Excellent Supercapacitive Performance Research Articles

High-performance binder-free flower-like (Ni0.66Co0.3Mn0.04)2(OH)2(CO3) array synthesized using ascorbic acid for supercapacitor applications

A binder-free electrode material composed of nickel-rich cobalt-manganese hydroxyl carbonate (Ni0.66Co0.3Mn0.04)2(OH)2(CO3) (NCMHC) flowers was grown directly on nickel foam in a facile hydrothermal reactor using l-ascorbic acid as a morphology-directing green reducing agent and carbonate source. The electrode material NCMHC exhibited an excellent specific capacitance of 4635 F g−1 (1854 C g−1) at a current density of 1 A g−1. Furthermore, the hybrid supercapacitor, which consisted of a NCMHC positive electrode and an activated carbon negative electrode, exhibited a good specific capacitance of 144.4 F g−1, high energy of 51.4 Wh kg−1, and high power density of 8000 W kg−1 as well as remarkable charge-discharge cycling stability (capacity retention) of 96% after 10,000 cycles, outperforming previously reported nickel-cobalt-manganese-based electrode materials. This exceptional capacitive performance of NCMHC was attributed to the synergistic combination of ternary metal ions with the optimal oxidation states to obtain ideal electrical conductivity and highly exposed active sites due to the array of a unique flower petal-like morphology with short ion-diffusion paths for efficient energy storage. The facile synthesis and excellent supercapacitive performance highlights the potential of the advanced electrode materials for the next generation hybrid supercapacitors.

Ultrathin Carbon Shell Entrapped Metal Co/Coo for High-Performance Electrochemical Supercapacitor

Nowdays, a series of transition-metal oxides (TMOs) such as MnO2, MoO3, Co3O4, CoO, and NiO have been widely studied as supercapacitive materials because of their low cost and high theoretical specific capacitance. As a low-oxidized cobalt compound, to date, CoO has been successfully applied as Li-ion battery anodes and showed satisfactory Li-ion storage capacities. The theoretical specific capacitance of CoO reaches 4292 F g-1. This value is higher than that of NiO (2573 F g-1), MnO2 (1370 F g-1), and Co3O4 (3560 F g-1). However, the practical application of CoO is severely hindered by its easily oxidized character (CoO is oxidized to Co3O4 after exposure in air) and the poor electrical conductivity (intrinsic semiconducting or insulating property). The poor conductivity is also one of the main reasons that limit the application of other TMOs in constructing high performance supercapacitors. To overcome these challgenges, we report a metallic Co doped CoO-based energy storage material by elaborately tailoring both the electrical conductivity and material configuration. The cobalt-doped CoO (denoted as CoO/Co) heterostructure is designed to improve the electrical conductivity. The metallic Co, acting as a current “expressway,” effectively improves the electrical conductivity of the composite, thus accelerating the electron transport. Additonally, an ultrathin layer of amorphous carbon is generated on the surface of heterostructure to prevent further oxidation of CoO/Co. This amorphous carbon shell serves as a surface stabilizer to hinder further oxidation of Co/CoO, thus sustaining good stability of supercapacitor. As a result, the as-prepared composite exhibits an excellent supercapacitor performance of 2165.7 F g-1 at a scanning rate of 10 mV s-1. An asymmetric supercapacitor cell fabricated using the c and active carbon achieves a maximum energy density of 146.3 Wh kg-1 at a power density of 1800 W kg-1, and the maximum of 27000 W kg-1 can be obtained with a remaining energy density of 63.0 Wh kg−1. Even more importantly, such a composite also showed a good cycling ability and improved long-term storage stability. As this supercapacitive material can be prepared with a high yield by a facial low-cost route, it is highly expected that it could be a promising material for electrochemical energy storage in practical applications.

Template free and facile microwave-assisted synthesis method to prepare mesoporous copper sulfide nanosheets for high-performance hybrid supercapacitor

Development of high energy density supercapacitor has stimulated a great deal of research over the past decade. The electrochemical performance of a hybrid supercapacitor is strongly affected by the structural morphology and the surface area of its electrode material. Herein, we report mesoporous nanosheet structures composed of copper sulfide which are synthesized by an instant and simple microwave-assisted method. The electrode material based on CuS nanosheets consist of mesoporous structures (pore diameter < 25 nm) and a large surface area (∼169m2g−1). This high surface area nanosheets structure provides more active sites for electrochemical reactions and short ion/electron diffusion path for excellent super-capacitive performance. The mesoporous CuS nanosheets electrode exhibits a high specific capacitance of 2535 Fg−1 at a current density of 1 Ag−1 in an aqueous electrolyte (2MKOH) with excellent rate capability. The fabricated device for practical application possesses an excellent energy density of 63.2 Whkg−1 at a high power density of 400W kg−1, the good specific capacitance of 177 Fg−1 at 0.5A g−1 and high cycling stability at 10 Ag−1 (88% retention after 10000 cycles).This work not only demonstrates the promising potential of the mesoporous CuS electrodes for application in the high-performance hybrid asymmetric capacitor but also shows a path to synthesize different transition metal sulfide architecture by using microwave radiation method.

Polyaniline nanoparticle coated graphene oxide composite nanoflakes for bifunctional multicolor electrochromic and supercapacitor applications

Graphene oxide (GO)/polyaniline (PANI) composite nanoflakes were fabricated by chemical oxidative polymerization of aniline onto GO nanoflakes. The electrochromic properties and the electrochemical capacitive behaviors of the GO/PANI composite nanoflake film were investigated. The GO/PANI nanocomposite film exhibits excellent electrochromic and supercapacitive performances. In comparison with neat PANI film, the GO/PANI composite nanoflake film shows larger optical modulation, faster response speed, larger coloration efficiency and better cycling stability. Moreover, an areal capacitance of (137 mF/cm2) is obtained for GO/PANI nanoflake film at a scanning rate of 5 mV/s, higher than that of neat PANI film (36 mF/cm2). The GO/PANI composite nanoflake film also shows enhanced electrochromic and supercapacitive durability. And the electrochromism also could be utilized as an indicator for the capacitance. The high-performance GO/PANI nanocomposite film shows promising features for multifunctional devices combining energy storage and electrochromism.

Dumbbell-shaped mixed bimetallic-oxides decorated on carbon-fiber textile for high-performance flexible symmetric solid-state pseudocapacitors

A novel dumbbell-shaped mixed bimetallic oxide (Ni1.71Co1.29O4) is directly anchored on activated carbon fiber textile (CFT) for high-performance flexible symmetric supercapacitors (NCO@CFT-FSSCs). The as-fabricated NCO@CFT-FSSC exhibits excellent supercapacitive performance by achieving the high-specific capacity of 200 mAh/g at 1 A/g with excellent rate capability of 71% at 10-folded high current density. The NCO@CFT-FSSC showed outstanding cycling stability over 5000 cycles by retaining 94.78% capacity at a current density of 12.5 A/g. Moreover, the NCO@CFT-FSSC possesses good flexible performance and maintained 89.64% capacity over 500 bending cycles. Therefore, the achieved fascinating charge storage capabilities along with excellent flexibility ensure that Ni1.71Co1.29O4 being a potential material for high-performance supercapacitors.

Flexible fiber-shaped supercapacitors with high energy density based on self-twisted graphene fibers

In this research, self-twisted graphene fibers are successfully prepared by a simple method. The assembled self-twisted graphene fiber exhibits excellent mechanical properties, the elongation is up to 26.3% and the tensile intensity reaches up to 244.8 MPa, which is higher than that of the previously reported graphene fibers. Based on the remarkable mechanical properties of self-twisted graphene fibers, the flexible fiber-shaped supercapacitors are fabricated. The fiber-shaped supercapacitor demonstrates outstanding flexibility, even at the knotted state the capacitance is very stable. Furthermore, the fiber-shaped supercapacitor exhibits excellent supercapacitive performance with high energy density (25.5 mWh cm−3) and long-term cycling stability, retaining 91% of the capacitance over 10,000 cycles. The outstanding performances of flexible fiber-shaped supercapacitors indicate the self-twisted graphene fibers have promising applications in portable and flexible energy storage devices.

Further Thermal Reduction of Reduced Graphene Oxide Aerogel with Excellent Rate Performance for Supercapacitors

Preparation of pure three-dimensional graphene (3DG) with high rate performance for supercapacitors is critical for fast rate charge/discharge. Here, 3DG was prepared via thermal annealing of freeze-dried reduced graphene oxide (RGO) hydrogel under inert gas protection. The formed 3DG as an electrode material for supercapacitors revealed a specific capacitance of 115 F·g−1 at a current density of 1 A·g−1, and a high capacitance retention of 70% as current density increased to 40 A·g−1. The excellent rate capability was mainly attributed to the reserved porous structure and higher electrical conductivity for 3DG after thermal reduction than its RGO hydrogel precursor.

Eco-friendly synthesis of porous graphene and its utilization as high performance supercapacitor electrode material

The successful application of porous graphene (PG) is hindered due to the lack of efficient and cost-effective method for its synthesis. Herein, we report a facile and eco-friendly method to produce PG through a low temperature solvothermal method. The structural and morphological characteristics of PG samples were investigated thoroughly. The as synthesized material is found to be a few layers thick (∼4–6 layers) with a surface area of 420 m2 g−1 and consisting of hierarchical pores on the surface of the sheets. A high specific capacitance of 666 F g−1 was obtained at a scan rate of 5 mV s−1, apart from longer cyclic stability with 87% retention of initial capacitance value after 10000 cycles for the PG 28 sample. The fabricated supercapacitor displayed an energy density of 26.3 Wh kg−1 and power density of 6120 W kg−1. Density functional theory calculations were also carried out to qualitatively support the enhanced capacitance by providing theoretical insight from electronic structure and density of states of PG. These results open a new avenue for greener synthesis of high-quality PG using environmentally friendly solvents, without the use of toxic chemicals, for excellent supercapacitor performance.

Preparation of partially-cladding NiCo-LDH/Mn3O4 composite by electrodeposition route and its excellent supercapacitor performance

A NiCo-LDH/Mn3O4 composite is synthesized on nickel foam substrate though a two-step electrodepositon process. The growth of Mn3O4 nanoneedles on NiCo-LDH nanosheets can greatly reduce the transport pathway of electrons and ions. Meanwhile, abundant active sites for redox reactions are generated and the structural endurance together with chemical stability of material is improved, thus strongly enhancing the electrochemical characteristics. When measured in a typical three-electrode cell, NiCo-LDH/Mn3O4 demonstrates a high specific capacity of 1.86 C cm−2 (1034.33 C g−1) at the current density of 1 mA cm−2, a superior rate capability of maintaining 76.88% at 20 mA cm−2 and 17.98% capacity loss after 5000 cycles. In addition, an all-solid-state hybrid supercapacitor device (HSC) is fabricated with NiCo-LDH/Mn3O4 as the cathode and commercially-used active carbon as the anode, which delivers a superior energy density of 57.03 Wh kg−1 at the power density of 765.8 W kg−1 and maintains 20.98 Wh kg−1 even when the power density increases to 9681.6 W kg−1. Therefore, the satisfactory electrochemical property enables NiCo-LDH/Mn3O4 to become a prospective electrode material in energy storage field.

Direct Ink Writing of Adjustable Electrochemical Energy Storage Device with High Gravimetric Energy Densities

Abstract3D printing graphene aerogel with periodic microlattices has great prospects for various practical applications due to their low density, large surface area, high porosity, excellent electrical conductivity, good elasticity, and designed lattice structures. However, the low specific capacitance limits their development in energy storage fields due to the stacking of graphene. Therefore, constructing a graphene‐based 2D materials hybridization aerogel that consists of the pseduocapacitive substance and graphene material is necessary for enhancing electrochemical performance. Herein, 3D printing periodic graphene‐based composite hybrid aerogel microlattices (HAMs) are reported via 3D printing direct ink writing technology. The rich porous structure, high electrical conductivity, and highly interconnected networks of the HAMs aid electron and ion transport, further enabling excellent capacitive performance for supercapacitors. An asymmetric supercapacitor device is assembled by two different 4‐mm‐thick electrodes, which can yield high gravimetric specific capacitance (Cg) of 149.71 F g−1 at a current density of 0.5 A g−1 and gravimetric energy density (Eg) of 52.64 Wh kg−1, and retains a capacitance retention of 95.5% after 10 000 cycles. This work provides a general strategy for designing the graphene‐based mixed‐dimensional hybrid architectures, which can be utilized in energy storage fields.

Formation of ultra-small Mn3O4 nanoparticles trapped in nanochannels of hollow carbon spheres by nanoconfinement with excellent supercapacitor performance

Abstract Ultra-small Mn3O4 nanoparticles are formed in the shell of hollow carbon spheres (HCS Mn3O4) via nanoconfinement growth. The HCS with special cylindrical channels (about 2 nm) provides the limited space for growth of Mn3O4 nanoparticles and serves as a conductive substrate in electrochemical applications. The unique hollow structure shortens the distance for electrolytes to access Mn3O4 during the charging/discharging process. In the hybrid HCS-Mn3O4 structure, the interaction between Mn3O4 nanoparticles and HCS was enhanced resulting in good conductivity and electrochemical properties. The two-electrode supercapacitor cell composed of HCS-Mn3O4 shows high capacitance and energy density. The highest specific capacitance of 430 F g−1 is achieved at a scanning rate of 1 mV s−1 and the largest energy density of 13.5 Wh kg−1 is observed at a power density of 0.3 kW kg−1 by HCS-Mn3O4-5 with 93.15% retention after 10,000 cycles in 5 M LiCl. Symmetric HCS-Mn3O4-5//HCS-Mn3O4-5 shows higher energy density of 22.6 Wh kg−1 at a power density of 0.4 kW kg−1 and power density of 3.3 kW kg−1 at an energy density of 16 Wh kg−1 with 1 M Li2SO4. The technique to prepare the HCS-Mn3O4 hybrid materials is simple and readily scalable to satisfy industrial demand.

A high-temperature phosphorization for synthesis of core-shell Ni-NixPy@C nanocomposite-immobilized sponge-like P-doped porous carbon with excellent supercapacitance performance

To effectively enhance the overall electrochemical performance of supercapacitors, a high-temperature phosphorization strategy was developed to fabricate core-shell Ni-NixPy@C nanocomposite-immobilized sponge-like P-doped porous carbon (Ni-NixPy@C/P-HPC). The Ni-NixPy@C/P-HPC was successfully constructed by a cross-linking process and subsequent high-temperature calcination. During the pyrolysis process in N2 multiple steps, including phosphating metal ions to Ni-NixPy nanoparticles, forming core-shell Ni-NixPy@C nanocomposites, doping P element into carbon skeleton and immobilizing core-shell Ni-NixPy@C nanocomposites onto porous carbon, were achieved simultaneously. The Ni-NixPy@C/P-HPC was studied using various characterization techniques. The results revealed that the obtained material integrated the advantages of interconnected P-doped framework (fast ion transport), nickel and nickel phosphide species (high theoretical specific capacitance), and graphene-like shell (excellent electrical conductivity and effective protection for activate sites). Therefore, the as-prepared hybrid delivered the outstanding electrochemical performance with ultrahigh specific capacity of up to 1275 F g−1 at 1 A g−1 and an excellent cycling stability with 92.5% capacity retention after 5000 cycles. Besides, the asymmetric supercapacitor using Ni-NixPy@C/P-HPC-900 and activated carbon as the anode and cathode materials exhibited a high energy density of 49.4 W h kg−1 at 250 W kg−1, and remained as high as 30.6 W h kg−1 even at 5000 W kg−1. Our research will open up a new way to synthesize transition metal phosphide@carbon composites with excellent electrochemical properties.

Novel chemical route for CeO2/MWCNTs composite towards highly bendable solid-state supercapacitor device

Electrode materials having high capacitance with outstanding stability are the critical issues for the development of flexible supercapacitors (SCs), which have recently received increasing attention. To meet these demands, coating of CeO2 nanoparticles have been performed onto MWCNTs by using facile chemical bath deposition (CBD) method. The formed CeO2/MWCNTs nanocomposite exhibits excellent electrochemical specific capacitance of 1215.7 F/g with 92.3% remarkable cyclic stability at 10000 cycles. Light-weight flexible symmetric solid-state supercapacitor (FSSC) device have been engineered by sandwiching PVA-LiClO4 gel between two CeO2/MWCNTs electrodes which exhibit an excellent supercapacitive performance owing to the integration of pseudocapacitive CeO2 nanoparticles onto electrochemical double layer capacitance (EDLC) behaved MWCNTs complex web-like structure. Remarkable specific capacitance of 486.5 F/g with much higher energy density of 85.7 Wh/kg shows the inherent potential of the fabricated device. Moreover, the low internal resistance adds exceptional stability along with unperturbed behavior even under high mechanical stress which can explore its applicability towards high-performance flexible supercapacitor for advanced portable electronic devices.

An efficient electrode material for high performance solid-state hybrid supercapacitors based on a Cu/CuO/porous carbon nanofiber/TiO2 hybrid composite.

A Cu/CuO/porous carbon nanofiber/TiO2 (Cu/CuO/PCNF/TiO2) composite uniformly covered with TiO2 nanoparticles was synthesized by electrospinning and a simple hydrothermal technique. The synthesized composite exhibits a unique morphology and excellent supercapacitive performance, including both electric double layer and pseudo-capacitance behavior. Electrochemical measurements were performed by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The highest specific capacitance value of 530 F g−1 at a current density of 1.5 A g−1 was obtained for the Cu/CuO/PCNF/TiO2 composite electrode in a three-electrode configuration. The solid-state hybrid supercapacitor (SSHSC) fabricated based on this composite exhibits a high specific capacitance value of 330 F g−1 at a current density of 1 A g−1 with 78.8% capacitance retention for up to 10,000 cycles. At the same time, a high energy density of 45.83 Wh kg−1 at a power density of 1.27 kW kg−1 was also realized. The developed electrode material provides new insight into ways to enhance the electrochemical properties of solid-state supercapacitors, based on the synergistic effect of porous carbon nanofibers, metal and metal oxide nanoparticles, which together open up new opportunities for energy storage and conversion applications.

One-step synthesis of 3D-interconnected porous carbons derived from ephedra herb using calcium chloride and urea as co-activation for high-performance supercapacitors

In this article, we propose a one-step strategy, utilizing calcium chloride and urea as co-activation, to synthesize 3D-interconnected porous carbon (3D-IPC) from ephedra herb. The 3D-IPC-based electrode displays excellent electrochemical performance for supercapacitors, such as a high specific capacitance of 240 F g−1 at 0.5 A g−1 and good rate capability. Especially, the symmetric supercapacitor assembled based on the 3D-IPC electrode material presents considerable energy density of 12.6 W h kg−1 at a power density 225 W kg−1, and 6.0 W h kg−1 at 9000 W kg−1 in 0.5 M Li2SO4 electrolyte. On the one hand, the urea was utilized as both activating agent for microporous pore formation in pyrolysis and nitrogen source to nitrogen doped into the 3D-IPC framework, as well as ideal synchronous carbonization and graphitization. On the other hand, ephedra herb collected from the Gobi Desert is reused as a high-value carbon material.

Novel dealloying-fabricated NiCo2S4 nanoparticles with excellent cycling performance for supercapacitors

In this work, NiCo2S4 nanoparticles for supercapacitors are successfully synthesized with a top-down strategy, using a novel dealloying method with an ion exchange reaction. The surface morphology and x-ray diffraction investigations demonstrated that NiCo2S4 nanoparticles are interconnected by ligaments of the synthesized sample. The dealloyed NiCo2S4 shows an enhanced electrochemical performance of about 1132.5 F g−1 at 0.5 A g−1; kinetic analysis implies a surface-controlled contribution from NiCo2S4 (53.86% capacitive contributions). Notably, the NiCo2S4//AC (active carbon) device displays a comparatively high energy density (22.83 Wh kg−1), maximum power density (1327.1 W kg−1) and superior cycling performance (capacitance retention of 108% after 30 000 cycles).

Synthesis of porous δ-MnO2 nanosheets and their supercapacitor performance

In this work, a hydrothermal method has been exploited to synthesize porous δ-MnO2 nanosheets. The influence of hydrothermal temperature on the synthesis of δ-MnO2 has been investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption-desorption isotherms, transmission electron microscopy (TEM) and electrochemical methods. The results show that the pure δ-MnO2 appears at the hydrothermal temperature from 130 to 170°C, and the hydrothermal temperature has a great influence on the morphology and BET surface area of as-prepared samples. The δ-MnO2 prepared at 150°C delivers high specific capacitances of 411Fg−1 at a scan rate of 5mVs−1 and 332.7Fg−1 at a current density of 0.5A g−1. The excellent supercapacitor performance is attributed to the porous nanosheets structure, which brings a large specific surface area, increases the active sites, and shortens the ion diffusion distance in δ-MnO2 electrodes. It is suggested that the optimal synthesizing temperature is 150°C in order to obtain pure δ-MnO2 with good electrochemical performance by hydrothermal method.

MnO2 Nanorods Embedded Reduced Graphene Oxide Nanocomposite with Ultrahigh Specific Capacitance and Excellent Cyclic Stability for High Performance Supercapacitors

Excellent cycling stability along with a high specific capacitance of the electrode material is the primary requirement for supercapacitor (SC) in recent years. Exceptionally simple and cost-effective solution process is employed for the first time to prepare [Formula: see text]-MnO2/rGO composites, in which KMnO4 content varies from (2[Formula: see text]mg, 4[Formula: see text]mg, 6[Formula: see text]mg and 8[Formula: see text]mg). The morphological analysis showed that [Formula: see text]-MnO2/rGO composites possess nanorod like morphology and were fully covered with rGO sheet. Among all composites, the sample with 6[Formula: see text]mg content of KMnO4 denoted as [Formula: see text]-MnO2/rGO composite (S–3) showed excellent supercapacitive performance with a specific capacitance of 720[Formula: see text]F/g at a current density of 4 A g[Formula: see text] with excellent cycling stability of 93% after 2000 cycles. Furthermore, these nanocomposites showed excellent supercapacitive properties with specific capacitances of 720–498 F/g at the current density of 4 A g[Formula: see text] with cycling stabilities of 71%, 68% and 60%, respectively.

Self-Templating Synthesis of 3D Hollow Tubular Porous Carbon Derived from Straw Cellulose Waste with Excellent Performance for Supercapacitors.

A three-dimensional hollow tubular porous carbon (SCPC) was prepared from straw cellulose waste through a self-templating method combined with NaOH activation. Straw cellulose acts both as carbon source and structural template. The obtained SCPC exhibits a 3D hierarchical porous network structure. SCPC has a high specific surface area, a high mesoporosity ratio, and a low resistivity, which make it display excellent electrochemical performance for supercapacitors. SCPC showed a high specific capacitance of 312.57 F g-1 in 6 m KOH at 0.5 A g-1 , an excellent rate performance of 281.32 F g-1 even at 15 A g-1 , and an outstanding cyclic stability of 92.93 % capacitance retention after 20 000 cycles at 1 A g-1 . SCPC-based supercapacitors can deliver an energy density of 8.67 Wh kg-1 at a power density of 3.50 kW kg-1 in 6 m KOH and an energy density of 28.56 Wh kg-1 at a power density of 14.09 kW kg-1 in 1 m Et4 NBF4 /PC, which demonstrates the possibility of applying SCPC in supercapacitors. This research not only offers a facile and sustainable method for the preparation of hierarchical porous carbon for electrochemical energy storage devices but also provides a highly efficient method for the utilization of biomass waste.

Biotemplate derived three dimensional nitrogen doped graphene@MnO2 as bifunctional material for supercapacitor and oxygen reduction reaction catalyst

Natural diatomite with abundant pores was used as a biotemplate for the massive production of three-dimensional (3D) porous graphene by chemical vapor deposition method. Subsequent template removal and nitrogen doping treatment yield nitrogen doped 3D graphene with preserved shape and complex internal features of the diatomite. After further deposition with MnO2 nanosheets, the N-doped 3D graphene@MnO2 (N-G@MnO2) hybrid exhibited excellent supercapacitor and good oxygen reduction reaction (ORR) performance. Accordingly, the porous N-G@MnO2 electrode exhibited a high specific capacitance (411.5 F g−1) and a good cycling performance (88.3% capacitance retention after 4000 charge/discharge cycling test). When tested in a two-electrode configuration, N-G@MnO2 achieved a wide potential window up to 1.8 V with a high energy density of 46.1 Wh kg−1. Furthermore, the as-prepared N-G@MnO2 showed good performance in oxygen reduction reaction, which is comparable to those of commercially available Pt/C electrode. The enhanced capacitive and electrocatalytic properties and stability is due to the synergistic interactions between the porous 3D graphene and MnO2 nanosheets. The results indicate that the 3D N-G@MnO2 could be useful for supercapacitor and ORR catalyst.