Three-dimensional structures of Ni nanoparticles undergoing significant morphological changes on oxidation were observed non-destructively using coherent X-ray diffraction imaging. The Ni particles were oxidized into Ni1O1 while forming pores of various sizes internally. For each Ni nanoparticle, one large void was identified at a lower corner near the interface with the substrate. The porosity of the internal region of the agglomerated Ni oxide was about 38.4%. Regions of high NiO density were mostly observed at the outer crust of the oxide or at the boundary with the large voids. This research expands our understanding of general catalytic reactions with direct observation of oxidation-induced nanoscale morphological changes.
Keywords: NiO; coherent X-ray diffraction imaging; oxidation; three-dimensional morphology.