Promising Proton Conductor for Intermediate-Temperature Fuel Cells: Li13.9Sr0.1Zn(GeO4)4

Commercialization of fuel cell technologies hinges on the development of solid electrolytes of sufficient ionic conductivity at intermediate temperatures (200–600 °C). Here we report a novel proton conductor derived from Li13.9Sr0.1Zn(GeO4)4 (LSZG), demonstrating the highest protonic conductivity (0.034 S cm–1 at 600 °C) among all known proton conducting ceramics, which is much higher than those of several well-known oxygen ion conducting electrolytes (e.g., ∼0.009 and 0.018 S cm–1, respectively, for zirconia- and ceria-based oxide electrolyte at 600 °C). Interestingly, after fully replacing the mobile Li+ ions by H+ through proper ion exchange, the H+ conductivity increases from 0.034 to 0.048 S cm–1 at 600 °C. A simple but effective ab initio molecular dynamics simulation study suggests a unique H+/Li+ transport mechanism: the proton in LSZG moves freely in the Li+ interstitial space within the 3D Li+ transport network (i.e., 4c and 4a sites, as the occupancies of the Li1 and Li2 sites are 55% and 16%, ...