Formic oscillations during

Samjeske G, OsawaM. 2005. Current oscillations during formic acid oxidation on a Pt electrode Insight into the mechanism by time-resolved IR spectroscopy. Angew Chem 44 5694-5698. 

The combination of the high sensitivity of SEIRAS and a rapid-scan FT-IR spectrometer enables the spectral collection simultaneously with electrochemical measurements such as cyclic voltammetry and potential-step chronoamperome-try. The time-resolved measurement can give some information on electrode kinetics and dynamics, as has been shown in Fig. 8.24. Figures 8.25 and 8.26 represent another example of millisecond time-resolved ATR-SEIRAS study of current oscillations during potentiostatic formic acid oxidation on a Pt electrode [123]. At a constant applied potential F of 1.1 V, the current oscillates as shown in Fig. 8.25 a. Synchronizing with the current oscillations, the band intensities of linear CO and formate oscillate as shown in Fig. 8.26 (and also in Fig. 8.25 c). 

Instabilities - Oscillations during the Oxidation of Formic Acid, Methanol, and Carbon Monoxide... 

S.2 Potential Oscillations during Formic Acid Oxidation... 

Potential oscillations during formic acid oxidation had been observed already in the 1920s [126]. As Fig. 32 shows [127], the upper potential limit is between 800 and 900 mV, as in the case of H2/CO oscillations. Introducing a model simulation, only the four (or five) rate constants of Eqs. (12-14) have to be employed. This has been done quite successfully by Okamoto and coworkers [128], reproducing the fingerprints of their experimental results. 

Fig. 32 Potential oscillations during formic acid oxidation at a smooth polycrystalline platinum electrode (a) 5 M HCOOH/0.5 M H2SO4, applied current density of 1.5 mA cm-2 (b) 1 M HCOOH and 0.5 M H2SO4, 0.25 mA cm [127].

A shortcoming of both models is that they do not capture the occurrence of complex periodic or aperiodic potential oscillations under current control, which were observed in many different electrolytes. Impressive studies of such complicated temporal motions during formic acid oxidation can e.g. be found in Refs. [118, 121], Schmidt et al. [131] suggest that the adsorption of anions, which leads to a competition for free surface sites not only between two species, formic acid and water, but between three species, formic acid, water and anions, can induce complex nonlinear dynamics. This conjecture is derived from differences in the oscillatory behavior found in perchloric and sulfuric acid for otherwise similar conditions. Complex motions were only observed in the presence of sulfuric acid. 

Fig. 53. (a) Cyclic voltammogram during the formic acid oxidation on a Bi-modified Pt ring electrode scan rate 5mV s-1. The change in the oscillation form close to t = 73.7 s (i.e. U = 0.16 V) indicates a qualitative change in the dynamics, (b) Spatio-temporal profile of the interfacial potential in the transition region of the oscillation form in (a). For the experimental set-up, see Fig. 49b. (Reproduced from J. Lee, J. Christoph, P. Strasser, M. Eiswrith and G. Ertl, J. Chem. Phys. (2001) 115, 1485 by permission of the American Institute of Physics.)...

Following a description in 1828 of an electrochemical cell which produced an oscillating current, a few examples of similar phenomena slowly came to light, such as a report in 1916 of the periodic liberation of carbon monoxide (CO) during a reaction caused by mixing methanoic (formic) acid (HCOOH) with concentrated sulfuric acid (Figure 8.1). 

During the oxidation of formic acid and formaldehyde on platinum electrodes, an oscillatory behavior is frequently observed. " The surface poisoning species play a central role in the triggering of the oscillatory phenomena. Recent studies on formic acid and formaldehyde oxidation confirm this view. Inzelt and Kert sz reported that by the use of electrochemical quartz crystal microbalance technique (EQCM), the periodical accumulation and consumption of strongly bound species can be observed in the course of potential oscillation produced by the galvanostatic oxidation of formic acid. 

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