The electrocatalytic oxidation of small organic molecules is of general importance for energy-related issues such as the fuel cells and electrochemical re-formation. The common emergence of current/potential oscillations in these reactions has implications on mechanistic aspects as well as on the overall conversion, and thus on the performance of practical devices. We investigate in this paper some general features of the electro-oxidation of formaldehyde, formic acid, methanol, and ethanol on platinum and in acidic media, with emphasis on the comparison of the activity under conventional and oscillatory regimes. The comparison is carried out by different means and generalized by the use of identical experimental conditions in all cases. In all four systems studied, the occurrence of potential oscillations is associated with excursions of the electrode potentials to lower values, which noticeably decreases the overpotential of the anodic reaction, when compared to that in the absence of oscillations. Quantitatively speaking, a 2-fold enhancement in the power density was observed in an idealized fuel cell operated with formaldehyde. This aspect, together with spontaneous self-cleaning processes, presents important advantages to the use of autonomous oscillations to reach both higher and long-term activities. Finally, some mechanistic aspects of the studied reactions are also discussed
The study of complex reaction under oscillatory conditions has been proven to be useful in uncovering features that are hidden under close to equilibrium regime. In particular, for the electro-oxidation of small organic molecules on platinum and platinum-based surfaces, such investigations have provided valuable mechanistic information, otherwise unavailable under nonoscillatory conditions. We present here the dynamics of production of volatile species along the oscillatory electro-oxidation of formic acid, methanol, and ethanol on platinum, as measured by online differential electrochemical mass spectrometry (DEMS). Besides the presentation of previously unreported DEMS results on the oscillatory dynamics of such systems, we introduce the use of multivariate linear regression to compare the estimated total faradaic current with the one comprising the production of volatile species, namely: carbon dioxide for formic acid, carbon dioxide and methylformate for methanol, and carbon dioxide and acetaldehyde for ethanol. The introduced analysis provided the best combination of the DEMS ion currents to represent the total faradaic current, or, equivalently, the maximum possible faradaic contribution of the volatile products for the global current. The mismatch between estimated total current and the one obtained by the best combination of partial currents of volatile products was found to be small for formic acid, 4 and 5 times bigger for ethanol and methanol, respectively, evidencing the increasing role played by partially oxidized, soluble species in each case. These results were discussed in connection with the mechanistic aspects of each system. Moreover, we have defined some descriptors to account for the production of volatile species, and discussed dynamics in terms of sample and populational covariances
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