Synthesis of spherical PANI particles via chemical polymerization in ionic liquid for high-performance supercapacitors

Non-Substituted Imidazolium-Based Electrolytes as Potential Alternatives to the Conventional Acidic Electrolytes of Polyaniline-Based Electrode Materials for Supercapacitors

Although disubstituted imidazolium cation is sterically crowded, hundreds of ionic liquids based on this cation have been reported as electrolytes for energy storage devices. In contrast to disubstituted imidazolium, non-substituted imidazolium is uncrowded sterically and has not yet been investigated as an electrolyte, to the best of our knowledge. Hence, imidazolium hydrogen sulfate [Imi][HSO4], in mixture with water, was studied as an electrolyte for PANI-based electrode materials. For comparison, pyrrolidinium with hydrogen sulfate or p-toluene sulfonate ([Pyrr][HSO4] or [Pyrr][PTS]), in mixture with water, were also investigated as alternatives to the conventional electrolyte (i.e., aqueous H2SO4) for PANI electrodes. Walden plots of binary mixture ionic liquid-water weight ratios with the optimal ionic conductivity (i.e., [Imi][HSO4]/water 48/52 wt% (195.1 mS/cm), [Pyrr][HSO4]/water 41/59 wt% (186.6 mS/cm), and [Pyrr][PTS]/water 48/52 wt% (43.4 mS/cm) along with the electrochemical performances of PANI in these binary mixtures showed that [Pyrr][HSO4]aq or [Imi][HSO4]aq are convenient electrolytes for PANI/PIL, as opposed to [Pyrr][PTS]aq. Furthermore, replacing the conventional aqueous electrolyte H2SO4 with [Imi][HSO4] aq increased the specific capacitance of PANI/PIL from 249.8 to 268.5 F/g at 15 mV/s. Moreover, PANI/PIL electrodes displayed a quasi-ideal capacitive behavior in [Imi][HSO4]aq (the correction factor of CPE4 was 0.99). This primary study has shown that non-substituted imidazolium as an electrolyte could enhance the electrochemical performances of PANI electrodes and could be a good alternative to the conventional electrolyte.

One-Step Electrodeposition of Polyaniline Nanorods on Carbon Cloth for High-Performance Flexible Supercapacitors

The electrochemical performance of the carbon cloth (CC)-based electrodes is determined by the kind, content, morphology, and size of the modified pseudocapacitive materials, as well as the interaction with CC. Also, such structural parameters were mainly dependent on the deposition condition. More uniform polyaniline (PANI) could be obtained by electrochemical polymerization in comparison to chemical oxidation polymerization. However, two steps of electrodeposition were usually needed for nucleation and growth. Here, based on the comprehensive optimization of the electrodeposition condition, well-defined PANI nanorods anchored on the functionalized carbon cloth (FCC) as flexible electrodes (FCC@PANI) were synthesized by a facile one-step electrochemical polymerization. Compared with the FCC electrode, the resultant FCC@PANI-4 sample possessed good cycling stability (98.3% capacitance retention after 10,000 cycles), higher specific capacitances of 2312 mF cm-2 (1.0 mA cm-2) and 107 F g-1 (1.0 A g-1) with the boosting ratio in the areal specific capacitance (CA), and mass specific capacitances (Cm) of 169 and 181%, respectively. The improvement in both specific capacitance and cycling stability was obtained by the strong interaction between the FCC and the modified PANI nanorods with enhanced utilization efficiency of electroactive materials. Furthermore, the symmetric solid-state device assembled using the FCC@PANI-4 electrode delivered a maximum energy density of 0.079 mWh cm-2 at a power density of 0.363 mW cm-2.

Electrochemical performance optimization of the polyaniline electrodeposited on ITO substrate

We have elaborated polyaniline films on ITO substrate (indium tin oxide), by electrochemical process in different electrolytes (HCl, H2SO4, HNO3, and H3BO3), which allowed us to study the effect of the counter ion on electrochemical energy storage performances of polyaniline as electrode material in supercapacitors. The study of the different obtained films performances was carried out by cyclic voltammetry and galvanostatic charge-discharge method and is interpreted by the SEM technique. We found that there is a clear dependence on the specific capacitance of the counter ion. Justified by its porous structure, the PANI/ITO electrode doped with SO42- has the highest specific capacitance, 57.3 mF/cm2 at a current density of 0.2 mA/cm2 and 64.8 mF/cm2 at 5 mV/s. The deep analysis by Dunn's method allowed us to conclude that the faradic process dominates the energy storage in the case of PANI/ITO electrode elaborated in boric acid (99%). On the contrary, the capacitive character is the most contributory in the case of electrodes elaborated in H2SO4, HCl, and HNO3. The study at different potentials (0.80, 0.85, 0.90, 0.95, and 1.0 V/SCE) from 0.2 M monomer aniline showed that the deposition at 0.95 V/SCE leads to higher specific capacitance (24.3 mF/cm2 at scan rate 5 mV/s and 23.6 mF/cm2 at 0.2 mA/cm2) with a coulombic efficiency of 94%. By varying the concentration of the monomer while keeping a potential fixed at 0.95 V/SCE, we also found that the specific capacitance increases with monomeric concentration.

Fabrication of 3D HierarchicalSphericalHoneycomb-Like Nd2O3/Co3O4/Graphene/Nickel Foam Composite Electrode Material for High-Performance Supercapacitors

A 3D hierarchical spherical honeycomb-like composite electrode materialof neodymium oxide (Nd₂O₃), cobalt tetraoxide (Co₃O₄), and reduced graphene oxide (rGO) on nickel foam (named as Nd₂O₃/Co₃O₄/rGO/NF) were successfully fabricated by combining the hydrothermal synthesis method and the annealing process. Nickel foam with a three-dimensional spatial structure was used as the growth substrate without the use of any adhesives. The Nd₂O₃/Co₃O₄/rGO/NF composite has outstanding electrochemical performance and can be used directly as an electrode material for supercapacitors (SCs). By taking advantage of the large specific surface area of the electrode material, it effectively slows down the volume expansion of the active material caused by repeated charging and discharging processes, improves the electrode performance in terms of electrical conductivity, and significantly shortens the electron and ion transport paths. At a 1 A/g current density, the specific capacitance reaches a maximum value of 3359.6 F/g. A specific capacitance of 440.4 F/g with a current density of 0.5A/g is still possible from the built symmetric SCs. The capacitance retention rate is still 95.7% after 30,000 cycles of testing at a high current density of 10 A/g, and the energy density is 88.1 Wh/kg at a power density of 300 W/kg. The outcomes of the experiment demonstrate the significant potential and opportunity for this composite material to be used as an electrode material for SCs.

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.

Encapsulating polyaniline within porous MIL-101 for high-performance corrosion protection

The metal corrosion possesses a serious threat to the safety and loss of property. The anticorrosion study on metal-organic frameworks (MOFs) remains rarely reported. Therefore, it is desirable to build MOFs-based anticorrosion coating with long-term corrosion resistance. Herein, we prepared a novel MOF-polymer anticorrosion composite PANI@MIL-101 by encapsulating polyaniline (PANI) within the pores of MIL-101 with in-situ polymerization of aniline monomer. The N₂ adsorption-desorption and transmission electron microscopy (TEM) of PANI@MIL-101 illustrate that PANI is successfully encapsulated in the pores of MIL-101 with in-situ polymerization. PANI@MIL-101 was dispersed in epoxy resin (EP) to prepare anti-corrosive coatings. The Tafel potentiodynamic polarization measurements and electrochemical impedance spectroscopy show that PANI@MIL-101/EP coating system has superior corrosion protection with the lowest i_corr value and the highest |Z|_0.01 value compared with MIL-101/EP coating, PANI/EP coating and EP coating. A possible anticorrosion mechanism of PANI@MIL-101 was discussed. This work reveals that MOF-polymer composite materials are superb candidates for high-performance corrosion protection.

Ionic Liquid-Based Electrolytes for Energy Storage Devices: A Brief Review on Their Limits and Applications

Since the ability of ionic liquid (IL) was demonstrated to act as a solvent or an electrolyte, IL-based electrolytes have been widely used as a potential candidate for renewable energy storage devices, like lithium ion batteries (LIBs) and supercapacitors (SCs). In this review, we aimed to present the state-of-the-art of IL-based electrolytes electrochemical, cycling, and physicochemical properties, which are crucial for LIBs and SCs. ILs can also be regarded as designer solvents to replace the more flammable organic carbonates and improve the green credentials and performance of energy storage devices, especially LIBs and SCs. This review affords an outline of the progress of ILs in energy-related applications and provides essential ideas on the emerging challenges and openings that may motivate the scientific communities to move towards IL-based energy devices. Finally, the challenges in design of the new type of ILs structures for energy and environmental applications are also highlighted.

Metal Nanoparticles in Ionic Liquids

During the last years ionic liquids (ILs) were increasingly used and investigated as reaction media, hydrogen sources, catalysts, templating agents and stabilizers for the synthesis of (monometallic and bimetallic) metal nanoparticles (M-NPs). Especially ILs with 1,3-dialkyl-imidazolium cations featured prominently in the formation and stabilization of M-NPs. This chapter summarizes studies which focused on the interdependencies of the IL with the metal nanoparticle and tried to elucidate, for example, influences of the IL-cation, -anion and alkyl chain length. Qualitatively, the size of M-NPs was found to increase with the size of the IL-anion. The influence of the size of imidazolium-cation is less clear. The M-NP size was both found to increase and to decrease with increasing chain lengths of the 1,3-dialkyl-imidazolium cation. It is evident from such reports on cation and anion effects of ILs that the interaction between an IL and a (growing) metal nanoparticle is far from understood. Factors like IL-viscosity, hydrogen-bonding capability and the relative ratio of polar and non-polar domains of ILs may also influence the stability of nanoparticles in ionic liquids and an improved understanding of the IL-nanoparticle interaction would be needed for a more rational design of nanomaterials in ILs. Furthermore, thiol-, ether-, carboxylic acid-, amino- and hydroxyl-functionalized ILs add to the complexity by acting also as coordinating capping ligands. In addition imidazolium cations are precursors to N-heterocyclic carbenes, NHCs which form from imidazolium-based ionic liquids by in situ deprotonation at the acidic C2-H ring position as intermediate species during the nanoparticle seeding and growth process or as surface coordinating ligand for the stabilization of the metal nanoparticle.

Removal of elevated level of chromium in groundwater by the fabricated PANI/Fe3O4 nanocomposites

In this work, we report the reduction of chromium concentration in the polluted groundwater samples from Madurai Kamaraj University area, India, where the dissolved salts in groundwater are reported as serious health hazards for its inhabitants. The water samples have intolerable amounts of total dissolved solids (TDS) and chromium is a prominent pollutant among them. Chromium reduction was achieved by treating the polluted groundwater with PANI/Fe₃O₄ nanocomposites synthesized by in situ polymerization method. Further experimentation showed that the nanocomposites exhibit better chromium removal characteristics upon increasing the aniline concentration during the synthesis. We were able to reduce chromium concentration in the samples from 0.295 mg L^-1 to a tolerable amount of 0.144 mg L^-1. This work is expected to open doors for chromium-free groundwater in various regions of India, when improved to an industrial scale.

Crosslinked Carbon Nanotubes/Polyaniline Composites as a Pseudocapacitive Material with High Cycling Stability

The poor cycling stability of polyaniline (PANI) limits its practical application as a pseudocapacitive material due to the volume change during the charge-discharge procedure. Herein, crosslinked carbon nanotubes/polyaniline (C-CNTs/PANI) composites had been designed by the in situ chemical oxidative polymerization of aniline in the presence of crosslinked carbon nanotubes (C-CNTs), which were obtained by coupling of the functionalized carbon nanotubes with 1,4-benzoquinone. The composite showed a specific capacitance of 294 F/g at the scan rate of 10 mV/s, and could retain 95% of its initial specific capacitance after 1000 CV cycles. Such high electrochemical cycling stability resulting from the crosslinked skeleton of the C-CNTs makes them potential electrode materials for a supercapacitor.

Nanoparticles in ionic liquids: interactions and organization

Interactions between nanoparticles and ionic liquids can lead to a variety of organized structures.