Synthesis of Bifunctional Catalysts for Metal-Air Batteries Through Direct Deposition Methods

Rechargeable metal- air batteries, such as Li- air and Zn- air batteries, have gained renewed interest because of their high theoretical energy density, safety and low cost. The air electrode, with bifunctional electrocatalysts for the oxygen reduction reaction ( ORR) and the oxygen evolution reaction ( OER), plays the most important role in determining battery performance. Direct deposition of catalysts on the air electrode, using methods such as electrodeposition, electroless deposition, chemical vapor deposition ( CVD) and physical vapor deposition ( PVD), is shown to be a viable way to fabricate durable and active catalysts with high efficiency and low cost. This review examines recent research activities which apply direct deposition methods to prepare bifunctional catalysts. The benefits and drawbacks of these methods are compared to provide guidelines for their application.