2 binding strength (~50–100 kJ/mol CO2) in the neutral state and release CO2 with near theoretical Faradaic efficiency upon electro-oxidation, distinct from prevailing molecular capture mechanisms. While initial NHI structures exhibited redox irreversibility due to solvent-based hydrogen abstraction, an improved design, based on phenylene-linked bis(NHI), achieves redox reversibility by charge delocalization on the benzene ring. This design enables an unprecedented 2 CO2/e- swing, doubling the Faradaic efficiency of known sorbents. A symmetric EMCC system demonstrated stable cycling performance over 40 cycles and operated > 500 mV more positive than the oxygen reduction reaction, with projected theoretical minimum energy consumption of ~10 kJ/mol CO2.