Electrochemical preparation of peroxodisulfuric acid using boron doped diamond thin film electrodes

We have investigated the electrochemical oxidation of sulfuric acid on boron-doped synthetic diamond electrodes (BDD) obtained by HF CVD on p-Si. The results have shown that high current efficiency for sulfuric acid oxidation to peroxodisulfuric acid can be achieved in concentrated H2SO4 (>2 M) at moderate temperatures (8–10 °C). The main side reaction is oxygen evolution. Small amounts of peroxomonosulfuric acid (Caro's acid) have also been detected. A reaction mechanism involving hydroxyl radicals, HSO4− and undissociated H2SO4 has been proposed. According to this mechanism electrogenerated hydroxyl radicals at the BDD anode react with HSO4− and H2SO4 giving peroxodisulfate

Kinetic modelling of the electrochemical mineralization of organic pollutants for wastewater treatment

The electrochemical mineralization of organic pollutants is a new technology for treatment of dilute wastewater (COD< 5gL−1). In this method, use of the electrical energy can produce complete oxidation of pollutants on high oxidation power anodes. An ideal anode for this type of treatment is a boron-doped diamond electrode (BDD) characterized by a high reactivity towards oxidation of organics. In the present work kinetic aspects of organic mineralization is discussed. The proposed theoretical kinetic model on boron-doped diamond anodes is in excellent agreement with experimental results. In addition economic aspects of electrochemical organic mineralization are reporte

The Industrial Electrolytic Regeneration of Mn2(SO4)3 for the Oxidation of Substituted Toluene to the Corresponding Benzaldehyde

A new industrial process for the electrolytic regeneration of Mn2(SO4)3 is presented in which:– a slurry of MnSO4/Mn2(SO4)3 in 55% H2SO4 is used as a carrier,– the electrolyte is purified with an optimum mode before electrogeneration, and–a new industrial electrochemical reactor is developed for an economical electrogeneration of Mn2(SO4)

Electrosynthesis of trimethylorthoformate on BDD electrodes

The anodic methoxylation of formaldehyde dimethylacetal (FADMA) to trimethylorthoformate (TMOF) in basic methanol was investigated on boron-doped diamond (BDD) electrodes. Cyclic voltammetry and preparative electrolysis have shown that FADMA is electrochemically inactive in the solvent stability region; nevertheless FADMA can be oxidized in the potential region of methanol oxidation. A reaction scheme involving intermediates of methanol oxidation (methoxy radicals) has been propose

The phenomenon of "permanent” electrochemical promotion of catalysis (P-EPOC)

The phenomenon of electrochemical promotion of catalysis (EPOC) is most often fully reversible. Subsequent to long-lasting polarization, however, the new steady-state open-circuit catalytic activity after current interruption may remain significantly higher than that before polarization. This phenomenon, discovered in our laboratory in the late 1990s and called permanent electrochemical promotion of catalysis (P-EPOC), has been observed on both oxide (IrO2, RuO2) and metal (Rh) catalysts. P-EPOC is out of the state-of-the-art model of reversible EPOC, which considers the gas-exposed catalyst surface as the unique location of charge storage via backspillover of electrochemically generated promoter species accompanied by their consumption in the catalytic reaction (‘sacrificial' promoter). Double step chronoamperometric and linear sweep voltammetric characterization of Pt catalyst deposited on YSZ solid electrolyte revealed the existence of a somewhat delayed oxygen storage occurring at the vicinity of the catalyst/electrolyte interface during prolonged anodic polarization. It is proposed that oxygen stored at this location, hidden for the reactant, and then released during relaxation was at the origin of P-EPOC on the Pt/YSZ catalyst observed in catalytic combustion of ethylene with oxygen. The effect of this ‘hidden' promoter on the catalytic reaction rate was found to be highly non-Faradai

Charge storage at the Pt/YSZ interface

The electrochemical behavior of Pt/YSZ electrodes in oxygen containing atmosphere at 450°C has been investigated by double-step chronoamperometry and programmed linear sweep cyclic voltammetry. The response of the O2(g),Pt/YSZ system in these experiments could be separated into a time dependent and a steady state contribution, the former being dominated by pseudocapacitive processes. It is proposed that Pt-O type species were stored via different processes at three different locations in the O2(g),Pt/YSZ system: (1) Build-up of a platinum oxide monolayer at the Pt/YSZ binary interface. (2) Formation of Pt-O species at the triple phase boundary and their spreading-out along the Pt/gas interface. (3) Growth of the platinum oxide layer from the binary Pt/YSZ interface toward the bulk of the platinum electrod

Solid electrochemical mass spectrometry (SEMS) for investigation of supported metal catalysts under high vacuum

A new experimental set-up, coupling electrochemistry and mass spectroscopic techniques, for the investigation of a solid electrochemical cell under high vacuum conditions (HV) is presented. Two configurations are realized allowing the investigation of both the electrochemical and electrocatalytical behavior of a thin Pt layer on yttria stabilized zirconia (YSZ). We can readily select the atmosphere down to 10−6 Pa partial pressure and determine the response of the system in less than 1s. Under HV conditions, YSZ appears electrochemically active and we have identified, in the cathodic potential domain, the reduction/oxidation process of zirconia and in the anodic domain, the platinum oxidation/reduction and the oxygen evolution reactions. In a catalytic active gas mixture, despite the Faradaic enhancement of the CO oxidation observed over Pt/YSZ during an anodic polarization, an intriguing sustainable enhanced Pt/YSZ catalyst activity is achieved after current interruptio

Electrochemical comparison of IrO2 prepared by anodic oxidation of pure iridium and IrO2 prepared by thermal decomposition of H2IrCl6 precursor solution

Surface redox activities, oxygen evolution reaction (OER), oxidation of formic acid (FA), and anodic stability were investigated and compared for IrO2 electrodes prepared by two techniques: the thermal decomposition of H2IrCl6 precursor (TDIROF) and the anodic oxidation of metallic iridium (AIROF). Surface redox activities involved on the AIROF were found to be much faster than those involved on the TDIROF. Concerning the oxygen evolution reaction, both films show a similar mechanism and specific electrocatalytic activities. The situation seems to be different for FA oxidation. In fact, on TDIROF, the oxidation of FA and the OER compete involving the same surface redox couple Ir(VI)/Ir(IV) contrary to FA oxidation on AIROF, where the Ir(V)/Ir(IV) surface redox couple is involved. Finally, electrode stability measurements have shown that contrary to TDIROF, which are very stable under anodic polarization, the AIROF are rapidly corroded under anodic treatment. This corrosion is enhanced even further in the presence of formic aci

Effects of carbonate on the electrolytic removal of ammonia and urea from urine with thermally prepared IrO2 electrodes

Recent studies have shown that electrolysis can be an efficient process for nitrogen removal from urine. These studies have been conducted with urea solutions or fresh urine, but urine collected in NoMix toilets and urinals has a substantially different composition, because bacteria hydrolyse urea quickly to ammonia and carbonate. In this study, we compared electrochemical removal of nitrogen from synthetic solutions of fresh and stored urine using IrO2 anodes. We could show that in fresh urine both ammonia and urea are efficiently eliminated, mainly through chlorine-mediated oxidation. However, in stored urine the presence of carbonate, arising from urea hydrolysis, leads to an inhibition of ammonia oxidation. We suggest two parallel mechanisms to explain this effect: the competition between chloride and carbonate oxidation at the anode and the competition between chlorate formation, enhanced by the buffering effect of carbonate, and ammonia oxidation for the consumption of active chlorine in the bulk. However, further experiments are needed to support the latter mechanism. In conclusion, this study highlights the negative consequences of the presence of carbonate in urine solutions, but also in other wastewaters, when subjected to an electrolytic treatment on IrO2 in alkaline medi