Abstract
We have performed a density functional theory investigation of the {111} facet of a 201 Pt atom nanoparticle (NP), in order to explain its particular reactivity compared to a corresponding (111) surface. Then, notable differences in physical properties and reactivity between {111} facets and (111) surfaces can be correlated with (i) strain effect due to the contraction of surface Pt-Pt distance and (ii) electrochemical effects due to spontaneous negative charging of the {111} facet leading to a very strong local electric field (20 × 106 V*cm-1). The latter effect only occurs in systems of nanometric size such as nanoparticles because of the combination of the nanoparticle high capacitance and of different local work functions in facets and edges. The nanoparticle {111} facet with an adsorbed CO molecule exhibits an electronic structure, adsorption energy, and C-O stretch frequency extremely close to that of a strained and charged (111) surface. This study suggests that metallic NPs behave like intrinsic electrochemical systems with a potential tuned by their size and shape explaining part of their specific reactivity. Reciprocally, large NP facet reactivity could be investigated by simple charged strained surfaces that would give inexpensive models. Finally, this intrinsic electrochemical effect could be used to better understand charge transfer effects on catalysis and electrocatalysis and help to design new kinds of tunable catalysts.