Al Incorporation Activates Epitaxial Ni₂P/Ni(OH)₂ Heterostructures for Improved Electrocatalytic Water Splitting

Herein, the development of Al-doped epitaxial Ni₂P/Ni(OH)₂ heterostructured nanosheets (NSs) supported by Ni foam, referred to as Al-Ni₂P/Ni(OH)₂ NSs, and their application as a bifunctional electrocatalyst for alkaline water splitting. The Al-Ni₂P/Ni(OH)₂ NSs exhibits excellent electrocatalytic performance for the hydrogen evolution reaction, achieving 10 mA cm^-2 at a low overpotential of 99.8 mV, together with a current retention of 87.1% after long-term stability test for 40 h, outperforming previously reported nonnoble metal catalysts. In addition, the catalytic activity of Al-Ni₂P/Ni(OH)₂ NSs for the oxygen evolution reaction surpasses that of the state-of-the-art RuO₂ catalyst and other nonnoble metal catalysts reported elsewhere in term of overpotential of 289.7 mV at 10 mA cm^-2 and current retention of 92.8% after 40 h of continuous operation. As expected, an electrolyzer assembled using two Al-Ni₂P/Ni(OH)₂ NS electrodes as cathode and anode demonstrates highly efficient overall water splitting, with a low cell voltage of 1.62 V at 10 mA cm^-2, along with excellent long-term durability and stability. This promising electrocatalytic activity of the Al-Ni₂P/Ni(OH)₂ NSs is attributed to the synergistic effects of the epitaxial heterostructure, cation doping, unique geometrical structure, and optimized chemical composition.