In this study, we synthesized three monofacet Au nanocrystals with well-defined shapes[4], including octahedra, cubes and truncated ditetragonal prisms (TDPs), which are enclosed by {111}, {100}, and {310} surfaces, respectively. The surface cleanness and high crystallinity of Au nanocrystals are confirmed by several structural characterization techniques, and by electrochemical characterizations including cyclic voltammetry (CV) and thallium underpotential deposition (Tl UPD). The Au octahedral and cubic nanocrystals demonstrate good resemblance of the ORR behaviors to those on their bulk single-crystal counterparts. Intriguingly, the TDP particles enclosed with twelve {310} facets catalyze the 4e ORR over the full potential range that has not been seen. Density functional theory (DFT) calculations were carried out for the ORR on the three Au surfaces without and with co-adsorbed water. The DFT-calculated free energy diagrams, in combination with experimental electrochemical results, elucidate how the surface proton transfers activate the facet- and potential-dependent 4e ORR on Au {100} and {310}. The new insight helps mechanism studies of facet-sensitive catalytic reactions, and provides guidance for designing nanocatalysts with optimal surface structures for various reactions.
Acknowledgment
The research was carried out at the Center for Functional Nanomaterials and the Chemistry Division of Brookhaven National Laboratory, supported by the U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. DE-SC0012704. We acknowledge the computational 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 No. DE-AC02-05CH11231.
References
[1] N. M. Marković, R. R. Adzić, V. B. Vešović, J. Electroanal. Chem. 1984, 165, 121-133.
[2] R. R. Adzić, N. M. Marković, V. B. Vešović, J. Electroanal. Chem. 1984, 165, 105-120.
[3] S. Strbac, R. R. Adzic, J. Electroanal. Chem. 1996, 403, 169-181.
[4] F. Lu, Y. Zhang, S. Liu, D. Lu, D. Su, M. Liu, Y. Zhang, P. Liu, J. X. Wang, R. R. Adzic, O. Gang, J. Am. Chem. Soc. 2017, 139, 7310-7317.