Electrochemically Regenerated Amine for CO₂ Capture Driven by a Proton-Coupled Electron Transfer Reaction

Abstract

Electrochemical CO2 capture driven by a proton-coupled electron transfer (PCET) reaction, exploiting the CO2 hydration/dehydration equilibrium through pH swing, has the potential for low-energy capture as it eliminates the sensible heat from the temperature-swing process. However, carbonate salts used in the pH swing method suffered from poor reaction kinetics and crystal accumulation, which could potentially clog electrodes and become electrically disconnected. While amines are widely applied in various methods as efficient capturing agents, their capture energy consumption is generally higher than 100 kJ/mol CO2. Here, we propose a scheme of electrochemical CO2 capture driven by a PCET reaction using amines instead of carbonates as CO2 capture agents. In this scheme, H+ generated by the PCET reaction will promote CO2 desorption from the amine–CO2 compound, and the CO2 absorption of amines can be achieved through the consumption of H+ by the PCET reaction. Furthermore, we establish a thermodynamic model of the energetic cost of the method by introducing a multibuffer system of amines, showing that the introduction of amines will moderate the pH swing during the four-stage cycle, resulting in a 45.2% reduction in theoretical CO2 capture energy consumption compared to carbonate. Besides, we validated the model and obtained an experimental energy cost of 21.0 kJe/mol with 0.15 bar CO2 (g) captured using a hydrogen cycle. We expect that this strategy of introducing a multibuffer system to reduce CO2 capture energy consumption could provide a reference for low-energy consumption electrochemical CO2 capture in the future.