Oxygen reduction reaction on stepped platinum surfaces in alkaline media

The oxygen reduction reaction (ORR) in 0.1 M NaOH on platinum single crystal electrodes has been studied using hanging meniscus rotating disk electrode configuration. Basal planes and stepped surfaces with (111) and (100) terraces have been employed. The results indicate that the Pt(111) electrode has the highest electrocatalytic activity among all the studied surfaces. The addition of steps on this electrode surface significantly diminishes the reactivity of the surface towards the ORR. In fact, the reactivity of the steps on the surfaces with wide terraces can be considered negligible with respect to that measured for the terrace. On the other hand, Pt(100) and Pt(110) electrodes have much lower activity than the Pt(111) electrode. These results have been compared with those obtained in acid media to understand the effect of the pH and the adsorbed OH on the mechanism. It is proposed that the surface covered by adsorbed OH is active for the reduction of the oxygen molecules.This work has been financially supported by the MICINN (Spain) (project CTQ2010-16271-FEDER) and Generalitat Valenciana (project PROMETEO/2009/045, -FEDER)

New insights into the hydrogen peroxide reduction reaction and its comparison with the oxygen reduction reaction in alkaline media on well-defined platinum surfaces

The hydrogen peroxide reduction reaction (HPRR) is investigated at pH = 13 on the Pt basal planes and stepped surfaces with (1 1 1) terraces separated by either monatomic (1 0 0) or (1 1 0) steps. A quantitative analysis of the surface structure effect revealed that Pt(1 1 1) is the most active surface and its activity progressively decreases when steps are introduced. Additionally, inhibition of the HPRR is observed at low potentials, which onset potential is governed by the OHads and the point of maximum entropy (pme) of the interphase. Experiments with different rotation rates suggest the formation of an HPRR intermediate linked to the inhibition process, which is more strongly adsorbed on (1 1 0) than (1 0 0) steps. Finally, a comparison of the HPRR and ORR (oxygen reduction reaction) illustrated the important differences for both reactions, which are dependent on the step density. These divergences have been discussed based on adsorbed intermediates and O2 interactions with the Pt surface.Financial support from Ministerio de Ciencia e Innovación (Project PID2019-105653 GB-100) and Generalitat Valenciana (Project PROMETEO/2020/063) is acknowledged

On the oxidation mechanism of C1-C2 organic molecules on platinum. A comparative analysis

The rational design of better electrocatalysts for the oxidation of C1–C2 organic molecules requires the detailed knowledge of their oxidation mechanism. Pt single crystals are powerful tools to study, in a simple way, the surface structure effect on the different reaction pathways. Here, the oxidation mechanism of these molecules is compared so that the knowledge gained with the simpler mechanism is transferred in the analysis of the more complex ones. The goal is to design strategies so that the platinum electrodes improve their performance in their oxidation by the appropriate modification with other elements by attacking the bottlenecks in the reaction mechanism.Financial support from Ministerio de Ciencia e Innovación (Project no. PID2019-105653GB-100 and FJC2018-038607-I) and Generalitat Valenciana (Projects PROMETEO/2020/063 and CDEIGENT/2019/018) is acknowledged

Catalizadores de Pt-Sn para la reacción de oxidación de etanol

En los últimos años se ha incrementado el interés por el desarrollo de nuevos sistemas energéticos, alternativos al uso de combustibles fósiles, solidarios con el medio ambiente y sostenibles. Un ejemplo de este tipo de tecnologías son las pilas de combustible de etanol directo (DEFC), las cuales permiten la obtención de energía a partir de la oxidación electroquímica del etanol y cuya principal limitación radica en la búsqueda de catalizadores con una relación eficiencia catalítica/precio elevada. En este contexto, los catalizadores de Pt-Sn se han posicionado como firmes candidatos para la oxidación de etanol de forma eficiente. Sin embargo, para un desarrollo óptimo que los haga competentes en el mercado, es imprescindible una investigación y desarrollo más exhaustivo de los mismos. De esta forma, el objetivo principal de esta Tesis Doctoral se centra en el estudio fundamental de la influencia de la estructura superficial de los catalizadores de Pt-Sn en el mecanismo para la reacción de oxidación de etanol (ROE) y la oxidación de monóxido de carbono adsorbido (principal veneno catalítico durante la ROE), junto a la síntesis y caracterización de nanopartículas de Pt-Sn soportadas sobre carbón, altamente eficientes para la ROE.In the last few years, the interest in developing new and more environmentally friendly energy systems as an alternative to the use of fossil fuels has drastically increased. Direct ethanol fuel cells (DEFCs) represent a clear example, since these cells can provide energy from the electrochemical oxidation of an abundant material as ethanol. The main problem lies on finding a catalyst with a high catalytic efficiency/cost ratio. In this sense, Pt-Sn catalysts have been positioned as strong candidates for the efficient oxidation of ethanol. However, for an optimum development in order to make them commercially competitive, an exhaustive research about the behavior of these catalysts for the oxidation of ethanol is necessary. In this sense, the objective of this Doctoral Thesis is the fundamental study of the influence of Pt-Sn catalysts surface structure on the ethanol (EOR) and adsorbed carbon monoxide (main catalytic poison during the EOR) oxidation reactions, as well as the synthesis and characterization of highly efficient Pt-Sn nanoparticles supported on carbonaceous materials. Well-defined Pt single crystals (Pt (111), Pt (100) and Pt (110)) decorated with Sn adatoms were employed to investigate the influence of the surface catalyst structure on the reactions previously mentioned. The use of Sn modified Pt single crystals allowed to demonstrate, not only the high dependence of the EOR and the adsorbed carbon monoxide oxidation reaction mechanisms on the surface catalyst structure, but also the improvement in the electrocatalytic activity by adding Sn adatoms. The geometry of the adsorption of Sn adatoms on Pt depending on Pt surface structure, as well as the difference in the electroactivity of the catalyst with Sn coverage, were also studied by using these electrodes. The optimum Sn coverage (value that exhibits the highest activity for EOR) was established. Differences in the mechanism toward the EOR and the influence of surface adatoms on the mechanism itself were elucidated applying differential electrochemical mass spectrometry (DEMS). Although the role of Pt surface structure in the electrocatalytic activity of Pt-Sn catalysts toward EOR was investigated by the use of well-defined Pt single crystals, from a practical point of view, the use and commercialization of this type of electrodes is totally unrealistic, since catalysts with high catalytic efficiency but an appropriate cost are preferred. To fulfill this problem, the synthesis of nanocrystals with small sizes, to obtain large specific areas, has received substantial research interest over the past decades. In this sense, during this Doctoral Thesis, Pt-Sn nanoparticles supported on different carbon materials were synthesized by the formic acid reduction method (FAM). A series of techniques were employed for the physicochemical characterization of the synthesized catalysts in order to determine the crystallite size and the lattice parameter, to check the correct dispersion of the particles on the carbon support, as well as to elucidate the total and the surface catalyst composition. Different Pt-Sn atomic ratios and carbon supports were employed with the purpose of studying the influence of both, the nature of the support and the amount of Sn on the catalyst, for the adsorbed carbon monoxide oxidation reaction and the EOR. Conventional electrochemical techniques, such as cyclic voltammetry and chronoamperometry, were used to analyze the electrocatalytic activity of the synthesized materials. On the other hand, spectroclectrochemical in situ techniques were applied in order to establish the changes in the mechanism promoted by the employment of different carbon supports and Pt-Sn atomic ratios. Finally, the knowledge gained about the influence of the surface structure of the Pt-Sn electrodes on the activity toward the EOR and the Pt-Sn nanoparticles synthesis supported on carbon, was exploited to synthesize highly efficient shape-controlled Pt-Sn nanoparticles (cubic Pt-Sn nanoparticles)

On the nature of adsorbed species on Platinum Single Crystal electrodes

The dependence of voltammetric currents on multiple parameters (concentration, pH, temperature, etc) has become a primary source of information in interfacial studies of noble metal electrodes. Peak potential, charge, and width are intimately related to surface structure and reactivity. However, this interpretation usually neglects the complexity of the redox processes involved. For the so-called hydrogen adsorption region in platinum, anion competitive adsorption plays an important role that is usually overlooked. While charge displacement already demonstrated decades ago the existence of anion adsorption contributions, only recently a combination of several surface-sensitive techniques has proven unambiguously the presence of OH adsorbed on step site at potentials much lower than usually considered. This information must not be neglected when analysing the properties of complex catalysts such as those composed of nanoparticles since it is of great importance for understanding its overall reactivity, for comparing with computational results, and for performing coulometric analysis.This research was funded by Ministerio de Ciencia e Innovación (Spain) grant number PID2019-105653GB-I00) and Generalitat Valenciana (Spain) grant number PROMETEO/2020/063

Ethanol Electro-oxidation Reaction Selectivity on Platinum in Aqueous Media

Ethanol fuel cells require selective catalysts for complete oxidation of the fuel, which involves C–C bond cleavage. From experiments on well-defined surfaces and calculations, the mechanism controlling the ethanol electro-oxidation selectivity on platinum in aqueous media as a model system is elucidated. Adsorbed OH favors ethanol adsorption and conversion into adsorbed ethoxy, which favorably evolves to adsorbed COCH3. On Pt(111), adsorbed OH is also readily incorporated into adsorbed COCH3 to yield acetic acid. A higher barrier for this latter step on Pt(100) enables the COCH3 dehydrogenation to adsorbed COCH2, favoring C–C bond cleavage. As adsorbed OH plays an essential role as a reactant in this process, its adsorption properties have a decisive impact on this reaction. Furthermore, the adsorbed OH diffusion rate on the surface, which depends on the adsorbate/media/surface interaction at the interface, modulates the availability of this key reactant. These results highlight that the search for selective electrocatalysts requires holistic consideration of reactants, adsorbates, media, and substrate.This research was funded by Ministerio de Ciencia e Innovación (Spain) grant nos. PID2019-105653GB-I00 and FJC2018-038607-I and Generalitat Valenciana (Spain) grant no. PROMETEO/2020/063

Spectroelectrochemical study of carbon monoxide and ethanol oxidation on Pt/C, PtSn(3:1)/C and PtSn(1:1)/C catalysts

PtSn-based catalysts are one of the most active materials toward that contribute ethanol oxidation reaction (EOR). In order to gain a better understanding of the Sn influence on the carbon monoxide (principal catalyst poison) and ethanol oxidation reactions in acidic media, a systematic spectroelectrochemical study was carried out. With this end, carbon-supported PtSnx (x = 0, 1/3 and 1) materials were synthesized and employed as anodic catalysts for both reactions. In situ Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS) indicate that Sn diminishes the amount of bridge bonded CO (COB) and greatly improves the CO tolerance of Pt-based catalysts. Regarding the effect of Sn loading on the EOR, it enhances the catalytic activity and decreases the onset potential. FTIRS and DEMS analysis indicate that the C-C bond scission occurs at low overpotentials and at the same potential values regardless of the Sn loading, although the amount of C-C bond breaking decreases with the rise of Sn in the catalytic material. Therefore, the elevated catalytic activity toward the EOR at PtSn-based electrodes is mainly associated with the improved CO tolerance and the incomplete oxidation of ethanol to form acetic acid and acetaldehyde species, causing the formation of a higher amount of both C2 products with the rise of Sn loading.This research was funded by Fundación Cajacanarias (project BIOGRAF) the Spanish Ministry of Economy and Competitiveness (MINECO) under projects CTQ2011-28913-C02 and ENE2014-52158-C02 (co-funded by FEDER). R.R. acknowledges the FPI program (MINECO) for financial support. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI

Towards the understanding of the interfacial pH scale at Pt(1 1 1) electrodes

The determination of the potentials of zero total and free charge, pztc and pzfc respectively, were made in a wide pH range by using the CO displacement method and the same calculation assumptions used previously for Pt(1 1 1) electrodes in contact with non-specifically adsorbing anions. Calculation of the pzfc involves, in occasions, long extrapolations that lead us to the introduction of the concept of potential of zero extrapolated charge (pzec). It was observed that the pztc changes with pH but the pzec is independent of this parameter. It was observed that the pztc > pzec at pH > 3.4 but the opposite is true for pH > 3.4. At the latter pH both pzec and pztc coincide. This defines two different pH regions and means that adsorbed hydrogen has to be corrected in the “acidic” solutions at the pztc while adsorbed OH is the species to be corrected in the “alkaline” range. The comparison of the overall picture suggests that neutral conditions at the interface are attained at significantly acidic solutions than those at the bulk.Support from MINECO (Spain) through project CTQ2013-44083-P is greatly acknowledged. E.S. also thanks CNPq (Brazil) for the scholarship (grant No. 200939/2012-2)

Plataforma web para la promoción y desarrollo de la innovación y el emprendimiento

En el presente artículo se presenta una recopilación del análisis y desarrollo de una plataforma web que permite la promoción y desarrollo de la innovación y emprendimiento desde el punto de vista académico y empresarial, siendo esta investigación al mismo tiempo una idea innovadora respaldada por la FAREM-Estelí, la cual cuenta con un Centro de Investigación para la Innovación y Emprendimiento (CIIEMP) en donde se aplicó el desarrollo de esta plataforma. Para un mejor desarrollo y optimización del sitio web se tomaron en cuenta aspectos y temas acerca de la innovación y emprendimiento para obtener un mayor conocimiento del trabajo que se estaba realizando, en el desarrollo del mismo se utilizó la metodología ágil SCRUM, tomándose aspectos importantes como: desarrollo de módulos esenciales al principio, entregas rápidas por etapas, reuniones con el grupo de desarrollo y con el cliente para cumplir con las expectativas planteadas en los requerimientos

Plataforma web para la promoción y desarrollo de la innovación y el emprendimiento

En el presente artículo se presenta una recopilación del análisis y desarrollo de una plataforma web que permite la promoción y desarrollo de la innovación y emprendimiento desde el punto de vista académico y empresarial, siendo esta investigación al mismo tiempo una idea innovadora respaldada por la FAREM-Estelí, la cual cuenta con un Centro de Investigación para la Innovación y Emprendimiento (CIIEMP) en donde se aplicó el desarrollo de esta plataforma. Para un mejor desarrollo y optimización del sitio web se tomaron en cuenta aspectos y temas acerca de la innovación y emprendimiento para obtener un mayor conocimiento del trabajo que se estaba realizando, en el desarrollo del mismo se utilizó la metodología ágil SCRUM, tomándose aspectos importantes como: desarrollo de módulos esenciales al principio, entregas rápidas por etapas, reuniones con el grupo de desarrollo y con el cliente para cumplir con las expectativas planteadas en los requerimientos