ORALS

SESSION: PhysicalThuPM1-R10	Vayenas International Symposium on Physical Chemistry and its applications for sustainable development
Thu Oct, 24 2019 / Room: Aphrodite B (100/Gr. F)
Session Chairs: Angelos Efstathiou; Alexandros Katsaounis; Session Monitor: TBA

14:50: [PhysicalThuPM107] Keynote
The Role of the Promoting Ionic Species in Electrochemical Promotion and in Metal-Support Interactions. The Case of CO<sub>2</sub> Hydrogenation on Ru Based Catalysts
Dimitrios Grigoriou¹ ; Dimitrios Zagoraios¹ ; Alexandros Katsaounis² ; Constantinos Vayenas¹ ; ¹University of Patras, Patras, Greece; ²Department of Chemical Engineering, University of Patras, Patras, Greece;
Paper Id: 105 [Abstract]

The reaction of CO₂ hydrogenation is of high environmental interest since it allows for the transformation of the logistically challenging H₂, gained from renewable sources, to the much more manageable hydrocarbons.<br />CO₂ hydrogenation takes place mainly through the following two reactions:<br />xCO₂ + (2x-z+y/2)H₂ --> C_xH_xO_z + (2x-z)H₂O<br />and<br />CO₂ + H₂ --> CO + H₂O The first reaction directly produces hydrocarbons whereas the second one, also known as RWGS, produces syngas which is useful in the synthesis of several hydrocarbons.<br />With CO₂ being a rather inert molecule, the reaction of CO₂ hydrogenation requires high pressures and temperatures, as well as the existence of a good catalyst. The development of an efficient catalyst is a requirement for the extensive application of a strategy where renewable energy is stored as HCs. An important parameter for the development of an efficient catalyst is the metal-support interactions. Those interactions have been closely identified as the underlying reason for Electrochemical Promotion of Catalysis [1-5]. Conversely, EPOC has proven itself as a valuable tool for the study of metal support interactions. Promoters of catalysts alter the catalytic activity and selectivity by modifying the bonds of the reactants on the active sites and the work function of the catalytic surface. Electropositive promoters enhance the chemisorption of electron-acceptors and weaken the bonds of electron donors. Electronegative promoters have the opposite effect [1-5]. Ruthenium is a catalyst widely used to produce methane from CO₂. In this study, we present an example of how electrochemical promotion of catalysis (EPOC) can elucidate the role of solid electrolytes (YSZ, BZY), supporting Ru porous films or nanoparticles.<br />The results of the study have shown that the electrolytic features of the support (anionic or cationic or mixed conductor) can have a very pronounced and dominant effect on the activity and selectivity of the supported metal nanoparticles. The mechanism of the interaction can be studied conveniently via EPOC and then the support can be chosen accordingly. Nucleophilic EPOC behavior suggests that the reaction will be enhanced when using an anionic catalyst support, such as YSZ, and electrophilic EPOC behavior suggests that the reaction will be enhanced using a cationic support, such as BZY. Thus, one may conclude, again, that EPOC (or NEMCA effect) and MSI are functionally identical and only operationally different [1, 2] since they both rely on ion spillover. The use of EPOC can significantly facilitate the choice of catalyst support.

References:
[1] C.G. Vayenas, S. Bebelis, C. Pliangos, S. Brosda, D. Tsiplakides, Electrochemical Activation of Catalysis: Promotion, Electrochemical Promotion and Metal-Support Interactions, Kluwer Academic/Plenum Publishers, New York, 2001.\n[2] 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, Ionically Conducting Ceramics as Active Catalyst Supports, Chemical Reviews, 113 (2013) 8192-8260.\n[3] A. Katsaounis, Recent developments and trends in the electrochemical promotion of catalysis (EPOC), Journal of Applied Electrochemistry, 40 (2010) 885-902.\n[4] D. Tsiplakides, S. Balomenou, Milestones and perspectives in electrochemically promoted catalysis, Catalysis Today, 146 (2009) 312-318.\n[5] A. De Lucas-Consuegra, J. Gonzalez-Cobos, Y. Garcia-Rodriguez, A. Mosquera, J.L. Endrino, J.L. Valverde, Enhancing the catalytic activity and selectivity of the partial oxidation of methanol by electrochemical promotion, Journal of Catalysis, 293 (2012) 149-157.

SESSION: PhysicalThuPM2-R10	Vayenas International Symposium on Physical Chemistry and its applications for sustainable development
Thu Oct, 24 2019 / Room: Aphrodite B (100/Gr. F)
Session Chairs: Vasileios Kyriakou; Dimitrios Zagoraios; Session Monitor: TBA

17:10: [PhysicalThuPM212]
Electrochemical Promotion of Methane Oxidation over Nanodispersed Pd/Co3O4 Catalysts
Dimitrios Zagoraios¹ ; Dimitrios Zagoraios² ; Alexandros Katsaounis³ ; Angel Caravaca⁴ ; Ioanna Kalaitzidou⁴ ; Athanasia Athanasiadi⁵ ; Spyros Ntais⁴ ; Philippe Vernoux⁶ ; Constantinos Vayenas² ; ¹University of Patras, Dept. of Chemical Engineering, Patras, Greece; ²University of Patras, Patras, Greece; ³Department of Chemical Engineering, University of Patras, Patras, Greece; ⁴University of Lyon, Lyon, France; ⁵University of Patras Dept. of Chemical Enginnering, Patras, Achaia, Greece; ⁶University LYON 1, Lyon, France;
Paper Id: 59 [Abstract]

During the last two decades, the Electrochemical Promotion of Catalysis (EPOC) phenomenon has been studied extensively for many catalytic reactions, including hydrocarbon oxidation reactions and hydrogenations [1-3]. The EPOC effect is based on the modification of the work function of a metal, which also serves as a working electrode, leading to an alteration in the chemisorption bond strength of the reactants. This effect is observed when small currents or potentials are applied to a catalyst deposited on a solid electrolyte. In the majority of the studies, the catalysts/electrodes consisted of porous noble metal films (Pt, Pd, Rh) prepared, for instance, by calcination of organometallic pastes [4]. This results in low metal dispersion and low active surface area, therefore limiting the overall catalytic activity. In view of further practical application of the EPOC phenomenon to industrial catalysts, we should be able to enhance the activity of nanodispersed materials. In this study, for the very first time, we observed an enhanced catalytic activity of a Pd nanodispersed catalyst supported on a porous Co₃O₄ semiconductor film. The Pd/Co₃O₄ composite powder was deposited on an yttria-stabilized zirconia (YSZ) solid electrolyte without the presence of an interlayer film. The observed enhancement was non-Faradaic, with apparent Faradaic efficiency values as high as 80. The Pd/Co₃O₄ catalyst was characterized thoroughly by means of a wide variety of physicochemical techniques, such as TEM, SEM, TGA, ICP and BET. Using supported catalysts as catalytic films for electrochemical promotion studies may lead to the practical utilization of EPOC in the chemical industry or in gas exhaust treatment.

References:
[1] C.G. Vayenas, S. Bebelis, I.V. Yentekakis, H.G. Lintz, Catal. Today. 11 (1992) 303-438.\n[2] C.G. Vayenas, S. Bebelis, C. Pliangos, S. Brosda, D. Tsiplakides Electrochemical Activation of Catalysis: Promotion, Electrochemical Promotion and Metal-Support Interactions, Kluwer Academic/Plenum Publishers, New York, 2001.\n[3] C.G. Vayenas, J. Solid State Electrochem. 7-8 (2011) 1425-1435.\n[4] C. Jimenez-Borja, S. Brosda, F. Matei, M. Makri, B. Delgado, F. Sapountzi, D. Ciuparu, F. Dorado, J.L. Valverde, C.G. Vayenas, Appl. Catal. B Environ. 128 (2012) 48-54.

SESSION: PhysicalFriPM1-R10	Vayenas International Symposium on Physical Chemistry and its applications for sustainable development
Fri Oct, 25 2019 / Room: Aphrodite B (100/Gr. F)
Session Chairs: Katerina Aifantis; Eftychia Martino; Session Monitor: TBA

15:15: [PhysicalFriPM108]
Experimental Investigation and Mathematical Modeling of Triode PEM Fuel Cells
Eftychia Martino¹ ; Alexandros Katsaounis² ; Constantinos Vayenas³ ; ¹University of Patras, Dept. of Chemical Engineering, Patras, Achaia, Greece; ²Department of Chemical Engineering, University of Patras, Patras, Greece; ³University of Patras, Patras, Greece;
Paper Id: 58 [Abstract]

Triode operation of fuel cells is an alternative approach for enhancing fuel cells’ power output under severe poisoning conditions which lead to high overpotentials. This innovation was developed and applied firstly on SOFCs and later on PEMFCs [1-4]. In a triode fuel cell, in addition to the anode and the cathode, there is a third auxiliary electrode in contact with the solid electrolyte (e.g. polymer electrolyte membrane in the case of PEMFCs). This electrode forms, together with the cathode, a second (auxiliary) electric circuit operating in parallel with the conventional main circuit of the fuel cell. The auxiliary circuit runs in the electrolytic mode, pumping ions (i.e. protons in the case of a PEMFC) from the cathode to the auxiliary electrode. This way, imposition of a potential difference between the auxiliary electrode and the cathode permits the primary circuit of the fuel cell to operate under previously inaccessible, i.e larger than 1.23 V, anode - cathode potentials. The triode operation of humidified PEM fuel cells has been investigated both with pure H₂ and with CO poisoned H₂ feed over commercial Vulcan supported Pt(30%)-Ru(15%) anodes. It was found that triode operation, which involves the use of a third, auxiliary, electrode, leads to up to 400% power output increase with the same CO poisoned H₂ gas feed. At low current densities, the power increase is accompanied by an increase in overall thermodynamic efficiency. A mathematical model, based on Kirchhoff’s laws, has been developed which is in reasonably good agreement with the experimental results. In order to gain some additional insight into the mechanism of triode operation, the model has been also extended to describe the potential distribution inside the Nafion membrane via the numerical solution of the Nernst-Planck equation. Both models and experiments have shown the critical role of minimizing the auxiliary-anode or auxiliary-cathode resistance, and this has led to improved comb-shaped anode or cathode electrode geometries.

References:
[1] S.P. Balomenou, C.G. Vayenas, Triode Fuel Cells and Batteries, J. Electrochem. Soc. 151 (2004) A1874. doi:10.1149/1.1795511.
[2] S.P. Balomenou, F. Sapountzi, D. Presvytes, M. Tsampas, C.G. Vayenas, Triode fuel cells, Solid State Ionics. 177 (2006) 2023-2027. doi:10.1016/j.ssi.2006.02.046.
[3] F.M. Sapountzi, S.C. Divane, M.N. Tsampas, C.G. Vayenas, Enhanced performance of CO poisoned proton exchange membrane fuel cells via triode operation, Electrochim. Acta. 56 (2011) 6966-6975. doi:10.1016/j.electacta.2011.06.012.
[4] E. Martino, G. Koilias, M. Athanasiou, A. Katsaounis, Y. Dimakopoulos, J. Tsamopoulos, C.G. Vayenas, Experimental investigation and mathematical modeling of triode PEM fuel cells, Electrochim. Acta. 248 (2017) 518-533. doi:10.1016/j.electacta.2017.07.168.