G. Fóti

Electrochemical oxidation of water on synthetic boron-doped diamond thin film anodes

Electrolysis in aqueous 1 M HClO4 and 1 M H2SO4 solutions has been carried out under galvanostatic conditions using boron-doped diamond electrodes (BDD). Analyses of the oxidation products have shown that in 1 M HClO4 the main reaction is oxygen evolution, while in H2SO4 the main reaction is the formation of H2S2O8. In both electrolytes small amounts of O3 and H2O2 are formed. Finally, a simplified mechanism involving hydroxyl radicals formed by water discharge has been proposed for water oxidation on boron-doped diamond anodes.

Electrochemical Behavior of Synthetic Diamond Thin Film Electrodes

The inertness and unique electrochem. properties of diamond present great potential for a variety of applications in aggressive environments. Preliminary results showed the widest known electrochem. window before water decompn., allowing new possibilities for both anodic and cathodic reactions. Studies of the oxidn. of org. compds. was performed with alcs. such as isopropanol, phenol and org. acids. Cyclic voltammetry demonstrates no activity in the potential range where water is stable. In the potential region of oxygen evolution, the org. compds. are mainly oxidized to CO2. No deactivation or redn. in the thickness of the electrode was obsd. No fouling of the diamond surface was detected. Also, no hydrodynamic effects were obsd. Concd. (1 M) and dild. (3 * 10-4 M) cyanide solns. were oxidized on diamond electrodes both in the presence and in the absence of chloride ions. The results show a direct oxidn. with a current efficiency of .apprx.40% for concd. solns. At low cyanide concns., the current efficiency is strongly increased by the presence of Cl-. Electrochem. redn. of cadmium and copper was carried out on diamond electrodes. Nonadherent deposits were obtained on diamond cathodes. [on SciFinder (R)]

Microemulsion Synthesized Pt ∕ Ru ∕ Sn Nanoparticles on BDD for Alcohol Electro-oxidation

Ternary Pt-based nanoparticles (nominal composition Pt80Ru10Sn10 ) were synthesized via the microemulsion route and deposited onto boron-doped diamond (BDD) electrode. The particle size measured by transmission electron microscopy was in the 2–5nm diam range. X-ray photoelectron spectroscopy revealed a slightly different surface composition from that of the bulk and showed no chemical shift of the Pt4f7∕2 line in ternary Pt∕Ru∕Sn nanoparticles. For both methanol and ethanol electro-oxidation, the ternary catalyst exhibited lower onset potentials than either pure Pt or the corresponding bimetallic (Pt∕Ru and Pt∕Sn ) catalysts. The ternary Pt∕Ru∕Sn catalyst was more efficient for methanol oxidation than for complete oxidation of ethanol, because ethanol electro-oxidation was stopped at acetaldehyde and/or acetic acid formation, the ternary catalyst being unable to activate the C-C bond scission.

Electrochemical Promotion of Ethylene Oxidation over Rh Catalyst Thin Films Sputtered on YSZ and TiO2 / YSZ Supports

The effect of electrochem. promotion of catalysis or nonfaradaic electrochem. modification of catalytic activity or electropromotion was studied for the model reaction of ethylene oxidn. on sputter-coated Rh films. The thin (40 nm) Rh films were deposited on Y2O3-stabilized-ZrO2 (YSZ) and on YSZ coated with a thin porous TiO2 layer. The catalytic activity of Rh for C2H4 oxidn. can be reversibly enhanced via anodic current or potential application by up to a factor of 80 and the increase in the oxidn. rate is up to 2000 times larger than the rate of supply of O2- to the Rh catalyst-electrode. Smaller anodic currents cause periodic catalytic rate and potential oscillations. The TiO2 layer was found to enhance the open-circuit catalytic activity and to stabilize the electrochem. promoted catalyst state. The obsd. pronounced electrochem. promotion behavior is due to the anodically controlled migration (back spillover) of O2- species from YSZ to the Rh/gas interface and the concomitant destabilization, via repulsive lateral interactions, of the formation of surface Rh2O3. The electropromotion of such thin metal catalyst films with metal dispersion near 10% is of significant importance for the practical use of the electrochem. promotion of catalysis. [on SciFinder (R)]

Electrochemical promotion of Rh catalyst in gas-phase reduction of NO by propylene

The concept of non-faradaic electrochemical modification of catalytic activity (NEMCA) has been applied for the in situ control of catalytic activity of a rhodium film deposited on YSZ (yttria stabilized zirconia) solid electrolyte towards reduction of 1000 ppm NO by 1000 ppm C3H6 in presence of excess (5000 ppm) O2 at 300 °C. A temporary heating at this feed composition results in a long-lasting deactivation of the catalyst under open circuit conditions due to partial oxidation of the rhodium surface. Positive current application (5 μA) over both the active and the deactivated catalysts gives rise to an enhancement of N2 and CO2 production, the latter exceeding several hundred times the faradaic rate. While active rhodium exhibits a reversible behaviour, electrochemical promotion on the deactivated catalyst is composed of a reversible and an irreversible part. The reversible promotion results from the steady-state accumulation of current-generated active species at the gas exposed catalyst surface whereas the irreversible effect is due to the progressive reduction of the catalyst resulting in an increased recovery rate of lost catalytic activity. The results are encouraging with respect to application of rhodium for the catalytic removal of NO from auto-exhaust gases under lean-burn conditions.

Investigation of the Anodic Oxidation of Acetic Acid on Boron-Doped Diamond Electrodes

Reference GGEC-ARTICLE-2008-058doi:10.1149/1.2823459View record in Web of Science Record created on 2008-01-29, modified on 2016-08-08

Electrochemical behaviour of DSA type electrodes prepared by induction heating

DSA type electrodes (IrOx/Ti) were prepd. by induction heating technique which allows a rapid decompn. of the precursor under anaerobic conditions. With this type of electrode, an activation process is obsd. in cyclic voltammetry which can be related to the presence of metallic Ir within the coatings. The electrooxidn. of alcs. in acid medium was studied by cyclic voltammetry. In the presence of alcs., a large current enhancement was obsd. at E >= 1.3 V/normal H electrode. This great reactivity can be due to high iridium oxidn. states, Ir(V) and Ir(VI), present in the oxide layer in this potential range. [on SciFinder (R)]

Characterization of DSA type electrodes prepared by rapid thermal decomposition of the metal precursor

A new technique is presented for the prepn. of DSA type electrodes. In this technique, the precursor is rapidly decompd. on the substrate by treatment in an induction electromagnetic field. The effects of the rapid heating of H2IrCl6.6H2O precursor on Ti substrate on the morphol. and the compn. of the coating are presented. Formation of metallic Ir is obsd. using this technique. [on SciFinder (R)]

Pt/Ti electrode preparation methods: application to the electrooxidation of isopropanol

Platinum coatings on Ti were prepared by a two-step process: partial thermal decomposition of chloroplatinic acid followed by electroreduction of the coating. Effects of preparation temperature and of cathodic polarization on the roughness factor were studied. Roughness factors greater than 570 were achieved, leading to an enhancement of the activity towards isopropanol electrooxidation in 1 M H2SO4.

Dimensionally Stable Anode-Type Anode Based on Conductive p-Silicon Substrate

In the search for a good dimensionally stable anode-type electrode, p-silicon (1-3 mW cm) has been chosen as the substrate material due to its high anodic stability and its reasonable cost compared to titanium and tantalum. Several p-Si/IrO2 electrodes have been prepd. by thermal decompn. at different temp. The effect of prepn. temp. on the morphol. and electrochem. properties has been investigated by SEM anal., X-ray diffraction, and cyclic voltammetry in 1 M HClO4 showing that p-Si/IrO2 prepd. at 450 DegC presents a high surface area and a low degree of crystallinity, while increasing the calcination temp. resulted in a decrease of true area and an increase in crystallite size. The activity of p-Si/IrO2 electrodes for simple electron transfer reactions and for complex electrode reactions has been also studied by cyclic voltammetry and linear polarization in solns. contg. the hydroquinone/benzoquinone redox couple and various org. compds. (isopropanol, tert-butanol, methanol). Finally, the anodic stability of a p-Si/IrO2 electrodes prepd. at 450 DegC has been tested by an accelerated service life test. p-Silicon based electrodes were shown to have the highest standardized service life compared with that of titanium- or tantalum-based electrodes. [on SciFinder (R)]