Low-energy-consumption electrochemical CO2 capture driven by biomimetic phenazine derivatives redox medium

Abstract

To reduce the energy consumption of CO2-capture methods, proton carriers can be used to drive the CO2 capture in a pH-swing way via the proton coupled electron transfer (PCET) reactions, which are electrochemically regenerable by electrolysis, surpassing the energy-intensive thermal regeneration of traditional monoethanolamine (MEA) absorption method in terms of energy efficiency. However, the low solubility of PCET organics limits its CO2 capture capacity and thus the application. We develop a low energy consuming, high-capacity CO2-capture cell using a phenazine-based organic as the proton carrier as the PCET redox medium, which has high proton capacity and fast PCET kinetics. The quasi-reversible redox-PCET of the phenazine derivative effectively swings the pH of NaHCO3/Na2CO3 aqueous electrolyte at the cathode and the anode, which work as the CO2 absorption/desorption half-cell respectively. This electrochemical CO2-capture cell with an optimal derivative (7,8-dihydroxyphenazine-2-sulfonic acid, noted as DHPS) demonstrates a 95.8% average current efficiency at 10 mA cm−2 and a superior low-electrolysis energy consumption of 0.49 GJ per ton of CO2.