Electrochemical Promotion Of Catalysis Research Articles

Electrochemical Promotion of Catalysis

Electrochemical Promotion of Catalysis (EPOC), also called Non-Faradaic Electrochemical Modification of Catalytic Activity (NEMCA), is a promising concept for boosting catalytic processes and advancing the frontiers of catalysis [1]. This innovative field aims to modify in-operando both the activity and the selectivity of catalysts, in a reversible and controlled manner. EPOC utilizes solid electrolyte materials (ionically conducting ceramics) as catalytic carriers. Ions contained in these electrolytes are electrochemically supplied to the catalyst surface and act as promoting agents to modify the catalyst electronic properties in order to achieve optimal catalytic performance. It thus provides a unique means of varying promoter levels at the metal surface under reaction conditions by simply changing the potential of the catalyst film. The main advantage of EPOC is that the electrochemical activation magnitude is much higher than that predicted by Faraday’s law. Therefore, EPOC requires low currents or potentials. Moreover, promoting species such as O2- cannot be formed via gaseous adsorption and cannot be easily dosed by chemical ways. The EPOC technology consists in the implementation of catalysis in an electrochemical cell by using electrochemical catalysts which consist of a catalytic layer interfaced on an ionically conducting ceramic support. The latter serves as an electrically controlled source or sink of ionic promoter species that activate and modulate the behavior of the catalytic surface. Figure 1a displays a typical EPOC reactor. The catalytic layer, typically 40 nm to 10 mm thick, is deposited on a dense solid electrolyte membrane (Figure 1a). This catalytic layer must be electronic conductor to allow the polarization. Therefore, the catalyst is also an electrode and is then named catalyst-electrode. A counter-electrode and a reference electrode, both catalytically inert, are deposited on the other side of the membrane (Figure 1a). An electrical current density (1-500 µA/cm2) or potential (±2 V) is applied between the catalyst and the counter electrode. The reactants are co-fed over the porous electrochemical catalytic layer. Figure 1b displays a typical example of an EPOC experiment for the propane deep oxidation. The electrochemical catalyst was composed of a Pt thin film deposited by Physical Vapor Deposition (PVD) on a dense membrane of Yttria-Stabilized Zirconia (YSZ), an O2- ionic conductor. A positive current (from +10 up to +500µA) can strongly increase the propane conversion with a non-Faradaic manner, since the activation is up to 300 times higher than that predicted by the Faraday’s law through the electrochemical oxidation of propane. This latter reaction will be used to highlight recent advances of the EPOC technology both for the understanding (18O2 isotopic exchange) of the process and its applications via the proof of concept of electropromoted nanoparticles. [1] P. Vernoux, L. Lizarraga, M.N. Tsampas, F.M. Sapountzi, A. De Lucas-Consuegra, J.L. Valverde, S. Souentie, C.G. Vayenas, D. Tsiplakides, S. Balomenou, E.A. Baranova, Chem. Rev. 113 (2013) 8192. Figure 1

Investigation of Heterogeneous Catalysts by an Electrochemical Method: Ceria and Titania-Supported Iridium Nanoparticles for Ethylene Oxidation

Electrochemical promotion of catalysis (EPOC) is a well-established phenomenon in heterogeneous catalysis for enhancing catalytic activity through the application of a small electrical stimulus between the catalyst-working and counter electrode deposited on a solid electrolyte (e.g., yttria-stabilized zirconia (YSZ))1. This electrical stimulus causes the backspillover of ionic species, in this case O2-, from the solid electrolyte to the catalyst surface. A resulting change in catalytic activity is due to the modification of the electronic properties of the catalyst. The extent to which these properties can be modified depends on several factors, such as temperature, type of catalyst material and solid electrolyte, catalyst morphology, e.g., particle size and dispersion, ionic conductivity, and gas phase composition 2,3. EPOC is an interfacial phenomenon where two-phase boundaries, i.e., catalyst/gas and catalyst/solid electrolyte, as well as the three-phase boundary (tpb), i.e., electrolyte/catalyst/gas phase play a key role in the reaction. Recent EPOC studies have shown catalytic enhancement of highly dispersed, nano-structured catalysts through the use of mixed ionic electronic conducting (MIEC) materials, i.e., CeO2 4 and TiO2 5, which are in contact with the YSZ solid-electrolyte. This approach allows for considerable reduction of the mass of metal catalyst required, while maintaining the electrical conductivity of the working electrode needed to complete the electrochemical cell 6,7. Both CeO2 and TiO2 are considered reducible supports. More specifically, CeO2, due to its non-stoichiometry, has the ability to undergo conversion between Ce4+ and Ce3+ quite easily 7. TiO2 has also been known to strongly influence the performance of the supported metal catalysts due to this reducibility 8. These properties make the use of ceria- and titania-containing catalysts of interest for many catalytic applications. This study investigates the complete oxidation of ethylene over low particle size (1.1 nm) ruthenium and (1.0 nm) iridium nanoparticles supported on CeO2 and TiO2 under open (o.c.) and closed circuit conditions. Furthermore, detailed electrochemical characterization of the Ir- and Ru- based catalysts was carried out using a steady-state polarization technique. The results obtained were correlated with their o.c. catalytic performance. The discussion of this study includes the effect of temperature and applied potential on the catalytic activity of the supported and freestanding Ir and Ru catalysts. Ru and Ir nanoparticles, synthesized using a polyol reduction method, were supported on CeO2 and TiO2 resulting in a 1 wt% catalyst loading (RuNPs/CeO2, IrNPs/CeO2, RuNPs/TiO2 and IrNPs/TiO2). The supported and free-standing nanoparticle catalysts were deposited on one side of a YSZ solid electrolyte disk in order to apply polarization 4. Gold counter and reference electrodes were applied on the opposite side of YSZ disk 9. Figure 1 shows representative polarization curves of the Ir/CeO2 catalyst at various temperatures. Positive current density (i) is due to electrochemical oxidation of ethylene and oxygen evolution at the tpb, whereas anodic current density is due to O2 electro-reduction. As can be seen, the rate of both positive and negative current densities (i) increases with temperature, indicating an increase in the reaction rates at the tpb as a result of an increase in electrolyte conductivity. i was also found to increase from 1.26, 3.5 to 29.5 µA.cm-2 for 350, 375 and 400 oC, respectively. As a result, this indicates that as temperature is increased, there is more available O2- at the tpb. A combination of open circuit catalytic and electrochemical measurements was used to evaluate and understand the catalytic performance of highly-dispersed Ru- and Ir-based, free-standing, and CeO2 and TiO2-supported catalysts with regards to the effect of O2- ions from the support. The presence of CeO2 and TiO2 was shown to play a significant role in enhancing the catalytic activity of Ru and Ir nanoparticles. Acknowledgment The financial support from Natural Science and Engineering Research Council (NSERC) is acknowledged.

Electrochemically Driven Gas Phase Ethylene and CO Oxidation on Pt/Yttria-Stabilized Zirconia Catalysts

Solid electrolytes such as yttria stabilized zirconia (YSZ) and doped-ceria (Sm-CeO2 or Gd-CeO2) are widely used in the fuel cells, sensors and in heterogeneous catalysis, particularly in electrochemical promotion of catalysis (EPOC) [1, 2]. The bulk ionic O2- conductivity of YSZ is caused by the presence of oxygen vacancies and becomes significant above 600 °C. Several recent studies showed that YSZ can finely disperse and stabilize nanoparticles and strongly enhance the catalytic activity of nanostructured catalysts through the action of the thermally induced O2-promoters [2], which makes it very promising support material in heterogeneous catalysis [1-4]. Recently [3,4], we reported the oxidation of CO and ethylene over Pt nanoparticles (NPs) with the average size of 2.5 ± 0.5 nm deposited on ionic and mixed ionic-electronic conductors (MIEC) supports: YSZ, ceria (CeO2) and samarium doped-ceria (SDC) in the absence of oxygen in the gas feed. The full conversion of 909 ppm of CO and C2H4 by reaction with lattice O2- from the conductive ceramic supports was achieved in the temperature range of 120–240 °C depending on the support. The conversion was observed already at temperature as low as 70 °C indicating that surface O2- is an active reactant, because bulk ionic conductivity of YSZ, ceria and doped-ceria is insignificant below 350 °C. The proposed redox mechanism of CO and C2H4 oxidation by O2- involves formation of local nano-galvanic cells at the three-phase boundary (tpb), that is, Pt NPs/conducting ceramic support/gas phase, where anodic and cathodic processes occur simultaneously but separated in space. The anodic reaction is CO or C2H4 electro-oxidation by oxygen ions from YSZ and/or carbon oxidation that can cover Pt surface during CO and C2H4 oxidation. Whereas, the cathodic reaction is the partial surface reduction of zirconia or ceria at the three-phase boundary (tpb). In the present work, we present the Pt particle size effect on the oxidation of CO and ethylene in the absence of O2 in the gas feed [4]. NPs of Pt with four average particle sizes, 1.9, 3.0, 4.4 and 6.7nm, were synthesized using the polyol method and ethylene glycol as a reducing and stabilizing agent. Scanning transmission electron microscopy (STEM) coupled with energy-dispersed X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) were used to evaluate Pt/YSZ properties. Furthermore, CO and ethylene oxidation in the presence of 3.5 kPa oxygen is studied and compared with the catalytic activity without O2 in the gas phase. The catalytic measurements in the absence of gaseous O2 revealed a strong dependence of CO and C2H4 conversion on the mean Pt particle size. The highest intrinsic rates and turnover frequency were found for Pt NPs having the smallest size at the lowest temperature, which are also characterized by the lowest activation energy. The largest Pt NPs (6.7 nm) do not show any catalytic activity up to 400 °C for both reactions. Figure 1 shows the effect of Pt particle size on CO electro-oxidation in the absence of O2. The observed particle size effect was attributed to (i) the larger number of nano-galvanic cells formed by the smaller Pt NPs, as was confirmed by the length of tpb estimated for each catalyst; (ii) the higher electronic interaction between the smallest Pt and YSZ (i.e., shorter charge transfer distances). XPS measurements revealed that the deposition of platinum NPs causes a change in the chemical environment of Y and Zr atoms with a change in the relative intensities of the O1s components attributed to the ‘active’ oxygen species (chemisorbed oxygen, OH- groups). In addition, the Pt4f peak shows a BEs downshift when compared to the platinum foil indicating a charge transfer from YSZ to Pt. In conclusion, in the absence of oxygen in the gas feed, the oxidation reactions occur via nano-galvanic cell mechanism, where CO and ethylene are electro-oxidized at tpb by O2- from YSZ and zirconia undergoes partial surface reduction. In the presence of oxygen, the mechanism is different and in addition to electrochemical reactions at tpb, the backspillover of promoting O2- species from YSZ to Pt surface takes place simulatneously with the catalytic oxidation of CO and C2H4 by molecular O2. [1] P. Vernoux, L. Lizarraga, M.N. Tsampas, F.M. Sapountzi, A. De Lucas-Consuegra, J.-L. Valverde, S. Souentie, C.G. Vayenas, D. Tsiplakides, S. Balomenou, E.A. Baranova, Chem. Rev. 113 (2013) 8192. [2] P. Vernoux, M. Guth, X. Li, Electrochem. Solid-State Lett. 12 (2009) E9. [3] R.J. Isaifan, E.A. Baranova, Electrochem. Commun. 27 (2013) 164. [4] R. J. Isaifan, S. Ntais, M. Couillard, E.A. Baranova, J. Catal. 324 (2015) 32. Figure 1

The role of ceria in LSM-GDC composite cathode for electrochemical reduction of nitric oxide

Electrochemical reduction of nitric oxide (NO) in a solid state cell reactor (SSCR) is conducted at intermediate-temperature (500–550°C) using three (La0.85Sr0.15)0.9MnO3 (LSM)- Ce0.8Gd0.2O2 (GDC) composite cathodes (LSM:GDC=3:1, 2:2 and 1:3wt.%, denoted respectively as LSM-GDC31, LSM-GDC22, and LSM-GDC13). GDC-free LSM cathode is compared as blank sample. The NO conversion and current generation are evaluated. In the absence of oxygen, NO apparent conversion at the closed circuit state at 550°C is almost 60%, and the corresponding current density at 0.3V is 17mAcm−2 with LSM-GDC22. NO apparent conversion and current produced are greatly enhanced up to 80% and 66.7mAcm−2 in 2000ppm NO-10% O2 at 500°C due to the electrochemical promotion of catalysis (EPOC). The combined electrochemical impedance spectra, in-situ diffuse reflectance infrared fourier transform spectra, scanning electron microscope and Raman spectra are applied and prove that the oxygen-storage properties of ceria improves the selectivity towards NO electrochemical reduction in oxygen-rich atmosphere. In addition, the introduction of GDC enhances the electrode activities due to the increased three phase boundary (TPB) for oxygen reduction reaction.

A Review of Surface Analysis Techniques for the Investigation of the Phenomenon of Electrochemical Promotion of Catalysis with Alkaline Ionic Conductors

Electrochemical Promotion of Catalysis (EPOC) with alkali ionic conductors has been widely studied in literature due to its operational advantages vs. alkali classical promotion. This phenomenon allows to electrochemically control the alkali promoter coverage on a catalyst surface in the course of the catalytic reaction. Along the study of this phenomenon, a large variety of in situ and ex situ surface analysis techniques have been used to investigate the origin and mechanism of this kind of promotion. In this review, we analyze the most important contributions made on this field which have clearly evidenced the presence of adsorbed alkali surface species on the catalyst films deposited on alkaline solid electrolyte materials during EPOC experiments. Hence, the use of different surface analysis techniques such as scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning photoelectron microscopy (SPEM), or scanning tunneling microscopy (STM), led to a better understanding of the alkali promoting effect, and served to confirm the theory of electrochemical promotion on this kind of catalytic systems. Given the functional similarities between alkali electrochemical and chemical promotion, this review aims to bring closer this phenomenon to the catalysis scientific community.

ChemInform Abstract: Applications of Yttria Stabilized Zirconia (YSZ) in Catalysis

AbstractReview: 82 refs.

Applications of the Electrochemical Promotion of Catalysis in Methanol Conversion Processes

In this work, three possible applications of the phenomenon of electrochemical promotion of catalysis (EPOC) are demonstrated for methanol conversion processes: enhancement of the catalytic activity, modification of the catalytic selectivity and partial oxidation of the catalyst. For that purpose, a Ni catalyst film prepared via a physical vapour deposition technique was electrochemically promoted by K+ in different methanol conversion reactions for hydrogen production. Under methanol decomposition and steam reforming conditions, application of certain negative overpotentials and subsequent back-spillover of K+ promoter ions led to an increase in the Ni catalytic activity through electrophilic EPOC behaviour. On the other hand, under methanol partial oxidation conditions, the K+ ions caused a decrease in the catalytic selectivity toward H2 and CO while they favoured selectivity toward CO2 and H2CO. This effect was explained by an increase in the Ni oxidation state due to O2 activation induced by K+ ions, as shown by post-reaction X-ray diffraction analysis. All the potassium-induced effects were reversible between negative and positive polarizations. This shows the different possibilities of the EPOC phenomena on nickel catalysts in heterogeneous catalysis. Specifically, the in situ modification of catalytic activity and selectivity in methanol conversion reactions would be interesting for on-board hydrogen production processes, where the attenuation of catalyst deactivation and the control of metal oxidation state would also play a key role.

Mechanistic modeling of NO electrochemical reduction in a micro-tubular cell: Effects of CO2/H2O components and electrochemical promotion

A two dimensional model coupling the mass balance and momentum balance processes was developed for a micro-tubular electrochemical cell for NOx reduction. The effect of electrochemical promotion of catalysis (EPOC) on NO decomposition was considered in the kinetic model. The cell was consisted of La0.6Sr0.4Co0.95Cu0.05O3−δ (LSCC)–Ce0.9Gd0.1O1.95 (GDC) catalytic electrode, YSZ electrolyte, Ni–YSZ anode. The model was validated by comparing the simulation results with experimental data from the literature. Parametric simulations were conducted to investigate the effects of CO2 and H2O on the NO conversion performance. Results revealed that the presence of CO2 and H2O are beneficial to the NO reduction. The improvement by H2O was stronger than that by CO2. The effects of temperature on NO conversion were investigated. The distributions of the gas compositions along the channel and catalytic electrode were discussed to analyze the inner diffusion and reaction processes. Gas flow rate was another influential factor and low gas velocity was advantageous for the NOx reduction reaction kinetics.

ChemInform Abstract: Electron Donation‐Backdonation and the Rules of Catalytic Promotion

AbstractReview: 108 refs.

Electron Donation–Backdonation and the Rules of Catalytic Promotion

The rules of classical and electrochemical promotion of catalysis, which allow for the prediction of the effect of electropositive and electronegative promoters on catalytic rate and selectivity on the basis of the catalytic reaction kinetics, are compared with experiment for all relevant catalytic studies during the last two decades and are used to show that the rate versus catalyst work function dependence always parallels the rate versus electron donor reactant dependence. This generalized rule is rationalized both by considering the interaction of the electric field in the effective double layer at the metal catalyst–gas interface with the electric dipoles of the adsorbed reactants and also by considering the electron donation–backdonation between the adsorbed reactants and the catalyst. This generalized promotional rule allows for promoter selection on the basis of the reaction kinetics.

Role of Lattice Oxygen in the Propane Combustion Over Pt/Yttria-Stabilized Zirconia : Isotopic Studies

Nanoparticles of platinum were dispersed on an oxygen ionically conducting support, Yttria-Stabilized Zirconia (YSZ), on non-doped zirconia and on silica. The role of the support oxygen lattice in the mechanism of propane deep oxidation was investigated by using 18O2 Temperature-Programmed Desorption, catalytic activity measurements using isotopic oxygen, and isotopic exchange experiments. The results emphasize that the propane combustion mechanism on Pt/YSZ presents a different pathway compared with that involved on Pt/SiO2 and Pt/ZrO2 because, propane is preferentially oxidized by lattice YSZ oxygen species on Pt/YSZ. Strong Pt nanoparticles/YSZ interactions generate a promoted state similar to that observed on polarizations during electrochemical promotion of catalysis.

Improved Catalytic Reactor for the Electrochemical Promotion of Highly Dispersed Ru Nanoparticles with CeO2 Support

Electrochemical promotion of catalysis (EPOC) is a promising method for enhancing catalytic activity through the application of a small electrical stimulus between the catalyst-working and counter electrode deposited on a solid electrolyte 1. The electronic properties of the catalyst can be modified resulting in a change in catalytic activity. In the case of yttria-stabilized zirconia (YSZ) as a solid electrolyte, the addition or removal of O2- species on the catalyst surface can be controlled in situ depending on the specified reaction conditions. Fully reversible and “permanent” or “persistent” EPOC has been reported for more than 70 various catalytic systems 1. In reversible EPOC experiments, the reaction rate returns to its initial value after the electrical stimulus is interrupted. For permanent EPOC (P-EPOC), the reaction rate remains at a higher value than the initial open circuit value 2,3. Despite receiving much attention, this phenomenon has not yet reached commercial application. One of the main technical factors preventing such development is the use of thick film catalysts with low surface areas and high material costs 4.Ceria, CeO2, is a mixed ionic-electronic conducting (MIEC) material that conducts O2- due to oxygen vacancies in the crystallographic structure in addition to conducting electrons at elevated temperatures. Furthermore, due to its non-stoichiometry, CeO2 has the ability to undergo conversion between Ce4+ and Ce3+ quite easily 5. These properties make the use of ceria-containing catalysts of interest for many applications. In heterogeneous catalysis, Pt group metals deposited on CeO2 show a metal-support interaction (MSI) effect associated with charge transfer between the two solids that are in contact. In EPOC studies, using a MIEC can also ensure electrical connectivity between highly dispersed nanoparticle catalysts 6.In this study, electrochemical enhancement of catalytic activity of a low particle size (1.9 nm) ruthenium nanoparticles catalyst for ethylene oxidation was investigated. Ru nanoparticles, synthesized using a modified polyol reduction method, were supported on CeO2 resulting in a 1 wt% Ru loading (RuNPs/CeO2) (i.e., typical in heterogeneous catalysis studies).The highly dispersed RuNPs/CeO2 catalyst powder was supported on a YSZ solid electrolyte in order to apply polarization. The discussion of this study includes the effect of the partial pressure of ethylene with constant partial pressure of oxygen, temperature, and applied positive and negative current on the catalytic activity of the RuNPs/CeO2 catalyst as well as the role of the cerium redox state in the observed persistent effect. In addition, the catalytic properties of the RuNPs/CeO2 catalyst is compared to that of larger Ru particles supported on CeO2 (TD-Ru/CeO2) (same metal loading) and blank CeO2, both supported on a YSZ solid electrolyte.Characterizations of the catalysts were carried out using TEM and SEM. In addition, XPS analysis was done for the RuNPs/CeO2catalyst as prepared and “spent” (after the reaction). Overall, it was observed that only the RuNPs/CeO2 catalyst could be catalytically enhanced, showing a pronounced enhancement (up to 2.5 times) of the catalytic rate for negative polarization. The opposite effect was observed for positive polarization. This effect of both positive and negative polarization is illustrated by Fig.1. Fig. 1.Transient effect of current application for C2H4 oxidation over Ru/CeO2 on YSZ electrolyte at 350°C for an applied current of -2 μA for 4 hours and +2 μA for 6 hours (0.012 kPa C2H4).Apparent Faradaic efficiencies up to 100 were also determined, indicating a non-Faradaic effect. In addition, a persistent effect was observed, showing stability up to 16 hours after current interruption. The modification of the cerium oxidation state (i.e., reduction from Ce4+ to Ce3+) is proposed to enhancethe catalytic performance of the Ru nanoparticles. This is due to the presence of more oxygen vacancies in the ceria interlayer causing a stronger metal-support interaction.These results demonstrate the feasibility of in-situ modification of the metal support-interaction between Ru nanoparticles and CeO2catalytic support.

Investigation of the Electrochemical Promotion of Catalysis origins on electrochemical catalysts with oxygen ion conductive supports: Isotopic labeling mechanistic studies

The EPOC concept upon positive polarization of Pt/YSZ has been investigated with plethora of techniques. It is attributed to the presence of O δ − species with the compensating charge in the metal catalyst. However, the origin of EPOC in the case of negative polarization is not yet well established. This study gives, for the first time, an insight of this mechanism. Isotopical labelling studies were conducted on a Pt/YSZ(O 2 − ) electrochemical catalyst for investigating the origins of Electrochemical Promotion of Catalysis (EPOC) using propane combustion as a model reaction. • Isotopic labeling studies carried out to investigate EPOC mechanism on Pt/YSZ. • Negative current application only affects the region near the tpb. • Positive current application causes an effect in the overall gas/solid interface. • Significant production of C 16 O 18 O is attributed to surface oxygen exchange at tpb. • Surface oxygen exchange seems to generate active oxygen species.

ChemInform Abstract: Promotion, Electrochemical Promotion and Metal‐Support Interactions: Their Common Features

AbstractReview: 95 refs.

Promotion, Electrochemical Promotion and Metal–Support Interactions: Their Common Features

The catalytic activity and selectivity of metals can be significantly modified via the action of promoters, via the interaction with the support (metal–support interactions, MSI) or, when the support has some ionic mobility, via the application of electrical potential (±2 V) between the catalyst and the support, a phenomenon known as electrochemical promotion of catalysis (EPOC). During the last two decades it is becoming increasingly obvious that chemical (classical) promotion, EPOC and MSI are, via the action of spillover of promoting species, very closely related, to the point that the differences between them are only operational and not functional. This impressive similarity is apparently closely related to the gradual substitution of classical insulating supports (SiO2, Al2O3) with ionically conducting or mixed ionically-electronically conducting ceramic supports in many commercial catalysts during the last 25 years. In this perspective we focus on a few key experiments which have demonstrated this striking similarity and we also discuss some recent advances on the electrochemical promotion of finely dispersed catalysts which appear to be of significant practical interest. Comparison of MSI and Electrochemical Promotion for C2H4 oxidation on Rh

Electrochemical promotion of catalysis (EPOC): Perspectives for application to gas emissions treatment

Heterogeneous Catalysis and Electrocatalysis can be used very effectively on air pollution control. Air emissions coming either from mobile sources or from stationary sources, including volatile organic emissions, nitrogen oxides, hydrocarbons and carbon monoxide could be well converted to harmless non-pollutants at reasonable temperatures with cost-effective systems utilizing heterogeneous catalysis and suitable catalysts. Some of the disadvantages of conventional heterogeneous catalysts are the high production cost (since most of them are metal supported catalysts), the short life time (due to the catalyst deactivation) and the weakness to control their activity during the catalytic process. A new phenomenon of Solid State Electrochemistry called Electrochemical Promotion of Catalysis (EPOC) combined with classical heterogeneous catalysis could be applied in order to overcome some of the above problems. In this paper we are trying to show with characteristic examples how EPOC could be useful in environmentally important reactions (oxidations, reductions, etc). The results show that EPOC reveals great perspectives in environmental issues and especially in gas emissions treatment technology. The utilization of EPOC could be really useful since we can increase the catalytic activity, alter the selectivity to the desirable products and simultaneous control the reaction rate during a given electrocatalytic process.

The role of sodium surface species on electrochemical promotion of catalysis in a Pt/YSZ system: The case of ethylene oxidation

The role of sodium addition as foreign (impurity) species on the electrochemical promotion of ethylene oxidation in a Pt/YSZ system was investigated. It was found that the presence of sodium surface species on the catalyst surface can significantly affect its catalytic and electrocatalytic properties, but there is no clear evidence at this stage that such species are necessary for the observation of EPOC. Under negative polarisation, low coverage sodium was found to have a pronounced effect on the electrochemical promotion of ethylene oxidation as an electronic promoter. The reaction changed behaviour from electrophilic at low sodium coverage (0.11%) and low to intermediate oxygen partial pressure (pO2⩽3.0kPa) to electrophobic at high sodium coverage (65%) and under high oxygen partial pressures (pO2=8.0kPa). In between the two sets of conditions, the reaction showed volcano-type behaviour depending on the coverage of sodium and gas-phase oxygen partial pressure.

Enhancing the combustion of natural gas by electrochemical promotion of catalysis

In this work, the electrochemically promoted combustion of natural gas over porous Pd catalyst–electrodes interfaced with yttria-stabilized zirconia (YSZ) is reported for the first time. A rate enhancement up to 250% on the CO2 formation upon positive polarizations was obtained at temperatures as low as 340°C. Different electropromoted behaviors depending on the reactants consumptions (methane, ethane and propane) were explained with regard to the bond strength between these reactants and the catalyst.

Electrochemical promotion of a Pt catalyst supported on La0.6Sr0.4Co0.2Fe0.8O3 − δ hollow fibre membranes

The use of wireless electrochemical promotion of catalysis (EPOC) of a Pt catalyst supported on a mixed ionic electronic conducting hollow fibre membranes is investigated. This reactor configuration offers high surface areas per unit volume and is ideally suited for scaled-up applications. The MIEC membrane used is the La0.6Sr0.4Co0.2Fe0.8O3 perovskite (LSCF) with a Pt catalyst film deposited on the outer surface of the LSCF membrane. Experimental results showed that after initial catalyst deactivation (in the absence of an oxygen chemical potential difference across the membrane) the catalytic rate can be enhanced by using an oxygen sweep and wireless EPOC can be used for the in situ regeneration of a deactivated catalyst.

Electrochemical promotion of catalysis with highly dispersed Pt nanoparticles

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.