Proton conduction and full hydration of BaSc_0.6Lu_0.2Mo_0.2O_2.8

抄録

Ceramic proton conductors have attracted increasing attention due to their potential to improve the efficiency of electrochemical devices, such as fuel cells. BaSc_0.8Mo_0.2O_2.8 exhibits high proton conductivity, however, it is not fully hydrated, resulting in a low proton carrier concentration. Here, we report the full hydration and high proton concentration of a new material, large-sized Lu-substituted BaSc_0.8Mo_0.2O_2.8 (BaSc_0.6Lu_0.2Mo_0.2O_2.8). Due to the larger ionic radius of Lu³⁺ than Sc³⁺, the lattice volume of BaSc_0.6Lu_0.2Mo_0.2O_2.8 was larger than that of BaSc_0.8Mo_0.2O_2.8, which can be responsible for the full hydration and higher water uptake of BaSc_0.6Lu_0.2Mo_0.2O_2.8 compared with BaSc_0.8Mo_0.2O_2.8. The bulk conductivity of BaSc_0.6Lu_0.2Mo_0.2O_2.8 (0.01 S cm⁻¹ at 400 °C) was higher than that of the leading materials such as BaZr_0.8Y_0.2O_2.9 and BaCe_0.9Y_0.1O_2.95 (e.g., 19 times higher than BaCe_0.9Y_0.1O_2.95 at 243 °C). This is attributable to the higher proton concentration 0.40 of BaSc_0.6Lu_0.2Mo_0.2O_2.8 compared with 0.17 of BaZr_0.8Y_0.2O_2.9 and 0.08 of BaCe_0.9Y_0.1O_2.95. The bulk conductivity of BaSc_0.6Lu_0.2Mo_0.2O_2.8 was lower than that of BaSc_0.8Mo_0.2O_2.8 and BaSc_0.8W_0.2O_2.8 due to its lower proton diffusion coefficient D. The D of BaSc_0.6Lu_0.2Mo_0.2O_2.8 exhibited a non-Arrhenius behavior, and its activation energy for D increased with decreasing temperature, which is attributable to proton trapping.