H2 In Situ Inducing Strategy on Pt Surface Segregation Over Low Pt Doped PtNi5 Nanoalloy with Superhigh Alkaline HER Activity

Abstract Surface segregation constitutes an efficient approach to enhance the alkaline hydrogen evolution reaction (HER) activity of bimetallic Pt x Ni y nanoalloys. Herein, a new strategy is proposed by utilizing the small gas molecule of H 2 as the structure directing agent (SDA) to in situ induce Pt surface segregations over a series of PtNi 5 ‐ n samples with extremely low Pt doping (Pt/Ni = 0.2). Impressively, the sample of PtNi 5 ‐0.3 synthesized under 0.3 MPa H 2 delivers an extremely low overpotential of 26.8 mV (−10 mA cm −2 ) and Tafel slope of 19.2 mV dec −1 , which is superior to most of the previously reported Pt x Ni y electrocatalysts. This is substantially related to the strong H 2 in situ inducing effect to generate Pt‐rich@Ni‐rich core‐shell nanostructure of PtNi 5 ‐0.3 with an ultrahigh Pt surface content of 46%. The specific mechanistic effects of H 2 during the PtNi 5 ‐ n synthesis process are well illustrated based on the combined experimental and theoretical studies. The density functional theory mechanism simulations further unravel that the evolved active site of PtNi 5 ‐ n can efficiently reduce the reaction Gibbs free energies; especially for the scenario of PtNi 5 ‐0.3, the downward‐shifted d band center of the Pt active site significantly reduces the PtH bond strength, eventually resulting in the lowest absolute value of Δ G H .