A review on advancement in non-noble metal based oxides as bifunctional catalysts for rechargeable non-aqueous Li/air battery

Rechargeable non-aqueous Li/air battery is considered as a better alternative for Li-ion batteries for electric vehicle and large-scale energy storage because of its high theoretical energy density, ~ 11,400 Wh kg− 1, close to that of fossil fuel, gasoline (13,000 Wh kg− 1). However, the exorbitant over voltage mainly caused by sluggish Oxygen Reduction Reaction (ORR) and Oxygen Evolution Reaction (OER) impedes the extraction of full potential of Li/air system. Essentially Li/air system needs bifunctional catalyst to enhance the rate of both OER and ORR. The formation of insoluble discharge product, oxides of Li and decomposition of non-aqueous electrolytes complicate the mechanism of ORR/OER and hence finding an effective catalyst for non-aqueous Li/air system is a challenging task. Even the catalytic activity of well-known catalysts for ORR/OER of aqueous system could not be translated to non-aqueous Li/air system. Different kind of materials like noble metals, non-noble metals and their oxides as well as carbon based materials have been investigated for their bifunctional catalytic activity in non-aqueous Li/air system. In this context, this paper presents the overview of advancement in bifunctional low-cost non-noble transition metal oxides based catalysts for non-aqueous Li/air battery.