Unlocking the\nElectrocatalytic Behavior of Cu<sub>2</sub>MnS<sub>2</sub> Nanoflake-Anchored\nrGO for the Oxygen Evolution\nReaction in an Alkaline Medium

A catalyst of the oxygen evolution reaction (OER) that\nis viable,\naffordable, and active for effective water-splitting applications\nis critical. A variety of electrocatalysts have been discovered to\nreplace noble metal-based catalysts. Of these, transition metal-based\nsulfides are essential for incorporating carbonaceous materials to\nimprove electrical conductivity, resulting in better electrocatalytic\nperformance. Our study illustrates the synthesis of Cu<sub>2</sub>MnS<sub>2</sub> (CMS) nanoflakes and their different rGO composites\n(10 to 40 wt %) via a hydrothermal technique for an effective water\noxidation reaction. The X-ray diffraction pattern reveals that the\nprepared Cu<sub>2</sub>MnS<sub>2</sub> nanoflakes exhibit a cubic\ncrystal structure. The high-resolution scanning electron microscopy\nand the high resolution transmission electron microscopy images corroborate\nthe formation of the nanoflake-like morphology of Cu<sub>2</sub>MnS<sub>2</sub> with the strong interaction of rGO. The selected area electron\ndiffraction analysis pattern reveals a polycrystalline nature. The\nFourier transform infrared spectrum shows the existence of a metal\nsulfur vibrational band at 590 cm<sup>–1</sup>, and Raman analysis\n infers the presence of rGO. The X-ray photoelectron spectroscopy\nspectra reveal the oxidation states of the elements present in the\nsamples. Using Brunauer–Emmett–Teller analysis, the\nsurface area of CMS-20 is found to be 117.04 m<sup>2</sup>/g. The\nmeasured OER overpotentials using linear sweep volammetry and the\nvalues are 380, 370, 340, 376, and 400 mV at 10 mA/cm<sup>2</sup> for\nCMS, CMS-10, CMS-20, CMS-30, and CMS-40, respectively, and the corresponding\nTafel slope values are 179, 158, 149, 206, and 240 mV/decade, respectively.\nThe electrochemical active surface area is estimated using cyclic\nvoltammetry for all of the catalysts, where CMS-20 showed a larger\nsurface area. Also, the same catalyst exhibits good stability for\n∼24 h at a constant potential, which is confirmed via chronoamperometry.\nThus, combining transition metal-based sulfides with carbonaceous\nmaterials indicates improved catalytic behavior for the preparation\nof high-performance OER electrocatalysts. Overall, the prepared CMS-20\nperformed as an efficient OER electrocatalyst and can be utilized\nfor practical applications in energy conversion.