Solid oxide fuel cells (SOFC) are solid state electrochemical devices which operate at high temperatures up to 1000°C. Their components, particularly cathode and anode are structurally and chemically very complex. Specifically the porosity and internal surface area is a functionality per se and needs to be optimized so as to warrant optimum electrochemical conversion of fuel to electricity with a long service live. The assessment of the pore space is therefore instrumental for the functionality assessment. In contrast, the solid electrolyte shall have little or no porosity so as to present a good barrier to parasitic gas diffusion from anode to cathode, and vice versa. Of importance is ultimately the size of the electrochemical active interface. Traditionally, optical and electron microscopy imaging methods have been employed for the assessment of the pore space of such electrode assemblies. More recently, focussed ion beam tomography methods have been applied with success.

We provide an alternative method which requires no image analysis methods and which has a very high spatial resolution and element specific sensitivity. The method of choice is small angle scattering, which we have employed on a set of industry grade SOFC assemblies which were taken from stacks that had been run with sulfur ruch and sulfur depleted fuel, compared against the pristine electrodes. We present a detailed qualitative and quantitative assessment which is based on the chemical contrast variation and enhancement by using synchrotron radiation with tunable X-ray energy (anomalous small angle X-ray scattering).

With the data which obtained we are able to sketch a sulfur poisoning degradation model for the electrochemical interface (triple phase boundary) of the SOFC.

[1] A. J. Allen, J. Ilavsky, P. R. Jemian, A. Braun, Evolution of electrochemical interfaces in solid oxide fuel cells (SOFC): a Ni and Zr resonant anomalous ultra-small-angle X-ray scattering study with elemental and spatial resolution across the cell assembly, RSC Adv., 2014, 4, 4676-4690.