Next-generation Supercapacitors Research Articles

Superior electrochemical performance of neodymium oxide-based Nd2CeMO3 (M = Er, Sm, V) nanostructures for supercapacitor application

• Synthesis of novel Nd 2 CeMO 3 (M = Er, Sm, V) nanostructures via sol–gel route. • Detail analysis by XRD, FTIR, FE-SEM, EDX, IV, CV, GCD, EIS, and ECSA. • High specific capacitance (1319F/g), energy density (225 Wh/kg), and power density (82.4 W/kg). • The boosted electrochemical performance of Nd 2 O 3 by Ce-Er co-doping. • The scalable methodology for next-generation supercapacitor electrode designs. Rare earth neodymium oxide-based Nd 2 CeMO 3 (M = Er, Sm, V) nanostructures were synthesized using a simple and versatile sol–gel method for supercapacitor applications and characterized with various analytical techniques. X-ray diffraction confirmed the effective doping of Ce and the co-doping of Er, Sm, and V in the Nd 2 O 3 matrix having a single hexagonal phase. FTIR further confirmed the formation of neodymium oxide matrix having metal–oxygen-metal bonding vibration. FE-SEM images revealed nanoplates type morphology, and EDX evident the existence of desired elements Nd, Ce, Er, Sm, V, and O in grown samples. IV results showed that the electrical conductivity of co-doped samples was high. The electrochemical measurements such as CV, GCD, EIS, and ECSA exhibited that all the fabricated nanostructures have pseudo-capacitive nature. However, the Er-Ce co-doped Nd 2 O 3 electrode has higher specific capacitance (1319F/g), energy density (225 Wh/kg), and power density (82.4 W/kg), using 1 M KOH electrolyte having 5 A/g current density. Further, the single Ce doped and Sm, V co-doped electrodes have shown higher performance than pure Nd 2 O 3 electrodes. In addition, the Nd 2 CeErO 3 electrode presented superb cycling stability; maintained 96 % initial specific capacitance at the 1000th cycle. The formation of the plate-like morphology in the Nd 2 CeErO 3 electrode provides a larger surface area for ions transportation, also higher conductivity, fast charge transfer (EIS results), and high electrochemical active surface area (ECSA results) are considered responsible for boosting supercapacitive behavior. This superficial and scalable fabrication methodology (co-doping) offers an effective route to boost the electrochemical performance of Nd 2 O 3 and introduce novel electrode designs for next-generation supercapacitor advancements.

Zeolitic imidazolate framework-67 derived Al-Co-S hierarchical sheets bridged by nitrogen-doped graphene: Incorporation of PANI derived carbon nanorods for solid-state asymmetric supercapacitors

Metal sulfides have been widely enticed as battery-type electrodes in supercapacitor devices because of their maximal theoretical capacitance. Nevertheless, their lower conductivity and ion transport kinetics can largely restrict their rate performance, hence the practical usage in fields of demanding high power devices. Therefore, the design of new electrodes with higher energy and power densities remains a highly challenging task. To the best of our knowledge, a novel hierarchical composite of Al-CoS2 on nitrogen-doped graphene (NG) is prepared based on a zeolite imidazole framework using a simple and scalable hydrothermal process. In this hybrid, ultrathin Al-CoS2 nanosheet arrays are vertically orientated on the NG framework to limit self-aggregation, hence increasing the electrical property and cycle stability of composite. It is investigated that the Al/Co feeding ratio plays a crucial role in controlling the obtained hierarchical structure of Al-Co-S sheets and their electrode performance. Also, Al3+ can influence remarkably the morphology and electrochemical property of the resultant graphene composite. An effective synergism is noticed between the redox Al-CoS2 and NG resulting in fast electron transfer and charging-discharging processes. Surprisingly, when the as-developed composite is utilized as a positive electrode at an applied current density of 1 A/g, a specific capacitance of 1915.8 F/g is attained with ultra-long cycle stability (96%, 10,000 cycles) and an excellent retention rate (∼89%). As a consequence, when a solid-state asymmetric supercapacitor (ASC) device is made by combining an Al-CoS2@NG hybrid with a negative electrode made of polyaniline (PANI) derived carbon nanorods (PCNRs), it demonstrates remarkable specific capacitance (188 F/g), energy density (66.9 Wh/kg), and cyclic stability of 92% after 10,000 cycles. This may open the pathway for the application of the next-generation supercapacitors in the future.

Facile hydrothermal synthesis of ZnFe2O4 nanostructures for high-performance supercapacitor application

Nowadays, binary transition metal oxides have attracted wide attention as an electrode material for supercapacitor applications. In this respect, we report a facile and cost-effective hydrothermal route for the synthesis of ZnFe2O4 nanostructures on nickel foam using a binder-free approach. The as-synthesized ZnFe2O4 nanostructures were characterised to study the structural, morphological and electrochemical properties. When utilized as an electrode for supercapacitor, ZnFe2O4 delivered superior specific capacitance of 552 F/g at a scan rate of 5 mV/s with a long term cyclic stability for 1000 cycles. This excellent electrochemical performance ZnFe2O4 electrode material suggests its potential use for next-generation supercapacitors.

Constructing a hollow core-shell structure of RuO2 wrapped by hierarchical porous carbon shell with Ru NPs loading for supercapacitor

Hollow core-shell structure nanomaterials have been broadly used in energy storage, catalysis, reactor, and other fields due to their unique characteristics, including the synergy between different materials, a large specific surface area, small density, large charge carrying capacity and so on. However, their synthesis processes were mostly complicated, and few researches reported one-step encapsulation of different valence states of precious metals in carbon-based materials. Hence, a novel hollow core-shell nanostructure electrode material, RuO2@Ru/HCs, with a lower mass of ruthenium to reduce costs was constructed by one-step hydrothermal method with hard template and co-assembled strategy, consisting of RuO2 core and ruthenium nanoparticles (Ru NPs) in carbon shell. The Ru NPs were uniformly assembled in the carbon layer, which not only improved the electronic conductivity but also provided more active centers to enhance the pseudocapacitance. The RuO2 core further enhanced the material's energy storage capacity. Excellent capacitance storage (318.5 F·g−1 at 0.5 A·g−1), rate performance (64.4%) from 0.5 A·g−1 to 20 A·g−1, and cycling stability (92.3% retention after 5000 cycles) were obtained by adjusting Ru loading to 0.92% (mass). It could be attributed to the wider pore size distribution in the micropores which increased the transfer of electrons and protons. The symmetrical supercapacitor device based on RuO2@Ru/HCs could successfully light up the LED lamp. Therefore, our work verified that interfacial modification of RuO2 and carbon could bring attractive insights into energy density for next-generation supercapacitors.

A facile and environmentally friendly method for preparing supercapacitor electrode carbon-based materials with ultra-long cycling stability

With the demand for next-generation energy storage equipment and industrial applications, the development of carbon-based electrode materials with more comprehensive electrochemical performance and more convenient production process has become a top priority. Here, an N/O co-doped carbon material (Z-700) was prepared by one-step carbonization with 2,6-bis(2-pyrazin-2-yl)− 4-(4-(tetrazol-5-yl)phenyl)pyridine acting as the carbon and nitrogen source. Z-700 is a clastic carbon material with non-uniform size and low specific surface area (4.1 m2/g). However, when assembled into supercapacitors, Z-700 has excellent comprehensive capacitance performance, such as a specific capacitance of 218.6F/g (0.5 A/g), a specific energy of 43.7 Wh/kg, a cycling stability of more than 100,000 cycles, and a charge/discharge rate less than 2 s (10 A/g). In addition, the assembled symmetric supercapacitor has excellent capacitance performance. This high-performance carbon-based electrode material has great application potential in industry and next-generation supercapacitors.

Efficient Activation Engineering from the Inside Out toward Hierarchically Porous Carbon Framework as Electrode Materials for Supercapacitors

Over the past decades, the KOH-involved activation has been established to obtain porous carbons for supercapacitors. However, from the perspective of economic efficiency and practicability, it is significant yet urgent to explore a simple way to minimize the use of corrosive KOH for efficient fabrication of supercapacitive carbons without sacrificing electrochemical properties. Herein, we first develop a simple yet efficient activation strategy from the inside out, where the KOH activator (∼40 wt %) is uniformly located in poly(vinyl alcohol) (PVA) hydrogel as the precursor, to fabricate a three-dimensional hierarchically porous carbon framework (denoted as PC-K). Compared with the porous carbon obtained by physically mixing KOH and PVA, the PC-K with hydrophilic surface is endowed with an even larger specific surface area, a higher pore volume, and higher-content mesopores, ensuring abundant active sites and rapid ion/electron transport. Such attractive merits result in encouraging electrochemical capacitances of the PC-K electrode with a loading of 5 mg cm–2 both in symmetric devices and three-electrode systems with 6 M KOH and 1 M H2SO4 as aqueous electrolytes, which is particularly better than other carbons synthesized with more KOH addition. More significantly, the contribution here provides a guiding methodology for the feasible commercial synthesis of advanced porous carbons toward next-generation supercapacitors.

Electrically Conductive Photoluminescent Porphyrin Phosphonate Metal–Organic Frameworks

AbstractHerein, the design and synthesis of a highly photoluminescent and electrically conductive metal–organic framework [Zn{Cu‐p‐H6TPPA}]⋅2 [(CH3)2NH] (designated as GTUB3), which is constructed using the 5,10,15,20‐tetrakis [p‐phenylphosphonic acid] porphyrin (p‐H8TPPA) organic linker, is reported. The bandgap of GTUB3 is measured to be 1.45 and 1.48 eV using diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy, respectively. The PL decay measurement yields a charge carrier lifetime of 40.6 ns. Impedance and DC measurements yield average electrical conductivities of 0.03 and 4 S m−1, respectively, making GTUB3 a rare example of an electrically conductive 3D metal–organic framework. Thermogravimetric analysis reveals that the organic components of GTUB3 are stable up to 400 °C. Finally, its specific surface area and pore volume are calculated to be 622 m2 g−1 and 0.43 cm3 g−1, respectively, using grand canonical Monte Carlo. Owing to its porosity and high electrical conductivity, GTUB3 may be used as a low‐cost electrode material in next generation of supercapacitors, while its low bandgap and high photoluminescence make it a promising material for optoelectronic applications.

Fabrication of MoO3 Nanowires/MXene@CC hybrid as highly conductive and flexible electrode for next-generation supercapacitors applications

A facile hydrothermal and ultrasonication method used to synthesize the MoO3 nanowires (NWs) intercalated MXene composite. MoO3/MXene nanocomposite was fabricated on carbon cloth (CC) to prepare the MoO3/MXene@CC electrode. Intercalation of MoO3 NWs in MXene layers prevented the collapse of Al etched MXene sheets and enhanced the conductive channels in ultimate nanostructures. When applied for electrochemical measurements, MoO3/MXene@CC significantly improved specific capacity. For pristine MoO3@CC, the specific capacitance was calculated as 466.7 F/g (at 5 mV/s) and 442 F/g (at 1 A/g) from cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) data, respectively. Meanwhile, MoO3/MXene@CC showed a high specific capacitance of 783.4 F/g at 5 mV/s and 775 F/g at 1 A/g under the CV and GCD measurements. Electrochemical impedance spectroscopy (EIS) data evaluated the resistivity performance of MoO3/MXene@CC. The calculated equivalent series resistance (RES) and charge transfer resistance (RCT) values for MoO3/MXene@CC were 5.4 Ω and 31.3 Ω, respectively. Moreover, MoO3/MXene@CC showed excellent cyclic stability with 96.4% retention of its initial specific capacitance even after 6000 cycles. Results suggest that the prepared MoO3/MXene@CC hybrid can be used as an efficient electrode material for electrochemical energy storage applications.

A Sustainable Approach for Preparing Porous Carbon Spheres Derived from Kraft Lignin and Sodium Hydroxide as Highly Packed Thin Film Electrode Materials.

A green synthetic strategy to design biomass-derived porous carbon electrode materials with precisely tailored structure and morphology has always been a challenging goal because these materials can fulfill the demands of next-generation supercapacitors and other electrochemical devices. Potassium hydroxide (KOH) is extensively utilized as an activator since it can produce porous carbon with high specific surface area and well-developed porous channels. The exploitation of sodium hydroxide (NaOH) as an activating agent is less referenced in the literature, although it offers some advantages over KOH in terms of low cost, less corrosiveness, and simple handling procedure, all of which are appealing particularly from an industrial viewpoint. The motivation for this present study is to fabricate porous carbon spheres in a sustainable manner via a spray drying approach followed by a carbonization process, using Kraft lignin as the carbon precursor and NaOH as an alternative activation agent instead of the high-cost and high-corrosive KOH for the first time. The structure of carbon particles can be accurately transitioned from a compact to hollow structure, and the surface textural properties can be easily tuned by altering the NaOH concentration. The obtained porous carbon spheres were applied as highly packed thin film electrode materials for supercapacitor devices. The specific capacitance value of porous carbon spheres with a highly compact structure (high packing density) is 66.5 F g-1, which is higher than that of commercial activated carbon and other biomass-derived carbon. This work provides a green processing for producing low-cost and environment-friendly porous carbon spheres from abundant Kraft lignin and important insight for selecting NaOH as an activator to tailor the morphology and structure, which represents an economical and sustainable approach for energy storage devices.

Nanostructured CoFe2O4 and their nanohybrid with rGO as an efficient electrode for next-generation supercapacitor

Herein, we adopted the hydrothermal method to produce a novel, flexible, and self-supporting electrode based on nanostructured CoFe2O4 and rGO nanohybrid for supercapacitor applications. Hydrothermally prepared CoFe2O4/rGO material was characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman study, Fourier transform infrared spectroscopy (FT-IR), current-voltage (I–V) tests, and Thermogravimetric analysis (TGA) to examine the shape, particle size, structure, composition, electronic conductivity, and % rGO content. We performed Galvanostatic charge-discharge (GCD), impedance study, and cyclic voltammetry (CV) tests in 3 M KOH electrolyte to examine the electrochemical characteristics of the nanohybrid-based working electrode. A self-supported CoFe2O4/rGO@CC electrode containing 20% graphene had a high specific capacitance of 1245 Fg-1 at 01 Ag-1. Almost 83.8% of specific capacitance was retained even at 12 Ag-1, revealing the excellent rate performance of the as-prepared electrode. Furthermore, the nanohybrid electrode lost just 8.8% of its specific capacity after 5500 GCD trails, demonstrating its higher activity rate. The impedance measurements revealed that the addition of rGO contents boosted the nanohybrid's inherent conductivity, due to which the rate of the Faradaic redox reaction also increased. The observed enhancement in electrochemical properties of the CoFe2O4/rGO@CC electrode is due to its improved conductivity, nanoarchitecture, self-supporting design, flexible current collector, and hybrid composition. Our CoFe2O4/rGO@CC electrode has a lot of potential for use in the emerging supercapacitor because of its integrated features.

Framework materials for supercapacitors

Abstract Framework materials, including metal–organic framework materials (MOFs), Prussian blue/Prussian blue analogs (PB/PBAs), and covalent framework materials (COFs), are promising candidates for fabricating electrodes for use in electrochemical devices, especially supercapacitors. Supercapacitors have been widely investigated over the past decade. Active materials as electrode materials are vital to the development of the next generation of supercapacitors. Therefore, designing and fabricating novel electrode materials endowed with superior specific capacitance, perfect cycling stabilities, and distinguished power/energy density are crucial. In this review, we focus on framework materials – MOFs, PB/PBAs, and COFs – and report electrode materials based on their pristine forms, derivatives, and composites for supercapacitors. Recent advances and potential applications of framework materials in supercapacitors are also discussed. Furthermore, we discuss the opportunities and challenges for the future direction of supercapacitors based on framework materials.

Asymmetric supercapacitors based on porous MnMoS4 nanosheets-anchored carbon nanofiber and N, S-doped carbon nanofiber electrodes

Electrode materials with high electrochemical activity and a favorable morphology are highly desired for improving the energy density of supercapacitors. A ternary metal sulfide with higher electrochemical activity and capacity than mono-metal sulfides offers immense promise as an energy storage material. In the present investigation, an advanced flexible hybrid electrode material composed of porous manganese molybdenum sulfide (MnMoS4) nanosheets supported on flexible carbon nanofiber (CNF) mat has been prepared via three sequential steps: (i) electrospinning, (ii) stabilization/carbonization, and (iii) hydrothermal reaction. Advantages from the rich electrochemical redox properties of MnMoS4 and the 3D interconnected network architecture of porous CNF mat, a large specific capacitance of 2187.5 F/g (at 1 A/g), and a good capacity retention ability (>87%) were achieved for the MnMoS4 @CNF hybrid electrode. In addition, asymmetric supercapacitor (ASC) devices were assembled by utilizing two different binder-free electrodes, i.e., MnMoS4 @CNF mat as the positive electrode and N, S doped CNF mat as the negative electrode, and evaluated their capacitive performances in two different electrolytes, i.e., KOH and Na2SO4. As-assembled ASC with 1 M Na2SO4 electrolyte delivered a high energy density of 72.5 Wh kg−1 and a power density of 2.7 kW kg−1 together with a capacity retention of 93.5% after 5000 cycles. The overall outcome of this investigation indicates that the binder-free nanostructured MnMoS4 @CNF hybrid mat has great potential for the development of next-generation supercapacitor devices.

Cobalt-based metal oxide coated with ultrathin ALD-MoS2 as an electrode material for supercapacitors

A novel approach of preparing a composite supercapacitor electrode consisting of ternary metal oxide nanostructure decorated with transition metal sulfide is presented. High-surface area NiCo2O4 nano-sheets grown on Ni-foam are coated with an ultrathin layer of MoS2 by atomic layer deposition (ALD) and the hybrid structure reveals superior electrochemical performance. The composite is thoroughly studied with several characterizations like XRD, Raman, XPS, SEM and TEM. A comparative study with MoS2 coated Co3O4 electrodes not only ensures the advantage of the more conducting sulfide layer in enhancing the supercapacitor performance significantly but also establishes the superiority of the ternary oxide (NiCo2O4) for this application. The thinner and well-connected nano-sheets of NiCo2O4 provides the more interface between the electrode and the electrolyte whereas an optimal thickness of MoS2 helps to maximize the performance of the device. The high areal capacitance (2445 mF cm−2), enhanced rate capability of the optimized NiCo2O4-MoS2 composite is therefore ascribed to the synergistic effect of high-surface area of the oxide nano-sheets and better electronic conductivity of the sulfide. The current study thus opens a route to combine the conventional hydrothermal synthesis of ternary oxide nanostructures with ALD grown layered transition metal dichalcogenides to achieve a superior electrode for next-generation supercapacitor.

Fabrication of a flower-like Cu(OH)2 nanoarchitecture and its composite with CNTs for use as a supercapacitor electrode

Fabrication of nanostructured electro-active materials with an ordered organization improved the overall performance of supercapacitor devices (SCDs). In this spirit, we developed Cu(OH)2 nano-flakes that were statistically ordered to resemble flowers. To increase the specific capacitance and kinetics of the electroactive sample, we employed ultra-sonication to fabricate a Cu(OH)2 nanocomposite with conductive and capacitive carbon nanotubes (CNTs). The textural and functional group analyses of the wet-chemically produced samples were completed using the XRD and FTIR techniques. I–V, FESEM, and EDX measurements Analyses of pure Cu(OH)2 and its CNT-based nanocomposites were conducted to evaluate the materials' electrical conductivity, morphology, and chemistry, respectively. The electrochemical characteristics of the as-prepared material's electrodes were investigated, and the CNT-based nanocomposite electrode demonstrated an outstanding specific capacity (Csp) and a promising rate of performance. Our CNT-based nanocomposite had a Cs of 733 Fg-1 at 1 Ag-1 and dropped 8.7% after 4 × 103 cycles. The higher electrochemical properties of the nanocomposite are governed by the nano-flakes-like architecture of the Cu (OH)2 and the more conductive CNT matrix. According to the obtained findings, our manufactured Cu(OH)2/CNT based electrode has great promise for practical applications in next-generation supercapacitor, which are known to be very efficient.

Role of Redox Additive Modified Electrolytes in Making Na-Ion Supercapacitors a Competitive Energy Storage Device

The study shows the importance of moving towards hollow nanostructures for obtaining next-generation supercapacitors and batteries. Amongst various sodium-based electrode materials, NaFePO4 is one of the most promising cathodic material because of its high electrochemical potential, structural, and thermal stability. To use this material in high performance Na-ion based energy storage device, it is imperative to combine it with a suitably optimized carbon structures and a redox additive modified electrolyte. This strategy is unequivocally established in the paper. On addition of redox additive, the performance can be improved by 50%. This makes the Na-ion supercapacitor competitive with other metal ion based systems. the performance by as high as 50%. This makes the Na-ion supercapacitors competitive with other metal ion based systems.

Recent developments in polypyrrole/manganese oxide-based nanocomposites for thin film electrodes in supercapacitors: a minireview.

This review article highlights the recent developments in the synthesis and electrochemical performance of polypyrrole/manganese oxide thin-film electrodes synthesized by various chemical methods for supercapacitor applications. In the class of conducting polymers for electrode applications, polypyrrole (Ppy) is considered an important polymer due to its low cost and abundance. Ppy's polymeric composition and structural properties, however, pose stability concerns and have a drawback of a short life cycle over long-term charge-discharge processes, limiting its potential for industrial and commercial utilization. Recently, manganese oxide (MnO2) has been actively explored as a supercapacitor electrode material due to its low cost, high theoretical specific capacitance and abundance. Ppy/MnO2 thin film electrodes revealed high specific capacitance and stability, making them excellent candidates for next-generation supercapacitor electrode materials.

Direct carbonization of sodium lignosulfonate through self-template strategies for the synthesis of porous carbons toward supercapacitor applications

Commercial supercapacitors rely on expensive porous carbon electrode materials. Therefore, it is essential to search for low-cost porous carbon electrode materials for next-generation supercapacitors. In this work, we produced lignin-derived porous carbon from alkalized sodium lignosulfonate. The carboxyl and phenolic hydroxyl are bonded with potassium ions in alkalized sodium lignosulfonate molecules. As a result, the introduced potassium ions on carboxyl and phenolic hydroxyl groups and sodium ions on sulfonate groups act as the porogens for preparing porous carbons. The alkalized sodium lignosulfonate is pyrolysis carbonized to produce porous carbon materials for asymmetric and symmetric supercapacitors. Developed pores inside the lignin-derived porous carbons are generated from the self-template role of the generated inorganic metal carbonates and metal sulfates. The introduced alkali metal ions in alkalized sodium lignosulfonate play extra roles of templates. Our work made a new paradigm shift that lignin could be transformed into porous carbon electrodes through self-template methodologies for future supercapacitor applications.

Self-templating synthesis of hierarchical porous carbon with multi-heteroatom co-doping from tea waste for high-performance supercapacitor

Exploring porous carbon (PC)-based materials from low-cost, renewable precursors has always been a challenging objective, since they meet the demands of next-generation supercapacitors and electrochemical devices. Herein, hierarchical multi-heteroatoms co-doped PC (MHPC) materials are successfully achieved by the carbonization and activation of tea waste that used as the self-template. The natural structure of the tea leaves combined with the activation strategy favor the formation of special hierarchical MHPC materials, which are constructed by ultrathin MHPC nanosheets. In addition, the heteroatomic doped carbon derived from organic compounds in tea leaves can act as an ideal precursor to fabricate the resultant heteroatomic functionalized carbon nanosheets. Such heteroatoms content of carbon nanosheets are adjustable by altering pyrolysis condition to effectively enhance the electrochemical performance of PC. After activation by KOH, the as-prepared MHPC, especially MHPC-3 (weight ratio of KOH/pre-carbonized tea waste is 3:1) has a superior supercapacitance of up to 170 and 132 F g−1 at current density of 0.5 and 10 A g−1 in KOH electrolyte, and an excellent capacitance retention of ∼94.8% over 14,000 cycles at 3 A g−1. The result reported here provides valuable guidelines of high-performance energy storge devices from natural sources at the industrial scale.

Systematic investigation on the electrochemical performance of Cd-doped ZnO as electrode material for energy storage devices

Many researchers have focused on enhancing the performance of energy storage devices to satisfy the growing demand for energy worldwide. This paper is an attempt to tune the capacitive behavior of pristine ZnO through its Cd doping via the simple synthetic method. To examine their electrochemical behavior, samples of modified ZnO with three concentrations of the dopant (Cd) (3, 6, and 9 wt% Cd-doped ZnO) were prepared. The as-prepared products were characterized by spectral as well as analytical techniques. The 9 wt% Cd-doped ZnO electrode, featuring fast electrolyte permeation and rich electrochemically active sites, showed an excellent specific capacitance (Csp) of 627 Fg−1 at a current density of 1 Ag-1 and substantial cycling stability of 93.3% even after 5000 GCD cycles. The addition of dopants enhanced electrical conductivity due to effective charge transfer and electron transport. The unique nanorod-like structure was found to be responsible for the exceptional electrochemical properties of the samples. Until now, there were no reports on Cd-doped ZnO nanorods as electrode material for supercapacitors. This work provides a simple and cost-effective method for fabricating a 9 wt% Cd-doped ZnO electrode, which may open up new possibilities for efficient electrodes in next-generation supercapacitors.

Design principle of MoS2/C heterostructure to enhance the quantum capacitance for supercapacitor application

1T Molybdenum disulfide (1T-MoS2) has been widely studied experimentally as an electrode for supercapacitors due to its excellent electrical and electrochemical properties. Whereas the capacitance value in MoS2 is limited due to the lower density of electrons near the Fermi level, and unable to fulfill the demand of industry i.e. quantum capacitance preferably higher than 300 μF/cm2. Here, we investigated the performance of 2H, 1T, and 1T′ phases of MoS2 in its pristine form and heterostructures with carbon-based structures as an electrode in the supercapacitors using density functional theory. Specifically, we reported that the underneath carbon nanotube (CNT) is responsible for the structural phase transition from 1T to 1T′ phase of MoS2 monolayer in 1T′-MoS2/CNT heterostructure. This is the main reason for a large density of states near Fermi level of 1T′-MoS2/CNT that exhibits high quantum capacitance (CQ) of 500 μF/cm2 at a potential of 0.6 V. Also, we observed that the nitrogen doping and defects in the underneath carbon surface amplify the CQ of heterostructure for a wider range of electrode potential. Therefore, the 1T′-MoS2/N doped CNT can be explored as an electrode for next-generation supercapacitors.