Biocharged supercapacitors - cheaper wood-based solutions

Wood Focus magazine
,
16 Dec 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.