Parametrical Coordinates and Microsamples to Investigate Real SOFCs in Operating Stacks
Authors: Piccardo Paolo , Spotorno Roberto , Ouweltjes Jan Pieter , Stoynov Zdravko , Vladikova Daria 
Published: February 2020

One of the issues defining the performance of an SOFC stack is to estimate and check during operation the behavior of all components, i.e.: the cell, the sealant, the interconnects and the scaffolding. Each component has at least one function which is not strictly related to the power or heat generation but all are strategic and fundamental because any degradation or change in properties may lead to the failure of the whole stack.

The behavior of materials is strongly related to physical parameters like temperature, surrounding atmospheres, coupling among two or more materials (e.g. electrolyte, sealant, metal).

A twofold approach by experimental (e.g. segmented cells or instrumented short stacks) and modelling sessions allows to predict a number of parameters (e.g. temperature, fuel utilization) by fixing the others. This procedure engages the creation of refining loops between the experimental measures and the predicted ones. The final result is that regardless the cell or layer taken into account in a stack most of the electrochemical and physical behaviors can be predicted in a zone defined by "parametrical coordinates" or, in other words, areas of the stack standing in a similar range of parameters have similar behaviors. To take advantage of such important achievements in the field of modelling applied to SOFC stacks it is important to consider all components being all inter-related, and working conditions as close as possible to the real ones. The experiments with real stacks or with segmented cells in short stacks are thus more and more important but at the same time quite expensive and mainly for long lasting sessions of durability and estimation of the degradation rate they are prone to as unpredictable as dramatic events leading to failure (e.g. black-out).

In this paper an opportunity offered by experiments and samples specifically designed in the EU FP7 project ENDURANCE (contract FCH-JU 621207) is introduced. The samples have the shape and size of a button cell and contain all components present in a stack: the cell (cut from an industrial batch and treated as the real cells for stacking), the metal with coating (interconnects and scaffolding) and the sealant. These samples are tested in a test rig defined as Real Life Tester (RLT) meant to reproduce the same operating conditions (i.e. temperature, mechanical load, gases composition, polarization) as those inside a real stack with the possibility to smoothly and rapidly change parameters and thus "parametrical coordinates" so that the operator can virtually move the sample across the stack and check in real time the response of the sample in a specific zone. The sample and the experiment itself are cost effective and offer the opportunity to soundly contribute to the assessment of stack components behavior in the "real world".

ACKNOWLEDGEMENTS

The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) Fuel Cells and Hydrogen Joint Undertaking (FCH-JU-2013-1) under grant agreement No 621207.