Search

The origin of the electrochemical promotion of catalysis (EPOC) was investigated via oxygen temperature-programmed desorption (O2-TPD) from a polycrystalline Pt film interfaced with YSZ. TPD experiments were carried out under operating conditions similar to those used for catalytic activity measurements. This study has clearly shown that an anodic current generates the migration of “backspillover” ionic oxygen species from YSZ toward the Pt surface. These ionic species act as promoters and enable the formation of weakly adsorbed oxygen species coming from the gas phase which are more reactive and thus responsible for the activity enhancement. The effect of polarization is to carry or to remove the promoting ionic species on the Pt surface. Therefore, electrochemical promotion of catalysis can be considered as an electrically controlled metal support interaction, where the support is an O2− conducting solid electrolyte. [ABSTRACT FROM AUTHOR]

Abstract: Porous Pt–YSZ composites were prepared by impregnation of a commercial YSZ powder by a platinic precursor (H2PtCl6) followed by isostatic pressing and sintering at 1000 °C. Two different contents of platinum were introduced, i.e., 1 and 5 wt.%. Electrical and electrochemical properties of these samples were investigated between 350 and 600 °C by using impedance spectroscopy under various atmospheres including He, O2/He, and C3H8/O2/He. The catalytic activity of these samples for the propane combustion has also been investigated in the same temperature range. Dispersed platinum particles in YSZ at the surface of YSZ grains acted as an additional blocker of the ionic conductivity. This additional grain boundary was ascribed to the formation of platinum oxides or of a layer of chemisorbed oxygen on dispersed Pt particles. The interfacial process seemed to be characterized by a predominant low-frequency contribution, whatever the temperature, the Pt loading, and the atmosphere. This contribution was interpreted in terms of an oxygen concentration polarization. It was found to vary in the same way as the grain boundary process. The catalytic performances of porous Pt–YSZ composites for propane combustion were higher than those of Pt films deposited on a dense YSZ pellet. Unfortunately, we did not evidence any electrochemical promotion of the catalytic activity in our operating conditions. [Copyright &y& Elsevier]

Abstract: The development of electrochemical promotion necessitates new solid electrolytes with improved ionic conduction at lower temperatures. Among them, Na Super Ionic Conductor (NaSICon), i.e. Na3Zr2Si2PO12, is a promising Na+ conducting electrolyte. The Pt/NaSICon system was evaluated for the electrochemical promotion of propene combustion both with large excess of oxygen (for volatile organic contaminants, VOCs, abatement) and near the stoichiometry (for energy production). [Copyright &y& Elsevier]

The non-faradaic electrochemical modification of catalytic activity (NEMCA) was investigated in selective catalytic reduction (SCR) of NO by propene on Pt films deposited on NASICON, a Na+ conducting solid electrolyte. This study was carried out under lean-burn conditions. In such a system, electrochemical promotion is shown to strongly enhance both the catalytic activity and the selectivity to N2. Such an improvement can be obtained using low overpotentials, applying −100 mV to the Pt catalyst-electrode enhances the selectivity to N2 from 41 to 61%. The use of NASICON allows work to be done at quite low temperatures (about 300 °C) compatible with the treatment of automotive exhausts. [Copyright &y& Elsevier]

Abstract: A honeycomb monolith of YSZ (yttria stabilized zirconia) was used, for the first time, as a solid electrolyte to perform electrochemical promotion of the deep oxidation of methane. The goal of this study was to validate the concept of Electrochemical Promotion of Catalysis (EPOC) by using Pd particles dispersed on the channels surface of a YSZ dense honeycomb monolith. The Pd catalyst was an effective material as methane conversion reached 20% at about 320°C. The catalytic properties of the monolithic electrochemical catalyst were investigated upon electrical polarization at 400°C. Non faradaic effects were observed both under positive and negative polarizations with a maximum of the faradaic efficiency of 47. [Copyright &y& Elsevier]

Abstract: Pt nanoparticles were dispersed in the porosity of a LSCF-GDC electrode interfaced on a dense GDC membrane. Small positive polarizations can strongly increase (38%-enhancement) the catalytic performance of Pt nanoparticles for propane deep oxidation at low temperatures with apparent Faradaic efficiency values up to 85. This study clearly demonstrates that the catalytic activity of metallic nanoparticles dispersed in the porosity of a mixed ionic electronic conducting electrode can be strongly electropromoted. [Copyright &y& Elsevier]

Abstract: The effect of electrochemical promotion of catalysis was investigated for the water–gas shift reaction over porous Pt catalyst electrodes interfaced with 8%mol Yttria-stabilized Zirconia. A fuel cell type electrochemical reactor was used at temperatures from 300°C to 400°C, under ratio values from 2.85 to 31. A negative order dependence of the catalytic reaction rate on P CO and a positive one on was found under open-circuit and polarization conditions. Positive potential application (+2.5V), i.e., O2− supply to the catalyst surface, causes a small decrease in the catalytic reaction rate, while negative potential application (−1.5V) results in a pronounced rate increase, up to 200%, with apparent faradaic efficiency values up to 110. The rate increase obtained with negative polarization can be attributed to the weakening of the Pt–CO bond strength but also, to the increase in surface concentration of oxygen ion vacancies near the Pt-gas-support three-phase boundaries necessary for water dissociation. [Copyright &y& Elsevier]

Abstract: The NOx abatement efficiency of an electrochemical NOxTRAP catalyst Pt–Ba/YSZ was investigated at 500°C with different oxygen partial pressures in the storage phase. Cathodic polarization was found to promote the NOx storage capacity even under lean-burn conditions. The duration until full NOx storage was drastically increased by ~80s in the presence of 6% of oxygen. During regeneration phases, NO electrochemical reduction occurs and can remove ~10% of NOx. Electrochemical activation of the NOx storage capacity was linked with the generation of oxygen vacancies on the YSZ surface induced by negative polarization. [Copyright &y& Elsevier]

Abstract: We have conducted a study on the preferential CO oxidation in hydrogen-rich stream (PROX) coupling catalysis and electrochemistry, i.e., by using an electrochemical catalyst (Pt/K-βAl2O3). It was shown that PROX activity and selectivity of a Pt catalyst can be strongly enhanced by electrochemical pumping of potassium ions from the solid electrolyte support. The observed promotional effect was attributed to a decrease in the CO and H2 chemisorption and to an increase in the O2 chemisorption which led to a relative increase in the CO oxidation reaction vs. the H2 oxidation. The electrochemical promotion allowed decreasing the operating temperature window of the Pt catalyst and attenuating the inhibiting effect of H2 on both catalytic activity and selectivity. In addition some of the catalytic results were supported by in situ electrochemical characterization techniques such as cyclic voltammetry and open circuit potential measurements. Finally a very interesting permanent NEMCA effect was shown. It demonstrated the high stability of the formed promoting species and the potential for a further development of NEMCA effect in PROX real configurations. [Copyright &y& Elsevier]

Abstract: This study reports the possibility of working in NO x storage/reduction process under fixed lean burn reaction conditions by using a tubular Pt/K-βAl2O3/Pt electrochemical catalyst. This system allows to electrochemically trap NO x as potassium nitrates in the film polarized negatively, and simultaneously to regenerate from storage compounds the opposite catalyst film (polarized positively), both working under the same lean burn atmosphere. In addition, it has been shown that the system is able to store CO2 as potassium carbonates. The obtained results have been supported by linear sweep voltammetry carried out under different reaction conditions which has provided useful information about the different competitive trapping processes. [Copyright &y& Elsevier]

Abstract: A novel technique was explored for the preparation of a Pt-C catalyst-working electrode film of low particle size (15nm), which can be electrochemically promoted at low temperatures. A Pt/C commercial catalyst powder was used as a precursor of the catalyst film on the solid electrolyte cell. The removal at low temperatures of the initial C matrix on the sprayed catalyst ink, allows to have a Pt/C catalyst-working electrode layer with a suitable morphology, thermal stability and electronic conductivity as supported by several characterization techniques (TGA, XRD, SEM, C analysis and electrical resistance measurements). The Pt-C catalyst film was successfully electrochemically promoted (by potassium ions) for the simultaneous CO and C3H6 oxidation reactions under a gas atmosphere which simulates an exhaust stream coming from a gasoline engine. The obtained higher catalytic activity, in comparison with previous studies and the occurrence of an oscillatory phenomenon, which can be electrochemically modified, are interesting results for this new Pt-C based electrochemical catalyst. [Copyright &y& Elsevier]