Copper electrocatalysts can reduce CO to hydrocarbons at high overpotentials. However, a mechanistic understanding of CO reduction on nanostructured Cu catalysts has been lacking. Herein we show that the structurally precise ligand-protected Cu-hydride nanoclusters, such as CuHL (L is a dithiophosphate ligand), offer unique selectivity for electrocatalytic CO reduction at low overpotentials. Our density functional theory (DFT) calculations predict that the presence of the negatively charged hydrides in the copper cluster plays a critical role in determining the selectivity of the reduction product, yielding HCOOH over CO with a lower overpotential. The HCOOH formation proceeds via the lattice-hydride mechanism: first, surface hydrides reduce CO to HCOOH product, and then the hydride vacancies are readily regenerated by the electrochemical proton reduction. DFT calculations further predict that hydrogen evolution is less competitive than HCOOH formation at the low overpotential. Confirming the predictions, electrochemical tests of CO reduction on the CuHL cluster demonstrate that HCOOH is indeed the main product at low overpotential, while H production dominates at higher overpotential. The unique selectivity afforded by the lattice-hydride mechanism opens the door for further fundamental and applied studies of electrocatalytic CO reduction by copper-hydride nanoclusters and other metal nanoclusters that contain hydrides.

Copper hydride clusters of variable nuclearity are derived from hydrogen and HCOOH as emerging energy storage materials and models.

A structural study of ligand exchange on chalcogen‐passivated copper nanoclusters is far less developed. Herein, we report the synthesis of polyhydrido copper nanoclusters [Cu20H11{Se2P(O iBu)2}9] (2) passivated by Se‐donor ligands via ligand replacement reaction on [Cu20H11{S2P(O iPr)2}9] (1) with NH4[Se2P(O iBu)2]. In parallel to the synthesis of 2, cluster [Cu20H11{S2P(CH2CH2Ph)2}9] (4) was produced by the ligand exchange reaction on a new derivative of 1, that is [Cu20H11{S2P(O nPr)2}9] (3). Solid state structures of both clusters 2 and 4 were unequivocally established by single‐crystal X‐ray diffraction studies and cluster 4 epitomizes exceptional case to preserve both the shape and size of the nanocluster during the course of ligand exchange. Structurally precise cluster 2 is the second example where the copper hydride nanocluster is stabilized by Se‐donor ligands. The anatomy of 2 can be visualized as a twisted cuboctahedral Cu13 core, two triangular faces of which are capped by a Cu6 cupola and a single Cu atom along the C3 rotational axis.