In this study, we design a triphasic Ni₂P − Fe₂P − CoP heterostructure appearing under the form of a hierarchical 3D core–shell hybrid (CoP@Ni₂P − Fe₂P) for bifunctionally catalyzing both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline medium. Density functional theory results indicate that the rich interfaces of Ni₂P − Fe₂P − CoP architecture exhibit the best electronic properties and enhanced multiple electroactive site number with optimum hydrogen adsorption energy, significantly surpassing the CoP, CoP−Ni₂P, or CoP−Fe₂P cases. Therefore, the electrolyzer cell of CoP@Ni₂P − Fe₂P_(+,−) requires a small operating voltage of 1.51 V to reach 10 mA cm⁻² during alkaline water splitting, outperforming the commercial catalyst couple of Pt/C₍₋₎//RuO₂₍₊₎ and numerous earlier reports. In addition, the solar-driven water splitting system demonstrates a high solar-to-hydrogen (STH) conversion of 15.33 %, along with excellent long-term stability. The results open a potential approach to design innovative high-performance electrocatalysts for practical green hydrogen production via electrochemical water splitting process.