Biocharged supercapacitors - cheaper wood-based solutions

Materials World magazine
26 Nov 2013

A supercapacitor made using wood-biochar has been proven to produce as much power as carbon-based devices, according to a study by researchers working at the University of Illinois in the USA. Manufacturing the low-cost supercapacitor could also produce a useful by-product.

Supercapacitors are usually used in lowpower electronics such as photographic flashes and portable media players. But most of these devices make use of activated carbon sourced from fossil fuels. Activated carbon models must be created using a complicated and costly procedure to develop microstructures in the material. Junhua Jiang, Senior Research Engineer at the University’s Illinois Sustainable Technology Centre, led the study. His team managed to recreate the properties of these devices using the natural network of pores in biochar – created by heating wood in a low-oxygen environment. Jiang said, ‘Biochar is a nanostructured material with diverse and fascinating patterns. Higher performance may be obtained but the increased costs associated with this could be a limitation,’ Jiang explained.

The researchers activated the biochar using mild nitric acid. Jiang said, ‘Several nitrates such as potassium nitrate and calcium nitrate could be created as a by-product, depending on the composition of the biochar. Potassium nitrate is used in fertilisers as a source of nitrogen and potassium – two macronutrients for plants.’

The team experimented with a range of wood varieties to find the best-performing material, ‘We have studied a range of biochars prepared from more than 30 wood feedstocks. Some of the samples, such as red cedar, maple and cherry, work particularly well.’ The group examined the capacitive performance of each wood variety and plan to publish its findings. Jiang suggested that the performance of biochars could be attributed to differing pore structures where ions are stored and released when used in a supercapacitor.

The wood-based device can match the performance of existing models but with fewer adverse effects on the environment. Jiang says, ‘The performance of our biochar supercapacitors is comparable to conventional activated-carbon devices and even those created using state-of-theart advanced materials such as carbon nanotubes and graphene.’ Jiang claims that the supercapacitors are also five to 10 times cheaper than existing technologies. This reduced cost could help promote their use in energy storage for solar panels and wind turbines.

The team also believes that the biochar-based supercapacitors could be crushed and used as an organic soil amendment at the end of its useful life.