Durian has been popularly labeled as “the king of fruits” in Southeast Asia because of its combination of flavorful pulp and pungent smell. Opinions about its smell are sharply divided between “very aromatic” from those who love it and “very putrid” from those who hate it. For scientists doing research in energy storage, any kinds of fruit that have the potential to become materials for batteries or capacitors are “good” regardless of taste or smell. Recently, a research team at the University of Sydney in Australia has created electrode materials out of durian and jackfruit. These materials, in turn, could be used in building high-performance supercapacitors that can rapidly charge smartphones and tablets.

Supercapacitors represent another kind of energy storage technology. Whereas the operation of batteries (such as lithium-ion batteries) is primarily based on chemistry, the operation of capacitors is primarily based on physics. In comparison, capacitors have a higher power density that leads to more rapid charge and discharge. Batteries, on the other hand, have a higher energy density that leads to more energy stored for the same weight. Capacitors also have another major advantage: a much longer cycle life. When properly used, capacitors can undergo charging and discharging almost infinitely.

Typically, a capacitor comprises two electrical conductors separated by a dielectric medium and two electrodes. Carbon materials (e.g., activated carbon, carbon nanotubes, and graphene sheets) are now being used for the electrode and the coating of the conductor because their high porosity improves the performance of a capacitor.

Many companies and research agencies are now looking for carbon materials that can be sourced in an environmentally sustainable way and have all the right attributes for energy storage applications. Organic wastes such as coconut husks, almond shells, and walnut shells have been considered as potential feedstock for processes that can yield advanced carbon materials. In the study done by the team at the University of Sydney, the sticky jackfruit and infamous durian were chosen. Both jackfruit and durian have a spongy and fibrous core that be transformed into a porous electrode material with a substantial surface area.

The research team took samples from the respective cores of the two fruits and subjected them to a complicated procedure to obtain carbon aerogel. The samples were first rinsed with water and then steamed in an autoclave for 10 hours at 180°C. Afterwards, they were rinsed with water again and freeze-dried in a vacuum environment for 24 hours at minus 80°C. Finally, they were heated in a furnace for an hour at 800°C and then cooled naturally. The pyrolysis process created a jackfruit-based carbon aerogel and a durian-based counterpart. They are black in color and structurally porous.

The study by the research team reveals that the pieces of carbon aerogel derived from jackfruit and durian all scored very high marks in storage capability, cycling stability, and other performance areas. They can be used to replace existing active carbon materials for capacitors. The two fruits also appear to be more suited for manufacturing carbon aerogel compared with other kinds of organic wastes.

However, laboratory data also indicate that the carbon aerogel made from durian has larger pores and thus a greater surface area versus the jackfruit-based counterpart. At a current density of 1A/g, the former’s specific capacitance is 591F/g, whereas the latter’s specific capacitance is 292F/g.

Vincent G. Gomes, an associated professor of chemical engineering at the University of Sydney and a co-author of the study, said that the process that his team has developed for manufacturing carbon aerogel will extract a lot of values from kitchen and agricultural wastes. Using organically based materials for supercapacitors will not only generate additional economic activities but also reduce environmental pollution. Gomes added that sustainable solutions for meeting the growing demand for energy storage are necessary in the context of limited resources.

 (News source: TechNews. Photo credit: Pixabay.)