Construction of high-capacitance carbonate-rich bimetallic layered (hydr)oxides onto ZIF-67–derived Co/CoO-N-carbon hybrid cubes for high-performance symmetric supercapacitors

Herein, we fabricated carbonate-rich bimetallic layered hydr(oxides) (CoMnO_x), which are primarily used as active materials for supercapacitors, using a simple hydrothermal method. CoMnO_x was deposited onto cobalt oxide (CoO), which was produced by pyrolyzing ZIF-67 at 800 °C under N₂ atmosphere. The Co/CoO cubes synthesized using carbonized ZIF-67 (ZIFC) were covered with CoMnO_x shells with high reduction efficiency and abundant Co active sites and surface O species. The effects of the carbonate species present between the CoMnO_x layers and at the surface of the hybrid CoMnO_x@ZIFC materials were evaluated using PXRD and XPS. The peaks at the binding energies of 290 and 400 eV in the C 1s and N 1s XPS profiles of CoMnO_x@ZIFC, respectively, indicate the presence of carbonate species and coordination of CoO and Co with the N-rich carbon materials, respectively. The FE-SEM images of CoMnO_x@ZIFC revealed the partial decomposition of the cubic structure of ZIFC, which agreed with previously reported data. Moreover, the elemental composition of CoMnO_x@ZIFC was confirmed using EDS mapping and point analysis. The CoMnO_x@ZIFC electrodes exhibited a remarkable specific capacitance/capacitor of 963 F g⁻¹/588 C g⁻¹ at 1 A g⁻¹ and excellent cycling stability over 1000 cycles, which was superior to those of previously reported MOF-derived carbonate-based materials in alkaline electrolytes. The CoMnO_x@ZIFC||CoMnO_x@ZIFC symmetric supercapacitor exhibited an energy density of 60.75 W h kg⁻¹ with a power density of 5947 W kg⁻¹ and an exceptional cycling stability (>99.5 %) after 3000 cycles.