Ligand functionalization of mononuclear Pt-polyoxometalate for enhanced hydrogen evolution reaction activity

Hydrogen evolution reaction (HER) in electrocatalytic water splitting for producing green hydrogen has recently emerged as a promising approach to address the current energy and environmental challenges. In this study, we prepared and characterized the mononuclear Pt-polyoxometalate clusters [Pt₁Mo₆(OH)₆O₁₈](NH₄)₂ (PtMo₆) and [Pt₁Mo₆(OH)₃O₁₈)O₃C₅H₉]TBA₂ (PtMo₆-L, TBA: tetrabutylammonium) as HER electrocatalysts with enhanced activity. The HER performance of PtMo₆-L coated onto glassy carbon is superior to that of naked PtMo₆ and comparable to that of commercial 20 wt.% Pt/C, with an overpotential of 37 mV@10 mA·cm⁻² and a Tafel slope of 42 mV·dec⁻¹. The HER follows the Heyrovsky–Volmer mechanism over PtMo₆-L, similar to Pt/C, but the Tafel–Volmer mechanism over PtMo₆. Experimental and density functional theory calculation results indicate that the Pt–O–H group in the polyoxometalate clusters is the active site for the HER. Moreover, mechanistic studies reveal that the negatively charged C₅H₉-bonded O1 in PtMo₆-L is prone to proton adsorption and activation, thereby enhancing electrocatalytic HER activity. Overall, this study provides new insights into the polyoxometalate structure–electrocatalytic property relationship at the precise atomic and molecular levels, advancing HER research.