Jerzy Sobkowski

Kinetics of carbon dioxide adsorption on a platinum electrode

Summary The kinetics of CO2 adsorption on a platinized electrode were investigated by radiometric method. It was shown that the CO2 adsorption is due to surface reaction with hydrogen adsorbed on the electrode. The rate of adsorption increases with the electrode potential in the range of 0.05–0.15 V and follows the secondorder reaction. In the range of 0.20–0.25 V the rate of adsorption decreases according to the first-order reaction. The COOH radical is postulated as a product of CO2+Hads reaction. In the range of potentials 0.05–0.20 V the maximum surface concentration of adsorbed species is ca. 9.6×1014 molecules cm−2. The bulk concentration of CO2 and temperature do not influence the surface concentration. The apparent heat of activation of CO2+Hads reaction are 50.0 kJ mol−1 at 0.05 V and 38.5 kJ mol−1 at 0.20 V, respectively.

Comparative study of adsorption and oxidation of formic acid and methanol on platinized electrodes in acidic solution

Abstract The results of a radio-and electrochemical study of the adsorption of HCOOH and CH 3 OH and the oxidation of their chemisorption products on platinized electrode in 0.5 M H 2 SO 4 have been presented and some remarks on the mechanism of the electrode processes have been given. It has been concluded that the rate determining step in adsorption of both fuels should be considered as charge transfer process. No heterogeneity of the platinum surface has been detected. It is supposed that the strongly bound intermediate is a composition of C x OOH and CO radicals coupled by hydrogen bonding. Water molecules adsorbed on the electrode surface are most likely the surface oxidant involved in the oxidation of the chemisorbed species.

Effect of surface order on adsorption of sulfate ions on silver electrodes

Adsorption of sulfate ions was studied on three basal planes and a polycrystalline surface of silver in 0.1 M HClO4 by radiometric and electrochemical methods. On all four surfaces, adsorption was found to be reversible with respect to the potential and bulk solution concentration of sulfate. Radiometrically determined adsorption isotherms show a clear difference in sulfate adsorption on individual planes. Adsorption of the anion on the basal planes of silver decreases in the sequence: Ag(111)≥Ag(110)>Ag(100). As expected, the polycrystalline silver electrode exhibits intermediate adsorption properties between the most and the least active basal planes. Thermodynamic parameters of adsorption were calculated by fitting the Frumkin isotherm equation to the experimental data points. High values of surface concentration for adsorbed sulfate on the (111) and (110) planes of silver can be accounted for by a match between a tetrahedral structure of the anion and a trigonal distribution pattern of the surface atoms of silver on these planes.

Influence of tin on the oxidation of methanol on a platinum electrode

Abstract The influence of adsorbed tin and tin(IV) ions on the oxidation of methanol chemisorbed species as well as the methanol from the bulk of the solution was studied on a Pt electrode by voltammetric and radiometric methods. It was found that tin is not adsorbed as an ad-atom but rather as a divalent ion. Enhancement of the electrocatalytic oxidation of chemisorbed species derived from methanol was observed only in the potential range from 0.4 to 0.8 V. The influence of some factors on the electrocatalytic properties of platinum is discussed.

Effect of anions and pH on the adsorption and oxidation of methanol on a platinum electrode

Abstract The influence of various anions and pH on methanol oxidation as well as its products of chemisorption on platinum has been studied by voltammetric and radiometric methods. It was found that the rate of methanol oxidation from the bulk solution was lowest for Na 2 CO 3 and highest for NaOH solutions. The influence of anions on the chemisorbed species of methanol on a platinum electrode has also been investigated.

The comparative study of CO2 + Hads reaction on platinum electrode in H2O and D2O☆

The observed isotopic effect in CO2 + Hads reaction showed that at 0.05 V the rate determining step is formation whereas at 0.2 V the reorientation of adsorbed intermediate: is probably the slowest step of reaction. The oxidation of adsorbed product is slower in D2SO4 than H2SO4 solution like the surface oxidation of platinum. The rate determining step of COOHads oxidation is a reaction with OHads.

The adsorption of carbon monoxide on a platinum electrode

Abstract The adsorption of CO from 0.5 M H2SO4 solution on platinum has been studied using CO labelled with C-14. The adsorption of CO on Pt occurs in the potential range of hydrogen adsorption as well as in the double layer region. In the whole potential range the rate of adsorption follows first order kinetics. From the surface concentrations and charges for oxidation of adsorbed species it follows that the product of chemisorption consists at least of two kinds of species. One of them is the COOH radical probably formed by the reaction of CO with water.

The behaviour of iron electrode in CO2− saturated neutral electrolyte—I. Electrochemical study

Abstract The properties of iron electrode in CO2-saturated sodium chloride supporting electrolyte were investigated by cyclic voltammetry of static and rde-Ferrovac electrode in the potential region from −1.1 to −0.3 V (nhe). In addition to the reduction of H3O+ ions formed due to the protolysis of carbonic acid, the direct (activated) reduction of both H2CO3 molecules and HCO−3 ions was observed. It is proposed that catalytic, ErC′i mechanism accounts for the occurrence of the latter processes.

Electrochemical reduction of CO2 and oxidation of adsorbed species on the rhodium electrode

Abstract The adsorption of CO2 on the rhodium electrode and the oxidation of the adsorption products were investigated by the use of a radiochemical method, by cyclic voltammetry and by chronoamperometry. The adsorption process occurs in the hydrogen region and the oxidation of the resulting organic species takes place in the oxygen region of the electrode potentials, respectively. Making use of the charges involved in the hydrogen asorption and in the oxidation of the organic adsorbate, the net composition of the CO2 adsorption products was found to be best represented (for Eads >0.000 V) by the carbon atom bonded to four adsorption sites. It was also found that a surface oxidant is needed for the r.d.s. of the oxidation process. This report refers to some earlier works concerning the interactions of CO2 with noble metal surfaces. In particular it is shown that the CO2 adsorption probably does not pass through the activated CO2 intermediates which are weakly bonded to the bare Rh sites. It is more likely that two Rh-H sites and the CO2 molecule from the bulk of solution are involved in the adsorption mechanism (r.d.s.)

Kinetics of adsorbed “CO2” oxidation on a platinum electrode

Summary The mechanism of oxidation of adsorbed CO2 on a platinum electrode was investigated. The results show that one electron is needed for oxidation of one molecule of adsorbed “CO2”. This oxidation process follows the first order kinetics. These data and results for kinetics adsorption (previously reported) show that the radical COOH is a final product of adsorption of CO2 on Pt.