The Potential-Dependent Structure of PtNi Alloy Electrocatalysts and Its Effect on Electrocatalytic Activity.

The distribution of elements within alloy nanoparticles is a critical parameter for their electrocatalytic performance. Here, we use the case of a PtNi alloy to show that this elemental distribution can dynamically respond to the applied potential, leading to strongly potential-dependent catalytic properties. Starting from the PtNi core and Pt shell structure that forms in acid electrolyte due to Ni leaching, our electrochemical X-ray photoelectron spectroscopy measurements show that the Ni atoms can be reversibly moved between the core of the particles and the near-surface region using the applied potential. Through potential jump measurements, we show that this Ni migration modulates the hydrogen evolution reaction activity of the particles by over 30%. These observations highlight the potential of incorporating in situ restructuring of alloys as the final step in electrocatalyst design.