In situ-grown Co₃S₄ sheet-functionalized metal-organic framework via surface engineering as a HER catalyst in alkaline media

The development of an appropriate catalyst for the hydrogen evolution reaction (HER) in alkaline media remains challenging. Pt catalysts, which are the most conventional HER catalysts, are prone to corrosion in alkaline media. To overcome this limitation, we developed another transition metal catalyst for the HER in alkaline media. In this study, a Co MOF was grown on a nickel foam substrate in the presence of surfactants via a simple hydrothermal reaction, and the material was sulfurized to Co MOF/Co₃S₄ sheet in Na₂S solution through a chemical bath reaction. The morphology, crystallinity, and composition of Co MOF/Co₃S₄ sheet were studied by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The HER properties in alkaline media were measured by linear sweep voltammetry, electrochemical impedance spectroscopy, and Tafel plot analysis. Cyclic voltammetry was used to determine the electrochemically active surface area (ECSA) using a three-electrode system. The best catalytic performance was observed for P-Co MOF/Co₃S₄ sheet; it exhibited the lowest overpotential at −10 mA cm⁻² (117.9 mV), the lowest Tafel slope (96 mV dec⁻¹), and a high ECSA (57.9 mF cm⁻²). The increased binding energy for cobalt and sulfur and the increased attraction of hydride or protons to evolve hydrogen was attributed to the high catalytic performance in alkaline media. Most importantly, the catalytic performance for the HER did not degrade remarkably even after 24 h of operation.