Hierarchical Edge-Rich Nickel Phosphide Nanosheet Arrays as Efficient Electrocatalysts toward Hydrogen Evolution in Both Alkaline and Acidic Conditions

Searching highly active, high stability, low-cost electrocatalysts toward the hydrogen evolution reaction (HER) is imperative for electrochemical hydrogen production. We propose an effective synthetic method to obtain self-supported, hierarchical, and edge-rich nickel phosphide nanosheet arrays on nickel foam (Ni 2 P NSs-NF), which are successfully employed as a high-efficiency, three-dimensional (3D) binder-free electrode for the HER. Benefiting from the 3D open nanostructure with abundant edges in the Ni 2 P NSs, the Ni 2 P NSs-NF electrode exhibits superior activity for the HER both in alkaline and acidic conditions. It requires low overpotentials of 89 mV in the alkaline solution (1 M KOH) and 67 mV in the acidic solution (0.5 M H 2 SO 4 ) to drive 10 mA cm –2 with low Tafel slopes of 82 and 57 mV dec –1, respectively. Besides, the hierarchical Ni 2 P NSs-NF electrode shows no apparent performance decay toward the HER even after 10,000 cycles. Theoretical calculation results prove that the free energy of hydrogen adsorption on the (211) crystal facet of Ni 2 P is closest to zero (−0.03 eV), which is supposed to be the most active site toward the HER. The freestanding edge-rich Ni 2 P NSs-NF electrode is prospective for large-scale preparation of hydrogen.