Engineered porous Ni2P-nanoparticle/Ni2P-nanosheet arrays via the Kirkendall effect and Ostwald ripening towards efficient overall water splitting

Transitional metal phosphides with array-like structure grown on conductive support materials are promising bifunctional catalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). In this study, a method was developed to synthesize directly porous Ni2P nanosheet arrays and Ni2P nanoparticles onto nickel foam via a hydrothermal reaction followed by a phosphorization process. Mechanistic studies revealed that the allomorphs of Ni2P nanosheets and Ni2P nanoparticles in the array-like structure were formed via the Kirkendall effect and Ostwald ripening. A fully functional water electrolyzer containing Ni2P as electrodes for the OER and HER exhibited promising activity and stability. At 10 mA·cm−2, a Ni2P cell voltage of 1.63 V was obtained, which was only 0.05 V smaller than that found for Pt/C/NF||RuO2/NF cell. The enhanced electrocatalytic performance resulted from the favorable porosity of the Ni2P arrays and the synergistic effect between Ni2P nanosheets and Ni2P nanoparticles.