Application of Non-Precious Bifunctional Catalysts for Metal-Air Batteries

Zinc-air batteries have several advantages in comparison with the lithium-ion technology as they enable the use of earth-abundant elements, work at low cost, are lightweight, and are also much safer in application. In addition to the chemistry related to the zinc electrode, efficient and stable bifunctional catalysts are required for oxygen reduction reaction (ORR, for discharging) and oxygen evolution reaction (OER, for charging) on the air-electrode side. Herein, a family of non-precious metal catalysts is investigated as possible bifunctional composite: metal-nitrogen-carbon (MNC) catalysts for ORR, and metal oxyhydroxides as OER catalysts (Ox). The effect of transition metal and metal loading in these composite MNC + Ox catalysts on ORR and OER activities in half-cell measurements is discussed. The catalysts were characterized using X-ray diffraction and Raman spectroscopy to identify their phase composition. For the most active material, a potential gap of 0.79 V between OER and ORR was obtained, respectively. In a zinc-air cell, this catalyst moreover showed a peak power density of 62 mW cm(-2) and a charge-discharge gap of 0.94 V after 26 h of charge-discharge cycling.