Electrochemical Diagnosis of SOFC Cells Incorporating Reference Electrodes

Solid Oxide Fuel Cells (SOFCs) and Solid Oxide Electrolysis Cells (SOECs) are recognised for their potential energy efficiency inducing a reduction of greenhouse gas emissions 1 . However, the development of new, reliable and robust oxygen electrode materials remains a crucial challenge in improving overall performance. Based on the latest developments in research about electrodes materials and microstructures, 2,3 the present study is dedicated to new architectured oxygen electrodes as well as method for diagnosing electrodes. The study of the response of electrochemical systems in a three-electrode configuration has already been published in the literature using a single reference electrode (RE) 4 . It therefore becomes possible to separately determine the potential drop of the working electrode (WE), from that of the counter electrode (CE) 5 . Moreover, placing a RE on the oxygen side and hydrogen side enables a more comprehensive analysis of the electrochemical contribution of each electrode during operation. This technique will be helpful to diagnose the electrodes behaviour during operation but also to check the stability of materials or observe degradation during ageing tests. For this purpose, an electrolyte composed of gadolinium doped ceria (GDC) has been elaborated and its ion conductivity has been verified. Then, a porous GDC backbone has been deposited by screen printing on the electrolyte using optimised ink. This backbone was then infiltrated with a solution of praseodymium nitrate to obtain the architectured electrode GDC-Pr 6 O 11 . Finally, the Area Specific Resistance (ASR) has been measured on symmetrical half cells under air in the temperature range 800 °C to 500 °C. This work is first implemented in a three-electrode configuration. A symmetrical half-cell, composed of Pr₆O₁₁-GDC10/GDC10/GDC10-Pr₆O₁₁, is prepared according to the previously described protocol. The reference electrode is deposited around one of the two electrodes of the half-cell using a platinum lacquer. Electrochemical impedance spectroscopy measurements coupled to the application of a voltage varying from 0 to 1 V are then carried out over a temperature range from 800 °C to 600 °C, in order to characterise the polarizability of the structured electrode. Secondly, a four-electrode configuration was set up on a commercial cell which was made of NiO-8YSZ/8YSZ/GDC10/GDC-Pr 6 O 11 with the optimised oxygen electrode screen printed on it. Afterward, reference electrodes were placed on each side of the cell. This approach makes it possible not only to assess the performance of the electrode developed at the ICMCB, but also to dissociate the electrochemical contributions of each electrode. (1) Stambouli, A. B.; Traversa, E. Solid Oxide Fuel Cells (SOFCs): A Review of an Environmentally Clean and Efficient Source of Energy. Renewable & substainable energy reviews 2002 . (2) Tucker, M. C.; Cheng, L.; DeJonghe, L. C. Selection of Cathode Contact Materials for Solid Oxide Fuel Cells. Journal of Power Sources 2011 , 196 (20), 8313–8322. https://doi.org/10.1016/j.jpowsour.2011.06.044. (3) Nicollet, C.; Flura, A.; Vibhu, V.; Fourcade, S.; Rougier, A.; Bassat, J.-M.; Grenier, J.-C. Preparation and Characterization of Pr2NiO4+δ Infiltrated into Gd-Doped Ceria as SOFC Cathode. J Solid State Electrochem 2016 , 20 (7), 2071–2078. https://doi.org/10.1007/s10008-016-3211-x. (4) Cimenti, M.; Co, A. C.; Birss, V. I.; Hill, J. M. Distortions in Electrochemical Impedance Spectroscopy Measurements Using 3‐Electrode Methods in SOFC. I – Effect of Cell Geometry. Fuel Cells 2007 , 7 (5), 364–376. https://doi.org/10.1002/fuce.200700019. (5) Finklea, H.; Chen, X.; Gerdes, K.; Pakalapati, S.; Celik, I. Analysis of SOFCs Using Reference Electrodes. J. Electrochem. Soc. 2013 , 160 (9), F1055–F1066. https://doi.org/10.1149/2.093309jes. Figure 1