Energy-filtered environmental transmission electron microscopy for the assessment of solid–gas reactions at elevated temperature: NiO/YSZ–H2 as a case study

•EFTEM is used to assess solid–gas reactions at elevated temperatures.•This novel approach provides local, quantitative chemical and structural data.•A 3D insight into how the reaction proceeds is obtained under certain assumptions.•Reaction mechanisms and their link to microstructure can be established.

A novel approach, which is based on the analysis of sequences of images recorded using energy-filtered transmission electron microscopy and can be used to assess the reaction of a solid with a gas at elevated temperature, is illustrated for the reduction of a NiO/ceramic solid oxide fuel cell anode in 1.3 mbar of H2. Three-window elemental maps and jump-ratio images of the O K edge and total inelastic mean free path images are recorded as a function of temperature and used to provide local and quantitative information about the reaction kinetics and the volume changes that result from the reaction. Under certain assumptions, the speed of progression of the reaction front in all three dimensions is obtained, thereby providing a three-dimensional understanding of the reaction.