A. Thorel et A. Chesnaud à la conférence internationale “Sofia Electrochemical Days” (SED 2017)

Du 10 au 13 mai 2017, Alain Thorel et Anthony Chesnaud ont participé à la conférence internationale "Sofia Electrochemical Days" (SED 2017) qui s'est déroulée à – Institute of Electrochemistry and Energy System, Bulgarian Academic of Sciences -.

A cette occasion Anthony Chesnaud a été sollicité pour une conférence plénière (appelée key-note lecture) intitulée : "Improvement of SOFC performances by a mesoscopic architecture of the electrolyte/electrode interfaces" (30 minutes). ci-dessous le résumé de cette présentation.

Co-authors :

Anthony Chesnaud*, Francesco Delloro, Maya Geagea, André-Pierre Abellard, Jian Ouyang, Bo Chi, Tang Shi, Fu Peifang, Raphaël Ihringer, Alain Thorel

Abstract :

In this work, we have explored how the increase of exchange surfaces via the mesoscopic scale corrugation of electrode/electrolyte interfaces in a SOFC could improve the electrochemical performances, from theoretical and experimental points of view. Based on masses and charges conservation, gas transport and electrochemical reaction kinetics, an electrochemical model was established and implemented in the COMSOL Multiphysics software. It shows that the presence of a mesoscopic periodic pattern (parallelepipeds, pyramids, ellipsoids) at the electrolyte/electrode interfaces, along with an electrolyte the thickness of which (some 15 µm) must be significantly smaller than the dimensions of the pattern (some 100 µm), leads to a strong increase of the exchange surface as compared with flat surface, hence to higher exchange currents and cell performances. The model shows that the patterns must display concave and convex singularities so as to confine the cathode material on the cathode side and the anode material on the anode side, hence the active layers on both sides, so that a much larger number of TPB are solicited and involved in the chemical reactions, reducing then the activation overpotential, as compared with a flat surface. It is also shown that the geometrical feature can be chosen so that it minimizes the concentration overpotential. Finally, the modeling provided us with key information regarding the geometry of the pattern (shape, width and depth, distance between them, …) so that a larger exchange current is obtained. For example, an increase of the exchange current of about 60% was calculated for a parallelepipedic pattern with 70 μm width and 100 μm depth, each geometric feature separated from the other by a few hundred microns. With the use of laboratory standard ceramic processes (tape casting, screen printing, bar coating, cold pressing, cold stamping), we have implemented such mesoscopic architectures on green self supported anodes (YSZ + Ni) on top of which a thin layer (15 µm) of electrolyte (YSZ) was deposited, then co-sintered along with the anode. A LSCF cathode was then deposited on top of the assembly, then sintered. The first electrical and electrochemical results show that the increase of the power density was even higher than what was anticipated by the modeling, reaching more than the double of the value for flat interfaces. The results are discussed here in terms of the geometry of the pattern and its evolution during sintering, as well as of activation and concentration overpotentials.