Birnessite based nanostructures for supercapacitors: challenges, strategies and prospects

On the need for simultaneous electrochemical testing of positive and negative electrodes in carbon supercapacitors

Effect of vacancy modification on the quantum capacitance of silicene- based electrode in efficient supercapacitors

Ni,Zn-codoped MgCo2O4 electrodes for aqueous asymmetric supercapacitor and rechargeable Zn battery

Nickel and cobalt oxides are promising electrode materialsforsupercapacitors, but their poor conductivity and sluggish kineticsseriously hinder their application. Herein, a simple one-step calcinationmethod was proposed to prepare carbon-incorporated NiO@Co3O4 (denoted as CNC) using a NiCo Prussian blue analogue(NiCo-PBA) as a precursor. The effect of calcination temperature onthe electrochemical behavior of CNC was investigated. Benefiting fromthe relatively large specific surface area and porous structure characteristics,when used as an electrode for supercapacitors, the CNC obtained at400 °C shows the typical features of a battery-type electrode,with a good specific capacitance of 208.5 F g–1 at1 A g–1 and a rate capability of 70.8% at 30 A g–1. The hybrid supercapacitor (HSC) constructed withthe optimum CNC electrode can provide a high energy density of 32.6Wh kg–1 at the corresponding power density of 750.0W kg–1 and an excellent cycling stability of 87.1%over 5000 cycles. This study provides a simple calcination methodfor preparing MOF-derived high-conductivity mixed metal oxide electrodematerials for supercapacitors.

Polyaniline modified graphene and carbon nanotube composite electrode for asymmetric supercapacitors of high energy density

As one kind of conducting polymer composite, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) has been widely used as an electrode for energy storage and conversion devices because of its optical transmittance, flexibility, and high electrical conductivity etc. Here, we prepared binding-free PEDOT:PSS fibers (PFs) electrodes with high capacitive performance for supercapacitors via a facile method followed by various solvent treatments. Dimethyl sulfoxide (DMSO)-treated electrodes displayed a better specific capacitance (Cs) of 202 F/g at 0.5 A/g with higher elongation at break, flexibility, and conductivity of 140.7 S/cm, compared to those of pristine PEDOT:PSS materials. More importantly, the DMSO-treated fibers possessed improved stability, which retained 105% of the initial Cs after 22 000 long cycles at 10 A/g. It is believed that the fabricated PFs will be promising organic electrodes for portable supercapacitors and other flexible electronic devices in the near future.

Supercapacitor is a promising energy storage device, which has many advantages including long service lifetime, great power density, fast charge-discharge processes, and green environmental protection. The properties and performance of supercapacitors are greatly dependent on the electrode materials; hence the selection of the electrode material is crucial. There are many metal oxides which have been reported for supercapacitors and ultracapacitors; however, its performance is not that as expected. Thus high-performance electrode materials with large surface area and specific capacitance have been a topic of interest for the development of high-performance supercapacitors. Recently, two-dimensional (2D) transition metal dichalcogenides having layered structures, such as MoS2, VS2, SnS2, CoS2, and WS2, have received significant attention because they offer good energy density, power density, and cycling stability. Among them, the layered molybdenum disulfide (MoS2) is considered to have great potential for its applications as supercapacitors. MoS2 nanosheet is composed of one Mo atomic layer sandwiched between two S layers by covalent bonding, and with these triple layers stacked together to form a layered structure, is expected to act as an excellent energy storage material. It is because of the 2D electron–electron correlations among Mo atoms which would aid in enhancing planar electric transportation properties. MoS2 nanosheets can deliver excellent pseudocapacitance because of the Mo ions having oxidation states ranging from +2 to +6, which enable them to be used as high-performance electrode materials in supercapacitors. Indeed, as a graphene analogue, MoS2 nanosheets exhibit unique physical, optical, and electrical properties correlated with its 2D ultra-thin atomic layer structure and high surface area, making it very interesting for its use as electrodes in high-performance supercapacitors and also a promising supporting material to stabilize metal nanoparticles (NPs), forming hierarchical composites. The specific capacitance of MoS2 is still very limited in alone for energy storage applications. The combination of MoS2 and other conducting materials such as graphene, carbon nanotubes (CNTs), or ceramic nanomaterials such a zirconium (Zr) may overcome these deficiencies. This chapter gives a clear picture of the applications of MoS2 as high-performance electrode in supercapacitors.

Nickel-cobalt phosphate/graphene foam as enhanced electrode for hybrid supercapacitor

Hierarchical CuCo2S4@NiMn-layered double hydroxide core-shell hybrid arrays as electrodes for supercapacitors

Hierarchical-structured copper sulfide nanoneedles were grown on multi-walled carbon nanotube backbone (denoted as CuS@CNT) as electrodes for supercapacitors via a facile template-based hydrothermal conversion approach and further by simply impregnating sulfur into CuS@CNT (S@CuS@CNT) as electrodes for Li-S batteries. The electrochemical measurements showed that the resultant CuS@CNT composite electrodes deliver outstanding electrochemical performance with a specific capacitance up to 566.4 F g−1 and cyclic stability of 94.5 % of its initial capacitance after 5000 cycles at a current density of 1 A g−1. A synergistic effect arising from the unique hierarchical structure was responsible for the electrode performance, including a large surface area of 49.3 m2 g−1 and active CuS ultrafine nanoneedles firmly bonded to the highly conductive carbon nanotube (CNT) backbone. When used as an electrode material for Li-S batteries, the S@CuS@CNT (S content 59 wt%) exhibited satisfying electrochemical performance. The S@CuS@CNT electrode showed that coulombic efficiency was close to 100 % and capacity maintained more than 500 mA h g−1 with progressive cycling up to more than 100 cycles even at a high current density. This strategy of stabilizing S with a small amount of copper sulfide nanoneedles can be a very promising method to prepare free-standing cathode material for high-performance Li-S batteries. The fabrication strategy presented here is low cost, facile, and scalable, which can be considered as a promising material for large-scale energy storage device. In particular, the use of CNT as backbone for the growth of active materials presents many potential merits owing to its lightweight, biodegradable, and stretchable characteristics.

Sandwich-like nitrogen-enriched porous carbon/graphene composites as electrodes for aqueous symmetric supercapacitors with high energy density

The thermocatalytical synthesis conditions required for the activation of wood charcoal with NaOH in terms of the formation of pores in its structure were investigated. The present study was conducted to explore the potential application of activated carbons as electrodes in supercapacitors with organic electrolyte. The total pore volume and micro- and mesopore ratio were controlled by the activation temperature and alkali addition rate. The working characteristics of carbon electrodes (e.g., specific capacity and ohmic losses) in supercapacitors are strongly influenced by the properties of the pores in their structures. Herein, the optimal ratio of raw material to activator and activation temperature are established: an increase in the ratio of NaOH to carbonizate rate by a factor of 2 and setting the synthesis temperature at 700°C positively influence the electrochemical characteristics of supercapacitors and provide them with specific capacities of up to 160 F g-1.

A novel MnO 2 petal nanosheet@carbon sphere core‐shell structure was successfully fabricated by adjusting the quantity of the KMnO 4 precursor employed during the in situ growth of MnO 2 on the surface of carbon spheres via a facile hydrothermal method. In the presence of low KMnO 4 contents, only MnOOH was generated. In contrast, upon increasing the quantity of KMnO 4 , δ‐MnO 2 nanorods and petal nanosheets were obtained, thereby allowing the formation of the core‐shell structured δ‐MnO 2 petal nanosheet@carbon sphere composites. However, beyond a certain point, further increases in the KMnO 4 content were unfavorable. Although, prepared MnO 2 /carbon sphere composites of different morphologies can be used for supercapacitors (SCs) electrode materials, we found that the core‐shell structured MnO 2 petal nanosheet@carbon sphere composites exhibited the optimal capacitance performances in all the composites. These composites exhibited an excellent specific capacitance of 231 F⋅g −1 under a current density of 0.5 A⋅g −1 . Furthermore, they also demonstrated an impressive cycling stability. Indeed, after 1,000 cycles at 10 A⋅g −1 , the MnO 2 petal nanosheet@carbon spheres exhibited 96% of their initial capacitance in a 1 M Na 2 SO 4 aqueous electrolyte. The synergistic effect between δ‐MnO 2 and the porous carbon spheres in the unique core‐shell structured is responsible for the excellent cycle life.

Electrospun SiOC ceramic fiber mats as freestanding electrodes for electrochemical energy storage applications

Medium-temperature fluoroalkylation of microporous activated carbons (ACs) with 1,1,1,2-tetrafluoroethane is presented. Supercapacitor (SC) electrodes based on the fluoroalkylated ACs showed enhanced specific capacitance and high specific energy in electrolytes, either aqueous potassium hydroxide solution or tetraethylammonium tetrafluoroborate-acetonitrile solution. We found the largest increase in the specific capacitance, up to 89 F g–1, and in the specific energy, up to 7.5 Wh kg–1, at the voltage of 1.5 V. The specific capacitance of the SC electrode based on the sample prepared at 350 °C increases by a factor of ~ 2–3 × for certain scan rates in the organic electrolyte. The fluoroalkylated ACs have good electrochemical stability in the tested model systems. We associate the registered enhanced SC parameters with an increase in the total fluorine content and high specific surface areas of the carbon electrode materials. The surface “isolated fluorine” formed during fluoroalkylation at 300–400 °C ensures the production of improved electrode materials for SC applications. Fluoroalkylation is a simple and cost-effective method of improving the specific capacitance of carbon-based SC electrodes.