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

Abstract

Summary 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.

High‐performance activated carbons for electrochemical double layer capacitors: Effects of morphology and porous structures

“…[4][5][6][7] Generally, SCs are divided into two categories; one, referred to as electric double-layer capacitors (EDLCs), is based on the accumulation of electrolyte ions near the surface of electrode materials in the form of electrical double layer (EDL), 8,9 and the other one, referred to as pseudocapacitor, involves "reversible" Faradic reaction 10 and is mainly based on either metal oxides [11][12][13] or conductive polymers. [14][15][16][17][18] Recently, there has been great interest in pseudo-capacitors due to their relatively higher Faradic capacitances than EDLCs. 19,20 However, the long-term cycling stability and rate performance of EDLCs is superior to pseudo-capacitors, 21,22 and EDLCs are still competitive candidates for practical applications.…”

Holey graphene/MnO 2 nanosheets with open ion channels for high‐performance solid‐state asymmetric supercapacitors

“…High‐performance supercapacitors are expected to be operated at high energy densities, with a high voltage and long cycle life . To evaluate the practical application of the HG/MnO 2 ‐2 composite, a SSAS is designed by employing the HG/MnO 2 ‐2 and the HG as the positive and negative electrode materials, respectively, and the PVA/KCl gel as the electrolyte (Figure A).…”

“…High-performance supercapacitors are expected to be operated at high energy densities, with a high voltage and long cycle life. [54][55][56] To evaluate the practical application of the HG/MnO 2 -2 composite, a SSAS is designed by employing the HG/MnO 2 -2 and the HG as the positive and negative electrode materials, respectively, and the PVA/KCl gel as the electrolyte ( Figure 8A). To match the positive and negative charges of the assembled SSAS, the electrochemical potential windows of the electrodes are first estimated by CV at 20 mV s −1 ( Figure 8B).…”

Nickel cobalt oxide nanowires‐modified hollow carbon tubular bundles for high‐performance sodium‐ion hybrid capacitors

“…Unfortunately, the power density is inadequate for applications and SIBs still suffer from poor cyclic stability . Having already been employed in various applications, electric double‐layer capacitors (EDLCs) have longer lifespans and higher power density than those of batteries, but their energy density is low due to inherent defects . Combining the advantages of SIBs and EDLCs, one effective strategy is to develop hybrid devices that use electrodes with different sodium storage mechanisms.…”