The Sb–Pt₄ “Inverted Pyramid” in D0₂₃-Type Pt₃Sb for Highly Efficient pH-Universal HER Catalysis

We synthesized high-crystalline Pt_<i>x</i>Sb_<i>y</i> nanocrystals (NCs) via a hot-injection method (D0₂₃-type tetragonal Pt₃Sb, hexagonal PtSb, and cubic PtSb₂). The Pt₃Sb NCs exhibited isotropic microstrains (ε_a = ε_b = 0.022, ε_c = 0.01) due to the presence of inverted-pyramid Sb-Pt₄ along the [001] axis, which enhanced the hydrogen evolution reaction (HER) performance. This special structure afforded Pt₃Sb NCs with low overpotentials of 71 mV in 0.5 M H₂SO₄ and 84 mV in 1.0 M KOH at 10 mA cm^-2. Differential charge density calculations showed the Sb-Pt₄ expanded electron states of Pt sites, promoted conjugate delocalization of π bonds, and facilitated H adsorption, which was confirmed by the XPS and XAS characterizations. The higher d-band occupation near the Fermi level (d-band center, ε_d = -2.34 eV) provided increased free electrons and boosted electrical conductivity. Comparative studies of hypothetical Pt₃P and Pt₃Bi crystallites highlighted crucial roles of Sb in the Sb-Pt₄ pyramid in Pt₃Sb which significantly improved HER performance.