Local reaction environment for selective electroreduction of carbon monoxide

Abstract

The electroreduction of CO₂ to multi-carbon products (C₂₊) is an attractive route for high-density renewable energy storage, but catalytic selectivity toward a desired C₂₊ product is low. Although the pH in the vicinity of the catalysts has previously been correlated with selectivity of C₂₊ products, solid evidence of the local pH effect on specific C₂₊ products is lacking. Here, we present a very simple strategy for experimentally probing the local pH value in GDE-based high-rate CO electroreduction via the CO₂ capture rate. From the local pH determination method as well as the consideration of other possibilities that may influence the C₂₊ formation, we explicitly demonstrate that the increased OH⁻ concentration near the cathodic GDE surface in CO reduction can significantly facilitate acetate formation via a homogeneous solution reaction which is the key step, influenced by local pH near the cathode surface, correspondingly inhibiting other C₂₊ products such as ethanol, n-propanol and C₂H₄. Notably, a total C₂₊ faradaic efficiency of >90% that encompasses up to nearly 50% acetate faradaic efficiency is achieved via elevating average local OH⁻ concentration. In addition, the exploration of the link between local CO availability and the specific C₂₊ selectivity demonstrates that high CO coverage is required for C₂₊ formation owing to a preferred CO coupling. Further analysis indicates that a certain intermediate should be directly shared for acetate and ethanol, but the relevant reaction paths of this intermediate may be separated from that of C₂H₄.