A review of performance optimization of MOF-derived metal oxide as electrode materials for supercapacitors

Metal-organic frameworks (MOFs), as new class of porous materials, are constructed by inorganic metal centers and bridging organic links. Recently, MOFs have been proved to be effective templates for preparing metal oxides with large surface areas and controlled shape by directly annealing in air. There are lots of reports about metal-organic framework-derived metal oxides as electrode materials for supercapacitors. Metal-organic framework-derived metal oxides can offer higher capacitances compared with that prepared by other synthetic methods, likely attribute to high surface areas and optimal pore sizes. However, at present, the specific capacitances of MOF-derived metal oxides received are far lower than theoretical values, and the cycle numbers could not meet practical demands. Accordingly, much effort has been made to improve the performance by further modifying MOFs. Thus, this paper focused on the advances in performance optimization of MOF-derived metal oxide as electrode materials for supercapacitors as follows: Dual metal MOF-derived binary metal oxides. Metal oxides with 2 metal cations possess better electrical conductivity and richer redox active sites than single metal oxides. Metal-organic framework-derived carbon/metal oxide composites (MO@C) or graphene/MOF-derived graphene/metal oxide composites. Doping carbon not only facilitate transportation of electrodes but also contribution to extra double-layer capacitance. Hybrid MOF-derived metal oxide composites (MO@MO). Metal oxide composites can produce some synergistic effects that the individuals cannot provide. Metal-organic framework-derived metal oxides with a hollow structure. The Hollow structure could shorten ion diffusion distance and adapt to volume expansion generated during the ion intercalated/extracted process.