A key challenge in the field of electrochemical
carbon dioxide
reduction is the design of catalytic materials featuring high product
selectivity, stability, and a composition of earth-abundant elements.
In this work, we introduce thin films of nanosized metal–organic
frameworks (MOFs) as atomically defined and nanoscopic materials that
function as catalysts for the efficient and selective reduction of
carbon dioxide to carbon monoxide in aqueous electrolytes. Detailed
examination of a cobalt–porphyrin MOF, Al<sub>2</sub>(OH)<sub>2</sub>TCPP-Co (TCPP-H<sub>2</sub> = 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrabenzoate)
revealed a selectivity for CO production in excess of 76% and stability
over 7 h with a per-site turnover number (TON) of 1400. In situ spectroelectrochemical
measurements provided insights into the cobalt oxidation state during
the course of reaction and showed that the majority of catalytic centers
in this MOF are redox-accessible where Co(II) is reduced to Co(I)
during catalysis