Long-Life Air Electrode for Rechargeable Zinc-Air Batteries

Abstract

Energy storage technology is attracting more attention with world-wide increase of renewable energy deployment, such as solar and wind power. With energy storage, electrical energy from photovoltaic cells or wind turbines can be stored when production exceeds consumption and back to the grid when load is demanded. The energy storage devices can also serve as a part of distributed power generation system for remote islands or uninterruptible power supply applications. Usually the system is installed in rural areas and even subjected to harsh temperatures and punishing humidity. Therefore, reliable and efficient energy storage is required. However, most existing mature energy storage technologies, such as Ni-Cd, Ni-MH and Li-ion, can barely satisfy both issues of safety and low cost. Metal air batteries have high theoretical specific energy density, being capable of fulfilling multiple needs for the next generation of mobile/stationary energy storage system. They are also environmentally benign, and inexpensive; frequently used metal anodes including Al, Zn, and Fe are naturally abundant. However, an air electrode with the capability of possessing both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) efficiently is still not well developed at the moment. In the present work, the bifunctional air electrode composed of alpha phase of manganese oxides or silver particles, as ORR catalysts, grown on the surface of stainless steel mesh catalyzing OER, was fabricated via electro-deposition method. This as-synthesized oxygen electrode was used directly for zinc-air battery assembly without polymer binders, which have low conductivity and suffer from detaching when immersion in alkaline solutions, leading to battery failure and short cycle life. In our system, the zinc-air battery was assembled with as-synthesized air cathode, 6M KOH/0.2M zinc acetate electrolytes and zinc foil anode. The battery was operated at the current density of 20 mA/cm2and its charge/discharge potential was 1.95V/1.15V, respectively. In addition, it showed stable performance with >80% coulombic efficiency over 1000 recharge cycles. Acknowledgement: Authors would like to thank the Bureau of Energy (BOE), Ministry of Economy Affair (MOEA), Taiwan for the financial support.