Fabrication of MOF-derived mixed metal oxides with carbon residues for pseudocapacitors with long cycle life

High electroactivity and good mechanical robustness of electrode materials are essential to deliver excellent electrochemical energy storage performance. Herein, metal–organic frameworks (MOF) derived mixed metal oxides (MMO, ZnO@NiO and Co3O4@NiO) are prepared by a two-step annealing process in air. Zinc-based MOF (ZIF-8) and cobalt-based MOF (ZIF-67) were employed, respectively, as hard templates for the chemical encapsulation of Ni(OH)2 nanostructures by hydrothermal synthesis. The as-prepared ZIF-8@Ni(OH)2 and ZIF-67@Ni(OH)2 were then converted to corresponding MMO through annealing in air. Meanwhile, MOF-derived carbon was preserved in the as-fabricated MMO structure, thus improving the electronic conductivity as well as the mechanical stability of the materials. In virtue of these features, high specific capacitance of 1017 and 744 F·g−1 can be delivered at a current density of 1 A·g−1 for the Co3O4@NiO and ZnO@NiO samples, respectively. In addition, both of the samples have shown excellent cycling performance, which exhibited excellent capacitance retentions of 90.1% and 93.0% after 10,000 cycles for the Co3O4@NiO and ZnO@NiO samples, respectively, demonstrating their very promising use in next-generation pseudocapacitors.