Conducting polymers-based electrochemical supercapacitors—Progress and prospects

Constructing the Interconnected and Hierarchical Nanoarchitectonics in Coal-Derived Carbon for High-Performance Supercapacitor

Because of the deep and zigzag microporous structure, porous carbon materials exhibit inferior capacitive performance and sluggish electrochemical kinetics for supercapacitor electrode materials. Herein, a single-step carbonation and activation approach was utilized to synthesize coal-based porous carbon with an adjustable pore structure, using CaO as a hard template, KOH as an activator, and oxidized coal as precursors to carbon. The obtained sample possesses an interconnected and hierarchical porous structure, higher SSA (1060 m2 g-1), suitable mesopore volume (0.25 cm3 g-1), and abundant surface heteroatomic functional groups. Consequently, the synthesized carbon exhibits an exceptionally high specific capacitance of 323 F g-1 at 1 A g-1, along with 80.3% capacitance retention at 50 A g-1. The assembled two-electrode configuration demonstrates a remarkable capacitance retention of up to 95% and achieves Coulombic efficiency of nearly 100% with 10,000 cycles in a 6 M KOH electrolyte. Furthermore, the Zn-ion hybrid capacitor also exhibits a specific capacity of up to 139.1 mA h g-1 under conditions of 0.2 A g-1. This work offers a simple method in preparation of coal-based porous carbon with controllable pore structure.

Improving the electrochemical characteristics and performance of a neutral all-iron flow battery by using the iron reduction bacteria

At present, the all-iron redox flow batteries (RFBs) have greater application potential due to high accessibility of electrolytes compared to traditional RFBs. Meanwhile, although electroactive bacteria can accelerate the electrons transfer, their potential to improve the performance of RFBs has been overlooked. Previously, we had confirmed that ferrous-oxidizing bacteria (FeOB) could enhance the performance of an all-iron RFB, therefore we conducted several batch experiments and chronopotentiometry experiments by using the ferric-reducing bacteria (FeRB) or mixed culture (FeOB and FeRB) to demonstrate whether they have the same or stronger effects on Fe3+-DTPA/Na4[Fe(CN)6] RFB. The results showed that the experimental reactors could achieve higher charging current density and initial cathodic potential during constant voltage charging process. The electrochemical impedance spectroscopy data and cyclic voltammetry curves demonstrated that the polarization impedance increased slower and reduction peak potential of experimental groups also emerged a positive shift compared to CK. According to chronopotentiometry experiments results, the microbes could function at maximum 0.3 M, 12 mA/cm2, and also improved the charging specific capacity. Combined the SEM pictures and microbial composition analysis, the main functional electroactive FeRB were Alcaligenes, Corynebacterium and Bacillus, which indicated to have important potential in improving the performance of RFBs.

Recent Progress in Polyaniline and its Composites for Supercapacitors

Polyaniline (PANI) has piqued the interest of nanotechnology researchers due to its potential as an electrode material for supercapacitors. Despite its ease of synthesis and ability to be doped with a wide range of materials, PANI's poor mechanical properties have limited its use in practical applications. To address this issue, researchers investigated using PANI composites with materials with highly specific surface areas, active sites, porous architectures, and high conductivity. The resulting composite materials have improved energy storage performance, making them promising electrode materials for supercapacitors. Here, we provide an overview of recent developments in PANI-based supercapacitors, focusing on using electrochemically active carbon and redox-active materials as composites. We discuss challenges and opportunities of synthesizing PANI-based composites for supercapacitor applications. Furthermore, we provide theoretical insights into the electrical properties of PANI composites and their potential as active electrode materials. The need for this review stems from the growing interest in PANI-based composites to improve supercapacitor performance. By examining recent progress in this field, we provide a comprehensive overview of the current state-of-the-art and potential of PANI-based composites for supercapacitor applications. This review adds value by highlighting challenges and opportunities associated with synthesizing and utilizing PANI-based composites, thereby guiding future research directions.

Resent Development of Binder-Free Electrodes of Transition Metal Oxides and Nanohybrids for High Performance Supercapacitors - A Review

The entire world is aware of the serious issue of global warming and therefore utilizing renewable energy sources is the most encouraging steps toward solving energy crises, and as a result, energy storage solutions are necessary. The supercapacitors (SCs) have a high-power density and a long cycle life, they are promising as an electrochemical conversion and storage device. In order to achieve high electrochemical performance, electrode fabrication must be implemented properly. Electrochemically inactive and insulating binders are utilized in the conventional slurry coating method of making electrodes to provide adhesion between the electrode material and the substrate. This results in an undesirable "dead mass," which lowers the overall device performance. In this review, we focused on binder-free SCs electrodes based on transition metal oxides and composites. With the best examples providing the critical aspects, the benefits of binder-free electrodes over slurry-coated electrodes are addressed. Additionally, different metal-oxides used in the fabrication of binder-free electrodes are assessed, taking into account the various synthesis methods, giving an overall picture of the work done for binder-free electrodes. The future outlook is provided along with the benefits and drawbacks of binder-free electrodes based on transition metal oxides.

Atomic Layer Deposition-A Versatile Toolbox for Designing/Engineering Electrodes for Advanced Supercapacitors

Atomic layer deposition (ALD) has become the most widely used thin-film deposition technique in various fields due to its unique advantages, such as self-terminating growth, precise thickness control, and excellent deposition quality. In the energy storage domain, ALD has shown great potential for supercapacitors (SCs) by enabling the construction and surface engineering of novel electrode materials. This review aims to present a comprehensive outlook on the development, achievements, and design of advanced electrodes involving the application of ALD for realizing high-performance SCs to date, as organized in several sections of this paper. Specifically, this review focuses on understanding the influence of ALD parameters on the electrochemical performance and discusses the ALD of nanostructured electrochemically active electrode materials on various templates for SCs. It examines the influence of ALD parameters on electrochemical performance and highlights ALD's role in passivating electrodes and creating 3D nanoarchitectures. The relationship between synthesis procedures and SC properties is analyzed to guide future research in preparing materials for various applications. Finally, it is concluded by suggesting the directions and scope of future research and development to further leverage the unique advantages of ALD for fabricating new materials and harness the unexplored opportunities in the fabrication of advanced-generation SCs.

Hydrothermal Carbonization of Cellulose with Ammonium Sulfate and Thiourea for the Production of Supercapacitor Carbon

Doping with heteroatoms is the main method used to enhance energy storage with carbon materials, and polyatomic doping is one of the main challenges. Hydrothermal carbonization of cellulose was performed at 240 °C for 1 h. Ammonium sulfate and thiourea dopants were selected as the sources of inorganic nitrogen and organic nitrogen in the preparation of supercapacitor carbon. The effects of boric acid on the properties of the resulting hydrochar after KOH activation were examined. The results showed that the proportion of functional groups and the specific surface area of the activated hydrochar were reduced by the addition of boric acid, and the formation of micropores was inhibited. The hydrochar obtained from the reaction of cellulose and organic nitrogen compounds had a better pore size distribution and electrochemical properties after activation. The largest specific surface area (952.27 m2/g) was obtained when thiourea was used as the sole dopant. In a three-electrode system, the specific capacitance of the activated hydrochar reached 235.8 F/g at a current density of 1 A/g. After 20,000 charging and discharging cycles at a current density of 10 A/g, the capacitance retention rate was 99.96%. Therefore, this study showed that supercapacitor carbon with good electrochemical properties was obtained by the direct reactions of cellulose with organic nitrogen compounds.

Understanding the Effect of Deposition Technique on the Structure-Property Relationship of Polyaniline Thin Films Applied in Potentiometric pH Sensor

The comprehension of potentiometric pH sensors with polymeric thin films for new and advanced applications is a constant technological need. The present study aimed to explore the relationship between the sensitivity and correlation coefficient of potentiometric pH sensors and the structure-property relationship of polyaniline thin films. The effect of the deposition method on the sample's properties was evaluated. Galvanostatically electrodeposited and spin-coated polyaniline thin films were used as the sensing stage. Samples were electrodeposited with a current density of 0.5 mA/cm2 for 300, 600, and 1200 s and were spin coated for 60 s with an angular velocity of 500, 1000, and 2000 rpm. The electrodeposited set of films presented higher average sensitivity, 73.4 ± 1.3 mV/pH, compared to the spin-coated set, 59.2 ± 2.5 mV/pH. The electrodeposited films presented higher sensitivity due to their morphology, characterized by a larger roughness and thickness compared to spin-coated ones, favoring the potentiometric response. Also, their oxidation state, evaluated with cyclic voltammetry and UV-VIS spectroscopy, corroborates their sensing performance. The understanding of the structure-property relationship of the polymeric films affecting the pH detection is discussed based on the characteristics of the deposition method used.

Porosity-Engineered CNT-MoS2 Hybrid Nanostructures for Bipolar Supercapacitor Applications

Bipolar supercapacitors that can store many fold higher capacitance in negative voltage compared to positive voltage are of great importance if they can be engineered for practical applications. The electrode material encompassing high surface area, better electrochemical stability, high conductivity, moderate distribution of pore size, and their interaction with suitable electrolytes is imperative to enable bipolar supercapacitor performance. Apropos of the aforementioned aspects, the intent of this work is to ascertain the effect of ionic properties of different electrolytes on the electrochemical properties and performance of a porous CNT-MoS₂ hybrid microstructure toward bipolar supercapacitor applications. The electrochemical assessment reveals that the CNT-MoS₂ hybrid electrode exhibited a two- to threefold higher areal capacitance value of 122.3 mF cm^-2 at 100 μA cm^-2 in 1 M aqueous Na₂SO₄ and 42.13 mF cm^-2 at 0.30 mA cm^-2 in PVA-Na₂SO₄ gel electrolyte in the negative potential window in comparison to the positive potential window. The CNT-MoS₂ hybrid demonstrates a splendid Coulombic efficiency of ∼102.5% and outstanding stability with capacitance retention showing a change from 100% to ∼180% over 7000 repeated charging-discharging cycles.

Three-dimensional electro-Fenton system supplied with a nanocomposite of microbial cellulose/Fe3O4 for effective degradation of tetracycline

In this study, the catalytic activity of the modified microbial cellulose/Fe₃O₄ (MMC/ Fe₃O₄) composite was studied for tetracycline (TC) degradation and mineralization in a three-dimensional electro-Fenton system (3D-EF). The MC/Fe₃O₄ was modified at 400 °C for 60 min. The MMC/ Fe₃O₄ was fully analyzed (morphological, structural, chemical properties). Complete degradation and 65% mineralization of TC was achieved in the 3D-EF process (0.5 g L^-1 MMC/ Fe₃O₄, 10 mM NaCl electrolyte, and neutral pH) within 20 min and electrical energy consumption (EEC) 0.86 kwh g^-1 TC under the 6.66 mA cm^-2. High degradation efficiency TC, in 3D-EF system was attributed to significant single oxygen (¹O₂), superoxide(O₂^•-) participation and less to Hydroxyl radical (OH^•). Reusability of the MMC/ Fe₃O₄ was successfully carried out for five consecutive runs. Accordingly, greencompositeof MMC/ Fe₃O₄ can be considered as an efficient and durable particle electrode (PE) to degrade and mineralize emerging pollutants in an aquatic environment.

Thin Films of Polyaniline-Based Nanocomposites with CeO2 and WO3 Metal Oxides Applied to the Impedimetric and Capacitive Transducer Stages in Chemical Sensors

There is a recognized need for the development of cost-effective, stable, fast, and optimized novel materials for technological applications. Substantial research has been undertaken on the role of polymeric nanocomposites in sensing applications. However, the use of PANI-based nanocomposites in impedimetric and capacitive electrochemical sensors has yet to be understood. The present study aimed to explore the relationship between the sensitivity and linearity of electrochemical pH sensors and the composition of nanocomposites. Thin films of PANI/CeO₂ and PANI/WO₃ were deposited via spin coating for characterization and application during the electrochemical impedance and capacitance spectroscopy (EIS and ECS) transduction stages. The findings showed that the optimized performance of the devices was extended not only to the sensitivity but also to the linearity. An increase of 213% in the ECS sensitivity of the PANI/CeO₂ compared to the metal oxide and an increase of 64% in the ECS linearity of the PANI/WO₃ compared to the polymeric sensitivity were reported. This study identified the structure-property relationship of nanocomposite thin films of PANI with metal oxides for use in electrochemical sensors. The developed materials could be applied in devices to be used in different fields, such as food, environment, and biomedical monitoring.

Enhanced electrical conductivity and stretchability of ionic-liquid PEDOT:PSS air-cathodes for aluminium-air batteries with long lifetime and high specific energy

A hydrogel film, poly-3,4-ethylenedioxythiophene (PEDOT):polystyrenesulfonate (PSS), containing an ionic liquid, is used as an air-cathode for a metal-air battery and its performance is investigated. This work presents the development of the air-cathode and the characterization of its physical, chemical and mechanical properties. Moreover, in view of wearable batteries, these air-cathodes are implemented within a flexible aluminium-air battery. It contains an aluminium anode, an electrolyte made of cellulose paper imbibed with an aqueous sodium chloride solution and the PEDOT:PSS air-cathode. Characterisation tests showed that the ionic liquid did not change the air-cathode chemically, while the electric conductivity increased considerably. The anode has an acceptable purity and was found to be resistant against self-corrosion. Discharge tests showed operating voltages up to 0.65 V, whereas two batteries in series could deliver up to 1.3 V at a current density of 0.9 mA cm^-2 for almost a day, sufficient for monitoring and medical devices. Several discharge tests with current densities from 0.25 up to 2.5 mA cm^-2 have presented operating lifetimes from 10 h up until over a day. At a current density of 2.8 mA cm^-2, the operating voltage and lifetime dropped considerably, explained by approaching the limiting current density of about 3 mA cm^-2, as evidenced by linear sweep voltammetry. The batteries showed high specific energies up to about 3140 Wh kg^-1. Mechanical tests revealed a sufficient stretchability of the air-cathode, even after battery discharge, implying an acceptable degree of wearability. Together with the reusability of the air-cathode, the battery is a promising route towards a low-cost viable way for wearable power supply for monitoring medical devices with long lifetimes and high specific energies. Optimization of the air-cathode could even lead to higher power applications.

A Novel Synthesized 1D Nanobelt-like Cobalt Phosphate Electrode Material for Excellent Supercapacitor Applications

In the present report, we synthesized highly porous 1D nanobelt-like cobalt phosphate (Co₂P₂O₇) materials using a hydrothermal method for supercapacitor (SC) applications. The physicochemical and electrochemical properties of the synthesized 1D nanobelt-like Co₂P₂O₇ were investigated using X-ray diffraction (XRD), X-ray photoelectron (XPS) spectroscopy, and scanning electron microscopy (SEM). The surface morphology results indicated that the deposition temperatures affected the growth of the 1D nanobelts. The SEM revealed a significant change in morphological results of Co₂P₂O₇ material prepared at 150 °C deposition temperature. The 1D Co₂P₂O₇ nanobelt-like nanostructures provided higher electrochemical properties, because the resulting empty space promotes faster ion transfer and improves cycling stability. Moreover, the electrochemical performance indicates that the 1D nanobelt-like Co₂P₂O₇ electrode deposited at 150 °C deposition temperature shows the maximum specific capacitance (Cs). The Co₂P₂O₇ electrode prepared at a deposition temperature 150 °C provided maximum Cs of 1766 F g^-1 at a lower scan rate of 5 mV s^-1 in a 1 M KOH electrolyte. In addition, an asymmetric hybrid Co₂P₂O₇//AC supercapacitor device exhibited the highest Cs of 266 F g^-1, with an excellent energy density of 83.16 Wh kg^-1, and a power density of 9.35 kW kg^-1. Additionally, cycling stability results indicate that the 1D nanobelt-like Co₂P₂O₇ material is a better option for the electrochemical energy storage application.

NiO/Ni Nanowafer Aerogel Electrodes for High Performance Supercapacitors

Transition metal oxide aerogels are a fascinating class of compounds that have received considerable attention in the last decade owing to their unique and exceptional properties, including high porosity, large surface area, and ultralow density. In this study, α-Ni(OH)₂ aerogels and annealed NiO/Ni aerogels were used to design and fabricate a two-electrode supercapacitor device. The physicochemical properties of the as-synthesized aerogels were characterized through X-ray diffraction, scanning electron microscopy, transmission electron microscopy, the Brunauer-Emmett-Teller theory, and X-ray photoelectron spectroscopy studies. The annealed NiO/Ni aerogels showed a (specific capacitance of 1060 F/g) specific capacity of 422 C/g at 1 A/g current density and with good cycling stability (up to 10,000 cycles). The supercapacitor also demonstrated an energy density of 32.4 Wh/kg and power density of 1800 W/kg at a current density of 2 A/g. The specific capacitance of NiO/Ni aerogels was more than twice that of the α-Ni(OH)₂ aerogels. The practical applications of the aerogel were demonstrated by fabricating a two-electrode device.

Design of ZIF-67 nanoflake derived NiCo-LDH/rGO hybrid nanostructures for aqueous symmetric supercapattery application under alkaline condition

Well-defined polyhedral ZIF-67 metal-organic frameworks (MOFs) are usually synthesized using methanol as solvent. In this work, methanol is replaced with deionized water as a solvent to synthesize ZIF-67 MOFs with unique nanoflake morphology. The ZIF-67 nanoflakes are synthesized directly byin situmethod on reduced graphene oxide (rGO) to obtain ZIF-67/rGO-xprecursors which are further transformed into NiCo-layered double hydroxide nanocomposites (NiCo-LDH/rGO-x,x = 10, 30, 50 and 90 mg of rGO). The NiCo-LDH/rGO-xnanostructured composites are found to be excellent materials for battery type supercapacitor (supercapattery) applications. Among these samples, the NiCo-LDH/rGO-30 composite gives maximum specific capacity of 829 C g^-1(1658 F g^-1) at a current density of 1 A g^-1and high rate capability. The as fabricated 2-electrode symmetric Swagelok deviceNiCo-LDH/rGO-30NiCo-LDH/rGO-30delivered a high energy density of 49.2 Wh kg^-1and a power density of 4511 W kg^-1, and enabled us to glow red, blue and white LED bulbs using three coin cells. The device can show good capacity retention even after 3000 continuous charge-discharge cycles. The NiCo-LDH/rGO-30 composite,in situderived from ZIF-67 MOF in combination with optimal amount of rGO, is an excellent material to deliver both high energy density and high power density in supercapattery devices.

Electrochemical Investigation of PANI:PPy/AC and PANI:PEDOT/AC Composites as Electrode Materials in Supercapacitors

The electrochemical deposition of the composites polyaniline (PANI):polypyrrole (PPy)/activated carbon (AC) and polyaniline (PANI): 3, 4-polyethylenedioxythiophene (PEDOT)/AC films is carried out in this work. The electrochemical character of the fabricated samples is investigated via cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and electrochemical impedance spectroscopy (EIS) using a three-electrode setup. The values of the specific capacitance of the composites PANI:PPy/AC and PANI:PEDOT/AC at a current density of 1 Ag⁻¹ are evaluated as 586 Fg⁻¹ and 611 Fg⁻¹, respectively. The values of energy density are 40 Whkg⁻¹ and 2094 Wkg⁻¹, whereas power density is recorded as 44 Whkg⁻¹ and 2160 Wkg⁻¹ for respective composites PANI:PPy/AC and PANI:PEDOT/AC. Moreover, the respective composites appeared to retain cyclic stabilities of 92% and 90%. This study points to the potential of the prepared composites for application as electrodes in supercapacitors.

Recent Advancements of Polyaniline/Metal Organic Framework (PANI/MOF) Composite Electrodes for Supercapacitor Applications: A Critical Review

Supercapacitors (SCs), also known as ultracapacitors, should be one of the most promising contenders for meeting the needs of human viable growth owing to their advantages: for example, excellent capacitance and rate efficiency, extended durability, and cheap materials price. Supercapacitor research on electrode materials is significant because it plays a vital part in the performance of SCs. Polyaniline (PANI) is an exceptional candidate for energy-storage applications owing to its tunable structure, multiple oxidation/reduction reactions, cheap price, environmental stability, and ease of handling. With their exceptional morphology, suitable functional linkers, metal sites, and high specific surface area, metal–organic frameworks (MOFs) are outstanding materials for electrodes fabrication in electrochemical energy storage systems. The combination of PANI and MOF (PANI/MOF composites) as electrode materials demonstrates additional benefits, which are worthy of exploration. The positive impacts of the two various electrode materials can improve the resultant electrochemical performances. Recently, these kinds of conducting polymers with MOFs composites are predicted to become the next-generation electrode materials for the development of efficient and well-organized SCs. The recent achievements in the use of PANI/MOFs-based electrode materials for supercapacitor applications are critically reviewed in this paper. Furthermore, we discuss the existing issues with PANI/MOF composites and their analogues in the field of supercapacitor electrodes in addition to potential future improvements.

Conjugated Molecules and Polymers in Secondary Batteries: A Perspective

Intrinsically conducting polymers constituting a subclass of macromolecules, as well as a still growing family of large, conjugated molecules, oligomers, and polymers, have attracted research interest for the recent decades. Closely corresponding to the fascination of these materials, combining typical properties of organic polymers and metallic materials, numerous applications have been suggested, explored, and sometimes transferred into products. In electrochemistry, they have been used in various functions beyond the initially proposed and obvious application as active masses in devices for electrochemical energy conversion and storage. This perspective contribution wraps up basic facts that are necessary to understand the behavior and properties of the oligo and polymers and their behavior in electrochemical cells for energy conversion by electrode reactions and associated energy storage. Representative examples are presented and discussed, and an overview of the state of research and development is provided. Particular attention is paid to stability and related aspects of practical importance. Future trends and perspectives are indicated.

Experimental and Computational Studies of Azo Dye-Modified Luminol Oligomers: Potential Application in Lithium Ion Sensing

With a view to design novel conjugated oligomers via a facile technique for its possible application in sensors, the present work reports oligomerization of Bismarck Brown (BB) dye with luminol. The structure was confirmed via IR studies, while the electronic transitions were confirmed by UV-visible studies. Morphological studies were carried out via SEM. Computational studies were carried out using the DFT method with a B3LYP 6-311G(d) basis set to investigate the optimized geometry, band gap, and vibrational and electronic transitions data. The HOMO-LUMO energies showed significant reduction in the band gap upon increasing the content of BB dye. The computational IR and UV spectra were noticed to be in close agreement with the experimental results. Spectrophotometric determination of Li ion was attempted using lithium chloride and a lithium carbonate drug commonly used in the treatment of bipolar disorder. The detection limit was noticed to be as low as 5.1 × 10-6 M, which could be used to design a Li ion sensor.

Dielectric Barrier Discharge Plasma Jet (DBDjet) Processed Reduced Graphene Oxide/Polypyrrole/Chitosan Nanocomposite Supercapacitors

Reduced graphene oxide (rGO) and/or polypyrrole (PPy) are mixed with chitosan (CS) binder materials for screen-printing supercapacitors (SCs) on arc atmospheric-pressure plasma jet (APPJ)-treated carbon cloth. The performance of gel-electrolyte rGO/CS, PPy/CS, and rGO/PPy/CS SCs processed by a dielectric barrier discharge plasma jet (DBDjet) was assessed and compared. DBDjet processing improved the hydrophilicity of these three nanocomposite electrode materials. Electrochemical measurements including electrical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charging-discharging (GCD) were used to evaluate the performance of the three types of SCs. The Trasatti method was used to evaluate the electric-double layer capacitance (EDLC) and pseudocapacitance (PC) of the capacitance. The energy and power density of the three types of SCs were illustrated and compared using Ragone plots. Our experiments verify that, with the same weight of active materials, the combined use of rGO and PPy in SCs can significantly increase the capacitance and improve the operation stability.

Enhanced Storage Performance of PANI and PANI/Graphene Composites Synthesized in Protic Ionic Liquids

Polyaniline (PANI) was synthesized using oxidative polymerization in a mixture of water with pyrrolidinium hydrogen sulfate [Pyrr][HSO₄], which is a protic ionic liquid PIL. The obtained PANI (PANI/PIL) was compared with conventional PANI (PANI/HCl and PANI/HSO₄) in terms of their morphological, structural, and storage properties. The results demonstrate that the addition of this PIL to a polymerization medium leads to a fiber-like morphology, instead of a spherical-like morphology, of PANI/HSO₄ or an agglomerated morphology of PANI/HCl. In addition, PAN/PIL exhibits an improvement of the charge transfer kinetic and storage capability in H₂SO₄ 1 mol·L^-1, compared to PANI/HCl. The combination of PANI/PIL and graphene oxide (GO), on the other hand, was investigated by optimizing the PANI/GO weight ratio to achieve the nanocomposite material with the best performance. Our results indicate that the PANI/PIL/GO containing 16 wt% of GO material exhibits a high performance and stability (223 F·g^-1 at 10 A·g^-1 in H₂SO₄ 1 mol·L^-1, 4.9 Wh·Kg^-1, and 3700 W·Kg^-1 @ 10 A·g^-1). The obtained results highlight the beneficial role of PIL in building PANI and PANI/GO nanocomposites with excellent performances for supercapacitor applications.

Exploring the Functional Properties of Sodium Phytate Doped Polyaniline Nanofibers Modified FTO Electrodes for High-Performance Binder Free Symmetric Supercapacitors

The performance of high-rate supercapacitors requires fine morphological and electrical properties of the electrode. Polyaniline (PANI), as one of the most promising materials for energy storage, shows different behaviour on different substrates. The present study reports on the surface modification of fluorine doped tin oxide (FTO) with the sodium phytate doped PANI without any binder and its utilization as a novel current collector in symmetric supercapacitor devices. The electrochemical behaviour of the sodium phytate doped PANI thin film with and without a binder on fluorine doped tin oxide (FTO) as current collector was investigated by cyclic voltammetry (CV). The electrode without a binder showed higher electrocatalytic efficiency. A symmetrical cell configuration was therefore constructed with the binder-free electrodes. The device showed excellent electrochemical performance with high specific capacities of 550 Fg⁻¹ at 1 Ag⁻¹ and 355 Fg⁻¹ at 40 Ag⁻¹ calculated from galvanostatic discharge curves. The low charge transfer and solution resistances (R_CT and R_S) of 7.86 Ωcm² and 3.58 × 10⁻¹ Ωcm², respectively, and superior rate capability of 66.9% over a wide current density range of 1 Ag⁻¹ to 40 Ag⁻¹ and excellent cycling stability with 90% of the original capacity over 1000 charge/discharge cycles at 40 Ag⁻¹, indicated it to be an efficient energy storage device. Moreover, the gravimetric energy and power density of the supercapacitor was remarkably high, providing 73.8 Whkg⁻¹ at 500 Wkg⁻¹, respectively. The gravimetric energy density remained stable as the power density increased. It even reached up to 49.4 Whkg⁻¹ at a power density of up to 20 Wkg⁻¹.

Improvement of capacitive performance of polyaniline based hybrid supercapacitor

This study focuses on synthesis of polyaniline composites and application as electrode material in the fabrication of hybrid supercapacitors. Hybrid supercapacitors were fabricated using aluminum foil as current collector, and conductive Polyaniline (PANI) composites as electrode materials. Cobalt oxide (Co2O3), ammonium peroxydisulfate (APS) were used along with PANI in the preparation of electrodes of the supercapacitor. Polyaniline and its various composites were used in the cathode and activated carbon in the anode (positive electrodes) of the asymmetric hybrid supercapacitor. Electrochemical performance of the supercapacitors has been evaluated on the basis of capacitive properties (i.e. capacitance, energy density and power density). Area of the supercapacitor, applied voltage for charging and composition of cathode materials have been optimized in this study. The optimum area of the supercapacitor was found 30 cm2 at optimum voltage 5 V. The result showed that supercapacitor fabricated using polyaniline (PANI) as cathode material with Al foil as current collector provided highest capacitance of 249 F/g, Energy density of 31 Wh/kg and Power density of 18 W/kg. Among various PANI composites (Ni-PANI, Cu-PANI, CNF-PANI) synthesized in this study, Ni-PANI composite showed highest capacitance of 336 F/g, energy density of 42 Wh/kg, and power density of 31 W/kg. The result indicates that Ni-PANI composite has high potential as cathode materials for the hybrid supercapacitor.

Electropolymerized Poly(3,4-ethylenedioxythiophene)/Screen-Printed Reduced Graphene Oxide-Chitosan Bilayer Electrodes for Flexible Supercapacitors

An electropolymerized poly(3,4-ethylenedioxythiophene) (PEDOT)/screen-printed reduced graphene oxide (rGO)-chitosan (CS) bilayer material was coated on carbon cloth to form electrodes for gel-electrolyte flexible supercapacitors. The conductive polymer and carbon-based materials mainly contribute pseudocapacitance (PC) and electrical double-layer capacitance (EDLC), respectively. The high porosity and hydrophilicity of the PEDOT/rGO-CS bilayer material offers a large contact area and improves the contact quality for the gel electrolyte, thereby enhancing the capacitive performance. Cyclic voltammetry (CV) under a potential scan rate of 2 mV/s revealed that a maximum areal capacitance of 1073.67 mF/cm² was achieved. The capacitance contribution ratio PC/EDLC was evaluated to be ∼67/33 by the Trasatti method. A 10,000-cycle CV test showed a capacitance retention rate of 99.3% under a potential scan rate of 200 mV/s, indicating good stability. The areal capacitance remains similar under bending with a bending curvature of up to 1.5 cm^-1.

High Energy Density Heteroatom (O, N and S) Enriched Activated Carbon for Rational Design of Symmetric Supercapacitors

Carbon-based symmetric supercapacitors (SCs) are known for their high power density and long cyclability, making them an ideal candidate for power sources in new-generation electronic devices. To boost their electrochemical performances, deriving activated carbon doped with heteroatoms such as N, O, and S are highly desirable for increasing the specific capacitance. In this regard, activated carbon (AC) self-doped with heteroatoms is directly derived from bio-waste (lima-bean shell) using different KOH activation processes. The heteroatom-enriched AC synthesized using a pretreated carbon-to-KOH ratio of 1:2 (ONS@AC-2) shows excellent surface morphology with a large surface area of 1508 m²  g^-1 . As an SC electrode material, the presence of heteroatoms (N and S) reduces the interfacial charge-transfer resistance and increases the ion-accessible surface area, which inherently provides additional pseudocapacitance. The ONS@AC-2 electrode attains a maximum specific capacitance (C_sp ) of 342 F g^-1 at a specific current of 1 Ag^-1 in 1 m NaClO₄ electrolyte at the wide potential window of 1.8 V. Moreover, as symmetric SCs the ONS@AC-2 electrode delivers a maximum specific capacitance (C_sc ) of 191 F g^-1 with a maximum specific energy of 21.48 Wh kg^-1 and high specific power of 14 000 W kg^-1 and excellent retention of its initial capacitance (98 %) even after 10000 charge/discharge cycles. In addition, a flexible supercapacitor fabricated utilizing ONS@AC-2 electrodes and a LiCl/polyvinyl alcohol (PVA)-based polymer electrolyte shows a maximum C_sc of 119 F g^-1 with considerable specific energy and power.

Waffle-Like Carbons Combined with Enriched Mesopores and Highly Heteroatom-Doped Derived from Sandwiched MOF/LDH/MOF for High-Rate Supercapacitor

Supercapacitors (SCs) are promising for powering mobile devices, electric vehicles and smart power grids due to their fast charge/discharge rate, high power capability and robust cycle stability. Nitrogen-doped porous carbons are great alternatives because they provide pseudocapacitance without losing their power rate. Nanoporous carbon derived from metal organic frameworks (MOFs) is an ideal precursor for preparing heteroatom-doped carbons due to their abundant nitrogen contents and incredible specific surface areas. However, severe aggregations and the leakage of nitrogen can occur during harsh carbonization. In this study, we used CoAl-LDH (cobalt aluminum layered double hydroxide) as an in-situ growth substrate, allowing Co-based MOF to uniformly grow onto the CoAl-LDH to form a sandwiched MOF/LDH/MOF structure. After acid etching, we obtained waffle-like nanoporous carbons (WNPC). WNPC exhibited high nitrogen and oxygen retention (7.5 wt% and 9.1 wt%) and a broad mesopores distribution with specific surface areas of 594 m²g⁻¹, which promoted a sieving effect. This renders a specific capacitance of 300.7 F·g⁻¹ at 1 A·g⁻¹ and the high retention (72%) of capacitance at 20 A·g⁻¹, ensuring its use at high-rate supercapacitor electrodes. Finally, the WNPC symmetric supercapacitor reaches a superior specific energy of 27 W·h·kg⁻¹ at a power of 500 W·kg⁻¹, and a good cycle stability (85% capacitance retention after 10,000 cycles).

Boosting the Utilization and Electrochemical Performances of Polyaniline by Forming a Binder-Free Nanoscale Coaxially Coated Polyaniline/Carbon Nanotube/Carbon Fiber Paper Hierarchical 3D Microstructure Composite as a Supercapacitor Electrode

Nanoscale polyaniline (PANI) is formed on a hierarchical 3D microstructure carbon nanotubes (CNTs)/carbon fiber paper (CFP) substrate via a one-step electrochemical polymerization method. The chemical and structural properties of the binder-free PANI/CNTs/CFP electrode are characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The specific capacitance of PANI/CNTs/CFP tested in a symmetric two-electrode system reaches 731.6 mF·cm^-2 (1354.7 F·g^-1) at a current density of 1 mA·cm^-2 (1.8 A·g^-1). The symmetric supercapacitor device demonstrates excellent cycling performance up to 10,000 cycles with a capacitance retention of 81.4% at a current density of 1 mA·cm^-2 (1.8 A·g^-1). The results demonstrate that the binder-free CNTs/CFP composite is a strong backbone for depositing ultrathin PANI layers at a high mass loading. The hierarchical 3D microstructure PANI/CNTs/CFP provides enough space and transporting channels to form an efficient electrode-electrolyte interface for the supercapacitance reaction. The formed nanoscale PANI film coaxially coated on the sidewalls of CNTs enables efficient charge transfer and a shortened diffusion length. Hence, the utilization efficiency and electrochemical performances of PANI are significantly improved. The rational design strategy of a CNT-based binder-free hierarchical 3D microstructure can be used in preparing various advanced energy-storage electrodes for electrochemical energy-storage and conversion systems.

Electrode Materials for Supercapacitors: A Review of Recent Advances

The advanced electrochemical properties, such as high energy density, fast charge–discharge rates, excellent cyclic stability, and specific capacitance, make supercapacitor a fascinating electronic device. During recent decades, a significant amount of research has been dedicated to enhancing the electrochemical performance of the supercapacitors through the development of novel electrode materials. In addition to highlighting the charge storage mechanism of the three main categories of supercapacitors, including the electric double-layer capacitors (EDLCs), pseudocapacitors, and the hybrid supercapacitors, this review describes the insights of the recent electrode materials (including, carbon-based materials, metal oxide/hydroxide-based materials, and conducting polymer-based materials, 2D materials). The nanocomposites offer larger SSA, shorter ion/electron diffusion paths, thus improving the specific capacitance of supercapacitors (SCs). Besides, the incorporation of the redox-active small molecules and bio-derived functional groups displayed a significant effect on the electrochemical properties of electrode materials. These advanced properties provide a vast range of potential for the electrode materials to be utilized in different applications such as in wearable/portable/electronic devices such as all-solid-state supercapacitors, transparent/flexible supercapacitors, and asymmetric hybrid supercapacitors.