Electrochemical Performance of MnO 2 ‐based Air Cathodes for Zinc‐air Batteries

This paper compares the oxygen reduction on four MnO 2 ‐based air cathodes assembled in home‐made electrochemical cells, with some particular observations on α ‐MnO 2 cathode. The results show that the catalytic activity decreases in the following order: electrolytic MnO 2 (EMD) > natural MnO 2 (NMD) > β ‐MnO 2 > α ‐MnO 2 . The maximum power density of the zinc‐air battery with EMD as the catalyst reaches up to 141.8 mW cm −2 at the current density of 222.5 mA cm −2 , which is about 60%, 20% and 10% higher than that of α ‐MnO 2 (90.0 mW cm −2 at 120.3 mA cm −2 ), β ‐MnO 2 (121.5 mW cm −2 at 150.4 mA cm −2 ) and NMD (128.2 mW cm −2 at 207.8 mA cm −2 ), respectively. It is believed that its unique crystal structure and biggest BET surface area make EMD have the smallest charge transfer resistance ( R ct ), thus EMD has the highest activity.