Carbon-Based Composites for Supercapacitor

Supercapacitor is an emerging technology that promises to play an advance role in new generation electronic devices and systems. Carbon (activated carbon, graphene and carbon nanotube) have attracted tremendous attention for their potential applications in supercapacitor technologies due to their excellent mechanical strength, good electrical conductivity, high electron mobilities, excellent chemical stability in acidic and basic medium, good thermal stability in wide range of temperature, various morphological structures, and large specific surface area. This chapter aims to assess the current status of carbon nanomaterials and their composites for supercapacitor application by discussing the literature in this field and presenting a perspective for future research in supercapacitor technologies

The oscillatory electro-oxidation of formic acid : insights on the adsorbates involved from time-resolved ATR-SEIRAS and UV reflectance experiments

The support of the University of Aberdeen is gratefully acknowledged. F.W.H. and H.V. acknowledge São Paulo Research Foundation (FAPESP) for the scholarship (grant #2014/08030-9, grant #2017/07286-8) and financial support (grant #2013/16930-7). HV (grant #306151/2010-3) acknowledges Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support. This study was also supported by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.Peer reviewedPostprin

Mass transfer phenomena induced by surface gas flow rate in the hanging meniscus configuration: A case study of the methanol electro-oxidation reaction on Pt(100)

The study of electrochemical systems using single-crystal electrodes under conditions that allow the occurrence of an oscillatory response can be a valuable tool to obtain a proper correlation between structure, composition, and electrocatalytic activity. Measurements with single-crystal electrodes are usually performed in the hanging meniscus configuration, so, it is essential to understand the impact of different experimental parameters on the electrochemical response, mainly under oscillatory regime, which are very sensitive to the electrochemical environment. In this study, we investigated the influence of surface gas flow rate, commonly used to avoid the contribution of the oxygen reduction reaction to the electrochemical response, on the methanol electro-oxidation reaction on Pt(100) electrodes. Controlled experiments were conducted to analyze the effect of this parameter on the electrochemical behavior in the chronoamperometric, voltammetric, and oscillatory responses. The results show that while chronoamperometric and voltammetric profiles remain relatively unaffected by varying gas flow rates, the oscillatory response undergoes significant changes. The induction period, the existence region of potential oscillations, and the transition between oscillatory patterns are notably influenced. The observed effects suggest that the subtle agitation caused by increased gas flow rate enhances mass transfer phenomena near the electrode surface, impacting the presence of soluble species and their role in the oscillatory behavior. In addition, the occurrence of mixed-mode oscillations is attributed to the periodic re-establishment of methanol concentration in the double layer. The findings highlight the importance of controlling the surface gas flow rate to ensure reliable and reproducible results in electrochemical experiments performed in the hanging meniscus configuration.E.P-S. acknowledges Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support (#140644/2020-2). H.V. acknowledges São Paulo Research Foundation (FAPESP) for financial support (#2019/22183-6); the support of the RCGI – Research Centre for Gas Innovation, hosted by the University of São Paulo (USP) and sponsored by FAPESP (#2020/15230-5) and Shell Brasil, and the strategic importance of the support given by ANP (Brazil's National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation; and the CNPq for financial support (#306060/2017-5). This work is also partially financed by Ministerio de Ciencia e Innovacion (Project PID2019-105653GB-I00) and Generalitat Valenciana (Project PROMETEO/2020/063). This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001

Energy Consumption Model for Green Computing

This chapter shows the environmental measurement factors that define the indicators within an architecture composed of Goods, Networks and Services (GNS). These references are obtained from the energy consumptions in the measurement processes. This lets obtaining several analyses important from the behavior in the energy consumption schemes. The application of these factors was determined from the energy generation processes, whose units are in metrics adequate for electricity and heat according to each system observed, and the same from the energetic consumption of the same data centers that helped to determine these characteristics. These indicators applied in an environment of Information and Communications Technology (ICT) define comparisons and be specified as the basis characterizing the analysis of energetic performance. The tests show the energy consumption and carbon footprint. This experiment seeks to increase the quality of services and decrease the energy consumption. This let us use efficiently the computational resources minimizing the environment impact. To achieve this target, it was used to apply indicators in green computing environment, like it can be mentioned: The Power Usage Effectiveness (PUE) and Data Center Effectiveness (DCE). With the use of these indicators can derive a generic model of energy consumption for a GNS system

Oscillatory instabilities during the electrocatalytic oxidation of methanol on platinum

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.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.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)CNP

Unraveling the impact of temperature on the reaction kinetics of the electro-oxidation of methanol on Pt(1 0 0)

Methanol is one of the key molecules in the challenge towards a sustainable future, particularly as a renewable hydrogen carrier fuel and as a low-carbon and net carbon-neutral liquid chemical. For most applications, it is imperative to understand the impact of temperature on the methanol electro-oxidation reaction (MEOR). In this study, the influence of the temperature on the kinetics of the MEOR and the parallel reaction pathways is assessed by investigating responses in both conventional and oscillatory regimes using a single-crystal Pt(1 0 0) electrode. Our findings demonstrate that chronoamperometric measurements under steady-state conditions provide more reliable values for apparent activation energies compared to transient conditions. Furthermore, a temperature-dependent shift in the dominance of specific oxidation pathways is observed, analogous to a kinetic and thermodynamic control mechanism, preventing the complete poisoning of the electrode surface. Specifically, oxidation pathways leading to the formation of reaction byproducts predominate at lower temperatures, while the oxidation pathway via COad becomes dominant at temperatures exceeding 30 °C. Moreover, our research shows that, at shorter times, temperature changes minimally affect the mean potential required to sustain the applied current during the oscillations in a galvanostatic experiment, which is closely linked with the voltaic efficiency. However, over longer periods, when mass transport phenomena become significant and mixed-mode oscillations occur, elevated temperatures increase the mean potential, resulting in reduced voltaic efficiency. Therefore, to facilitate the complete conversion of methanol to CO2 without increasing the mean potential for current maintenance, it is essential not only to increase the temperature but also to improve the mass transport conditions to mitigate the mixed-mode oscillations, despite their lower minima reached during oscillation. This idea challenges the conventional assumption that a lower minimum potential implies a lower mean potential during oscillations. This advancement propels our understanding to a more sophisticated level, providing valuable insights to guide the materials design to increase the conversion efficiency and optimize the operating temperature of devices crucial to energy conversion.E.P-S. acknowledges Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support (#140644/2020-2). H.V. acknowledges the São Paulo Research Foundation (FAPESP) for financial support (#2019/22183-6); the support of the RCGI – Research Centre for Gas Innovation, hosted by the University of São Paulo (USP) and sponsored by FAPESP (#2020/15230-5) and Shell Brasil, and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas and Biofuels Agency) through the R&D levy regulation; and the CNPq for financial support (#306060/2017-5). This work is also partially financed by Ministerio de Ciencia e Innovación (Project PID2022-137350NB-I00). This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001

Effect of temperature on the electro-oxidation of ethanol on platinum

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.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Pesquisa (CNPq

The Role of Surface Sites on the Oscillatory Oxidation of Methanol on Stepped Pt[n(111) × (110)] Electrodes

Reaction rates and mechanisms of most electrocatalytic reactions are known to critically depend on the structure of the electrode surface. Examples of structure sensitive electrocatalytic systems include the reduction of oxygen and the oxidation of small organic molecules on platinum, for example. Even more intricate is the effect of the interfacial structure on the oscillatory dynamics commonly observed in some electrocatalytic systems. This is somewhat expected because several adsorption and reaction steps are simultaneously active during self-organized potential or current oscillations. Herein we present results of the effect of surface structure on the oscillatory electro-oxidation of methanol in acidic media on Pt(111), Pt(110), and stepped surfaces Pt(776), Pt(554), Pt(775), and Pt(332). The system was investigated at two methanol concentrations and under voltammetric and galvanostatic regimes. The voltammetric activity toward the electro-oxidation of methanol on stepped surfaces followed this sequence: Pt(776) < Pt(554) < Pt(775) < Pt(332), at high methanol concentration. The reaction rates increase with the density of (110) sites, but small (111) terraces were also found to contribute to the overall process. In terms of potential oscillations, we found specificities that were unambiguously assigned to the surface structure. In particular, the following features were found according to the specific surface studied: period-adding sequences of mixed-mode oscillations; a new type of mixed-mode oscillation; and a particular separation between two types of sequential oscillations. The understanding of the relationship between the surface structure and the underlying dynamics of the surface chemistry during oscillations is a key challenge and our findings in this direction are discussed.G.T.F. and H.V. (Grant 2013/16930-7) acknowledge São Paulo Research Foundation (FAPESP) for financial support. H.V. (Grant 306060/2017-5) and GTF (Grant 305273/2017-5) acknowledges Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) for financial support. This study was partially financed by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001

The effect of Pt surface orientation on the oscillatory electro-oxidation of glycerol

In the present paper, we have studied the influence of (bi)sulfate anion (0.1 and 0.5 M) on the electro-oxidation of glycerol on basal Pt(hkl) and stepped surfaces belonging to the series of Pt(S)[n(1 1 1) × (1 1 1)]. Cyclic voltammograms and derivative voltammetry pointed out that the catalytic activity decreases for Pt(1 1 1) and Pt(1 1 0) and, to a minor extent, for stepped surfaces in 0.5 mol/L H2SO4. Chronoamperometric curves demonstrated that above 0.60 V (vs RHE), for both concentrations (0.1 and 0.5 mol/L H2SO4), stepped surfaces and Pt(1 1 0) showed greater ability to catalyze the glycerol electro-oxidation in comparison with Pt(1 1 1). Potential oscillations were mapped along with slow galvanodynamic sweeps and studied at constant current. For Pt(1 1 1), no oscillations were found in the galvanodynamic regime, however, under the galvanostatic regime, period 1 oscillations were observed after a long induction period. The oscillations showed a very similar profile for stepped surfaces, even for the Pt(3 3 2) surface, which has a high density of (1 1 0) steps. Pattern changes were observed only for Pt(1 1 0) compared to other surfaces. Therefore, we conclude that (1 1 0) step sites influence the oscillatory behavior, thus the insertion of the steps favors the path of formation of inactive species, which compete for the same catalytic sites in a given potential region. The extinction of the mechanism oscillatory occurs differently due to the intrinsic characteristics of each surface electrode for the formation of (hydro)oxides.The authors acknowledge FAPESP (Grants No. 2013/16930-7 and 2019/22183-6), FAPEAL (process 60030-001076/2016), CAPES - Brasil (CAPES, Grant No. 0001, and for the scholarship, GBM, 88887.341974/2019-00). HV (Grant No. 306060/2017-5) and GTF (Grant No. 313455/2021-0) acknowledge CNPq for financial support. We gratefully acknowledge the support of the RCGI – Research Centre for Gas Innovation, hosted by the University of São Paulo (USP) and sponsored by FAPESP (2014/50279-4 and 2020/15230-5) and Shell Brazil, and the strategic importance of the support given by ANP (Brazil’s National Oil, Natural Gas, and Biofuels Agency) through the R&D levy regulation