Comparative supercapacitive analysis of 2-methylimidazole derived cobalt nickel oxides (CoNiO2 and Co2NiO4) and subsequent fabrication of asymmetric supercapacitor devices

An attempt to pursue optimization study of a bi-metal organic framework derived cobalt nickel oxides has been demonstrated here to achieve best supercapacitive performance. The synthesis process was started with formation of Co-MOF by coordination of Co2+ metal ion with organic ligand 2-MeIM, following coordination of Ni2+ to the Co-MOF to construct Co2+ and Ni2+ dual metal coordinated organic cluster. The final oxides CoNiO2 (abbreviated as CNOa) and Co2NiO4 (abbreviated as CNOb), were obtained by breakdown of the organic moiety in a high temperature annealing process. While, the starting Co-MOF material yielded only Cs of 768 F g−1 (with 67% Cs retention after 8000 cycles) but the optimized CNOa with composition of Co: Ni molar ratio 1:1 revealed higher Cs of 1624 F g−1 with 86.5% Cs retention after 8000 cycles. The electrode material CNOb with Co:Ni molar ratio: 2:1 demonstrated Cs of 1329 F g−1 with 72.8% Cs retention. The superior specific capacitance, electrochemical reversibility and elevated cycle stability in CNOa was achieved from several positive virtues inherited in electrode material, such as: hierarchical nanoleaves with rough surface, bigger pore volume, thinner surface thickness of active material and definitely higher surface area. Two sets of asymmetric supercapacitor devices (CNOa//GNP, CNOb//GNP) were fabricated for comparison of the energy and power output. Superior energy density of 48.12 Wh Kg−1 was perceived from CNOa//GNP with commendable cycle stability of 92.8% whereas, CNOb//GNP delivered energy density of 40.18 Wh Kg−1 with 85.2% cycle stability experimented after 8000 GCD cycles.