Electroreduction of CO₂ to CO Paired with 1,2-Propanediol Oxidation to Lactic Acid. Toward an Economically Feasible System

In industrial electrochemical processes it is of paramount importance to achieve efficient, selective processes to produce valuable chemicals while minimizing the energy input. Although the electrochemical reduction of CO₂ has received a lot of attention in the past decades, an economically feasible process has not yet been developed. Typically, the electrochemical reduction of CO₂ is paired to water oxidation, forming oxygen, but an alternative strategy would be coupling the CO₂ reduction reaction to an oxidation in which a higher-value product is co-produced, significantly improving the economic feasibility for CO₂ reduction as a whole. Importantly, both reactions need to be chosen wisely to ensure their compatibility and to minimize the voltage requirements for the redox system. In this study, as an example of this approach, we demonstrate such a match: the electroreduction of CO₂ to CO, paired with the electrooxidation of 1,2-propanediol to lactic acid. Combining these reactions decreases energy consumption by ∼35%, increases product value of the system, and results in combined faradaic efficiencies of up to 160% when compared to the CO₂ reduction reaction in which oxygen is formed in the anode.