Characterization of high Zr/Ce ratio Ba(Zr,Ce,Y)O3−δ proton conductors: investigating the impact of Y on the properties of materials†

Abstract

Acceptor-substituted Ba(Zr,Ce)O₃ proton conducting oxides have attracted significant attention due to their excellent proton conductivity at intermediate temperatures (400–600 °C). A high Zr/Ce ratio is crucial for maintaining stability in humid or other harsh atmospheres. Herein, a systematic study was conducted on the phase composition, microstructure, and the resulting hydration ability and electrochemical performance of high Zr/Ce ratio Ba(Zr,Ce)O₃ solid solutions with different Y substitution levels (10 at% to 30 at%). In this substitution range, no apparent secondary phase can be found from XRD, leading to a continuous increase in hydration content. A Y-rich phase was observed in SEM for compositions with high levels of Y substitution. The impact of Y on proton conduction was examined using EIS, with particular attention on elucidating the effects of varying amounts of Y on bulk proton conduction. The increase of proton conductivity was primarily due to the increased charge carrier (proton) concentration caused by Y substitution. Different concentrations of Y have little effect on proton mobility, indicating a compromise between different mechanisms such as the Y trapping effect and the nano-percolation effect. Grain boundary proton conduction was discussed combining the TEM-EDS results to explain the space charge layer effect. Mechanical properties and thermo-chemical stability were also considered to pave the way for real applications.