Surface structure effects on the electrochemical oxidation of ethanol on platinum single crystal electrodes

Abstract

Ethanol oxidation has been studied on Pt(111), Pt(100) and Pt(110) electrodes in order to investigate the effect of the surface structure and adsorbing anions using electrochemical and FTIR techniques. The results indicate that the surface structure and anion adsorption affect significantly the reactivity of the electrode. Thus, the main product of the oxidation of ethanol on the Pt(111) electrode is acetic acid, and acetaldehyde is formed as secondary product. Moreover, the amount of CO formed is very small, and probably associated with the defects present on the electrode surface. For that reason, the amount of CO2 is also small. This electrode has the highest catalytic activity for the formation of acetic acid in perchloric acid. However, the formation of acetic acid is inhibited by the presence of specifically adsorbed anions, such as (bi)sulfate or acetate, which is the result of the formation of acetic acid. On the other hand, CO is readily formed at low potentials on the Pt(100) electrode, blocking completely the surface. Between 0.65 and 0.80 V, the CO layer is oxidized and the production of acetaldehyde and acetic acid is detected. The Pt(110) electrode displays the highest catalytic activity for the splitting of the C-C bond. Reactions giving rise to CO formation, from either ethanol or acetaldehyde, occur at high rate at any potential. On the other hand, the oxidation of acetaldehyde to acetic acid has probably the lower reaction rate of the three basal planes.

The breaking of the CC bond in ethylene glycol oxidation at the Pt(111) electrode and its vicinal surfaces

“…The appearance of these bands indicates that the C-C bond of the EG molecule has been broken at low potentials, resulting in the formation and accumulation of adsorbed CO and demonstrating that CO is the poison present on the electrode surface. This behavior is somewhat different to that shown by ethanol, where the amount of CO formed and accumulated on the Pt(111) surface is very small [1]. The band at 2343 cm -1 , corresponding to the asymmetrical stretching mode of CO 2 in solution, is already visible at 0.6 V RHE.…”

“…Platinum single crystal working electrodes preparation, reagents and experimental procedures, including FTIR set-up, is the same as described in previous papers [1][2][3][4][5][6]. Pt(111) and its vicinal surfaces Pt(S)[n(111)x(100)], with Miller indices Pt(n+1, n-1, n-1) and Pt(S)[n(111)x(111)] or Pt(S)[(n-1)(111)x(110)], with Miller indices Pt(n, n, n-2), where n is the number of terrace rows, were used.…”

“…Among possible fuels, ethanol CH 3 CH 2 OH is very promising for a series of reasons [1]. The main problem is the formation of acetate as final product, especially at model Pt(111) electrode.…”

The correlation of electrochemical and fuel cell results for alcohol oxidation in acidic and alkaline media

“…Some reaction routes are more desirable and the information of which surface morphologies catalyze preferred routes is significant. For instance, ethanol oxidation occurs through the dual path mechanism presented in Figure 11 (Section 3.1.3) and Figure 21 represents the same schematic with the additional information of which paths are most favorable of each low-index Pt surfaces determined by Colmati et al [69]. According to these authors on Pt(111) terraces ethanol oxidation occurs via acetaldehyde to acetic acid and only a small CO 2 fragment is observed.…”

“…Nevertheless, this molecule has the thermodynamically stable C-C bond that is difficult to cleave at low temperatures. Similarly as with methanol the first step of ethanol oxidation is the adsorption of the ethanol molecule on the catalyst surface followed by two parallel paths (reaction 1 and 3) [46,69] presented in the Figure 11.…”