Experimental Investigation

Abstract

An experimental analysis of the physical processes occurring in a Planar Anode Supported Solid Oxide Fuel Cell is presented in this chapter. Experiments were done to determine the main electrochemical and transport processes taking place in the cell functional layers. To this end, several measurements were made which consisted of tracing current–voltage curves and quantifying fuel cell impedance. The measurements were obtained by changing the main parameters determining fuel cell operation. In particular, the work focused on changes in operating temperature and variation of fuel flow and composition in the anode channels and of oxidant flow in the cathode channels. Most of these independent variables were investigated with the aim being to investigate their interaction effects on cell voltage or impedance. In respect of fuel flow and composition, there were three main experimental activities. In the first, pure hydrogen was used as fuel for the SOFC, changing just the molar flow and operating on a range of fuel utilization between 20 and 80%. In the second, hydrogen was diluted by inert gases differing in molar weight: helium and nitrogen were employed with a different molar concentration in the range of 20–80 molar %. Finally, chemical reactive mixtures in SOFC thermodynamic conditions were tested with particular interest devoted to H₂/CO₂ and CH₄/CO₂ mixtures. Oxidant flow was changed in the same manner as fuel flow and experiments were then carried out to operate in a range of oxidant utilization between 20 and 80%. In all these experiments the operating temperature varied in the range of 650–800°C. The results of E–i curves and Impedance Spectra are consistent with the expected physical behavior of the fuel cell; in particular, it is possible to understand the evolution, over a wide temperature window, of the limiting cell overpotentials as a function of different operating conditions. The analysis is very insightful in terms of understanding the basic physical phenomena of an Anode Supported SOFC. In particular, the wide range of experimental results could prove useful in the building or validating of SOFC models.