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Transition metal sulfides with designed nanostructures are expected to provide superior electrochemical performance when used as electrode materials for pseudocapacitors compared to their oxide counterparts. In this paper, hollow Co3S4 dodecahedra were successfully prepared using cobalt‐based zeolite imidazolium skeleton (ZIF‐67) as the precursor and thioacetamide (TAA) as the sulfur source combined with a facile one‐step vulcanization process. The hollow cavity structure not only shortens the carrier transport distance but also provides a higher specific surface area and abundant active sites, which promotes an efficient mass transfer process. In addition, the one‐step synthesis of hollow Co3S4 has greater advantages than the one‐step synthesis in terms of cost control and process simplification. The specific capacitance of the produced hollow Co3S4 nanopolyhedra was 668 F/g at 1 A/g and remained at 353 F/g at 10 A/g when used as a pseudocapacitor electrode, demonstrating its superior multiplication capability. In addition, the capacitance retention is 86.4% after 5000 cycles at 4 A/g, indicating its long cycle stability. Notably, employing commercial activated carbon as negative electrode and the as‐prepared hollow Co3S4 polyhedrons as positive electrode, the assembled asymmetry supercapacitor device delivers a high energy density of 20.7 Wh/kg at a power density of 716 kW/kg. The capacitance value of the device remains up to 81.4% after 2000 charging/discharging cycles. The simple synthesis process opens new opportunities to develop advanced hollow nanostructures exhibiting potential for various applications. [ABSTRACT FROM AUTHOR]

Carbon materials play an important role in supercapacitors due to their structural diversity, rich surface morphology, excellent chemical stability and highly active surfaces. Currently, there are many reports on the synthesis methods for carbon-based materials. The molten salt method stands out among the many methods for its advantages of economy, environmental protection, high efficiency, and maneuverability. Here, we focus on the different roles played by molten salts as templates, sealants, reaction media, and catalysts from the point of view of their functions. The properties and selection principles of the molten salts are discussed in depth, focusing on the morphology, structure, and capacitive properties of the carbon materials prepared using the molten salt strategy. Finally, the current research status of the preparation of carbon-based materials by the molten salt method is summarized, the shortcomings of existing technology are pointed out, and the prospects for its development are envisioned. It is hoped that this review can provide some basic knowledge for the preparation of carbon-based materials by the molten salt method and promote further research on molten salt technology. [ABSTRACT FROM AUTHOR]

The construction of electrode materials with high rate and excellent cycling stability is the key to supercapacitors. Due to their remarkable high conductivity and great electrochemical activity, transition bimetallic sulfides are extremely appealing electrode materials for supercapacitors, but their synthesis is still challenging. In this study, a NiCo bimetallic sulfide (NiCo2S4) microspheres with porous structure were prepared via direct vulcanization of NiCo‐EG complexes followed by a thermal treatment, which were pre‐synthesized via coordination of ethylene glycol (EG) with transition metal ions (Ni2+, Co2+) under hydrothermal condition. Some experimental parameters were investigated, including the control of NiCo2S4 microspheres produced by the ratio of precursor NiCo‐EG to different masses of sulfur sources, which in turn affects the electrochemical properties. When applied as electrode for supercapacitor, the NiCo2S4 microspheres obtained under optimal condition delivered a high capacitance (1386 F g−1 at 1 A g−1), excellent rate capability (845 F g−1 at 10 A g−1) and stable cycling performance (80.05% after 5000 cycles at 10 A/g). Furthermore, for checking the practicality of the produced NiCo2S4 microspheres, an asymmetric supercapacitor device was built using activated carbon (AC) as the negative electrode and NiCo2S4 microspheres as the positive electrode. The assembled NiCo2S4//AC cell had a power density of 799.9 W kg−1 and an energy density of 30.5 Wh kg−1, confirming that the structurally optimized NiCo2S4 porous nanomicrospheres have excellent electrochemical properties and have a wide range of application prospects. [ABSTRACT FROM AUTHOR]

Considering their high abundance in the earth, iron-based materials have occasionally been regarded as promising electrode materials for supercapacitors. However, monometallic iron-based electrodes still demonstrate an insufficient specific capacitance value in comparison to monometallic Mn-, Ni-, and Co-based compounds and their combined materials. Herein, an enhanced iron-based heterostructure of Fe3O4@Fe2P was prepared via the in situ phosphorization of Fe3O4. Compared to pristine Fe3O4, the Fe3O4@Fe2P heterostructure showed a capacity enhancement in KOH aqueous solution. The improved electrochemical performance can be attributed to both the core shell structure, which favors buffering the collapse of the electrode, and the synergistic effect between the two iron compounds, which may provide abundant interfaces and additional electrochemically active sites. Moreover, the assembled asymmetric supercapacitor device using the Fe3O4@Fe2P heterostructure as the positive electrode and activated carbon as the negative electrode delivers a high energy density of 13.47 Wh kg−1, a high power density of 424.98 W kg−1, and an acceptable capacitance retention of 78.5% after 5000 cycles. These results clarify that monometallic Fe based materials can deliver a potential practical application. In addition, the construction method for the heterostructure developed here, in which different anion species are combined, may represent a promising strategy for designing high-performance electrodes. [ABSTRACT FROM AUTHOR]

Supercapacitors which have been widely used in portable electronics and hybrid electric vehicles are considered to be fascinating energy storage devices owing to their higher energy density than traditional capacitors and higher power density than batteries. The performance of supercapacitors is much dependent on the properties of the used electrode materials, and much effort has been devoted to exploring high‐performance electrodes. During the past decade, cobalt‐based materials, especially Co3O4 and its composites, have been regarded as prominent electrode materials for supercapacitors in view of their relatively low cost, high theoretical specific capacitance, non‐toxicity, and excellent electrochemical activity. In this review, we attempt to provide some basic insights into the rational design of Co3O4 based materials/composites and their capacitive properties for supercapacitors. The electrochemical advantages of Co3O4 as a supercapacitor material are summarized, and many examples are illustrated. The remaining challenges in exploration of Co3O4‐based materials as efficient electrodes for supercapacitors are also discussed and the future research directions are offered. [ABSTRACT FROM AUTHOR]

Supercapacitors with high power density and excellent cycle life are considered to be a promising energy storage system for electric vehicle application. Because of low cost and high abundant, the preparation of iron oxides-based supercapacitors has become significant. Here, we reported the preparation of magnetite supercapacitors by using a facile one-step solvothermal method, where Mn has been used as the doping element to modify the electrochemical properties of FeO. The simply prepared supercapacitor showed a much higher electrochemical capacitance in contrast to reported FeO-based electrochemical capacitors. The electrochemical capacitance at this supercapacitor can be as high as 268.4 F g when the Mn doped reached 1.5 mmol. There was not significant decrease in the capacitance after recycling 600 at 2 A g in KOH aqueous solution. The excellent properties in the supercapacitor share a promising prospect with the development of a next generation of high- performance energy storage devices. Graphical Abstract: [ABSTRACT FROM AUTHOR]

Herein, a sequential pyrolysis and oxidation strategy is developed to prepare Co3O4 nanoparticles embedded in N‐doped porous carbon (Co3O4@N‐pC) using a bimetal zeolitic imidazolate framework (ZIF‐67@ZIF‐8) as precursors, which is first obtained via a simple wet‐chemical process. The electrochemical performances of Co3O4@N‐pC, ZIF‐67@ZIF‐8 precursors, and Co@N‐Pc intermediates (the direct pyrolysis products from ZIF‐67@ZIF‐8) are studied as supercapacitor electrodes in comparison. The results reveal that the specific capacitance of the optimized Co3O4@N‐pC electrode can reach up to 422.8 F g−1 at 1 A g−1 with a good rate capability (256 F g−1 at 5 A g−1) and excellent long‐term cycling stability (87.9% retention after 5000 cycles). Such performance is superior over ZIF‐67@ZIF‐8 precursors (232 F g−1 at 1 A g−1, 168.9 F g−1 at 5 A g−1, and 82.7% retained after 5000 cycles) and Co@N‐pC intermediates (218.4 F g−1 at 1 A g−1, 171 F g−1 at 5 A g−1, and 76.3% retained after 5000 cycles). The findings in this work are expected to provide a new avenue to explore other metal oxide/carbon materials for various applications. [ABSTRACT FROM AUTHOR]