MOF‐Derived Hollow Cage NixCo3−xO4 and Their Synergy with Graphene for Outstanding Supercapacitors |
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Authors: | Anjali Jayakumar Rajini P Antony Ronghua Wang Jong‐Min Lee |
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Affiliation: | 1. School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore, Singapore;2. Analytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai, India;3. College of Materials Science and Engineering, Chongqing University, Chongqing, P. R. China |
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Abstract: | Highly optimized nickel cobalt mixed oxide has been derived from zeolite imidazole frameworks. While the pure cobalt oxide gives only 178.7 F g?1 as the specific capacitance at a current density of 1 A g?1, the optimized Ni:Co 1:1 has given an extremely high and unprecedented specific capacitance of 1931 F g?1 at a current density of 1 A g?1, with a capacitance retention of 69.5% after 5000 cycles in a three electrode test. This optimized Ni:Co 1:1 mixed oxide is further used to make a composite of nickel cobalt mixed oxide/graphene 3D hydrogel for enhancing the electrochemical performance by virtue of a continuous and porous graphene conductive network. The electrode made from GNi:Co 1:1 successfully achieves an even higher specific capacitance of 2870.8 F g?1 at 1 A g?1 and also shows a significant improvement in the cyclic stability with 81% capacitance retention after 5000 cycles. An asymmetric supercapacitor is also assembled using a pure graphene 3D hydrogel as the negative electrode and the GNi:Co 1:1 as the positive electrode. With a potential window of 1.5 V and binder free electrodes, the capacitor gives a high specific energy density of 50.2 Wh kg?1 at a high power density of 750 W kg?1. |
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Keywords: | asymmetric supercapacitors energy storage graphene nickel cobalt mixed oxide optimization |
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