Increased Charge Storage Research Articles

Enhancing Capacity Performance by Utilizing the Redox Chemistry of the Electrolyte in a Dual‐Electrolyte Sodium‐Ion Battery

AbstractA strategy is described to increase charge storage in a dual electrolyte Na‐ion battery (DESIB) by combining the redox chemistry of the electrolyte with a Na+ ion de‐insertion/insertion cathode. Conventional electrolytes do not contribute to charge storage in battery systems, but redox‐active electrolytes augment this property via charge transfer reactions at the electrode–electrolyte interface. The capacity of the cathode combined with that provided by the electrolyte redox reaction thus increases overall charge storage. An aqueous sodium hexacyanoferrate (Na4Fe(CN)6) solution is employed as the redox‐active electrolyte (Na‐FC) and sodium nickel Prussian blue (Nax‐NiBP) as the Na+ ion insertion/de‐insertion cathode. The capacity of DESIB with Na‐FC electrolyte is twice that of a battery using a conventional (Na2SO4) electrolyte. The use of redox‐active electrolytes in batteries of any kind is an efficient and scalable approach to develop advanced high‐energy‐density storage systems.

In situ surface decoration of Fe3C/Fe3O4/C nanosheets: Towards bi-functional activated carbons with supercapacitance and efficient dye adsorption

This work reports a bi-functional activated porous carbon (PC) prepared from a biomass tofu, with excellent capacities for charge storage and adsorption of organic dyes, which is enabled by decorating with Fe3C/Fe3O4/C nanosheets. The in-situ growth and self-assembly of the nanosheets on the carbon surface are achieved by a one-step catalytic carbonization of tofu simultaneously with FeCl3 and ZnCl2 catalysts. Due to the high surface area and unique iron compounds-containing and sheet-like structures, the PCs exhibit an electrochemical capacitance of 315 F g−1 at 0.5 A g−1 as supercapacitor electrodes, and an ultrahigh adsorption capacity of 918 mg g−1 for methylene blue (MB) and 868 mg g−1 for Rhodamine B (RhB). This study provides a new perspective for understanding the effects of surface engineering on increasing charge storage and dye adsorption ability of biomass-derived PCs as well as for developing bi-functional PCs with novel magnetic properties.

Maximizing Volumetric Removal Capacity in Capacitive Deionization by Adjusting Electrode Thickness and Charging Mode

Capacitive deionization (CDI) is an emerging desalination technology based on the same charge storage principles as in electrical double-layer supercapacitors (EDLC's). In this study, electrodes of differing thicknesses were tested using constant current (CC-CDI) and constant voltage (CV-CDI) operational modes in order to study the best way of sequestering the highest amount of ions under different salt concentration scenarios. CV-CDI was used to calculate electrode time constants (RC) and thereby determine a suitable current density for desalinating the solution. Results showed that the voltage pulse produced a fast but heterogeneous layer of ion adsorption, presumably, on the most accessible part of the electrode surface. Thus, volumetric specific capacitance under CV-CDI mode might vary from 17–24 F cm−3 and 14–20 F cm−3 for 50 μm and 180 μm electrodes, respectively. Nevertheless, results demonstrated that, under the constant current mode, it is possible to increase charge storage by 30% for a CDI cell consisting of thin electrodes and as much as 80% for thicker electrodes simply by controlling current density and, therefore, the rate capability. Moreover, the analysis of the charge efficiency indicated that a proper selection of the current density can result in efficiencies above 80% regardless the salt concentration scenario.

Characteristics of Transparent, PEDOT:PSS Coated Indium-Tin-Oxide (ITO) Microelectrodes.

This paper reports on electrochemical and optical characteristics of flexible, transparent microelectrodes, which consist of thin poly-(3, 4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS) spun onto indium-tin-oxide (ITO) electrodes for potential applications in biomedical optoelectronic devices. Although PEDOT:PSS/ITO combined films have been extensively investigated for applications in optical devices, such as solar cells and LEDs, PEDOT:PSS/ITO films for use in electrophysiological recording have not been well-characterized yet. In this work, PEDOT:PSS coated ITO microelectrodes with various diameters of 10 μm, 37 μm, 50 μm and 80 μm were microfabricated and characterized, and their properties were compared with plain ITO microelectrodes. Experimental results demonstrate that PEDOT:PSS coated ITO electrodes exhibit decreased electrochemical impedance, well-performed stability in saline, and increased charge storage capacity while preserving excellent optical transparency and mechanical flexibility. Equivalent circuit models were fitted to the experimental results to analytically extract interface capacitance, charge transfer resistance and solution resistance at the electrode-electrolyte interface.

Doubling up: Increasing Charge Storage in Organic Donors and Acceptors for Non-Aqueous Redox Flow Batteries

A limited number of organic compounds have been reported as stable electron donors and acceptors for non-aqueous redox flow batteries, with even fewer materials studied as two-electron donors and/or acceptors. Yet, assuming that the solubility of the neutral and charged species were retained and that the molecular weight did not significant increase, doubling the charge storage capabilities of the redox molecule would lead to proportionally increases in electrolyte capacity. Pursuant to this goal, this paper reports on design strategies utilized to increase molecular stability in doubly oxidized and reduced states of organic compounds whilst retaining atom economy and high solubility. In particular, we highlight progress in phenothiazine and naphthoquinone derivatives designed to serve as two-electron donors and two-electron acceptors, respectively.

New Avenue for Appendage of Graphene Quantum Dots on Halloysite Nanotubes as Anode Materials for High Performance Supercapacitors

Graphene quantum dots (GQDs) are a newly developed graphene family with good electrical conductivity and high theoretical capacitance, while halloysite nanotubes (HNTs) are naturally occurring layered mineral materials containing high active sites for energy storage support. The combination of HNTs and GQDs can offer a new strategy on the fabrication of eco-friendly electrode materials for high performance supercapacitor applications. Herein, an environmentally friendly GQD-HNT nanocomposite is fabricated in the presence of (3-aminopropyl)-triethoxysilane to provide increased charge storage sites as well as to allow for the fast charge transport for supercapacitor application. Morphological and surface analytical results show that 5–10 nm GQDs are homogeneously distributed on the surface of APTES-coated HNTs via amide linkage. This new and novel layered nanocomposite can provide accessible electroactive sites and low resistance to accelerate the electrons and electrolyte ion transport, resulting in excell...

Critical influence of reduced graphene oxide mediated binding of M (M = Mg, Mn) with Co ions, chemical stability and charge storability enhancements of spinal-type hierarchical MCo2O4 nanostructures

This paper reports that addition of reduced graphene oxide (rGO) in MgCo2O4 improves the binding of Mg with Co thereby minimizing magnesium dissolution in aqueous alkaline electrolytes and the resulting MgCo2O4/rGO electrodes offered impressive improvements in charge storage properties. An isostructural high performing material, MnCo2O4, is used as a benchmark material in this work. The Mg analogues stored >30% more charges than the Mn-analogues in the 3M LiOH electrolyte despite the former's lower BET surface area; rGO modification further increased charge storage by >60% than the unmodified analogues. Electrochemical measurements show that a larger surface fraction of the Mg analogue is electrochemically active, irrespective of whether or not rGO is present, which arise from, typically for MgCo2O4/rGO, lower internal resistance, lower Warburg impedance, and lower charge transfer resistance than the other electrodes.

Doubling up: Increasing Charge Storage in Organic Donors and Acceptors for Non-Aqueous Redox Flow Batteries

Redox flow batteries (RFBs) are promising candidates for grid storage, with a few large-scale systems currently in operation. However, current systems have not met the stringent cost and/or safety requirements needed for widespread implementation. Replacing vanadium with organic compounds may lower materials cost, and utilizing non-aqueous (aprotic) electrolyte solvents, in place of water, could enable a 2- to 3-fold increase in operating voltage. Both features make non-aqueous RFBs candidates for large-scale stationary storage. Currently a limited number of organic compounds have been reported as stable electron donors and acceptors, with even fewer materials being studied as small molecule two-electron donors and/or two-electron acceptors. Yet if the amount of charged stored within an individual molecule were raised without significantly increasing the molecular weight, then electrolyte capacity could be increased proportionally, assuming solubility of neutral and charged species is retained. Our recent efforts have focused on the development of highly soluble electron donors and acceptors with stable oxidized and reduced states. This presentation will focus on design strategies utilized to increase molecular stability in all relevant states of charge as well as solubility. In particular, we highlight the design, synthesis, and electrochemical analysis of phenothiazine and napthoquinone derivatives designed to serve as two-electron donors and two-electron acceptors, respectively. We show that tactical placement of substituents leads to improved stability of doubly oxidized and doubly reduced species, whilst retaining atom economy and that high solubility.

Multiscale Pore Network Boosts Capacitance of Carbon Electrodes for Ultrafast Charging.

Increasing charge storage capability during fast charging (at ultrahigh current densities) has been a long-standing challenge for supercapacitors. In this work, a novel porous carbon foam electrode with multiscale pore network is reported that achieves a remarkable gravimetric capacitance of 374.7 ± 7.7 F g-1 at a current density of 1 A g-1. More importantly, it retains 235.9 ± 7.5 F g-1 (60% of its capacitance at 1 A g-1) at an ultrahigh current density of 500 A g-1. Electron microscopy studies reveal that this carbon structure contains multiscale pores assembled in a hierarchical pattern. The outstanding capacitive performance benefits from its extremely large surface area of 2905 m2 g-1, as around 88% of the electric charges are stored via electrical double layer. Significantly, electrochemical analyses show that the hierarchical porous structure containing macro-, meso-, and micropores allows efficient ion diffusion and charge transfer, resulting in the excellent rate capability. The findings pave the way for improving rate capability of supercapacitors and enhancing their capacitances at ultrahigh current densities.

High energy lithium ion battery electrode materials; enhanced charge storage via both alloying and insertion processes

A series of nano-sized tin-doped metal oxides of titanium(IV), niobium(V) and vanadium(IV), were directly synthesized using a continuous hydrothermal process and used for further testing without any post-treatments. Each of the as-prepared powders was characterized via a range of analytical techniques including powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy and Brunauer-Emmett-Teller surface area measurements, as well as being investigated as an electrode material in a lithium-ion coin cell (vs lithium metal). All the tin-doped nanomaterials showed higher specific capacities compared to their undoped metal oxide counterparts. The increased charge storage was discussed to originate from the electrochemical activation of the tin dopant as an alloying material. Overall, this work presents a reliable method of combining stable insertion materials with high capacity tin alloying materials under scaled-up conditions.

Conducting polymer microspherical cups for organic bioelectronics

Event Abstract Back to Event Conducting polymer microspherical cups for organic bioelectronics Milad Khorrami1, Martin Antensteiner1 and Mohammad Reza Abidian1 1 University of Houston, Biomedical Engineering, United States Current metallic-based implantable microscale bioelectronics have high impedance and low charge storage capacity, which result in both low signal-to-noise ratio and low charge injection electrode-tissue interfaces. Moreover, these electrodes without anti-inflammatory compounds are less likely to maintain their functionality due to unfavorable reactive tissue responses. Therefore, there is need to produce devices capable of delivering therapeutic compounds while maintaining their electrical performance. Poly(pyrrole) (PPy) has gained significant interest for biomedical applications owing to its excellent biocompatibility, electrical properties, and mechanical actuation. Poly(lactic-co-glycolic) acid (PLGA) is biodegradable and highly biocompatible, making it an ideal matrix for drug encapsulation. In this study, we have produced PPy microspherical cups from template PLGA microspheres. These conductive microstructures have large surface areas, granting low impedance values and high charge storage capacities for bioelectronics applications. PPy, poly(styrenesulfonate), benzyltriethylammonium chloride, PLGA, silicon wafer (Si) substrates and chloroform were used as purchased. Gold (Au) electrodes were fabricated on Si wafers (two circles with diameters 1.5mm and 5.0mm connected with a rectangle 1mm X 10mm). A thin layer of titanium (10nm) was deposited to support Au layer (100nm). Briefly, 4/2wt% PLGA/BTEAC was dissolved in chloroform and sprayed onto the Si using an applied electrical field of 100kVm-1 and 500μl/hr flow rate. PLGA particles were then coated with PPy/PSS using electrochemical deposition with current density 0.5mA/cm2 for 5 different time durations. The PLGA cores were then dissolved in chloroform to create PPy microspherical cups. Impedance spectroscopy (IS) and cyclic voltammetry (CV) were performed on all samples and a gold reference to investigate the impedance and charge storage capacity. The size and shape of PPy microstructures were characterized using Scanning Electron Microscopy. Fig. 1 shows the electropolymerized PPy on the surface of Au electrodes and around PLGA microspheres after 1, 2, 4, and 6 min. Fig. 2 demonstrates PPy cups after removal of PLGA cores. Fig. 3A shows the IS data for bare Au, PPy cups, and fully PPy-coated PLGA cores (8 min of deposition) from 1 to 10kHz. Electrodeposition of PPy on PLGA cores followed by removal of the PLGA significantly decreased the bare Au impedance (e.g. from 445 ± 63 Ω to 354 ± 39 Ω for 8 min coating at 1kHz, a difference of 20%). The additional surface area obtained by removal of the PLGA cores significantly increased the effective surface area of electrode, thus lowering the impedance. Fig. 3B shows the CV for bare gold, PPy cups, and fully PPy-coated PLGA microspheres. The PPy coating significantly increased the charge storage capacity from 2.5mC/cm2 (bare gold) to 47.5mC/cm2 (8 min), an increase of nearly 95%. We successfully demonstrated: (1) electrochemical deposition of PPy around the electrosprayed PLGA microspheres, (2) degradation of PLGA microspheres to fabricate PPy microspherical cups, and (3) improvement of electrical properties of Au electrodes by decreasing impedance and increasing charge storage capacity. This study demonstrates the potential of our conductive microstructures for neural interfacing and neural regeneration while retaining functionality for drug delivery. The authors would like to thank Fatemeh Fallahianbijan and support from National Institute of Health R01 NS087224. Keywords: electric, microstructure, polymer, biomedical application Conference: 10th World Biomaterials Congress, Montréal, Canada, 17 May - 22 May, 2016. Presentation Type: Poster Topic: Regenerative medicine: biomaterials for control of tissue induction Citation: Khorrami M, Antensteiner M and Abidian M (2016). Conducting polymer microspherical cups for organic bioelectronics. Front. Bioeng. Biotechnol. Conference Abstract: 10th World Biomaterials Congress. doi: 10.3389/conf.FBIOE.2016.01.02641 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 27 Mar 2016; Published Online: 30 Mar 2016. Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Milad Khorrami Martin Antensteiner Mohammad Reza Abidian Google Milad Khorrami Martin Antensteiner Mohammad Reza Abidian Google Scholar Milad Khorrami Martin Antensteiner Mohammad Reza Abidian PubMed Milad Khorrami Martin Antensteiner Mohammad Reza Abidian Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. 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Effect of Meso- and Micro-Porosity in Carbon Electrodes on Atomic Layer Deposition of Pseudocapacitive V2O5 for High Performance Supercapacitors

Electrochemical capacitors can deliver high power density and long cyclability, but it is necessary to increase their energy density to promote their widespread use.1,2 The charge storage capacity of supercapacitors can be increased by adding a pseudocapacitance material to create a Faradaic charge storage layer. High surface area activated carbon electrodes can give good power performance, but adding a conformal pseudocapacitance layer could further improve charge storage. The pseudocapacitive properties of V2O5 have been well studied and V2O5 has been incorporated into V2O5/carbon nanotube composites, but it has not been studied with activated carbon.3,4 In this work, we show that atomic layer deposition (ALD) of V2O5 is a viable means to add pseudocapacitance to supercapacitors constructed from activated carbon powders. Commercially available activated carbon powders with varying microporous and mesoporous surface areas were characterized before and after ALD of V2O5 using nitrogen adsorption, FTIR, mass uptake, SEM and TEM analysis. An acid treatment of the activated carbon before ALD aided in V2O5 deposition. For the ALD process, we used vanadium tri-isopropoxide and water to grow thin films of amorphous V2O5 on the activated carbon electrodes. The V2O5 ALD on the high surface-area microporous carbon with pore diameters less than 11 Å decreased the net microporous surface area, thereby decreasing the available area for charge storage in the electrochemical double layer and the capacitance of the supercapacitor. The mesoporous carbon with slightly less starting surface area, however, showed increased charge storage capacity, consistent with more conformal coatings in the larger mesopores. For the mesoporous electrodes, we used cyclic voltammetry, galvanostatic charging/discharging, and electrochemical impedance spectroscopy (EIS) to evaluate detailed changes in supercapacitor performance as a function of pseudocapacitive V2O5 ALD coating thickness. 1.5 nm thick films of V2O5 deposited on mesoporous carbon increased the capacitance by 46%. The V2O5 exhibited a maximum pseudocapacitance of 540 F/g(V2O5) from a 0.5 nm thick V2O5 film. Electrodes with up to 4.5 nm thick V2O5 films maintained high capacitive current (91-93% of total current), similar to uncoated electrodes (89%), and minimal diffusion limited current. Electrodes coated with 33 nm of V2O5 reported no net change in capacitance compared to uncoated electrodes due to decreased surface area (70% decrease) and reduced capacitive current (67% of total current). EIS analysis reported low equivalent series resistance for all of the electrodes, and similar capacitance and diffusion trends as seen with cyclic voltammetry. Electrodes coated with 4.5 nm of V2O5 maintained 89% capacitance after 10,000 charge/discharge cycles, compared to 88% for the uncoated electrodes. This work demonstrates the basic challenges for ALD on highly porous electrodes, and points to further analysis of the V2O5 ALD process that could further improve supercapacitor performance.

Gold nanoparticle density-multiplication by tuning block copolymer self-assembly processes toward increased charge storage

Enhanced charge storage in flash memories using AuNPs as charge storage centers enabled through block copolymer self - assembly processes.

Synthesis and Electrochemical Behavior of Ceria Based Bi-Layer Films by Dip Coating Technique.

Ceria based bi-layer films of CeO2-CdS and CeO2-TiO2 were prepared by sol-gel based hydrothermal route combined with dip-coating. The synthesized samples were subjected to various characterizations such as X-ray diffraction, Field emission scanning electron microscopy, thermo-gravimetric analysis, UV-Vis absorption and photoluminescence studies. The prepared materials were dissolved in naffion solution and disposed as a thin film on glassy carbon electrode by dip coating technique. Electrochemical Li+ intercalation/deintercalation was performed by cyclic voltammetry and these results indicate that the CeO2/LiClO4 system is electrochemically reversible. The total intercalation/deintercalation of the CeO2 film, CeO2-CdS and CeO2-TiO2 bi-layer films was determined by cyclic voltammetry, which showed increased charge storage capacity.

Photoelectrochemical Studies on High Specific Capacitance-Photoactive Interfaces Based on Poly 3,4- Ethylenedioxythiophene/Metal Oxides Assemblies

Inorganic/organic interfaces (IOI) consist of TiO2/PEDOT (poly 3,4-ethylenedioxythiophene) and (PMo12O40 )3− or MoO3/PEDOT were subject to photoelectrochemical studies in both aqueous nano- suspensions and in thin solid films. The effects PEDOT modifier caused on the photoelectrochemi- cal behavior of the IOI were investigated using (Fe(CN)6) 4− as the photoactive hydrated electron donor agent. Results show that native PEDOT or PEDOT doped with MoO3 thin films increased charge storage capability evident by the high capacitive current. In the case of nano suspensions composed of TiO2/PEDOT the adsorption process of (Fe(CN)6) 3− (photolysis product) control of the photoactivity outcome of the IOI assemblies. TiO2/PEDOT shows a lower heterogeneous photo- chemical response than native TiO2 in short term photolysis times. At longer photolysis times the IOI shows photoactivity greater than that of native TiO2. The interface activities were explained by analyzing the IOI junction characteristics, such as electron affinity, work function and hole/elec- trons barrier heights. The aqueous nano-systems retained moderate stability as indicated by the reproducibility of their photocatalytic activities. Both (Fe(CN)6)4− and PEDT contributed to the stability of native TiO2 surfaces.

Redox Electrolytes in Supercapacitors

Most methods for improving supercapacitor performance are based on developments of electrode materials to optimally exploit their storage mechanisms, namely electrical double layer capacitance and pseudocapacitance. In such cases, the electrolyte is supposed to be electrochemically as inert as possible so that a wide potential window can be achieved. Interestingly, in recent years, there has been a growing interest in the investigation of supercapacitors with an electrolyte that can offer redox activity. Such redox electrolytes have been shown to offer increased charge storage capacity, and possibly other benefits. There are however some confusions, for example, on the nature of contributions of the redox electrolyte to the increased storage capacity in comparison with pseudocapacitance, or by expression of the overall increased charge storage capacity as capacitance. This report intends to provide a brief but critical review on the pros and cons of the application of such redox electrolytes in supercapacitors, and to advocate development of the relevant research into a new electrochemical energy storage device in parallel with, but not the same as that of supercapacitors.

Evaluation of poly(3,4-ethylenedioxythiophene)/carbon nanotube neural electrode coatings for stimulation in the dorsal root ganglion

Objective. The dorsal root ganglion is an attractive target for implanting neural electrode arrays that restore sensory function or provide therapy via stimulation. However, penetrating microelectrodes designed for these applications are small and deliver low currents. For long-term performance of microstimulation devices, novel coating materials are needed in part to decrease impedance values at the electrode-tissue interface and to increase charge storage capacity. Approach. Conductive polymer poly(3,4-ethylenedioxythiophene) (PEDOT) and multi-wall carbon nanotubes (CNTs) were coated on the electrode surface and doped with the anti-inflammatory drug, dexamethasone. Electrode characteristics and the tissue reaction around neural electrodes as a result of stimulation, coating and drug release were characterized. Hematoxylin and eosin staining along with antibodies recognizing Iba1 (microglia/macrophages), NF200 (neuronal axons), NeuN (neurons), vimentin (fibroblasts), caspase-3 (cell death) and L1 (neural cell adhesion molecule) were used. Quantitative image analyses were performed using MATLAB. Main results. Our results indicate that coated microelectrodes have lower in vitro and in vivo impedance values. Significantly less neuronal death/damage was observed with coated electrodes as compared to non-coated controls. The inflammatory response with the PEDOT/CNT-coated electrodes was also reduced. Significance. This study is the first to report on the utility of these coatings in stimulation applications. Our results indicate PEDOT/CNT coatings may be valuable additions to implantable electrodes used as therapeutic modalities.

Electrochemical studies on nanometal oxide-activated carbon composite electrodes for aqueous supercapacitors

In present study, the electrochemical performance of eco-friendly and cost-effective titanium oxide ( TiO 2)-based and zinc oxide-based nanocomposite electrodes were studied in neutral aqueous Na 2 SO 3 electrolyte, respectively. The electrochemical properties of these composite electrodes were studied using cyclic voltammetry (CV), galvanostatic charge–discharge (CD) and electrochemical impedance spectroscopy (EIS). The experimental results reveal that these two nanocomposite electrodes achieve the highest specific capacitance at fairly low oxide loading onto activated carbon (AC) electrodes, respectively. Considerable enhancement of the electrochemical properties of TiO 2/AC and ZnO /AC nanocomposite electrodes is achieved via synergistic effects contributed from the nanostructured metal oxides and the high surface area mesoporous AC. Cations and anions from metal oxides and aqueous electrolyte such as Ti 4+, Zn 2+, Na + and [Formula: see text] can occupy some pores within the high-surface-area AC electrodes, forming the electric double layer at the electrode–electrolyte interface. Additionally, both TiO 2 and ZnO nanoparticles can provide favourable surface adsorption sites for [Formula: see text] anions which subsequently facilitate the faradaic processes for pseudocapacitive effect. These two systems provide the low cost material electrodes and the low environmental impact electrolyte which offer the increased charge storage without compromising charge storage kinetics.

High-Charge Capacity Electrodes Using 1,4-Benzoquinone Doped Polypyrrole

There is currently a strong need for high energy/high power energy storage systems for small and large scale applications such as portable electronics, transportation, and energy generation by intermittent sources. The performance of current technologies (batteries and supercapacitors) falls short of requirements for using electrical energy efficiently. Supercapacitors and advanced lithium ion batteries are attracting considerable research attention, and both device types will likely fill specific roles in diverse energy applications.Pseudocapacitors are one class of supercapacitors that have the ability to store higher amounts of charge compared to purely electrical double layer capacitors (EDLC) due to the inherent properties of their faradaic charge storage mechanism. In these devices, the bulk redox material stores electrical energy by a transfer of charge between the electrode and current collector. For wide scale implementation, it is important to consider materials that are low cost, environmentally friendly and highly abundant, especially for stationary energy storage. Electroactive conductive polymers have the potential to address these major issues, along with having good intrinsic conductivity (ranging from a few S cm − 1 to 500 S cm − 1 in the doped state[1]), fast doping and de-doping processes, and ease of manufacture, particularly as thin films. Conducting polymer electrodes, however, still require improvement of their electrical charge capacity and stability.Previous research has shown that polymers containing redox groups, such as sodium lignosulfate, can be entrapped within polymer electrodes to increase the electrode’s charge capacity. [2] In this presentation, we will shown that the charge capacity of conducting polymer electrodes can be further increased by confining a readily available prototypical organic redox molecule, such as 1,4-benzoquinone (QN) as shown in Figure 1. This redox molecule presents a theoretical charge capacity of 496 mA h g-1 whereas polypyrrole (PPy) has that of 135 mA h g-1 [3]. When electrodes are prepared using typical current settings and monomer concentrations, electrode synthesis is challenging. Here, we will discuss the effects of deposition conditions on film growth, QN confinement, and the electrochemical properties of the resulting polymer films.The combined redox processes of the pyrrole and the quinone resulted in films with increased charge storage capacity and capacitance, as shown in Figure 2. Figure 1. Schematic of the electrochemical processes occurring during charge and discharge of the PPy/QN electrodes. Figure 2. Specific capacitance vs. potential of PPy/QN films with increasing composition of quinone, along with the pure polypyrrole control electrode. In PPy/QN electrode materials, the highest average specific capacitance of 550 F g-1 was achieved when films were prepared with a pyrrole concentration of 0.085 M (QN=0.09 M), which represents a significant improvement over pure PPy with a highest average specific capacitance of 249.0 F g-1. Using higher concentrations of pyrrole during film synthesis resulted in higher masses (increased thickness) due to the availability of the monomer, but lower compositions of QN in the film. On the other hand, lower concentrations of pyrrole lead to poor polymer deposition as most of the current was consumed by the reversible oxidation of quinone rather than the irreversible oxidation of the monomer necessary for electrochemical synthesis. This work will enable the development of supercapacitor materials that combine the high storage capacity properties of redox molecules with the high conductivity and capacitance of intrinsically conducting polymers such as PPy.[1] G.A. Snook, P. Kao, S.A. Best. Journal of Power Sources. 196 (2011) 1-12[2] G. Milczarek, O. Inganäs. Science. 335 (2012) 1468-1471.[3] K. Naoi, M. Morita. The Electrochemical Society Interface. 17 (2008) 44-48

A graphene oxide/conducting polymer nanocomposite for electrochemical dopamine detection: origin of improved sensitivity and specificity.

Neuromodulatory dopamine (DA) acts as an essential signaling molecule in the central nervous system (CNS), and its dysfunction has been implicated in neurological disorders such as Parkinson's disease and schizophrenia. Due to its inherent redox properties, DA can be detected electrochemically by monitoring changes in current as the molecule is oxidized. Many electrode materials for electrochemical detection have been developed to monitor DA, but properties such as sensitivity and specificity must be optimized. We describe a conducting polymer (CP) nanocomposite of poly(3,4-ethylendioxythiophene) (PEDOT) doped with GO nanosheets, and report its superior DA detection performance over bare glassy carbon electrode (GCE) substrates. The GO/PEDOT electrode exhibits favorable electrical properties such as lowered impedance and increased charge storage capacity. The nanocomposite demonstrates improved sensitivity to the oxidation of DA at its surface. Meanwhile, interference from competing analyte, ascorbic acid (AA), is minimized. Mechanistic studies indicate that electrostatic interactions drive the increased sensitivity toward DA, and improved electrocatalysis of AA oxidation by the nanocomposite enables the selective discrimination of DA signals from those of AA. The described performance of the GO/PEDOT nanocomposite accentuates its promise for improving detection capabilities of electrochemical biosensors for the accurate and reliable detection of DA signals in biological samples.