Charge storage at Pt/YSZ interface as the origin of `permanent´ electrochemical promotion of catalysis

Tuning of the catalytic reaction rate by electric polarization of the interface between an electron conducting catalyst and an ion conducting support, called electrochemical promotion of catalysis (EPOC), is most often fully reversible. Its state-of-the-art model regards the gas-exposed catalyst surface as the unique location of charge storage via backspillover of electrochemically generated species, responsible for promotion. After long-lasting anodic polarization, a permanent effect (P-EPOC) was observed in ethylene combustion with oxygen over Pt/YSZ catalyst. Double step chronoamperometric and linear sweep voltammetric analysis revealed delayed oxygen storage, located presumably at the vicinity of the catalyst/electrolyte interface. It is proposed that oxygen stored at this location, hence hidden for the reactants and then released during relaxation, was at the origin of the observed P-EPOC. The effect of this ´hidden´ promoter on the catalytic reaction rate was found to be highly non Faradaic

INVESTIGATION OF HPLC PACKINGS BY LIQUID MIXTURE ADSORPTION

The adsorption isotherms of methanol (1) - benzene (2) and benzene (1) - n-heptane (2) mixtures on four different HPLC silica gel were recorded to determine the types of the liquid mixture adsorption isotherms. Based on the experimental results, qualitative statements could be made regarding the relationship between chromatographic and mixture adsorption properties

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 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

Estimation of the effectiveness factor of an outer-sphere redox couple (Fe3+/Fe2+) using rotating disk Ti/IrO2 electrodes of different loading

The effectiveness factor; E f , defined as the fraction of the surface that participates effectively in a given reaction, is an important parameter when operating three-dimensional (3D) electrodes. The rotating disk electrode (RDE) technique with the Fe3+/Fe2+ redox couple as a probe reaction has been used for the evaluation of the effectiveness factor of 3D Ti/IrO2 electrodes with different IrO2 loading. For this purpose, steady-state polarization measurements using Ti/IrO2 rotating disk electrodes in 0.5M Fe3+/Fe2+ in 1M HCl were carried out under well-defined hydrodynamic conditions. The low-field approximation relation has been used for the estimation of the exchange current densities j 0, of the Fe3+/Fe2+ redox couple. It was found for this redox couple that the effectiveness factor is very low (<2%) and essentially the 2D electrode surface area works effectively in the steady-state polarization measurement