Unlocking Superior Acidic Hydrogen Evolution Reaction with Ultralow Pt: Synergistic Electronic Modulation in Trimetallic PtNiCoO _<i>x</i> /Hollow Carbon Sphere Catalyst

The development of electrocatalysts with low Pt loading is crucial for advancing affordable hydrogen evolution reaction (HER) technology. We report a PtNiCoOx/hollow carbon sphere (HCS) trimetallic catalyst with a Pt loading ≤ 4 wt % outperforming a commercial 20 wt % Pt/C due to strong Pt–Ni/Co oxide synergy within an HCS support. PXRD and EXAFS confirmed Pt incorporation into Ni/Co oxides, resulting in lattice contraction, weak alloying, and structural distortion that promote electronic modulation. Pair distribution function fitting revealed nanoscale domains of mixed alloy and oxide phases, while transmission electron microscopy showed uniform nanoparticles with core–shell morphology. X-ray photoelectron spectroscopy indicated metallic Pt0 and oxidized Pt2+ species with a 2.8 eV positive shift in Pt binding energy, evidencing charge transfer from Ni/Co oxides to Pt. Electrochemical tests yielded an onset overpotential of 0.3 mV, η10 of 0.9 mV, and Tafel slope of 36 mV dec–1, matching Pt/C in exchange current density (0.614 mA cm–2). Stability tests showed a minor initial decline due to Ni/Co leaching followed by possible surface Pt enrichment and negligible performance loss. The data demonstrate that core–shell architecture, lattice strain, phase heterogeneity, and electronic coupling could be key to the observed high HER activity with minimal Pt loading.