Interfacial Charge Transfer and Chemical Bonding in a Ni-LaNbO4 Cermet for Proton-Conducting Solid-Oxide Fuel Cell Anodes

In this work, we present an atomic scale study of the structural and chemical characteristics of interfaces between Ni and LaNbO4 grains in Ni–LaNbO4 cermets, a model composite material for anodes in proton-conducting solid-oxide fuel cells (SOFC). Electron energy loss spectroscopy (EELS) performed in an aberration-corrected scanning transmission electron microscope reveals the absence of reaction or interdiffusion layers at the interface. Changes in the valence state of Ni as well as in the electronic structure of La, reflected by changes in the EELS fine features at the interface, are shown to be related to charge transfer across the interface. The experimental results are in excellent agreement with ab initio calculations based on density functional theory, which predict that direct chemical bonds are formed between the metal and the ceramic at this abrupt interface, resulting in a redistribution of electronic charge across the interface.