In Situ Synthesis Strategy for Hierarchically Porous Ni₂P Polyhedrons from MOFs Templates with Enhanced Electrochemical Properties for Hydrogen Evolution

Abstract

The development of highly active and stable noble metal-free electrocatalysts of hydrogen evolution reaction (HER) under both acidic and basic conditions for renewable-energy conversion techniques is of great significance. Herein, a practical in situ synthesis strategy for a three-dimensional Ni₂P polyhedron with a hierarchically porous structure was presented, which was efficiently obtained from a nickel centered metal-organic frameworks (MOF-74-Ni) by direct low-temperature phosphorization. The as-prepared Ni₂P polyhedron showed a high BET surface area (175.0 m²·g^-1), hierarchically porous property, and outstanding metal dispersion, which well inherited the morphology and porosity of its MOF precursor. Compared with Ni₂P particles obtained from a nonporous precursor, the as-prepared Ni₂P polyhedron used as electrocatalyst exhibited excellent electrocatalytic performance toward the HER, with a low overpotential of 158 mV to produce the cathodic current density of 10 mA cm^-2. A small Tafel slope of 73 mV per decade is obtained for Ni₂P polyhedron, which revealed a Volmer-Heyrovsky mechanism during the HER. In addition, benefiting from the structural stability, the porous Ni₂P polyhedron used as a electrocatalyst showed satisfactory long-term durability for the HER in acidic media.