On the activation energy of the formic acid oxidation reaction on platinum electrodes

A temperature dependent study on the formic acid oxidation reaction has been carried out in order to determine the activation energy of this reaction on different platinum single crystal electrodes, namely Pt(1 0 0), Pt(1 1 1), Pt(5 5 4) and Pt(5 4 4) surfaces. The chronoamperometric transients obtained with pulsed voltammetry have been analyzed to determine the current densities through the active intermediate and the CO formation rate. From the temperature dependency of those parameters, the activation energy for the direct reaction and the CO formation step have been calculated. For the active intermediate path, the activation energy are in the range of 50–60 kJ/mol. On the other hand, a large dependence on the electrode potential is found for the activation energy of the CO formation reaction on the Pt(1 0 0) electrode, and the activation energy values for this process range between 20 and 100 kJ/mol. These results have been explained using a reaction mechanism in which the oxidation of formic acid requires the presence of a pre-adsorbed anion on the electrode surface

Effects of the anion adsorption and pH on the formic acid oxidation reaction on Pt(111) electrodes

The effects of solution pH and anion adsorption for the formic acid oxidation reaction on the Pt(111) electrode have been examined using electrochemical techniques. Regarding the pH effects, it has been found that oxidation currents for this reaction increase with pH, which indicates that solution formate is involved in the reaction mechanism. Unexpectedly, the adsorption of sulfate on the Pt(111) electrode has a positive effect on the oxidation of formic acid, which also suggests that adsorbed anions are also involved in the mechanism. The activation energy calculated from temperature dependent measurements diminishes with the solution pH and also in the presence of adsorbed sulfate. These measurements corroborate the involvement of solution formate and anions in the oxidation mechanism. Using these results, a rate equation for the oxidation of formic acid is proposed. The current values calculated from this equation are in very good agreement with the experimental currents in perchloric acid solutions.This work has been financially supported by the MICINN (Spain)(project CTQ2010-16271) and Generalitat Valenciana (project PROMETEO/2009/045, FEDER)

The role of formic acid/formate equilibria in the oxidation of formic acid on Pt(111)

[EN] The formic acid oxidation reaction has been studied in concentrated perchloric acid solutions (up to 9.14M (60%)) on the Pt (111) surface to explore the relationships between interfacial properties and kinetics. It is found that, as the concentration of perchloric acid in the supporting electrolyte increases, the current markedly decreases, making it possible to detect adsorbed formate on the surface by voltammetric methods. With the aid of DFT calculations, it is shown that the diminution in current is the result of two opposing factors: the reduction in the concentration of free formate in solution and electrode charge effects which encourage the adsorption of formate in a particular configuration. Additionally, the electrochemical behavior under highly acidic conditions suggests the formation of clathrate structures and emphasizes the relevance of the water structure effect in electrode adsorption processes.This work has been financially supported by the Ministerio de Economia, Industria y Competitividad through the project CTQ2016-76221-P. CBR also thanks his Postdoctoral fellowship to Generalitat Valenciana (APOSTD/2017/010).Busó-Rogero, C.; Ferre-Vilaplana, A.; Herrero, E.; Feliu, JM. (2019). The role of formic acid/formate equilibria in the oxidation of formic acid on Pt(111). Electrochemistry Communications. 98:10-14. https://doi.org/10.1016/j.elecom.2018.11.011S10149

Understanding the Effect of the Adatoms in the Formic Acid Oxidation Mechanism on Pt(111) Electrodes

The engineered search for new catalysts requires a deep knowledge about reaction mechanisms. Here, with the support of a combination of computational and experimental results, the oxidation mechanism of formic acid on Pt(111) electrodes modified by adatoms of the p block is elucidated for the first time. DFT calculations reveal that some adatoms, such as Bi and Pb, have positive partial charge when they are adsorbed on the bare surface, whereas others, such as Se and S, remain virtually neutral. When the partial charge is correlated with previously reported experimental results for the formic acid oxidation reaction, it is found that the partial positive charge is directly related to the increase in catalytic activity of the modified surface. Further, it is obtained that such a positive partial charge is directly proportional to the electronegativity difference between the adatom and Pt. Thus, the electronegativity difference can be used as an effective descriptor for the expected electrocatalytic activity. This partial positive charge on the adatom drives the formic acid oxidation reaction, since it favors the formation and adsorption of formate on the adatom. Once adsorbed, the neighboring platinum atoms assist in the C–H bond cleavage. Finally, it is found that most of the steps involved in the proposed oxidation mechanism are barrierless, which implies a significant diminution of the activation barriers in comparison to that of the unmodified Pt(111) electrode. This diminution in the activation barrier has been experimentally corroborated for the Bi–Pt(111) electrode, supporting the proposed mechanism.This work has been financially supported by the MINECO (Spain) (project CTQ2013-44083-P) and Generalitat Valenciana (project PROMETEOII/2014/013)

Enhanced catalytic activity and stability for the electrooxidation of formic acid on lead modified shape controlled platinum nanoparticles

High catalytic activity for formic acid oxidation reaction (FAOR) is demonstrated in Pb modified shape-controlled Pt nanoparticles (NPs). Cyclic voltammetry is used to follow the effective modification of Pt NPs by Pb. Octahedral shaped Pt NPs (having a (111) preferential surface structure) modified by Pb are proved the most active electrocatalyst studied towards FAOR and display a catalytic activity of c.a. 7 mA cm−2 at 0.5 V in 0.1 M formic acid solution. This current density represents an enhancement factor of 29.5 with respect to the unmodified Pt NPs and this is 2.7 and 2.3 times higher than that found on Tlθ/100-Pt NPs and Sbθ/111-Pt NPs, respectively, some of the most active electrocatalysts based on adatoms modified Pt NPs reported so far. This outstanding activity is displayed at maximum Pb coverage and also confers a wide electrocatalyst stability over the entire potential range studied. FAOR is also studied using scanning electrochemical microscopy (SECM) by the micropipette delivery/substrate collection (MD/SC) working mode as a preliminary rapid test to identify active electrocatalysts. In particular, the remarkable activity enhancement exhibited by a Pt ultramicroelectrode (100 μm diameter) modified by Pb is rapidly imaged by SECM providing preliminary catalyst performance information. Thus, this technique emerges as a suitable and fast method to test, and in some cases quantify, catalyst activity for reactions of interest in fuel cell applications.This work has been financially supported by the MICINN (Spain)(projects CTQ2013-44083-P and CTQ2013-48280-C3-3-R), Generalitat Valenciana (project PROMETEOII/2014/013, FEDER) and CNRS (project Défi Instrumentation aux limites 2015)

Formic acid electrooxidation on thallium-decorated shape-controlled platinum nanoparticles: an improvement in electrocatalytic activity

Thallium modified shape-controlled Pt nanoparticles were prepared and their electrocatalytic activity towards formic acid electrooxidation was evaluated in 0.5 M sulfuric acid. The electrochemical and in situ FTIR spectroscopic results show a remarkable improvement in the electrocatalytic activity, especially in the low potential region (around 0.1–0.2 V vs. RHE). Cubic Pt nanoparticles modified with Tl were found to be more active than the octahedral Pt ones in the entire range of Tl coverages and potential windows. In situ FTIR spectra indicate that the promotional effect produced by Tl results in the inhibition of the poisoning step leading to COads, thus improving the onset potential for the complete formic acid oxidation to CO2. Chronoamperometric experiments were also performed at 0.2 V to evaluate the stability of the electrocatalysts at constant potential. Finally, experiments with different concentrations of formic acid (0.05–1 M) were also carried out. In all cases, Tl-modified cubic Pt nanoparticles result to be the most active. All these facts reinforce the importance of controlling the surface structure of the electrocatalysts to optimize their electrocatalytic properties.This work has been financially supported by the MICINN (Spain) (project CTQ2010-16271) and Generalitat Valenciana (project PROMETEO/2009/045 – FEDER)

Oxygen crossover effect on palladium and platinum based electrocatalysts during formic acid oxidation studied by scanning electrochemical microscopy

The electrocatalytic activity towards formic acid oxidation reaction (FAOR) in the presence of simultaneous oxygen reduction reaction (ORR) displayed by 5 different metallic nanoparticles (NPs) (Pt100, Pt75Pd25, Pt50Pd50, Pt25Pd75 and Pd100) was studied and compared using chronoamperometry and the micropipette delivery/substrate collection (MD/SC) mode of the scanning electrochemical microscopy (SECM). This is of special interest for understanding the O2 crossover effect in direct formic acid fuel cells (DFAFCs) and to search highly selective electrocatalysts useful in mixed-reactant fuel cells (MRFCs). A detailed analysis of the SECM results in comparison with chronoamperometry demonstrates, for the first time, the relevant role played by dissolved O2 in solution on the Pd100 NPs deactivation during FAOR, which cannot be explained neither by the specific adsorption of dichloroethane (DCE) on Pd nor by a simple addition of two opposed currents coming from simultaneous FAOR and ORR. Two main mechanistic factors are proposed for explaining the different sensitivity towards O2 presence in solution during FAOR when comparing Pd- and Pt-rich catalysts. On the one hand, the relevance of H2O2 production (ORR byproduct) and accumulation on Pd NPs, which alters its performance towards FAOR. On the other hand, the predominance of the poisoning pathway forming COads during FAOR on Pt NPs, whose oxidation is facilitated in the presence of traces of O2. Interestingly, the deactivation effect displayed on Pd100 NPs during FAOR due to the H2O2 generation and accumulation becomes negligible if a convective regime is applied in solution. SECM is proved as a fast and powerful technique for studying O2 crossover effect in different electrocatalysts and for identifying highly selective electrocatalysts candidates for MRFCs. In particular, among the samples evaluated, Pt75Pd25 NPs present the highest average performance for FAOR in 0.5 M H2SO4 solution in the presence of O2 within the potential range under study (0.3–0.7 V vs RHE).This work was financially supported by CNRS (projet ImaECell, Défi Instrumentation aux limites 2015), MINECO (projects CTQ2013-44083-P and CTQ2013-48280-C3-3-R) and Generalitat Valenciana (project PROMETEOII/2014/013). J. Solla-Gullón acknowledges financial support from VITC (Vicerrectorado de Investigación y Transferencia de Conocimiento) of the University of Alicante

Formic acid electrooxidation on thallium modified platinum single crystal electrodes

Formic acid electrooxidation on Tl modified Pt single crystal electrodes has been carried out in sulfuric acid media. Voltammetric experiments demonstrated that Pt(100) modified by Tl displays a significant enhancement towards formic acid oxidation both lowering the oxidation onset potential and increasing the maximum current density in the positive going-sweep. A similar behavior has been observed in Pt(s)[(100)x(111)] stepped surfaces. On the other hand, for Pt(111) surfaces, the incorporation of Tl also induced a shift of the oxidation onset to lower potential values, a diminution of the hysteresis between the positive and negative going-sweep and also an increase of the oxidation currents. These results have been corroborated using in situ FTIR experiments, where the CO adsorption band disappears completely when Pt(100) and its vicinal surfaces are modified by Tl adatom, leading to the formation of CO2 at lower overvoltages.This work has been financially supported by the MINECO (Spain) (projects CTQ2013-44083-P and CTQ2013-48280-C3-3-R) and Generalitat Valenciana (project PROMETEOII/2014/013, FEDER)

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

Clonal chromosomal mosaicism and loss of chromosome Y in elderly men increase vulnerability for SARS-CoV-2

The pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, COVID-19) had an estimated overall case fatality ratio of 1.38% (pre-vaccination), being 53% higher in males and increasing exponentially with age. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, we found 133 cases (1.42%) with detectable clonal mosaicism for chromosome alterations (mCA) and 226 males (5.08%) with acquired loss of chromosome Y (LOY). Individuals with clonal mosaic events (mCA and/or LOY) showed a 54% increase in the risk of COVID-19 lethality. LOY is associated with transcriptomic biomarkers of immune dysfunction, pro-coagulation activity and cardiovascular risk. Interferon-induced genes involved in the initial immune response to SARS-CoV-2 are also down-regulated in LOY. Thus, mCA and LOY underlie at least part of the sex-biased severity and mortality of COVID-19 in aging patients. Given its potential therapeutic and prognostic relevance, evaluation of clonal mosaicism should be implemented as biomarker of COVID-19 severity in elderly people. Among 9578 individuals diagnosed with COVID-19 in the SCOURGE study, individuals with clonal mosaic events (clonal mosaicism for chromosome alterations and/or loss of chromosome Y) showed an increased risk of COVID-19 lethality