New Layered Proton-Conducting Oxides Li_xAl_0.6Co_0.4O₂ and Li_xAl_0.7Co_0.3O₂

Single-phase layered oxides with nominal composition LiAl_0.6Co_0.4O₂ and LiAl_0.7Co_0.3O₂ were synthesised and tested as electrolytes for H₂/air fuel cells. The maximum current and power densities of 382mAcm^-2 and 108mWcm^-2, respectively, were achieved at 650°C when a 0.70mm-thick LiAl_0.6Co_0.4O₂ pellet was used as the electrolyte. The ionic conductivity of LiAl_0.7Co_0.3O₂ was 4.0×10^-2Scm^-1 at 725°C, which was derived from the series resistance of the impedance spectra of the H₂/air fuel cells. For LiAl_0.6Co_0.4O₂, the highest ionic conductivity was 7.7×10^-2Scm^-1, observed at 625°C. In the LiAl_1-yCo_yO₂ series, the proton conductivity and working temperature of the materials are closely related to the composition. It is essential to integrate the multivalent element into the layered-oxide lattice to achieve high proton conductivity, as the proton conduction is a coherent effect between the reduction of the multivalent element, such as cobalt, and the insertion of protons.