Electrosynthesis of Co Mn layered-double-hydroxide as a precursor for Co-Mn-MOFs and subsequent electrochemical sulfurization for supercapacitor application

Today, researchers are focusing on improving the electrochemical efficiency of supercapacitors by designing and evolving synthesis routes for battery-type hierarchical materials. This study proposes a green method for creating high-efficiency positive electrode materials with a mesoporous heterostructure on Ni foam (NF) using a metal-organic framework (MOF)-derived approach. A binder-free electrosynthesis technique was utilized to grow CoMn-layered double hydroxide (CoMn-LDH) and exchange ions to obtain a porous metal precursor, namely binary Co-Mn-MOF. The MOF arrays were then electrochemically converted to CoMn-sulfide (CMS), which exhibits excellent conductivity and a mesoporous structure, enabling it to serve as a 3D continuous network for ion and electron conduction in energy storage. The synthesized sample was characterized using various techniques, including field-emission scanning electron microscopy (FESEM), elemental mapping, high-resolution transmission electron microscopy (HR-TEM), energy-dispersive X-ray analysis (EDX), Brunauer-Emmett-Teller (BET) surface area analysis, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Among the prepared electrode samples, CoMn−S with an Mn/Co feeding ratio of 1:2 demonstrated outstanding electrochemical properties. Based on this platform, CMS was applied and validated as a positive electrode in supercapacitors, exhibiting a high specific capacity of 1091C g−1 at 1 A g−1 in a three-electrode configuration and remarkable cycling life (85 % capacitance retention over 7000 cycles at 25 A g−1). Furthermore, an assembled asymmetric supercapacitor (ASC) device using CMS as the cathode and AC as the anode demonstrated satisfactory electrochemical performance. The CMS//AC device delivers an energy density of 84 Wh kg−1 at a high power density of 1191.4 W kg−1 and maintains stable electrochemical stabilities (92 % capacitance retention even after 7000 cycles). This synthesis approach opens up a new avenue for developing binder-free electrodes with hierarchical structures using metal sulfides, thereby enhancing the electrochemical performance of hybrid supercapacitors.