Next-generation Supercapacitors Research Articles

Recent Advances in Polyaniline/Graphene Nanocomposites for Supercapacitor Applications: Synthesis, Properties, and Future Directions

Electrochemical capacitors or supercapacitors have attracted the attention of researchers and industries in the recent past because of the differences in the features and potential applications in comparison to the Li-ion batteries. Supercapacitors have been one of the most investigated applications in literature based on graphene-related materials. This review aims to provide the most recent advancement on the use of graphene and polyaniline (PANI) nanocomposite towards enhancing the supercapacitor properties. The synthesis methods of the graphene and PANI nanocomposite, the characteristics of the nanocomposite and its utilization in supercapacitors are discussed. Graphene and PANI are both well-known materials that possess fascinating physical and electrochemical characteristics, and in the last several years, they have been investigated for numerous applications by many researchers. Together with such advantages as enhanced physical and electrochemical characteristics, mechanical strength, and density, composites of both materials can be a potent material for supercapacitor usage.The preparation methods of graphene, PANI, and its composites described by the authors of the research article include in-situ polymerization, chemical vapor deposition, and hydrothermal-assisted polymerization. These characterization techniques include SEM, TEM, FTIR, XRD, DSC, and TGA to determine other properties of the nanocomposite which shows enhanced properties of graphene and PANI. The electrochemical properties of the nanocomposites are evaluated through cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) and the achieved values indicate high specific capacitance, cycling stability, and charge-discharge abilities. These outcomes demonstrate the excellent applicability of PANI/graphene nanocomposites as high-performance supercapacitors and encourage the confidence in the effectiveness of the study. Several factors affecting properties of the nanocomposites have been reported in the previous studies, and it is clear from this study how various properties and their relation affects the overall performance of the nanocomposite. Altogether, PANI/graphene nanocomposites have the potential to be used as next-generation supercapacitors, which is still unexplored fully to meet the demands to enhance the high-performance energy storage devices.

Microporous tungsten oxide spheres coupled with Ti3C2Txnanosheets for high-volumetric capacitance supercapacitors.

In the contemporary landscape of technological advancements, the burgeoning demand for portable electronics and flexible wearable devices has necessitated the development of energy storage systems with superior volumetric performance. Tungsten oxide (WO3), known for its high density and theoretical capacitance, is a promising electrode material for supercapacitors. However, low conductivity and poor cycling stability are still the key bottlenecks for its application. Herein, a novel composite comprising hollow porous WO3 spheres (HPWS) derived by template method was electrostatic self-assembled on the surface of the Ti3C2Tx nanosheets. The resulting electrodes exhibited ultra-high volumetric capacitance of 1930 F cm-3 at 1 A g-1 and rate capability of 46% at 50 A g-1, attributed to enhanced ion accessibility from microporous structure and electron transport from conductive network of Ti3C2Tx even at a high packing density of 3.86 g cm-3. Utilizing HPWS/Ti3C2Tx as the negative electrode and porous carbon as the positive electrode, the assembled asymmetric supercapacitor achieved an energy density of 31 Wh kg-1 at a power density of 650 W kg-1 with over 107% capacitance retention after 5000 cycles. This work provides a promising approach for developing next-generation supercapacitors with ultra-high volumetric capacitance.

Tailoring the electrochemical performance of novel BaS and their N-rGO composites for developing next-generation pseudocapacitor electrodes

The exploration of prospective versatile materials with desired morphology for energy storage applications has been reckoned to be a foremost challenge for researchers of the era. In this study, the metal sulfides and their composite with N-rGO are synthesized by facile hydrothermal approach. X-ray diffraction (XRD) pattern of the sample having cubic phase confirms its high crystallinity and purity. Photoelectron Spectroscopy (XPS) depicts utterly the constituent elements and states. Scanning electron microscope (SEM) and Transmission electron microscope (TEM) portray porous-type morphology with a high surface area.I-V measurements ensure the high conductivity of these composites whereas Fourier Transform Infrared Spectroscopy (FTIR) displays the presence of the vibrational bonds. Zeta potential of BaS is determined to be moderately negative, suggesting the existence of negatively charged entities on its surface. Brunauer-Emmett-Teller (BET) corroborates that N-rGO based composite contains a mesoporous structure with an average pore size (2.01 nm) elongated the large surface area (82.21 m2/g). The thermal stability of the composite is envisioned via Thermal gravimetric analysis (TGA). So far as the electrochemical analysis, CV results are much enough to affirm the pseudocapacitive nature of all the fabricated electrodes. An impressive cyclic stability, retaining 98.1 % of its initial capacitance over 10000th cycles is determined through N-rGO based electrode. GCD test unveils exceptional Cs of 913.34 F/g at 1 A/g with Energy density (Ed) 62.106 Wh/kg and Power density (Pd) 2896.47 W/kg and EIS provides valuable insights, showing a small semi-circle in the Nyquist plot, which indicates low charge transfer resistance. The results from the two-electrode experiment indicate that BaS/N-rGO has a specific capacitance (Cs) of 533.96 F/g at 1 A/g. Finally, our symmetrical solid-state supercapacitors exhibit exceptional capacitive performance to power LED. These results confidently indicate that the incorporation of N-rGO with metal sulfides presents promising prospects for the next-generation supercapacitor electrodes to excel the energy storage technological applications.

Enhanced electrochemical performance with exceptional capacitive retention in Ce–Co MOFs/Ti3C2Tx nanocomposite for advanced supercapacitor applications

This study introduces a high-performance Ce–Co MOFs/Ti3C2Tx nanocomposite, synthesized via hydrothermal methods, designed to advance supercapacitor technology. The integration of Ce–Co metal-organic frameworks (MOFs) with Ti3C2Tx (Mxene) yields a composite that exhibits superior electrochemical properties. Structural analyses, including X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM), confirm the successful formation of the composite, featuring well-defined rod-like Ce–Co MOFs and layered Ti3C2Tx sheets.Electrochemical evaluation highlights the exceptional performance of the Ce–Co MOFs/Ti3C2Tx nanocomposite, achieving a specific capacitance of 483.3 Fg⁻1 at 10 mVs⁻1, a notable enhancement over the 200 Fg⁻1 of Ce–Co MOFs. It also delivers a high energy density of 78.48 Whkg⁻1 compared to 19 Whkg⁻1 for Ce–Co MOFs. Remarkably, the nanocomposite shows outstanding cyclic stability with a capacitance retention of 109 % after 4000 cycles and electrochemical surface area (ECSA) of 845 cm2, coupled with a reduced charge transfer resistance (Rct) of 2.601 Ω and an equivalent series resistance (ESR) of 0.8 Ω. These findings demonstrate that the Ce–Co MOFs/Ti3C2Tx nanocomposite is a groundbreaking material, offering enhanced energy storage, conductivity, and durability, positioning it as a leading candidate for next-generation supercapacitors.

Binder-free Ni-doped In/Mn oxalate electrode for next-generation supercapacitors

The worth of electrochemical energy storage systems is significantly influenced by the nature of the electrode material. In this work, metal oxalates have emerged as cost-effective and robust candidates for application in supercapacitors. In this context, a binder-free electrode composed of in-situ Ni-doped In/Mn oxalate was synthesized. The nickel foam served a dual function, acting both as a structural framework and as a source of nickel. X-ray diffraction (XRD) analysis verified the crystalline nature of the in-situ Ni-doped In/Mn oxalate. Morphological assessment using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed the presence of a hybrid one-dimensional/two-dimensional morphology within the in-situ Ni-doped In/Mn oxalate. Electrochemical evaluations indicated that the in-situ Ni-doped In/Mn oxalate electrode exhibits characteristics akin to those of a battery, maintaining 88.8 % of its initial capacity. Furthermore, it demonstrated a superior specific capacity, amounting to 1238.3 F g−1 at a current density of 1 A g−1. The inclusion of nickel during the material's synthesis process is posited to significantly augment its overall electrochemical performance and properties.

(Nanocarbons Division Poster Award, 3rd Place) Hybrid Supercapacitance and Stability of Fe-Based Metal-Organic Frameworks/Graphene Oxide Nanoribbons Composite Allover the pH Range

Adopting renewable energy sources is growing fast, and hence it should be accompanied by tremendous efforts to develop energy storage technologies that can mitigate the intermittent nature of these sources. Supercapacitors (SCs) are considered among the most promising technologies for that purpose due to their high durability, power density, and charging/discharging competency. SCs have two types according to their electrochemical charge storage mechanism: pseudocapacitance (PCs) or battery-like behavior and electrochemical double-layer capacitors (EDLCs). The development of next-generation supercapacitors requires a holistic approach that integrates both mechanisms. Because of their huge surface area, porous structure, and abundance of active redox sites, metal-organic frameworks (MOFs) have exceptional potential in energy storage devices. However, due to the MOFs’ low conductivity and stability, they are in need to be mixed with highly conductive and stable materials such as carbon-based ones.In this work, Fe-based MOFs were selected to be responsible for mainly the battery-like contribution to the overall supercapacitance due to the presence of the redox-active sites. Even though little attention has been given to the Fe-based MOFs they showed a promising performance in several solutions, with low stability.1,2 To enhance the Fe-MOFs stability and conductivity and add an EDLC component to the overall capacitance behavior graphene oxide nanoribbon (GONRs) was used. The GONRs' exceptional properties such as ultrathin two-dimensional structures, superior mechanical behavior, strong chemical stability, and high electrical conductivity make them promising materials for supercapacitor applications.In this study, Fe-MOFs were synthesized using a hydrothermal method,3 and GONRs were prepared using an oxidative unzipping method.4 A composite of Fe-MOFs/GONRs was prepared by physical mixing. The physical and chemical properties of the synthesized Fe-MOFs, GONRs, and Fe-MOFs/GONRs were characterized using XRD, SEM, TEM, FT-IR, Raman spectroscopy, and XPS. Since the electrolyte properties have a substantial impact on the supercapacitive behavior and stability of the electrode materials, the specific capacitance of the prepared composites was measured in 1M H2SO4, 1M KOH, 1M K2SO4, and 1M KCl utilizing different evaluation systems (three and two-electrode systems). The Fe-MOFs/GONRs composite showed a significant synergistic effect in comparison to its pure components. Further discussion will be given regarding the pH and ion size/type effect on the supercapacitive performance and stability.

Organic Trimer Molecule Electrode as a High-Performance Next-Generation Supercapacitor Material

As greenhouse gas emissions such as CO2 continue to increase on a global scale, countries around the world are making changes to reduce their net emissions. One of the primary actions being taken is attempting to decarbonize the transportation sector by moving away from fossil fuel-powered vehicles and adopting electric vehicles (EVs). Supercapacitors are electrical energy storage devices similar in concept to batteries, however they achieve a higher power output, faster charge and discharge rates, and greater longevity. These properties make them excellent devices to work in tandem with batteries that advance their collective performance capabilities in EVs. Supercapacitors using inorganic materials such as transition metal oxides have been explored extensively and although there have been advancements in the field, they continue to struggle with limitations such as mechanical degradation during cycling, low conductivity which slows the charging-discharging processes, and the utilization of environmentally toxic metals. On the other hand, quinones are a class of organic materials considered as the most promising candidates for organic electrodes due to their ≥ 2 reversible redox-active carbonyl groups, inexpensiveness, ease of structural modifications, and environmental sustainability. However, like many organic materials, they suffer from low electrical conductivity and dissolution in electrolyte. To minimize dissolution while retaining and improving its advantages, polymerizing quinones has become a popular modification alternative, especially via polyimide and polythioether bonds. However, because polymer chains are so large and inherently have low electronic conductivity, polymerizing quinones inhibits charge transfer throughout a matrix with a carbon substrate (i.e., rGO, CNT, carbon black) due to interference with the conductive network.In this research, a smaller molecule was made from covalently bonding two different quinones via imide bonds to make an organic trimer. This helped reduce dissolution in electrolyte compared to its monomeric components via increasing the molecular weight while also improving the energy storage capabilities as a supercapacitor electrode. This is attributed to this molecule retaining the original redox active sites of its monomers and its conjugated network which allows it to achieve a 6-electron transfer mechanism per molecule. Its smaller size compared to a polymer is also hypothesized to reduce the degree of conductivity interruptions it causes when part of a carbon substrate network. While polymer chains can agglomerate easily, decreasing its available specific surface area, this trimer may be more available to participate in Faradaic processes. This research hereby reports an electrode material with very high capacitance (318 Fg-1 at 5 mVs-1) and good cycling stability utilizing a low-cost carbon black substrate for supercapacitor applications to improve the performance of next-generation EVs.

Elevating capacitive features of hydrothermally produced CeVS3 utilizing rGO for supercapacitor applications

This work presents the fabrication of a novel CeVS3/rGO nanocomposite using an easy hydrothermal route for supercapacitor applications. Physical studies revealed that CeVS3 showed flakes-like morphology, which is successfully decorated on reduced graphene oxide (rGO) sheets in nanocomposite. The electrochemical studies exhibited that fabricated CeVS3/rGO showed improved capacitive behavior with notable specific capacitance (Cs) of 1516 F/g at 1 A/g current density (jd) as well as excellent rate capability due to combined effect of CeVS3 nanoflakes and rGO sheets. Nanocomposite also demonstrated a lower resistance of 0.21 Ω than pure material, which have a charge transfer resistance (Rct) of 0.48 Ω. Furthermore, a two-electrode symmetric study was carried out in KOH solution (2.0 M), demonstrating a specific energy (SE) of 18.73 Wh/kg and specific power (SP) of 264.5 W/kg with remarkable cyclic stability after 5000 cycles. These findings demonstrated that innovative CeVS3/rGO can be utilized in next-generation supercapacitor applications.

Electrochemical stability and superior capacitance of bismuth cobalt metal-organic framework incorporated with vanadium disulfide nanosheet for supercapacitor application

The development of a novel supercapacitor electrode material consisting of bismuth and cobalt-based metal-organic framework (MOF) intercalated on vanadium disulfide (VS2) nanosheets (BiCo-MOF@VS2). The composite combines the high porosity and tunable functionality of MOFs with excellent conductivity and high theoretical capacitance of VS2. The MOF structure is designed to incorporate bismuth and cobalt, which enhance electrochemical performance. The VS2 nanosheets provide a conductive support matrix for the MOF, facilitating electron transport and promoting fast charge-discharge rates. Researchers used a suite of techniques to characterize the fabricated electrodes to understand the relationship between material properties and performance. These techniques analyzed the morphology, crystal structure, and electrochemical properties of the materials. The electrochemical performance of BiCo-MOF@VS2 electrodes for supercapacitor applications is investigated using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy. The research shows that these composite electrodes are highly promising for use in supercapacitors needing top performance. They deliver impressive capacitance, handle rapid charge and discharge cycles well, and maintain stability over time. We found that the electrochemical behavior is optimum when BiCo-MOF@VS2 is used, which is a result of the synergistic effects of VS2 dispersion and the BiCo-MOF. BiCo-MOF and VS2 have shown specific capacitance values of 282 and 199 F g−1, compared to the two electrode materials, BiCo-MOF@VS2 demonstrated an impressive specific capacitance of 472 F g−1 at 1 A g−1, and cyclic stability with 85 % retention even after 3000 cycles at 9 A g−1 current density tested in 1 M KOH solution. This novel material holds promise for developing next-generation supercapacitors with exceptional energy storage capabilities.

A review of EDLC and pseudocapacitance with synergistic integration of carbon-based and metal oxide materials for enhanced electrochemical energy storage

This paper provides a comprehensive analysis of the recent advancements in electrochemical double-layer capacitors (EDLCs) and pseudocapacitance, emphasizing the pivotal role of carbon-based materials, metal oxides, conducting polymers, and composites in augmenting the energy storage landscape. Through a systematic collection of electrochemical performance metrics, we elucidate the inherent advantages of these materials, such as superior electrical conductivity, enhanced surface area, and chemical robustness, which are instrumental in the development of next-generation supercapacitors. We discuss the integration of novel materials like reduced graphene oxide/hexagonal boron nitride composites, carbon onions, and various metal oxides that contribute to a significant increase in energy density and cycling stability. This work also highlights innovative fabrication techniques and synthesis methodologies that have resulted in electrodes with remarkable performance enhancements. Furthermore, the exploration of synergistic effects between different materials has led to hybrid structures that exhibit improved capacitive properties and operational efficiency.

Development of cost-efficient BaMnO3/rGO nanocomposite as electrode for energy storage applications in supercapacitor

The excessive fossil fuels utilization leads to environment contamination along with energy loss and is becoming a serious issue in these days. Therefore, to handle these energy issues, alternative sources and energy-storing devices like supercapacitors are in demand in the modern era. Many perovskites have been used in supercapacitors as electrode material but because of its less cyclic stability and poor conductivity, rGO mixed to enhance the electrochemical properties of perovskite. Therefore, we used rGO with BaMnO3 to fabricate BaMnO3/rGO nanocomposite through hydrothermal method for supercapacitor electrodes. After different physical analyses, BaMnO3/rGO nanocomposite showed remarkable electrode applications having distinct nanostructure with increased surface area, conductivity, crystallinity and improved morphology. The electrode material demonstrated a substantial surface area (54.32 m2 g−1) measured by Brunner–Emmett–Teller analysis, while scanning electron microscopy results showed that BaMnO3 dispersed tightly on rGO. The fabricated electrode material demonstrated a specific capacitance of 1359.85 F g−1, energy density of 78.62 Wh kg−1 and power density of 322.6 W kg−1 at 1 A g−1 current density. Furthermore, the Nyquist plot revealed a low value of Rct (0.04 Ω), indicating good electrical conductivity, while the material displayed stability even after 5000th cycle. This work revealed that, such extraordinary and outstanding qualities of BaMnO3/rGO nanocomposite provide a viable option for use in next-generation supercapacitor applications along with high stability and cost effectiveness.

Understanding Electrolyte Ion Size Effects on the Performance of Conducting Metal-Organic Framework Supercapacitors.

Layered metal-organic frameworks (MOFs) have emerged as promising materials for next-generation supercapacitors. Understanding how and why electrolyte ion size impacts electrochemical performance is crucial for developing improved MOF-based devices. To address this, we investigate the energy storage performance of Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) with a series of 1 M tetraalkylammonium tetrafluoroborate (TAABF4) electrolytes with different cation sizes. Three-electrode experiments show that Cu3(HHTP)2 exhibits an asymmetric charging response with all ion sizes, with higher energy storage upon positive charging and a greater charging asymmetry with larger TAA+ cations. The results further show that smaller TAA+ cations demonstrate superior capacitive performances upon both positive and negative charging compared to larger TAA+ cations. To gain further insights, electrochemical quartz crystal microbalance measurements were performed to probe ion electrosorption during charging and discharging. These reveal that Cu3(HHTP)2 has a cation-dominated charging mechanism, but interestingly indicate that the solvent also participates in the charging process with larger cations. Overall, the results of this study suggest that larger TAA+ cations saturate the pores of the Cu3(HHTP)2-based electrodes. This leads to more asymmetric charging behavior and forces solvent molecules to play a role in the charge storage mechanism. These findings significantly enhance our understanding of ion electrosorption in layered MOFs, and they will guide the design of improved MOF-based supercapacitors.

Ionic-storage capacitance enhanced by a self-assembled CoO-Nafion nanocoating on single-walled carbon nanotubes

We introduce a novel approach for enhancing ion-storage capabilities through the self-assembled formation of ternary nanowires, consisting of a CoO-and-Nafion nanocomposite encasing metallic single-walled carbon nanotubes (SWNTs). These nanowires highlight the indispensable role of the conductor-semimetallic SWNT-CoO heterojunction in expediting the redox reaction kinetics of the CoO while the Nafion component facilitates the transport of hydroxide ions. Consequently, supercapacitors comprising the ternary nanowires deliver the specific capacitance of calculated 18.84 mF cm−2, five times higher than those obtained at the counterpart devices that lack Nafion and/or CoO. This self-assembly method precisely organizes functional components within the nanowires, aligning with electrochemical principles to optimize charge transfer and minimize concentration gradients for improved electrochemical polarization. Our function-enhanced ternary nanowires, together with their straightforward synthetic process, promise an alternative opportunity for formulating high-performance ion-storage electrodes and thus pave the way for their application in next-generation supercapacitor technologies.

Exploration of the role of oxygen-deficiencies coupled with Ni-doped V2O5 nanosheets anchored on carbon nanocoils for high-performance supercapacitor device

Electronic structural engineering via integration of oxygen deficiencies and a variety of dopants in metal oxide electrodes has fascinated the research interest for developing next-generation supercapacitors. Herein, by incorporating Ni dopants and creating O vacancies, it has thoroughly been explored the potential of vanadium oxide (V2O5) nanosheets anchored on the carbon nanocoils (CNCs) grown on nickel foam (NF) for supercapacitor electrodes (OV-Ni-V2O5/CNCs/NF). We validate a synergistic effect provided by heterostructure designed with multifunctional nano geometries. It is found that O vacancies and Ni dopants alter the electronic states of V2O5 with enhanced electrical conductivity and enriched redox active sites. We optimized O vacancies and achieved a specific capacity of 3485F g−1 (1742.5C g−1) at 1 A/g, representing ∼ 3.8 × higher compared to the best prior report. Furthermore, an asymmetric supercapacitor device was assembled with binder-free electrodes, using O0.075-V2O5/CNCs/NF as a cathode and sulfur-doped CNCs as an anode, which delivered a high energy density of 144 W h kg−1 and long-term stability of 5000 cycles, which is superior to most of the previous studies. This study paves a rational strategy to design high-performance electrodes for next-generation supercapacitors and other energy storage technologies.

Solvothermal growth of silver-doped vanadium pentoxide microurchins as a cathode material for all-solid-state asymmetric supercapacitors

This study aims to improve the electrochemical properties of vanadium pentoxide by inserting silver cations into the vanadium oxide lattice. The porous silver-doped V2O5 (Ag-V2O5) microurchins were grown via a facile one-step solvothermal process. The enhanced mesoporosity and interlayer d-spacing upon silver-doping, as confirmed by Brunauer–Emmett–Teller (BET) and X-ray diffraction analyses, played an important role in facilitating the intercalation/de-intercalation of electrolyte ions and thus enhancing the capacitive performance of V2O5. The Ag-V2O5 electrode delivered a superior capacitance of 535.6 F/g at 0.5 A/g and a higher rate capacity of 78.8% in non-aqueous lithium perchlorate electrolyte compared to sodium perchlorate electrolyte. Furthermore, the specific capacitance of V2O5 was remarkably increased by ∼56% upon 5.33 at% Ag-doping. An all-solid-state asymmetric supercapacitor (ASC) was fabricated using Ag-V2O5 as the cathode, activated carbon cloth as the anode, and LiClO4-loaded poly(acrylonitrile-co-1-vinylimidazole-co-itaconic acid) as a solid electrolyte. The ASC was stably operating in a wide potential window of 0–1.6 V and delivered a high energy of 53.8 Wh kg−1. Most importantly, the ASC exhibits a slow self-discharge rate with only 7.7% voltage loss after 17 h when charged at 1.6 V. Hence, these impressive electrochemical performances of Ag-V2O5 make it a promising cathode material for next-generation supercapacitors.

Experimental and computational analysis of the structure-activity relationship of ionic gel electrolytes based on bistrifluoromethanesulfonimide salts for supercapacitors

Ionic gel (IG) electrolytes are emerging as promising components for the development of next-generation supercapacitors (SCs), offering benefits in terms of safety, cost-effectiveness, and flexibility. The ionic conductivity, stability, and mechanical properties of the gel electrolyte are relevant factors to be considered and the key to improving the performance of the SC. However, the structure–activity relationship between the internal structure of IGs and their SC properties is not fully understood. In the current study, the intuitive and regular structure–activity relationship between the structure and properties of IGs was revealed via combining computational simulation and experiment. In terms of conductivity, the ionic liquid (IL) ([EMIM][TFSI]) in the IG has a high self-diffusion coefficient calculated by molecular dynamics simulation (MDS), which is conductive to transfer and then improves the conductivity. The radial distribution function of the MDS shows that the larger the g(r) between the particles in the polymer network, the stronger the interaction. For stability, IGs based on [EMIM][TFSI] and [EOMIM][TFSI] ILs have higher density functional theory calculated binding energy, which is reflected in the excellent thermal stability and excellent capacitor cycle stability. Based on the internal pore size distribution and stress-strain characterization of the gel network ([ME3MePy][TFSI] and [BMIM][TFSI] as additives), the highly crosslinked aggregate network significantly reduces the internal mesoporous distribution and plays a leading role in improving the mechanical properties of the network. By using this strategy, it will be possible to design the ideal structure of the IG and achieve excellent performance.

Synthesis of Ni-VO2@C/SO42− composite using cashew leaves for supercapacitor application

Cashew leaves were used to synthesize composites based on vanadium dioxide (VO2@C/SO42−) and on nickel-doped vanadium dioxide (Ni-VO2@C/SO42−) by a green process. The choice of nickel doping is motivated by the fact that the ionic radius of V (IV) and that of Ni2+ are nearly equal (0.72 Å) and also Ni has advantages of low toxicity and cheapness. The structural and morphological properties were analysed by XPS, XRD, Raman, RBS, EDX, SEM and BET. Electrochemical measurements show that the Ni-VO2@C/SO42− composite exhibits a high specific capacitance of 355 F g−1 at a specific current of 1 A g−1 with an excellent Coulombic efficiency of 97 % at 10 A g−1. To evaluate practical applications, a device was assembled in which Ni-VO2@C/SO42− composite and activated carbon (AC) were used as cathode and anode respectively. The device thus prepared displays an energy density of 21 W h kg−1 and an excellent power density of 972 W kg−1 at a cell voltage of 1.6 V and a specific current of 1 A g−1. Stability tests also show an excellent Coulomb efficiency of 98 % and a retention capacity of 88 % at 10 A g−1 after 10,000 cycles. This remarkable electrochemical performance is due to the good synergy between VO2, SO42− and carbon, together with the effect of nickel doping. This finally confirms that this Ni-VO2@C/SO42− composite could be used to develop advanced cathodes for the next generation of supercapacitors.

Fabrication of nickel-copper sulfide nanoparticles decorated on metal-organic framework composite for supercapacitor application by hydrothermal process

Due to their flexible porous structure, metal-organic frameworks (MOFs) have a lot of potential as materials for making electrodes for next-generation supercapacitors. The current study is about making controlled syntheses of NiCuS and NiCuS@MOFs composites from nickel and copper precursors, as well as 2-MeI and BDC ligands using ultrasonication to help the hydrothermal process. The fabricated composite materials were characterized by Raman, XRD, FTIR, XPS, and HR-TEM analysis for confirmation of structural and morphological properties. The fabricated composite electrode showed excellent specific capacitance of 535 F g− 1 at 0.5 A/g (three electrode configuration) and 122 F g− 1 at 0.5 A/g (symmetric configuration) and cyclic retention (86.5 %) up to 8000 cycles in the presence of 1 M KOH electrolyte. Furthermore, the fabricated composite electrode (NiCuS@MOF-BDC/SSC) via two electrode configurations showed an energy density of E = 15.82 kh/kg and a power density of P = 9316 kW/kg and excellent cyclic stability and retention. The improved electrochemical performances of the electrode materials were due to the surface, morphological, porous nature, and synergistic effect of the composite structure via the ultrasonication-hydrothermal reaction process. Therefore, the fabricated composite samples were found to have great potential for electrochemical supercapacitor applications.

In situ growth of a redox-active metal-organic framework on electrospun carbon nanofibers as a free-standing electrode for flexible energy storage devices.

The rational construction of free-standing and flexible electrodes for application in electrochemical energy storage devices and next-generation supercapacitors is an emerging research focus. Herein, we prepared a redox-active ferrocene dicarboxylic acid (Fc)-based nickel metal-organic framework (MOF) on electrospun carbon nanofibers (NiFc-MOF@CNFs) via an in situ approach. This in situ approach avoided the aggregation of the MOF. The NiFc-MOF@CNF flexible electrode showed a high redox-active behavior owing to the presence of ferrocene and flexible carbon nanofibers, which led to unique properties, including high flexibility and lightweight. Furthermore, the prepared electrode was utilized in a supercapacitors (SC) without the use of any binder, which achieved a specific capacity of 460 C g-1 at 1 A g-1 with an excellent cyclic retention of 82.2% after 25 000 cycles and a good rate capability. A flexible asymmetric supercapacitor device was assembled, which delivered a high energy density of 56.25 W h kg-1 and a long-lasting cycling performance. Also, the prepared electrode could be used as a freestanding electrode in flexible devices at different bending angles. The obtained cyclic voltammetry curves showed negligible changes, indicating the high stability and good flexibility of the electrode. Thus, the use of the in situ strategy can lead to the uniform growth of redox-active MOFs or other porous materials on CNFs.

Wasted rose-derived porous carbons with unique hierarchical heteroatom-enriched structures as a high-performance supercapacitor electrode

High-quality and low-cost activated carbons (ACs) are highly considered as high-performance electrode materials for next-generation supercapacitors.