TEM/STEM Analysis of NiO Reduction to Ni during Annealing in H₂ Atmosphere

Nickel oxide (NiO) reduction to Ni during annealing in hydrogen gas (H2) atmosphere is of practical interest for catalytical applications [1] and for production of metallic Ni [2] particles. Recent in-situ TEM study [3] using monitoring of structure changes by EELS indicated that Ni reduction proceeds by Ni nucleation on NiO surface with further growth of Ni crystallites (often expitaxially) and the movement of growth front that is accompanied by the formation of pores within the NiO grains to accommodate the volume shrinkage associated with the reduction process. While this study was performed on NiO powder, the present study was focusing on structure evolution in bulk polycrystalline material.