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Electrochemical conversion of CO2 to useful products at temperatures below 100 °C is nearing the commercial scale. Pilot units for CO2 conversion to CO are already being tested. Units to convert CO2 to formic acid are projected to reach pilot scale in the next year. Further, several investigators are starting to observe industrially relevant rates of the electrochemical conversion of CO2 to ethanol and ethylene, with the hydrogen needed coming from water. In each case, Faradaic efficiencies of 80% or more and current densities above 200 mA cm−2 can be reproducibly achieved. Here we describe the key advances in nanocatalysts that lead to the impressive performance, indicate where additional work is needed and provide benchmarks that others can use to compare their results. This Perspective describes the key advances in nanocatalysts that have led to the impressive electrochemical conversion of CO2 to useful products and provides benchmarks that others can use to compare their results.

Electrolysis is a potentially useful approach for converting carbon dioxide into chemicals and fuels. The most active electrocatalysts for efficiently mediating the carbon dioxide reduction reactio...

Gas diffusion electrodes (GDEs) mediate the transport of reagents, products, and electrons in electrochemical reactors designed to reduce CO2 into fuels or chemicals. While the ratio of ionomer to electrocatalyst in the precursor catalyst ink is typically assumed not to change after being deposited on the GDE, we show herein that this assumption is likely not valid. Moreover, we discovered that the faradaic efficiency for formate, which is considered to be inconsequential relative to CO when using Ag electrocatalysts, can be modulated by 20% by a mere 5 wt% change in GDE Nafion® content. We were able to resolve these small differences in GDE composition by developing an X-ray fluorescence (XRF) spectroscopic protocol that quantifies the sulfonate groups appended to the polytetrafluoroethylene (PTFE) backbone of Nafion®. Using this protocol, we were able to determine how to precisely control the relative amount of ionomer to electrocatalyst for each GDE. We also found that maintaining a uniform ionomer–catalyst composition across the entire GDE can likely be done more effectively with automated spray coating than with manual deposition methods. We recommend following these procedures in order to generate reproducible CO2RR performance parameters in flow cells.

Molecular catalysts that combine high product selectivity and high current density for CO2 electrochemical reduction to CO or other chemical feedstocks are urgently needed. While earth-abundant metal-based molecular electrocatalysts with high selectivity for CO2 to CO conversion are known, they are characterized by current densities that are significantly lower than those obtained with solid-state metal materials. Here, we report that a cobalt phthalocyanine bearing a trimethyl ammonium group appended to the phthalocyanine macrocycle is capable of reducing CO2 to CO in water with high activity over a broad pH range from 4 to 14. In a flow cell configuration operating in basic conditions, CO production occurs with excellent selectivity (ca. 95%), and good stability with a maximum partial current density of 165 mA cm−2 (at −0.92 V vs. RHE), matching the most active noble metal-based nanocatalysts. These results represent state-of-the-art performance for electrolytic carbon dioxide reduction by a molecular catalyst., Molecular electrocatalysts reducing CO2 to CO with high selectivity and high rate are urgently needed. A cobalt phthalocyanine complex is capable of reducing CO2 to CO in water with a maximum partial current density up to 165 mA cm−2, matching the most active noble metal-based nanocatalysts.