Spontaneous pattern formation in reaction-diffusion systems was theoretically proposed by Alan M. Turing in 1952. His breakthrough conceptions of chemical self-organization were able to explain how patterns emerge in nature and the symmetry breaking, which are of utmost importance, for instance, in the context of origin of life. Along with the experimental observations in the Belousov-Zhabotinsky reaction and the development of the nonequilibrium thermodynamics by Prigogine and co-workers, Turing predictions are considered the foundation of the field of Nonlinear Chemical Dynamics. This review aims to describe the basis of Turing structures with their consequent scientific achievements and to provide future directions in the development of this field.

Spatiotemporal pattern formation in reaction-transport systems takes place spontaneously when the system is kept far from thermodynamic equilibrium. Targets, reaction fronts, waves, spirals, spots and stripes are some typical examples of selforganized structuring. In electrochemical systems, monitoring spatiotemporal patterns of potential in the solid/liquid interface can be done by the use of equally distributed microprobes located close to the working electrode. However, the physical size of each probe can limit the spatial resolution and alter mass transport properties. In contrast, the direct measurement of discrete electrodes does not suffer from this limitation and allows the accurate manipulation of the spatial coupling through changes in resistors connected to the electric circuit. In this paper, the development of an electrochemical setup for multichannel data acquisition with spatiotemporal resolution is described, especially to monitor low levels of currents usually observed in the electro-oxidation of small organic molecules.

O íon boroidreto tem se mostrado um promissor combustível alternativo. Grande parte das pesquisas aborda o aspecto eletrocatalítico da eletrooxidação deste combustível sobre platina e ouro. Apesar das conhecidas limitações cinéticas e do intrincado mecanismo, nosso Grupo relatou recentemente a ocorrência de duas regiões de biestabilidade e autocatálise no potencial do eletrodo durante a interação em potencial de circuito aberto entre este íon e a superfície de platina oxidada. Seguindo esta contribuição, neste trabalho fenômenos ainda mais complicados são apresentados: a presença de oscilações eletroquímicas durante a eletrooxidação do íon boroidreto em platina em meio alcalino. Oscilações de corrente foram associadas a duas janelas distintas de instabilidades e caracterizadas no plano de potencial-resistência. As características dinâmicas de tais oscilações sugerem a existência de mecanismos distintos de acordo com a região de potencial. Resultados publicados anteriormente obtidos sob regime não-oscilatório foram usados para fornecer algumas dicas sobre as reações superficiais por trás da dinâmica observada.

The borohydride ion has been pointed as a promising alternative fuel. Most of the investigation on its electrochemistry is devoted to the electrocatalytic aspects of its electrooxidation on platinum and gold surfaces. Besides the known kinetic limitations and intricate mechanism, our Group has recently found the occurrence of two regions of bi-stability and autocatalysis in the electrode potential during the open circuit interaction of borohydride and oxidized platinum surfaces. Following this previous contribution, the occurrence of more complicated phenomena is here presented: namely the presence of electrochemical oscillations during the electrooxidation of borohydride on platinum in alkaline media. Current oscillations were found to be associated to two distinct instability windows and characterized in the resistance-potential parameter plane. The dynamic features of such oscillations suggest the existence of distinct mechanisms according to the potential region. Previously published results obtained under non-oscillatory regime were used to give some hints on the surface chemistry behind the observed dynamics.

Neste trabalho, investigou-se pela primeira vez a eletrooxidação de etanol em eletrodepósitos de Pt e PtRu em meio ácido através da técnica de absorção e reflexão de infravermelho em superfície com reflexão total atenuada (ATR-SEIRAS) in situ. O desenho experimental elimina as fracas absorbâncias associadas a espécies adsorvidas, usualmente observadas para superfícies eletrodepositadas (rugosas), e permite que se acompanhe o recobrimento superficial por CO em função do potencial, para ambos os catalisadores. A dinâmica da adsorção-oxidação de CO foi acompanhada por ATR-SEIRAS (para quatro concentrações de etanol) e correlacionada com expressões derivadas de um modelo cinético simples. A análise cinética sugere que o desenvolvimento da camada de CO não é influenciado pela presença de Ru ou pela concentração de etanol. Os resultados apontam que a quebra da ligação C-C independe do recobrimento com Ru e provavelmente acontece em sítios de Pt.

Herein, it was investigated for the first time the electro-oxidation of ethanol on Pt and PtRu electrodeposits in acidic media by using in situ surface enhanced infrared absorption spectroscopy with attenuated total reflection (ATR-SEIRAS). The experimental setup circumvents the weak absorbance signals related to adsorbed species, usually observed for rough, electrodeposited surfaces, and allows a full description of the CO coverage with the potential for both catalysts. The dynamics of adsorption-oxidation of CO was accessed by ATR-SEIRAS experiments (involving four ethanol concentrations) and correlated with expressions derived from a simple kinetic model. Kinetic analysis suggests that the growing of the CO adsorbed layer is nor influenced by the presence of Ru neither by the concentration of ethanol. The results suggest that the C-C scission is not related to the presence of Ru and probably happens at Pt sites.

We present in this work the influence of temperature on the dynamics of homogeneous chemical systems containing bromate and 1,4-cyclohexanedione (1,4-CHD) in acidic media. In particular, the following systems were studied: bromate/1,4-CHD/acid, bromate/1,4-CHD/ferroin/acid and bromate/1,4-CHD/trisbipyridine ruthenium/acid. Investigations were carried out by means of an electrochemical probe, at five temperatures between 5 and 45 °C. Activation energies (Ea) were estimated in different ways for the pre-oscillatory and oscillatory regimes. In any case, the Ea was found to depend on the catalyst, composition and initial concentrations. In addition, it was observed that ferroin and trisbipyridine ruthenium act as catalysts only during the transition between the induction period and oscillatory regime.

We present in this work an experimental investigation of the effect of temperature (from 25 to 180 ºC) in the electro-oxidation of ethanol on platinum in two different phosphoric acid concentrations. We observed that the onset potential for ethanol electro-oxidation shifts to lower values and the reaction rates increase as temperature is increased for both electrolytes. The results were rationalized in terms of the effect of temperature on the adsorption of reaction intermediates, poisons, and anions. The formation of oxygenated species at high potentials, mainly in the more diluted electrolyte, also contributes to increase the electro-oxidation reaction rate.

Descreve-se neste artigo a observação experimental de dinâmica oscilatória durante a oxidação eletrocatalítica de metanol sobre platina. Além das, previamente relatadas, oscilações de potencial, oscilações de corrente obtidas sob controle potenciostático também são apresentadas. A região de existência de oscilações de corrente é mapeada no plano de bifurcação voltagem aplicada x resistência. Conjuntamente com investigações eletroquímicas, espectroscopia FTIR in situ também foi aplicada nestes estudos. Apesar de não ter sido possível acompanhar eventuais variações de intermediários reacionais durante as oscilações, tais experimentos revelaram que a cobertura média de monóxido de carbono permanece consideravelmente alta durante as oscilações. Os resultados são discutidos e comparados com as oscilações observadas na eletrooxidação de ácido fórmico, um sistema cujo comportamento é mais entendido e amplamente fundamentado por dados espectroscópicos obtidos in situ.

It is described in this paper the experimental observation of oscillatory dynamics during the electrocatalytic oxidation of methanol on platinum. Besides the previously reported potential oscillations, current oscillations obtained under potentiostatic control are also presented. The existence region of current oscillations is mapped in an applied voltage x resistance bifurcation diagram. Conjointly with electrochemical investigations, in situ FTIR spectroscopy was also employed in the present studies. Although we were not able to follow eventual intermediate coverage changes during the oscillations, those experiments revealled that the mean coverage of adsorbed carbon monoxide remains appreciably high along the oscillations. Results are discussed and compared with the oscillations observed in the electrooxidation of formic acid, a system whose behavior is more understood and widely supported by in situ spectroscopic data.

It is investigated in the present contribution the oscillatory co-electrodeposition of CuSn on a polycrystalline gold surface in the presence of Triton X-100 surfactant and citric acid as additive, in acidic media. The experiments were conducted under potentiostatic control and the system dynamics characterized in terms of the morphology and stability of the current oscillations. Besides modulations in the frequency and amplitude of the current oscillations, several patterned states were observed, including relaxation-like and mixed mode oscillations. The oscillations were found to be very robust and some time series presented regular motions up to about two hours.

New chemical systems have been recently designed for the study of complex phenomena such as oscillatory dynamics in the temporal domain and spatiotemporal pattern formation. Systems derived from oscillators based on the chemistry of bromate are the most extensively studied, with the celebrated Belousov-Zhabotinsky (BZ) reaction being the most popular example. Problems such as the formation of bubbles (CO2) and solid precipitate in the course of the reaction and the occurrence of simply short-lived oscillations under batch conditions are very common and, in some cases, compromise the use of some of these systems. It is investigated in this paper the dynamic behavior of the bromate/hypophosphite/acetone/dual catalyst system, which has been sugested as an interesting alternative to circumvent those inconvenients. In this work, manganese and ferroin are employed as catalysts and the complete system (BrO3-/H2PO2-/acetone/Mn(II)-ferroin) is studied under batch conditions. Temporal symmetry breaking was studied in a reactor under agitation by means of simultaneous records of the potential changes of platinum and Ag/AgBr electrodes, both measured versus a reversible hydrogen electrode. Additionally, spatio-temporal formation of target patterns and spiral waves were obtained when the oscillating mixture was placed in a quasi two-dimensional reactor.

In this work, cathodes employed in secondary lithium batteries are reviewed. These cathodes have great technologic and scientific importance, specifically, materials for cathodes as electronic conductor polymers (ECP), transition metal oxides (TMO) and nanocomposites of ECP/TMO. The use of a specific cathodic material is based in some intrinsic characteristics that improve the performance of the battery. Thus, some vantages and disvantages of these insertion compounds are discussed, as lithium insertion capacity, energy density, and the ciclability of these materials.

The concepts of dissipation and feedback are contained in the behavior of many natural dynamical systems. They have been used to predict the evolution of populations leading to the formulation of the quadratic logistic equation (QLE). More recently, the QLE has been used to provide a better understanding of physicochemical systems with promising results. Many physical, chemical and biological dynamic phenomena can be understood on the basis of the QLE and this work describes the main aspects of this equation and some recent applications, with emphasis on electrochemical systems. Also, it is illustrated the concept of potential energy as a convenient way of describing the stability of the fixed points of the QLE.

A study of the kinetics of oxygen evolution in alkaline conditions from ceramic films of Mn2O3 supported on stainless steel was carried out. This study has been done through the determination of transfer coefficients, Tafel slopes and exchange currents using potentiodynamic and quasi-potentiostatic measurements. The activation energy was determined as a function of the overpotential and, additionally, the electrode active surface was estimated. The results are consistent with data already published for other electrodes, implying that the methods used in this work were reliable and precise.

Among in situ techniques, the electrochemical quartz crystal microbalance (EQCM) is a powerful tool for the study of electrochemical reactions that produce mass changes in the electrode/solution interface. This review present some systems in which the EQCM combined with classical electrochemical techniques, gives relevant information for understanding the charge transport process at a molecular level. The aim of this review is to do a brief description of experimental arrangements, with emphasis on some special cares that must be considered by the users. Secondly, some chosen electrochemical systems where the technique was successfully applied are discussed. Finally, a brief analysis of electroacoustic impedance experiments was done in order to show when the Sauerbrey equation can be used.

Um dos problemas mais importantes associado à utilização da polianilina como material catódico em baterias recarregáveis de lítio está relacionado à degradação na densidade de energia devido à participação massiva de ânions durante o processo de compensação de cargas. Este trabalho descreve a síntese de uma polianilina auto-dopada, poli-(anilina-co-N-ácido propanossulfônico-anilina), e avalia suas propriedades em meio aquoso, considerando o aumento na participação de prótons no mecanismo de eletroneutralização. A caracterização foi feita utilizando análise elementar e espectroscopias no infravermelho e ultravioleta-visível. As propriedades eletroquímicas foram investigadas com a microbalança eletroquímica a cristal de quartzo e voltametria cíclica. Os resultados obtidos mostram que a participação de prótons no processo redox da poli-(anilina-co-N-ácido propanossulfônico-anilina) aumentou, em relação à polianilina.

One of the most important problems associated with use of polyaniline as a cathode material in rechargeable lithium batteries is related to energy density degradation due to the predomination of anion participation in the charge compensation process. This work describes the synthesis of a self-doped polyaniline, poly-(aniline-co-N-propanesulfonic acid-aniline), and evaluates its properties in aqueous acid solutions, with special attention to the increase of proton participation in the electroneutralization mechanism. The characterization was carried out using elemental analysis, FTIR and UV-vis spectroscopies. Electrochemical properties were investigated with the electrochemical quartz crystal microbalance and cyclic voltammetry. The results obtained show that proton participation was increased for the redox process of poly-(aniline-co- N-propanesulfonic-acid-aniline) in relation to polyaniline.