Oxidation mechanism of formic acid on the bismuth adatom-modified Pt(111) surface

In order to improve catalytic processes, elucidation of reaction mechanisms is essential. Here, supported by a combination of experimental and computational results, the oxidation mechanism of formic acid on Pt(111) electrodes modified by the incorporation of bismuth adatoms is revealed. In the proposed model, formic acid is first physisorbed on bismuth and then deprotonated and chemisorbed in formate form, also on bismuth, from which configuration the C-H bond is cleaved, on a neighbor Pt site, yielding CO2. It was found computationally that the activation energy for the C-H bond cleavage step is negligible, which was also verified experimentally.This work has been financially supported by the MINECO (Spain) (project CTQ2013-44083-P) and Generalitat Valenciana (project PROMETEOII/2014/013).Perales Rondón, JV.; Ferre Vilaplana, A.; Feliu, J.; Herrero, E. (2014). Oxidation mechanism of formic acid on the bismuth adatom-modified Pt(111) surface. Journal of the American Chemical Society. 136(38):13110-13113. https://doi.org/10.1021/ja505943hS13110131131363

Pseudo-single crystal electrochemistry on polycrystalline electrodes : visualizing activity at grains and grain boundaries on platinum for the Fe2+/Fe3+ redox reaction

The influence of electrode surface structure on electrochemical reaction rates and mechanisms is a major theme in electrochemical research, especially as electrodes with inherent structural heterogeneities are used ubiquitously. Yet, probing local electrochemistry and surface structure at complex surfaces is challenging. In this paper, high spatial resolution scanning electrochemical cell microscopy (SECCM) complemented with electron backscatter diffraction (EBSD) is demonstrated as a means of performing ‘pseudo-single-crystal’ electrochemical measurements at individual grains of a polycrystalline platinum electrode, while also allowing grain boundaries to be probed. Using the Fe2+/3+ couple as an illustrative case, a strong correlation is found between local surface structure and electrochemical activity. Variations in electrochemical activity for individual high index grains, visualized in a weakly adsorbing perchlorate medium, show that there is higher activity on grains with a significant (101) orientation contribution, compared to those with (001) and (111) contribution, consistent with findings on single-crystal electrodes. Interestingly, for Fe2+ oxidation in a sulfate medium a different pattern of activity emerges. Here, SECCM reveals only minor variations in activity between individual grains, again consistent with single-crystal studies, with a greatly enhanced activity at grain boundaries. This suggests that these sites may contribute significantly to the overall electrochemical behavior measured on the macroscale

Conducting fabrics of polyester coated with polypyrrole and doped with graphene oxide

Polyester (PES) has been coated with polypyrrole (PPy) to produce conducting fabrics. Graphene oxide (GO) has been used in different concentrations (10, 20 and 30% weight) as counter ion to neutralize the positive charges of the PPy structure. Fourier transform infrared spectroscopy with attenuated total reflection (FTIR-ATR), energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) of the PPy/GO powders corroborated the incorporation of GO as counter ion due to the presence of O in the EDX spectrum, as well as an excess of C, arising from GO contribution. The doping level (N+/N) decreased with the GO content. Field emission scanning electron microscopy (FESEM) showed the formation of the PPy/GO coating and the incorporation of GO in the composite. Electrochemical impedance spectroscopy (EIS) in solid state and solution, cyclic voltammetry (CV) and scanning electrochemical microscopy (SECM) were used to test the electrical properties and electroactivity of the fabrics. There was a decrease in the electrical properties and electroactivity as the GO content increased. The conductivity of the fabrics could be tuned by varying the GO content.Spanish Ministerio de Ciencia e Innovación (contract CTM2011-23583) for the financial support. Conselleria d'Educació, Formació i Ocupació (Generalitat Valenciana) for the Programa VALi+D Postdoctoral Fellowship. C2011-UMINHO-2C2T-01 FCT funding from Programa Compromisso para a Ciência 2008, Portugal. XPS studies were performed at CEMUP (University of Porto, Portugal) facilities. Electron Microscopy Service of the UPV (Universitat Politècnica de València) is gratefully acknowledged for help with FESEM and EDX characterization

Characterization of azo dyes on Pt and Pt/polyaniline/dispersed Pt electrodes

The electrochemical characterization of two organic dyes (amaranth and procion orange MX-2R) has been performed on Pt electrodes and Pt electrodes coated with polyaniline and dispersed Pt. Electrodes with different Pt loads have been synthesized and characterized obtaining that a load of 300 ¿g cm -2 was the optimum one. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) was employed to observe the distribution and morphology of the Pt nanoparticles. The electroactivity of the electrodes has also been characterized by means of scanning electrochemical microscopy (SECM). The chemical characterization of Pt dispersed Pani coated Pt electrodes (Pt-Pani-Pt) was performed by means of X-ray photoelectron spectroscopy (XPS). The electrochemical characterization of the dyes has been performed by means of cyclic voltammetry. Voltammograms have shown that the presence of the dyes diminishes characteristic Pt oxidation and reduction peaks. However, redox processes due to the dyes, appeared in the voltammograms. The different species responsible of these redox processes were generated in the vicinity of the electrode and were not adsorbed on the electrode surface since after stirring, the different redox processes disappeared. Characterization with different scan rates showed that redox processes of both dyes were controlled by diffusion. © 2012 Elsevier B.V.Authors thank to the Spanish Ministerio de Ciencia e Innovacion and European Union Funds (FEDER) (contracts CTM2010-18842-C02-02 and CTM2011-23583) and Universitat Politecnica de Valencia (Vicerrectorado de Investigacion PAID-06-10 contract 003-233) for the financial support. J. Molina is grateful to the Conselleria d'Educacio (Generalitat Valenciana) for the FPI fellowship. A.I. del Rio is grateful to the Spanish Ministerio de Ciencia y Tecnologia for the FPI fellowship.Molina Puerto, J.; Fernández Sáez, J.; Del Río García, AI.; Bonastre Cano, JA.; Cases Iborra, FJ. (2012). Characterization of azo dyes on Pt and Pt/polyaniline/dispersed Pt electrodes. Applied Surface Science. 258:6246-6256. doi:10.1016/j.apsusc.2012.02.150S6246625625

Determination of Specific Electrocatalytic Sites in the Oxidation of Small Molecules on Crystalline Metal Surfaces

The identification of active sites in electrocatalytic reactions is part of the elucidation of mechanisms of catalyzed reactions on solid surfaces. However, this is not an easy task, even for apparently simple reactions, as we sometimes think the oxidation of adsorbed CO is. For surfaces consisting of non-equivalent sites, the recognition of specific active sites must consider the influence that facets, as is the steps/defect on the surface of the catalyst, cause in its neighbors; one has to consider the electrochemical environment under which the “active sites” lie on the surface, meaning that defects/steps on the surface do not partake in chemistry by themselves. In this paper, we outline the recent efforts in understanding the close relationships between site-specific and the overall rate and/or selectivity of electrocatalytic reactions. We analyze hydrogen adsorption/desorption, and electro-oxidation of CO, methanol, and ammonia. The classical topic of asymmetric electrocatalysis on kinked surfaces is also addressed for glucose electro-oxidation. The article takes into account selected existing data combined with our original works.M.J.S.F. is grateful to PNPD/CAPES (Brazil). J.M.F. thanks the MCINN (FEDER, Spain) project-CTQ-2016-76221-P

Synthesis of Pt nanoparticles on electrochemically reduced graphene oxide by potentiostatic and alternate current methods

Reduced graphene oxide (RGO) has been synthesized on Pt wires by means of a potentiodynamic method between +0.6 V and -1.4'V for 20 scans. Cyclic voltammetry characterization of the coatings showed the typical capacitative behavior of graphene. Pt nanoparticles were synthesized on Pt-RGO electrodes by means of potentiostatic methods and a comparison between different synthesis potentials (-0.16, 0, +0.2 and +0.4 V) for the same synthesis charge (mC.cm(-2)) was established. The electrodes obtained were characterized in 0.5 M H2SO4 solution to observe the characteristic oxidation and reduction processes of the Pt surface. A 0.5 M H2SO4/0.5 M CH3OH solution was used to measure the catalytic properties of the deposits against methanol oxidation. The most appropriate potential to perform the synthesis was 0 V followed by -0.16 V and +0.2 V. The morphology of the coatings varied depending on the potential applied as observed by scanning electron microscopy. Alternate current methods were also used to synthesize Pt nanoparticles and compare the results with the traditional potentiostatic method. Different frequencies were used: 0.1, 1, 10, 100, 1000 and 10000 Hz. Alternate current synthesis is more efficient than traditional potentiostatic methods, obtaining more electroactive coatings with less effective synthesis time. (C) 2014 Elsevier Inc. All rights reserved.Authors wish to thank to the Spanish Ministerio de Ciencia e Innovacion (contract CTM2011-23583) and Universitat Politecnica de Valencia (Vicerrectorado de Investigacion PAID-06-10 contract 003-233) for the financial support. J. Molina is grateful to the Conselleria d'Educacio, Formacio i Ocupacio (Generalitat Valenciana) for the Programa VALi+D Postdoctoral Fellowship. A.I. del Rio is grateful to the Spanish Ministerio de Ciencia y Tecnologia for the FPI fellowship.Molina Puerto, J.; Fernández Sáez, J.; Del Río García, AI.; Bonastre Cano, JA.; Cases Iborra, FJ. (2014). Synthesis of Pt nanoparticles on electrochemically reduced graphene oxide by potentiostatic and alternate current methods. Materials Characterization. 89:56-68. https://doi.org/10.1016/j.matchar.2014.01.003S56688