Development of 3D Urchin-Shaped Coaxial Manganese Dioxide@Polyaniline (MnO2@PANI) Composite and Self-Assembled 3D Pillared Graphene Foam for Asymmetric All-Solid-State Flexible Supercapacitor Application

Dynamically Cross-Linked, Self-Healable, and Stretchable All-Hydrogel Supercapacitor with Extraordinary Energy Density and Real-Time Pressure Sensing

Wearable electronics with flexible, integrated, and self-powered multi-functions are becoming increasingly attractive, but their basic energy storage units are challenged in simultaneously high energy density, self-healing, and real-time sensing capability. To achieve this, a fully flexible and omni-healable all-hydrogel, that is dynamically crosslinked PVA@PANI hydrogel, is rationally designed and constructed via aniline/DMSO-emulsion-templated in situ freezing-polymerization strategy. The PVA@PANI sheet, not only possesses a honeycombed porous conductive mesh configuration with superior flexibility that provides numerous channels for unimpeded ions/electron transport and maximizes the utilization efficiency of pseudocapacitive PANI, but also can conform to complicated body surface, enabling effective detection and discrimination of body movements. As a consequence, the fabricated flexible PVA@PANI sheet electrode demonstrates an unprecedented specific capacitance (936.8 F g-1 ) and the assembled symmetric flexible all-solid-state supercapacitor delivers an extraordinary energy density of 40.98 Wh kg-1 , outperforming the previously highest-reported values of stretchable PVA@PANI hydrogel-based supercapacitors. What is more, such a flexible supercapacitor electrode enables precisely monitoring the full-range human activities in real-time, and fulfilling a quick response and excellent self-recovery. These outstanding flexible sensing and energy storage performances render this emerging PVA@PANI hydrogel highly promising for the next-generation wearable self-powered sensing electronics.

Activation of MnO6 Units via an Interfacial Electric Field: Electron Injection into Mn t2g for Rapid and Stable Sodium Ion Storage in CeO2 /MnOx

Manganese-based oxides (MnOx ) suffer from sluggish charge diffusion kinetics and poor cycling stability in sodium ion storage. Herein, an interfacial electric field (IEF) in CeO2 /MnOx is constructed to obtain high electronic/ionic conductivity and structural stability of MnOx . The as-designed CeO2 /MnOx exhibits a remarkable capacity of 397 F g-1 and favorable cyclic stability with 92.13% capacity retention after 10,000 cycles. Soft X-ray absorption spectroscopy and partial density of states results reveal that the electrons are substantially injected into the Mn t2g orbitals driven by the formed IEF. Correspondingly, the MnO6 units in MnOx are effectively activated, endowing the CeO2 /MnOx with fast charge transfer kinetics and high sodium ion storage capacity. Moreover, In situRaman verifies a remarkably increased structural stability of CeO2 /MnOx , which is attributed to the enhanced Mn─O bond strength and efficiently stabilized MnO6 units. Mechanism studies show that the downshift of Mn 3d-band center dramatically increases the Mn 3d-O 2p orbitals overlap, thus inhibiting the Jahn-Teller (J-T) distortion of MnOx during sodium ion insertion/extraction. This work develops an advanced strategy to achieve both fast and sustainable sodium ion storage in metal oxides-based energy materials.

Difunctional Microelectrode Arrays for Single-Cell Electrical Stimulation and pH Detection

Due to its direct effect on biomolecules and cells, electrical stimulation (ES) is now widely used to regulate cell proliferation, differentiation, and neurostimulation and is even used in the clinic for pain relief, treatment of nerve damage, and muscle rehabilitation. Conventional ES is mostly studied on cell populations, but the heterogeneity of cancer cells results in the inability to access the response of individual cells to ES. Therefore, detecting the extracellular pH change (ΔpHe) after ES at the single-cell level is important for the application of ES in tumor therapy. In this study, cellular ΔpHe after periodic impulse electrostimulation (IES) was monitored in situ by using a polyaniline (PANI)-modified gold microelectrode array. The PANI sensor had excellent sensitivity (53.68 mV/pH) and linear correlation coefficient (R2 = 0.999) over the pH range of 5.55-7.41. The cells showed different degrees of ΔpHe after the IES with different intervals and stimulation potential. A shorter pulse interval and a higher stimulation potential could effectively enhance stimulation and increase cellular ΔpHe. At 0.5 V potential stimulation, the cellular ΔpHe increased with decreasing pulse interval. However, if the pulse interval was long enough, even at a higher potential of 0.7 V, there was no significant additional ΔpHe due to the insufficient stimulus strength. Based on the above conclusions, the prepared PANI microelectrode arrays (MEAs) were capable of stimulating and detecting single cells, which contributed to the deeper application of ES in tumor therapy.

Unveiling the potential of PANI@MnO2@rGO ternary nanocomposite in energy storage and gas sensing

The development of advanced materials for energy storage and gas sensing applications has gained significant attention in recent years. In this study, we synthesized and characterized PANI@MnO2@rGO ternary nanocomposites (NCs) to explore their potential in supercapacitors and gas sensing devices. The ternary NCs were synthesized through a multi-step process involving the hydrothermal synthesis of MnO2 nanoparticles, preparation of PANI@rGO composites and the assembly to the ternary PANI@MnO2@rGO ternary NCs. The structural, morphological, and compositional characteristics of the materials were thoroughly analyzed using techniques such as XRD, FESEM, TEM, FTIR, and Raman spectroscopy. In the realm of gas sensing, the ternary NCs exhibited excellent performance as NH3 gas sensors. The optimized operating temperature of 100 °C yielded a peak response of 15.56 towards 50 ppm NH3. The nanocomposites demonstrated fast response and recovery times of 6 s and 10 s, respectively, and displayed remarkable selectivity for NH3 gas over other tested gases. For supercapacitor applications, the electrochemical performance of the ternary NCs was evaluated using cyclic voltammetry and galvanostatic charge-discharge techniques. The composites exhibited pseudocapacitive behavior, with the capacitance reaching up to 185 F/g at 1 A/g and excellent capacitance retention of approximately 88.54% over 4000 charge-discharge cycles. The unique combination of rGO, PANI, and MnO2 nanoparticles in these ternary NCs offer synergistic advantages, showcasing their potential to address challenges in energy storage and gas sensing technologies.

A colorimetric sensing platform with smartphone for organophosphorus pesticides detection based on PANI-MnO2 nanozyme

Organophosphorus pesticides (OPs) are of great concern due to its potential harms on human health and the environment. Herein, a budget-friendly, rapid and convenient colorimetric sensing platform is developed for detection of OPs in the environmental and food samples. The sensing element, PANI-MnO2 nanozyme with excellent oxidase mimetic activity is synthesized at room temperature, which is able to directly oxidize 3,3,5,5-tetramethylbenzidine (TMB) to generate blue colored oxidized TMB (OxTMB) within 2 min. Ascorbic acid (AA) can inhibit the oxidization reaction of TMB, consequently causing the blue color fading. Ascorbic acid 2-phosphate (AAP) could be hydrolyzed to produce AA by alkaline phosphatase (ALP). In the presence of OPs can effectively decrease ALP activity, resulting in the recovery of catalytic activity of PANI-MnO2. Therefore, sensitive and selective OPs detection is achieved. Under the optimal conditions, excellent detection performance in term of glyphosate as a model is achieved with a linear range from 0.50 to 50 μM, the detection limit is 0.39 μM (S/N = 3). The utility of method is further improved by combining a portable smartphone platform with a color picking application. The colorimetric platform achieves instrument-free detection of OPs and overcomes the uneven color distribution of traditional paper-based chip, providing an alternative strategy for the qualitative discernment and semi-quantitative analysis of OPs on-site.

Transferring and Retaining of Different Polyaniline Nanofeatures via Electrophoretic Deposition for Enhanced Sensing Performance

Nanofeatured polyaniline (PANI) electrodes have demonstrated impressive sensing performance due to the enhanced electrolyte diffusion and ion transport. However, the retaining of these nanostructures on substrates via electrophoretic deposition (EPD) faces an insurmountable challenge from the involved dedoping process. Here, camphorsulfonic acid is utilized with high steric effects to dope PANI (PANI-CSA) that can be directly used EPD without involving a dedoping process. Five different nanofeatures (sea cucumber-like, nanofiber, amorphous, nanotube, and nanorod) are synthesized, and they have been all successfully transferred onto indium tin oxide substrate in a formic acid/acetonitrile system, namely a morphology memory effect. The mechanism of retaining these nanofeatures is revealed, which is realized via the processes of dissolution of PANI-CSA, codoping and solvation, and reassembly of basic units into the original nanofeature. The enhanced protonation level by the codoping of formic acid and solvation of acetonitrile plays the key role in retaining these nanofeatures. This method is also applicable to transfer PANI/gold nanorod composites (PANI-CSA/AuNRs). The PANI-CSA/AuNRs electrode as an ascorbic acid sensor has shown an excellent sensing performance with a sensitivity up to 872.7 µA mm^-1 cm^-2 and a detection limit of as low as 0.18 × 10^-6 m.

Green Conductive Hydrogel Electrolyte with Self-Healing Ability and Temperature Adaptability for Flexible Supercapacitors

Conductive hydrogels (CHs) are ideal electrolyte materials for the preparation of flexible supercapacitors (FSCs) due to their excellent electrochemical properties, mechanical properties, and deformation restorability. However, most of the reported CHs are prepared by the chemical crosslinking of synthetic polymers and thus usually display the disadvantages of poor self-healing abilities and nonadaptability at environmental temperatures, which greatly limits their application. To overcome these problems, in the present work, we constructed a sodium alginate-borax/gelatin double-network conductive hydrogel (CH) by a dynamic crosslinking between sodium alginate (SA) and borax via borate bonds and hydrogen bonding between amino acids in gelatin and SA chains. The CH displays an excellent elongation of 305.7% and fast self-healing behavior in 60 s. Furthermore, a phase-change material (PCM), Na₂SO₄·10H₂O, was introduced into the CH, which, combined with the nucleation effect of borax, improved the ionic conductivity and temperature adaptability of the CH. The flexible supercapacitor (FSC) assembled with the obtained CH as the electrolyte exhibits a high specific capacitance of 185.3 F·g^-1 at a current density of 0.25 A·g^-1 and good stability with 84% capacitance retention after 10 000 cycles and excellent temperature tolerance with a resistance variation of 2.11 Ω in the temperature range of -20-60 °C. This green CH shows great application potential as an electrolyte for FSCs, and the preparation method can be potentially expanded to the fabrication of self-repairing FSCs with good temperature adaptabilities.

Multi-responsive mesoporous polydopamine composite nanorods cooperate with nano-enzyme and photosensitizer for intensive immunotherapy of bladder cancer

Bladder cancer is a common malignancy in the urinary system. Defects of drug molecules in bladder during treatment, such as passive diffusion, rapid clearance of periodic urination, poor adhesion and permeation abilities, lead to low delivery efficiency of conventional drugs and high recurrence rate of disease. In this study, we designed multi-responsive mesoporous polydopamine (PDA) composite nanorods cooperating with nano-enzyme and photosensitizer for intensive immunotherapy of bladder cancer. The strongly adhesive mesoporous PDA with wheat germ agglutinin on nanoparticles could specifically adhere to epithelial glycocalyx and made the nanoparticles aggregate in urinary pathways. Meanwhile, 2,3-dimethylmaleic anhydride could be hydrolyzed in acidic conditions of tumor microenvironment, giving it a positive charge (charge reversal), which is more amenable to enter cancer cells. Afterwards, manganese dioxide nanorods could catalyze the reaction of excess H₂ O₂ in tumor microenvironment to generate active oxygen, so as to change the hypoxic environment in tumor, and achieve a pH-responsive for slow release of PD-L1. After the ICG was irradiated by infrared light, a large amount of singlet oxygen was generated, thereby enhancing the therapeutic effect and reducing toxicity in vivo. Besides, mesoporous PDA with indocyanine green photothermal agent could have a local heat up quickly under the near-infrared light to kill cancer cells, thereby enhancing therapeutic efficacy. Accordingly, this mesoporous PDA composite nanorods shed a light on bladder tumor treatment.

Mechanically Robust and Elastic Graphene/Aramid Nanofiber/Polyaniline Nanotube Aerogels for Pressure Sensors

The preparation of graphene-based aerogels with excellent mechanical strength, elasticity, and compressibility is still a challenge. Herein, we demonstrate a robust, elastic, and lightweight graphene/aramid nanofiber/polyaniline nanotube (rGO/ANF/PANIT) aerogel that is prepared by mixing graphene oxide (GO), ANF, and PANIT dispersions, followed by thermal treatment at 90 °C, freeze-drying, and a low-temperature annealing process. The PANIT bonds the graphene sheets tightly, benefitting the formation of composite gels. The ANF tightly interconnects the graphene sheets and further reinforces the composite network framework significantly, hence endowing rGO/ANF/PANIT composite aerogels with robust mechanical property. The prepared aerogels present a low density of ∼12 mg cm^-3, high conductivity, good resilience, and high compressibility. The rGO/ANF/PANIT aerogels as pressure sensors exhibit a high sensitivity of 1.73 kPa^-1, low detection limit (40 Pa), wide detection range, and excellent compressive cycle stability, highlighting the promising applications in pressure-sensitive electrical devices, including medical health detection, wearable electronics, and intelligent packaging fields.

The combination of MnO2@Lipo-coated gefitinib and bevacizumab inhibits the development of non-small cell lung cancer

It can be found from a large number of cancer treatments that use of anti-cancer drugs alone often presents low efficacy and high side effects. This study aims to develop a new drug carrier with tumor-specific response, controlled release in vivo and high tumor-suppressive property. Inorganic nano-materials MnO₂ with pH and glutathione (GSH, abundant in cancer cells) responsiveness were used to construct sustained-release functional nano-liposome to be an excellent in vivo pH-sensitive drug delivery system. Some hydrophilic MnO₂, gefitinib (Geb), and bevacizumab (Beb) were encapsulated in the phospholipid vesicles (liposomes), so as to integrate several anti-tumor drugs (MnO₂-PDA@Lipo@Geb@Beb) to achieve effective treatment of non-small cell lung cancer (NSCLC). Part of the MnO₂ nanorods on the lipid shell had the properties of pH and GSH responsiveness, which could further enhance anti-cancer efficacy. Cell assay results showed that MnO₂-PDA@Lipo@Geb@Beb nano-drug had an effective inhibition on A549 cell progression and showed excellent biocompatibility. In vivo results further confirmed that MnO₂-PDA@Lipo@Geb@Beb nano-drug could effectively inhibit the growth of NSCLC cells. Overall, it can be inferred from the above experimental results that the nanocomposite drug is expected to be widely used in the clinical application of lung cancer.

Synthesis, Characterization and Electrochemical Performance of a Redox-Responsive Polybenzopyrrole@Nickel Oxide Nanocomposite for Robust and Efficient Faraday Energy Storage

A polybenzopyrrole@nickel oxide (Pbp@NiO) nanocomposite was synthesized by an oxidative chemical one-pot method and tested as an active material for hybrid electrodes in an electrochemical supercapattery device. The as-prepared composite material exhibits a desirable 3D cross-linked nanostructured morphology and a synergistic effect between the polymer and metal oxide, which improved both physical properties and electrochemical performance. The unprocessed material was characterized by X-ray diffraction, FTIR and UV-Vis spectroscopy, scanning electron microscopy/energy disperse X-ray analysis, and thermogravimetry. The nanocomposite material was deposited without a binder on gold current collectors and investigated for electrochemical behavior and performance in a symmetrical two- and three-electrode cell setup. A high specific capacity of up to 105 C g^-1 was obtained for the Pbp@NiO-based electrodes with a gravimetric energy density of 17.5 Wh kg^-1, a power density of 1925 W kg^-1, and excellent stability over 10,000 cycles.

Designing flexible, smart and self-sustainable supercapacitors for portable/wearable electronics: from conductive polymers

The rapid development of portable/wearable electronics proposes new demands for energy storage devices, which are flexibility, smart functions and long-time outdoor operation. Supercapacitors (SCs) show great potential in portable/wearable applications, and the recently developed flexible, smart and self-sustainable supercapacitors greatly meet the above demands. In these supercapacitors, conductive polymers (CPs) are widely applied due to their high flexibility, conductivity, pseudo-capacitance, smart characteristics and moderate preparation conditions. Herein, we'd like to introduce the CP-based flexible, smart and self-sustainable supercapacitors for portable/wearable electronics. This review first summarizes the flexible SCs based on CPs and their composites with carbon materials and metal compounds. The smart supercapacitors, i.e., electrochromic, electrochemical actuated, stretchable, self-healing and stimuli-sensitive ones, are then presented. The self-sustainable SCs which integrate SC units with energy-harvesting units in one compact configuration are also introduced. The last section highlights some current challenges and future perspectives of this thriving field.

High-Throughput and Real-Time Monitoring of Single-Cell Extracellular pH Based on Polyaniline Microarrays

Real-time monitoring of extracellular pH (pHe) at the single-cell level is critical for elucidating the mechanisms of disease development and investigating drug effects, with particular importance in cancer cells. However, there are still some challenges for analyzing and measuring pHe due to the strong heterogeneity of cancer cells. Thus, it is necessary to develop a reliable method with good selectivity, reproducibility, and stability for achieving the pHe heterogeneity of cancer cells. In this paper, we report a high-throughput, real-time measuring technique based on polyaniline (PANI) microelectrode arrays for monitoring single-cell pHe. The PANI microelectrode array not only has a high sensitivity (57.22 mV/pH) ranging from pH 6.0 to 7.6 but also exhibits a high reliability (after washing, the PANI film was still smooth, dense, and with a sensitivity of 55.9 mV/pH). Our results demonstrated that the pHe of the cancer cell region is lower than that of the surrounding blank region, and pHe changes of different cancer cells exhibit significant cellular heterogeneity during cellular respiration and drug stimulation processes.

Enhanced Pseudocapacitive Performance of Symmetric Polypyrrole-MnO2 Electrode and Polymer Gel Electrolyte

Herein, the nanostructured polypyrrole-coated MnO₂ nanofibers growth on carbon cloth (PPy-MnO₂-CC) to serve as the electrodes used in conjunction with a quasi-ionic liquid-based polymer gel electrolyte (urea-LiClO₄-PVA) for solid-state symmetric supercapacitors (SSCs). The resultant PPy-MnO₂-CC solid-state SSCs exhibited a high specific capacitance of 270 F/g at 1.0 A/g in a stable and wide potential window of 2.1 V with a high energy/power density (165.3 Wh/kg at 1.0 kW/kg and 21.0 kW/kg at 86.4 Wh/kg) along with great cycling stability (capacitance retention of 92.1% retention after 3000 cycles) and rate capability (141 F/g at 20 A/g), exceeding most of the previously reported SSCs. The outstanding performance of the studied 2.1 V PPy-MnO₂-CC flexible SSCs could be attributed to the nanostructured PPy-coated MnO₂ composite electrode and the urea-LiClO₄-PVA polymer gel electrolyte design. In addition, the PPy-MnO₂-CC solid-state SSCs could effectively retain their electrochemical performance at various bending angles, demonstrating their huge potential as power sources for flexible and lightweight electronic devices. This work offers an easy way to design and achieve light weight and high-performance SSCs with enhanced energy/power density.

Preparation and Properties of an Ultrahigh-Energy-Density Aqueous Supercapacitor with a Superconcentrated Electrolyte and a Sr-Modified Lanthanum Zirconate Flexible Electrode

Although supercapacitors are considered to play a vital role in flexible electronic devices, there are still some problems that need to be overcome, such as low energy density and narrow electrochemical stability windows in aqueous electrolytes. Herein, we have successfully synthesized a series of Sr-modified La₂Zr₂O₇ (LZO-x) nanofibers as a new electrode material by a facile electrospinning technique. To determine the best doping sample, the changes in structures and electrochemical performances of La₂Zr₂O₇ (LZO-x) nanofibers with various Sr contents are investigated carefully. Then, the LZO-0.2 sample shows the highest capacitance (1445 mF·cm^-2). Furthermore, we also develop a low-cost superconcentrated electrolyte, which achieves a wide electrochemical stability window of 2.7 V using a working electrode (LZO-0.2). Finally, we use the LZO-0.2 electrode and the superconcentrated electrolyte to fabricate a flexible supercapacitor device, which shows an excellent capacitance of 175 F·g^-1 at a current density of 1.15 A·g^-1. Moreover, the aqueous device has excellent cycle stability and outstanding flexibility, and the energy density of this device is 177.2 Wh·kg^-1 and the corresponding power density is 1557.7 W·kg^-1.

A SnO2QDs/GO/PPY ternary composite film as positive and graphene oxide/charcoal as negative electrodes assembled solid state asymmetric supercapacitor for high energy storage applications

The work demonstrates tin oxide quantum dots/graphene oxide/polypyrrole (SnO₂QDs/GO/PPY) ternary composite deposited on titanium foil as a positive electrode and graphene oxide (GO)/charcoal on titanium foil as negative electrode separated by polyvinyl alcohol/potassium hydroxide (PVA/KOH) gel-electrolyte as a solid-state asymmetric supercapacitor for high energy storage applications. Here, tin oxide quantum dots (SnO₂QDs) were successfully synthesized by a hydrothermal technique, and SnO₂QDs/GO/PPY ternary composite was synthesized by an in situ method with pyrrole monomer, SnO₂, and GO. A pH value controlled, which maintained the uniform size of SnO₂QDs dispersed on PPY, through GO ternary composite was used for fabricating the asymmetric supercapacitor electrode with the configuration (SnO₂QDs/GO/PPY)/GO/charcoal (85 : 10 : 5). The device achieved the highest specific capacitance of 1296 F g⁻¹, exhibited an energy density of 29.6 W h kg⁻¹ and the highest power density of 5310.26 W kg⁻¹ in the operating voltage from 0 to 1.2 V. The device also possessed excellent reliability and retained the capacitance of 90% after 11 000 GCD cycles. This ternary composite is a prominent material for potential applications in next-generation energy storage and portable electronic devices.

Representation of the synthesis steps of SnO₂QDs/GO/PPY ternary composites and SnO₂QDs/GO/PPY//GO/charcoal asymmetric supercapacitor device.

A ionic liquid enhanced conductive hydrogel for strain sensing applications

Strain-sensitive and conductive hydrogels have attracted extensive research interest due to their potential applications in various fields, such as healthcare monitoring, human-machine interfaces and soft robots. However, low electrical signal transmission and poor tensile properties still limit the application of flexible sensing hydrogels in large amplitude and high frequency motion. In this study, a novel ionic liquid segmental polyelectrolyte hydrogel consisting of acrylic acid (AAc), 1-vinyl-3-butylimidazolium bromide (VBIMBr) and aluminum ion (Al³⁺) was prepared by molecular design and polymer synthesis. The cationic groups and amphiphilicity of ionic liquid chain segments effectively improve the tensile behavior of the polyelectrolyte hydrogel, with a maximum tensile strength of 0.16 MPa and a maximum breaking strain of 604%. The introduction of ionic liquid segments increased the current carrying concentration of polyelectrolyte hydrogel, and the conductivity reached the initial 4.8 times (12.5 S/m), which is a necessary condition for detecting various amplitude and high frequency limb movements. The flexible electronic sensor prepared by this polyelectrolyte hydrogel efficiently detects the movement of different parts of the human body stably and sensitively, even in extreme environment (-20 °C). These outstanding advantages demonstrate the great potential of this hydrogel in healthcare monitoring and wearable flexible strain sensors.

Boron-Decorated Pillared Graphene as the Basic Element for Supercapacitors: An Ab Initio Study

In this work, using the first-principle density functional theory (DFT) method, we study the properties of a new material based on pillared graphene and the icosahedral clusters of boron B12 as a supercapacitor electrode material. The new composite material demonstrates a high specific quantum capacitance, specific charge density, and a negative value of heat of formation, which indicates its efficiency. It is shown that the density of electronic states increases during the addition of clusters, which predictably leads to an increase in the electrode conductivity. We predict that the use of a composite based on pillared graphene and boron will increase the efficiency of existing supercapacitors.

Free-standing electrochemically coated MoSx based 3D-printed nanocarbon electrode for solid-state supercapacitor application

The 3D-printing technology offers an innovative approach to develop energy storage devices because of its ability to create facile and low cost customized electrodes for modern electronics. Among the recently explored 2D nanomaterials beyond graphene, molybdenum sulfide (MoS_x) has been found as a promising material for electrochemical energy storage devices. In this study, a nanocarbon-based conductive filament was 3D-printed and then activated by solvent treatment, followed by electrodeposition of MoS_x on the printed nanocarbon electrode's surface. The conductive nanocarbon fibers allow a coaxial deposition of a thin MoS_x layer. The MoS_x layer contributes to pseudocapacitive charge storage mechanisms to obtain higher capacitances. In a three-electrode test system with 1 M H₂SO₄ as electrolyte, the MoS_x coated 3D-printed electrode (MoS_x@3D-PE) electrode shows a capacitance of 27 mF cm^-2 at the scan rate of 10 mV s^-1, and a capacitance of 11.6 mF cm^-2 at the current density of 0.13 mA cm^-2. Extending to solid-state supercapacitor (SS-SC), the cells were fabricated using the MoS_x@3D-PE with different designs and polyvinyl alcohol (PVA)/H₂SO₄ as gel electrolyte. An interdigital-shaped SS-SC provided a specific capacitance of 4.15 mF cm^-2 at a current density of 0.05 mA cm^-2. Moreover, it showed a stable cycle life where 10% capacitance loss was found after 10 000 cycles. Briefly, this study reports the integration of 3D-printing and room-temperature electrodeposition techniques allowing a simple way of fabricating customized free-standing 3D-electrodes for use in SC applications.

PANI/MoO3−x shell–core composites with enhanced rate and cycling performance for flexible solid-state supercapacitors and electrochromic applications

PANI/MoO_3−x shell–core composites show enhanced electrochemical and electrochromic performance as a bi-functional electrode material for flexible solid-state supercapacitors, attributed to a synergistic effect from PANI nanorods and MoO_3−x nanobelts.

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.

Hydrothermally Assisted Synthesis of Porous Polyaniline@Carbon Nanotubes-Manganese Dioxide Ternary Composite for Potential Application in Supercapattery

In this study, ternary composites of polyaniline (PANI) with manganese dioxide (MnO₂) nanorods and carbon nanotubes (CNTs) were prepared by employing a hydrothermal methodology and in-situ oxidative polymerization of aniline. The morphological analysis by scanning electron microscopy showed that the MnO₂ possessed nanorod like structures in its pristine form, while in the ternary PANI@CNT/MnO₂ composite, coating of PANI over CNT/MnO₂, rods/tubes were evidently seen. The structural analysis by X-ray diffraction and X-ray photoelectron spectroscopy showed peaks corresponding to MnO₂, PANI and CNT, which suggested efficacy of the synthesis methodology. The electrochemical performance in contrast to individual components revealed the enhanced performance of PANI@CNT/MnO₂ composite due to the synergistic/additional effect of PANI, CNT and MnO₂ compared to pure MnO₂, PANI and PANI@CNT. The PANI@CNT/MnO₂ ternary composite exhibited an excellent specific capacity of 143.26 C g^-1 at a scan rate of 3 mV s^-1. The cyclic stability of the supercapattery (PANI@CNT/MnO₂/activated carbon)-consisting of a battery type electrode-demonstrated a gradual increase in specific capacity with continuous charge-discharge over ~1000 cycles and showed a cyclic stability of 119% compared to its initial value after 3500 cycles.

Cobalt Oxide Nanograins and Silver Nanoparticles Decorated Fibrous Polyaniline Nanocomposite as Battery-Type Electrode for High Performance Supercapattery

In this study, silver (Ag) and cobalt oxide (Co₃O₄) decorated polyaniline (PANI) fibers were prepared by the combination of in-situ aniline oxidative polymerization and the hydrothermal methodology. The morphology of the prepared Ag/Co₃O₄@PANI ternary nanocomposite was studied by scanning electron microscopy and transmission electron microscopy, while the structural studies were carried out by X-ray diffraction and X-ray photoelectron spectroscopy. The morphological characterization revealed fibrous shaped PANI, coated with Ag and Co₃O₄ nanograins, while the structural studies revealed high purity, good crystallinity, and slight interactions among the constituents of the Ag/Co₃O₄@PANI ternary nanocomposite. The electrochemical performance studies revealed the enhanced performance of the Ag/Co₃O₄@PANI nanocomposite due to the synergistic/additional effect of Ag, Co₃O₄ and PANI compared to pure PANI and Co₃O₄@PANI. The addition of the Ag and Co₃O₄ provided an extended site for faradaic reactions leading to the high specific capacity. The Ag/Co₃O₄@PANI ternary nanocomposite exhibited an excellent specific capacity of 262.62 C g⁻¹ at a scan rate of 3 mV s⁻¹. The maximum energy and power density were found to be 14.01 Wh kg⁻¹ and 165.00 W kg⁻¹, respectively. The cyclic stability of supercapattery (Ag/Co₃O₄@PANI//activated carbon) consisting of a battery type electrode demonstrated a gradual increase in specific capacity with a continuous charge–discharge cycle until ~1000 cycles, then remained stable until 2500 cycles and later started decreasing, thereby showing the cyclic stability of 121.03% of its initial value after 3500 cycles.

Inherent Impurities in Graphene/Polylactic Acid Filament Strongly Influence on the Capacitive Performance of 3D-Printed Electrode

Additive manufacturing or 3D-printing have become promising fabrication techniques in the field of electrochemical energy storage applications such as supercapacitors, and batteries. Of late, a commercially available graphene/polylactic acid (PLA) filament has been commonly used for Fused Deposition Modeling (FDM) 3D-printing in the fabrication of electrodes for supercapacitors and Li-ion batteries. This graphene/PLA filament contains metal-based impurities such as titanium oxide and iron oxide. In this study, we show a strong influence of inherent impurities in the graphene/PLA filament for supercapacitor applications. A 3D-printed electrode is prepared and subsequently thermally activated for electrochemical measurement. A deep insight has been taken to look into the pseudocapacitive contribution from the metal-based impurities which significantly enhanced the overall capacitance of the 3D-printed graphene/PLA electrode. A systematic approach has been shown to remove the impurities from the printed electrodes. This has a broad implication on the interpretation of the capacitance of 3D-printed composites.

High-performance supercapacitors based on polyaniline nanowire arrays grown on three-dimensional graphene with small pore sizes

Three-dimensional graphene (3D GR)-based hybrids have received significant attention due to their unique structures and promising applications in supercapacitors. In this paper, 3D GR with small pore sizes has been prepared by chemical vapor deposition using commercial nickel nanowires as the template. After nitric acid treatment, the hydrophilicity of 3D GR improved. Polyaniline nanowire arrays (PANI NWAs) have been successfully grown on its surface by in situ polymerization to obtain hybrid PANI NWA/3D GR. The results show that PANI NWAs with a length of ∼300 nm vertically grow on 3D GR with a pore diameter of ∼2 μm. The small pore size of 3D GR not only improves the mechanical properties of 3D GR, but also provides numerous sites for the growth of PANI NWAs. Meanwhile, PANI NWAs provide a shorter ion diffusion path and larger contact area with the electrolyte. Due to the unique structure, the hybrid exhibits a high specific capacitance of 789.9 F g^-1 at 10 mV s^-1. When it is assembled into a symmetric supercapacitor, it exhibits an energy density of 32.2 W h kg^-1 at a power density of 793.3 W kg^-1 and maintains a good cycle stability of 90% after 5000 cycles at 1.0 A g^-1.

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.

Highly Efficient Quasi-Solid-State Asymmetric Supercapacitors Based on MoS2/MWCNT and PANI/MWCNT Composite Electrodes

Molybdenum disulfide (MoS₂) and polyaniline (PANI) electrodes were decorated with multi-walled carbon nanotubes (MWCNTs) on the basis of a facial hydrothermal and in situ polymerization methods and served in the asymmetric supercapacitor (ASC). The MoS₂ and MWCNTs with a mole ratio of 1:1 in MoS₂|MWCNTs electrode exhibited better electrochemical properties through extensive electrochemical studies, in terms of the highest specific capacitance of 255.8 F/g at 1 A/g, low internal resistance, and notable electrochemical stability with retention of the initial specific capacitance at 91.6% after 1000 cycles. The as-prepared PANI|MWCNTs electrode also exhibited good specific capacitance of 267.5 F/g at 1 A/g and remained 97.9% capacitance retention after 1000 cycles. Then, the ASC with MoS₂|MWCNTs and PANI|MWCNTs composite electrodes were assembled with polyvinyl alcohol (PVA)-Na₂SO₄ gel electrolyte, which displayed good electrochemical performance with the specific capacitance of 138.1 F/g at 1 A/g, and remained the energy density of 15.09 Wh/kg at a high power density of 2217.95 W/kg. This result shows that this ASC device possesses excellent electrochemical properties of high energy density and power output and thus showing a potential application prospect.

Chemical Vapor Deposition of Carbon Nanocoils Three-Dimensionally in Carbon Fiber Cloth for All-Carbon Supercapacitors

An Au/K bicatalyst-assisted chemical vapor deposition process using C₂H_2(g) to grow high-density carbon nanocoils (CNCs) uniformly on the fibers in carbon fiber cloth substrates three-dimensionally was developed. An as-deposited substrate (2.5 × 1.0 cm²) showed a high electrochemical active surface area (16.53 cm²), suggesting its potential usefulness as the electrode in electrochemical devices. The unique one-dimensional (1D) helical structure of the CNCs shortened the diffusion pathways of the ions in the electrolyte and generated efficient electron conduction routes so that the observed serial resistance R _s was low (3.7 Ω). By employing two-electrode systems, a liquid-state supercapacitor (SC) in H₂SO_4(aq) (1.0 M) and a solid-state SC with a polypropylene (PP) separator immersed in H₂SO_4(aq) (1.0 M)/polyvinylalcohol were assembled and investigated by using CNC-based electrodes. Both devices exhibited approximate rectangular shape profiles in the cyclic voltammetry measurements at various scan rates. The observations indicated their electric double-layer capacitive behaviors. From their galvanostatic charge/discharge curves, the specific capacitances of the liquid SC and the solid SC were measured to be approximately 137 and 163 F/g, respectively. In addition, the solid-state CNC-based SC possessed excellent energy density (15.3 W h/kg) and power density (510 W/kg). The light weight solid SC (0.1965 g, 2.5 × 1.0 cm²) was bendable up to 150° with most of the properties retained.

Three-dimensional “skin-framework” hybrid network as electroactive material platform for high-performance solid-state asymmetric supercapacitor

Three-dimensional (3D) electrode materials are ideal candidates for use in fabricating high-performance supercapacitors (SCs), owing to their unique network structure and excellent electrochemical properties. In this study, an aerogel film produced by the freeze-drying self-aggregation of multiwall carbon nanotubes (MWCNTs) and cellulose nanofibers (CNFs) served as the “skin”, and an inter-connected 3D network of nickel foam (NF) as the “framework”, for the fabrication of an MWCNT/CNF-NF (called MCN) hybrid material with a distinct “skin-framework” architecture. Considering the metrics of excellent conductivity, high wettability, binder-free and unique 3D “skin-framework” structure, the MCN hybrid material has great potential as an electroactive material platform in constructing state-of-the-art asymmetric supercapacitor (ASC) electrodes. By incorporating MCN with electroactive manganese dioxide (MnO₂) and active carbon (AC), MnO₂-MCN and AC-MCN composite electrodes with respective high areal capacitances of 1784.8 (equal to 469.7 F g⁻¹) and 868.8 mF cm⁻² (equal to 126.3 F g⁻¹) at 5 mA cm⁻² were successfully prepared. Further, both kinds of electrodes exhibited high charge/discharge ability rates and good cycle performance. Moreover, an optimally assembled MnO₂-MCN//AC-MCN solid-state ASC was reversibly charged/discharged at voltages as high as 1.8 V and possessed a remarkable volumetric capacity of 9.83 F cm⁻³ and an energy density of 4.25 mW h cm⁻³, as well as good cycle stability.

3D “skin-framework” architecture of the MCN with large interfacial contact area and high electrical conductivity enable it to serve as a powerful electroactive platform for high-performance solid-state MnO₂-MCN//AC-MCN ASC device.

Sandwich-like NiCo layered double hydroxide/reduced graphene oxide nanocomposite cathodes for high energy density asymmetric supercapacitors

Lab-synthesized sandwich-like LDH/rGO composites were assembled into asymmetric supercapacitors exhibiting high energy density and excellent cycling stability.

Recycled Carbon Fiber-Supported Polyaniline/Manganese Dioxide Prepared via One-Step Electrodeposition for Flexible Supercapacitor Integrated Electrodes

The exploration of multifunctional electrode materials has been a hotspot for the development of high-performance supercapacitors. We have used carbon fiber plates recovered from construction waste to prepare high-quality flexible carbon fiber materials by pyrolysis of epoxy resin. The as-prepared recycled carbon fiber has a diameter of 8 μm and is the perfect substrate material for flexible electrode materials. Furthermore, polyaniline and manganese dioxide are uniformly deposited on the recycled carbon fiber by one-step electrodeposition to form an active film. The recycled carbon fiber/polyaniline/MnO₂ composite shows an excellent specific capacitance of 475.1 F·g⁻¹ and capacitance retention of 86.1% after 5000 GCD cycles at 1 A·g⁻¹ in 1 M Na₂SO₄ electrolyte. The composites optimized for electrodeposition time have more electroactive sites, faster ions and electron transfer, structural stability and higher conductivity, endowing the composites promising application prospect.