ORALS

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

15:55: [PhysicalThuPM209] Keynote
High Temperature Proton and Co-Ionic Electrochemical Membrane Reactors a) Co2/H2o Co-Electrolysis and b) Nh3 Synthesis
Ioannis Garagounis¹ ; Vasileios Kyriakou² ; Anastasios Vourros¹ ; Demetrios Stoukides¹ ; Michael Stoukides¹ ; ¹Aristotle University, Thessaloniki, Greece; ²Dutch Institute for Fundamental Energy Research (DIFFER), Eindhoven, Netherlands;
Paper Id: 46 [Abstract]

Solid state proton conductors can operate at high temperatures (> 500 ^oC) and have been applied in the construction of sensors, fuel cells and hydrogen separators. In the past two decades, they have also been used in the construction of electrochemical membrane reactors. The advantage of high temperature conductors, versus those operating at low temperatures, is that they operate in the temperature range within which a large number of industrially important catalytic hydro-reactions and dehydrogenation reactions take place. In most of the earlier applications of electrochemical membrane reactors in catalytic research, the reaction of interest took place on the working electrode while the counter electrode served for the formation of protons from a hydrogen containing compound. These electrochemical reactors, however, would become more competitive if useful chemicals were produced on both, working and counter electrodes [1, 2]. Results on two reaction systems in which both, cathode and anode were properly utilized are presented here. The first is the production of methanol and oxygen from CO₂ and H₂O. Steam and CO₂ are introduced at the anode and cathode side, respectively, of a co-ionic (H⁺ and O^2-) conductor. Steam is electrolyzed to form O₂ and protons (H⁺). The latter are transferred to the cathode and react with CO₂ to form CH₃OH. The second system is an electrochemical Haber-Bosch (H-B) Process [3]. A mixture of steam and methane is fed to the anode chamber. Nitrogen is fed over the cathodic electrode. Hydrogen produced at the anode is "pumped" electrochemically (in the form of protons) to the cathode, where it reacts with N₂ to produce NH₃. A preliminary energy analysis indicates that, at faradaic efficiencies above 30% and at cell bias as low as 0.4 V, the electrochemical H-B becomes more efficient than the conventional H-B Process with respect to both, energy consumption and CO₂ emissions.

References:
[1] S.H. Morejudo, R. Zanon, S. Escolastico, I. Yuste, H. Malerød-Fjeld, P.K. Vestre, W.G. Coors, A. Martínez, T. Norby, J.M. Serra, C. Kjølseth, Science, 353 (2016) 563-566.
[2] A.Vourros, V. Kyriakou, I. Garagounis, E. Vasileiou, M. Stoukides, Solid State Ionics, 306 (2017) 76-81.
[3] V. Kyriakou, I. Garagounis, E. Vasileiou, A. Vourros, M. Stoukides, Catalysis Today, 286 (2017) pp. 2-13.

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

16:45: [PhysicalThuPM211]
Exsolution of Transition Metal Nanoparticles for Solid Oxide Co-Electrolysis of CO2-H2O
Vasileios Kyriakou¹ ; Dragos Neagu² ; Michail Tsampas³ ; ¹Dutch Institute for Fundamental Energy Research (DIFFER), Eindhoven, Netherlands; ²Newcastle University, Newcastle, United Kingdom; ³DIFFER, Eindhoven, Netherlands;
Paper Id: 112 [Abstract]

The production of synthetic fuels from renewable energy could be a more efficient solution for a sustainable future without the need of huge investments for modifications in the existing infrastructure [1,2]. The raw material of synthetic fuels via the Fischer-Tropsch process is syngas (H²⁺CO) and is primarily generated by fossil fuels. The co-electrolysis of carbon dioxide and steam in a solid oxide electrolysis cells (SOECs) is an emerging route to produce syngas and thus store renewable electricity in the form of chemical bonds [2]. The commonly employed materials for fuel electrodes (cathode) in the process are Ni based cermets that exhibit high ionic-electronic conductivity and electrocatalytic activity. Nevertheless, Ni-YSZ electrodes suffer from coarsening under redox conditions and coking under carbon rich environments [3]. To circumvent coarsening, a reducing agent, such as hydrogen or carbon monoxide, is always co-fed with CO₂-H₂O in order to keep Ni in a reducing state [2]. Perovskite oxide ceramics (ABO3) are the most promising alternative fuel electrodes. Perovskites exhibit mixed ionic-electronic conductivity as single phases and can accommodate several kinds of defects under redox conditions, allowing them to adapt to various external conditions and therefore maintain stability and functionality under redox environments [4]. Lanthanum titanates constitute an intriguing class of perovskites, exhibiting chemical, dimensional, thermal and mechanical stability. By controlling deficiency of the A-site, transition metal nanoparticles may be exsolved to the surface from the perovskite oxide backbone under reducing environments. The grown particles are uniformly dispersed as well as anchored to the perovskite scaffold, thus rendering them more catalytically active and chemically stable compared to the oxide supported counterparts prepared by infiltration [5-7]. Along these lines, here we report on the electrochemical performance of (LaCa)(MTi)O₃ (M=transition metal) as fuel electrodes for high temperature CO₂-H₂O co-electrolysis. The cells are characterized and tested at 800-850°C under several feed mixtures (CO₂/H₂O, H₂O/H₂, CO₂/ H₂O/H₂, CH₄/H₂O-CO₂) and applied voltages.

References:
[1] J.A.Ritter, A.D, Ebner, Separation Science and Technology 2007, 42, 1123-1193.
[2] S. D. Ebbesen, R. Knibbe, M. Mogensen, Journal of Electrochemical Society 2012, 159, F482-F489. P. Hjalmarsson,
[3] S. D. Ebbesen, C. Graves, A. Hauch, S. H. Jensen, M. Mogensen, Journal of the Electrochemical Society 2010, 157, B1419-B1429.
[4] Y. Zheng, J. Wang, B. Yu, W. Zhang, J. Chen, J. Qiao, J. Zhang, Chem. Soc. Rev.
46 (2017) 1427-1463.
[5] D. Neagu, G. Tsekouras, D.N, Miller, H,Menard, J.T.S. Irvine, Nature Chemistry 2013, 11, 916-923.
[6] J-H. Myung, D. Neagu, D.N, Miller, J.T.S. Irvine, Nature 2016, 537 (7621), 528-531.
[7] L. Ye, M. Zhang, P. Huang, G. Guo, M. Hong, C. Li, J.T.S. Irvine, K. Xie, Nature Communications 2017, 8, 14785, doi: 10.1038/ncomms14785.