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

Thermodynamic studies of anion adsorption at the Pt(111) electrode surface from glycolic acid solutions

Kinetic glycolic acid (GA) oxidation and thermodynamic glycolate adsorption have been studied on Pt single crystal electrodes. The voltammetric profiles of Pt(111), Pt(100), and Pt(110) in 0.1 M GA are shown, and the effect of the inclusion of steps on the Pt(111) surface has been studied by cyclic voltammetry. For Pt(111) electrode, different concentrations and sweep rates have been applied, revealing that both adsorption and oxidation processes take place. By establishing the appropriate conditions, a complete thermodynamic analysis has been performed by using the electrode potential and the charge as independent variables. Total charge density curves, surface pressure at total charge density and at constant electrode potential were determined to calculate the Gibbs excess and the charge number at constant electrode potential for glycolate adsorption on Pt(111). Maximum glycolate coverage on the surface reaches a value of ∼6.0 × 1014 ions/cm2. Spectroscopic results show the formation of CO2 during the oxidation of glycolic acid, indicating that the cleavage of the C–C bond occurs during the oxidation process.The work was carried out under the financial support by the MINECO (Spain) (project CTQ2013-44083-P) and Generalitat Valenciana (project PROMETEOII/2014/013)

The breaking of the C-C bond in ethylene glycol oxidation at the Pt(111) electrode and its vicinal surfaces

Ethylene glycol (EG) oxidation has been studied on Pt(111) and its vicinal surfaces in acidic media by cyclic voltammetry and infrared spectroscopy. Even at Pt(111) the C-C bond is readily broken and CO is formed at low potentials. Both types of steps catalyze the EG oxidation to CO2, being the {110} steps the most catalytic for the splitting of the C-C bond. Spectroscopic results show that glycolic acid and oxalic acid are produced mainly at the close-packed terraces.Financial support by MICINN (project No. CTQ2010-16271)

Weakening the C – C bond: On the behavior of glyoxylic acid on Pt(111) and its vicinal surfaces

Adsorption and oxidation of glyoxylic acid (GA) on platinum single crystals were investigated by spectroelectrochemical techniques. Among basal planes, Pt(111) is taken as a model surface for reactivity studies in order to point out the Csingle bondC bond breaking. For a standard GA concentration (0.1 M), self-poisoning by adsorbed CO (COads) is the main process dominating the positive-going sweep. The presence of (110) steps on (111) terraces contribute in the Csingle bondC bond cleavage, leading to CO formation, while (100) steps do not show a significant effect. Poison stripping allows GA oxidation in a lower potential range in the negative-going sweep. By working with different GA concentrations (10− 5–0.1 M), surface blockage is hindered, pointing out an alternative reaction pathway, where GA is oxidized in a poison-free surface. Fourier transform infrared spectroscopy (FTIR) experiments allowed the identification of CO2, formic (FA) and oxalic acid (OA) as main products of GA oxidation. We highlight an activity peak at 0.01 M GA, concomitant to the presence of CO2 absorption bands at lower potentials (0.2 V). The formation of CO2 at potentials where CO cannot be oxidized suggests a change in the preferential reaction pathway, where GA is completely oxidized through an active intermediate distinct to COads.This work was carried out under financial support of MICINN (project no. CTQ2013-44083-P). R.M.H. acknowledges support from Generalitat Valenciana under Santiago Grisolia Program (GRISOLIA/2013/008)

Understanding the electrochemical hydrogenation of acetone on Pt single crystal electrodes

The heterogeneous upgrading of biomass by means of electrocatalytic hydrogenation is an attractive way to refine products for industrial and pharmaceutical purposes. Also, the efficient electrochemical reduction of carbonyl compounds can act as hydrogen vectors, and therefore energy vectors. In this manuscript, we render further fundamental insights into the electrochemical reduction of acetone as a model molecule of carbonyl compounds. The structural sensitivity of the reaction is demonstrated by using platinum single crystal electrodes with low Miller indices and stepped electrodes with (110) terraces and either (111) or (100) monoatomic steps. Among the basal planes, Pt(110) is the only one active for the electroreduction of acetone. The inclusion of (111) steps on the (110) terraces does not significantly alter the behavior of Pt(110), but increasing the (100) step density has been observed to decrease the activity. We attribute this different performance to a geometrical effect of the active sites. By using different supporting electrolytes, we have found that sulfate competes with acetone for the surface sites, thus modifying the adlayer interfacial structure and hampering acetone reactivity.This research was funded by Ministerio de Ciencia e Innovación (Spain) grant number PID2019-105653GB-I00), Generalitat Valenciana (Spain) grant number PROMETEO/2020/063. RMAA. acknowledges the financial support from Generalitat Valenciana (CDEIGENT/2019/018)

Evidence of Local pH Changes during Ethanol Oxidation at Pt Electrodes in Alkaline Media

Local changes of the interfacial pH can significantly affect the rate and mechanism during the course of an electrodic reaction. For instance, different pH values will have a significant effect on the equilibrium properties of both solution and surface species, altering the reactions kinetics. Ethanol oxidation at platinum electrodes in alkaline media involves the fast consumption of OH− species that will change the local pH at the electrode surface, decreasing the reaction rate. In this study, the local pH change during ethanol oxidation in alkaline media is accomplished by using rotating ring-disc electrode (RRDE) experiments. The current at the ring when polarized at the onset of hydrogen evolution serves as a measure of the local pH in the vicinity of the electrode. The results show that the current at the ring at 0.1 V (vs. RHE) becomes more negative during ethanol oxidation, owing to a change in the equilibrium potential of the hydrogen evolution reaction caused by a change in the local pH.Financial support from Aalto University, Academy of Finland, MINECO, and Generalitat Valenciana through projects CTQ2013–44083-P and PROMETEOII/2014/013 is acknowledged

Trimetallic catalyst based on PtRu modified by irreversible adsorption of Sb for direct ethanol fuel cells

In this work, PtRu/C–Sb materials prepared by adding a Sb salt to the ink of commercial PtRu/C were studied as catalysts for ethanol oxidation. The prepared trimetallic catalysts showed enhanced properties for ethanol oxidation through a wide range of surface coverages. However, coverage higher than 0.7 of Sb on PtRu/C causes the decrease of the catalytic activity suggesting that specific sites composed of 3 metals are necessary to achieve the highest performance. In situ Fourier Transform Infrared Spectroscopy experiments were also performed to compare the reaction products of the bimetallic and trimetallic catalysts. The catalysts were also tested under fuel cell conditions. Also in this case, higher power densities, higher open-circuit voltages and better stability than the bimetallic substrate were found. With this catalyst preparation method, the catalysts showed 2 times higher current densities than for the PtRu catalysts and 6 times better than for pure Pt anodes.The financial support from Aalto University is acknowledged. This work made use of the Aalto University Nanomicroscopy Center (Aalto-NMC) premises. J.M.F. and R.M.A.A. would like to thank MICINN through Project CTQ2013-44083-P

Nuevos materiales didácticos para descubrir los aspectos más cotidianos de la Electroquímica

A pesar del amplio abanico de aplicaciones que posee la electroquímica, con importantes repercusiones en muchos aspectos de la vida cotidiana, los egresados de química de las universidades españolas poseen en general un notable desconocimiento de esta materia. Con objeto de hacer más atractivo el aprendizaje de esta parte de la química, al tiempo que se revelan algunas de sus aplicaciones menos conocidas, se han preparado nuevos materiales didácticos. En ellos se describen de manera divulgativa algunas de las aplicaciones más importantes de la electroquímica, como son las baterías, síntesis de aluminio, o su uso en biosensores. Los nuevos materiales se han suministrado al alumnado del primer curso del grado de química de la Universidad de Alicante y se ha pedido su opinión a través de una encuesta. En general la recepción ha sido buena, aunque la respuesta de los estudiantes ha sido algo escasa. Para dar mayor difusión, se está creando una página web con estos mismos contenidos. Esta página web se ha puesto a disposición de los alumnos de la asignatura Electroquímica de 4º curso de la licenciatura (plan a extinguir) de Química y de nuevo se pedirá su opinión a través de un formulario web

On the quality and stability of preferentially oriented (100) Pt nanoparticles: An electrochemical insight

Previous knowledge shed by single crystal electrochemistry path the way to obtain better catalysts aiming fuel cell purposes. In this sense, tailoring shape-controlled nanoparticles has been a strategy followed over the past years to optimize the activity, selectivity and stability of electrocatalytic surface sensitive reactions by maximizing the exposure of certain facets of the nanocatalyst. In the present paper, preferentially oriented (100) nanoparticles synthesized by different methodologies have been electrochemically characterized and compared. The voltammetric profile of these cubic nanoparticles has also been compared with different platinum single crystal stepped surfaces, showing a singular fitting to the characteristic response of Pt(510). Subtle changes on the surface structure of platinum nanocubes due to surface degradation upon storage time in aqueous solution are pointed out in this work. The characteristic fingerprints of platinum surfaces and CO oxidation profiles have demonstrated to be powerful surface probes for the in situ detection of these minor structural reorganizations.This work has been supported by the Ministry of Economy and Competitiveness (MINECO) through the project CTQ2016-76221-P and Generalitat Valenciana (project PROMETEO II/2014/013). J.S.G. acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante

The Surface Processes on Ru/Pt(111) as Probed by Cyclic Voltammetry and in Situ Surface-Enhanced Raman Spectroscopy

Information about the chemical adsorption and surface oxidation of Ru under electrochemical conditions is of great importance for understanding the structure–activity relationship in Ru-based materials. Quasi-single-crystalline Ru films on single-crystal Pt(111) electrodes (Ru/Pt(111)) were prepared by the forced-deposition method along with inductive heating treatment. The adsorption of both hydrogen and oxygen species on Ru/Pt(111) was studied by cyclic voltammetry and CO displacement. The potential of zero total charge on Ru/Pt(111) is ca. 0.12 V. A detailed study on oxygen species was carried out by in situ surface-enhanced Raman spectrometry. Ru–O was found to form at E > 0.1 V, and the conversion of Ru–O into RuO2 occurred at E = 0.3 V. The reversible oxidation occurs up to 1.0 V. Our results suggest that Ru/Pt(111), which exhibits electrochemical properties similar to those of Ru(0001), may serve as an alternative for Ru study as well as a model system for understanding ligand and strain effects.We gratefully acknowledge the funding by the China Scholarship Council (CSC), the National Natural Science Foundation of China (nos. 22172151 and 21972131), the Ministerio de Ciencia e Innovación (Spain) grant nos. PID2019-105653GB-I00 and FJC2018-038607-I, and Generalitat Valenciana (Spain) grant number PROMETEO/2020/063