Engineering oxygen vacancy to accelerate proton conduction in Y-doped BaZrO3

Proton conducting oxides have drawn great interest as electrolytes for proton-conducting reversible solid oxide cells (P-RSOCs), but suffered from the inferior ionic conductivity. To accelerate proton conduction, oxygen vacancy engineering via calcium-doping is proposed and validated, which generates more oxygen vacancies to increase proton concentration and importantly tailors the position of oxygen vacancy to accelerate proton diffusion. TG and EIS results show that calcium-doped BaZr0.8Y0.2O3-δ (BZY2), BaZr0.8Ca0.1Y0.2O3-δ (BZCa1Y2), owns higher proton concentration, and demonstrates ionic conductivity of 0.008 S cm−2 at 700 °C, 2.7 times higher than BZY2. The lower activation energy of conductivity in BZCa1Y2 confirms the faster proton conduction behaviour. DFT calculation concludes that oxygen vacancies prefer to cluster with Ca site and proton diffusion barrier is decreased most when vacancy is tailored to generate nearing Ca. When considering the concentration of proton and oxygen vacancy, proton diffusion coefficient obtained from Ab-initio Molecular Dynamics simulation is 1.1 × 10−5 cm2s−1 for BZCa1Y2 in 200 °C, larger than BZY2 (9.0 × 10−6 cm2s−1) and verifying the accelerated proton diffusion due to the tailored oxygen vacancy. The oxygen vacancy engineering provides a further understanding of proton diffusion in proton conducting oxides and a new promising opportunity to improve conductivity.