Tin disulphide/nitrogen-doped reduced graphene oxide/polyaniline ternary nanocomposites with ultra-high capacitance properties for high rate performance supercapacitor

In this work, tin disulfide/nitrogen-doped reduced graphene oxide/polyaniline ternary composites are synthesized via in situ polymerization of aniline monomers on the surface of tin disulfide/nitrogen-doped reduced graphene oxide nanosheets binary composites with different loading of the conducting polymers. The tin disulfide/nitrogen-doped reduced graphene oxide/polyaniline ternary composites electrode shows much higher specific capacitance, specific energy and specific power values than those of pure polyaniline and tin disulfide/nitrogen-doped reduced graphene oxide binary composites. The highest specific capacitance, specific energy and specific power values of 1021.67 F g⁻¹, 69.53 W h kg⁻¹ and 575.46 W kg⁻¹ are observed for 60% polyaniline deposited onto tin disulfide/nitrogen-doped reduced graphene oxide composites at a current density of 1 A g⁻¹. The above composites also show superior cyclic stability and 78% of the specific capacitance can be maintained after 5000 galvanostatic charge–discharge cycles. The good charge-storage properties of tin disulfide/nitrogen-doped reduced graphene oxide/polyaniline ternary composites is ascribed to the organic–inorganic synergistic effect. This study paves the way to consider tin disulfide/nitrogen-doped reduced graphene oxide/polyaniline ternary composites as excellent electrode materials for energy storage applications.

In this work, SnS₂/NRGO/PANI ternary composites are synthesized via in situ polymerization of aniline monomers on the surface of SnS₂/NRGO nanosheets binary composites with different loading of the conducting polymers.     

One-pot mechanochemical exfoliation of graphite and in situ polymerization of aniline for the production of graphene/polyaniline composites for high-performance supercapacitors

Graphene/polyaniline composites have attracted considerable attention as high-performance supercapacitor electrode materials; however, there are still numerous challenges for their practical applications, such as the complex preparation process, high cost, and disequilibrium between energy density and power density. Herein, we report an efficient method to produce graphene/polyaniline composites via a one-pot ball-milling process, in which aniline molecules act as both the intercalator for the exfoliation of graphite and the monomer for mechanochemical polymerization into polyaniline clusters on the in situ exfoliated graphene sheets. The graphene/polyaniline composite electrode delivered a large specific capacitance of 886 F g⁻¹ at 5 mV s⁻¹ with a high retention of 73.4% at 100 mV s⁻¹. The high capacitance and rate capability of the graphene/polyaniline composite can contribute to the fast electron/ion transfer and dominantly capacitive contribution because of the synergistic effects between the conductive graphene and pseudocapacitive polyaniline. In addition, a high energy density of 40.9 W h kg⁻¹ was achieved by the graphene/polyaniline-based symmetric supercapacitor at a power density of 0.25 kW kg⁻¹, and the supercapacitor also maintained 89.1% of the initial capacitance over 10 000 cycles.

Efficient ball-milling production of graphene/polyaniline composites as supercapacitor electrodes with enhanced capacitive contribution, rate capability, and specific capacitance.     

Ultrafine MnO2 nanowires grown on RGO-coated carbon cloth as a binder-free and flexible supercapacitor electrode with high performance

Reduced graphene oxide coated carbon cloth has been used as a substrate for the growth of ultrafine MnO₂ nanowires (CC/RGO/MnO₂), forming binder-free and flexible supercapacitor electrode materials. The experimental results indicate that a maximum area-specific capacitance of 506.8 mF cm⁻² was gained from the CC/RGO/MnO₂ electrode at the current density of 0.128 mA cm⁻². Furthermore, the electrode exhibits excellent cycling stability (98.6% specific capacitance was still retained after 10 000 galvanostatic charge–discharge (GCD) tests when the current density was 1.28 mA cm⁻²). What''s more, the area-specific capacitance of the CC/RGO/MnO₂ electrode was hardly changed, when the electrode was operated under bending mechanical conditions. In addition, the charge storage performance and mechanism of the MnO₂ nanostructures was discussed.

Reduced graphene oxide coated carbon cloth has been used as a substrate for the growth of ultrafine MnO₂ nanowires (CC/RGO/MnO₂), forming binder-free and flexible supercapacitor electrode materials.     

Investigation on the role of different conductive polymers in supercapacitors based on a zinc sulfide/reduced graphene oxide/conductive polymer ternary composite electrode

Conductive polymers, such as polyaniline (PANI), polypyrrole (PPy), polythiophene (PTh) and poly 3,4-ethylenedioxythiophene (PEDOT), play an important role in the application of pseudocapacitors. It is necessary to explore the effects of different conductive polymers in electrode composites. Herein, we prepare zinc sulfide/reduced graphene oxide (ZnS/RGO) by the hydrothermal method, and conductive polymers (PANI, PPy, PTh and PEDOT) doped with the same mass ratio (polymer to 70 wt%) via in situ polymerization on the surface of ZnS/RGO composite. For the supercapacitor application, the ZnS/RGO/PANI ternary electrode composite possesses the best capacitance performance and cycle stability out of all of the polymer-coated ZnS/RGO composites. In the three-electrode system, the discharge specific capacitance and cycle stability of ZnS/RGO/PANI are 1045.3 F g⁻¹ and 160% at 1 A g⁻¹ after 1000 loops. In a two-electrode symmetric system, the discharge specific capacitance and cycle stability of ZnS/RGO/PANI are 722.0 F g⁻¹ and 76.1% at 1 A g⁻¹ after 1000 loops, and the greatest energy and power density of the ZnS/RGO/PANI electrode are 349.7 W h kg⁻¹ and 18.0 kW kg⁻¹. In addition, conductive polymers can effectively improve the voltage range of the electrode composites in 6 M KOH electrolyte for the two-electrode system. The discharge voltage ∼1.6 V makes them promising electrode materials for supercapacitors.

Conductive polymers, such as polyaniline (PANI), polypyrrole (PPy), polythiophene (PTh) and poly 3,4-ethylenedioxythiophene (PEDOT), play an important role in the application of pseudocapacitors.     

Synthesis of 1,3-dicarbonyl-functionalized reduced graphene oxide/MnO2 composites and their electrochemical properties as supercapacitors

A novel 1,3-dicarbonyl-functionalized reduced graphene oxide (rDGO) was prepared by N-(4-aminophenyl)-3-oxobutanamide interacting with the epoxy and carboxyl groups of graphene oxide. The high-performance composite supercapacitor electrode material based on MnO₂ nanoparticles deposited onto the rDGO sheet (DGM) was fabricated by a hydrothermal method. The morphology and microstructure of the composites were characterized by field-emission scanning electron microscopy, transmission electron microscopy, Raman microscopy and X-ray photoelectron spectroscopy. The obtained results indicated that MnO₂ was successfully deposited on rDGO surfaces. The formed composite electrode materials exhibit excellent electrochemical properties. A specific capacitance of 267.4 F g⁻¹ was obtained at a current density of 0.5 A g⁻¹ in 1 mol L⁻¹ H₂SO₄, while maintaining high cycling stability with 97.7% of its initial capacitance after 1000 cycles at a current density of 3 A g⁻¹. These encouraging results are useful for potential energy storage device applications in high-performance supercapacitors.

A novel functionalized reduced graphene oxide and MnO₂ composite was prepared as a supercapacitor electrode material.     

Facile preparation of flexible binder-free graphene electrodes for high-performance supercapacitors

A facile two-step strategy to prepare flexible graphene electrodes has been developed for supercapacitors using thermal reduction of graphene oxide (GO) and thermally reduced graphene oxide (TRGO) composite films. The tunable porous structure of the GO/TRGO film provided channels to release the high pressure generated by CO₂ gas. The graphene electrode obtained from reduced-GO/TRGO (1 : 1 in mass ratio) film showed great flexibility and high film density (0.52 g cm⁻³). Using the EMI-BF₄ electrolyte with a working voltage of 3.7 V, the as-fabricated free-standing reduced-GO/TRGO (1 : 1) film achieved a great gravimetric capacitance of 180 F g⁻¹ (delivering a gravimetric energy density of 85.6 W h kg⁻¹), a volumetric capacitance of 94 F cm⁻³ (delivering a volumetric energy density of 44.7 W h L⁻¹), and a 92% retention after 10 000 charge/discharge cycles. In addition, the solid state flexible supercapacitor with the free-standing reduced-GO/TRGO (1 : 1) film as the electrodes and the EMI-BF₄/poly (vinylidene fluoride hexafluopropylene) (PVDF-HFP) gel as the electrolyte also demonstrated a high gravimetric capacitance of 146 F g⁻¹ with excellent mechanical flexibility, bending stability, and electrochemical stability. The strategy developed in this study provides great potentials for the synthesis of flexible graphene electrodes for supercapacitors.

A supercapacitor electrode is developed with a free-standing graphene film by a facile two-step strategy. The graphene electrode achieved a gravimetric capacitance of 180 F g⁻¹ and a volumetric capacitance of 94 F cm⁻³.     

Highly flexible reduced graphene oxide@polypyrrole–polyethylene glycol foam for supercapacitors

A flexible and free-standing 3D reduced graphene oxide@polypyrrole–polyethylene glycol (RGO@PPy–PEG) foam was developed for wearable supercapacitors. The device was fabricated sequentially, beginning with the electrodeposition of PPy in the presence of a PEG–borate on a sacrificial Ni foam template, followed by a subsequent GO wrapping and chemical reduction process. The 3D RGO@PPy–PEG foam electrode showed excellent electrochemical properties with a large specific capacitance of 415 F g⁻¹ and excellent long-term stability (96% capacitance retention after 8000 charge–discharge cycles) in a three electrode configuration. An assembled (two-electrode configuration) symmetric supercapacitor using RGO@PPy–PEG electrodes exhibited a remarkable specific capacitance of 1019 mF cm⁻² at 2 mV s⁻¹ and 95% capacitance retention over 4000 cycles. The device exhibits extraordinary mechanical flexibility and showed negligable capacitance loss during or after 1000 bending cycles, highlighting its great potential in wearable energy devices.

A flexible and free-standing 3D reduced graphene oxide@polypyrrole–polyethylene glycol (RGO@PPy–PEG) foam was developed for wearable supercapacitors.     

One-step cathodic electrodeposition of a cobalt hydroxide–graphene nanocomposite and its use as a high performance supercapacitor electrode material

In this study, Co(OH)₂-reduced graphene oxide has been synthesized using a simple and rapid one-step cathodic electrodeposition method in a two electrode system at a constant current density on a stainless steel plate, and then characterized as a supercapacitive material on Ni foam. The composites were characterized by FT-IR, X-ray diffraction, scanning electron microscopy, and cyclic voltammetry using a galvanostatic charge/discharge test. The feeding ratios of the initial components for electrodeposition had a significant effect on the structure and electrochemical performance of the Co(OH)₂-reduced graphene oxide composite. The results show that the 1 : 4 (w/w) ratio of GO : CoCl₂·6H₂O was optimum and produced an intertwined composite structure with impressive supercapacitive behavior. The specific capacitance of the composite was measured to be 734 F g⁻¹ at a current density of 1 A g⁻¹. Its rate capability was ∼78% at 20 A g⁻¹ and its capacitance retention was 95% after 1000 cycles of charge–discharge. Moreover, its average energy density and power density were calculated to be 60.6 W h kg⁻¹ and 3208 W kg⁻¹, respectively. This green synthesis method enables a rapid and low-cost route for the large scale production of Co(OH)₂-reduced graphene oxide nanocomposite as an efficient supercapacitor material.

In this study, Co(OH)₂-reduced graphene oxide has been synthesized using a simple and rapid one-step cathodic electrodeposition method in a two electrode system at a constant current density on a stainless steel plate, and then characterized as a supercapacitive material on Ni foam.     

Template-assisted synthesis of NiCoO2 nanocages/reduced graphene oxide composites as high-performance electrodes for supercapacitors

Here we reported a coordinating etching and precipitating method to synthesize a complex binary metal oxides hollow cubic structure. A novel NiCoO₂/rGO composite with a structure of NiCoO₂ nanocages anchored on layers of reduced graphene oxide (rGO) were synthesized via a simple template-assisted method and the electrochemical performance was investigated by cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy tests as a faradaic electrode for supercapacitors at a graphene weight ratio of 1 wt% (1%). When used as electrode materials for electrochemical capacitors, the NiCoO₂/rGO composites achieved a specific capacity of 1375 F g⁻¹ at the current density of 1 A g⁻¹ and maintained 742 F g⁻¹ at 10 A g⁻¹. After 3000 cycles, the supercapacitor based on these nanocage structures shows long-term cycling performance with a high capacity of 778 F g⁻¹ at a current density of 1 A g⁻¹. These outstanding electrochemical performances are primarily attributed to the special morphological structure and the combination of mixed transition metal oxides and rGO, which not only maintains a high electrical conductivity for the overall electrode but also prevents the aggregation and volume expansion of electrochemical materials during the cycling processes.

Here we reported a coordinating etching and precipitating method to synthesize a complex binary metal oxides hollow cubic structure.     

High electrochemical performance of ink solution based on manganese cobalt sulfide/reduced graphene oxide nano-composites for supercapacitor electrode materials

Large scale supercapacitor electrodes were prepared by 3D-printing directly on a graphite paper substrate from ink solution containing manganese cobalt sulfide/reduced graphene oxide (MCS/rGO) nanocomposites. The MCS/rGO composite solution was synthesized through the dispersion of MCS NPs and rGO in dimethylformamide (DMF) solvent at room temperature. Their morphology and composition were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive X-ray diffraction (EDS). The role of rGO on decreasing charge transfer resistance and enhancing ion exchange was discussed. The MCS/rGO electrode exhibits an excellent specific capacitance of 3812.5 F g⁻¹ at 2 A g⁻¹ and it maintains 1780.8 F g⁻¹ at a high current density of 50 A g⁻¹. The cycling stability of the electrodes reveals capacitance retention of over 92% after 22 000 cycles at 50 A g⁻¹.

Large scale supercapacitor electrodes were prepared by 3D-printing directly on a graphite paper substrate from ink solution containing manganese cobalt sulfide/reduced graphene oxide (MCS/rGO) nanocomposites.     

Ice-interface assisted large-scale preparation of polypyrrole/graphene oxide films for all-solid-state supercapacitors

In this paper, large-scale, self-standing polypyrrole/graphene oxide (PPy/GO) nanocomposite films were prepared by an environmentally friendly and easy-to-operate confined polymerization method, and were also assembled as electrode materials for symmetric all-solid-state supercapacitors. In this paper, large-scale, self-standing polypyrrole/graphene oxide (PPy/GO) nanocomposite films were prepared by an environmentally friendly and easy-to-operate confined polymerization method, and were also assembled as electrode materials for symmetric all-solid-state supercapacitors. The morphology, chemical structure and electrochemical property were characterized by field emission scanning electron microscope (FESEM), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), galvanostatic charge–discharge (GCD), and electrochemical impedance spectroscopy (EIS), respectively. The lamellar structure of GO and both strong interaction with ice and pyrrole could promote polymerization of pyrrole and improve the compactness of the film. With the aid of GO, the conjugation length of PPy increased, the resistance of the material decreased, and the electrochemical energy storage of the composite film was significantly enhanced. In the case of 2.5 wt% GO, the prepared PPy/GO nanocomposite supercapacitor exhibited a high area specific capacitance of 97.3 mF cm⁻² at 1 mA cm⁻². Furthermore, the PPy/GO film supercapacitor also showed excellent cycling stability and good flexibility.

A confirned polymerization method was employed to fabricate self-standing PPy/GO film for all-solid-state supercapacitor.     

N/O co-enriched graphene hydrogels as high-performance electrodes for aqueous symmetric supercapacitors

In this study, an easy one-pot hydrothermal strategy was used to prepare N/O co-enriched graphene hydrogels (NOGHs) using graphene oxide (GO) solution and n-propylamine as a reactant. The n-propylamine can be used not only as a reductant, nitrogen dopant and structure regulator, but also as a spacer to inhibit the agglomeration of graphene sheets. Benefiting from the synergistic effect between the heteroatoms (N, O), 3D porous structures and high specific surface area, the as-prepared NOGH samples present excellent electrochemical properties. Remarkably, the NOGH-140 based binder-free symmetric supercapacitor shows a high specific capacitance of 268.1 F g⁻¹ at the current density of 0.3 A g⁻¹ and retains 222.5 F g⁻¹ (82.9% of its initial value) at 10.0 A g⁻¹ in 6 M KOH electrolyte. Furthermore, the assembled device also displays a notable energy density (9.3 W h kg⁻¹) and outstanding cycling performance (1.8% increase of its initial specific capacitance after 10 000 cycles at 10 A g⁻¹). The simple preparation method and excellent electrochemical properties indicate that NOGHs can be used as electrode materials for commercial supercapacitors.

N/O co-enriched graphene hydrogel based supercapacitors were assembled. Owing to the synergistic effect between the heteroatoms (N, O), 3D porous structures and high specific surface area, they present excellent electrochemical properties.     

Boron/nitrogen co-doped carbon synthesized from waterborne polyurethane and graphene oxide composite for supercapacitors

We report B/N co-doped carbon materials synthesized by an efficient and easy one-step carbonization method with ferric catalyst treatment from a precursor with boric acid treatment after the formation of the composite between waterborne polyurethane (WPU) and graphene oxide (GO). The nitrogen content was improved with the introduction of numerous melamine in the synthetic process of WPU. In addition, WPU possessed a repetitive basic unit urethane bond (–NHCOO); thus, nitrogen heteroatom could be efficiently introduced into the WPU/GO composite from WPU as a nitrogen-rich carbon. In addition, the specific surface area was increased by the boric acid treatment and washing process. The ferric catalyst treatment could prevent the formation of inert B–N bonds. Thus, the synthesized B/N co-doped carbon materials exhibited high specific capacitance (330 F g⁻¹ at 0.5 A g⁻¹), superior rate performance, and excellent cycling stability. Furthermore, the assembled symmetric supercapacitor displayed a good energy density (7.9 W h kg⁻¹ at 505 W kg⁻¹) and a good capacitance retention of about 89.9% after 5000 charge–discharge cycles in 6 M KOH electrolyte. Therefore, the as-prepared B/N co-doped carbon materials show a promising future in supercapacitor application.

We report B/N co-doped carbon materials synthesized by a carbonization method with ferric catalyst treatment from a precursor with boric acid treatment after the formation of the composite between waterborne polyurethane and graphene oxide.     

Facile synthesis of NF/ZnOx and NF/CoOx nanostructures for high performance supercapacitor electrode materials

NF/ZnOx nanocone and NF/CoOx nanoparticle electrode materials were fabricated on a nickel foam surface using a simple chemical bath deposition approach and assessed as an electrode material for high-performance supercapacitors (SCs). The electrochemical properties of the NF/ZnOx and NF/CoOx electrodes were examined by cyclic voltammetry, galvanostatic charge–discharge tests, and electrochemical impedance spectroscopy. The fabricated NF/ZnOx and NF/CoOx SCs devices exhibited a good specific capacitance of 2437 and 2142 F g⁻¹ at a current density of 20 mA g⁻¹, respectively, in a three electrode system. Furthermore, the NF/ZnOx and NF/CoOx electrode materials showed acceptable long cycle-life stability with 97.8% and 95.8% specific capacitance retention after 3000 cycles at a current density of 22 mA g⁻¹ in a 2 M aqueous KOH solution. Furthermore, the NF/ZnOx and NF/CoOx SCs showed a high energy density of 54.15 W h kg⁻¹ and 47.6 W h kg⁻¹ at a power density of 499.8 W kg⁻¹ and 571.2 W kg⁻¹, respectively, with maximum operating voltage of 0.5 V. Overall, NF/ZnOx and NF/CoOx electrode materials are promising electrodes for electrochemical energy storage applications.

NF/ZnOx nanocone and NF/CoOx nanoparticle electrode materials were fabricated on a nickel foam surface using a simple chemical bath deposition approach and assessed as an electrode material for high-performance supercapacitors.     

Porous carbon derived from metal–organic framework@graphene quantum dots as electrode materials for supercapacitors and lithium-ion batteries

The C@GQD composite was prepared by the combination of metal–organic framework (ZIF-8)-derived porous carbon and graphene quantum dots (GQDs) by a simple method. The resulting composite has a high specific surface area of 668 m² g⁻¹ and involves numerous micro- and mesopores. As a supercapacitor electrode, the material showed an excellent double-layer capacitance and a high capacity retention of 130 F g⁻¹ at 2 A g⁻¹. The excellent long-term stability was observed even after ∼10 000 charge–discharge cycles. Moreover, the composite as an anode material for a lithium-ion battery exhibited a good reversible capacity and outstanding cycle stability (493 mA h g⁻¹ at 100 mA g⁻¹ after 200 cycles). The synergistic effect of a MOF-derived porous carbon and GQDs was responsible for the improvement of electrochemical properties.

The C@GQD composite was prepared by the combination of metal–organic framework (ZIF-8)-derived porous carbon and graphene quantum dots (GQDs) by a simple method.     

Preparation of cobalt sulfide@reduced graphene oxide nanocomposites with outstanding electrochemical behavior for lithium-ion batteries

Cobalt sulfide@reduced graphene oxide composites were prepared through a simple solvothermal method. The cobalt sulfide@reduced graphene oxide composites are composed of cobalt sulfide nanoparticles uniformly attached on both sides of reduced graphene oxide. Some favorable electrochemical performances in specific capacity, cycling performance, and rate capability are achieved using the porous nanocomposites as an anode for lithium-ion batteries. In a half-cell, it exhibits a high specific capacity of 1253.9 mA h g⁻¹ at 500 mA g⁻¹ after 100 cycles. A full cell consists of the cobalt sulfide@reduced graphene oxide nanocomposite anode and a commercial LiCoO₂ cathode, and is able to hold a high capacity of 574.7 mA h g⁻¹ at 200 mA g⁻¹ after 200 cycles. The reduced graphene oxide plays a key role in enhancing the electrical conductivity of the electrode materials; and it effectively prevents the cobalt sulfide nanoparticles from dropping off the electrode and buffers the volume variation during the discharge–charge process. The cobalt sulfide@reduced graphene oxide nanocomposites present great potential to be a promising anode material for lithium-ion batteries.

Cobalt sulfide@reduced graphene oxide nanocomposites obtained through a dipping and hydrothermal process, exhibit ascendant lithium-ion storage properties.     

Microstructure and electrochemical performance of 3D hierarchical porous graphene/polyaniline composites

Porous graphene materials show outstanding performance in energy storage field due to their unique microstructure and properties. To construct 3D hierarchical porous graphene and combine with conductive polyaniline is an effective way to realize high energy density and good cycling stability. The interlamellar macroporous structure of 3D graphene was constructed by polystyrene (PS) microspheres and nickel foam as double templates. The mesoporous structure was etched in 3D macroporous graphene sheets by potassium hydroxide (KOH) chemical activation. And 3D hierarchical porous graphene (3D-hpGr) composited with polyaniline (PANI) by in situ chemical oxidative polymerization to obtain 3D-hpGr/PANI composites. The effect of the introduction of 3D-hpGr on microstructure, morphology and electrochemical performance of the composites was investigated. PANI nanowire arrays successfully decorate the surface of the 3D-hpGr sheets when the amount of 3D-hpGr reaches 40% (wt%). The specific capacitance of 3D-hpGr/PANI40 reaches 573 F g⁻¹ at 0.5 A g⁻¹, much higher than that of pure PANI (419 F g⁻¹). The retention ratio of 3D-hpGr/PANI40 retains 84% of its initial specific capacitance after 1000 cycles at 1.0 A g⁻¹, and the cycling stability of all composites is higher than that of pure PANI (69%). The potential drop of 3D-hpGr/PANI composites decreases from 0.339 V to 0.139 V, and the energy density increases consequently. The energy density of 3D-hpGr/PANI40 reaches 31.2 W h kg⁻¹ at the power density of 0.709 kW kg⁻¹.

3D hierarchical porous graphene/polyaniline composites show outstanding performance in energy storage field due to their unique microstructure and properties.     

Effects of Cu2+/Zn2+ on the electrochemical performance of polyacrylamide hydrogels as advanced flexible electrode materials

Previously, solid-state electrode materials have been utilized for the fabrication of energy storage devices; however, their application is impeded by their brittle nature and ion mobility problems. To address issues faced in such a modern era where energy saving and utility is of prior importance, a novel approach has been applied for the preparation of electrode materials based on polyacrylamide hydrogels embedded with reduced graphene oxide and transition metals, namely, Cu²⁺ and Zn²⁺. The fabricated hydrogel exhibits high electrical properties and flexibility that make it a favorable candidate to be used in energy storage devices, where both elastic and electrical properties are desired. For the first time, a multi-cross-linked polyacrylamide hydrogel was constructed and compared in the presence of other electro-active materials such as reduced graphene oxide and transition metals. Polyacrylamide hydrogels embedded with reduced graphene oxide demonstrate excellent electrical properties such as specific capacitance, least impedance, low phase angle shift and AC conductivity of 22.92 F g⁻¹, 2115 Ω, 2.88° and 0.67 μδ m⁻¹ respectively as compared to Cu²⁺- and Zn²⁺-loaded hydrogels, which block all available active sites causing an increase in impedance with a parallel decrease in capacitance. The capacitance retention and coulombic efficiency calculated were 88.22% and 77.23% respectively, indicating high stability up to 150 cycles at 0.1 A g⁻¹. Storage moduli obtained were 10.52 kPa, which infers the more elastic nature of the hydrogel loaded with graphene oxide than that of other synthesized hydrogels.

A novel approach has been applied for the preparation of electrode materials based on polyacrylamide hydrogels embedded with reduced graphene oxide and transition metals, Cu²⁺ and Zn²⁺. The fabricated hydrogel exhibits high electrical properties and flexibility.     

N and S co-doped graphene enfolded Ni–Co-layered double hydroxides: an excellent electrode material for high-performance energy storage devices

The performance of hybrid supercapacitors (HSCs) can be increased via the selection of higher capacitive electrode materials. Thus, layered double hydroxides (LDHs) have received extensive consideration in HSCs owing to their good ion-exchange properties, structural flexibility, and large specific surface area. Ni–Co-based LDHs show better specific capacitance, good synergy, and high-rate capability in aqueous electrolytes. However, LDHs suffer from low conductivity, which curbs the charge transfer and mass diffusion throughout the electrochemical process. Thus, the high performance of LDH-based supercapacitors is impeded. Hence, composites of LDH and conducting materials are used. Owing to its extraordinary conducting property, huge surface area, and cost-effectiveness, reduced graphene oxide (rGO) is used as conducting material for LDH-based composite electrodes. Moreover, via the incorporation of heteroatoms (N, S, etc.) into rGO, its electrochemical properties are further enhanced. Here, a novel composite electrode is prepared by wrapping Ni–Co-LDH with N and S-co-doped rGO (LDH-rGO-NS) via a hydrothermal process. The XPS C 1s spectra established the existence of N and S doping in the rGO. The electrochemical performance is enhanced due to an excellent ion/charge transfer rate because of N and S co-doping. The LDH-rGO-NS electrode offers a good charge transfer resistance of 0.24 Ω. The obtained anodic and cathodic b-values are 0.73 and 0.72, respectively. An admirable specific capacitance of 1388 F g⁻¹ is accomplished at a sweep rate of 100 mV s⁻¹. Furthermore, the obtained retention capacity is ∼71% after 2000 cycles. Moreover, the achieved specific capacitance is 2193 F g⁻¹ at the discharge current density of 5 A g⁻¹. The excellent electrochemical properties reveal the LDH-rGO-NS composites as encouraging electrode materials for HSCs.

A novel graphene embedded Ni–Co-LDH electrode was developed. The charge transportation rate was enhanced via N and S heteroatom doping, which results in an excellent discharge capacitance of 2193 F g⁻¹ at 5 A g⁻¹.     

Mo-doped ZnO nanoflakes on Ni-foam for asymmetric supercapacitor applications

A single-step hydrothermal route for synthesizing molybdenum doped zinc oxide nanoflakes was employed to accomplish superior electrochemical characteristics, such as a specific capacitance of 2296 F g⁻¹ at current density of 1 A g⁻¹ and negligible loss in specific capacitance of 0.01025 F g⁻¹ after each charge–discharge cycle (up to 8000 cycles). An assembled asymmetric supercapacitor (Mo:ZnO@NF//AC@NF) also exhibited a maximum energy density and power density of 39.06 W h/kg and 7425 W kg⁻¹, respectively. Furthermore, it demonstrated a specific capacitance of 123 F g⁻¹ at 1 A g⁻¹ and retained about 75.6% of its initial capacitance after 8000 cycles. These superior electrochemical characteristics indicate the potential of this supercapacitor for next-generation energy storage devices.

Mo:ZnO nanoflakes were synthesized by single-step hydrothermal route to achieve superior electrochemical performance.