Robust bifunctional oxygen electrocatalyst with a “rigid and flexible” structure for air-cathodes

The development of highly active air-cathodes with robust stability and a low price is of crucial significance for rechargeable Zn–air batteries and remains a great challenge. Herein, for the first time, we report a “rigid and flexible” material consisting of three-dimensional (3D) porous nickel-manganese oxide (Ni6MnO8) coupled with 1D ultrathin Au nanowires (Au-NWs) as an efficient bifunctional oxygen electrocatalyst, adopting α-naphthol-Au(III) as a precursor of Au-NWs and pre-formed Ni6MnO8 as a support. Ni6MnO8 acts not only as a robust carbon-free support that is stable in alkaline electrochemical conditions, but also as a highly active component for the oxygen evolution reaction (OER), while flexible Au-NWs contribute to the excellent oxygen reduction reaction (ORR) activity and act as a flexible conductive electronic network. The coupling of Ni6MnO8 and Au-NWs plays a complementary role in the two types of oxygen electrocatalytic reactions. Accordingly, their advantages have been optimally harnessed while overcoming their deficiencies. Moreover, a Zn–air battery assembled with such a rigid and flexible air-cathode has lower charge and discharge overpotentials and a higher cyclic stability than those with a mixed Pt/C+RuO2 catalyst. A hybrid material that improves the performance of zinc–air batteries has been developed by researchers in China and Singapore. Metal–air batteries, in which one electrode is made from a metal while the other reacts with oxygen in ambient air, can hypothetically store much more energy per unit mass than other types of rechargeable device but this improved performance has not yet been demonstrated. Yawen Tang from the Nanjing Normal University, China, Jong-Min Lee from the Nanyang Technological University, Singapore, and colleagues have developed an improved air-cathode material made of rigid nickel-manganese oxide microspheres linked by flexible gold nanowires. The oxide material provides the required chemical versatility and stability, while the gold gives the hybrid material its electrical conductivity. A zinc–air battery assembled with this electrode exhibits excellent electrocatalytic performance.