Controllable Preparation of Polyaniline–Graphene Nanocomposites using Functionalized Graphene for Supercapacitor Electrodes

In order to explore the effect of graphene surface chemistry on electrochemical performance based on polyaniline–graphene hybrid material electrodes, four different polyaniline–graphene nanocomposites were fabricated with graphene oxide, reduced graphene oxide, aminated graphene and sulfonated graphene as carriers, respectively. The nanocomposites feature various structures and morphologies, which could be used to more deeply understand the morphology and structure effects caused by surface chemistry on electrochemical performance. The experimental results reveal that functionalized electronegative graphene was conducive to the vertical and neat growth of polyaniline (PANI) nanorods. The array architecture endowed the PANI–GS nanocomposite with a large ion‐accessible surface area and high‐efficiency electron‐ and ion‐transport pathways. Meanwhile, the introduction of sulfonic acid functional groups accelerated the redox reaction with doping and dedoping of the PANI. Thereby, the PANI–GS nanocomposite exhibited a high specific capacitance of 863.2 F g^?1 at a current density of 0.2 A g^?1 and the excellent rate capability of 67.4 % (581.6 F g^?1 at 5 A g^?1), which were much better than the other three nanocomposites produced.     

In situ polymerization and reduction to fabricate gold nanoparticle‐incorporated polyaniline as supercapacitor electrode materials

Nanocomposites of gold nanoparticles and polyaniline are synthesized by using HAuCl₄ and ammonium peroxydisulfate as the co‐oxidant involving in situ polymerization of aniline and in situ reduction of HAuCl₄. Through these in situ methods, the synthesized Au nanoparticles of ca. 20 nm embedded tightly and dispersed uniformly in polyaniline backbone. With the Au content in composite increasing from 4.20 to 24.72 wt.%, the specific capacitance of the materials first increased from 334 to 392 F g⁻¹ and then decreased to 298 F g⁻¹. Based on the real content of PANI in composite material, the highest specific capacitance is calculated to be 485 F g⁻¹ at the Au amount of 19.15 wt.%, which remains 55.6% after 5000 cycles at the current density of 2 A g⁻¹. Finally, the asymmetric supercapacitor of AuNP/PANI||AC and the symmetric supercapacitor of AuNP/PANI||AuNP/PANI are assembled. The asymmetric supercapacitor device shows a better electrochemical performance, which delivers the maximum energy density of 7.71 Wh kg⁻¹ with power density of 125 W kg⁻¹ and maximum power density of 2500 W kg⁻¹ with the energy density of 5.35 Wh kg⁻¹.     

A platinized stainless steel fiber with in‐situ coated polyaniline/polypyrrole/graphene oxide nanocomposite sorbent for headspace solid‐phase microextraction of aliphatic aldehydes in rice samples

The surface of a stainless steel fiber was made larger, porous and cohesive by platinizing for tight attachment of its coating. Then it was coated by a polyaniline/polypyrrole/graphene oxide (PANI/PP/GO) nanocomposite film using electrochemical polymerization. The prepared PANI/PP/GO fiber was used for headspace solid‐phase microextraction (HS‐SPME) of linear aliphatic aldehydes in rice samples followed by GC‐FID determination. To achieve the highest extraction efficiency, various experimental parameters including extraction time and temperature, matrix modifier and desorption condition were studied. The linear calibration curves were obtained over the range of 0.05–20 μg g⁻¹ (R ² > 0.99) for C₄–C₁₁ aldehydes. The limits of detection were found to be in the range of 0.01–0.04 μg g⁻¹. RSD values were calculated to be <7.4 and 10.7% for intra‐ and inter‐day, respectively. The superiority of the prepared nanocomposite SPME fiber was established by comparison of its results with those obtained by polydimethylsiloxane, carbowax–divinylbenzene, divinylbenzene–carboxen–polydimethylsiloxane and polyacrylate commercial ones. Finally, the nanocomposite fiber was used to extract and determine linear aliphatic aldehydes in 18 rice samples.     

Perovskite SrCo0.9Nb0.1O3−δ as an Anion‐Intercalated Electrode Material for Supercapacitors with Ultrahigh Volumetric Energy Density

We have synthesized and characterized perovskite‐type SrCo_0.9Nb_0.1O_3−δ (SCN) as a novel anion‐intercalated electrode material for supercapacitors in an aqueous KOH electrolyte, demonstrating a very high volumetric capacitance of about 2034.6 F cm⁻³ (and gravimetric capacitance of ca. 773.6 F g⁻¹) at a current density of 0.5 A g⁻¹ while maintaining excellent cycling stability with a capacity retention of 95.7 % after 3000 cycles. When coupled with an activated carbon (AC) electrode, the SCN/AC asymmetric supercapacitor delivered a specific energy density as high as 37.6 Wh kg⁻¹ with robust long‐term stability.     

Fabrication of Polyaniline/Graphene/Polyester Textile Electrode Materials for Flexible Supercapacitors with High Capacitance and Cycling Stability

Vertical polyaniline (PANI) nanowire arrays on graphene‐sheet‐coated polyester cloth (RGO/PETC) were fabricated by the in situ chemical polymerization of aniline. The 3D conductive network that was formed by the graphene sheets greatly enhanced the conductivity of PANI/RGO/PETC and improved its mechanical stability. PANI nanowire arrays increased the active surface area of PANI, whilst the hierarchically porous structure of the PANI/RGO/PETC electrode facilitated the diffusion of the electrolyte ions. Electrochemical measurements showed that the composite electrode exhibited a maximum specific capacitance of 1293 F g^?1 at a current density of 1 A g^?1. Capacitance retention was greater than 95 %, even after 3000 cycles, which indicated that the electrode material has excellent cycling stability. Moreover, the electrode structure endowed the PANI/RGO/PETC electrode with a stable electrochemical performance under mechanical bending and stretching.     

Hierarchical Micro‐Mesoporous Carbon‐Framework‐Based Hybrid Nanofibres for High‐Density Capacitive Energy Storage

Advanced methods, allowing the controllable synthesis of ordered structural nanomaterials with favourable charges transfer and storage, are highly important to achieve ideal supercapacitors with high energy density. Herein, we report a microliter droplet‐based method to synthesize hierarchical‐structured metal–organic framework/graphene/carbon nanotubes hybrids. The confined ultra‐small‐volume reaction, give well‐defined hybrids with a large specific‐surface‐area (1206 m² g^?1), abundant ionic‐channels (narrow pore of 0.86 nm), and nitrogen active‐sites (10.63 %), resulting in high pore‐size utilization (97.9 %) and redox‐activity (32.3 %). We also propose a scalable microfluidic‐blow‐spinning method to consecutively generate nanofibre‐based flexible supercapacitor electrodes with striking flexibility and mechanical strength. The supercapacitors display large volumetric energy density (147.5 mWh cm^?3), high specific capacitance (472 F cm^?3) and stably deformable energy‐supply.     

Design of Advanced MnO/N‐Gr 3D Walls through Polymer Cross‐Linking for High‐Performance Supercapacitor

Three‐dimensional, vertically aligned MnO/nitrogen‐doped graphene (3D MnO/N‐Gr) walls were prepared through facile solution‐phase synthesis followed by thermal treatment. Polyvinylpyrrolidone (PVP) was strategically added to generate cross‐links to simultaneously form 3D wall structures and to incorporate nitrogen atoms into the graphene network. The unique wall features of the as‐prepared 3D MnO/N‐Gr hybirdes provide a large surface area (91.516 m² g^?1) and allow for rapid diffusion of the ion electrolyte, resulting in a high specific capacitance of 378 F g^?1 at 0.25 A g^?1 and an excellent charge/discharge stability (93.7 % capacity retention after 8000 cycles) in aqueous 1 m Na₂SO₄ solution as electrolyte. Moreover, the symmetric supercapacitors that were rationally designed by using 3D MnO/N‐Gr hybrids exhibit outstanding electrochemical performance in an organic electrolyte with an energy density of 90.6 Wh kg^?1 and a power density of 437.5 W kg^?1.     

Microwave‐Induced In Situ Synthesis of Zn2GeO4/N‐Doped Graphene Nanocomposites and Their Lithium‐Storage Properties

Zn₂GeO₄/N‐doped graphene nanocomposites have been synthesized through a fast microwave‐assisted route on a large scale. The resulting nanohybrids are comprised of Zn₂GeO₄ nanorods that are well‐embedded in N‐doped graphene sheets by in situ reducing and doping. Importantly, the N‐doped graphene sheets serve as elastic networks to disperse and electrically wire together the Zn₂GeO₄ nanorods, thereby effectively relieving the volume‐expansion/contraction and aggregation of the nanoparticles during charge and discharge processes. We demonstrate that an electrode that is made of the as‐formed Zn₂GeO₄/N‐doped graphene nanocomposite exhibits high capacity (1463 mAh g^?1 at a current density of 100 mA g^?1), good cyclability, and excellent rate capability (531 mAh g^?1 at a current density of 3200 mA g^?1). Its superior lithium‐storage performance could be related to a synergistic effect of the unique nanostructured hybrid, in which the Zn₂GeO₄ nanorods are well‐stabilized by the high electronic conduction and flexibility of N‐doped graphene sheets. This work offers an effective strategy for the fabrication of functionalized ternary‐oxide‐based composites as high‐performance electrode materials that involve structural conversion and transformation.     

Layered Al‐substituted Cobalt Hydroxides/GO Composites for Electrode Materials of Supercapacitors

In this work, Al‐substituted α‐Co(OH)₂/GO composites with supercapacitive properties were prepared by chemical co‐precipitated method in which cobalt nitrate and aluminum nitrate were used as the raw material, and graphite oxide was employed as carrier. The as‐prepared materials were characterized by X‐ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and fourier transform infrared spectroscopy (FT‐IR). Cyclic voltammetry (CV) and galvanostatic charge/discharge measurements showed that the Al‐substituted α‐Co(OH)₂/GO electrode material had excellent electrochemical capacitance. The specific capacitance of 1137 F·g⁻¹ was achieved in 6 mol/L KOH solution at a current density of 1 A·g⁻¹ within a potential range of 0–0.5 V. Moreover, only 12% losses of the initial specific capacitance were found after 500 cycles at a current density of 1 A·g⁻¹.     

β‐Co(OH)2 Nanosheets: A Superior Pseudocapacitive Electrode for High‐Energy Supercapacitors

In this work, β‐Co(OH)₂ nanosheets are explored as efficient pseudocapacitive materials for the fabrication of 1.6 V class high‐energy supercapacitors in asymmetric fashion. The as‐synthesized β‐Co(OH)₂ nanosheets displayed an excellent electrochemical performance owing to their unique structure, morphology, and reversible reaction kinetics (fast faradic reaction) in both the three‐electrode and asymmetric configuration (with activated carbon, AC). For example, in the three‐electrode set‐up, β‐Co(OH)₂ exhibits a high specific capacitance of ∼675 F g⁻¹ at a scan rate of 1 mV s⁻¹. In the asymmetric supercapacitor, the β‐Co(OH)₂∥AC cell delivers a maximum energy density of 37.3 Wh kg⁻¹ at a power density of 800 W kg⁻¹. Even at harsh conditions (8 kW kg⁻¹), an energy density of 15.64 Wh kg⁻¹ is registered for the β‐Co(OH)₂∥AC assembly. Such an impressive performance of β‐Co(OH)₂ nanosheets in the asymmetric configuration reveals the emergence of pseudocapacitive electrodes towards the fabrication of high‐energy electrochemical charge storage systems.     

Conductive Microporous Covalent Triazine‐Based Framework for High‐Performance Electrochemical Capacitive Energy Storage

Nitrogen‐enriched porous nanocarbon, graphene, and conductive polymers attract increasing attention for application in supercapacitors. However, electrode materials with a large specific surface area (SSA) and a high nitrogen doping concentration, which is needed for excellent supercapacitors, has not been achieved thus far. Herein, we developed a class of tetracyanoquinodimethane‐derived conductive microporous covalent triazine‐based frameworks (TCNQ‐CTFs) with both high nitrogen content (>8 %) and large SSA (>3600 m² g^?1). These CTFs exhibited excellent specific capacitances with the highest value exceeding 380 F g^?1, considerable energy density of 42.8 Wh kg^?1, and remarkable cycling stability without any capacitance degradation after 10 000 cycles. This class of CTFs should hold a great potential as high‐performance electrode material for electrochemical energy‐storage systems.     

Design and green synthesis of 1-(4-ferrocenylbutyl)piperazine chemically grafted reduced graphene oxide for supercapacitor application

In this paper, we report the green synthesis of 1-(4-ferrocenylbutyl)piperazine chemically grafted rGO (P.Fc/rGO) as a battery-type supercapacitor electrode material. For this purpose, initially, the ability of the aqueous Damson fruit extract is investigated in the reduction reaction of graphene oxide (GO). 1-(4-ferrocenylbutyl)piperazine (P.Fc) is synthesized via nucleophilic substitution reaction of piperazine with as-synthesized 4-chlorobutylferrocene. In continue, P. Fc is incorporated to GO by ring-opening reaction of epoxide groups on the GO surface. In the next step, the modified reduction method by aqueous Damson fruit extract was used to prepare the P.Fc/rGO from P.Fc/GO. The prepared materials were characterized by various techniques including FT-IR, Uv–vis, XRD, SEM, EDX, and BET. N₂ adsorption–desorption data of P.Fc/rGO nanocomposite shows that the surface area is 37.746 m² g⁻¹. The capability of P.Fc/rGO nanocomposite for using as an energy storage electrode material in battery-type supercapacitor was examined by investigation of its electrochemical behavior by CV, EIS, and GCD measurements. The charge storage capacity of 1,102 mAh g⁻¹ is achieved at 2.5 A g⁻¹. This nanocomposite shows 89% retention of charge storage capacity after 2000 CV cycles.     

Facile synthesis of polyaniline/TiO2/graphene oxide composite for high performance supercapacitors

The polyaniline/TiO₂/graphene oxide (PANI/TiO₂/GO) composite, as a novel supercapacitor material, is synthesized by in situ hydrolyzation of tetrabutyl titanate and polymerization of aniline monomer in the presence of graphene oxide. The morphology, composition and structure of the composites as-obtained are characterized by SEM, TEM, XRD and TGA. The electrochemical property and impedance of the composites are studied by cyclic voltammetry and Nyquist plot, respectively. The results show that the introduction of the GO and TiO₂ enhanced the electrode conductivity and stability, and then improved the supercapacitive behavior of PANI/TiO₂/GO composite. Significantly, the electrochemical measurement results show that the PANI/TiO₂/GO composite has a high specific capacitance (1020 F g⁻¹ at 2 mV s⁻¹, 430 F g⁻¹ at 1 A g⁻¹) and long cycle life (over 1000 times).     

Synthesis of Phosphorus‐Doped Graphene and its Wide Potential Window in Aqueous Supercapacitors

Phosphorus‐doped (P‐doped) graphene with the P doping level of 1.30 at % was synthesized by annealing the mixture of graphene and phosphoric acid. The presence of P was confirmed by elemental mapping and X‐ray photoelectron spectroscopy, while the morphology of P‐doped graphene was revealed by using scanning electron microscopy and transmission electron microscopy. To investigate the effect of P doping, the electrochemical properties of P‐doped graphene were tested as a supercapacitor electrode in an aqueous electrolyte of 1 M H₂SO₄. The results showed that doping of P in graphene exhibited significant improvement in terms of specific capacitance and cycling stability, compared with undoped graphene electrode. More interestingly, the P‐doped graphene electrode can survive at a wide voltage window of 1.7 V with only 3 % performance degradation after 5000 cycles at a current density of 5 A g^?1, providing a high energy density of 11.64 Wh kg^?1 and a high power density of 831 W kg^?1.     

In Situ Synthesis of CoCeSx Bimetallic Sulfide Nanoparticles on a Bi-Pyrene Terminated Molecular Wire Modified Graphene Surface for Supercapacitors

The excellent electrical conductivity of graphene is due to its highly-conjugated structures. Manipulation of the electronic and mechanical properties of graphene can be achieved by controlling the destruction of its in-sheet conjugation system. Herein, we report the preparation of CoCeS_x−SA@BPMW@RGO through π-π stacking interactions at the molecular level. In this study, sodium alginate was reacted with Co²⁺ and Ce³⁺, and the composite was loaded onto a graphene surface. The graphene sheets were prepared using a bi-pyrene terminated molecular wire (BPMW) to avoid re-stacking of the grapheme sheets, thereby forming nanoscale spaces between sheets. The angle between the BPMW coplanar pyrene group and the phenyl group was 33.2°, and the graphene layer is supported in an oblique direction. Finally, a three-dimensional porous composite was obtained after annealing and vulcanization. The obtained CoCeS_x−SA@BPMW@RGO exhibited excellent electrical conductivity and remarkable cycle stability. When the current density was 1 A g⁻¹, its specific capacitance was as high as 1004 F g⁻¹. BPMW modifies graphene through the synergistic effect of π-π stacking interaction and special structure to obtain excellent electrochemical performance. Moreover, a solid-state asymmetric supercapacitor device was fabricated based on the synthesized CoCeS_x−SA@BPMW@RGO hybrid, which exhibited a power density of 979 W kg⁻¹ at an energy density of 23.96 Wh kg⁻¹.     

Capacitive Properties of the Binder‐Free Electrode Prepared from Carbon Derived from Cotton and Reduced Graphene Oxide

The binder‐free composite films of reduced graphene oxide (rGO ) and activated carbon derived from cotton (aCFC ) have been fabricated and used as electrodes for electrochemical capacitors (ECs ) to avoid the decrease of capacitive performance in traditional process caused by the additional binder. The optimal aCFC is prepared at 850 °C when the mass ratio of carbon and potassium hydroxide is 1 to 4. The optimal composite film prepared from the mass ratio of aCFC /GO =2/1 exhibits porous structure, and has a specific surface area of 849.6 m²•g⁻¹ and a total pore volume of 0.61 mL •g⁻¹. Based on the two‐electrode system testing in 6.0 mol/L KOH electrolyte, the optimal composite has specific capacitance of about 202 F•g⁻¹, 374 mF •cm⁻² and 116 F•cm⁻³ in terms of mass, area and volume, and shows excellent rate capability and good cyclic stability (91.7% retention of the initial capacitance after 5000 cycles). Furthermore, the assembled solid‐state ECs by using KOH /polyvinyl alcohol as electrolyte show good mechanical stability and capacitive performances after repeated bending cycles. It is proved that this method is effective to fabricate binder‐free electrodes for ECs and will open up a novel route for the reuse of waste cotton.     

Enhanced Supercapacitor Performance Using a Co3O4@Co3S4 Nanocomposite on Reduced Graphene Oxide/Ni Foam Electrodes

To avoid an enormous energy crisis in the not-too-distant future, it be emergent to establish high-performance energy storage devices such as supercapacitors. For this purpose, a three-dimensional (3D) heterostructure of Co₃O₄ and Co₃S₄ on nickel foam (NF) that is covered by reduced graphene oxide (rGO) has been prepared by following a facile multistep method. At first, rGO nanosheets are deposited on NF under mild hydrothermal conditions to increase the surface area. Subsequently, nanowalls of cobalt oxide are electro-deposited on rGO/Ni foam by applying cyclic-voltammetry (CV) under optimized conditions. Finally, for the synthesis of Co₃O₄@Co₃S₄ nanocomposite, the nanostructure of Co₃S₄ was fabricated from Co₃O₄ nanowalls on rGO/NF by following an ordinary hydrothermal process through the sulfurization for the electrochemical application. The samples are characterized by using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The obtained sample delivers a high capacitance of 13.34 F cm⁻² (5651.24 F g⁻¹) at a current density of 6 mA cm⁻² compared to the Co₃O₄/rGO/NF electrode with a capacitance of 3.06 F cm⁻² (1230.77 F g⁻¹) at the same current density. The proposed electrode illustrates the superior electrochemical performance such as excellent specific energy density of 85.68 W h Kg⁻¹, specific power density of 6048.03 W kg⁻¹ and a superior cycling performance (86% after 1000 charge/discharge cycles at a scan rate of 5 mV s⁻¹). Finally, by using Co₃O₄ @Co₃S₄/rGO/NF and the activated carbon-based electrode as positive and negative electrodes, respectively, an asymmetric supercapacitor (ASC) device was assembled. The fabricated ASC provides an appropriate specific capacitance of 79.15 mF cm⁻² at the applied current density of 1 mA cm⁻², and delivered an energy density of 0.143 Wh kg⁻¹ at the power density of 5.42 W kg⁻¹.     

A High-Performance Asymmetric Supercapacitor Based on Tungsten Oxide Nanoplates and Highly Reduced Graphene Oxide Electrodes

Tungsten oxide/graphene hybrid materials are attractive semiconductors for energy-related applications. Herein, we report an asymmetric supercapacitor (ASC, HRG//m-WO₃ ASC), fabricated from monoclinic tungsten oxide (m-WO₃) nanoplates as a negative electrode and highly reduced graphene oxide (HRG) as a positive electrode material. The supercapacitor performance of the prepared electrodes was evaluated in an aqueous electrolyte (1 m H₂SO₄) using three- and two-electrode systems. The HRG//m-WO₃ ASC exhibits a maximum specific capacitance of 389 F g⁻¹ at a current density of 0.5 A g⁻¹, with an associated high energy density of 93 Wh kg⁻¹ at a power density of 500 W kg⁻¹ in a wide 1.6 V operating potential window. In addition, the HRG//m-WO₃ ASC displays long-term cycling stability, maintaining 92 % of the original specific capacitance after 5000 galvanostatic charge–discharge cycles. The m-WO₃ nanoplates were prepared hydrothermally while HRG was synthesized by a modified Hummers method.     

Non‐Covalent Functionalization of Graphene with Bisphenol A for High‐Performance Supercapacitors

The reduced graphene oxide (RGO)/bisphenol A (BPA) composites were prepared by an adsorption‐reduction method. The composites are characterized by X‐ray diffraction (XRD), UV‐vis, thermogravimetric (TG) analysis, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM). The results confirm that BPA is adsorbed on the basal plane of RGO by π‐π stacking interaction. Furthermore, the electrochemical behaviors were evaluated by cyclic voltammetry, galvanostatic charge/discharge techniques and electrochemical impedance spectroscopy (EIS). The results show that the RGO/BPA nanocomposites exhibit ultrahigh specific capacitance of 466 F·g^?1 at a current density of 1 A·g^?1, excellent rate capability (more than 81% retention at 10 A·g^?1 relative to 1 A·g^?1) and superior cycling stability (90% capacitance decay after 4000 cycles). Consequently, the RGO/BPA nanocomposites can be regarded as promising electrode materials for supercapacitor applications.     

Post-synthetic Modification of Covalent Organic Frameworks through in situ Polymerization of Aniline for Enhanced Capacitive Energy Storage

Covalent organic frameworks (COFs) having layered architecture with open nanochannels and high specific surface area are promising candidates for energy storage. However, the low electrical conductivity of two-dimensional COFs often limits their scope in energy storage applications. The conductivity of COFs can be enhanced through post-synthetic modification with conducting polymers. Herein, we developed polyaniline (PANI) modified triazine-based COFs via in situ polymerization of aniline within the porous frameworks. The composite materials showed high conductivity of 1.4–1.9×10⁻² S cm⁻¹ at room temperature with a 20-fold enhancement of the specific capacitance than the pristine frameworks. The fabricated supercapacitor exhibited a high energy density of 24.4 W h kg⁻¹ and a power density of 200 W kg⁻¹ at 0.5 A g⁻¹ current density. Moreover, the device fabricated using the conducting polymer-triazine COF composite could light up a green light-emitting diode for 1 min after being charged for 10 s.