Abstract
The rise in energy consumption is largely driven by the growth of population. The supply of energy to meet that demand can be fulfilled by slowly introducing energy from renewable resources. The fluctuating nature of the renewable energy production (i.e., affected by weather such as wind, sun light, etc.), necessitates the increasing demand in developing electricity storage systems. Reliable energy storage system will also play immense roles to support activities related to the internet of things. In the past decades, metal-air batteries have attracted great attention and interest for their high theoretical capacity, environmental friendliness, and their low cost. However, one of the main challenges faced in metal-air batteries is the slow rate of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) that affects the charging and the discharging performance. Various types of nanostructure manganese oxide with high specific surface area and excellent catalytic properties have been synthesized and studied. This review provides a discussion of the recent developments of the nanostructure manganese oxide and their performance in oxygen reduction and oxygen evolution reactions in alkaline media. It includes the experimental work in the nanostructure of manganese oxide, but also the fundamental understanding of ORR and OER. A brief discussion on electrocatalyst kinetics including the measurement and criteria for the ORR and the OER is also included. Finally, recently reported nanostructure manganese oxide catalysts are also discussed.
Highlights
The continuous growth of population has led to the increase in energy consumption.Most of the energy demand has been produced through the combustion of fossil fuels
The few important electrocatalytic kinetic parameters required to extract and compare the performance of an electrocatalyst by conducting linear scan voltammetry (LSV) using potentiostat are: (i) onset potential (Ei0 ), (ii) overpotential (η), (iii) current density exchange (i0 ), (iv) Tafel slope of anodic and cathodic for both the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) and lastly (v) number of electrons transferred in reaction (n) for the ORR
The electrochemical testing of catalysts for ORR or OER is usually performed by a rotating disk electrode (RDE) or a rotating ring disk electrode (RRDE)
Summary
The continuous growth of population has led to the increase in energy consumption. Most of the energy demand has been produced through the combustion of fossil fuels. Zinc-air batteries do not require a storage casing which is typically heavy and space consuming They have received tremendous attention because of the advantage of high specific energy density with a constant discharge voltage. The search for more economic and robust catalysts with high catalytic activities have becoming the main key in the development of the zinc-air batteries. Manganese oxide is an attractive alternative thanks to its robust OER and ORR performance [10,13,14,15]. This review focuses on the effect of different nanostructures on the electrocatalytic performance of manganese oxide as a bifunctional electrode for ORR and OER in alkaline media. This paper reviews recent developments of the nanostructure manganese oxide and their performance in oxygen reduction and oxygen evolution reactions in alkaline media. Recently reported nanostructure manganese oxide catalysts are discussed
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