Facile preparation of large-area self-supported porous nickel phosphide nanosheets for efficient electrocatalytic hydrogen evolution

Metal phosphide structures have been widely explored for electrocatalytic hydrogen evolution reaction (HER) owing to their high activity and durability, and the phosphidation reaction is very important for the preparation of metal phosphides. In this paper, we reported a facile, effective, and practical phosphidation strategy to prepare nickel phosphide structures by placing a Ni foam above the red phosphorus powder with a distance of 1 cm in a covered crucible. As-prepared self-supported hierarchical Ni₅P₄/NiP₂ biphase porous nanosheets exhibited an excellent HER activity. The overpotential for a current density of 10 mA/cm² and the Tafel slope are as low as 92 mV and 52.8 mV/dec, respectively, both of which are much better than those delivered by the Ni₅P₄ nanosheets prepared by the conventional carry-gas upstream-downstream method. The complete phosphidation reaction, high electrochemically active surface area, and the Ni₅P₄/NiP₂ biphasic synergistic effect account for the outstanding HER performance. Moreover, the porous Ni₅P₄/NiP₂ nanosheets exhibited excellent stability under both accelerated degradation test and long-term durability test. Besides, this method can be employed to prepare large-area self-supported hierarchical porous Ni₅P₄/NiP₂ nanosheets with nearly same HER activities and long-term stability, suggesting a high potential for practical application.