Integrated CO2 capture and electrochemical conversion: coupled effects of transport, kinetics and thermodynamics in the direct reduction of captured-CO2 adducts†

Abstract

Upgrading anthropogenic CO₂ from concentrated point sources or directly from the atmosphere is a valuable approach in closing the carbon cycle. Existing processes capture the CO₂, concentrate it into pure gas streams, transport it, and then convert it into fuels and chemicals in a separate process plant. This sequential approach results in higher energy and operating costs which can be reduced by integrating the capture and conversion steps to directly reduce the captured CO₂-bound adduct to value-added products. The direct reduction of the captured CO₂-bound adduct is called the captured-CO₂ reduction reaction (c-CO₂RR). Understanding of c-CO₂RR has been obscured by the higher intrinsic complexity of the system. The CO₂ capture media is a complex space of several buffer reactions that allow the co-existence of different carbon species in solution depending on CO₂ loading, temperature, pressure, and pH. In order to design improved capture agents and catalysts for integrated CO₂ capture and conversion, it is essential to identify the carbon source and the primary factors influencing product formation on a c-CO₂RR catalyst. This review delineates the strategies to determine the active carbon species for integrated CO₂ capture and conversion systems. Furthermore, it summarizes the fundamental applications of mass transport, thermodynamics, and kinetics across various c-CO₂RR scenarios.