Electric cars and power tools could harness this hemp technology, the US researchers say.
They presented their work at the American Chemical Society meeting in San Francisco.
"People ask me: why hemp? I say, why not?" said Dr David Mitlin of Clarkson University, New York, who describes his device in the journal ACS Nano.
"We're making graphene-like materials for a thousandth of the price - and we're doing it with waste.
"The hemp we use is perfectly legal to grow. It has no THC in it at all - so there's no overlap with any recreational activities."
Secret sauce In countries including China, Canada and the UK, hemp can be grown industrially for clothing and building materials.
But the leftover bast fibre - the inner bark - typically ends up as landREAD MORE