Approaches to Enhancing Electrical Conductivity of Pristine Metal–Organic Frameworks for Supercapacitor Applications

Abstract

Metal–organic frameworks (MOFs), known as porous coordination polymers, have attracted intense interest as electrode materials for supercapacitors (SCs) owing to their advantageous features including high surface area, tunable porous structure, structural diversity, etc. However, the insulating nature of most MOFs has impeded their further electrochemical applications. A common solution for this issue is to transform pristine MOFs into more stable and conductive metal compounds/porous carbon materials through pyrolysis, which however losses the inherent merits of MOFs. To find a consummate solution, recently a surge of research devoted to improving the electrical conductivity of pristine MOFs for SCs has been carried out. In this review, the most related research work on pristine MOF‐based materials is reviewed and three effective strategies (chemical structure design of conductive MOFs (c‐MOFs), composite design, and binder‐free structure design) which can significantly increase their conductivity and consequently the electrochemical performance in SCs are proposed. The conductivity enhancement mechanism in each approach is well analyzed. The representative research works on using pristine MOFs for SCs are also critically discussed. It is hoped that the new insights can provide guidance for developing high‐performance electrode materials based on pristine MOFs with high conductivity for SCs in the future.

Largely Pseudocapacitive Two-Dimensional Conjugated Metal–Organic Framework Anodes with Lowest Unoccupied Molecular Orbital Localized in Nickel-bis(dithiolene) Linkages

“…Recently, two-dimensional conjugated metal–organic frameworks (2D c -MOFs) have been recognized as an ideal material platform for designing functional porous materials with atomic precision. − Their in-plane ring-fused conjugated structures with high electrical conductivities and defined quasi-one-dimensional porous nanochannels with large specific surface areas provide efficient electron/ion transport pathways, making 2D c -MOFs particularly suitable as electrode materials for SCs. − Moreover, both aromatic ligands ( e.g. , phthalocyanine and dibenzochrysene) , and square-planar metal coordination linkages ( e.g.…”

Revealing energy storage mechanism of CsPbBr3 perovskite for ultra-stable symmetric supercapacitors

“…The SC using 0.1 M TBAPF 6 is named SS-0.1, while the one using 1 M TBAPF 6 in DCM is named SS-1, respectively. The CV curves of SS-1 [Figure 4A] at different scan rates over a potential window of 0-1.0 V are even closer to a rectangle than the CV curves in a three-electrode system, further confirming the EDLC behaviour of the CsPbBr 3 nanocrystals [10,13] . The shape of the CV is well maintained at a high scan rate of 50 mV s -1 , indicating good rate performance.…”

“…Liu et al used carbon nanotubes wrapped around CsPbBr 3 as the anode of a Li-ion battery, which exhibited a reversible capacity of 644.6 mAh g -1 at a current density of 100 mA g -1 due to the embedded pseudocapacitive behaviour [8] . Further studies have shown that the reduction of Pb 2+ , generating different forms of LiPb alloys, may be responsible for the observed energy storage behaviour, although there are still many open questions regarding the operational mechanism of perovskite electrodes [8][9][10] . Supercapacitors, also called electrochemical capacitors, are a type of energy storage device that is complementary to batteries with distinctive advantages such as much faster charge and discharge rates (higher power density) [11] , outstanding cycling capability and the ability to operate over a broader temperature range [12][13][14] , However, compared to battery research, the study of perovskite in supercapacitors is very rare.…”

“…Only a few reports on perovskite supercapacitors have been reported so far. For example, Zhou et al in situ grown MAPbI 3 (methylammonium lead iodide) on a FTO (fluorine-doped tin oxide) glass substrate by a solution method and demonstrated the potential of MAPbI 3 as an electrode material and solid electrolyte [10] . Popoola et al fabricated a symmetric MAPbI 3 supercapacitor with an areal capacitance of 21.50 μF/cm 2[15] .…”

Intrinsically Conducting Polymer Composites as Active Masses in Supercapacitors

“…Metal–organic frameworks (MOFs) and their composites have been considered as active masses in supercapacitor electrodes [ 239 , 240 , 241 , 242 ]; combined with ICPs, the obtained composites were examined for various electrochemical applications [ 243 ]. The poor electronic conductivity of MOFs was noticed as a major hindrance to their use in a supercapacitor electrode; forming composites [ 156 , 244 , 245 , 246 ], including ICPs, is an obvious solution [ 77 , 242 ]. Only a few experimental observations focused on material science aspects were recorded.…”