Electrochemical condition optimization and techno-economic analysis on the direct CO₂ electroreduction of flue gas

Direct CO₂ electroreduction of flue gas is a technology that simplifies CO₂ capture and purification process and directly utilizes CO₂ in flue gas. Low CO₂ reduction reaction selectivity caused by the low CO₂ partial pressure and side reactions competition is the challenge. In this study, a direct CO₂ electroreduction system for multicomponent flue gases was established. A two-dimensional steady model was developed by considering major electrode reactions of flue gas in Cu_xO-based catalysts. General influence criteria and optimum operation window for the potential, temperature, and pressure were proposed. In addition, a techno-economic analysis of the flue gas electrolysis system was conducted. The results demonstrated that the CO₂ electroreduction reaction performances are weak at atmospheric pressure owing to the side reaction competition and small reactant concentration. A method involving pressurization and catholyte inlet temperature declination is proposed to break the stalemate of tiny reactant concentrations and ensure the dominance of the CO₂ electroreduction reaction. The selectivity and current density of the CO₂ reduction reaction were 71% and − 148 mA/cm² at −1.17 V vs. reversible hydrogen electrode potential (RHE), respectively, under the conditions of an inlet electrolyte temperature of 273 K and an operating pressure of 20 atm. C₁ products with excellent yields are the dominant products. Furthermore, the techno-economic analysis showed that the flue gas electrolysis system has higher profitability and lower cost than the purified CO₂ electrolysis system. The present results can be used to optimize the electrolyzer operating parameters and construct CO₂ reduction systems.