Electronics from Peanut Shells

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May 30, 2025&bullet; Physics 18, 112

Balla Ngom has developed a sustainable energy-storage device that is made from agricultural byproducts.

Batteries and other electronic storage devices are often expensive, but Balla Ngom—a physicist from Cheikh Anta Diop University in Senegal—has a way to make them for peanuts. Or, more precisely, from peanut shells. For the past ten years, Ngom has been looking for sustainable manufacturing processes that utilize agricultural waste products, such as peanut shells and rice husks, to form electrode materials. He and his colleagues have fabricated a small, plant-derived supercapacitor that could be used in handheld electronic devices. He is now looking for investors to help develop techniques for larger storage devices that could supply electricity in remote areas.

Ngom presented some of this work at the Senegal session of the American Physical Society’s Global Physics Summit in March—one of several satellite sessions that were hosted around the world. Physics Magazine caught up with Ngom to dig into more of the details of this green synthesis.

All interviews are edited for brevity and clarity.

How did you get started on this sustainable electronics project?

In 2014, I was in South Africa for a postdoc, and I began working on how to transform biomass into advanced nanomaterials. With my colleagues, we developed a process to produce oxides from agricultural residues—the parts of the plants that are left over after the main part is harvested. A few years later, I had an idea: Instead of just producing oxides, let’s also use the carbon from the plants. Combining the carbon and the oxide gives a composite material that has interesting electronic properties. In my lab here in Senegal, we’ve developed an all-in-one process for transforming biomass into a composite material that can be used in clean and affordable energy storage devices.

What sort of residues can you use?

The economy in Senegal is based mostly on agriculture, and there is a huge industry around peanut production. The farmers often don’t know what to do with all the shells. Some people burn them for domestic heating, which is not good for the environment. We have shown that shells are a good starter material for our composite fabrication process. But other residues can work as well. We’ve had success with hibiscus plants, banana peels, cashew leaves, and rice husks.

Can you describe what you do with these leftovers?

Okay, we have a bunch of peanut shells, for example. We wash them to remove dirt and other impurities, then we dry and grind them into a powder. The next steps are similar to how you would prepare a cup of tea. The powder is added to deionized water and left for a couple of hours. The result is a liquid extract (the “tea”) and a solid residue (the “leaves”). The liquid extract has the carbon compounds that we desire. But it also has the right chemical properties for creating oxides. For example, if we want a nickel oxide, we can add nickel nitrite, a salt, to the extract and heat the mixture in an oven. The resulting oxide-carbon composite has good charge-storing properties. We can also use the solid residue to make a highly-conducting substance called activated carbon.

What can you do with these biomass-derived materials?

We make supercapacitors from them. A supercapacitor is like a battery. The difference is that a supercapacitor typically doesn’t store as much energy as a battery of the same mass, but it can deliver more power, which is energy per time. That high-power delivery is why supercapacitors are often used to crank a car engine or to smooth over short gaps in electricity supply. But as they usually run out of energy quickly, they are not ideal for electric cars or portable electronics. We’re hoping to change that. Our biomass-derived supercapacitors can store energy with relatively high density, so they could potentially be used in traditional battery applications.

Can you give some numbers?

Currently, you can buy supercapacitors that have power densities of 2000–3000 watts per kilogram. That’s very good. But their energy densities are down around 5 watt-hours per kilogram. Batteries, for comparison, offer energy densities of around 200 watt-hours per kilogram. We have made supercapacitors that supply 55 watt-hours per kilogram. That’s a factor of ten improvement over the current market. The power densities are on the low end, at around 760 watts per kilogram. So our challenge now is to maintain the power density, while at the same time increase the energy density.

Where could one of these supercapacitors be used?

I have small prototypes that could work in a remote control, for example. But I'm looking for investors who could help extend the project to make larger supercapacitors. The end goal would be to have a factory in Africa that uses local resources to make affordable energy storage devices.

Where do you imagine such devices being used?

In the rural areas of Africa, people are still using traditional energy sources, such as wood burning. If we can offer an economical device, we could encourage the use of renewable energy in those areas. Solar panels, for example, could be integrated with a storage device to offer electricity for house lighting or for small-scale refrigeration. Such a system could also be part of a circular economy, in which the stored energy is used to pump water for irrigation, supporting small farms that grow crops whose residues could be fed back into the fabrication of the storage devices.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics Magazine based in Lyon, France.