High-Concentration Electrosynthesis of Formic Acid/Formate from CO2: Reactor and Electrode Design Strategies

The electrochemical CO2 reduction reaction (CO2RR), driven by renewable energy, provides a potential carbon-neutral avenue to convert CO2 into valuable fuels and feedstocks. Conversion of CO2 into formic acid/formate is considered one of the economical and feasible methods, owing to their high energy densities, and ease of distribution and storage. The separation of formic acid/formate from the reaction mixtures accounts for the majority of the overall CO2RR process cost, while the increment of product concentration can lead to the reduction of separation cost, remarkably. In this paper, we give an overview of recent strategies for highly concentrated formic acid/formate products in CO2RR. CO2RR is a complex process with several different products, as it has different intermediates and reaction pathways. Therefore, this review focuses on recent study strategies that can enhance targeted formic acid/formate yield, such as the all-solid-state reactor design to deliver a high concentration of products during the reduction of CO2 in the electrolyzer. Firstly, some novel electrolyzers are introduced as an engineering strategy to improve the concentration of the formic acid/formate and reduce the cost of downstream separations. Also, the design of planar and gas diffusion electrodes (GDEs) with the potential to deliver high-concentration formic acid/formate in CO2RR is summarized. Finally, the existing technological challenges are highlighted, and further research recommendations to achieve high-concentration products in CO2RR. This review can provide some inspiration for future research to further improve the product concentration and economic benefits of CO2RR.