Scalable Defect Engineering of Pt₃Te₄ Nanosheets Activates an Electro-Switchable and Termination-Dependent PtO₂ Skin...

Topological materials are promising electrocatalysts for the hydrogen evolution reaction (HER) because of their protected electronic states and exceptional carrier mobility. Among them, the topological metal Pt₃Te₄ (mitrofanovite) exhibits low Tafel slopes in the nanocrystals. Realizing this potential in scalable catalyst systems requires nanoscale texturing coupled with precise control of the surface chemistry under operating conditions. Herein, we demonstrate that hydrogen peroxide (H₂O₂)-assisted liquid-phase exfoliation (LPE) of bulk Pt₃Te₄ yields nanoporous nanosheets that retain their metallic character and are chemically preconditioned to develop a bias-controlled PtO₂ skin that governs the catalytic activity. Crucially, spectromicroscopy resolves termination-selective oxidation: PtO₂ forms exclusively on PtTe₂-like terminations, whereas Pt₂Te₂ terminations remain metallic. Operando ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) in an electrochemical cell revealed the bias-dependent emergence of surface oxide phases in H₂O₂-treated nanosheets. The joint effect of the higher accessible site density imparted by nanoporosity and the emergence of a bias-controlled PtO₂/PtTe₂-terminated Pt₃Te₄ surface junction rationalizes the improved catalytic activity: the overpotential at 10 mA cm^-2 decreases by ∼30% (from 113.1 to 78.7 mV), while the exchange current density more than triples (from 0.106 to 0.347 mA cm^-2), all with an unchanged Tafel slope (∼53 mV dec^-1) and sustained stability over 50 h in acid. By combining a single scalable top-down step with operando proof that the catalytically active oxide is switched on by bias rather than being a static passivation layer, this study establishes a precise interface-engineering principle for Pt₃Te₄ nanosheets and a practical path to efficient, scalable HER catalysts based on nanosheets of topological metals.