New Layered Proton‐Conducting Oxides LixAl0. 6Co0. 4O2 and LixAl0. 7Co0. 3O2

Single-phase layered oxides with nominal composition LiAl0.6Co0.4O2 and LiAl0.7Co0.3O2 were synthesised and tested as electrolytes for H2/air fuel cells. The maximum current and power densities of 382 mA cm−2 and 108 mW cm−2, respectively, were achieved at 650 °C when a 0.70 mm-thick LiAl0.6Co0.4O2 pellet was used as the electrolyte. The ionic conductivity of LiAl0.7Co0.3O2 was 4.0×10−2 S cm−1 at 725 °C, which was derived from the series resistance of the impedance spectra of the H2/air fuel cells. For LiAl0.6Co0.4O2, the highest ionic conductivity was 7.7×10−2 S cm−1, observed at 625 °C. In the LiAl1−yCoyO2 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.