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

Abstract

Herein, we fabricated carbonate-rich bimetallic layered hydr(oxides) (CoMnOx), which are primarily used as active materials for supercapacitors, using a simple hydrothermal method. CoMnOx 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 CoMnOx shells with high reduction efficiency and abundant Co active sites and surface O species. The effects of the carbonate species present between the CoMnOx layers and at the surface of the hybrid CoMnOx@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 CoMnOx@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 CoMnOx@ZIFC revealed the partial decomposition of the cubic structure of ZIFC, which agreed with previously reported data. Moreover, the elemental composition of CoMnOx@ZIFC was confirmed using EDS mapping and point analysis. The CoMnOx@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 CoMnOx@ZIFC||CoMnOx@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.