In Situ-Grown Graphdiyne Interfaces on Cu-Retained CoCuFe Phosphide-Like Octahedra for Overall Water Splitting

A Cu-retention-assisted precursor-conversion strategy is developed to construct a graphdiyne (GDY)-coupled CoCuFe phosphide-like heterostructure for alkaline water electrolysis. Octahedral Cu₂O directs the particle morphology and serves as a Cu source, whereas the CoFe Prussian blue analogue (PBA) shell supplies the Co and Fe species required to form the multimetal phosphide-like framework. In situ growth of GDY preserves the precursor-derived architecture and establishes interfacial contact between the π-conjugated GDY layer and the phosphide-like domain. The resulting GDY@P-CoCuFe requires overpotentials of 211 and 88.5 mV to reach 10 mA cm^-2 for the oxygen and hydrogen evolution reactions, respectively, in 1.0 M KOH. When employed as both the anode and cathode in a symmetric electrolyzer, GDY@P-CoCuFe delivers 10 mA cm^-2 at a cell voltage of 1.45 V and maintains stable operation for 100 h. Spectroscopic analyses and density functional theory calculations suggest that interfacial charge redistribution and the formation of Cu-adjacent P sites contribute to favorable hydrogen adsorption. Post-operation characterization further reveals partial oxyhydroxide-like surface reconstruction during OER, while the underlying phosphide-like framework and GDY structure remain largely preserved. These findings demonstrate that combining controlled Cu retention with direct GDY interfacial growth provides an effective route for developing efficient and durable bifunctional electrocatalysts.