title: MOF-Derived Hollow Cage NixCo3-xO4and Their Synergy with Graphene for Outstanding Supercapacitors.
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-1as 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-1at 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-1at 1 A g-1and 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-1at a high power density of 750 W kg-1.
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore, 637459, Singapore.
authors.forename: Anjali
authors.initials: A
authors.lastname: Jayakumar
authors.affiliation: Analytical Chemistry Division, Bhabha Atomic Research Centre, Mumbai, 400085, India.
authors.forename: Rajini P
authors.initials: RP
authors.lastname: Antony
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore, 637459, Singapore.|College of Materials Science and Engineering, Chongqing University, No. 174 Shazhengjie Road, Chongqing, 400044, P. R. China.
authors.forename: Ronghua
authors.initials: R
authors.lastname: Wang
authors.affiliation: School of Chemical and Biomedical Engineering, Nanyang Technological University, Singapore, 637459, Singapore.
authors.forename: Jong-Min
authors.initials: JM
authors.lastname: Lee
keywords: asymmetric supercapacitors; energy storage; graphene; nickel cobalt mixed oxide; optimization