Single-phase ultrathin holey nanoflower Ni₅P₄ as a bifunctional electrocatalyst for efficient water splitting

Designing efficient non-precious electrocatalysts to boost water splitting for green energy is a worthy and crucial objective, while it is still an enormous challenge. Herein, single-phase Ni₅P₄ ultrathin porous nanosheets grown on Ni foam constructed using the three-dimensional single-phase hierarchical nanoflower Ni₅P₄ (defined as 3D SHF-Ni₅P₄) were assembled via a simple hydrothermal and phosphating process in an enclosed space. Benefitting from the special structure and morphology of 3D hierarchical porous ultrathin nanosheets, as well as their increasing number of active sites, the 3D SHF-Ni₅P₄ exhibited outstanding performance with low overpotentials of 180 mV and 106 mV for achieving a current density of 10 mA cm^-2 in 1 M KOH toward both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER), and the Tafel slopes were 54 mV dec^-1 and 79 mV dec^-1, respectively. The overall water separation setup, using 3D SHF-Ni₅P₄ as both the cathode and anode in 1.0 M KOH, achieved a current density of 10 mA cm^-2 at a low voltage of 1.47 V, which surpasses that of the commercial Pt C/NF||RuO₂/NF (1.52 V). This work highlights an achievable strategy for the controllable fabrication of a 3D single-phase hierarchical nanoflower Ni₅P₄ electrocatalyst, constructed with ultrathin porous nanosheets containing plenty of active sites. It provided new insights into developing cost-effective single-phase electrocatalysts towards green energy by water splitting.