Intrinsic activity and poisoning rate for HCOOH oxidation on platinum stepped surfaces

Abstract

Pulsed voltammetry has been used to study formic acid oxidation on platinum stepped surfaces to determine the kinetics of the reaction and the role of the surface structure in the reactivity. From the current transients at different potentials, the intrinsic activity of the electrode through the active intermediate reaction path (j(theta = 0)), as well as the rate constant for the CO formation (k(ads)) have been calculated. The kinetics for formic acid oxidation through the active intermediate reaction path is strongly dependent on the surface structure of the electrode, with the highest activity found for the Pt(100) surface. The presence of steps, both on (100) and (111) terraces, does not increase the activity of these surfaces. CO formation only takes place in a narrow potential window very close to the local potential of zero total charge. The extrapolation of the results obtained with stepped surfaces with (111) terraces to zero step density indicates that CO formation should not occur on an ideal Pt(111) electrode. Additionally, the analysis of the Tafel slopes obtained for the different electrodes suggests that the oxidation of formic acid is strongly affected by the presence of adsorbed anions, hydrogen and water.

On the electrochemical properties of platinum stepped surfaces vicinal to the (100) pole. A computational study

“…For other reactions, such as methanol or ethanol oxidation the reactivity of this series of stepped surfaces is also very similar. This is in contrast to that observed for the surfaces with (111) terraces, for which significant changes are observed [15,21,25]. The similar behavior of the stepped surfaces with (100) terraces clearly indicates that the general reactivity of the step and (100) terrace sites is comparable.…”

“…For the surfaces vicinal to the (111) stereographic pole, that is, those containing terraces with (111) symmetry, significant effects in reactivity of the surface have been found. For those surfaces, the step sites are the active sites on these surfaces for the oxidation of adsorbed CO [14], the cleavage of the C-C bond in the ethanol oxidation reaction [15][16][17][18], or the formation of CO in the formic acid oxidation reaction [19][20][21], whereas the (111) terrace sites have a negligible activity for those processes. On the other hand, for the surfaces vicinal to the (100) pole, the reactivity of the (100) domains is much less affected by the presence of the steps.…”

CO oxidation on stepped-Pt(111) under electrochemical conditions: insights from theory and experiment

“…[35]. In summary, single crystal electrodes were flame-annealed, cooled down in a H2 + Ar atmosphere and protected by a water film [36].…”

“…It has been shown that steps often have an important effect on the reactivity of surfaces. For instance, (111)-steps on vicinal Pt(111) surfaces are able to break the C−C bond in the ethanol oxidation reaction, so that the final product is CO2 and not acetic acid [1][2][3]; or that CO formation from formic acid only takes place on (111)-steps [4,5].…”

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

“…[16][17][18] The addition of Bi adatoms to pristine Pt(111) single crystal electrodes diminishes the overpotentials and increase the current density up to 30-40 times that measured for the unmodified surface. 15 Such improvement is clearly related to the deposition of Bi on the terraces, since it reaches the maximum for coverages close to the saturation value. For low and moderate Bi coverages, only isolated or <1 nm islands have been seen by STM, which supports the random distribution model of adatoms on the surface.…”