Local reaction environment for selective electroreduction of carbon monoxide†
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.