Phase-segregated PtNi5 rhombic dodecahedra enable excellent electrocatalytic hydrogen evolution in the full pH range

Pt-based alloy catalysts hold significant promise for the hydrogen evolution reaction (HER). Shape controlled synthesis of these nanocrystals, exposing specific facets and representing an effective strategy for enhancing both intrinsic activity and cost effectiveness, remains unexplored yet. Herein, this study reports the exploration of a novel synthetic strategy of rhombic dodecahedral PtNi₅ alloy nanocrystals. Due to the unique phase segregation of the Pt-rich component at the ridges and the Ni-rich component at the facets, the PtNi₅ rhombic dodecahedral catalyst exhibits excellent performance towards the HER, achieving low overpotentials of 9, 11 and 26 mV at a current density of 10 mA cm⁻² and Tafel slopes of 25, 33, and 125 mV dec⁻¹ in 0.5 M H₂SO₄, 1 M KOH and 1 M PBS, respectively, superior to those of its spherical counterpart. It maintains a stable HER performance for over 700 hours at 50 mA cm⁻² in an acidic medium for full water splitting in a two-electrode setup, with a voltage of 1.85 V. The theoretical calculations over the vertexes, edges and facets of the rhombic dodecahedron model indicate that Pt–Pt bridge sites and Pt–Pt–Ni hollow sites at the edges of the rhombic dodecahedra are the most active and rich sites for hydrogen desorption in the Tafel mechanism, while Ni sites on the vertexes behave as H₂O adsorption sites and those on the facets have the lowest energy barriers for water splitting. These findings underscore the importance of shape-controlled synthesis of polyhedral nanocrystals for rational design of low-Pt alloy catalysts towards hydrogen evolution.