Separation and conversion of CO2 reduction products into high-concentration formic acid using bipolar membrane electrodialysis

• Published in: Journal of membrane science 2024-08, Vol.708, p.123016, Article 123016
• Main Authors: Wang, Zihao, Yan, Junying, Wang, Huangying, Fu, Weicheng, He, Duyi, Wang, Baoying, Wang, Yaoming, Xu, Tongwen
• Format: Article
• Language: English
• Subjects: Carbon neutrality; Formic acid; Ion exchange membrane; Ion transport; Water splitting
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/j.memsci.2024.123016

Electrochemical CO2 reduction to value-added chemicals such as formate represents a crucial pathway in advancing carbon-neutral fuel production. However, the separation of formate from KHCO3 electrolyte solutions and its conversion to formic acid remain cost intensive steps in this process. This study demonstrated the use of bipolar membrane electrodialysis (BMED) to efficiently convert and concentrate formic acid directly from a cathodic solution for CO2 electroreduction. The migration of formate ions during BMED was optimized under different cell configurations and current densities. Mathematical modelling was developed to predict the concentration evolution curves of formic acid production. The results showed that formic acid diffusion through an anion-exchange membrane was more pronounced than that a bipolar membrane; the former diffusion was a key factor that limited the formic acid concentration and reduced the current efficiency. A formic acid concentration of 3.49 mol/L was obtained at an optimum current density of 40 mA/cm2 and a salt-to-acid compartment volume ratio of 25:1. Thus, BMED has emerged as a viable and effective technique for isolating high-purity formic acid from a cathodic solution for CO2 electroreduction. [Display omitted] •The BMED is used for separating and converting CO2 electro-reduction products.•The highest formic acid concentration obtained was 3.49 mol/L.•Modelling was developed to predict the acid concentration evolution.•The diffusion of formic acid through AEMs exceeds the diffusion through BPMs.