Towards Higher Rate Electrochemical CO2 Conversion: From Liquid-Phase to Gas-Phase Systems

Abstract

Electrochemical CO2 conversion offers a promising route for value-added products such as formate, carbon monoxide, and hydrocarbons. As a result of the highly required overpotential for CO2 reduction, researchers have extensively studied the development of catalyst materials in a typical H-type cell, utilizing a dissolved CO2 reactant in the liquid phase. However, the low CO2 solubility in an aqueous solution has critically limited productivity, thereby hindering its practical application. In efforts to realize commercially available CO2 conversion, gas-phase reactor systems have recently attracted considerable attention. Although the achieved performance to date reflects a high feasibility, further development is still required in order for a well-established technology. Accordingly, this review aims to promote the further study of gas-phase systems for CO2 reduction, by generally examining some previous approaches from liquid-phase to gas-phase systems. Finally, we outline major challenges, with significant lessons for practical CO2 conversion systems.

CO2 Reduction to CO with 19% Efficiency in a Solar-Driven Gas Diffusion Electrode Flow Cell under Outdoor Solar Illumination

“…In contrast, gas diffusion electrode (GDE) assemblies do not suffer these same restrictions. [29][30][31][32][33][34][35] In a GDE using 1 atm CO 2 vapor, CO 2 is transported in the vapor phase and reacts at a thin (<100 nm) solid-liquid-gas phase interface. In this configuration liquid state concentration and diffusion do not limit the conversion rate, resulting in lower overpotentials and higher current densities for CO 2 reduction.…”

Fundamentals of Gas Diffusion Electrodes and Electrolysers for Carbon Dioxide Utilisation: Challenges and Opportunities

“…Instead, in gas-fed electrolysers, the CO 2 is introduced and brought in gas form as close as possible to the catalyst layer ( Figure 2b). Aqueous-fed electrolysers are vastly used in research laboratories, leading to many published scientific papers [9,24,[54][55][56][57]. This extensive use is a result of their ease of operation and adaptability to multiple types of electrode materials and configurations, making them ideal for the rapid and cost-effective study of CO 2 R catalysts.…”

Comparative Life Cycle Assessment of Electrochemical Upgrading of CO2 to Fuels and Feedstocks

“…reduction to multi-carbon products in alkaline environment, 19,[39][40][41] the inherent carbonate formation in such electrolyte often leads to significant loss of CO2 and consequently low CO2 single-pass conversion efficiency (up to ~43%%). 38,42,43 In this context, two-step electrochemical CO2 conversion approach is appealing; since the first step i.e., the electrolyzer for CO2-to-CO conversion is commercially available today at full-scale with high stability and selectivity towards CO (~100%).…”