Copper electrocatalysts can reduce CO2 to hydrocarbons at high overpotentials. However, a mechanistic understanding of CO2 reduction on nanostructured Cu catalysts has been lacking. Herein we show that the structurally precise ligand-protected Cu-hydride nanoclusters, such as Cu32H20L12 (L is a dithiophosphate ligand), offer unique selectivity for electrocatalytic CO2 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 CO2 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 CO2 reduction on the Cu32H20L12 cluster demonstrate that HCOOH is indeed the main product at low overpotential, while H2 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 CO2 reduction by copper-hydride nanoclusters and other metal nanoclusters that contain hydrides.
Bibliographical noteFunding Information:
This work was supported by the University of California, Riverside. This research used resources of the National Energy Research Scientific Computing Center, a DOE Office of Science User Facility supported by the Office of Science of the U.S. Department of Energy under Contract DE-AC02-05CH11231. D.L. acknowledges support from a Korea CCS R&D Center (KCRC) grant (NRF-2014M1A8A1074219) and NRF grants (NRF-2014R1A2A1A11051032 and 2009-0093823). C.W.L. acknowledges support from the Ministry of Science and Technology in Taiwan (MOST 103-2113-M-259-003)
© 2017 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Colloid and Surface Chemistry