Voltammetry In Acidic Media Research Articles

Improved stability of PtOx sol-gel-modified diamond electrodes covered with a Nafion® film

The modification of boron-doped diamond (BDD) electrodes with platinum oxide particles deposited by the Sol-gel method and using several pre- and post-treatments of the surface is described. The electrochemical stability of the resulting catalytic coatings was evaluated by cyclic voltammetry in acid medium and was much greater than those previously reported in the literature for others deposition methods. A thermal pre-treatment of the BDD surface yielded electrodes that retained 91.6% of the coated material after 1000 voltammetric cycles carried out between the water decomposition reactions. The application of a Nafion® film on top of the coating preserved integrally the deposited platinum oxide. The use of such modified electrodes for practical applications is now feasible under the present experimental conditions.

Electrochemical Behavior of Fluorinated Boron-Doped Diamond

The surface properties and the electrochem. behavior of a fluorinated B-doped diamond (F-BDD) electrode prepd. by plasma treatment in CF4-He mixt. was studied by XPS and cyclic voltammetry in acidic media. The results showed C-F bonding (C-CF and C-F) on the surface of F-BDD, which made the surface more hydrophobic. Also hydrogen evolution was shifted to more cathodic potentials for fluorinated diamond, as compared with untreated BDD. Finally, the higher cathodic overpotential for hydrogen evolution permitted Ni deposition and nitrate redn. [on SciFinder (R)]

Application of an electrochemical quartz crystal microbalance to a study of water adsorption at gold surfaces in acidic media

Changes in surface mass at a Au electrode during cyclic voltammetry in acidic media were monitored with an electrochemical quartz-crystal microbalance. An unexpectedly large increase in surface mass was observed during the positive potential scan in the pre-oxide region beginning ca. 0.5 V negative of the potential for onset of formation of surface oxide (AuO). This mass increase is virtually independent of the acid and is interpreted on the basis of adsorption of H 2O via hydrogen bonding to the submonolayer of hydrous oxide (AuOH) generated in the pre-oxide region. The mass increase is consistent with an increase in surface hydration by about 32 H 2 O molecules per AuOH site.

On the electrochemical reduction of nicotinamide in an acid medium

A study has been carried out on the reduction of nicotinamide (NA) by dc and DP polarography and linear sweep cyclic voltammetry in acidic media (pH < 3). Tafel slopes and reaction orders were also obtained at potentials corresponding to the foot of the polarographic wave. In the pH range studied the species in solution is the form protonated in the pyridine ring. In very strong acidic medium the rate-determining step of the process is a protonation reaction placed between two one-electron transfers. For 0 < pH < 3 a gem-hydroxylamine formed after two one-electron transfers can eliminate an ammonia molecule by two concurrent reactions. The limiting current of the wave is partially controlled by these reactions and the process appears as ECE.

Electrochemical behaviour of N-methylnicotinamide in acidic media

N-Methylnicotinamide (MNA) was studied by dc and DP polarography and linear sweep cyclic voltammetry in acidic media (pH < 3). Tafel slopes and reaction orders were obtained from i — E curves traced at potentials corresponding to the foot of the polarographic wave. The results show that in the pH range studied the species in solution is the non-protonated one. In a strong acidic medium the overall process is irreversible. The reduction pathway consists of the reversible transfer of one electron and two H + ions followed by an irreversible one-electron transfer, which is the rate-determining step. At 1 < pH < 3, this process is in competition with the electrodimerization of MNA.

Electroanalytical studies of beta-adrenergic blocking agents; N-isopropylethanolamine derivatives; procainamide

The beta-adrenergic blocking agents metoprolol, oxprenolol, pindolol, practolol, propranolol and sotalol, and also the related procainamide, have been examined by anodic rotating disc electrode voltammetry in acidic media and in buffer media over the range of pH from 0 to 11.5. The best medium is 0.1 mol l–1 sulphuric acid, in which most of the compounds show obedience to the Levich relationship at platinum and gold electrodes. Rapid determinations of oxprenolol (up to 5 × 10–3 mol l–1), practolol, propranolol and procainamide give very satisfactory results. Electrode kinetic parameters for mass and charge transfer have been determined for the latter four compounds. Reaction mechanisms have been elucidated and differ for each compound. Cyclic voltammetry has not proved to be particularly informative, and is illustrated for propranolol.