Lawrence Berkeley National Laboratory

This review of design and operating conditions of electrochemical CO ₂ reduction covers electrolytes, electrodes, reactors, temperature, pressure, and pH effects.

Electrochemical CO ₂ reduction (CO ₂ R) is one of several promising strategies to mitigate CO ₂ emissions. Electrochemical processes operate at mild conditions, can be tuned to selective products, allow modular design, and provide opportunities to integrate renewable electricity with CO ₂ reduction in carbon-intensive manufacturing industries such as iron and steel making. In recent years, significant advances have been achieved in the development of highly efficient and selective electrocatalysts for CO ₂ R. However, to realize fully the potential benefits of new electrocatalysts in low cost, large scale CO ₂ R electrolyzers requires advances in design and engineering of the CO ₂ R process. In this review, we examine the state-of-the-art in electrochemical CO ₂ R technologies, and highlight how the efficiency of CO ₂ R processes can be improved through (i) electrolyzer configuration, (ii) electrode structure, (iii) electrolyte selection, (iv) pH control, and (v) the electrolyzer's operating pressure and temperature. Although a comprehensive review of catalytic materials is beyond this review's scope, we illustrate how other engineering and design decisions may also influence CO ₂ R reaction pathways because of effects on mass transfer rates, the electrode surface chemistry, interactions with intermediate reaction species, and rates of charge transfer.