Mechanistic Study of Electrocatalytic Oxidation of Formic Acid at Platinum in Acidic Solution by Time-Resolved Surface-Enhanced Infrared Absorption Spectroscopy

Abstract

Surface-enhanced infrared absorption spectroscopy (SEIRAS) combined with cyclic voltammetry or chronoamperometry has been utilized to examine kinetic and mechanistic aspects of the electrocatalytic oxidation of formic acid on a polycrystalline Pt surface at the molecular scale. Formate is adsorbed on the electrode in a bridge configuration in parallel to the adsorption of linear and bridge CO produced by dehydration of formic acid. A solution-exchange experiment using isotope-labeled formic acids (H(12)COOH and H(13)COOH) reveals that formic acid is oxidized to CO(2) via adsorbed formate and the decomposition (oxidation) of formate to CO(2) is the rate-determining step of the reaction. The adsorption/oxidation of CO and the oxidation/reduction of the electrode surface strongly affect the formic acid oxidation by blocking active sites for formate adsorption and also by retarding the decomposition of adsorbed formate. The interplay of the involved processes also affects the kinetics and complicates the cyclic voltammograms of formic acid oxidation. The complex voltammetric behavior is comprehensively explained at the molecular scale by taking all these effects into account.

Fundamental aspects of HCOOH oxidation at platinum single crystal surfaces with basal orientations and modified by irreversibly adsorbed adatoms

“…The role of formate in the oxidation mechanism of formic acid has be the subject of a strong debate [3][4][5]. In order to shed some light to the problem, fast scan experiments for formic acid oxidation in perchloric acid solutions were carried out.…”

“…This pathway was introduced by Capon and Parsons in 1973 [1] and later confirmed by DEMS [2]. The scheme of this mechanism is the following: Regarding the nature of the active intermediate, the question is not yet fully resolved [3][4][5]. It has been proposed that the active intermediate is adsorbed formate, but other experiments seem to contradict that observation [6][7][8][9][10].…”

Formic Acid Electrooxidation on Noble‐Metal Electrodes: Role and Mechanistic Implications of pH, Surface Structure, and Anion Adsorption

“…Nonetheless, the nature of the reactive intermediate for the direct pathway is still strongly debated in the literature, especially since adsorbed formate (HCOOads) has been detected by Osawa's group employing in situ Infrared (IR) spectro-electrochemistry [2] . This latter species has been proposed as candidate for the reactive intermediate species in numerous contributions [3][4][5][6][7][8] , while, oppositely, it has been considered as a site-blocking spectator species in other ones [9][10][11][12] . It should be noted that the conclusions were based on essentially equivalent experimental observations.…”

Oxidation Mechanism of Formic Acid on the Bismuth Adatom-Modified Pt(111) Surface

“…[8][9][10][11][12][13] Electrocatalytic reactions rates depend on the surface structure of the electrodes. So, Pt(111) electrodes exhibit low activity through the active intermediate and negligible CO formation, whereas Pt(100) surfaces show the highest activity for both routes.…”