The effect of temperature on the coupled slow and fast dynamics of an electrochemical oscillator

Abstract

The coupling among disparate time-scales is ubiquitous in many chemical and biological systems. We have recently investigated the effect of fast and, long-term, slow dynamics in surface processes underlying some electrocatalytic reactions. Herein we report on the effect of temperature on the coupled slow and fast dynamics of a model system, namely the electro-oxidation of formic acid on platinum studied at five temperatures between 5 and 45 °C. The main result was a turning point found at 25 °C, which clearly defines two regions for the temperature dependency on the overall kinetics. In addition, the long-term evolution allowed us to compare reaction steps related to fast and slow evolutions. Results were discussed in terms of the key role of PtO species, which chemically couple slow and fast dynamics. In summary we were able to: (a) identify the competition between two reaction steps as responsible for the occurrence of two temperature domains; (b) compare the relative activation energies of these two steps; and (c) suggest the role of a given reaction step on the period-increasing set of reactions involved in the oscillatory dynamics. The introduced methodology could be applied to other systems to uncover the temperature dependence of complex chemical networks.

The Effect of Solution pH and Temperature on the Oscillatory Electro‐Oxidation of Formic Acid on Platinum

“…As discernible in Figure (a), the temperature dependence of the oscillation frequency at pH 12 is rather weak, amounting to ‐ 20 ± 16 kJmol −1 . In contrast to the consistent observation of temperature (over)compensation in this system,, the behavior observed here is more likely to be due to the erratic dependence, as anticipated by irregular dynamics observed at high pH values. In the first border of the existing region of oscillations, there is also a poor linearity in the Arrhenius plots at pH 3, cf.…”

“…Apparent activation energies between 45 and 50 kJ mol −1 in strong acidic media are in good agreement with the literature ,,. A slight increase of the apparent activation energy is observed for increasing pH.…”

“…It recently turned out, that this parameter has a pivotal influence on the kinetics of the electro‐oxidation of formic acid and some investigations carried out, where formate in solution was claimed to be the precursor for the active intermediate . The electro‐oxidation of formic acid is known for a long time to undergo kinetic instabilities under several experimental conditions ,. Exploring such instabilities, c.f.…”

“…Exploring such instabilities, c.f. oscillatory kinetics, have been proved to be an interesting way to deepen the mechanistic understanding in this type of system ,,,. In this paper we investigate the effect of solution pH (and also of temperature at different pH) during the electro‐oxidation of formic acid on polycrystalline platinum.…”

Coupled Dynamics of Anode and Cathode in Proton‐Exchange Membrane Fuel Cells

“…A point that was never addressed is what happens to the cathode when the fuel cell is operated in an oscillatory regime. It is well known that the electro‐oxidation of small organic molecules is subject to oscillatory kinetics when the reaction current is kept constant (galvanostatic control) or under potentiostatic control when the resistance between the working electrode and the potentiostat exceeds a critical value . There are various studies on how autonomous oscillatory behavior occurs in fuel cells based on the electro‐oxidation of H 2 /CO and, recently, methanol and formic acid .…”