Nitrogen treatment generates tunable nanohybridization of Ni5P4 nanosheets with nickel hydr(oxy)oxides for efficient hydrogen production in alkaline, seawater and acidic media

Hybrid engineering of electrocatalysts is still very challenging for electrochemical water splitting. Ni5P4 is a promising electrocatalyst for hydrogen evolution reaction (HER) but the formation of phosphide-hydrogen on Ni5P4 (P-Hads) bonds usually weakens the HER activity. Herein, we report a simple nitrogen treatment strategy to controllably hybridize Ni5P4 porous nanosheets with amorphous nickel hydr(oxy)oxide [Ni2+δOδ(OH)2−δ] layer and utilize as efficient electrocatalyst for hydrogen evolution reaction (HER) in neutral (real seawater), alkaline and acidic media. The in situ derived Ni5P4@Ni2+δOδ(OH)2−δ hybrid nanosheets can be obtained by annealing the nickel hydroxide-precursor nanosheets coupled with decomposition of NaH2PO2·H2O in nitrogen atmosphere. Benefiting from the thin amorphous Ni2+δOδ(OH)2−δ coated layer, the optimized Ni5P4@Ni2+δOδ(OH)2−δ with 3 nm amorphous layer achieve a current density of 10 mA cm−2 at low overpotential of 87, 144 and 66 mV in alkaline, seawater and acidic media, respectively. Theoretical and experimental analyses show that the hybridization of Ni5P4 and Ni2+δOδ(OH)2−δ could not only serve as protection to further enhance the electrocatalytic properties and high surface area of the hybrid electrocatalyst but also create good electronic interaction and synergistic properties for suppressing P-Hads bonds, which is beneficial for promoting water adsorption and optimizing the free energy of hydrogen adsorption for triggering the catalytic pathway at all pH range. This work offers new insights for facile designing of non-precious transition metal compound hybrids for HER with enhancing electrocatalytic performance and opens a promising pathway for hydrogen production at all-pH range.