Kinetics and mechanism of “reduced CO2” electrooxidation on electrodispersed platinum in different acid solutions

Abstract

The electrooxidation of "reduced CO," electroadsorbates on electrodispersed platinum electrodes has been Investigated in 0.05 M HCIO,, 1 M HCIO,. 0.5 M H>SO, and 1 M H,PO, at 25OC through voltammetry and potential step techniques. The overall reaction comprrses three dtstmguishable processes. namely a first order triggering process. and two second order surface processes. The latter are influenced remarkably by the solution composition (anions). The second order reaction mechanism tnvolves two distingutshable "reduced CO," electroadsorbates which react independently with the OH spectes formed from H,O electrooxidation on the bare platinum sues as the reactton proceeds. An mteractron term has to be Included in the rate equations to account for the expertmental results. The mechanism interpretanon accounts for the values of the number of electrons per sue ranging from 1 to 2.

Kinetics of CO2 electroadsorption on electrodispersed platinum electrodes in acid solutions

“…0.6 V is obtained in 0.05 M HClO,, but the peak potential shifts positively with either a shoulder or a second partially overlapping anodic current peak in going from 0.05 M HCIO, to 1 M HClO,, 0.5 M H,S04 and 1 M H,PO,. These results confirm the complexity of the electrooxidation of reduced CO, adsorbates and the influence of anions on the process, as has been reported previously [17,18,22]. It should be noted that the data obtained for electrodispersed Pt electrodes are very reproducible, and in this case, the interference of possible adsorbable impurities in solution can be considered as negligible, as for large surface area Pt electrodes.…”

“…This effect is probably the result of a decrease in the local interaction energy (repulsive) among the remaining unreactive H adatoms as the adsorption of CO, proceeds. Finally, one can also note that the adsorption of CO, is only slightly sensitive to the electrolyte composition, in contrast to those processes related to the electrooxidation of the reduced CO, adsorbates [17,18,22]. By keeping these premises in mind, the interpretation of the kinetics of CO, electroadsorption on electrodispersed Pt in acid solutions can be approached in a way rather different from that advanced earlier for smooth and platinized Pt [ll-131, although sufficiently general to embrace results obtained with any type of Pt electrode.…”

“…Most of the experimental setup, i.e. the electrolysis cell and the electronic circuitry, were the same as already described in previous publications [21,22]. Electrodispersed Pt working electrodes with roughness factors, R, up to 70 were used.…”

“…Electrodispersed Pt working electrodes with roughness factors, R, up to 70 were used. The preparation and surface treatment of the working electrodes as well as the definition of R and its determination have been described extensively elsewhere [21,22,25]. Two groups (I and II) of electrolyte solutions were employed; group I included solutions consisting of different CO, saturated acidic solutions, namely, 0.05 M HClO,, 1 M HClO,, 0.5 M H,SO,, and 1 M H,PO,, and group II, solutions involving 0.5 M H,SO, with different CO, concentrations.…”

“…It is well known that CO,-containing adsorbates can be formed electrochemically on the surface of those metals which can electroadsorb H atoms, such as Pt, Rh, Pd and activated Au [4-201. The electrochemical oxidation of reduced CO, adsorbate either voltammetrically or potentiostatically has been investigated on bright and platinized Pt [4-131, and more recently on electrodispersed Pt electrodes, i.e. rough Pt electrodes with a definite structure [21,22]. In contrast, much less is known about the kinetics of the adsorbate electroformation [5,, an aspect of the entire electrochemical reaction which deserves further study to reach a better knowledge of the characteristics of the electroadsorbate.…”