Kinetics and mechanism of the electrochemical oxidation of graphite in bisulphate melts

The kinetics of the electrochemical oxidation of graphite to volatile compounds by electrolysing molten bisulphates in the temperature range from 180 to 320°C has been studied by conventional steady-state and non-steady-state measurements. CO2, CO and traces of SO2 are formed during the electrochemical reaction. Assuming 4 Faraday/mol of CO2, the anodic efficiency is about 90%. The CO2/CO ratio is about 2 and is independent of the cd in the range considered. The electrochemical reaction is compared to the thermal oxidation of graphite. The reaction is interpreted through a scheme involving consecutive reactions, where the rate-determining step, under Temkin conditions, is a thermal process involving a desorption of intermediates following either a first-order or second-order process depending on the type of adsorption obeyed. The activation energy derived from the rate constant at the rest potential is about 42·5 Kcal/mol.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Electrochemical oxidation of iodide dissolved in sodium-nitrate-potassium-nitrate eutectic melt on a platinum rotating disk electrode

The E/I curve related to the electrochemical oxidation of iodide dissolved in molten nitrates on a platinum rotating disk electrode involves two anodic waves. The first corresponds to a reversible two-electron process and the second to a reversible one-electron process. A definite ratio between the anodic limiting currents is established suggesting that the second anodic wave is not independent from the first one. The parameters related to the diffusion of the species participating in the reaction are evaluated.Les courbes de polarisation concernant l'oxydation électrochimique de l'iodure dissous dans des nitrates fondus sur une électrode à disque tournant de platine comprend deux ondes anodiques. La première appartient a un procèssus réversible de deux électrons et la deuxième à un procèssus réversible d'un seul électron. Une relation définie est établie entre les courants limites anodiques, indiquent que la deuxième onde anodique n'est pas indépendante de la première. Les paramètres relatifs à la diffusion des espèces qui participent à la réaction sont évalués.Die E/I-Kurven, die bei der elektrochemischen Oxydation von in geschmolzenen Nitraten gelöstem Jodid an einer rotierenden Scheibenelektrode aus Platin auftreten, umfassen zwei anodische Wellen. Die erste entspricht einem reversiblen Zweielektronen- und die zweite einem reversiblen Einelektronenprozess. Es wird ein genaues Verhältnis zwischen den anodischen Grenztrömen aufgestellt unter der Annahme, dass die zweite anodische Welle von der ersten nicht unabhängig ist. Es werden die Diffusionsparameter der Reaktionsteilnahmer angegeben.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Cancer stem cells-driven tumor growth and immune escape: the Janus face of neurotrophins

Cancer Stem Cells (CSCs) are self-renewing cancer cells responsible for expansion of the malignant mass in a dynamic process shaping the tumor microenvironment. CSCs may hijack the host immune surveillance resulting in typically aggressive tumors with poor prognosis. In this review, we focus on neurotrophic control of cellular substrates and molecular mechanisms involved in CSC-driven tumor growth as well as in host immune surveillance. Neurotrophins have been demonstrated to be key tumor promoting signaling platforms. Particularly, Nerve Growth Factor (NGF) and its specific receptor Tropomyosin related kinase A (TrkA) have been implicated in initiation and progression of many aggressive cancers. On the other hand, an active NGF pathway has been recently proven to be critical to oncogenic inflammation control and in promoting immune response against cancer, pinpointing possible pro-tumoral effects of NGF/TrkA-inhibitory therapy. A better understanding of the molecular mechanisms involved in the control of tumor growth/immunoediting is essential to identify new predictive and prognostic intervention and to design more effective therapies. Fine and timely modulation of CSCs-driven tumor growth and of peripheral lymph nodes activation by the immune system will possibly open the way to precision medicine in neurotrophic therapy and improve patient's prognosis in both TrkA- dependent and independent cancers

Kinetics and mechanism of the electrochemical oxidation of graphite in bisulphate melts

The kinetics of the electrochemical oxidation of graphite to volatile compounds by electrolysing molten bisulphates in the temperature range from 180 to 320°C has been studied by conventional steady-state and non-steady-state measurements. CO2, CO and traces of SO2 are formed during the electrochemical reaction. Assuming 4 Faraday/mol of CO2, the anodic efficiency is about 90%. The CO2/CO ratio is about 2 and is independent of the cd in the range considered. The electrochemical reaction is compared to the thermal oxidation of graphite. The reaction is interpreted through a scheme involving consecutive reactions, where the rate-determining step, under Temkin conditions, is a thermal process involving a desorption of intermediates following either a first-order or second-order process depending on the type of adsorption obeyed. The activation energy derived from the rate constant at the rest potential is about 42·5 Kcal/mol.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Electrochemical oxidation of iodide dissolved in sodium-nitrate-potassium-nitrate eutectic melt on a platinum rotating disk electrode

The E/I curve related to the electrochemical oxidation of iodide dissolved in molten nitrates on a platinum rotating disk electrode involves two anodic waves. The first corresponds to a reversible two-electron process and the second to a reversible one-electron process. A definite ratio between the anodic limiting currents is established suggesting that the second anodic wave is not independent from the first one. The parameters related to the diffusion of the species participating in the reaction are evaluated.Les courbes de polarisation concernant l'oxydation électrochimique de l'iodure dissous dans des nitrates fondus sur une électrode à disque tournant de platine comprend deux ondes anodiques. La première appartient a un procèssus réversible de deux électrons et la deuxième à un procèssus réversible d'un seul électron. Une relation définie est établie entre les courants limites anodiques, indiquent que la deuxième onde anodique n'est pas indépendante de la première. Les paramètres relatifs à la diffusion des espèces qui participent à la réaction sont évalués.Die E/I-Kurven, die bei der elektrochemischen Oxydation von in geschmolzenen Nitraten gelöstem Jodid an einer rotierenden Scheibenelektrode aus Platin auftreten, umfassen zwei anodische Wellen. Die erste entspricht einem reversiblen Zweielektronen- und die zweite einem reversiblen Einelektronenprozess. Es wird ein genaues Verhältnis zwischen den anodischen Grenztrömen aufgestellt unter der Annahme, dass die zweite anodische Welle von der ersten nicht unabhängig ist. Es werden die Diffusionsparameter der Reaktionsteilnahmer angegeben.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Electrochemical and Scanning Force Microscopy Characterization of Fractal Palladium Surfaces Resulting from the Electroreduction of Palladium Oxide Layers

Pd oxide layers were grown by applying to smooth Pd electrodes a potential reversal technique (PRT) in 1 M H2SO4 at 25 °C. The electroreduction of the Pd oxide layer was made either voltammetrically or potentiostatically, yielding a Pd overlayer with a large increase in surface area. The effective range of PRT conditions for increasing the Pd surface area was established. The increase in surface area of treated Pd was voltammetrically determined. The electrochemical behavior of treated Pd electrodes in acid revealed an enhancement of the H atom surface electroadsorption processes. This behavior is consistent with the fractal characteristics of the treated Pd electrode surface, as demonstrated by the analysis of scanning force microscopy imaging data.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Synthesis, Characterization and Electrocatalytic Activity of Bi- and Tri-metallic Pt-Based Anode Catalysts for Direct Ethanol Fuel Cells

Three Pt-based anode catalysts supported on Vulcan XC-72R (VC) were prepared by using a modified polyol process. These materials were characterized and tested by X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF) and Transmission Electron Microscopy (TEM). XRD and TEM analysis indicated that especially the ternary anode catalysts consisted of uniform nanosized particles with sharp distribution. The Pt lattice parameter was smaller, in the ternary PtSnIr catalyst whereas it increased with the addition of Sn and Rh, in the corresponding binary and ternary catalysts. Cyclic voltammetry (CV) measurements showed that Sn, Ir and Rh may act as promoter of Pt enhancing ethanol electro-oxidation activity. It was found that the direct ethanol fuel cell (DEFC) performances were significantly improved with these modified anode catalysts. This effect on the DEFC performance is attributed to the so-called bi-tri-functional mechanism and to the electronic interaction between Pt and additives. The performance increased significantly with the temperature. However, it was also possible to observe some decay with time for all catalysts due to the formation of surface poisons, probably consisting in CO-like species. At 60 °C, the PtSnIr catalyst showed the best performance, as a result of a proper morphology and promoting effectFacultad de Ciencias ExactasInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Synthesis, Characterization and Electrocatalytic Activity of Bi- and Tri-metallic Pt-Based Anode Catalysts for Direct Ethanol Fuel Cells

Three Pt-based anode catalysts supported on Vulcan XC-72R (VC) were prepared by using a modified polyol process. These materials were characterized and tested by X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF) and Transmission Electron Microscopy (TEM). XRD and TEM analysis indicated that especially the ternary anode catalysts consisted of uniform nanosized particles with sharp distribution. The Pt lattice parameter was smaller, in the ternary PtSnIr catalyst whereas it increased with the addition of Sn and Rh, in the corresponding binary and ternary catalysts. Cyclic voltammetry (CV) measurements showed that Sn, Ir and Rh may act as promoter of Pt enhancing ethanol electro-oxidation activity. It was found that the direct ethanol fuel cell (DEFC) performances were significantly improved with these modified anode catalysts. This effect on the DEFC performance is attributed to the so-called bi-tri-functional mechanism and to the electronic interaction between Pt and additives. The performance increased significantly with the temperature. However, it was also possible to observe some decay with time for all catalysts due to the formation of surface poisons, probably consisting in CO-like species. At 60 °C, the PtSnIr catalyst showed the best performance, as a result of a proper morphology and promoting effectFil: D'Urso, C.. Centro Nazionale della Ricerca. ITAE; ItaliaFil: Bonesi, Alejandro Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Triaca, Walter Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Castro Luna Berenguer, Ana Maria del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico la Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentina. Universidad Nacional de La Plata; ArgentinaFil: Baglio, V.. Centro Nazionale della Ricerca. ITAE; Italia; ItaliaFil: Aricò, A. S.. Centro Nazionale della Ricerca. ITAE; Italia; Itali

Synthesis, Characterization and Electrocatalytic Activity of Bi- and Tri-metallic Pt-Based Anode Catalysts for Direct Ethanol Fuel Cells

Three Pt-based anode catalysts supported on Vulcan XC-72R (VC) were prepared by using a modified polyol process. These materials were characterized and tested by X-Ray Diffraction (XRD), X-Ray Fluorescence (XRF) and Transmission Electron Microscopy (TEM). XRD and TEM analysis indicated that especially the ternary anode catalysts consisted of uniform nanosized particles with sharp distribution. The Pt lattice parameter was smaller, in the ternary PtSnIr catalyst whereas it increased with the addition of Sn and Rh, in the corresponding binary and ternary catalysts. Cyclic voltammetry (CV) measurements showed that Sn, Ir and Rh may act as promoter of Pt enhancing ethanol electro-oxidation activity. It was found that the direct ethanol fuel cell (DEFC) performances were significantly improved with these modified anode catalysts. This effect on the DEFC performance is attributed to the so-called bi-tri-functional mechanism and to the electronic interaction between Pt and additives. The performance increased significantly with the temperature. However, it was also possible to observe some decay with time for all catalysts due to the formation of surface poisons, probably consisting in CO-like species. At 60 °C, the PtSnIr catalyst showed the best performance, as a result of a proper morphology and promoting effectFacultad de Ciencias ExactasInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Investigation of a Pt–Fe/C catalyst for oxygen reduction reaction in direct ethanol fuel cells

Three cathode catalysts (60% Pt/C, 30% Pt/C and 60% Pt–Fe/C), with a particle size of about 2–3 nm, were prepared to investigate the effect of ethanol cross-over on cathode surfaces. All samples were studied in terms of structure and morphology by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Their electrocatalytic behavior in terms of oxygen reduction reaction (ORR) was investigated and compared using a rotating disk electrode (RDE). The tolerance of cathode catalysts in the presence of ethanol was evaluated. The Pt–Fe/C catalyst showed both higher ORR activity and tolerance to ethanol cross-over than Pt/C catalysts. Moreover, the more promising catalysts were tested in 5 cm2 DEFC single cells at 60 and 80 °C. An improvement in single cell performance was observed in the presence of the Pt–Fe catalyst, due to an enhancement in the oxygen reduction kinetics. The maximum power density was 53 mW cm−2 at 2 bar rel. cathode pressure and 80 °C.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada