A study of the electrochemical properties of conducting polymers for application in electrochemical capacitors

Electrochemical Doping and Structural Modulation of Conductive Metal-Organic Frameworks

In this study, we introduce an electrochemical doping strategy aimed at manipulating the structure and composition of electrically conductive metal-organic frameworks (c-MOFs). Our methodology is exemplified through a representative c-MOF, Ni3(HITP)2 (HITP=2, 3, 6, 7, 10, 11-hexaiminotriphenylene), synthesized into porous thin films supported by nanocellulose. While the c-MOF exhibits characteristic capacitive behavior in neutral electrolyte; it manifests redox behaviors in both acidic and alkaline electrolytes. Evidence indicates that the organic ligands within c-MOF undergo oxidation (p-doping) and reduction (n-doping) when exposed to specific electrochemical potentials in acidic and alkaline electrolyte, respectively. Interestingly, the p-doping process proves reversible, with the c-MOF structure remaining stable across cyclic p-doping/de-doping. In contrast, the n-doping is irreversible, leading to the gradual decomposition of the framework into inorganic species over a few cycles. Drawing on these findings, we showcase the versatile electrochemical applications of c-MOFs and their derived composites, encompassing electrochemical energy storage, electrocatalysis, and ultrafast actuation. This study provides profound insights into the doping of c-MOFs, offering a new avenue for modulating their chemical and electronic structure, thereby broadening their potential for diverse electrochemical applications.

Iron/vanadium co-doped tungsten oxide nanostructures anchored on graphitic carbon nitride sheets (FeV-WO3@g-C3N4) as a cost-effective novel electrode material for advanced supercapacitor applications

In this work, we studied the effect of iron (Fe) and vanadium (V) co-doping (Fe/V), and graphitic carbon nitride (g-C3N4) on the performance of tungsten oxide (WO3) based electrodes for supercapacitor applications. The lone pair of electrons on nitrogen can improve the surface polarity of the g-C3N4 electrode material, which may results in multiple binding sites on the surface of electrode for interaction with electrolyte ions. As electrolyte ions interact with g-C3N4, they quickly become entangled with FeV-WO3 nanostructures, and the contact between the electrolyte and the working electrode is strengthened. Herein, FeV-WO3@g-C3N4 is fabricated by a wet chemical approach along with pure WO3 and FeV-WO3. All of the prepared samples i.e., WO3, FeV-WO3, and FeV-WO3@g-C3N4 were characterized by XRD, FTIR, EDS, FESEM, XPS, Raman, and BET techniques. Electrochemical performance is evaluated by cyclic voltammetry (CV), galvanic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). It is concluded from electrochemical studies that FeV-WO3@g-C3N4 exhibits the highest electrochemical performance with specific capacitance of 1033.68 F g-1 at scan rate 5 mV s-1 in the potential window range from -0.8 to 0.25 V, that is greater than that for WO3 (422.76 F g-1) and FeV-WO3 (669.76 F g-1). FeV-WO3@g-C3N4 has the highest discharge time (867 s) that shows it has greater storage capacity, and its coulombic efficiency is 96.7%, which is greater than that for WO3 (80.1%) and FeV-WO3 (92.1%), respectively. Furthermore, excellent stability up to 2000 cycles is observed in FeV-WO3@g-C3N4. It is revealed from EIS measurements that equivalent series resistance and charge transfer values calculated for FeV-WO3@g-C3N4 are 1.82 Ω and 0.65 Ω, respectively.

Preparation and Characterization of Physically Activated Carbon and Its Energetic Application for All-Solid-State Supercapacitors: A Case Study

Biomass-derived activated carbons have gained significant attention as electrode materials for supercapacitors (SCs) due to their renewability, low-cost, and ready availability. In this work, we have derived physically activated carbon from date seed biomass as symmetric electrodes and PVA/KOH has been used as a gel polymer electrolyte for all-solid-state SCs. Initially, the date seed biomass was carbonized at 600 °C (C-600) and then it was used to obtain physically activated carbon through CO₂ activation at 850 °C (C-850). The SEM and TEM images of C-850 displayed its porous, flaky, and multilayer type morphologies. The fabricated electrodes from C-850 with PVA/KOH electrolytes showed the best electrochemical performances in SCs (Lu et al. Energy Environ. Sci., 2014, 7, 2160) application. Cyclic voltammetry was performed from 5 to 100 mV s^-1, illustrating an electric double layer behavior. The C-850 electrode delivered a specific capacitance of 138.12 F g^-1 at 5 mV s^-1, whereas it retained 16 F g^-1 capacitance at 100 mV s^-1. Our assembled all-solid-state SCs exhibit an energy density of 9.6 Wh kg^-1 with a power density of 87.86 W kg^-1. The internal and charge transfer resistances of the assembled SCs were 0.54 and 17.86 Ω, respectively. These innovative findings provide a universal and KOH-free activation process for the synthesis of physically activated carbon for all solid-state SCs applications.

A New Method to Prepare Stable Polyaniline Dispersions for Highly Loaded Cathodes of All-Polymer Li-Ion Batteries

A new method for the preparation of polyaniline (PANI) films that have a 2D structure and can record high active mass loading (up to 30 mg cm^-2) via acid-assisted polymerization in the presence of concentrated formic acid was developed. This new approach represents a simple reaction pathway that proceeds quickly at room temperature in quantitative isolated yield with the absence of any byproducts and leads to the formation of a stable suspension that can be stored for a prolonged time without sedimentation. The observed stability was explained by two factors: (a) the small size of the obtained rod-like particles (50 nm) and (b) the change of the surface of colloidal PANI particles to a positively charged form by protonation with concentrated formic acid. The films cast from the concentrated suspension were composed of amorphous PANI chains assembled into 2D structures with nanofibrillar morphology. Such PANI films demonstrated fast and efficient diffusion of the ions in liquid electrolyte and showed a pair of revisable oxidation and reduction peaks in cyclic voltammetry. Furthermore, owing to the high mass loading, specific morphology, and porosity, the synthesized polyaniline film was impregnated by a single-ion conducting polyelectrolyte-poly(LiM_n-r-PEGM_m) and characterized as a novel lightweight all-polymeric cathode material for solid-state Li batteries by cyclic voltammetry and electrochemical impedance spectroscopy techniques.

Ionic liquid dispersed highly conducting polymer electrolyte for supercapacitor application: Current scenario and prospects “ICSEM 2021”

Ionic liquid (IL) is now being considered as a novel contender in the development of highly conducting polymer electrolytes rather than a solvent. It has a significant impact on the electrochemical performance of polymer electrolytes. This study emphasizes the significance of low viscosity IL dispersion within a polymer (PVA) matrix. The electrical, structural and photoelectrochemical properties of the IL-doped polymer electrolyte are discussed in detail. These highly conducting IL doped solid polymer electrolytes show promise towards the development of highly efficient Supercapacitors.

Reversible Redox Processes in Polymer of Unmetalated Salen-Type Ligand: Combined Electrochemical in Situ Studies and Direct Comparison with Corresponding Nickel Metallopolymer

Most non-metalized Salen-type ligands form passivation thin films on electrode surfaces upon electrochemical oxidation. In contrast, the H₂(3-MeOSalen) forms electroactive polymer films similarly to the corresponding nickel complex. There are no details of electrochemistry, doping mechanism and charge transfer pathways in the polymers of pristine Salen-type ligands. We studied a previously uncharacterized electrochemically active polymer of a Salen-type ligand H₂(3-MeOSalen) by a combination of cyclic voltammetry, in situ ultraviolet-visible (UV-VIS) spectroelectrochemistry, in situ electrochemical quartz crystal microbalance and Fourier Transform infrared spectroscopy (FTIR) spectroscopy. By directly comparing it with the polymer of a Salen-type nickel complex poly-Ni(3-MeOSalen) we elucidate the effect of the central metal atom on the structure and charge transport properties of the electrochemically doped polymer films. We have shown that the mechanism of charge transfer in the polymeric ligand poly-H₂(3-MeOSalen) are markedly different from the corresponding polymeric nickel complex. Due to deviation from planarity of N₂O₂ sphere for the ligand H₂(3-MeOSalen), the main pathway of electron transfer in the polymer film poly-H₂(3-MeOSalen) is between π-stacked structures (the π-electronic systems of phenyl rings are packed face-to-face) and C-C bonded phenyl rings. The main way of electron transfer in the polymer film poly-Ni(3-MeOSalen) is along the polymer chain, while redox processes are ligand-based.

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.

Mechanical properties and structures under the deformation of thiophene copolymers with cyclic siloxane units

The control of cross-linking of polythiophene with cyclic siloxane was achieved and provided to their mechanical properties and elastic recovery. The cross-links led to high recovery of crystallite orientation under stretching.

Intercalation and flexibility chemistries of soft layered materials

Layered materials, alternate stackings of two or more components, are found in a wide range of scales. Chemists can design and synthesize layered structures containing functional units. The soft-type layered materials exhibit characteristic dynamic functions originating from two-dimensional (2D) anisotropy and structure flexibility. This feature article focuses on "intercalation" and "flexibility" as two new perspectives for designing soft layered materials. Intercalation of guests is a characteristic approach for design of layered structures. Flexibility is an important factor to control the dynamic functions of the layered structures. As a model case, the intercalation-induced tunable stimuli-responsive color-change properties of layered polydiacetylene (PDA) are introduced to study the impact of the intercalation and flexibility on the dynamic functions. Recently, layered materials have drastically expanded the research area from conventional rigid inorganic compounds to new self-assembled nanostructures consisting of organic components, such as polymers, metal-organic frameworks, and covalent-organic frameworks. These new layered architectures have potentials for exhibiting dynamic functions originating from the structure flexibility beyond the static properties originating from classical intercalation and host-guest chemistries. Therefore, intercalation and flexibility chemistries of soft layered materials are regarded as new perspectives for design of advanced dynamic functional materials.

Polycarbazole and Its Derivatives: Synthesis and Applications. A Review of the Last 10 Years

Polycarbazole and its derivatives have been extensively used for the last three decades, although the interest in these materials briefly decreased. However, the increasing demand for conductive polymers for several applications such as light emitting diodes (OLEDs), capacitators or memory devices, among others, has renewed the interest in carbazole-based materials. In this review, the synthetic routes used for the development of carbazole-based polymers have been summarized, reviewing the main synthetic methodologies, namely chemical and electrochemical polymerization. In addition, the applications reported in the last decade for carbazole derivatives are analysed. The emergence of flexible and wearable electronic devices as a part of the internet of the things could be an important driving force to renew the interest on carbazole-based materials, being conductive polymers capable to respond adequately to requirement of these devices.

Flexible Energy Storage System—An Introductory Review of Textile-Based Flexible Supercapacitors

Recently, researchers have become interested in exploring applications of rechargeable battery storage technology in different disciplines, which can help our daily life, such as textile-based supercapacitors. This paper briefly describes this development and classification of supercapacitors. Besides, various types of materials which are commonly used to prepare supercapacitors, such as carbons, metal oxides, alkaline earth metal salts and polymers, are introduced. Moreover, applications and methodology to prepare textile materials with supercapacitors are described. Finally, the commonly used non-destructive measuring methods for textile-based supercapacitors are also introduced.

Electrochemical Assessment of As-Deposited Co(OH)2 by Electrochemical Synthesis: The Effect of Synthesis Temperature on Performance

In this paper, the influence of an electrolytic temperature bath was used in the electrodeposition process on the size, color, and shape of the as-deposited Co(OH)2, and the electrochemical performance was investigated. Three different temperatures of 25, 60, and 95 °C were evaluated for the electrodeposition of Co(OH)2 on stainless steel plates (SSP). The electrochemical performance of the as-deposited electrodes (SSP) was measured in a symmetric electrochemical cell (EC) arrangement. XRD, SEM, and N2 physisorption analyses were carried out to evaluate the structure and morphological composition, along with the textural properties. Results showed that the hexagonal platelet micro-clusters of Co(OH)2 are formed in a mixed composition of both α-Co(OH)2 and β-Co(OH)2 phases, with the α-Co(OH)2 phase being the major phase formed in the electrodeposition process at temperatures below 95 °C, as suggested by the XRD analysis. Electrochemical cell performances were evaluated by galvanostatic cycling, results showed maximum areal capacity values of 1.97, 2.69, and 4.34 mA h cm–2 at a charge/discharge current of 6.25mA cm–2, for the as-deposited materials at 25, 60 and 95 °C, respectively. The specific power of the EC reached up to 19 kW kg–1 for the EC obtained material at 60 °C, with a specific energy of 2.8 W h kg–1. The maximum specific energy was reached at a current density of 6.25 mA cm−2, with a value of 10.79 W h kg–1 for the EC at 60 °C. These results offer some insight into how the morphology and composition of thin films can be tuned by the electrochemical synthesis temperature, yielding different electrochemical performances and areal capacity behaviors.

High-Energy Flexible Supercapacitor-Synergistic Effects of Polyhydroquinone and RuO2· xH2O with Microsized, Few-Layered, Self-Supportive Exfoliated-Graphite Sheets

An effective and straightforward route for tailoring the self-supporting, exfoliated flexible graphite substrate (E-FGS) using electrochemical anodization is proposed. E-FGS has essential features of highly exfoliated, few-layered, two-dimensional graphite sheets with the size of several tens of micrometers, interconnected along the axis of the substrate surface. The novel hierarchical porous structural morphology of E-FGS enables large active sites for efficient electrolyte ion and charge transport when used as electrode material for a supercapacitor. In order to effectively utilize this promising E-FGS electrode for energy storage purpose, a ternary composite is further synthesized with pseudocapacitive polyhydroquinone (PHQ) and hydrous RuO₂ (hRO). hRO is synthesized via a sol-gel route, while electropolymerization is utilized for the electrodeposition of PHQ over E-FGS. Ultimately, the fabricated self-supporting E-FGS-based flexible supercapacitor is capable of delivering areal specific capacitance values as high as 378 mF cm^-2 at a current density of 1 mA cm^-2. Addition of the pseudocapacitive component to the E-FGS texture leads to ∼10 times increase of the electrochemical charge storage capability. The imposition of mechanical forces to this flexible supercapacitor device results in trivial changes in electrochemical properties and is still capable of retaining 91% of the initial specific capacitance after 10 000 cycles. Alongside, the fabricated symmetrical solid-state flexible device exhibited a high energy density of 8.4 μWh cm^-2. The excellent performance along with the ease of synthesis and fabrication process of the flexible solid-state supercapacitor device using PHQ/hRO/E-FGS holds promise for large-scale production.

Three-dimensional design and fabrication of reduced graphene oxide/polyaniline composite hydrogel electrodes for high performance electrochemical supercapacitors

Graphene/polyaniline composite hydrogels (GH/PANI) were chemically synthesized by in situ polymerization of aniline monomer. Graphene hydrogels were obtained by a hydrothermal method and used in supercapacitors. The graphene/polyaniline composite hydrogel exhibits better electrochemical performance than the pure individual components as determined by cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopic measurements. A remarkable specific capacitance (C _sp) of 323.9 F g^-1 was measured using CV at a scan rate of 2 mV s^-1 at 25 °C. GCD measurements (311.3 F g^-1) and electrochemical impedance analysis also support these results. The numbers were obtained at extremely high loading masses: 7.14 mg cm^-2 for GH and GH/PANI synthesized at 0 °C, and 8.93 mg cm^-2 for GH/PANI synthesized at 25 °C. The corresponding areal capacitances are 1.14, 1.75 and 2.78 F cm^-2 for GH, and GH/PANI composite hydrogels synthesized at 0 °C and 25 °C, respectively. These values in F cm^-2 are 3.80, 5.83 and 9.27 times higher than commercially available activated carbon supercapacitors (∼0.3 F cm^-2 for a two electrode system). Moreover, the GH/PANI composite synthesized at 25 °C exhibits excellent stability with 99% initial capacitance retention after 1000 charge/discharge cycles. GH/PANI composites synthesized at 0 °C and 25 °C therefore hold promise for use in supercapacitor device applications.

Interface-Confined High Crystalline Growth of Semiconducting Polymers at Graphene Fibers for High-Performance Wearable Supercapacitors

We report graphene@polymer core-shell fibers (G@PFs) composed of N and Cu codoped porous graphene fiber cores uniformly coated with semiconducting polymer shell layers with superb electrochemical characteristics. Aqueous/organic interface-confined polymerization method produced robust highly crystalline uniform semiconducting polymer shells with high electrical conductivity and redox activity. When the resultant core-shell fibers are utilized for fiber supercapacitor application, high areal/volume capacitance and energy densities are attained along with long-term cycle stability. Desirable combination of mechanical flexibility, electrochemical properties, and facile process scalability makes our G@PFs particularly promising for portable and wearable electronics.

Substrate coating by conductive polymers through spontaneous oxidation and polymerization

A variety of substrates and substances were coated with conductive polymers at low temperature under ambient pressure. The substrate coating with heteroaromatic polymers proceeded through spontaneous oxidation and polymerization of the monomers, such as pyrrole (Py) and thiophene (Tp) derivatives. The monomer liquid, the solid nitrate oxidant, and the substrate were put in a closed vessel. The vapor of the activated monomer was spontaneously generated on the surface of the solid nitrate oxidant through the diffusion of the monomer vapor. The monomer and its activated species were adsorbed and polymerized on the surface of any substrate in the reaction vessel. The thickness was controlled by the reaction time. The substituents of the monomers had an influence on the coating rate. The morphology of the coated polymers was changed by the substrates with different wettabilities. The thin coating of the heteroaromatic polymer was applied to the preparation of an electrode for charge storage based on the redox reaction. The thin coating on the current collector showed an enhanced high-rate charge-discharge performance. The present synthetic approach can be applied to the coating of polymer materials on a variety of substrates from the monomer vapor under mild conditions.

NiO Nanoparticle Synthesis Using a Triblock Copolymer: Enhanced Magnetization and High Specific Capacitance of Electrodes Prepared from the Powder

Nickel oxide nanoparticles of diameter ∼21 nm were prepared by a sol-gel method using the triblock copolymer poly(ethylene glycol)-b-(propylene glycol)-b-(ethylene glycol). X-ray photoelectron spectroscopy analysis showed the presence of Ni²⁺ and Ni³⁺ ions in the material. The electrical conductivity of this material was due to small polaron hopping between Ni²⁺ and Ni³⁺ sites. The magnetization shown by these nanoparticles was much higher than that reported in the literature. This is ascribed to the presence of Ni³⁺ ions with uncompensated spin moments. Spin-glass behavior was exhibited by the material at 10.7 K. The electrochemical characterization of electrodes comprising of these NiO nanoparticles using cyclic voltammetric measurements showed a specific capacitance value of 810 F/g, the highest reported for this material. These materials will thus form one of the useful multifunctional systems.

A study of fused-ring thieno[3,4-e]pyrazine polymers as n-type materials for organic supercapacitors

Conjugated polymer pseudocapacitors achieve high capacitances because they store charge through fast, reversible redox reactions.

Preparation of layered graphene and tungsten oxide hybrids for enhanced performance supercapacitors

Graphene–tungsten oxide hybrids are prepared and used for enhanced performance supercapacitor electrode materials.

Storing energy in plastics: a review on conducting polymers & their role in electrochemical energy storage

This review article on conducting polymers discusses the background & theory behind their conductivity, the methods to nano-engineer special morphologies & recent contributions to the field of energy (e.g.supercapacitors, batteries and fuel cells).

Enhanced charge storage of ultrathin polythiophene films within porous nanostructures

In a single step polymerization and coating, oxidative chemical vapor deposition (oCVD) has been used to synthesize unsubstituted polythiophene. Coatings have been conformally coated within porous nanostructures of anodized aluminum oxide, titanium dioxide, and activated carbon. Significant enhancement in charge capacity has been found with ultrathin polythiophene coatings that preserve the surface area and pore space of the nanostructures. Pseudocapacitors consisting of ultrathin polythiophene coated within activated carbon yielded increases of 50 and 250% in specific and volumetric capacitance compared with bare activated carbon. Devices were stable up to the 5000 cycles tested with only a 10% decrease in capacitance.