Solid-state Supercapacitor Research Articles

High-performance supercapacitor electrodes: Hierarchical integration of bimetallic structures incorporating silver and copper phosphates with a 3D fernlike stellar dendritic architecture

Batteries and supercapacitors remain at the front of research within the field of energy storage technologies. Over the years, the continues evolution of battery and supercapacitor device components has demonstrated remarkable advancement, evolving from simple metal blocks to complex, porous, and engineered structures composed of metal-based active materials. Towards this goal, transition metal phosphates (TM-POs) offer significant role enhancing the properties and architecture of the resulting metal-based active materials. This study introduces a unique electrode material with a dendritic structure of silver copper phosphates, derived from AgPO3 integrated with hexagonal Cu2P2O7. The improved electrochemical performance of silver copper phosphates compared to pristine AgPO3 and Cu2P2O7 is demonstrated by its increased specific capacity, reduced resistivity, higher redox activity, and a more advantageous diffusion-dominated storage mechanism. An assembled solid-state symmetric (SSCs) device, using silver copper phosphate electrodes exhibits a capacitance of 298.5 F g−1 at 15 mA cm−2, and high energy density of 20.3 Wh kg−1 with superior power density, also retains 91.7 % of its capacitance after 7000 cycles. When assembled a solid-state asymmetric supercapacitor (SSACs), as an integrated device using activated carbon and silver copper phosphate electrodes exhibits a high energy density of 30.62 Wh kg−1 at a power density of 1334 W kg−1 with retaining its capacity retention of 87.9 % even after 10,000 cycles. The enhanced capacity performance is further evaluated through first-principle investigations, elucidating that the distinct and intact heterostructure of silver copper phosphate exhibits improved metallic characteristics. This research of innovative electrodes holding superior properties holds potential for advancing next-generation electrodes for supercapacitor devices.

MnO2/AgNPs Composite as Flexible Electrode Material for Solid-State Hybrid Supercapacitor

A MnO2/AgNP nanocomposite was synthesized using a sonochemical method and investigated as an electrode material in a solid-state hybrid supercapacitor. Aquivion’s sodium and lithium electrolyte membrane serves as an electrolyte and separator. For comparison, MnO2 was used as the active material. The developed supercapacitor containing a carbon xerogel as a negative electrode, the MnO2/AgNP composite as a positive electrode and a Na+-exchange membrane demonstrated the highest performance characteristics. These results indicate that the incorporation of silver nanoparticles into the MnO2 structure is a prospect for obtaining an active composite electrode material for solid-state supercapacitors.

Fabrication of a high-performance symmetrical supercapacitor based on electrochemically interconnected Cu:NiO@rGO:PANI/NF electrodes

A three-step electrodeposition synthesis was carried out to prepare a nanocomposite electrode of copper-doped nickel oxide and reduced graphene oxide-doped polyaniline with synergistic effects. Nickel foam was utilized as a current collector. XRD, FTIR and XPS studies confirm the molecular bond formation and molecular phase of the produced materials. According to the EDS results, the rGO:PANI/NF electrode contains 0.29 % nitrogen (N), 17.39 % carbon (C), and 9.81 % oxygen (O), while the Cu:NiO@rGO:PANI/NF electrode contains 8.24 % copper (Cu), 9.22 % carbon (C), 7.21 % oxygen (O), and 0.72 % nitrogen (N). The electrochemical performance of rGO:PANI/NF and Cu:NiO@rGO:PANI/NF electrodes were tested in a three-electrode cell with 3 M KOH aqueous electrolyte. High specific capacitances of 644.5 and 807.1 Fg−1 are achieved with the rGO:PANI/NF and Cu:NiO@rGO:PANI/NF electrodes at a current density of 20 Ag−1, respectively. The Cu:NiO@rGOPANI/NF also has a lower charge transfer resistance (RCT = 0.9 Ω) than the rGO:PANI/NF electrode (RCT = 3.8 Ω). This means NiO plays a crucial role in facilitating the transportation of charges between rGO:PANI. NiO acts as a “superhighway” that enables efficient and speedy charge transport. The expanded BET surface area of Cu:NiO@rGO:PANI/NF can be attributed to a well-interconnected network of PANI chains with NiO. In order to demonstrate a further application, an all-solid-state symmetrical supercapacitor (SSC) was then fabricated using the Cu:NiO@rGO:PANI/NF electrodes. The operating potential range is between 0 and 1.5 V. The device has a good capacitance of 81.9 Fg−1 at 4.5 Ag−1, and a capacitance retention of 97.6 % at a specific current of 10 Ag−1 after 10,000 cycles. The symmetrical device has a maximum energy density of 25.6 Wh kg−1 at a high power density of 1297.6 W kg−1 at 4.5 A g−1. In light of these results, the nanocomposite-based solid-state supercapacitor is considered to be a promising device for the development of high-performance symmetric supercapacitors.

Rational Design of Nanosheet Array-Like Layered-Double-Hydroxide-Derived NiCo2O4 In Situ Grown on Reduced-Graphene-Oxide-Coated Nickel Foam for High-Performance Solid-State Supercapacitors.

The investigation of high-performance supercapacitors is essential for accelerating the development of energy storage devices. In this work, a 3D hierarchical nanosheet array-like nickel cobaltite/reduced graphene oxide/nickel foam composite (NiCo2O4/rGO/NF) was assembled via an aqueous coprecipitation-hydrothermal strategy assisted by citric acid. Benefiting from a NiCo layered-double-hydroxide precursor with an atomic-level lattice confinement effect of metal ions and effective hybridization with rGO, the NiCo2O4/rGO/NF composite is featured as thin NiCo2O4 nanosheets (∼113.6 nm × 11.2 nm) composed of NiCo2O4 nanoparticles (∼10.9 nm) vertically staggered on the surface of a rGO-modified NF skeleton, leading to high surface area, abundant mesoporous structure, and active site exposure. The as-obtained NiCo2O4/rGO/NF was directly used as a binder-free integrated electrode for supercapacitors, achieving an excellent specific capacitance of 2863.4 F g-1 (1503.3 C g-1) at 1 A g-1, a superior rate performance of 2335.2 F g-1 at 20 A g-1, and a stability retention of 91.7% after 5000 cycles. More impressively, a solid-state asymmetric supercapacitor assembled by the present NiCo2O4/rGO/NF integrated electrode as the positive electrode and commercial activated carbon as the negative electrode achieved a high energy density of 69.2 Wh kg-1 at a power density of 800 W kg-1, and the energy density at a peak power density of 20004 W kg-1 still remained at 48.9 Wh kg-1, also showing a good cycling stability of 87.2% retention over 10000 cycles. The present facile synthesis strategy of the as-obtained NiCo2O4/rGO/NF nanosheet array composite can be used for the design and construction of many other transition-metal oxide/graphene/NF composite materials with excellent structural stability and performance in energy storage and other related areas.

Fabrication of CNT-N@Manganese Oxide Hybrid Nanomaterials through a Versatile One-Pot Eco-Friendly Route toward Engineered Textile Supercapacitors.

The expansion of the Internet of Things market and the proliferation of wearable technologies have generated a significant demand for textile-based energy storage systems. This work reports the engineered design of hybrid electrode nanomaterials of N-doped carbon nanotubes (CNT-N) functionalized with two types of manganese oxides (MOs)-birnessite (MnO2) and hausmannite (Mn3O4)-and their application in solid-state textile-based hybrid supercapacitors (SCs). A versatile citric acid-mediated eco-friendly one-pot aqueous precipitation process is proposed for the fabrication of the hybrids. Remarkably, different types of MOs were obtained by simply changing the reaction temperature from room temperature to 100 °C, without any post-thermal treatment. Asymmetric textile SCs were developed using cotton fabrics coated with CNT-N and the hybrids as textile electrodes, and poly(vinyl) alcohol/orthophosphoric acid as the solid-gel electrolyte. The asymmetric devices presented enhanced energy storage performance relative to the symmetric device based on CNT-N and excellent cycling stability (>96%) after 8000 charge/discharge cycles owing to synergistic effects between CNT-N and the MOs, which endowed nonfaradaic and pseudocapacitive features to the SCs. The asymmetric SC based on CNT-N@MnO2 featured 47% higher energy density and comparable power density to the symmetric CNT-N-based device (8.70 W h cm-2 at 309.01 μW cm-2 vs. 5.93 W h cm-2 at 346.58 μW cm-2). The engineered hybrid CNT-N@MO nanomaterials and the eco-friendly citric acid-assisted one-pot precipitation route open promising prospects not only for energy storage, but also for (photo)(electro)catalysis, wastewater treatment, and (bio)sensing.

Integrated free-standing WS2 3D-printed carbon supercapacitor with solid state electrolyte

ABSTRACT There is a huge need for energy storage devices due to the depletion of natural gas and the increasing requirement for portable electronic gadgets. Fused deposition modeling (FDM) 3D-printing has drawn tremendous interest for the fabrication of batteries and supercapacitors (SCs) due to its tabletop manufacturing technique, bespoke design, fast prototyping and user-friendly process. However, there are fewer available conductive filaments for FDM printing that are ideal from an energy storage standpoint. 2D transition metal dichalcogenide WS2 has been discovered to be a favourable material for electrochemical energy storage. As a result, in this work, we modified a carbon electrode that was 3D-printed by incorporating WS2 in order to enhance the capacitive performance of the SC electrode. The WS2-coated 3D-printed carbon electrode (WS2/3D-PCE) exhibits 2.8 times higher specific capacitance than the 3D-printed carbon electrode at 50 mV s−1. A solid-state symmetric supercapacitor (SS-SC) was fabricated with WS2/3D-PCE and polyvinyl alcohol (PVA)/Li2SO4 as gel electrolytes. Such modified 3D-PCE opens up the opportunities to design any custom-shaped electrode with tailored properties and pave a route for future research that will lead to more electrochemical devices for portable electronics.

High-performance asymmetric pseudocapacitor based on NiCo2O4@MnO2 cathode and N-doped graphene anode

The design and fabrication of scalable energy storage systems are crucial for portable applications, demanding advanced materials through large-scale and facile processing. In this report, an asymmetric solid-state pseudocapacitor (ASPC) is assembled using a core–shell NiCo2O4@MnO2 composite and solution-processed nitrogen-doped graphene (N-GP) as the positive and negative electrodes, respectively. With interconnected porous structures, the electrodes based on N-GP and NiCo2O4@MnO2 offer high specific capacitance and rate capability, broad operation voltage, and a binder-free design with no added conductive agent. With these benefits, the ASPC with a PVA-KOH electrolyte exhibits a specific capacitance of 103.3F g−1 at 1 A/g and exceptional energy density of 36.73 Wh kg−1 at a power density of 792 W kg−1. In addition, the specific capacitance retention reaches 90.9 % after 5000 cycles, indicating excellent cycling stability. In the broader context of solid-state supercapacitors based on solution-processed graphene, this ASPC exhibits highly competitive performance, establishing it as a promising candidate for advanced energy storage.

Metal oxide-mixed polymer-based hybrid electrochromic supercapacitor: improved efficiency and dual band switching

The inclusion of charge storage properties in electrochromic devices (ECDs) has gained much interest and has evolved into a promising emerging energy-related field due to multifunctional smart device applications. Here, an organic–inorganic solid-state asymmetric electrochromic supercapacitor device (ESCD) containing nano-CoTiO3-mixed poly-3-hexylthiophene and WO3 as two electrodes has been designed to study electrochromic and supercapacitor properties. The electrochemical properties of CoTiO3 show a pseudocapacitive-type charge storage capability, which has been utilized to enhance the electrochromic performance of the ESCD with additional charge storage ability. The device shows charge storage properties with fast charging and slow discharging, giving very high coulombic efficiency with a specific capacitance of 6.4 mF cm−2 at 0.2 mA cm−2 current density. The device shows excellent electrochromic supercapacitive properties with a color contrast of ∼50% and a short switching time of ∼1 s at a 515 nm wavelength with excellent cyclic stability. The device exhibits the capability to cut near infrared wavelength (700 nm and 850 nm) and has a potential application as a heat filtering device. Thus, the addition of pseudocapacitive-type materials in ECDs enhances the capacitive performance along with electrochromic properties, which makes ECDs more suitable for real life applications.

NiMnCo-LDH in-situ derived from ZIF-67@ZnO as self-supporting electrode for asymmetric supercapacitor device

Metal-organic frameworks have attracted much attention due to their abundant redox sites and tunable characteristics, which are advantageous for energy storage applications. However, the low electrical conductivity, poor physical strength and undesirable capacity seriously hinder their applications. Therefore, designing effective and convenient strategies to build composites with unique structures will be of practical significance. Herein, we successfully generate NMC-LDH/ZnO@CC nanocomposites by growing ortho-hexagonal nickel–cobalt layered double hydroxide (NMC-LDH) nanosheets in-situ on ZIF-67 precursor covering vertical arrays of ZnO nanorods. As a result of the unqiue ortho-hexagonal structure, highly ordered arrangement of active substances and multi-dimensional spaces of the prepared NMC-LDH/ZnO@CC binder-free electrode, its capacitance is as high as 9258 mF cm−2 at a current density of 2 mA cm−2 and the capacitance retention is maintained at 87.5 % after 5000 cycles. Furthermore, in order to explore the practical value of the prepared binder-free electrode, the NMC-LDH/ZnO@CC//AC solid-state asymmetric supercapacitor device is assembled. The energy density of the assembled supercapacitor is 24.6 W h kg−1 at a power density of 170 W kg−1 and 1020 W kg−1 at an energy density of 11.8 W h kg−1. In addition, a versatile instrument for monitoring air humidity, time and ambient temperature in portable environments can be powered by a single ultracapacitor unit for more than 30 min. Overall, this study provides a unique strategy for synthesizing ZIF derivatives with novel morphologies for electrochemical energy storage applications.

One fell swoop strategized bipolar energy device for triboelectric energy harvesting and electrochemical energy storage

Bipolar energy devices are an essential feature due to the enlargement of intelligent and portable electronics in the present decade. In this work, we demonstrated a bipolar energy device using binder-free MnO2 deposited on carbon cloth (CC) by a one-step electrochemical deposition process (EDP), which was employed for solid-state supercapacitor device (SSCD) and another side of CC with Kapton (KP) as TENG device. The efficiency of the bare CC electrode was boosted by growing uniform porous MnO2 nanoballs on the surface of CC, the standalone CC electrode was aided as a positive tribo-layer, and the Kapton film as the negative tribo-layer in the TENG device. The constructed CC-KP TENG device generated a maximum peak power of 15.11 μW, whereas the MnO2 SSCD delivered energy/power density of 37.41 Wh kg−1/10000 W kg−1, respectively. Overall, the results conclude that these types of bipolar energy devices were splendid and could be used in miniatured low-power electronic devices.

Stoichiometrically Optimized Electrochromic Complex [V2O2+ξ(OH)3-ξ] Based Electrode: Prototype Supercapacitor with Multicolor Indicator.

The systematic structure modification of metal oxides is becoming more attractive, and effective strategies for structural tunning are highly desirable for improving their practical color-modulating energy storage performances. Here, the ability of a stoichiometrically tuned oxide-hydroxide complex of porous vanadium oxide, namely [V2O2+ξ(OH)3-ξ]ξ = 0:3 for multifunctional electrochromic supercapacitor application is demonstrated. Theoretically, the pre-optimized oxide complex is synthesized using a simple wet chemical etching technique in its optimized stoichiometry [V2O2+ξ(OH)3-ξ] with ξ=0, providing more electroactive surface sites. The multifunctional electrode shows a high charge storage property of 610Fg-1 at 1Ag-1, as well as good electrochromic properties with high color contrast of 70% and 50% at 428 and 640nm wavelengths, faster switching, and high coloration efficiency. When assembled in a solid-state symmetric electrochromic supercapacitor device, it exhibits an ultrahigh power density of 1066mWcm-2, high energy density of 246mWhcm-2, and high specific capacitance of 290mFcm-2 at 0.2mAcm-2. A prepared prototype device displays red when fully charged, green when half charged, and blue when fully discharged. A clear evidence of optimizing the multifunctional performance of electrochromic supercapacitor by stoichiometrical tuning is presented along with demonstrating a device prototype of a 25cm2 large device for real-life applications.

Harvest pitch-based carbon nanosheets by oxidation and in-situ template strategy for all-solid-state supercapacitors

Transforming coal tar pitch (CTP) into porous carbon nanosheets (PCNS) offers a dual advantage: maximizing the value of CTP while pioneering novel carbon materials. A key challenge in synthesizing pitch-based PCNS lies in the hydrophobic nature and polycondensation of polycyclic aromatic hydrocarbons (PAHs) in CTP, limiting the integration of water-soluble additives and the formation of desired pore structures. In this study, oxidation process, commonly used in preparing pitch-based carbon fibers, was introduced into the synthesis pitch-based PCNS to address the aforementioned challenges. Through oxidization modification, hydrophilic functional groups rich in O, N and P were introduced to PAHs, while macromolecules were partially broken down into smaller aromatic compounds. Following oxidation, the carbon nanosheet structure was successfully achieved through co-carbonization of oxidized CTP and urea, during which the structure-directing agent C3N4 was generated in-situ. Moreover, the efficacy of oxidation modification in the formation of nanosheet structures was assessed by comparing the structures of porous carbon derived from CTP both pre- and post-oxidation. In final, pitch-based PCNS were used in supercapacitors. In three-electrode system, capacitance of PCNS attained 331.3 F/g at 0.5 A/g, and its response speed, capacitance retention rate and ion transfer speed were also excellent. For solid state supercapacitor, its energy density and cycle stability after 10,000 cycles were 8.3 Wh/kg and 92.4%, respectively.

Enhancement of capacitance of waterproof supercapacitors by controlling the thickness of their composite electrodes (graphene/ La0.2Gd1.8Zr2O7: La0.7Sr0.3MnO3)

We report the electrochemical performance of wrinkled/washable graphene-based supercapacitors (SCs). Sustainable graphene electrodes were fabricated by printing graphene microplates on recycled plastics (taken from wasted chip-packets), which provided flexibility to the SCs. The devices made with only graphene electrodes had an energy-density/specific-capacitance of 8.8 Wh kg−1/99.1 F g−1. To enhance the electrochemical properties of the SCs, a mixture of La0.2Gd1.8Zr2O7 (LGZ) and La0.7Sr0.3MnO3 (LSM) perovskites (redox materials) were added on their electrodes. After this, the energy-density/capacitance was enhanced to 53.1 Wh kg−1/596.90 F g−1, that is, an improvement of 503/502%, respectively. Subsequently, the solid state SCs were completely rolled or wrinkled, in consequence, the capacitance decreased by 12.1 and 35.6%, respectively. Even more, the SCs were immersed in water or subjected to washing/drying cycles using a washing-machine and the capacitance barely decreased by ⁓14.2%. Additionally, the thickness of the SC electrodes was varied in the range of 65–400 μm and obtained the maximum capacitance for a thickness of 330 μm. Overall, we demonstrated that incorporating the LGZ/LSM perovskite on the SC electrodes provided extra redox centers, which incremented the capacitance of the devices. The SCs reported here are waterproof and wrinkled, thus, they could provide energy to wearable devices.

Crystallinity transformation engineering of hydrous cobalt nickel phosphate cathodes for hybrid supercapacitor devices: Extrinsic/battery to intercalation type pseudocapacitors

The necessitating strategies of rationalizing nanostructures and crystallinity of electrode material are crucial to developing high-efficiency hybrid energy storage devices. To enhance the energy storage performance of bimetal phosphates, it is important to have a strategic blend of metal cations that can work together synergistically. So, this work describes the scalable preparation of binder-free cobalt nickel phosphates thin film cathodes with cations variation (Co/Ni) via the facile Successive Ionic Layer Adsorption and Reaction (SILAR) process. The distinct roles of cations in cobalt nickel phosphate electrodes resulted in a noteworthy structural transformation from crystalline to amorphous with an increment of Ni content. The change in cations composition influences the pseudocapacitive performance from extrinsic/battery to intercalation type, and cobalt nickel phosphate electrode with an ideal cations composition (Co:Ni) ratio of approximately 1:1 attain the highest specific capacitance (SCs) of 2142 F g−1 (1071 C g−1). To fulfil the demand for high-performance hybrid supercapacitor devices, aqueous (HASC) and solid-state (HSSC) supercapacitors are assembled using optimized cobalt nickel phosphate (S-CNP5) as a cathode. The HASC device represents maximum SCs of 120 F g−1 with specific energy (SE) and specific power (SP) of 42.59 Wh kg−1 and 1600 W kg−1, respectively. The flexible HSSC device shows impressive SCs of 89 F g−1 and SE of 31.54 Wh kg−1 at SP of 2057.14 W kg−1. The practical demonstration of an HSSC device to power a 12-white LED lamp suggests that the SILAR strategy offers commercializing insights for fabricating high-specific capacity hydrous cobalt nickel phosphate thin film cathodes.

Green and Facile Synthesis of Zn3V2O8−Ag@C Composite as an Efficient Electrode for Supercapacitor Application

AbstractThe present study demonstrates the synthesis of ternary composites of zinc vanadate (Zn3V2O8) with silver (Ag) and carbon matrix originated from the Bengal gram bean extract (BGBE) using a facile, economic, and environmentally sustainable rotational chemical bath deposition (R−CBD) method. From the electrochemical studies, it is found that the Zn3V2O8−Ag@C demonstrated improved electrochemical performance with the specific capacitance (Csp) of 380.1 F g−1, energy density (ED) of 52.7 Wh kg−1, with power density (PD) of 882.3 W kg−1 at 3 mA cm−2 current density and good capacitive retention of 89.8 % over 3000 charge–discharge (GCD) cycles, which is remarkably higher than the other electrode materials (Zn3V2O8, Zn3V2O8−Ag, Zn3V2O8@C). The combined merits of conductive silver (Ag) nanoparticle and carbonaceous material from BGBE assist in enhancing the overall electrochemical performance of Zn3V2O8−Ag@C. The Zn3V2O8−Ag@C nanocomposite was used as electrode material for the fabrication of a flexible symmetric solid–state supercapacitor device (SSC). The SSC device delivered a Csp of 69.17 F g−1 with an energy density (ED) of 13.8 Wh kg−1 at a 2 mA cm−2 current density. Moreover, the SSC shows a 90 % capacitive retention over the continuous GCD cycles.

Inorganic-polymer composite electrolytes: basics, fabrications, challenges and future perspectives

Abstract This review covers the basics of, inorganic-polymer composite electrolyte materials that combine inorganic components with polymer matrices to enhance the ionic conductivity and mechanical properties of the electrolyte. These composite electrolytes are commonly employed in solid-state batteries, fuel cells, supercapacitors, and other electrochemical devices. The incorporation of inorganic components, such as ceramic nanoparticles or metal oxides, into a polymer matrix provides several advantages. The inorganic components can improve the overall ionic conductivity by providing pathways for ion transport, reducing the tortuosity of the polymer matrix, and facilitating ion hopping between polymer chains. Additionally, inorganic materials often exhibit higher thermal and chemical stability compared to pure polymers, which can enhance the safety and durability of composite electrolytes. Polymer matrices used in inorganic-polymer composite electrolytes can vary, but common choices include polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), and polyethylene oxide/polypropylene oxide (PEO/PPO) blends. These polymers offer good mechanical flexibility and processability, allowing for the fabrication of thin films or membranes. The fabrication methods for inorganic-polymer composite electrolytes depend on the specific application and desired properties. Common approaches include solution casting, in situ polymerization, melt blending, and electrospinning. During the fabrication process, the inorganic components are typically dispersed or mixed with the polymer matrix, and the resulting composite is processed into the desired form, such as films, membranes, or coatings. The performance of inorganic-polymer composite electrolytes is evaluated based on their ionic conductivity, mechanical strength, electrochemical stability, and compatibility with the electrode materials. Researchers continue to explore various combinations of inorganic and polymer components, as well as optimization strategies, to further improve the overall performance of these composite electrolytes for advanced energy storage and conversion applications.

Polybenzidine-MnO2 nanocomposite on anodized graphite sheet as a novel system for high-performance supercapacitors

In this work, we report for the first time the in-situ synthesis of polybenzidine‑manganese oxide (PB-MnO2) nanocomposite on anodized graphite sheet (AGS). The PB-MnO2/AGS electrode is easily fabricated through the electrochemical anodization of the graphite sheet followed by the polymerization of the benzidine monomer using KMnO4 as an oxidant and MnO2 source. The results of various instrumental analysis confirm that the PB-MnO2 nanocomposite is successfully formed on the AGS without any binder. Cyclic voltammetry (CV), galvanostatic charge/discharge (GCD) and electrochemical impedance spectroscopy (EIS) techniques strongly prove the pseudocapacitive nature of the electrode. The PB-MnO2/AGS electrode shows a high capacitance of 950 mF cm−2 at 0.5 mA cm−2 in 1.0 M H2SO4 solution with a maximum power and energy density of 64.65 mWh cm−2 and 1.75 W cm−2. Solid-state symmetrical supercapacitor device fabricated with PB-MnO2/AGS electrode shows that this device has an excellent specific capacity of about 190.27 mF cm−2 at 0.5 mA cm−2 and maximum power and energy density of 12.375 W cm−2 and 85.625 mWh cm−2. The cyclic life of 87.22 % after 5000 GCD cycles without any ohmic drop indicates that the PB-MnO2/AGS electrode can be a promising candidate for the fabrication of high-performance supercapacitor devices in the future.

Engineered nano-architecture for enhanced energy storage capabilities of MoS2/CNT-heterostructures: A potential supercapacitor electrode

Hydrothermal synthesis was utilized to achieve the direct growth of molybdenum disulphide (MoS2) nanoflakes on carbon nanotubes (CNT). Through this method, MoS2/CNT heterostructures with engineered microstructure have been obtained by suitably optimizing the synthesis conditions. Raman, X-ray photoelectron spectroscopy, and electron microscopy have been utilized to characterize the heterostructure. The present study investigated the influence of varying amounts of CNT and MoS2 within the heterostructure on its electrochemical properties. The optimization of the heterostructure morphology has resulted in enhanced electrochemical performance, with a high specific capacitance of ∼436 F/g at 1 A/g, along with good rate capability. The charge storage mechanism was explained by using Dunn's power law. Further, the MoS2/CNT heterostructure was employed to fabricate a solid-state symmetric supercapacitor. The device exhibited a specific capacitance of ∼164 F/g at 1 A/g, along with good cyclic stability, retaining 96 % of its capacitance after 1000 cycles. Additionally, the device demonstrated high energy and power density values of ∼27 Wh/Kg and 603 W/Kg, respectively. The present study indicates that the MoS2/CNT heterostructure holds great promise as an electrode material for high-performance solid-state supercapacitor devices.

A versatile non-precious metal based electrode material endowed by layer-on-layer structure for methanol oxidation and supercapacitor applications

A high-performance non-noble metal-based electrode is the need of the hour to resolve the challenge of huge energy demand. Energy conversion and storage devices are the two ways to tackle this challenge. In this context, porous and non-noble metal-based electrodes NiCo2O4 (NCO), NiCo2O4/NiO (CNO) and NiCo2O4/NiO/rGO (CNOG) are developed as a bifunctional electrode for supercapacitor and methanol fuel cell applications. The binary composite of NiCo2O4 with NiO increases the redox sites and enhances its electrochemical activity. The low conductivity and problem of aggregation of transition metal oxides are overcome by developing a hybrid nanocomposite of NiCo2O4/NiO with reduced graphene oxide (rGO). The layer-on-layer morphology of CNOG, and the interfacial interactions among NiCo2O4 nanoflakes, NiO nanoparticles and rGO nanosheets increase the specific surface area of the hybrid, which leads to enhanced ion penetration into the active sites. CNOG acts as a potential anode catalyst for methanol oxidation with excellent structural stability. It exhibits a high methanol oxidation current density with low onset potential and faster kinetics. Symmetric supercapacitor CNOG//CNOG delivers specific capacitance of 59.4989 F/g, energy and power density of 6.69 Wh/kg and 698 W/kg respectively at 3 M KOH aqueous electrolyte. The solid-state symmetric supercapacitor (SSSC) using PVA/KOH electrolyte allows broader potential window, thereby outperforming the aqueous electrolyte. The SSSC exhibits specific capacitance of 88.8 F/g, energy and power density 20.84 Wh/kg and 1003 W/kg respectively at the same current density.

Facile chemical synthesis of BaO:MgO nanorods for designing distinctive solid-state asymmetric supercapacitor device with activated carbon

The successive ionic layer adsorption and reaction (SILAR) technique was adapted to produce the interconnected complex network of BaO:MgO nanorods on a flexible stainless-steel (SS) substrate surface. The phase and surface morphology of the BaO:MgO electrode were examined from the X-ray diffraction and scanning electron microscopy measurements, respectively, which endowed electrochemical specific capacitance (SC) of 528.77 F/g at a 2 mV/s scan rate with great rate capability and cycling performance of 94.33 % over 5000 cyclic voltammetry cycles. Fabricated BaO:MgO//AC asymmetric solid-state supercapacitor device, using polyvinyl alcohol and potassium hydroxide gel as an electrolyte, demonstrated distinctive energy storage performance, i.e., a specific capacitance (SC) of 259.07 F/g with an energy density of 57.27 Wh/kg and a power density of 2.34 kW/kg at a current density of 4 mA/cm2. The results demonstrated the facile method for synthesizing a spherical nanorod network of BaO:MgO and made them promising electrode materials for energy storage applications. The use of a solid-state supercapacitor device to illuminate an LED demonstrated the commercial feasibility of both the materials utilized and the design type.