Coral-Like Ni2P-Ni5P4 Polymorphs as Noble Metal-Free Catalysts for Efficient Water Splitting

Transition metal phosphides are perceived to be excellent electrocatalysts and have gradually become the primary candidates for highly efficient energy conversion devices. Coral-like Ni2P-Ni5P4 polymorphs with observable heterointerfaces were synthesized via hydrothermal method followed by low-temperature phosphidation. The phase structures and the electronic interaction of the heterointerfaces have been identified by X-ray diffraction and X-ray photoelectron spectroscopy. The resulting Ni2P-Ni5P4 catalyst exhibited a reasonable overpotential of 107 mV and a superior low overpotential of 238 mV at 10 mA cm−2 for hydrogen evolution reaction and oxygen evolution reaction in 1 M KOH, respectively. In addition, excellent water-splitting performance of 10 mA cm−2 at a low overpotential of 348 mV was obtained by combining the Ni2P-Ni5P4/NF as both cathode and anode, which is lower than that of the Pt/C and RuO2 catalyst couple. Such impressive performance might be ascribed to effective heterointerfaces of Ni2P-Ni5P4 polymorphs.