Techno-Economic Analysis of a Three-Compartment CO₂ Electrolyzer for Formic Acid Production

The electrochemical reduction of CO₂ to liquid fuels or chemicals offers a sustainable route to store renewable electricity in chemical form. Among potential products, formic acid stands out for its high energy density, ease of storage, and potential as a hydrogen carrier. However, maintaining selectivity at high product concentrations remains a key challenge for economic viability. Here, we present a techno-economic analysis of formic acid and formate production in two-compartment and three-compartment electrolyzers, using either water oxidation reaction or the hydrogen oxidation reaction at the anode. In two-compartment cells, operating in acidic media to directly produce formic acid is economically favorable compared to alkaline media, as it avoids post-protonation and improves CO₂ conversion efficiency by preventing carbonate formation. Three-compartment configurations achieve the best performance when high product concentrations are reached without compromising selectivity. Concentrations above 15 M require Faradaic efficiencies exceeding 70% for economic feasibility. Employing low-cost renewable hydrogen for HOR in a three-compartment cell can further reduce production costs, reaching values below $0.42 kg^-1 HCOOH at 70% Faradaic efficiency and 15 M product concentration. This approach holds strong potential for deployment in hard-to-abate sectors such as cement, steel, and ammonia synthesis, thereby supporting industrial decarbonization.