Fabrication and electrochemical characterization of polyaniline nanorods modified with sulfonated carbon nanotubes for supercapacitor applications

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.

Preparation of Symmetrical Capacitors from Lignin-Derived Phenol and PANI Composites with Good Electrical Conductivity

As a natural polymer, lignin is only less abundant in nature than cellulose. It has the form of an aromatic macromolecule, with benzene propane monomers connected by molecular bonds such as C-C and C-O-C. One method to accomplish high-value lignin conversion is degradation. The use of deep eutectic solvents (DESs) to degrade lignin is a simple, efficient and environmentally friendly degradation method. After degradation, the lignin is broken due to β-O-4 to produce phenolic aromatic monomers. In this work, lignin degradation products were evaluated as additives for the preparation of polyaniline conductive polymers, which not only avoids solvent waste but also achieves a high-value use of lignin. The morphological and structural characteristics of the LDP/PANI composites were investigated using ¹H NMR, Fourier-transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis and elemental analysis. The LDP/PANI nanocomposite provides a specific capacitance of 416.6 F/g at 1 A/g and can be used as a lignin-based supercapacitor with good conductivity. Assembled as a symmetrical supercapacitor device, it provides an energy density of 57.86 Wh/kg, an excellent power density of 952.43 W/kg and, better still, a sustained cycling stability. Thus, the combination of polyaniline and lignin degradate, which is environmentally friendly, amplifies the capacitive function on the basis of polyaniline.

A Review on the Application of Cobalt-Based Nanomaterials in Supercapacitors

Among many electrode materials, cobalt-based nanomaterials are widely used in supercapacitors because of their high natural abundance, good electrical conductivity, and high specific capacitance. However, there are still some difficulties to overcome, including poor structural stability and low power density. This paper summarizes the research progress of cobalt-based nanomaterials (cobalt oxide, cobalt hydroxide, cobalt-containing ternary metal oxides, etc.) as electrode materials for supercapacitors in recent years and discusses the preparation methods and properties of the materials. Notably, the focus of this paper is on the strategies to improve the electrochemical properties of these materials. We show that the performance of cobalt-based nanomaterials can be improved by designing their morphologies and, among the many morphologies, the mesoporous structure plays a major role. This is because mesoporous structures can mitigate volume changes and improve the performance of pseudo capacitance. This review is dedicated to the study of several cobalt-based nanomaterials in supercapacitors, and we hope that future scholars will make new breakthroughs in morphology design.

Activated Graphene Deposited on Porous Cu Mesh for Supercapacitors

A porous Cu (P-Cu) mesh was used as a current collector and its morphological effect on the supercapacitor performance was investigated. A porous surface was obtained by thermally annealing the Cu mesh using ammonia gas. Hierarchically porous activated graphene (AG) with a high specific surface area (SSA) was deposited on the P-Cu mesh using electrophoretic deposition, aided by graphene oxide (GO). GO was thermally converted to electrically conductive reduced graphene oxide (rGO). The AG/rGO that was deposited on the P-Cu mesh achieved a high specific capacitance of up to 140.0 F/g and a high energy density of up to 3.11 Wh/kg at a current density of 2 A/g in 6 m KOH aqueous electrolyte. The high SSA of AG and the porous surface morphology of the Cu mesh allowed efficient electric double-layer formation and charge transport. This work offers an alternative to improve supercapacitors by combining a porous metallic current collector with porous AG.

CE with multi-walled carbon nanotubes (MWCNTs). Part I. Functionalized and SDS coated MWCNTs as pseudo-stationary phases in nanoparticle EKC - Studies on retention energetics

In this study, multi-walled carbon nanotubes (MWCNTs) in either unmodified, hydroxylated (MWCNT-OH), carboxylated (MWCNT-COOH) or sulfonated (MWCNT-SO₃H) forms were incorporated into the running electrolytes in capillary electrophoresis (CE) to play the role of pseudo-stationary phases (PSPs) and perform nanoparticle electrokinetic capillary chromatography (NPEKC). MWCNT-COOH and MWCNT-SO₃H were derived from MWCNTs via their treatment with concentrated strong acids. These functionalized MWCNTs were characterized by Raman and FTIR spectroscopies to demonstrate their covalent functionalization. The study of MWCNT-SO₃H and MWCNT-OH as PSPs were introduced in this research report for the first time in NPEKC. The results obtained with functionalized MWCNTs were compared to those obtained using unmodified MWCNTs for better understanding the electrophoretic behavior of these functionalized MWCNTs. While only MWCNT-COOH allowed the separation of some nucleic acid bases and nucleosides, neutral solutes such as alkylbenzenes (ABs), phenyl alkyl alcohols (PAAs) and aniline derivatives in neutral forms (i.e., at basic pH) were not resolved in the presence of neither MWCNT-COOH nor MWCNT-SO₃H in the running electrolytes, indicating that these functionalized MWCNTs do not have enough surface charge density to function as effective PSPs in NPEKC. This necessitated the coating of the functionalized MWCNTs under investigation with sodium dodecyl sulfate (SDS) to bring about the separation of neutral solutes by NPEKC. The SDS coated MWCNTs whether unmodified or functionalized were characterized with two homologous series namely ABs and PAAs in order to evaluate their relative retention energetics under the same electrolyte composition. The results showed that the systems pairs SDS-MWCNT-COOH/SDS-MWCNTs and SDS-MWCNT-OH/SDS-MWCNTs were homoenergetics (i.e., same energetics) while the system pair SDS-MWCNT-SO₃H/SDS-MWCNTs was homeoenergetics (i.e., similar energetics). On the other hand, all the systems pairs SDS coated MWCNTs/SDS were homeoenergetics. Homoenergetics means that the solute retention has an identical physico-chemical basis and the differences observed in the magnitude of solute retention on the various PSPs are attributed to differences in the nonpolar phase ratios of the PSPs under otherwise the same electrolyte composition. Conversely, homeoenergetics signifies that the solute retention has a similar physico-chemical basis in the PSPs systems under investigation, which also differ in their phase ratios.

Supercapacitor Energy Storage Device Using Biowastes: A Sustainable Approach to Green Energy

The demand for renewable energy sources worldwide has gained tremendous research attention over the past decades. Technologies such as wind and solar have been widely researched and reported in the literature. However, economical use of these technologies has not been widespread due partly to cost and the inability for service during of-source periods. To make these technologies more competitive, research into energy storage systems has intensified over the last few decades. The idea is to devise an energy storage system that allows for storage of electricity during lean hours at a relatively cheaper value and delivery later. Energy storage and delivery technologies such as supercapacitors can store and deliver energy at a very fast rate, offering high current in a short duration. The past decade has witnessed a rapid growth in research and development in supercapacitor technology. Several electrochemical properties of the electrode material and electrolyte have been reported in the literature. Supercapacitor electrode materials such as carbon and carbon-based materials have received increasing attention because of their high specific surface area, good electrical conductivity and excellent stability in harsh environments etc. In recent years, there has been an increasing interest in biomass-derived activated carbons as an electrode material for supercapacitor applications. The development of an alternative supercapacitor electrode material from biowaste serves two main purposes: (1) It helps with waste disposal; converting waste to a useful product, and (2) it provides an economic argument for the substantiality of supercapacitor technology. This article reviews recent developments in carbon and carbon-based materials derived from biowaste for supercapacitor technology. A comparison between the various storage mechanisms and electrochemical performance of electrodes derived from biowaste is presented.

Synthesis and Electrochemical Capacitor Characterization of Novel Composite Materials with p-Type Conductive Polymer

Considering the importance of conductive polymer nanocomposite, the present paper attempts to create a method for increasing the conductivity of poly(o-aminophenol). Nanocomposite MnO2/poly(o-aminophenol) thin film was synthesized by using pulse potential electrodeposition technique on a graphite electrode. In this research, nanoparticles of MnO2 are used after synthesis to prepare polymer nanocomposites in one-step. Appending of MnO2 to polymer matrix increases the current. This current growth could be ascribed to the synergistic MnO2 nanostructure, which presents the superior surface area and smaller particle size that is increasingly acting sites. Morphology or samples composition was investigated by the scanning electron microscope and the UV-Vis method, which clearly indicate the formation of nanocomposites. The findings show that the capacitive behavior of MnO2-poly(o-aminophenol) is superior to poly(o-aminophenol), especially at high potential high temperatures. The results showed that MnO2/poly(o-aminophenol) had a higher level of activity and the electron transfer capability was faster than pure polymer film. The doped MnO2 polymer also has excellent cyclic performance and load discharge features. Additional electrochemical properties of these polymer composites were observed against pure polymer so that capacity of 645 Fg−1 has been designated.

Novel ternary nanocomposites of MWCNTs/PANI/MoS2: preparation, characterization and enhanced electrochemical capacitance

In this work, nanoflower-like MoS₂ grown on the surface of multi-walled carbon nanotubes (MWCNTs)/polyaniline (PANI) nano-stem is synthesized via a facile in situ polymerization and hydrothermal method. Such a novel hierarchical structure commendably promotes the contact of PANI and electrolyte for faradaic energy storage. In the meanwhile, the double-layer capacitance of MoS₂ is effectively used. The morphology and chemical composition of the as-prepared samples are characterized by scanning and transmission electron microscopies, X-ray diffraction and Fourier transform infrared spectra. The electrochemical performance of the samples is evaluated by cyclic voltammogram and galvanostatic charge-discharge measurements. It is found that the specific capacitance of the obtained MWCNTs/PANI/MoS₂ hybrid is 542.56 F g^-1 at a current density of 0.5 A g^-1. Furthermore, the MWCNTs/PANI/MoS₂ hybrid also exhibits good rate capability (62.5% capacity retention at 10 A g^-1) and excellent cycling stability (73.71% capacitance retention) over 3000 cycles.

Asymmetric Supercapacitor Electrodes and Devices

The world is recently witnessing an explosive development of novel electronic and optoelectronic devices that demand more-reliable power sources that combine higher energy density and longer-term durability. Supercapacitors have become one of the most promising energy-storage systems, as they present multifold advantages of high power density, fast charging-discharging, and long cyclic stability. However, the intrinsically low energy density inherent to traditional supercapacitors severely limits their widespread applications, triggering researchers to explore new types of supercapacitors with improved performance. Asymmetric supercapacitors (ASCs) assembled using two dissimilar electrode materials offer a distinct advantage of wide operational voltage window, and thereby significantly enhance the energy density. Recent progress made in the field of ASCs is critically reviewed, with the main focus on an extensive survey of the materials developed for ASC electrodes, as well as covering the progress made in the fabrication of ASC devices over the last few decades. Current challenges and a future outlook of the field of ASCs are also discussed.

Preparation and Application of Electrodes in Capacitive Deionization (CDI): a State-of-Art Review

As a promising desalination technology, capacitive deionization (CDI) have shown practicality and cost-effectiveness in brackish water treatment. Developing more efficient electrode materials is the key to improving salt removal performance. This work reviewed current progress on electrode fabrication in application of CDI. Fundamental principal (e.g. EDL theory and adsorption isotherms) and process factors (e.g. pore distribution, potential, salt type and concentration) of CDI performance were presented first. It was then followed by in-depth discussion and comparison on properties and fabrication technique of different electrodes, including carbon aerogel, activated carbon, carbon nanotubes, graphene and ordered mesoporous carbon. Finally, polyaniline as conductive polymer and its potential application as CDI electrode-enhancing materials were also discussed.

Rational design of polyaniline/MnO2/carbon cloth ternary hybrids as electrodes for supercapacitors

A ternary hybrid was fabricated by sequentially depositing polyaniline and MnO₂ on carbon cloth. It displayed a unique porous structure and possessed a good electrochemical performance with a high areal capacitance of 421.6 mF cm⁻² (0.2 mA cm⁻²).

Polyaniline nanowire arrays aligned on nitrogen-doped carbon fabric for high-performance flexible supercapacitors

A combination of vertical polyaniline (PANI) nanowire arrays and nitrogen plasma etched carbon fiber cloths (eCFC) was fabricated to create 3D nanostructured PANI/eCFC composites. The small size of the highly ordered PANI nanowires can greatly reduce the scale of the diffusion length, allowing for the improved utilization of electrode materials. A two-electrode flexible supercapacitor based on PANI/eCFC demonstrates a high specific capacitance (1035 F g(-1) at a current density of 1 A g(-1)), good rate capability (88% capacity retention at 8 A g(-1)), and long-term cycle life (10% capacity loss after 5000 cycles). The lightweight, low-cost, flexible composites are promising candidates for use in energy storage device applications.

Carbon-based layer-by-layer nanostructures: from films to hollow capsules

Over the past years, the layer-by-layer (LbL) assembly has been widely developed as one of the most powerful techniques to prepare multifunctional films with desired functions, structures and morphologies because of its versatility in the process steps in both material and substrate choices. Among various functional nanoscale objects, carbon-based nanomaterials, such as carbon nanotubes and graphene sheets, are promising candidates for emerging science and technology with their unique physical, chemical, and mechanical properties. In particular, carbon-based functional multilayer coatings based on the LbL assembly are currently being actively pursued as conducting electrodes, batteries, solar cells, supercapacitors, fuel cells and sensor applications. In this article, we give an overview on the use of carbon materials in nanostructured films and capsules prepared by the LbL assembly with the aim of unraveling the unique features and their applications of carbon multilayers prepared by the LbL assembly.