Highly Electroactive Ni Pyrophosphate/Pt Catalyst toward Hydrogen Evolution Reaction

Robust electrocatalysts toward the resourceful and sustainable generation of hydrogen by splitting of water via electrocatalytic hydrogen evolution reaction (HER) are a prerequisite to realize high-efficiency energy research. Highly electroactive catalysts for hydrogen production with ultralow loading of platinum (Pt) have been under exhaustive exploration to make them cutting-edge and cost-effectively reasonable for water splitting. Herein, we report the synthesis of hierarchically structured nickel pyrophosphate (β-Ni₂P₂O₇) by a precipitation method and nickel phosphate (Ni₃(PO₄)₂) by two different synthetic routes, namely, simple cost-effective precipitation and solution combustion processes. Thereafter, Pt-decorated nickel pyrophosphate and nickel phosphate (β-Ni₂P₂O₇/Pt and Ni₃(PO₄)₂/Pt) were prepared by using potassium hexachloroplatinate and ascorbic acid. The fabricated novel nickel pyrophosphate and nickel phosphate/Pt materials were utilized as potential and affordable electrocatalysts for HER by water splitting. The detailed electrochemical studies revealed that the β-Ni₂P₂O₇/Pt (1 μg·cm^-2 Pt) electrocatalyst showed excellent electrocatalytic performances for HER in acidic solution with an overpotential of 28 mV at -10 mA·cm^-2, a Tafel slope of 32 mV·dec, and an exchange current density ( j₀) of -1.31 mA·cm^-2, which were close to the values obtained using the Vulcan/Pt (8.0 μg·cm^-2 Pt), commercial benchmarking electrocatalyst with eight times higher Pt amount. Furthermore, the β-Ni₂P₂O₇/Pt electrocatalyst maintains an excellent stability for over -0.1 V versus RHE for 12 days, keeping j₀ equal after the stability test (-1.28 mA cm^-2). Very well-distributed Pt NPs inside the "cages" on the β-Ni₂P₂O₇ structure with a crystalline pattern of 0.67 nm distance to the Ni₂P₂O₇/Pt electrocatalyst, helping the Volmer-Tafel mechanism with the Tafel reaction as a major rate-limiting step, help to liberate very fast the Pt sites after HER. The high electrocatalytic performance and remarkable durability showed the β-Ni₂P₂O₇/Pt material to be a promising cost-effective electrocatalyst for hydrogen production.