Enhancement Of Electronic Conductivity Research Articles

Locally boosted Li2S nucleation on VO2 by loading carbon quantum dots for soft-packaged lithium-sulfur pouch cells.

VO2 affords ultrafast polysulfide adsorption on account of its oxidation potential, which matches the sulfur working window (1.7-2.8 V). Nevertheless, its nonconductive surface limits direct sulfur conversion. Herein, we gently load carbon quantum dots on VO2 to increase direct Li2S nucleation by enhanced electron conductivity. As a result, the soft-packaged lithium-sulfur pouch cell yields a capacity retention of 88.8% at 0.5C after 100 cycles and a decay rate of 0.17% per cycle over 200 cycles at 2C. The cell energy density of the multilayer cell is up to 386.1 W h kg-1.

Multi-Doping Exploration of (Sb, Bi and Ba) by First Principles on Ordered Zn–Si–P Compounds as High-Performance Anodes for Next-Generation Li-Ion Batteries

Chalcopyrite ZnSiP2 has emerged as a promising anode material for next generation Li-ion-based batteries due to its high theoretical capacity. First principles multiple-dopant effect computations were made on the structural, electronic, magnetic, and thermodynamic responses for chalcopyrite ZnSiP2(1−x)Sbx, ZnSiP2(1−x)Bix, Zn(1−x)BaxSiP2, and Zn1−xBaxSiP2(1−x)Sbx, using both the norm conserving, ultra-soft pseudopotentials with generalized gradient approximation (GGA+PBE) and the main frame of density functional theory. Lattice coefficient volume, bulk modulus, formation energy, and total energy of host materials were computed and compared with experimental and theoretical results. Energy band gap for the pure chalcopyrite ZnSiP2 system (1.4 eV) matches previous data and validates the accuracy of current calculations as doping concentration (x = 0.6, 0.9, and 0.12) of (Sb, Bi, and Ba) at Zn and P sites increases. The corresponding band gap decreases, resulting in greater enhancement in electronic conductivity. Finally, the phonon dispersion relation, phonon density of states, vibration frequencies of phonon, Gibbs free energy, enthalpy, entropy effect, and Debye temperature (θ D) were estimated to confirm the thermodynamic stability of both pure and doped systems. These investigations are predicted to contribute a deeper sympathy of the doping effects on ZnSiP2, facilitating further advancements in anode materials design for Li-ion batteries.

Ab Initio Prediction of Two-Dimensional GeSiBi2 Monolayer as Potential Anode Materials for Sodium-Ion Batteries.

The conceptualization and deployment of electrode materials for rechargeable sodium-ion batteries are key concerns for next-generation energy storage systems. In this contribution, the configuration stability of single-layer GeSiBi2 is systematically discussed based on first-principles calculations, and its potential as an anode material is further investigated. It is demonstrated that the phonon spectrum confirms the dynamic stability and the adsorption energy identifies a strong interaction between Na atoms and the substrate material. The electronic bands indicative of inherent metallicity contribute to the enhancement of electronic conductivity after Na adsorption. The multilayer adsorption of Na provides a theoretical capacity of 361.7 mAh/g, which is comparable to that of other representative two-dimensional anode materials. Moreover, the low diffusion barriers of 0.19 and 0.15 eV further guarantee the fast diffusion kinetics. These contributions signal that GeSiBi2 can be a compatible candidate for sodium-ion batteries anodes.

Pseudocapacitive TiNb0.8O4 microspheres for fast-charging and durable sodium storage

Titanium niobium oxides are promising anode materials for sodium-ion batteries (SIBs) due to their efficient ion diffusion channels. However, their poor electronic conductivity impedes the longevity of SIBs. To address these issues, core@shell TiNb0.8O4/C@C microspheres (TNO/C@C) have been developed to enhance electron conduction. The TNO/C@C, featuring a bulk and surface dual conductive configuration, outperforms pure TNO and other control samples such as TNO/C and TNO@C that rely solely on either bulk or surface electronic conductors. Thus, the TNO/C@C achieves a fast-charging rate of 200 C, allowing full charging in 2 s, and demonstrates long-term stability over 10,000 cycles. In-situ Raman analysis reveals a zero-strain feature during sodiation/desodiation, which minimizes structural degradation over repeated cycles. In-situ electrochemical impedance spectroscopy test indicates low electron resistance, enhancing both the rate capability and stability. Therefore, the bulk and surface dual conducting strategy offers new insights into robust and fast-charging SIBs.

A novel composite (Bi2WO6/TiS2) presenting an excellent Z-scheme photocatalytic degradation for methylene blue dye under the visible light irradiation

The current research direction in the field is the development of a Z-scheme composite photocatalyst for the purpose of degrading organic materials in water. The Solvo-thermal synthesis method was employed to successfully synthesize a novel Z-scheme photocatalyst namely Bi2WO6/TiS2@3 %, Bi2WO6/TiS2@6 % and Bi2WO6/TiS2@9 % which is driven by visible light. The materials physicochemical properties were assessed using several analytical methods i.e. XRD, EDX, SEM, TEM, FTIR, UV–vis, PL, Raman spectroscopy and EIS. The Bi2WO6/TiS2@6 % composite revealed the maximum photocatalytic efficiency in the removal of MB dye (98 %) in 70 min. The results of the free radical trap studies indicate that h+ and •O2− are the primary free radicals involved in the photocatalytic degradation. The photocatalytic performance of the composite was improved due to the creation of a heterojunction between Bi2WO6 and TiS2 resulted in enhanced electron conduction, efficient separation of photogenerated e- and h+. Furthermore, it has been shown through six cycle test that the hybrid material consisting of Bi2WO6/TiS2@6 % exhibited a consistent degrading capability (91 %) during the photodegradation process. This distinctive heterojunction photocatalyst material exhibits extensive potential for application in the elimination of organic contaminants and cleanup of the environment.

Cation doping and oxygen vacancies in the orthorhombic FeNbO4 material for solid oxide fuel cell applications: A density functional theory study.

The orthorhombic phase of FeNbO4, a promising anode material for solid oxide fuel cells (SOFCs), exhibits good catalytic activity toward hydrogen oxidation. However, the low electronic conductivity of the material specifically in the pure structure without defects or dopants limits its practical applications as an SOFC anode. In this study, we have employed density functional theory (DFT + U) calculations to explore the bulk and electronic properties of two types of doped structures, Fe0.9375A0.0625NbO4 and FeNb0.9375B0.0625O4 (A, B = Ti, V, Cr, Mn, Co, Ni) and the oxygen-deficient structures Fe0.9375A0.0625NbO3.9375 and FeNb0.9375B0.0625O3.9375, where the dopant is positioned in the first nearest neighbor site to the oxygen vacancy. Our DFT simulations have revealed that doping in the Fe sites is energetically favorable compared to doping in the Nb site, resulting in significant volume expansion. The doping process generally requires less energy when the O-vacancy is surrounded by one Fe and two Nb ions. The simulated projected density of states of the oxygen-deficient structures indicates that doping in the Fe site, particularly with Ti and V, considerably narrows the bandgap to ∼0.5eV, whereas doping with Co at the Nb sites generates acceptor levels close to 0eV. Both doping schemes, therefore, enhance electron conduction during SOFC operation.

Improved cycle stability and high-rate capability of LiNbO3-coated Li3VO4 as anode material for lithium-ion battery

Lithium vanadate (Li3VO4) has garnered considerable attention as an alternative negative electrode material for non-aqueous lithium-ion batteries due to its high capacity, energy efficiency, and stable discharge voltage. Nonetheless, the Li3VO4 material displays a low rate capability, attributed mainly to its poor intrinsic electronic conductivity. Here, we report the synthesis of lithium niobate LiNbO3-coated Li3VO4 (LVO@LNO) using a one-pot sol-gel method. The resulting LVO@LNO demonstrates a high reversible capacity of approximately 530 mAh/g, which is more than double that of free Li3VO4. To explore the effect of the LNO coating process on the morphological and structural properties, Raman, XRD, operando XRD, XPS, SEM and HTEM analyses were conducted. To explain the enhancement of electronic conductivity in our modified material after a LiNbO3 coating, we conducted an Ex-Situ electrochemical impedance (EIS) and Density Functional Theory (DFT) computational study. Additionally, we designed a full cell utilizing a 1 wt% LNO-coated LVO anode and NMC-811 cathode. The cell yielded an output voltage of approximately 2.8 V with a high initial specific capacity of 350 mAh/g versus to the anode, at 1C with a capacity retention of 85 % after 100 cycles.

Titania/graphene nanocomposites from scalable gas-phase synthesis for high-capacity and high-stability sodium-ion battery anodes

In sodium-ion batteries (SIBs), TiO2 or sodium titanates are discussed as cost-effective anode material. The use of ultrafine TiO2 particles overcomes the effect of intrinsically low electronic and ionic conductivity that otherwise limits the electrochemical performance and thus its Na-ion storage capacity. Especially, TiO2 nanoparticles integrated in a highly conductive, large surface-area, and stable graphene matrix can achieve an exceptional electrochemical rate performance, durability, and increase in capacity. We report the direct and scalable gas-phase synthesis of TiO2 and graphene and their subsequent self-assembly to produce TiO2/graphene nanocomposites (TiO2/Gr). Transmission electron microscopy shows that the TiO2 nanoparticles are uniformly distributed on the surface of the graphene nanosheets. TiO2/Gr nanocomposites with graphene loadings of 20 and 30 wt% were tested as anode in SIBs. With the outstanding electronic conductivity enhancement and a synergistic Na-ion storage effect at the interface of TiO2 nanoparticles and graphene, nanocomposites with 30 wt% graphene exhibited particularly good electrochemical performance with a reversible capacity of 281 mAh g−1 at 0.1 C, compared to pristine TiO2 nanoparticles (155 mAh g−1). Moreover, the composite showed excellent high-rate performance of 158 mAh g−1 at 20 C and a reversible capacity of 154 mAh g−1 after 500 cycles at 10 C. Cyclic voltammetry showed that the Na-ion storage is dominated by surface and TiO2/Gr interface processes rather than slow, diffusion-controlled intercalation, explaining its outstanding rate performance. The synthesis route of these high-performing nanocomposites provides a highly promising strategy for the scalable production of advanced nanomaterials for SIBs.

Reversible Enhancement of Electronic Conduction Caused by Phase Transformation and Interfacial Segregation in an Entropy‐Stabilized Oxide

AbstractEntropy‐stabilized oxide (ESO) research has primarily focused on discovering unprecedented structures, chemistries, and properties in the single‐phase state. However, few studies discuss the impacts of entropy stabilization and secondary phases on functionality and in particular, electrical conductivity. To address this gap, electrical transport mechanisms in the canonical ESO rocksalt (Co,Cu,Mg,Ni,Zn)O are assessed as a function of secondary phase content. When single‐phase, the oxide conducts electrons via Cu+/Cu2+ small polarons. After 2 h of heat treatment, Cu‐rich tenorite secondary phases form at some grain boundaries (GBs), enhancing grain interior electronic conductivity by tuning defect chemistry toward higher Cu+ carrier concentrations. 24 h of heat treatment yields Cu‐rich tenorite at all GBs, followed by the formation of anisotropic Cu‐rich tenorite and equiaxed Co‐rich spinel secondary phases in grains, further enhancing grain interior electronic conductivity but slowing electronic transport across the tenorite‐rich GBs. Across all samples, the total electrical conductivity increases (and decreases reversibly) by four orders of magnitude with heat‐treatment‐induced phase transformation by tuning the grains’ defect chemistry toward higher carrier concentration and lower migration activation energy. This work demonstrates the potential to selectively grow secondary phases in ESO grains and at GBs, thereby tuning the electrical properties using microstructure design, nanoscale engineering, and heat treatment, paving the way to develop many novel materials.

STUDY OF VOLTAGE AND ELECTRIC CURRENT GENERATED FROM CU-ZN ELECTRODES IN A MEDIUM OF SAWDUST AND COAL STOCKPILE WASTEWATER.

Industrialization has positive effects on the economy, but on the other hand, it also adversely impacts the environment and energy needs. This phenomenon needs to be solved in an integrated way, including using wastewater from coal stocks and sawdust as electrolyte media to generate electrical energy. This study aims to analyze the voltage and electric current generated by electrode pairs consisting of copper (Cu) and zinc (Zn) immersed in different sawdust media denoted as M1 (2 grams), M2 (4 grams), M3 (6 grams), and M4 (8 grams), dissolved in 100 milliliters of coal stockpile wastewater. Additionally, the study explores the effects of varying the distance between the Cu-Zn electrodes at 1, 2, and 3 cm. The results showed that the highest voltage generated from the combination of coal stockpile wastewater and sawdust was highest in M3 (6 grams of sawdust + 100 ml of coal stockpile wastewater at a distance of 1 cm at 0.736 volts. The highest electrical current generated by the Cu-Zn electrode in the M3 media combination was 0.221 mA. It is due to coal stockpile wastewater in M3 sawdust powder, which contains ions that enhance electron conduction compared to M4.

Oxygen Release Suppression and Electronic Conductivity Enhancement for High Performance Li‐ and Mn‐Rich Layered Oxides Cathodes by Chalcogenide Redox Couple and Oxygen Vacancy Generations

AbstractLi‐ and Mn‐rich layered oxides (LMROs) are promising cathode materials for next‐generation lithium‐ion batteries (LIBs) due to their high capacity and high energy density. However, they suffer from severe capacity and voltage fading during cycling, where the irreversible oxygen release during cycle is deemed to a severe factor. Herein, this put forward a general oxygen release suppression strategy by introducing small amounts of sodium chalcogenides during cathode slurry preparation. The formed unstable surface peroxide ions O22− of LMRO during charging is reduced to stable O2− by chalcogen ion and couples the formation of sodium chalcogenic oxides, which is reduced to sodium chalcogenides and O2− during discharging. As a result, the oxygen release is significantly suppressed and the structural stability of LMRO is greatly enhanced. Meanwhile, abundant surface oxygen vacancies are generated coupling with evidently increased carrier concentration and mobility, thus enhancing electronic conductivity significantly. The Li1.2Ni0.13Co0.13Mn0.54O2 cathode with 3 wt% Na2Se shows a capacity retention as high as 96.2% and a capacity of 225 mAh g−1 after 500 cycles at 1 C, coupling with a high capacity of 135 mAh g−1 at 10 C. The relevant mechanism for the improved electrochemical properties is revealed, which is hopefully helpful for novel strategy design to high‐performance LMRO cathodes.

An industrial mixed rare-earth oxide fuel cell with low cost and high electrochemical performance

Rare-earth oxides determine the commercialization and development of solid oxide fuel cells (SOFCs) for all the types, still remining challenges of high cost and low electrochemical performance. Here, we propose an industrial mixed rare-earth oxide fuel cell using the state-of-the-art industrial lanthanum-praseodymium-cerium (La-Pr-Ce, LCP) oxide electrolyte as a proof-of-concept, achieving low-cost and high electrochemical performance. The rare-earth oxides, La2O3, CeO2, PrO2 and LCP are prepared and studied by oversimplified solid reaction experiments with density functional theory (DFT) calculations. The LCP is simplified as La, Pr doped CeO2, in which the effects of rare-earth elements doping are concluded as follows: firstly, the Ce4+/Ce3+ redox pairs can be slightly suppressed by La, Pr co-doping; secondly, the bandgap of LCP is decreased to 2.01 eV with enhanced electron conductivity of 7.4 × 10−5 S cm−1, which may originate from Pr-doping. The power density output of industrial mixed rare-earth oxide fuel cells with La2O3, CeO2, PrO2 and LCP electrolytes achieve 630 mW cm−2, 639 mW cm−2, 469 mW cm−2 and 797 mW cm−2 at 500 °C, respectively, indicating that the LCP electrolyte presents ascendant performance output with the ionic conductivity of 0.248 S cm−1. The industrial mixed rare-earth oxide fuel cells not only broaden the exploit avenue for industrial mixed rare-earth oxides, but also unravel the roadblock for the industrialization of SOFCs at low temperatures below 500 °C.

Building g-C3N4/Fe2O3 heterojunctions on carbon nanotubes for enhanced electron conductivity and pseudocapacitive performances

Building g-C3N4/Fe2O3 heterojunctions on carbon nanotubes for enhanced electron conductivity and pseudocapacitive performances

Versatile Mixed Ionic-Electronic Conducting Binders for High-Power, High-Energy Batteries

The increasingly extensive use of Lithium-Ion Batteries (LIBs) requires further optimization of the devices to make use of their maximum practical specific capacity. Although the binder occupies a small fraction of the electrode mass, it is one of the most crucial components to achieve improved cell performance and cycle life. Conducting polymers such as PEDOT:PSS have been already studied as binders for high-performance lithium-ion batteries (LIBs) but without addressing the structure-property relationships of the binder in the electrode. Herein, we develop mixed ionic-electronic conducting (MIEC) binders based on PEDOT:PSS (PPSS) and PEDOT:PDADMA-TFSI (PPTFSI) for Li-ion cathodes and we compare their performances with conventional formulations containing PVDF binder in Li||LFP cells. Furthermore, the influence of electrode formulations, including addition of conducting carbon (C), to balance the required porosity; and the Organic Ionic Plastic Cristal (OIPC) N-ethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide) (C2mpyrTFSI, O), to promote a synergistic effect of ionic and electronic conductivity enhancement; are analyzed. Finally, the versatility of these proposed binders is demonstrated with graphite||LFP full cells, high-voltage active material (NMC 111) as well as different electrolyte types (from liquid 1M LiTFSI in DOL/DME and ionic liquid based, to solid state membranes) showing the same trends, with improved performances in comparison with conventional formulations.

Enhancement of lithiation on a graphane monolayer through extended H vacancy pathways: An ab initio study

The increasing interest for the need of large-scale energy-storage systems have led to the development of high-performance energy-storage devices such as lithium-ion batteries (LIBs). Two dimensional (2D) materials are promising candidates for fulfilling this requirement due to their peculiar physical properties. However, it is important to understand the role of multiple Li adatoms on the 2D materials, more especially when defects are involved. In this study, first-principles density functional theory (DFT) calculations were performed to study Li on the H vacancies (VH) following the line and zigzag pathways on a graphane sheet. The results of Li atom on a single H vacancy (VH1) reveal an immediate enhanced interaction based on the improved binding energies, high amount of charge transfer and significantly shortened Li height, as compared to those of pristine graphane counterpart. An increase in the number of H vacancies along the line pathway from one (VH1(L)) to five (VH5(L)) further improves the binding energies ranging from 1.82 eV to 2.91 eV. Considering a simultaneous increase of Li atoms and H vacancies following a line pathway (VH1(L) to five VH5(L)), the binding energies tend to reduce in order. However, it is still higher than the minimum Li standard bulk cohesive energy of 1.63 eV. We show that there is a possibility of uniform dispersion of Li atoms with less clustering on a graphane sheet. A transition from insulator to metallic character was observed from VH1(L) to VH5(L), due to an induced new Li states at the vicinity of the Fermi level, suggesting an enhancement of electronic conductivity in the graphane sheet. At five Li atom VH5(L) configuration along the line pathway, we obtained a relatively high storage capacity of 207.49 mAh/g with its corresponding lithiation potential of 1.48 V, comparable to those of well known two dimensional anode materials.

Improved cycling performance of silicon-based nanocomposites with pyrolytic polyacrylonitrile for lithium-ion batteries

The Si/FeSi2@C composite material offers several advantages due to its unique design. It effectively combines the high capacity and safety features of the Si negative electrode with FeSi2’s stabilizing properties. By incorporating a homogeneous carbon layer, the composite material enhances electrical conductivity and provides structural support, thereby mitigating the detrimental effects of significant volume expansion resulting from repeated insertion and extraction of lithium ions. Furthermore, the composite material contributes to stabilizing the solid-electrolyte interphase (SEI) film, which is a critical factor in battery performance. The improved SEI film stability, combined with the overall enhancement in electronic conductivity, significantly enhances the performance of the negative electrode. Test results demonstrate that the composite, consisting of pyrolyzed polyacrylonitrile and Si/FeSi2 nanoparticles, exhibits excellent electrochemical properties. During the first charging cycle, the composite material achieves a specific capacity of 1280 mAh g−1. Impressively, after 200 cycles, the specific capacity of the composite doubles compared to that of the raw material, indicating a remarkable improvement in cycling stability. These findings highlight the positive impact of rational material design on the performance of the Si/FeSi2@C composites.

A practical high-energy lithium-ion capacitor enabled by multiple conducting bridges triggered electrode current reallocation

Lithium-ion capacitors (LICs), consisting of a battery-type anode and capacitive cathode, hold great promise for achieving high-energy and high-power densities. However, the sluggish migration of electrons and ions in the anode hinders the attainment of the "dual-high" target. To circumvent this obstacle, we propose a novel strategy employing multiple conducting bridges to augment charge dynamics for the hard carbon (HC) anode and activated carbon (AC) cathode. In this approach, graphene nanosheets are deposited in-situ via a self-propagating high-temperature synthesis methodology to establish connections between isolated HC (or AC) powders. Subsequently, carbon nanotubes are introduced to fill the inter-particle gaps, forming a network of multiple conducting bridges. Through the experimental investigation and finite elemental simulation, we demonstrate that this approach triggers prompt inter-particle electrons and ions migration, resulting in a homogeneous redistribution of the current at the electrode scale. This engenders a substantial enhancement in electronic conductivity (∼3 fold), and a significant improvement in the ion diffusion. Consequently, we fabricate a 1000 F LIC pouch cell displaying a state-of-the-art device performance of 30.3 W h kg−1 and 8.1 kW kg−1, coupled with a remarkable cycle life of 87.9% retention after 10,000 cycles. This study thus represents a distinctive avenue for regulating charge dynamics at the electrode scale and optimizing the performance of practical LICs.

Achieving efficient incorporation of electron-withdrawing sites into carbon nitride nanosheets for boosting hydrogen generation

There is an acute demand for the development of high-performance photocatalysts for large-scale green H2 production using solar energy. To address this challenge, a novel approach has been proposed for the fabrication of high-performance 0D/2D carbon quantum dot/C3N4 nanosheet heterojunction (CQD/CNN) photocatalytic materials using a tandem synthesis strategy of carboxylated CQD-induced hydrothermal-pyrolysis. The incorporation of CQD into the synthesis of CNN significantly reduces its thickness, making the CQD/CNN low to 2.5 nm, which is a noteworthy one thirty-sixth in height of bulk CNN. The carboxylated CQD play a crucial role in regulating the proportion of oxygen-containing surface functional groups of CQD/CNN. The CQD/CNN heterojunction shows exceptional H2 production rates and demonstrated the ability to convert O2 into H2O2. The H2 production rate of CQD/CNN is gained to be 54.50 mmol g−1 under continuous 3.5 h visible light irradiation, which is a remarkable seven-fold enhancement in performance over bulk CNN. Moreover, the CQD/CNN photocatalyst achieves a maximum H2O2 concentration of 0.763 mmol/L, which is sixteen times higher than that of pure CNN (0.0475 mmol/L). Through elucidating the relationships between morphological/structural modulation and photocatalytic capability, the CO/C–O ratio is found to have the greatest impact on performance, indicating that the electron-withdrawing sites of CQD/CNN can be augmented by incorporating carboxylated CQD, and the electron-withdrawing group can enhance electron conduction and make electron transfer easier to occur, thereby improving the performance of the heterojunctions. Our findings provide a comprehensive framework for achieving desirable photocatalytic properties of C3N4 materials through electron-withdrawing functional group regulation.

Investigation of structural, optical, and electrochemical properties of niobium-doped Li4Ti5O12 for high-performance aqueous capacitor electrode

In this study, nanocrystalline niobium-doped lithium titanate Li4Ti5O12 (LTO) was successfully synthesized with various stoichiometric ratios (x = 0, 0.025, 0.05, 0.075, 0.1) using a niobium ethoxide precursor via the solid-state synthesis method. X-ray diffraction spectroscopy results revealed that the synthesized samples possess a spinel structure without any impurities, and lattice constants expanded from 8.357 Å to 8.363 Å as the concentration of niobium ions increased. Scanning electron microscopy (SEM) analysis demonstrated that particle sizes ranged from 1.13 to 1.56 μm. The smallest particle size was observed in the LTO-Nb-0.075 sample. The maximum absorptions were detected in the ultraviolet region, and the band gaps of Nb-doped Li4Ti5-xNbxO12 (x = 0, 0.025, 0.05, 0.075, 0.1) were determined using Tauc plots. These results showed that the band gaps of Nb-doped LTO were lowered compared to pure LTO, suggesting enhanced electron conductivity. X-ray photoelectron spectroscopy (XPS) measurements confirmed that the band gaps of Nb-doped samples decreased as the formation of oxygen vacancies and Ti3+ ions increased due to Nb5+ substitution. All synthesized samples displayed well-defined redox peaks in pairs during the cyclic voltammetry (CV) measurement. The optimal stoichiometric ratio for doping lithium titanate was found to be x = 0.075, as it yielded the highest specific capacitance of 3.59 F/g and the lowered band gap value of 3.13 eV. Therefore, this study provides further encouragement for applying LTO electrodes in aqueous capacitors and electrical uses.

Graphene-Enhanced Ion Transport in Dual-Conducting Composite Films of Polyacetylene and an Imidazolium Iodide Ionic Liquid

Dual-conducting polymer films were synthesized by dispersing graphene in an aqueous solution of poly(vinyl alcohol) and 1-propyl-3-methylimidazolium iodide ([C3mim]I) ionic liquid and thermally converting the poly(vinyl alcohol) to polyene in the presence of hydroiodic acid catalyst. The electrical and mechanical properties of the resulting free-standing films of the nanocomposite, containing different concentrations of graphene, were analyzed using electrochemical impedance spectroscopy (EIS) and dynamic mechanical analysis (DMA), respectively. Nyquist plots (imaginary vs real components of the frequency-dependent impedance) showed two characteristic arcs representing the composite's electronic and ionic conduction pathways. The conductivity values corresponding to both charge transport mechanisms increased with temperature and the graphene concentration. The enhancement in electronic conductivity is expected because of graphene's high electron mobility. Interestingly, ionic conductivity also showed a significant increase with graphene concentration, approximately triple the extent of the rise in the electronic conductivity, even though the loss and storage moduli of the films increased. (Generally, a higher modulus results in lower ionic conductivities in ionic gels.) Molecular dynamics simulations of the three-component system provided some insights into this unusual behavior. Mean square displacement data showed that the diffusion of the iodide anions was relatively isotropic. The iodide diffusion coefficient was higher in a blend with 5 vol % graphene than in blends with 3 vol % graphene or no graphene. The improvement is attributed to the interfacial effects of the graphene on the free volume of the blend. Furthermore, an exclusion of the iodide ions from the vicinity of graphene was observed in the radial distribution function analysis. The increase in the effective concentration of iodide due to this exclusion and the increase in its diffusion coefficient because of the excess free volume are the primary reasons for the observed enhancement in ionic conductivity by adding graphene.