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@TiO 2 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 TiO 2 followed by controlled phosphorization induces partial framework reconstruction, generating Co P active sites and Ti 3+ associated defect states while preserving the Co N 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 TiO 2 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@TiO 2 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 Co P sites act as the primary HER active centers following a Volmer-Heyrovsky pathway, whereas in-situ surface reconstruction of Co P into high valence CoOOH species governs OER activity. Consequently, the optimized P-ZIF-67@TiO 2 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.