Electroreduction of CO2 to formate on copper based electrocatalyst at high pressures with high energy conversion efficiency.

Electrocatalytic CO2 reduction (CO2RR) to valuable fuels is a promising approach to mitigate energy and environment problems, but controlling the reaction pathways and products remains challenging. Here, a novel Cu2O nanoparticle film is synthesized by square-wave (SW) electrochemical redox cycling of high purity Cu foils. The cathode afforded up to 98% Faradaic efficiency (FE) for CO2 electroreduction to nearly pure formate under ≧45 atm of CO2 in bicarbonate catholytes. When paired with a newly developed NiFe hydroxide-carbonate anode in KOH/borate anolyte, a two-electrode high-pressure electrolysis cell achieved a high energy conversion efficiency up to 55.8% stably for long-term formate production. While the high-pressure condition drastically increased the solubility of CO2 to enhance CO2RR and suppress hydrogen evolution, Cu2O (111) oriented film was found important to afford near ~100% CO2 reduction to formate. The results have implications to CO2 reduction into a single liquid product with high energy conversion efficiency.

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