Abstract
In the recent years investigations on the oxidation of small organic molecules (SOM) has been done extensively and under various conditions, where the general focus lied on formic acid, because of its model character and its possible application in fuel cells. Since Capon and Parsons published their articles about the formic acid oxidation on platinum (Pt), their dual-pathway mechanism is generally accepted. Here formic acid reacts either a quite sluggish, inactive pathway to CO2 and where a poisoning intermediate inhibits strongly the oxidation process, which has been proven to be CO [11]. On the other side an intermediate in the so-called active pathway, whose nature still is under strong debate. Previously carboxylate (COOH) and bridge-bonded formate (HCOO) [4], [5], [12], adsorbed on the surface, has been suggested as possible intermediates. But recently some publications suggested weakly adsorbed formate (HCOO-) as precursor for the active intermediate, where the pH was said to play a crucial role. During methanol oxidation several intermediates adsorb on the Pt surface, where formaldehyde and formic acid could be detected as stable byproducts. Thus, the oxidation of these byproducts plays a significant role here and the elucidation of their oxidation mechanism might help in a detailed understanding of the oxidation of SOM. Our group has shown recently, that the performance of measurements under oscillating conditions far from equilibrium can provide further insight in the oxidation kinetics and decouple parallel reaction pathways. Therefore, a new procedure was developed to normalize the applied current density in potentio-/galvanostatic measurements, which enables us to compare several parameters like frequency, derivative as poisoning rate, shape, amplitude and the size of the oscillating region. Since the influence of several parameters, like pH, temperature and coverage of poisoning species and intermediates, remains unclear yet, more investigations are to be done. Especially the detection of species on the surface is a crucial point, which requests very surface sensitive techniques. Applying ATR-SEIRAS has already proven to be such a powerful technique, Osawa and co-workers could contribute some further insight to the debate among the active intermediate in electro-oxidation of formic acid. Recently ATR-SEIRAS was applied in combination with cyclic voltammetry to discuss the oxidation mechanism on formic acid in further detail. Consequently more measurements with ATR-SEIRAS in combination with other techniques under oscillating conditions should provide us with a very detailed overview of the influences of the mentioned parameters. To the best of our knowledge, this has not been done yet, but might be a crucial step in the complete understanding of the oxidation of SOM. (AU)
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