Ligand-substituted inorganic-organic hybrid materials for efficient urea-assisted electrocatalytic water splitting

Strategies for the structural tuning of inorganic-organic hybrid materials are crucial for their technological application. We present a ligand replacement strategy for NiClOH-PmxPz1-x inorganic-organic hybrid nanorods (Pm = pyrimidine, Pz = pyrazine) to improve their performance in urea-assisted water splitting. Through partial substitution of pyrimidine ligands with pyrazines, oxygen vacancies were introduced into initially synthesized NiClOH-Pm nanorods. The NiClOH-PmxPz1-x composite material exhibits excellent performance in electrocatalytic urea oxidation, with a higher electrochemical double layer capacitance (23.8 mF cm-2) and a rather small Tafel slope (41.9 mV dec-1) compared to most previous reports, reaching potentials of 1.37 and 1.53 V at 10 mA cm-2 and 100 mA cm-2, respectively. The optimized ligand ratio (Pm/Pz = 33/1) enhances π-π interactions, which improves electron transfer between ligands and Ni centers, and thereby the catalytic efficiency. DFT calculations show that the adsorption of urea molecules on Ni centers takes precedence over the adsorption of OH- during the electrocatalytic process. This work offers a design strategy to improve the electrochemical performance of hybrid inorganic-organic materials through substitutional ligand design.