DOLORES · Degradation of Lifetime of fuel cell Resistance by Electrochemical impedance Spectroscopy

Degradation of Lifetime of fuel cell Resistance by Electrochemical impedance Spectroscopy

An increasingly important technology in the generation of clean electricity is based on solid oxide cells (SOCs) which can be operated in either fuel cell (SOFC) or electrolyser (SOEC) mode. SOCs are remarkably flexible in their: mode of operation, fuel characteristics, operating temperature and in their ability to switch mode of operation. They have high electrical efficiencies which, combined with their high temperature of operation, lead to overall system efficiencies as high as 80% for power generation. SOCs, therefore, are a key component of power supplies ranging from small scale domestic applications and electric or hybrid vehicles, to larger scale, combined heat and power systems for buildings and industrial complexes. They can play a key role in the hydrogen economy and chemical industries with potential for not only large scale production of hydrogen from water but also for conversion of carbon dioxide to syngas, which is a precursor for many synthetic fuels and chemicals. Degradation rates for commercial SOFC stacks are typically 1.5-2%/1000 hours which hinders their wider adoption. Understanding the origins and mechanisms of degradation is difficult, in part because several factors are involved and it is not clear which one is dominant. The ceramic electrolyte of choice in SOCs is YSZ due to its high oxide ion conductivity and stability in reducing atmospheres. Recent work at Sheffield showed that YSZ pellets with platinum electrodes, show the onset of electronic conductivity under the action of a small applied voltage. Following the previous results obtained in Sheffield, the main objective of the proposal is to better understand the electronic conductivity observed in YSZ ceramics. At present, SOCs have not reached full-scale commercial production; providing a solution to a previously-unrecognised degradation mechanism brings that a step closer to fruition. The main technique used to fully characterise the electrical performance of YSZ electrolytes was Impedance Spectroscopy. A new methodology the take full advantage of the technique has been developed for this project and it can be used not only to characterise ionic conductors, but also materials with other electrical properties such as electronic or mixed conductors or dielectrics. The use of the new methodology implemented for data analysis has resulted on new and unexpected results. The research has been focused on understanding the obtained results.

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