Pseudocapacitance Facilitates the Electrocatalytic Reduction of Carbon Dioxide

Abstract Electroreduction of CO₂ to value‐added products is a promising strategy for CO₂ reuse, where copper has a unique ability to produce oxygenates and C₂₊ products. Unfortunately, the electronic factors making copper so unique are unknown, which limits the ability to design improved catalysts. By combining in situ surface‐sensitive X‐ray resonant photoelectron spectroscopy with density functional theory calculations, the complex electronic structure of copper is uncovered during the electrocatalytic reduction of CO₂. It is found that the pseudocapacitive charging of copper, produced by the incorporation of protons and electrons into the subsurface, facilitates the activation of CO₂, while simultaneously increasing the barrier for H‐H coupling. The net result is that cathodic pseudocapacitive charge suppresses the hydrogen evolution reaction and promotes the production of hydrocarbons and oxygenated products on copper. These results represent a new paradigm in the understanding of CO₂ reduction, highlighting the key role of pseudocapacitive charge in the reaction.