Highly efficient electrocatalytic water oxidation based on non-precious metal oxides/sulfides derived from a FeCoNi-metal organic framework

One of the main challenges for oxygen evolution reaction (OER) is to develop electrocatalysts with high performance, suitable stability, and low cost. First-row transition metal compounds have received attention due to their high electrocatalytic activity and diverse electronic structure. Meanwhile, metal-organic frameworks (MOFs) have emerged as promising alternative for OER due to their porous structure and unsaturated metal sites. In this study, FeCoNi-MOF based on MIL-88B was synthesized by a hydrothermal method. Then, the performance of the catalyst was investigated and improved by calcination and sulfidation at three temperatures of 250 ℃, 350 ℃, and 450 ℃. The phase development and crystal structure parameters of the synthesized samples were confirmed through X-ray diffraction. Additionally, the intensity of the peaks increased with the rise in calcination temperature. Field emission scanning electron microscopy revealed well-defined and uniformly distributed nanorods and nanospheres particles of calcinated and sulfides samples. The weight percentage (wt%) of the elements in the samples were verified to align with their stoichiometric ratios. The synthesized catalysts were loaded onto a nickel foam by a one-step method, and their electrocatalytic properties were examined in the OER process in 1.0 M KOH alkaline solution. The (FeCoNi)-O250 ℃ electrocatalyst, maintaining its nanorod morphology, exhibited an overpotential of 313 mV at a current density of 10 mA.cm-² and a small, stable Tafel slope of 31.5 mV.dec−1 and good charge transfer of 0.73 mF. Cm−2. However, the (FeCoNi)-S250 ℃ electrocatalyst showed better performance in the OER process with an overpotential of 298 mV at a current density of 10 mA.cm-² and a small and stable Tafel slope of 29 mV.dec−1 and good charge transfer of 0.82 mF. Cm−2. In other words, a higher Cdl increased reaction rates or lower overpotentials required for the reaction to occur. Furthermore, the activity of this catalyst remained constant at a fixed current density of 10 mA.cm-² for 18 hours. Based on the electron microscopy observations, and electrochemical evaluations, this superior performance can be attributed to the morphological change from nanorods to porous nanospheres due to sulfidation, resulting in increased electrochemically active sites and decreased charge transfer resistance.