Weltnachrichten – AU – High-performance graphene hybrid material for highly efficient supercapacitors

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4th. January 2021

from the Technical University of Munich

In collaboration with Roland Fischer, Professor of Inorganic and Organometallic Chemistry at the Technical University of Munich (TUM), a highly efficient supercapacitor was developed. The basis of the energy storage system is a new, high-performance and sustainable graphene hybrid material that has performance data comparable to that of the batteries currently in use.

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Energy storage systems are usually associated with batteries and accumulators that provide energy for electronic devices. Nowadays, however, so-called supercapacitors are increasingly being installed in laptops, cameras, cell phones or vehicles.

Unlike batteries, they can store large amounts of energy quickly and extinguish them just as quickly. If, for example, a train brakes when entering the station, supercapacitors store the energy and deliver it again when the train needs a lot of energy very quickly when it starts.

One problem with supercapacitors so far has been the lack of energy density. While lithium accumulators achieve an energy density of up to 265 kilowatt hours (KW / h), supercapacitors have only supplied a tenth of this so far.

The team working with the TUM chemist Roland Fischer has now developed a new, high-performance and sustainable graphene hybrid material for supercapacitors. It serves as a positive electrode in the energy store. The researchers combine it with a tried and tested titanium and carbon-based negative electrode.

The new energy storage not only achieves an energy density of up to 73 Wh / kg, which roughly corresponds to the energy density of a nickel-metal hydride battery, but is also much more powerful than most other supercapacitors with a density of 16 kW / kg. The secret of the new supercapacitor is the combination of different materials – this is why chemists call the supercapacitor « asymmetrical ». ‘

The researchers are using a new strategy to overcome the performance limits of standard materials – they use hybrid materials. « Nature is full of highly complex, evolutionarily optimized hybrid materials – bones and teeth are examples. Their mechanical properties such as hardness and elasticity were naturally optimized by combining different materials, « says Roland Fischer.

The abstract idea of ​​combining basic materials was transferred to supercapacitors by the research team. As a basis, they used the novel positive electrode of the storage unit with chemically modified graphene and combined it with a nanostructured organometallic framework, a so-called MOF.

Decisive for the performance of graphene hybrids are on the one hand a large specific surface and controllable pore sizes and on the other hand a high electrical conductivity. « The high-performance capability of the material is based on the combination of the microporous MOFs with the conductive graphenic acid, » explains first author Jayaramulu Kolleboyina, a former visiting scientist who works with Roland Fischer.

A large surface area is important for good supercapacitors. It enables a large number of charge carriers to be collected within the material – this is the basic principle for storing electrical energy.

By clever material design, the researchers succeeded in connecting the graphenic acid with the MOFs. The resulting hybrid MOFs have a very large internal area of ​​up to 900 square meters per gram and are very powerful as positive electrodes in a supercapacitor.

This is not the only advantage of the new material, however. In order to obtain a chemically stable hybrid, one needs strong chemical bonds between the components. The bonds are apparently the same as those between amino acids in proteins, says Fischer: « In fact, we have linked the graphene acid to a MOF amino acid that creates a kind of peptide bond. « 

The stable connection between the nanostructured components has enormous advantages in terms of long-term stability: the more stable the connections, the more charging and discharging cycles are possible without significant performance impairment.

For comparison: a classic lithium storage device has a service life of around 5. 000 cycles. The new cell developed by the TUM researchers remains intact even after 10 weeks. 000 cycles a capacity of almost 90 percent.

Fischer emphasizes the importance of the unrestricted international cooperation that the researchers themselves controlled in order to develop the new supercapacitor. Jayaramulu Kolleboyina built the team accordingly. He was a visiting scientist from India who was invited by the Alexander von Humboldt Foundation and who is now head of the chemistry department at the newly founded Indian Technology Institute in Jammu.

« Our team has also networked with experts in electrochemistry and battery research in Barcelona as well as with experts in graphene derivatives from the Czech Republic, » reports Fischer. « We have also integrated partners from the USA and Australia. This wonderful international collaboration promises a lot for the future. «  »

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Supercapacitor, graphene, hybrid material, energy storage, nanotechnology, energy density, electric battery

World News – AU – High-performance graphene hybrid material for highly efficient supercapacitors
Related title :
Powerful hybrid graphene material for highly efficient supercapacitors
Highly efficient supercapacitors made from a sustainable graphene hybrid material

Ref: https://phys.org

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