Electrolyte Effects on N-Heterocyclic Imines as the Redox Sorbent for Electrochemical CO2 Capture

Abstract

N-Heterocyclic imines (NHIs) represent a promising class of sorbents for electrochemically mediated carbon capture (EMCC) due to their ability to bind CO₂ in the neutral state and operate reversibly at redox potentials more positive than that of oxygen. In this study, the effect of electrolyte composition on the thermochemical and electrochemical behavior of NHI-based systems is examined. Using reaction calorimetry and Raman and NMR spectroscopy, we demonstrate that Lewis acid cations stabilize the NHI–CO₂ adduct through charged interactions, and the solvent and anion donor number tune this stabilization by modulating the effective cation Lewis acidity. As a result, electrolyte salts can substantially increase the magnitude of the NHI–CO₂ reaction enthalpy, leading to higher CO₂ loading on NHI at low CO₂ partial pressure (10^–3 atm) and faster capture kinetics. The impacts of the electrolyte selection on NHI redox behavior as well as oxygen reduction were also investigated. The findings indicate that electrolyte design must balance the strength of cation–NHI–CO₂ stabilization, NHI redox activity, and the redox potential separation from oxygen reduction. By providing a mechanistic framework for how individual electrolyte components govern important process parameters, this work offers insights for optimizing electrolyte environments to achieve high-efficiency and reversible EMCC.