Stoichiometry-driven Te vacancy engineering in Pt_1+xTe₂ for enhanced hydrogen evolution

Defect engineering is a widely adopted strategy to enhance the catalytic performance of two-dimensional transition metal dichalcogenides (TMDs). Regulating the stoichiometry of layered TMDs is expected to effectively engineer defect structures and optimize catalytic performance. In this work, we report a stoichiometry-controlled and top-down strategy to fabricate highly active Pt_1+xTe₂ electrocatalysts for the hydrogen evolution reaction (HER). Bulk Pt_1+xTe₂ crystals with systematically varied Pt/Te ratios were synthesized via chemical vapor transport, enabling precise modulation of Te vacancy density. Structural characterizations reveal a composition-dependent structural evolution from PtTe₂ phase to Pt₃Te₄/Pt₂Te₂ mixed phases with increasing Pt content, while a moderate Pt excess (x ≈ 0.2) maximizes Te vacancy concentration without disrupting the PtTe₂ framework. Subsequent electrochemical exfoliation yields few-layer nanosheets with significantly enhanced surface area and exposed undercoordinated Pt active sites. Benefiting from vacancy-induced electronic structure modulation and optimized hydrogen adsorption energetics, the Pt_1.2Te₂ nanosheets exhibit outstanding HER performance in acidic media, with a low overpotential of 52.3 mV at 10 mA cm⁻², a small Tafel slope of 33.7 mV dec⁻¹, and excellent long-term stability. This study establishes a direct correlation between stoichiometry, defect structure, and catalytic activity, highlighting the effectiveness of combining composition regulation with top-down exfoliation for designing high-performance TMD electrocatalysts.