Enhanced grain boundary conductivity of Gd and Sc co-doping BaZrO₃ proton conductor for proton ceramic fuel cell

Applicability of BaZrO₃ proton conductor as electrolytes in fuel cells and electrolysis cells is limited due to lower grain boundary conductivity and serious sintering activity. Herein, we report the enhancement of grain boundary conductivity and sintering performance of BaZrO₃ proton conductor by Sc and Gd co-doping at B site. Combining experimental characterization and theoretical calculations, we found that the incorporation of Sc can effectively promote the generation of proton defects and lower the proton migration energy barrier. Meanwhile, the clustering of positively charged oxygen vacancy to acceptors can suppress proton trapping, thus positively affecting the long-range proton transport and effectively improving bulk conductivity. In addition, the space charge quantification by Mott-Schottky approximation confirms that Sc and Gd co-doping is significantly reduce the Schottky barrier height and the width of space charge layer, resulting in lower proton depletion and higher grain boundary conductivity. Benefiting from these two positive effects, these electrolytes show the highest proton conductivity of 2.99 × 10^-3 ∼ 3.63 × 10^-2 S cm⁻¹ in the temperature range of 250 ∼ 750 ℃. This indicates that co-doping of Gd and Sc is one of the effective and feasible strategy to improve the sinterability and conductivity of BaZrO₃-based proton conductors.