Eliminating redox-mediated electron transfer mechanisms on a supported molecular catalyst enables CO2 conversion to ethanol

Abstract

Molecular catalysts play a significant role in chemical transformations, utilizing changes in redox states to facilitate reactions. To date molecular electrocatalysts have efficiently produced single-carbon products from CO2 but have struggled to achieve a carbon–carbon coupling step. Conversely, copper catalysts can enable carbon–carbon coupling, but lead to broad C2+ product spectra. Here we subvert the traditional redox-mediated reaction mechanisms of organometallic compounds through a heterogeneous nickel-supported iron tetraphenylporphyrin electrocatalyst, facilitating electrochemical carbon–carbon coupling to produce ethanol. This represents a marked behavioural shift compared with carbon-supported metalloporphyrins. Extending the approach to a three-dimensional porous nickel support with adsorbed iron tetraphenylporphyrin, we attain ethanol Faradaic efficiencies of 68% ± 3.2% at −0.3 V versus a reversible hydrogen electrode (pH 7.7) with partial ethanol current densities of −21 mA cm−2. Separately we demonstrate maintained ethanol production over 60 h of operation. Further consideration of the wide parameter space of molecular catalyst and metal electrodes shows promise for additional chemistries and achievable metrics. The electrochemical reduction of CO2 on organometallic catalysts is commonly limited to two-electron products. Now, an iron tetraphenylporphyrin catalyst immobilized onto a nickel electrode is shown to achieve a Faradaic efficiency for ethanol of 68% due to the strong electronic coupling between the catalyst and the support.