Improving the fabrication of all-polythiophene supercapacitors

The influence of the preparation method in the properties of poly(3,4-ethylenedioxythiophene) (PEDOT) electrodes used to manufacture organic energy storage devices, as for example supercapacitors, have been examined by considering a reduction of both monomer and supporting electrolyte concentrations during the anodic polymerization reaction. Thus, the excellent electrochemical properties of PEDOT films prepared using quiescent solutions have been preserved by applying controlled agitation to the polymerization process, even though the concentration of monomer and supporting electrolyte were reduced 5 and 2 times, respectively. For example, the charge stored for reversible exchange in a redox process, the electrochemical stability and the current productivity of films achieved using quiescent solutions have been preserved using a dynamic reaction medium in which the concentrations of monomer and supporting electrolyte are several times lower. The excellent properties of PEDOT electrodes prepared using optimized dynamic conditions have also been proved by constructing a symmetric supercapacitor. This energy storage device, which has been used as power source for a LED bulb, is rechargeable and exhibits higher charge-discharge capacities than supercapacitors prepared with electrodes derived from quiescent solutions. In addition of bring an efficacious procedure for preparing cost-effective PEDOT films with excellent properties, the proposed dynamic conditions reduce the environmental hazards of depleted reaction media.Peer ReviewedPostprint (author's final draft

Nanophase-segregation in the dielectric layer enhances the charge storage capacity of polymeric electrochemical supercapacitors

Properties related with the charge storage capacity have been evaluated for three-layered films made with two sheets of poly(3,4-ethylenedioxythiophene) separated by a sheet of poly(N-methylpyrrole) or poly(3,4-ethylenedioxythiophene-co-N-methylpyrrole) (3l-PEDOT/PNMPy or 3l-PEDOT/P(EDOT-co-NMPy), respectively). The most distinctive trend of the copolymer, which shows electrochemical properties intermediate between those of the two homopolymers, is the formation of a biphasic structure, EDOT- and NMPy-rich blocks organizing separately. The ability to exchange charge reversibly is higher for 3l-PEDOT/P(EDOT-co-NMPy) than for 3l-PEDOT/PNMPy, the electroactivity and electrostability of such two 3-layered films being significantly better than that of single-layered PEDOT. Advantages of 3l-PEDOT/P(EDOT-co-NMPy) are mainly based on the nanophase-segregated structure of the copolymer. Thus, the intermediate layer can be considered as random disposition of ultrathin dielectrics having nanometric length and width. In terms of charge storage, the intermediate layer of 3l-PEDOT/P(EDOT-co-NMPy) can be viewed as a thin reservoir filled of heterogeneously distributed nanometric supercapacitors that are connected in series among them and in parallel to the PEDOT layers. The superiority of 3l-PEDOT/P(EDOT-co-NMPy) as organic electrochemical supercapacitor compared to other 3-layered systems, has been proved by powering a red LED bulb.Peer ReviewedPostprint (author's final draft

Interface porosity in multilayered all-conducting polymer electrodes

Multilayered films made with at least two different electroactive polymers, in which the least conducting one acts as a dielectric and separates the layers made with the other, behave as efficient electrodes for electrochemical supercapacitors. In this work, we present a simple strategy to develop improved multilayered electrodes with structured interfaces by enhancing the porosity of the dielectric. This has been achieved by growing sodium chloride crystals onto a conducting polymer layer and, after generation of all required layers using the layer-by-layer electrodeposition technique, salt crystals have been eliminated by water etching. Results from morphological and topographical studies on single-layered poly(3,4-ethylenedioxythiophene) (PEDOT), poly(N-methylpyrrole) (PNMPy), and poly(3,4-ethylenedioxythiophene-co-N-methylpyrrole) (COP), as well as electrochemical investigations on bi-layered films with enhanced porosity at the interface between the two layers, have been used to design new four-layered electrodes. These consist in two layers of PEDOT separated by two layers of nanosegregated COP with a porous interface in the middle. Although the properties of the new four-layered electrodes improve due to the porous interface, the highest specific capacitance corresponds to the two-layered electrode in which two PEDOT layers are separated by an ultra-porous interface.Postprint (author's final draft

Preparation and characterization of poly(N-methylpyrrole)/MoO3 hybrid composites

Poly(N-methylpyrrole)/molybdenum trioxide composites have been prepared by in situ anodic polymerization using a 75:25 acetonitrile:water monomer solution, exfoliated molybdenum trioxide particles, and supporting electrolyte as reaction medium. The incorporation of molybdenum trioxide increases the ability of poly(N-methylpyrrole) to exchange charge reversibly (i.e., the electroactivity) by 47%. This has been attributed to the structural changes induced by the molybdenum trioxide, which transforms the uniform and compact surface morphology of poly(N-methylpyrrole) into a more open structure with distinctive topographic features at different levels. These trends facilitate the access and escape of dopant ions during oxidation and reduction processes, respectively, with respect to poly(N-methylpyrrole).Postprint (author's final draft

Properties of Cu nanoparticles-poly(N-methylpyrrole) composites

© 2014 Society of Plastics Engineers. Spherical copper nanoparticles (Cu-NPs) have been immobilized on the compact surface of potentiostatically generated poly(N-methylpyrrole) (PNMPy) films by applying a reduction potential of -0.60 V to a deionized water solution of CuCl2. Although the number density of Cu-NPs obtained using this procedure is not high (4·106 cm-2), the average diameter is relatively high (?50 nm). The surface topology and roughness of films with Cu-NPs-PNMPy are intermediate between those obtained for as prepared PNMPy and reduced PNMPy. Analysis of the electrochemical properties indicates that Cu-NPs promote the electroactivity of the PNMPy, this effect being more evident for composited made with the thinnest PNMPy films. In opposition, the electrostability and electrical conductivity are not enhanced by deposited Cu-NPs. Similar findings are obtained for bilayered PNMPy-Cu-NPs-PNMPy films. POLYM. COMPOS., 37:594-601, 2016.Peer ReviewedPreprin

Electrodeposición de composites de poli(n-metilpirrol) con nanopartículas de Cu

Nanopartículas esféricas (NPs-Cu) se han inmovilizado en la superficie compacta de películas de poly(N-metilpirrol) (PNMPy) generadas potenciostáticamente por aplicación de un potencial de reducción de -0,60 V a una solución acuosa de CuCl2. Aunque la densidad numérica de NPs-Cu obtenidas usando este procedimiento no es alta (4•106 cm-2), el diámetro promedio es relativamente alto (~50 nm. La topología superficial y rugosidad de los films de Cu-NPs-PNMPy son intermedias entre aquellas obtenidas para el PNMPy y el PNMPy reducido. Análisis de las propiedades electroquímicas indican que las NPs-Cu promueven la electroactividad del PNMPy, este efecto es más evidente para el compuesto obtenido con los films de PNMPy más finos. Por el contrario, la electroestabilidad y conductividad eléctrica no se ha mejorado por deposición de NPs-Cu. Hallazgos similares se han obtenido para films bicapa PNMpy-Cu-NPs-PNMPy.Peer Reviewe

Properties of In situ polymerized poly(3,4-ethylenedioxythiophene)/alumina composites for energy storage applications

Composites formed by poly(3,4-ethylenedioxythiophene) and alumina (PEDOT/Al2O3) have been prepared by in situ anodic polymerization. For this purpose, the stability of 1:1 and 4:1 monomer:alumina aqueous solutions has been examined as a function of the pH (2.3, 4.0, 7.0, 8.8, or 10.8). Results indicate that the monomer behaves as a dispersant that remains stable at the studied basic pHs despite they are close to the isoelectric point of alumina. Although the thermal stability of the composites is considerably affected by the pH of the reaction medium, its influence on the surface morphology is very small. Independently, of the synthetic conditions, the electrochemical properties were better for PEDOT/Al2O3 than for pure PEDOT, reflecting that alumina particles promote the charge mobility. The highest specific capacitance (SC; 141 F/g), which was 55% higher than that obtained for pure PEDOT, was achieved for the composite prepared at pH¿=¿8.8 using a 4:1 monomer:alumina ratio. These conditions favor the participation of OH– groups as secondary doping agents without degrading the polymer matrix and enhance the specific surface of the films, facilitating the ionic mobility. On the other hand, application of a multi-step polymerization strategy has shown that interfaces originated by consecutive steps enhance the SC.Peer ReviewedPostprint (author's final draft

Polypropylene mesh for hernia repair with controllable cell adhesion/de-adhesion properties

Herein, a versatile bilayersystem, composed by a polypropylene(PP)mesh and a covalently bonded poly(N-isopropylacrylamide) (PNIPAAm) hydrogel, is reported. The cell adhesion mechanism was successfully modulated by controlling the architecture of the hydrogel in terms of duration of PNIPAAm graftingtime, crosslinker content, and temperature of material exposure in PBS solutions (belowandabove the LCST of PNIPAAm). The best in vitroresults with fibroblast (COS-1) and epithelial (MCF-7) cells was obtained with a mesh modified with porous iPP-g-PNIPAAm bilayer system, prepared via PNIPAAm grafting for 2 h at the lowest N,N'-methylene bis(acrylamide) (MBA)concentration (1 mM). Under these conditions, the detachment of the fibroblast-like cells was 50% lower than that of the control, after 7 days of cell incubation, which represents a high de-adhesionof cellsin a short period. Moreover, the whole system showed an excellent stability in dry or wet media, proving that the thermosensitive hydrogel was well adhered to the polymer surface, after PP fibreactivation by cold plasma. This study opens new insights on the development of anti-adherent meshes for abdominal hernia repairs.Peer ReviewedPublished versio

Recent progress in biomedical sensors based on conducting polymer hydrogels

Biosensors are increasingly taking a more active role in health science. The current needs for the constant monitoring of biomedical signals, as well as the growing spending on public health, make it necessary to search for materials with a combination of properties such as biocompatibility, electroactivity, resorption, and high selectivity to certain bioanalytes. Conducting polymer hydrogels seem to be a very promising materials, since they present many of the necessary properties to be used as biosensors. Furthermore, their properties can be shaped and enhanced by designing conductive polymer hydrogel-based composites with more specific functionalities depending on the end application. This work will review the recent state of the art of different biological hydrogels for biosensor applications, discuss the properties of the different components alone and in combination, and reveal their high potential as candidate materials in the fabrication of all-organic diagnostic, wearable, and implantable sensor devices.Peer ReviewedPostprint (published version

Regulating the superficial vacancies and OH- orientations on polarized hydroxyapatite electrocatalysts

Smart designs of hydroxyapatite (HAp) materials with customized electrical properties are drawing increasing attention for their wide range of potential applications. Such enhanced electrical properties directly arise from the number and orientation of OH- groups in the HAp lattice. Although different polarization treatments have been proposed to enhance the final conductivity by generating vacancies at high temperatures and imposing specific OH- orientations through electric voltages, no direct measurement showing the evolution that OH- groups undergo has been described yet. In this article, the first direct empirical observation that allows the characterization of both the generation of vacancies and the polarization of OH- groups is reported. The mechanisms behind the electrical enhancement are elucidated allowing to distinguish between charge accumulation at the crystal grains, which is due to the formed vacancies, and charge accumulation in the boundaries of particles. In addition, a linear dependence between the number of vacancies and the superficial charge is observed. Therefore, it is demonstrated that the charge accumulation at the micrometric grain boundaries has a great impact on the catalytic properties of the thermally stimulated polarized HAp. These results will be used for further optimization of the catalyst properties.Peer ReviewedPostprint (author's final draft