Optimization and performance evaluation of cobalt-based metal-organic frameworks (MOFs) as electrocatalysts for electrochemical water splitting

Cobalt benzene dicarboxylic acid (Co-BDC) metal-organic frameworks (MOFs), exhibiting superior hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities, are synthesized under solvothermal conditions both in the absence (CoB) and presence (CoB-W) of a water modulator. The electrocatalytic performances of these materials are systematically compared to elucidate the effect of the modulator. The incorporation of water as a green modulator significantly influences the crystal morphology and defect formation. X-ray diffraction (XRD) patterns of CoB and CoB-W match well with the simulated profiles, confirming the phase purity, while Fourier-transform infrared (FTIR) spectroscopy reveals the modulation-induced variation in the electronic structure of CoB-W. UV–Vis spectroscopy indicates narrow band gaps of 2.39 eV and 2.48 eV for CoB and CoB-W, respectively. Scanning electron microscopy (SEM) further confirms distinct morphological changes upon modulation. Electrochemical studies demonstrate that CoB-W exhibits an overpotential of 452 mV for OER and 211 mV for HER at a current density of 10 mA/cm2 in 1 M KOH, with corresponding Tafel slopes of 90 and 80 mV/dec. Moreover, CoB-W shows excellent HER performance characterized by low overpotential, high current density, and remarkable stability over 15 h of continuous operation. This study establishes a clear structure-property-performance correlation, highlighting the role of water as an effective and eco-friendly modulator in tailoring Co-BDC MOFs for high-efficiency bifunctional electrocatalysis toward sustainable energy conversion.