On the origin of the elusive first intermediate of CO 2 electroreduction

Significance The understanding of a catalytic reaction starts with understanding its first elementary step. Surprisingly, despite the large number of studies, it is unclear whether one common or two different first intermediates control the selectivity of CO 2 electroreduction to formate and CO. We settle this controversy for Cu, which is best known for its unique capacity to synthesize C 1+ products but is just emerging as a superior earth-abundant catalyst for CO and formate. We provide solid experimental and theoretical support of the one common first-intermediate (Hori’s) model, the first intermediate being carboxylate. This outcome is an essential milestone toward accurate specification of the reaction descriptors in the growing effort to accelerate the discovery of a viable CO 2 electroreduction catalyst.