Well-Defined Phase-Controlled Cobalt Phosphide Nanoparticles Encapsulated in Nitrogen-Doped Graphitized Carbon Shell with Enhanced Electrocatalytic Activity for Hydrogen Evolution Reaction at All-pH

Rational design and development of highly active, low-cost, and stable nonprecious metal electrocatalysts for hydrogen evolution reaction (HER) is extremely critical for making the water splitting process more economical and energy-saving. Herein, phase-controlled cobalt phosphide nanoparticles encapsulated in a nitrogen-doped graphitized carbon shell (termed CoxP@NC) were prepared by hydrogen reduction of organic-inorganic cobalt phosphonate hybrid materials with different Co/P molar ratios. Compared with the synthesized pure-phase CoP@NC and Co-2 P@NC, the hybrid-phase CoP/Co2P@NC exhibits enhanced HER activity at all-pH values, affording low overpotentials of 126 mV (0.5 M H2SO4, pH = 0), 198 mV (1.0 M KOH, pH = 14), and 459 mV (1.0 M PBS, pH = 7) to achieve a current density of 10 mA cm(-2). The high activity is ascribed to the doping of the N atom, enough accessible electrocatalytic active boundary sites, and synergistic interaction among the components, especially the electronic effect of CoP and Co2P. Additionally, the unique core-shell structure of CoP/Co2P@NC efficiently prevents the agglomeration and corrosion of metallic cores during the HER and consequently endows it high stability and durability. This study not only offers us an efficient electrocatalyst for HER at all-pH but also opens a novel strategy to synthesize core-shell catalysts for various applications.