Deposition Of Adatoms Research Articles

Electrocatalysis by ad-atoms Part XIII. Preparation of ad-electrodes with tin ad-atoms for methanol, formaldehyde and formic acid fuel cells

The practical application of the electrocatalysis by tin ad-atoms to organic fuel cell anodes has been studied. A simplified and versatile preparation method of the electrode having high specific surface area platinum with a well-defined tin coverage has been developed. It consists of underpotential deposition of ad-atoms and subsequent anodic treatment resulting in uniform dispersion of the ad-atoms over all the platinum clusters in the catalyst layer of the electrode. The resulting electrode exhibits enhancement effects in the specific activity over the pure platinum black electrode by a factor of 100 for methanol oxidation, of more than 1000 for formaldehyde oxidation and of 250 for formic acid oxidation, respectively. This method has the advantage that a much higher specific surface area of catalyst is obtained, as well as an optimum composition, compared with the electrochemical co-deposition or immersion methods proposed previously.

Electrocatalysis by AD-atoms: Part XIII. Preparation of ad-electrodes with tin ad-atoms for methanol, formaldehyde and formic acid fuel cells

The practical application of the electrocatalysis by tin ad-atoms to organic fuel cell anodes has been studied. A simplified and versatile preparation method of the electrode having high specific surface area platinum with a well-defined tin coverage has been developed. It consists of underpotential deposition of ad-atoms and subsequent anodic treatment resulting in uniform dispersion of the ad-atoms over all the platinum clusters in the catalyst layer of the electrode. The resulting electrode exhibits enhancement effects in the specific activity over the pure platinum black electrode by a factor of 100 for methanol oxidation, of more than 1000 for formaldehyde oxidation and of 250 for formic acid oxidation, respectively. This method has the advantage that a much higher specific surface area of catalyst is obtained, as well as an optimum composition, compared with the electrochemical co-deposition or immersion methods proposed previously.

Inhibition of the anodic dissolution of iron in alkaline solution by metal complex ions

The possible inhibiting effects of GaO 3 3−, GeO 3 2−, CrO 3 2−, and MoO 4 2− ions on anodic and cathodic reactions on iron in 5 M KOH were studied. It was shown that a concentration of these ions of 10 −3 M inhibits the anodic iron dissolution reaction 2–3 times, while no effect on the hydrogen evolution reaction was observed. The effect was explained by the underpotential deposition of adatoms of the metal complexing ions on the iron electrode.

Electrocatalytic oxidation of ethylene glycol in alkaline medium on paltinum-gold alloy electrodes modified by underpotential deposition of lead adatoms

Electrocatalytic oxidation of ethylene glycol in alkaline medium on paltinum-gold alloy electrodes modified by underpotential deposition of lead adatoms

Oxygen reduction on electrode surfaces modified by foreign metal ad-atoms: Lead ad-atoms on gold

Oxygen reduction on gold is considerably catalysed by foreign metal ad-atoms. The catalytic effects of lead have been studied in more detail as most illustrative. The two-electron reduction of O 2 to HO 2 − on Au changes into a four-electron process on Au modified by lead. In the potential region where AuOH constitutes the surface, the interaction of Pb ions with AuOH causes catalytic effects. At more negative potentials, on bare Au surface, the underpotential deposition of Pb ad-atoms gives rise to the catalytic effects. At AuOH surface modified by Pb ions the O 2 reduction involves a “series” mechanism, with only minute quantities of HO 2 − leaving the electrode surface. The reduction of HO 2 − is considerably catalysed. The mechanism of this reaction is changed from the rate-determining chemical step into the charge-transfer rate-determining step. The rate-determining step for O 2 reduction involves the first charge transfer: O 2+e→O 2 −(ads) The mechanism of HO 2 − formation is uncertain, while its reduction most probably involves a direct process. There are indications that on Au surface with Pb ad-atoms a “parallel” mechanism may be operative. The catalytic effect originates in the interaction of Pb 2+ with AuOH surface, which considerably reduces a partial negative charge on OH. Such a surfaces, as well as that of Au covered by Pb ad-atoms, are more suitable for adsorption of O 2, O 2 − and HO 2 − which considerably alters the free energy of adsorption of these species.

The electrochemical behavior of ad-atoms and their effect on hydrogen evolution: Part V. Selenium ad-atoms on gold

Hydrogen evolution on a platinum electrode proceeds through the atom + atom step which needs pairs of two nearest neighbor sites available for hydrogen evolution. The activity for hydrogen evolution decreases with the decrease of the number of pairs of platinum sites with the deposition of foreign ad-atoms. But on a gold electrode it proceeds through the atom + ion step so it does not need such pairs. In this paper, selenium ad-atoms were put on a gold electrode, in order to examine the difference in their effect on hydrogen evolution, which is expected from the difference in hydrogen evolution mechanism mentioned above. The activity decreases not with the number of pairs of gold surface sites but linearly with the number of gold surface sites with the deposition of Se ad-atoms on a gold electrode as expected. This affords experimental evidence for the validity of the electrochemical mechanism of hydrogen evolution on a gold electrode, from molecular level.

The electrochemical behavior of ad-atoms and their effect on hydrogen evolution Part IV. Tin and lead ad-atoms on platinum

Hydrogen evolution on a platinum electrode decays against X pt with the deposition of Sn ad-atoms and Pb ad-atoms in the same way as it decays with that of Ge ad-atoms, in which all of these ad-atoms occupy two platinum sites. In general the decay depends on the number of sites occupied by an atom of the ad-atom species. The potential ranges for oxygen adsorption by Sn ad-atoms and Pb ad-atoms are 0.45 to 1.24 V and 0.48 to 0.77 V, respectively, but the oxygen adsorbed by the latter ad-atoms is very small in amount.

The electrochemical behavior of ad-atoms and their effect on hydrogen evolution: Part IV. Tin and lead ad-atoms on platinum

Hydrogen evolution on a platinum electrode decays against X pt with the deposition of Sn ad-atoms and Pb ad-atoms in the same way as it decays with that of Ge ad-atoms, in which all of these ad-atoms occupy two platinum sites. In general the decay depends on the number of sites occupied by an atom of the ad-atom species. The potential ranges for oxygen adsorption by Sn ad-atoms and Pb ad-atoms are 0.45 to 1.24 V and 0.48 to 0.77 V, respectively, but the oxygen adsorbed by the latter ad-atoms is very small in amount.