Approaches on Improving Electroreduction of Carbon Monoxide to Acetate in Flow Electrolyzer

Abstract

Acetic acid (CH3COOH) is an important industrial chemical that is widely used in the generation of various products including medicals, food, solvent, synthetic fibers and fabrics. Although most acetic acid production today relies on the carbonylation process of methanol1, electrochemical synthesis method is a promising direction owing to its uniqueness in ambient conditions, utilization of renewable energy, and compatibility with bioengineering2. Cupper has the capability to electrochemically reduce CO2 to various C2 products but with low selectivity. The critical steps for acetate molecule generation from CO2/CO are the CO-dimerization and the nucleophilic attack of hydroxide ion on a ketene intermediate3, in which acetate production could be enhanced by electroreducing CO in alkaline electrolyte as compared to CO2 electroreduction in pH neutral solution. Meanwhile, the use of flow electrolyzer further improved the gas transport process by employing gas diffusion electrode, boosting the current and yield rate of products to industrial level. However, electrochemical reduction of CO to acetate on Cu-based electrocatalysts still suffers from low faradaic efficiency (<50%).4 In this talk, we will present our recent work on CO electroreduction to acetate by commercial Cu catalyst in flow electrolyzer. Parameters in terms of electrolyte molarity, catalyst loading, catalyst deposition method, and ionomer were manipulated to maximize the acetate production. Acetate was favored in high pH electrolyte by facilitating the nucleophilic attack of hydroxide ion process and suppressing competing proton transfer process towards ethylene and ethanol. Catalyst loading on gas diffusion electrode had great influence on the products selectivity, where low catalyst loading leans to ethylene generation, intermediate catalyst loading is selective to produce acetate, and high catalyst loading improves alcohol yield. A record 68% faradaic efficiency of acetate from CO with partial current density of 102 mA/cm2 was reached. Reference A. Dimian and A. Kiss, Chem. Eng. Res. Des., 159 (2020).S. Guo, T. Asset, and P. Atanassov, ACS Catal., 5172–5188 (2021) https://pubs.acs.org/doi/abs/10.1021/acscatal.0c04862.M. Jouny et al., Nat. Chem., 11, 846–851 (2019) https://doi.org/10.1038/s41557-019-0312-z.W. Luc et al., Nat. Catal., 2, 423–430 (2019) https://doi.org/10.1038/s41929-019-0269-8. Figure 1