Posted on November 12, 2021
University of Pretoria (UP) physicists successfully turned plant waste into a component of high-powered devices called supercapacitors. During testing, international researchers found that the component, known as activated carbon, is superior to commercially-available alternatives.
Professor Ncholu Manyala led the UP team alongside scientists from the University of Bologna, Italy. Prof Manyala is the SARChI Chair in Carbon Technology and Materials, as designated by the National Research Foundation (NRF).
“This work revolves around being able to produce energy using waste, manage that energy by storing it using waste materials, and also use that waste product to treat water and produce electricity using microbial fuel cells,” says Prof Manyala. It takes Africa and the world closer to a recycling loop where water used to grow food can be cleaned using energy from food waste. Researchers call this elusive loop the “Water-Energy-Waste Nexus”.
The researchers started with the idea of extracting valuable materials from the woody, sawdust-like waste from biodigesters. A biodigester converts biowaste, such as discarded food, into biogas used for cooking or generating electricity.
The dry waste from a biodigester is called lignin, which is usually repurposed as fertiliser for crops or to carpet the floors of livestock enclosures. Prof Manyala and his colleagues wanted to turn this lignin into activated carbon instead.
“The team in Italy provided us with the lignin raw material, which we took through the activation process that converted it into activated carbon,” says Prof Manyala. “We managed to create a highly porous carbon material, and used it to make supercapacitors.”
Prof Manyala’s team then put the supercapacitors to the test. After discharging high amounts of energy in over 15 000 cycles, they found that the technology retained its capacitance at over 80%.
Further tests by the Italian team showed that Prof Manyala’s activated carbon was superior to other commercially available options.
The carbon material also works in microbial fuel cells, which use microorganisms to produce electricity from waste. This electricity, in turn, can be used to treat wastewater for food crop irrigation.
Prof Manyala says the fact that a common biomass waste like lignin can be used to make supercapacitors is a huge leap forward for sustainability.
“If there's anything that Africa has in abundance, it is biomass,” Prof Manyala says. “This includes tree bark, pepper seeds, peanut shells, and even chicken bones.”
He says he will continue working with what he calls the “United States of Africa researchers” – a diverse group of physicists ready to convert biomass materials into parts for microbial fuel cells and supercapacitors.
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