New work on the chemical and crystallographic heterogeneities present in a Ni/NiO-YSZ solid oxide fuel cell electrode after re-oxidation

3D crystals in Solid Oxide Fuel Cell imageIn our latest work, we look with at the chemical and crystallographic heterogeneities present in a Ni/NiO-YSZ solid oxide fuel cell electrode after re-oxidation.

The research was carried out in collaboration with Dr Thomas Heenan from the Electrochemical Innovation Lab (EIL) at UCL Chemical Engineering, UCL Chemistry and ESRF.

The solid oxide fuel cell (SOFC) anode is often composed of nickel (Ni) and yttria-stabilized zirconia (YSZ). The yttria is added in small quantities (e.g., 8 mol %) to maintain the crystallographic structure throughout the operating temperatures (e.g., room-temperature to >800 °C). The YSZ skeleton provides a constraining structural support that inhibits degradation mechanisms such as Ni agglomeration and thermal expansion miss-match between the anode and electrolyte layers. Within this structure, the Ni is deposited in the oxide form and then reduced during start-up; however, exposure to oxygen (e.g., during gasket failure) readily re-oxidizes the Ni back to NiO, impeding electrochemical performance and introducing complex structural stresses. In this work, we correlate lab-based X-ray computed tomography using zone plate focusing optics, with X-ray synchrotron diffraction computed tomography to explore the crystal structure of a partially re-oxidized Ni/NiO-YSZ electrode. These state-of-the-art techniques expose several novel findings: non-isotropic YSZ lattice distributions; the presence of monoclinic zirconia around the oxidation boundary; and metallic strain complications in the presence of variable yttria content. This work provides evidence that the reduction–oxidation processes may destabilize the YSZ structure, producing monoclinic zirconia and microscopic YSZ strain, which has implications upon the electrode’s mechanical integrity and thus lifetime of the SOFC.

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A new cell for industrially relevant studies of operating PEM fuel cells using hard X-rays

Finden scientists’ new work on the design and application of a new cell for proton-exchange membrane fuel cells has been published in a new paper, “X-ray transparent proton-exchange membrane fuel cell design for in situ wide and small angle scattering tomography” in the Journal of Power Sources. The cell design and experimental work was performed by Isaac Martens and Jakub Drnec using ESRF’s ID31 beamline.

We have constructed a 5 cm2 proton exchange membrane hydrogen fuel cell optimized for transparency of high energy X-rays. This cell allows for in situ elastic scattering measurements (WAXS, SAXS) during electrochemical operation with minimal trade-offs in cell performance vs benchtop designs, and is capable of reaching automotive current densities. A key feature is that the beam enters the cell at grazing incidence to the electrodes, massively increasing the effective pathlength and therefore the signal-to-background ratio. The transparency in the plane of the sample permits imaging coupled with advanced techniques, such as X-ray diffraction computed tomography.

PEM fuel cells diag

The work was done at the The European Synchrotron (ESRF) and research partners included; University of British Columbia, Université Grenoble Alpes, University of Helsinki, Aalto University, Baltic Fuel Cells and University College London.

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