Intrinsic Strain Tuning of Electrocatalyst for Oxygen Reduction Reaction

Abstract

Surface strain is a powerful strategy to optimize the reactivity of electrocatalysts. Traditionally, surface strain in catalyst overlayer is imposed by external stress through the overlayer-substrate interfaces, which may lead to multiple stability and activity problems. In this presentation, we will introduce a way to generate and tune surface strain by utilizing intrinsic driving forces, i.e. intrinsic surface stress. For Pt(111) surface as an example, the tensile surface stress ( ~4.8 N/m) exerts a pressure on the order of 105 atmospheres on the surface atoms, which provides a strong driving force for surface contraction and reduction of the surface energy. While this surface pressure has little impact on the surface structure of symmetric Pt(111) surface, it can be released by introducing step type surface defects to break the surfaces symmetry constraint, which is accompanied with the contraction of surface lattice. Using well-defined Pt stepped surfaces, we demonstrate that the magnitude of surface strain is inversely proportional to the terrace width. Thus, the atomic-level control of terrace width enables generation and fine tuning of surface strain to optimize catalytic reactivity. Using oxygen reduction as an example, we show that the terrace-width dependent strain not only responses for the improved catalytic activity of a series of Pt-n(111)-(100) step surfaces, but also can be used to design electrocatalysts with simultaneously enhanced specific activity and mass activity.