Elucidating nickel oxide reduction in a Ni-YSZ solid oxide cell via in-situ X-ray nano holo-tomography

Reducing nickel oxide in solid oxide cell (SOC) electrodes is a critical step during the early stages of cell operation. It is considered crucial in shaping the final microstructure of the fuel electrode. In this work, we investigate the NiO reduction process in a state-of-the-art Solid Oxide Cell (SOC) using in-situ X-ray nano-holo-tomography. Results show a fast reaction kinetics and a reaction front from the outer to the inner regions of the sample. NiO reduction is complete in the first few seconds and the metallic Ni particles present a sponge-like structure, with many nanocrystallites and internal nano porosity. After reduction, the Ni network undergoes coarsening, increasing its particle size. Based on the acquired data, we propose a new chain of reaction mechanisms for forming the Ni nanocrystallites observed after reduction.