'Nanotrees' could deliver clean fuel

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SAN DIEGO, March 7 (UPI) -- U.S. engineers say a forest of tiny "nanowire trees" can cleanly capture solar energy without using fossil fuels and harvest it for hydrogen fuel generation.

Electrical engineers at the University of California, San Diego, writing in the journal Nanoscale, said nanowires made from abundant natural materials such as silicon and zinc oxide offer an inexpensive way to deliver hydrogen fuel on a mass scale.

"This is a clean way to generate clean fuel," Deli Wang, a professor in the Department of Electrical and Computer Engineering, said in a UCSD release Wednesday.

The trees' vertical structure and branches are keys to capturing the maximum amount of solar energy, Wang said, because the vertical structure of trees grabs and adsorbs light while flat surfaces would simply reflect it away.

The technology is similar to retinal photoreceptor cells in the human eye, he said.

The researchers' "3-D branched nanowire array" uses a process called photoelectrochemical water-splitting to separate water into oxygen and hydrogen and extract the hydrogen for use as a fuel.

The current conventional way of water-splitting to produce hydrogen relies on electricity from fossil fuels.

"Hydrogen is considered to be clean fuel compared to fossil fuel because there is no carbon emission, but the hydrogen currently used is not generated cleanly," Ke Sun, a Ph.D. student in electrical engineering who led the project, said.