In-situ electrochemical activation of a nickel metal-organic framework modified TiO2 photoanode for urea photoelectrocatalysis

Metal-organic frameworks (MOFs) possess a large specific surface area, porosity, and structural diversity, making them ideal candidates for catalysing the urea oxidation reaction (UOR). Even though MOF-based catalysts have been broadly investigated in urea electrocatalysis, few MOF catalysts are used for urea photoelectrocatalysis. The latter requires the MOF-based catalysts to efficiently separate and transport the photogenerated holes at the interface of photoanode-electrolyte junctions. In this study, a sulphur-containing organic ligand of 1,4-benzenedithiol (BDT) is innovatively employed to synthesize two-dimensional Ni-BDT MOFs from Ni(OH)2 nanosheets precursor. After the in-situ electrochemical activation of TiO2@Ni-BDT, the resultant MOF derivative modified TiO2 photoanode named as TiO2@Ni-BDT-A exhibits 3.83 times photocurrent in comparison with the pristine TiO2. A high photovoltage of 0.73 V and an impressive 82% photocurrent retention after a long-term stability test can also be observed. The improvements are attributed to the enhanced surface active sites and the active species of Ni(2−σ)+−SOx, which can efficiently promote charge separation, increase conductivity, improve donor concentration, and lower the charge transfer resistance. This work develops a sulphur-containing Ni-MOF as a co-catalyst for efficient urea photoelectrocatalysis, and an effective strategy of in-situ electrochemical activation to boost photoanode activity.