Non-precious metal electrocatalysts for rechargeable metal-air batteries

Rechargeable metal-air batteries (M= Li and Zn) have a high specific capacity and a lower cost than conventional Li-ion batteries and are predicted to be emerging power sources for electric vehicles and portable electronic devices. The performance of Li-O2 batteries is severely hampered by several constraints, such as poor round-trip efficiency, limited long cycling and higher reactivity of electrolyte, which are mainly coming from huge charge overpotential (1 V) of the cell.  The development of non-precious metal OER (oxygen evolution reaction) electrocatalysts to lower the charge overpotential is one of the key objectives of the current thesis. Two distinct types of O2 cathodes (based on fluoride and borate) have been developed in this area for use in Li-O2 batteries. In comparison to the fluoride perovskite OER electrocatalyst, the borate-based electrocatalyst exhibits a reduced charge overpotential (0.64 V) and remarkable cycling stability (up to 200 cycles).  Similarly, the performance of Zn-air batteries is hampered by an unsolved hindrance caused by the poor reaction kinetics of OER and oxygen reduction reaction (ORR). To fill this research gap, another objective of the thesis is to develop low-cost non-precious metal bi-functional electrocatalysts to improve the reaction kinetics of rechargeable Zn-air batteries. In order to improve the reaction kinetics during the cycling of rechargeable Zn-air batteries, two types of non-precious metal electrocatalysts, including perovskites and spinel-based materials, were developed. The perovskite-based bi-functional electrocatalyst exhibits a charge-discharge overpotential (0.78 V) even after 1400 cycles and has exceptional cycling stability for 240 hours. According to these findings, a very small amount of a noble metal, such as Ru, incorporated into the perovskite lattice results in a remarkable bi-functional cathode catalyst that is appropriate for use in practical applications.