In-situ synthesis of zeolitic imidazolate framework-67 (ZIF-67) derived phosphorous-doped cobalt composites as bifunctional catalyst for photo-assisted water electrolysis

A phosphorus modified ZIF-67@TiO2 photo assisted electrocatalytic heterostructure is developed to elucidate the structure performance relationship and the underlying reaction mechanism in alkaline water electrolysis. The in-situ growth of ZIF-67 on TiO2 followed by controlled phosphorization induces partial framework reconstruction, generating CoP active sites and Ti3+ associated defect states while preserving the CoN coordination network of the MOF. This unique structural evolution enables efficient charge separation, accelerated interfacial electron transfer, and improved utilization of photogenerated carriers.Electrochemical and optical characterizations reveal that TiO2 primarily functions as a photogenerated charge supplier, while phosphorized ZIF-67 serves as the dominant electrocatalytic component. Suppressed photoluminescence intensity and enhanced transient photocurrent responses confirm efficient inhibition of charge recombination and rapid photoinduced charge extraction across the heterointerface. As a result, the P-ZIF-67@TiO2 electrode exhibits markedly reduced overpotentials and charge-transfer resistance for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under illumination.Mechanistic analysis indicates that CoP sites act as the primary HER active centers following a Volmer-Heyrovsky pathway, whereas in-situ surface reconstruction of CoP into high valence CoOOH species governs OER activity. Consequently, the optimized P-ZIF-67@TiO2 catalyst delivers a low cell voltage of 1.75 V at 10 mA cm−2 under illumination and maintains stable operation at 100 mA cm−2 for over 5717 h. This work demonstrates that rational phosphorization induced structural modulation, providing mechanistic insights for designing noble-metal-free photo-assisted electrocatalysts for efficient alkaline water splitting.