Among the next emerging energy storage devices, metal–air batteries are focusing intense research and development and extensive interests in the energy field due to their high theoretical energy density (up to four times that of lithium-ion batteries) and potential low cost with high level of safety. Metal-Air technology provides a clean, safe, and reliable source of energy, with a modest profile of power and a very limited weight and cost.

Metal-air batteries are an attractive technology. They are safer and have a higher energy density than other types of batteries. The application of air as a cathode helps in lowering the cost and the weight considerably. The utilization of cheap metals as an anode further assists in lowering the cost.

A metal-air battery functions in an open system. This system comprises a porous air cathode, a metal anode, and an electrolyte. Air cathodes utilize their oxygen. Metal anodes include zinc, lithium, aluminium, and iron.

The fundamental working principle of a metal-air battery is to electrochemically reduce the oxygen from the air and oxidize the metal. This forms solid metal oxides that may be recycled.  This method allows for substantial reductions in the size and the weight of the battery.

Potential Metal-Air batteries applications:

Metal-air batteries can be used as small power sources for portable electronic devices like electric cars.

Metal-air batteries can be used as energy storage devices or as effective stations of energy transfer for renewable energy producers. This is because they can control the flow of energy from sources such as photovoltaic panels and wind turbines.

Metal-air batteries can be used in the treatment of water. The studies on the treatment of water conducted by metal-air batteries may be classified into three categories. These are the collection of compounds in water, the removal of heavy metals from water and the treatment of household sewage. The studies on metal-air batteries in this area are highly limited and very uncommon.

Metal-air batteries hold tremendous prospects for the desalination of water. A metal-air desalination battery is a self-powered device. It can desalinate water while also generating energy.

The combination of graphene as a structural support for metal oxide nanoparticles has shown a great profile for the ORR (Oxygen Reduction Reaction) and OER (Oxygen Evolution Reaction) in laboratory scale tests, which allows potential exploitation in this key application. Graphene-based electrocatalysts have attracted much attention due to their tuneable catalytic properties, high electrical conductivities, and large surface areas.

There is a major drawback to this technology, however, in its limited cyclability. In fact, there are only primary (non-rechargeable) batteries in the market due to the absence of alternatives that combine both ORR and OER reactions in the cathode of the battery in order to make secondary (rechargeable) batteries commercially viable.

 Fig 1. Comparative between state of the art/ Gnanomat catalyst.

Gnanomat has conducted developments in collaboration with an independent partner to bring some of the materials with outstanding profiles for ORR and OER to prototypes of secondary metal-air batteries. In these tests, secondary metal-air batteries electrodes containing Gnanomat catalyst optimised materials showed a satisfactory cyclability and confirmed viability to become a suitable alternative to state-of-the-art devices.

The formulation of the hybrid nanomaterials tested exhibited very good safety and toxicity profiles, in contrast to some of the alternatives under development in this field where critical and toxic materials are typically used. These results have allowed us to collaborate with metal-air batteries developers to bring these materials to commercial products.

We have also tested our materials in a primary zinc-air battery, (current highest maturity metal-air battery technology) with an industrial player with promising results with as yet un-optimised hybrid nanomaterials, suggesting a remarkable development opportunity towards bringing rechargeable metal-air battery devices to market in the near future.

Primary zinc-air batteries have very high energy densities and are applied in stationary solutions where long battery life is more important than power.