Metal-air batteries, in particular zinc-air batteries, can deliver larger energy density at lower production cost than most currently available battery technologies. The high energy density is associated with the use of oxygen as the active material which is not confined within the batteries. Although the technology of zinc-air batteries has matured, their further development has been hindered for various technical reasons. The most notable challenge is their short cycle life, which is critically linked to the lack of low-cost and robust bifunctional catalysts for the oxygen reduction reaction (ORR) and the oxygen evolution (OER).
In this context researchers at the Institute of Materials Research and Engineering of A*STAR, Singapore, have prepared a stable bifunctional manganese oxide catalyst directly on a carbon-paper air cathode by simply immersing carbon paper in a solution of Mn(NO3)2 in ethanol, and then oxidizing and drying the resulting material. Zinc-air batteries with this novel air cathode have an enhanced performance and show lower resistance, improved charge-discharge profile, and notable cycling stability in comparison to batteries prepared with conventional air cathodes having layers of powdered manganese oxide catalyst.
The directly grown catalysts display several structural features that are advantageous to battery operation. First, catalyst nanoparticles are in direct contact with the air cathode, which improves the electron transport between the catalyst and the external circuit. Second, the catalyst nanoparticles are distributed throughout the carbon paper and do not block the pores of the paper. Consequently, the catalyst is readily accessible and the charge-discharge profiles are enhanced. Finally, owing to the adhesion of the nanoparticles to the cathode, the catalyst particles do not detach and agglomerate during repeated charge-discharge cycles.
This research can be found in a special issue of ChemPlusChem in honor of Singaporeʼs Golden Jubilee. Click here to view the special issue for free during the month of August.