Electrochemical CO₂ Reduction to Hydrocarbons on a Heterogeneous Molecular Cu Catalyst in Aqueous Solution

Exploration of heterogeneous molecular catalysts combining the atomic-level tunability of molecular structures and the practical handling advantages of heterogeneous catalysts represents an attractive approach to developing high-performance catalysts for important and challenging chemical reactions such as electrochemical carbon dioxide reduction which holds the promise for converting emissions back to fuels utilizing renewable energy. Thus, far, efficient and selective electroreduction of CO₂ to deeply reduced products such as hydrocarbons remains a big challenge. Here, we report a molecular copper-porphyrin complex (copper(II)-5,10,15,20-tetrakis(2,6-dihydroxyphenyl)porphyrin) that can be used as a heterogeneous electrocatalyst with high activity and selectivity for reducing CO₂ to hydrocarbons in aqueous media. At -0.976 V vs the reversible hydrogen electrode, the catalyst is able to drive partial current densities of 13.2 and 8.4 mA cm^-2 for methane and ethylene production from CO₂ reduction, corresponding to turnover frequencies of 4.3 and 1.8 molecules·site^-1·s^-1 for methane and ethylene, respectively. This represents the highest catalytic activity to date for hydrocarbon production over a molecular CO₂ reduction electrocatalyst. The unprecedented catalytic performance is attributed to the built-in hydroxyl groups in the porphyrin structure and the reactivity of the copper(I) metal center.