Study of the Formic Acid Electrooxidation on Rhodium on Steady State Using a Flow Cell: Potential Dependence of the CO C
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ORIGINAL RESEARCH
Study of the Formic Acid Electrooxidation on Rhodium on Steady State Using a Flow Cell: Potential Dependence of the CO Coverage Gisela C. Luque 1 & María A. Montero 1 & María R. Gennero de Chialvo 1
&
Abel C. Chialvo 1
# Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The HCOOH electrooxidation reaction (FAO) was experimentally studied on rhodium electrode using a flow cell in a 0.5-M HCOOH + 0.5-M H2SO4 solution. It was obtained the steady-state current-potential curve by chronoamperometry, which demonstrated that the FAO is verified in the potential region 0.45 < E/V < 0.70. The amount of adsorbed CO on the electrode surface as a function of potential was quantified by stripping voltammetry after changing to a 0.50-M H2SO4 solution at closed electric circuit. It was established that the spontaneous dissociative adsorption of HCOOH on rhodium produces irreversibly adsorbed CO only for potential values E ≤ 0.40 V, and therefore, the FAO takes place in the absence of COad. These results can explain the current-potential profiles obtained when the FAO is studied by cyclic voltammetry at different values of the potential scan limits, where the behaviour is strongly influenced by the inhibition of reaction sites due to the adsorbed CO. A kinetic mechanism for the FAO on rhodium is proposed on the basis of the results obtained, which are also in agreement with recently published spectroscopic measurements. Keywords Formic acid electrooxidation . Rhodium electrode . COad inhibition . Kinetic mechanism
Introduction The formic acid electrooxidation (FAO) reaction has been intensively studied on noble metals due to its potential use as the anodic reaction in the low temperature fuel cells [1–24]. These studies were carried by cyclic voltammetry, sometimes complemented by spectroscopic techniques, being focused on the understanding of the kinetics and mechanism, with emphasis in the role played by the adsorbed intermediates. In the particular case of the adsorbed carbon monoxide
* Abel C. Chialvo [email protected] Gisela C. Luque [email protected] María A. Montero [email protected] María R. Gennero de Chialvo [email protected] 1
Instituto de Química Aplicada del Litoral, IQAL (UNL-CONICET), Programa de Electroquímica Aplicada e Ingeniería Electroquímica, PRELINE (FIQ-UNL), 2829 Santiago del Estero, Santa Fe, Argentina
(COad), many authors consider that it is a FAO reaction intermediate on noble metals, with a kinetics described through the Langmuir-Hinshelwood mechanism, while in other works, COad is taken as an inhibitor of active sites [24]. On the other hand, the use of cyclic voltammetry for the study of this reaction clearly shows an important hysteresis in the dependencies on potential of current and of the surface coverage of the reaction intermediates. This is related to the dynamic variation of the surface concentration of the adsorbed intermediate species produced during the HCOOH electrooxidation, which hinders the interpretation of the resul
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