Underlying nanoparticle behaviour revealed by In Situ TEM heating

Original article by Jorge Romero, Helena Prima-Garcia, Maria Varela, Sara G. Miralles, Víctor Oestreicher,
Gonzalo Abellán and Eugenio Coronado.

The development of supercapacitors holds great promise for future energy storage devices with a high cyclability and durability which can be used in our homes, cars and mobile phones to support the transition to sustainable energy. Even though a lot of effort has been devoted to improving the energy and power densities by optimizing the internal configuration of the capacitor, there is still room for further improvement. Now, researchers have found a way to dramatically improve the capacitance of an FeNi3–graphene hybrid capacitor with about 1100% (from 155 to 1850 F g−1), showing high stability with capacitance retention greater than 90% after 10 000 cycles. They achieved this impressive enhancement by cycling the electrode material in the presence of an applied magnetic field of 4000 G.

Fig. 1. Magnetic graphene–FeNi3 nanocomposite particle under applied magnetic field, pristine sample.

Fig. 2. Magnetic graphene–FeNi3 nanocomposite particle under applied magnetic field, after a 30 min annealing at 400 °C and fast quench back to RT. Arrow pointing out the nanometallic clusters.

In Situ TEM heating

To explain the behaviour of the nanoparticles under the external magnetic-field, Prof. Maria Varela from Universidad Complutense de Madrid, Spain and her colleagues performed in situ heating experiments using a DENSsolutions Lightning D9+ heating and biasing double tilt system. The magnetic field of the microscope objective lens combined with the heating stimuli, provided by the DENSsolutions’ system, were able to observe a significant magnetic field and temperature induced metal segregation of Fe/Ni surfaces forming nanometallic clusters of Ni (<5 nm).

Using these results, the authors were able to explain the dramatic increase of the specific capacitance of the device during the cycling. Furthermore, they opened the door to a systematic improvement of the capacitance values of hybrid supercapacitors, moving the research in this area towards the development of magnetically addressable energy-storage devices.

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