Lattice-Hydride Mechanism in Electrocatalytic CO Reduction by Structurally Precise Copper-Hydride Nanoclusters.

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.