Enhancing the Life Cycle of Zinc-Iodine Batteries in Ionic Liquid-Based Electrolyte.

Aqueous zinc-iodine (Zn-I2) batteries are gaining significant attention due to their low-cost, high safety and high theoretical capacity. Nevertheless, their long cycle and durability have been hampered due to the use of aqueous media that overtime lead to Zn dendrite formation, hydrogen evolution reaction, and polyiodide dissolution. Xiao et. al., recently reported the addition of an imidazolium-based ionic liquid (IL), to an aqueous electrolyte, that plays a key role in modifying the solvation of Zn2+ ions in the bulk electrolyte and the inner Helmotlz plane, which eliminates free H2O molecules to be present on the Zn anode surface. UV/Vis and NMR spectroscopy also indicates a strong interaction between imidazolium cation [EMIM]+ and I3-, thereby reducing polyiodide shuttling and enhancing the cycle life of the battery. Overall, a capacity decay rate of only 0.01 % per cycle after over 18,000 cycles at 4 Ag-1, is observed making the use of IL additives in aqueous electrolytes highly promising candidates for Zn-I2 batteries.

Innovative Strategy for Developing PEDOT Composite Scaffold for Reversible Oxygen Reduction Reaction.

Metal-air batteries are an emerging technology with great potential to satisfy the demand for energy in high-consumption applications. However, this technology is still in an early stage, facing significant challenges such as a low cycle life that currently limits its practical use. Poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer has already demonstrated its efficiency as catalyst for oxygen reduction reaction (ORR) discharge as an alternative to traditional expensive and nonsustainable metal catalysts. Apart from that, in most electrochemical processes, three phenomena are needed: redox activity and electronic and ionic conduction. Material morphology is important to maximize the contact area and optimize the 3 mechanisms to obtain high-performance devices. In this work, porous scaffolds of PEDOT-organic ionic plastic crystal (OIPC) are prepared through vapor phase polymerization to be used as porous self-standing cathodes. The scaffolds, based on abundant elements, showed good thermal stability (200 °C), with potential ORR reversible electrocatalytic activity: 60% of Coulombic efficiency in aqueous medium after 200 cycles.

Biobased Acrylic Latexes/Sodium Carboxymethyl Cellulose Aqueous Binders for Lithium-Ion NMC 811 Cathodes.

The increasing demands for sustainable energy storage technologies have prompted extensive research in the development of eco-friendly materials for lithium-ion batteries (LIBs). This research article presents the design of biobased latexes, which are fluorine-free and rely on renewable resources, based on isobornyl methacrylate (IBOMA) and 2-octyl acrylate (2OA) to be used as binders in batteries. Three different compositions of latexes were investigated, varying the ratio of IBOMA and 2OA: (1) Poly2OA homopolymer, (2) Poly(2OA0,6-co-IBOMA0,4) random copolymer, and (3) PolyIBOMA homopolymer. The combination of the two monomers provided a balance between rigidity from the hard monomer (IBOMA) and flexibility from the soft one (2OA). The study evaluated the performance of the biobased latexes using sodium carboxymethyl cellulose (CMC) as a thickener and cobinder by fabricating LiNi0.8Mn0.1Co0.1O2 (NMC 811) cathodes. Also, to compare with the state of the art, organic processed PVDF electrodes were prepared. Among aqueous slurries, rheological analysis showed that the CMC + Poly(2OA0,6-co-IBOMA0,4) binder system resulted in the most stable and well-dispersed slurries. Also, the electrodes prepared with this latex demonstrated enhanced adhesion (210 ± 9 N m-1) and reduced cracks compared to other aqueous compositions. Electrochemical characterization revealed that the aqueous processed cathodes using the CMC + Poly(2OA0,6-co-IBOMA0,4) biobased latex displayed higher specific capacities than the control with no latex at high C-rates (100.3 ± 2.1 vs 64.5 ± 0.8 mAh g-1 at 5C) and increased capacity retention after 90 cycles at 0.5C (84% vs 81% for CMC with no latex). Overall, the findings of this study suggest that biobased latexes, specifically the CMC + Poly(2OA0,6-co-IBOMA0,4) composition, are promising as environmentally friendly binders for NMC 811 cathodes, contributing to the broader goal of achieving sustainable energy storage systems.

Bio-based ether solvent and ionic liquid electrolyte for sustainable sodium-air batteries.

Sodium-air batteries (SABs) are receiving considerable attention for the development of next generation battery alternatives due to their high theoretical energy density (up to 1105 W h kg-1). However, most of the studies on this technology are still based on organic solvents; in particular, diglyme, which is highly flammable and toxic for the unborn child. To overcome these safety issues, this research investigates the first use of a branched ether solvent 1,2,3-trimethoxypropane (TMP) as an alternative electrolyte to diglyme for SABs. Through this work, the reactivity of the central tertiary carbon in TMP towards bare sodium metal was identified, while the addition of N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([C4mpyr][TFSI]) as a co-solvent proved to be an effective strategy to limit the reactivity. Moreover, a Na-ß-alumina disk was employed for anode protection, to separate the TMP-based electrolyte from the sodium metal. The new cell design resulted in improved cell performance: discharge capacities of up to 1.92 and 2.31 mA h cm-2 were achieved for the 16.6 mol% NaTFSI in TMP and 16.6 mol% NaTFSI in TMP/[C4mpyr][TFSI] compositions, respectively. By means of SEM, Raman and 23Na NMR techniques, NaO2 cubes were identified to be the major discharge product for both electrolyte compositions. Moreover, the hybrid electrolyte was shown to hinder the formation of side-products during discharge - the ratio of NaO2 to side-products in the hybrid electrolyte was 2.4 compared with 0.8 for the TMP-based electrolyte - and a different charge mechanism for the dissolution of NaO2 cubes for each electrolyte was observed. The findings of this work demonstrate the high potential of TMP as a base solvent for SABs, and the importance of careful electrolyte composition design in order to step towards greener and less toxic batteries.

Carrageenans as Sustainable Water-Processable Binders for High-Voltage NMC811 Cathodes.

Poly(vinylidene fluoride) (PVDF) is the most common binder for cathode electrodes in lithium-ion batteries. However, PVDF is a fluorinated compound and requires toxic N-methyl-2-pyrrolidone (NMP) as a solvent during the slurry preparation, making the electrode fabrication process environmentally unfriendly. In this study, we propose the use of carrageenan biopolymers as a sustainable source of water-processable binders for high-voltage NMC811 cathodes. Three types of carrageenan (Carr) biopolymers were investigated, with one, two, or three sulfonate groups (SO3-), namely, kappa, iota, and lambda carrageenans, respectively. In addition to the nature of carrageenans, this article also reports the optimization of the cathode formulations, which were prepared by using between 5 wt % of the binder to a lower amount of 2 wt %. Processing of the aqueous slurries and the nature of the binder, in terms of the morphology and electrochemical performance of the electrodes, were also investigated. The Carr binder with 3SO3- groups (3SO3-Carr) exhibited the highest discharge capacities, delivering 133.1 mAh g-1 at 3C and 105.0 mAh g-1 at 5C, which was similar to the organic-based PVDF electrode (136.1 and 108.7 mAh g-1, respectively). Furthermore, 3SO3-Carr reached an outstanding capacity retention of 91% after 90 cycles at 0.5C, which was attributed to a homogeneous NMC811 and a conductive carbon particle dispersion, superior adhesion strength to the current collector (17.3 ± 0.7 N m-1 vs 0.3 ± 0.1 N m-1 for PVDF), and reduced charge-transfer resistance. Postmortem analysis unveiled good preservation of the NMC811 particles, while the 1SO3-Carr and 2SO3-Carr electrodes showed damaged morphologies.

Enhanced Dissolution of Metal Oxides in Hydroxylated Solvents - Towards Application in Lithium-Ion Battery Leaching.

The recovery of critical metals from spent lithium-ion batteries (LIBs) is rapidly growing. Current methods are energy-intensive and hazardous, while alternative solvent-based strategies require more studies on their 'green' character, metal dissolution mechanism and industrial applicability. Herein, we bridged this gap by studying the effect of dilute HCl solutions in hydroxylated solvents to dissolve Co, Ni and Mn oxides. Ethylene glycol emerged consistently as the most effective solvent, dissolving up to four times more Co and Ni oxides than using aqueous acidic media, attributed to improved chloro-complex formation and solvent effects. These effects had a significant contribution compared to acid type and concentration. The highest Co dissolution (0.27 M) was achieved in 0.5 M HCl in 25 % (v/v) glycerol in water, using less acid and a significant amount of water compared to other solvent systems, as well as mild temperatures (40 °C). This solvent was applied to dissolve battery cathode material, achieving 100 % dissolution of Co and Mn and 94 % dissolution of Ni, following what was concluded to be a mixed mechanism. These results offer a simple alternative to current leaching processes, reducing acid consumption, enhancing atomic efficiency, and paving the way for optimized industrial hydrometallurgical processes leaning to 'greener' strategies.

Removal of polyvinylidene fluoride binder and other organics for enhancing the leaching efficiency of lithium and cobalt from black mass.

The agglomeration and encapsulation of recoverable materials of interest (e.g. metals and graphite) as a result of the presence of polyvinylidene fluoride (PVDF) in spent lithium-ion batteries (LIBs) with mixed chemistries (black mass) lower the extraction efficiency of metals. In this study, organic solvents and alkaline solutions were used as non-toxic reagents to investigate the removal of a PVDF binder from a black mass. The results demonstrated that 33.1%, 31.4%, and 31.4% of the PVDF were removed using dimethylformamide (DMF), dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO) at 150, 160, and 180 °C, respectively. Under these conditions, the peel-off efficiencies for DMF, DMAc, and DMSO were 92.9%, 85.3%, and approximately 92.9%, respectively. Using tetrabutylammonium bromide (TBAB) as a catalyst and 5 M sodium hydroxide (NaOH) at room temperature (RT- 21 °C-23 °C), 50.3% of PVDF and other organic compounds were eliminated. The removal efficiency was enhanced to approximately 60.5% when the temperature was raised to 80 °C using NaOH. Using 5 M potassium hydroxide at RT in a TBAB-containing solution, ca. 32.8% removal efficiency was obtained; raising the temperature to 80 °C further enhanced the removal efficiency to almost 52.7%. The peel-off efficiency was 100% for both alkaline solutions. Lithium extraction increased from 47.2% to 78.7% following treatment with DMSO and to 90.1% following treatment with NaOH via leaching black mass (2 M sulfuric acid, solid-to-liquid ratio (S/L): 100 g L-1 at 50 °C, for 1 h without a reducing agent) before and after removal of the PVDF binder. Cobalt's recovery went from 28.5% to 61.3% with DMSO treatment to 74.4% with NaOH treatment.

Unveiling the Impact of the Cations and Anions in Ionic Liquid/Glyme Hybrid Electrolytes for Na-O2 Batteries.

A series of hybrid electrolytes composed of diglyme and ionic liquids (ILs) have been investigated for Na-O2 batteries, as a strategy to control the growth and purity of the discharge products during battery operation. The dependence of chemical composition of the ILs on the size, purity, and distribution of the discharge products has been evaluated using a wide range of experimental and spectroscopic techniques. The morphology and composition of the discharge products found in the Na-O2 cells have a complex dependence on the physicochemical properties of the electrolyte as well as the speciation of the Na+ and superoxide radical anion. All of these factors control the nucleation and growth phenomena as well as electrolyte stability. Smaller discharge particle sizes and largely homogeneous (2.7 ± 0.5 µm) sodium superoxide (NaO2) crystals with only 9% of side products were found in the hybrid electrolyte containing the pyrrolidinium IL with a linear alkyl chain. The long-term cyclability of Na-O2 batteries with high Coulombic efficiency (>90%) was obtained for this electrolyte with fewer side products (20 cycles at 0.5 mA h cm-2). In contrast, rapid failure was observed with the use of the phosphonium-based electrolyte, which strongly stabilizes the superoxide anion. A high discharge capacity (4.46 mA h cm-2) was obtained for the hybrid electrolyte containing the pyrrolidinium-based IL bearing a linear alkyl chain with a slightly lower value (3.11 mA h cm-2) being obtained when the hybrid electrolyte contained similar pyrrolidinium-based IL bearing an alkoxy chain.

High Current Cycling in a Superconcentrated Ionic Liquid Electrolyte to Promote Uniform Li Morphology and a Uniform LiF-Rich Solid Electrolyte Interphase.

High-energy-density systems with fast charging rates and suppressed dendrite growth are critical for the implementation of efficient and safe next-generation advanced battery technologies such as those based on Li metal. However, there are few studies that investigate reliable cycling of Li metal electrodes under high-rate conditions. Here, by employing a superconcentrated ionic liquid (IL) electrolyte, we highlight the effect of Li salt concentration and applied current density on the resulting Li deposit morphology and solid electrolyte interphase (SEI) characteristics, demonstrating exceptional deposition/dissolution rates and efficiency in these systems. Operation at higher current densities enhanced the cycling efficiency, e.g., from 64 ± 3% at 1 mA cm-2 up to 96 ± 1% at 20 mA cm-2 (overpotential <±0.2 V), while resulting in lower electrode resistance and dendrite-free Li morphology. A maximum current density of 50 mA cm-2 resulted in 88 ± 3% cycling efficiency, displaying tolerance for high overpotentials at the Ni working electrode (0.5 V). X-ray photoelectron microscopy (XPS), time-of-flight secondary-ion mass spectroscopy (ToF-SIMS), and scanning electron microscopy (SEM) surface measurements revealed that the formation of a stable SEI, rich in LiF and deficient in organic carbon species, coupled with nondendritic and compact Li morphologies enabled enhanced cycling efficiency at higher currents. Reduced dendrite formation at high current is further highlighted by the use of a highly porous separator in coin cell cycling (1 mAh cm-2 at 50 °C), sustaining 500 cycles at 10 mA cm-2.

An investigation of commercial carbon air cathode structure in ionic liquid based sodium oxygen batteries.

In order to bridge the gap between theoretical and practical energy density in sodium oxygen batteries challenges need to be overcome. In this work, four commercial air cathodes were selected, and the impacts of their morphologies, structure and chemistry on their performance with a pyrrolidinium-based ionic liquid electrolyte are evaluated. The highest discharge capacity was found for a cathode with a pore size ca. 6 nm; this was over 100 times greater than that delivered by a cathode with a pore size less than 2 nm. The air cathode with the highest specific surface area and the presence of a microporous layer (BC39) exhibited the highest specific capacity (0.53 mAh cm-2).

Tuning Sodium Interfacial Chemistry with Mixed-Anion Ionic Liquid Electrolytes.

The interphase layer that forms on either the anode or the cathode is considered to be one of the critical components of a high performing battery. This solid-electrolyte interphase (SEI) layer determines the stability of the electrode in the presence of a given electrolyte as well as the internal resistance of a battery, and hence the overpotential of a cell. In the case of lithium ion batteries where carbonate based electrolytes are used, additives including hexafluorophosphate (PF6), bis-trifluoromethylsulfonimide (TFSI), (fluorosulfonyl)(trifluoromethanesulfonyl)imide (FTFSI), and fluorosulfonimde (FSI) are used to obtain favorable SEI layers. Ionic liquids and salts based on anions containing nitrile groups, including dicyanamide (DCA), offer a less expensive alternative to a fluorinated anion and have also been shown to support stable electrochemistry in lithium and sodium systems. However, longer term cycling leads to the eventual passivation of the electrode, presumed to be due to the instability of the DCA anion. We herein consider the use of a fluorinated anion to control the interfacial electrochemistry and provide a more stable SEI in DCA ILs. We investigate the addition of NaDCA, NaFSI, NaTFSI, and NaFTFSI to the methylpropylpyrrolidinium dicyanamide ([C3mpyr]DCA) ionic liquid. NaFSI was found to generate a more stable SEI layer, as evidenced by extended symmetric cell cycling, while the TFSI and FTFSI salts both lead to thicker, highly passivating surfaces. We use molecular dynamics, infrared spectroscopy and X-ray photoelectron spectroscopy to interrogate and discuss the influence of the anion on the bulk electrolyte, the interfacial electrolyte structure, and the formation of the SEI layer, in order to rationalize the contrasting electrochemical observations.

High Coulombic Efficiency Na-O2 Batteries Enabled by a Bilayer Ionogel/Ionic Liquid.

Sodium-oxygen (Na-O2) cells are a promising high energy density storage technology with a theoretical specific energy of 1605 Wh kg-1. However, this technology faces certain challenges in order to achieve both a high practical energy density as well as long-term cycling capability. In this Letter, a superior Coulombic cyclic efficiency, close to 100%, has been demonstrated by the use of a bilayer electrolyte composed of an ionogel and an ionic liquid electrolyte, reported herein for the first time. The presence of the ionogel plays a major role in the prevention of side reactions originating at the anode, providing a promising route to extend cell cycling, whereas the ionic liquid is essential to support high reaction rates at the cathode.

Controlling the Three-Phase Boundary in Na-Oxygen Batteries: The Synergy of Carbon Nanofibers and Ionic Liquid.

A series of electrospun binder-free carbon nanofiber (CNF) mats have been studied as air cathodes for Na-oxygen batteries using a pyrrolidinium-based electrolyte and compared with the commercial air cathode Toray 090. A tenfold increase in the discharge capacity is attained when using CNFs in comparison with Toray 090, affording a discharge capacity of 1.53 mAh cm-2 at a high discharge rate of 0.63 mA cm-2 . The good specific discharge and charge capacities of these CNFs are determined by the void space and the highly accessible surface of the carbon fiber. Furthermore, a threefold increase has been attained in terms of specific capacity by controlling the flooding of the air cathode and hence the location of the three-phase boundary within the CNF mat. The enhancement in performance has been correlated to the morphology, composition, distribution, and location of the discharge products. Sodium superoxide and peroxide were identified as the discharge products and, more importantly, the common side reaction discharge products, which are known to be detrimental to battery performance (including sodium fluoride, sodium hydroxide, and formate), were not observed, exemplifying the stability of the pyrrolidinium-based electrolyte and these binder-free CNF air cathodes.

Water-Facilitated Electrodeposition of Neodymium in a Phosphonium-Based Ionic Liquid.

Rare-earth metals are considered critical metals due to their extensive use in energy-related applications such as wind turbines and nickel-metal hybrid batteries found in hybrid electrical vehicles. A key drawback of the current processing methods includes the generation of large amounts of toxic and radioactive waste. Thus the efficient recovery of these valuable metals as well as cleaner processing methods are becoming increasingly important. Here we report on a clean electrochemical route for neodymium (Nd) recovery from [P6,6,6,14][TFSI], trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)amide which is amplified three times by the presence of water, as evidenced by the cathodic current density and thicker deposits. The role of Nd salt concentrations and water content as an additive in the electrochemistry of Nd3+ in [P6,6,6,14][TFSI] has been studied. The presence of metallic neodymium in the deposits has been confirmed by X-ray photoelectron spectroscopy.

Quasi-solid-State Electrolytes for Low-Grade Thermal Energy Harvesting using a Cobalt Redox Couple.

Thermoelectrochemical cells, also known as thermocells, are electrochemical devices for the conversion of thermal energy directly into electricity. They are a promising method for harvesting low-grade waste heat from a variety of different natural and manmade sources. The development of solid- or quasi-solid-state electrolytes for thermocells could address the possible leakage problems of liquid electrolytes and make this technology more applicable for wearable devices. Here, we report the gelation of an organic-solvent-based electrolyte system containing a redox couple for application in thermocell technologies. The effect of gelation of the liquid electrolyte, comprising a cobalt bipyridyl redox couple dissolved in 3-methoxypropionitrile (MPN), on the performance of thermocells was investigated. Polyvinylidene difluoride (PVDF) and poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-HFP) were used for gelation of the electrolyte, and the influence of the different polymers on the mechanical properties was studied. The Seebeck coefficient and diffusivity of the cobalt redox couple were measured in both liquid and gelled electrolytes, and the effect of gelation on the thermocell performance is reported. Finally, the cell performance was further improved by optimizing the concentration of the redox couple and the separation between the hot and cold electrodes, and the stability of the device over 25 h of operation is demonstrated.

Towards thermally stable high performance lithium-ion batteries: the combination of a phosphonium cation ionic liquid and a 3D porous molybdenum disulfide/graphene electrode.

We report a thermally stable high-performance lithium battery using an electrochemically synthesized three-dimensional porous molybdenum disulfide/graphene composite electrode and a phosphonium-based ionic liquid (IL) electrolyte. Benefiting from the structural merits of the chosen electrode and the thermal stability of the electrolyte, the cell coupled with a Li foil exhibits excellent rate performance and cycling capability at room temperature; and that is retained with an even better rate capability at an elevated temperature of 50 °C. This work may provide a new avenue for the development of safe and high performance lithium-ion batteries at high temperature.

Inorganic Nanoparticles/Metal Organic Framework Hybrid Membrane Reactors for Efficient Photocatalytic Conversion of CO2.

Photocatalytic conversion of carbon dioxide (CO2) to useful products has potential to address the adverse environmental impact of global warming. However, most photocatalysts used to date exhibit limited catalytic performance, due to poor CO2 adsorption capacity, inability to efficiently generate photoexcited electrons, and/or poor transfer of the photogenerated electrons to CO2 molecules adsorbed on the catalyst surface. The integration of inorganic semiconductor nanoparticles across metal organic framework (MOF) materials has potential to yield new hybrid materials, combining the high CO2 adsorption capacity of MOF and the ability of the semiconductor nanoparticles to generate photoexcited electrons. Herein, controlled encapsulation of TiO2 and Cu-TiO2 nanoparticles within zeolitic imidazolate framework (ZIF-8) membranes was successfully accomplished, using rapid thermal deposition (RTD), and their photocatalytic efficiency toward CO2 conversion was investigated under UV irradiation. Methanol and carbon monoxide (CO) were found to be the only products of the CO2 reduction, with yields strongly dependent upon the content and composition of the dopant semiconductor particles. CuTiO2 nanoparticle doped membranes exhibited the best photocatalytic performance, with 7 µg of the semiconductor nanoparticle enhancing CO yield of the pristine ZIF-8 membrane by 233%, and methanol yield by 70%. This work opens new routes for the fabrication of hybrid membranes containing inorganic nanoparticles and MOFs, with potential application not only in catalysis but also in electrochemical, separation, and sensing applications.

Electrochemical Behavior of PEDOT/Lignin in Ionic Liquid Electrolytes: Suitable Cathode/Electrolyte System for Sodium Batteries.

Biomass-derived polymers, such as lignin, contain quinone/ hydroquinone redox moieties that can be used to store charge. Composites based on the biopolymer lignin and several conjugated polymers have shown good charge-storage properties. However, their performance has been only studied in acidic aqueous media limiting their applications mainly to supercapacitors. Here, we show that PEDOT/lignin (PEDOT: poly(3,4-ethylenedioxythiophene)) biopolymers are electroactive in aprotic ionic liquids (ILs) and we move a step further by assembling sodium full cell batteries using PEDOT/lignin as electrode material and IL electrolytes. Thus, the electrochemical activity and cycling of PEDOT/lignin electrodes was investigated in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMPyrTFSI), 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide (BMPyrFSI), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMImTFSI) and 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMImFSI) IL electrolytes. The effects of water and sodium salt addition to the ILs were investigated to obtain optimum electrolyte systems for sodium batteries. Finally, sodium batteries based on PEDOT/lignin cathode with imidazolium-based IL electrolyte showed higher capacity values than pyrrolidinium ones, reaching 70 mAhg-1 . Our results demonstrate that PEDOT/lignin composites can serve as low cost and sustainable cathode materials for sodium batteries.

Stable Deep Doping of Vapor-Phase Polymerized Poly(3,4-ethylenedioxythiophene)/Ionic Liquid Supercapacitors.

Liquid-solution polymerization and vapor-phase polymerization (VPP) have been used to manufacture a series of chloride- and tosylate-doped poly(3,4-ethylenedioxythiophene) (PEDOT) carbon paper electrodes. The electrochemistry, specific capacitance, and specific charge were determined for single electrodes in 1-ethyl-3-methylimidazolium dicyanamide (emim dca) ionic liquid electrolyte. VPP-PEDOT exhibits outstanding properties with a specific capacitance higher than 300 F g(-1) , the highest value reported for a PEDOT-based conducting polymer, and doping levels as high as 0.7 charges per monomer were achieved. Furthermore, symmetric PEDOT supercapacitor cells with the emim dca electrolyte exhibited a high specific capacitance (76.4 F g(-1) ) and high specific energy (19.8 Wh kg(-1) ). A Ragone plot shows that the VPP-PEDOT cells combine the high specific power of conventional ("pure") capacitors with the high specific energy of batteries, a highly sought-after target for energy storage.

Insights into the reversible oxygen reduction reaction in a series of phosphonium-based ionic liquids.

New findings supporting the stability of the superoxide ion, O2˙(-), in the presence of the phosphonium cation, [P6,6,6,14](+), are presented. Extended electrochemical investigations of a series of neat phosphonium-based ILs with different anions, including chloride, bis(trifluoromethylsulfonyl)imide and dicyanamide, demonstrate the chemical reversibility of the oxygen reduction process. Quantum chemistry calculations show a short intermolecular distance (r = 3.128 Å) between the superoxide ion and the phosphonium cation. NMR experiments have been performed to assess the degree of long term degradation of [P6,6,6,14](+), in the presence of superoxide and peroxide species, showing no chemically distinct degradation products of importance in reversible air cathodes.