A PtRu catalyzed rechargeable oxygen electrode for Li-O2 batteries: performance improvement through Li2O2 morphology control.

Albeit ultrahigh in energy density, the Li-O2 battery technology still suffers from the high overpotential of Li2O2 oxidation upon charging and the low cyclability. In the present work, we use Pt2Ru/C as the oxygen-electrode catalyst and study how it improves the cell performance and changes the reaction mechanism, as compared with a carbon electrode. Multiple methods, including X-ray diffraction, transmission/scanning electron microscopy, Raman spectroscopy, and cyclic voltammetry, have been employed for material characterization and reaction monitoring. The Li-O2 cell with a Pt2Ru/C catalyst shows lower charge voltage, higher specific capacity, and enhanced cyclability than does a carbon catalyst. The key for this improvement is ascribed to the morphology change of Li2O2. Whereas the Li2O2 formed in the carbon electrode is rod-shaped, the Li2O2 in the Pt2Ru/C electrode is mud shaped and closely attached to the electrode substrate, thus benefiting the subsequent Li2O2 oxidation. This study indicates that the charging performance of the Li-O2 battery can be improved not only by using proper catalysts, but also by controlling the Li2O2 morphology during discharge.