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.

Automated summary

This study demonstrates the optimization of bimetallic organic framework derived cobalt nickel oxides for achieving enhanced supercapacitive performance. Different molar ratios of CoNiO2 and Co2NiO4 were synthesized, and the Co:Ni molar ratio of 1:1 showed the highest specific capacitance and excellent cycling stability. The asymmetric supercapacitor device CNOa//GNP exhibited superior energy density and cycle stability.