H 2 In Situ Inducing Strategy on Pt Surface Segregation Over Low Pt Doped PtNi 5 Nanoalloy with Superhigh Alkaline HER Activity

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 PtH bond strength, eventually resulting in the lowest absolute value of Δ G H .