Electrochemical CO₂ Fixation to α-Methylbenzyl Bromide in Divided Cells with Nonsacrificial Anodes and Aqueous Anolytes

Abstract

Electrocarboxylation of organic halides represents a CO2 utilization strategy and a green alternative for the synthesis of many industrially relevant carboxylic acids. However, current electrocarboxylation methods rely on the utilization of sacrificial metal anodes, which are not sustainable, require high voltages, and complicate the understanding of the reaction mechanism. Here, we demonstrate the feasibility of performing electrocarboxylation reactions in divided cells with aqueous anolytes and nonsacrificial anodes, thereby eliminating the reliance on sacrificial anodes and opening the door for coupling of this important reduction process with various electrooxidation reactions requiring aqueous electrolytes. Specifically, we report a detailed study of electrocarboxylation of (1-bromoethyl)benzene at a silver cathode coupled with an oxygen evolution reaction at a platinum anode in a divided cell with organic and aqueous compartments separated by ion-exchange membranes of different types. We examine how operating parameters, including membrane type, applied potential, substrate concentration, electrolyte, and temperature affect the overall process and the reaction product distribution. Based on the extensive experimental results, we propose a detailed mechanism for major electrochemical product formation accounting for both aprotic and protic environments. Systematic analysis and mechanistic insights presented in this study are expected to enable a rational catalyst, electrolyte, and system design tailored to electroorganic CO2 fixation with different organic substrates to obtain industrially relevant carboxylic acids at practical potentials and currents.