The current development of clean and high efficiency energy sources such as solar or wind energy sources has to be supported by the design and fabrication of energy storage systems. Electrochemical capacitors (or supercapacitors (SCs)) are promising devices for energy storage thanks to their highly efficient power management and possible small size. However, in comparison to commercial batteries, SCs do not have very high energy densities that significantly limit their applications. The value of energy density directly depends on the capacitance of full SCs and their cell voltage. Thus, an increase of SCs electrode specific capacitance together with the use of the wide potential window electrolyte can result in high performance SCs. Conductive polymer polyaniline (PANI) as well as carbonaceous materials graphene (G) or reduced graphene oxide (RGO) have been widely studied for usage in electrodes of SCs. Although pristine PANI electrodes have shown low cycling stability and graphene sheets can have low specific capacitance due to agglomeration during their preparation without a spacer, their synergetic effect can lead to high electrochemical properties of G/PANI composites. This review points out the best results for G/PANI composite in comparison to that of pristine PANI or graphene (or RGO). Various factors, such as the ratio between graphene and PANI, oxidants, time, and the temperature of chemical oxidative polymerization, which have been determined to influence the morphology, capacitance, cycling stability, etc. of the composite electrode materials measured in three-electrode system are discussed. Consequently, we provide an in-depth summary on diverse promising approaches of significant breakthroughs in recent years and provide strategies to choose suitable electrodes based on PANI and graphene.

Both polyaniline (PANI) and graphene are widely studied for their application as capacitive electrodes in energy storage devices. However, although PANI can be easy synthesized, is of low cost and has a higher specific capacitance than graphene, pristine PANI electrodes do not present long-term stability due to their large volume changes during release/doping of the electrolyte ions and surface area reduction with charge-discharge cycling. That is why a combination of PANI with carbonaceous materials, especially conductive and high-surface-area graphene as well as more widely used reduced graphene oxide (rGO), provides an effective approach to solve these problems. At the same time, the electropolymerization process is one of the possible methods for synthesis of PANI composites with G or rGO as freestanding electrodes. Therefore, no binders or additives such as carbon black or active carbon need to be used to obtain PANI/rGO electrodes by electrochemical polymerization (EP), in contrast to similar electrodes prepared by the chemical oxidative polymerization method. Thus, in this paper, we review recent advances in EP synthesis of PANI/rGO nanocomposites as high-performance capacitive electrode materials, combining the advantages of both electrical double-layer capacitance of rGO and pseudocapacitance of PANI, which hence exhibit long cycle life and high specific energy.

A monitorização da qualidade da água das redes de abastecimento públicas é efetuada periodicamente por entidades gestoras por método tradicionais de laboratório, exigindo a recolha de amostras de diversos locais da rede para este efeito. Este trabalho insere-se num projeto (WDS – Water Data Solutions), cujo objetivo é a otimização dos procedimentos operacionais envolvidos na gestão das redes de abastecimento de água num conceito de baixos custos. Assim, pretende-se construir um sistema que faça um controlo dos parâmetros necessários para assegurar a qualidade da água para consumo, que será instalado nos vários pontos de interesse de uma rede de abastecimento e que envie informações relativas a estes parâmetros regularmente, e com mínima necessidade de manutenção. Neste trabalho, foram testados sensores com elétrodos impressos (Phase zero sensors) na determinação da concentração de três metais pesados em água (Mercúrio, Cádmio e Chumbo) por voltametria cíclica. Em todos os metais foi possível obter uma reta de calibração para as concentrações testadas, com limiares de concentração de 1.2 × 10⁻⁶ mol.dm⁻³ (Hg),1.1 × 10⁻⁵ mol.dm⁻³ (Cd) e de 8.1 × 10⁻⁶ mol.dm-3 (Pb). Embora estes limites de deteção ainda se encontrem algo afastados dos limites máximos legais, a prova de conceito está definida. Os mesmos sensores foram utilizados na deteção do pH, funcionalizando o elétrodo de trabalho com PANI. O processo de deteção deste parâmetro consistiu na medição do potencial de circuito aberto (OCP) em águas com diferentes valores de pH, tendo sido obtida uma reta de calibração ideal e que segue os modelos teóricos (equação de Nernst). Paralelamente, foi desenvolvido um sistema de “língua eletrónica” (e-tongue) constituído por sensores simples resistivos que, numa análise preliminar, servirá como alarmística para alterações inesperadas no padrão de qualidade da água. A análise de dados foi feita por Redes Neuronais Artificiais. Os sensores são constituídos por pistas interdigitadas impressas de carbono com um filme ativo de PEDOT:PSS que, embora com limitações, apresentou a melhor avaliação de informação. Foi possível criar uma Rede Neuronal simples, que permitiu distinguir corretamente, por três conjuntos de sensores águas, entre água desionizada, água da torneira ou água de garrafa.

In this work, we studied the optical absorption spectral differences between doped and slightly doped polyaniline films and a derivative by photopyroelectric and photoacoustic spectroscopies. There exist great spectral differences between doped and slightly doped samples as shown by conventional optical absorption spectroscopy, but not greatly evidenced by photopyroelectric spectroscopy. The latter was applied to obtain thermal parameters such as thermal diffusivity and thermal conductivity, and as a result it showed that these thermal properties of polyaniline films are very similar for doped and slightly doped samples. Also it showed that for thicker films (about 20 μm), there are no significant optical absorption differences between them. However, for thin films both techniques showed greater optical absorption differences for doped and slightly doped samples, mainly detected by photoacoustic spectroscopy. These behaviors are in accordance with published results which is the granular metal model for polyaniline. This model explains the polyaniline polymeric matrix as formed by conductive islands in the insulating bulk material.

In this study, we carried out a quantitative depth profile analysis of the optical properties of slightly and strongly doped polyaniline (PANI) films, using both photoacoustic and photopyroelectric spectroscopies. As the thermal diffusion length varies inversely to chopper modulation frequency, then at high chopping frequencies information about the sample near the surface is obtained, while at low chopping frequencies the data come from deeper within the sample. The objective of this study is to analyze how the polyaniline doping process in acidic media occurs in the polymeric chain using the photothermal techniques. The results showed that polymeric chains of the doped samples are composed of undoped regions, while polymeric chains of slightly doped samples present doped regions to a lesser degree. These conclusions are in accordance with published results in which doped PANI films exhibit a granular conductive regions in a quasi undoped matrix. In addition, the photothermal spectra showed that the doping process of PANI, in which films are dipped in hydrochloric acid solution, is more effective in the external surface of the films.

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Abstract The non-isothermal decomposition kinetics of conductive polyaniline (PANI) and its derivatives, poly(o-methoxyaniline) (POMA) and poly(o-ethoxyaniline) (POEA), was investigated by thermogravimetric analysis (TGA), under inert and oxidative atmospheres, using Flynn-Wall-Ozawa’s approach to assess the kinetic parameters of the decomposition process. The order of reaction was found to be dependent on the degree of conversion indicating that both the early and the later stages of polymer degradation were next the zero or pseudo zero order kinetics, whereas the intermediate stages follow a first order kinetics. The activation energy was found to be dependent on both the degree of conversion and PANI derivative. Activation energy values vary from 125 to 250 kJ/mol, to decompositions carried out under nitrogen, and 75 to 120 kJ/mol to oxidative atmosphere. Parent PANI presented the best thermal stability and suggesting that thermal stability is also influenced by derivatization and type of atmosphere used.

The polyurethane (PU)/polyaniline (PANI) IPN, at three composition ratios (95/05, 75/25, 60/40), were analyzed, after the action of the urease enzyme, by means of the Hyperchem 8v software. Theoretical analysis of Gibbs free energy, FTIR, and 13C-NMR were done. The generation of functional groups due to hydrolysis was analyzed by FTIR. The 13C-NMR spectra of the three ratios showed a superposition of the individual spectra of PU and PANI and an appreciable decrease of the signals due to the action of the urease enzyme. The orbits showed that the electron density of the HOMO (Highest Occupied Molecular Orbital) is predominantly localized on the C-C bond, indicating that the binding of PU/PANI with the urease enzyme contains a vacant d-orbital. It is concluded that the adsorption of the urease enzyme increases the degree of hydrolysis of the IPN.

The production of low cost sensors to monitor environment in some industrial sectors is a current need. In aviculture centers, for example, the concentration of ammonia gas is related to humidity, and it is necessary to control it to avoid contamination. With this need in mind, this paper presents the preparation and characterization of a low cost humidity sensor based on poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) and polyaniline fully printed onto paper by a commercial HP printer. Using electrochemical impedance spectroscopy, an equivalent circuit containing resistive and capacitive parameters was proposed. The resistive parameter R1 is related to values of ambient humidity. The R1 values showed a sensitive response of 200% when relative humidity changes 80%, taking 10 min to reach saturation point. Moreover, the device showed good stability when humidity remained constant. These results indicate that the proposed device is suitable for applying as a humidity sensor that costs less than 1 Euro cent.