Running cars, homes and buildings on hydrogen has long thought to be the ultimate clean solution, but getting there has been tough.
Researchers at University of California, San Diego are creating a “nanoforest” that can capture solar energy and use it to generate hydrogen fuel.
Reporting in the journal Nanoscale, the team said nanowires, which are made from abundant natural materials like silicon and zinc oxide, also offer a cheap way to deliver hydrogen fuel on a mass scale.
The trees’ vertical structure and branches are keys to capturing the maximum amount of solar energy. That’s because the vertical structure of trees grabs and adsorbs light while flat surfaces simply reflect it, which is also similar to retinal photoreceptor cells in the human eye. In images of Earth from space, light reflects off of flat surfaces such as the ocean or deserts, while forests appear darker.
“This is a clean way to generate clean fuel,” said Deli Wang, professor in the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering.
Wang’s team has mimicked this structure in their “3D branched nanowire array” which uses a process called photoelectrochemical water-splitting to produce hydrogen gas. Water splitting refers to the process of separating water into oxygen and hydrogen in order to extract hydrogen gas to be used as fuel. This process uses clean energy with no green-house gas byproduct. By comparison, the current conventional way of producing hydrogen relies on electricity from fossil fuels.
By harvesting more sun light using the vertical nanotree structure, researchers have developed a way to produce more hydrogen fuel efficiently compared to planar counterparts.
The vertical branch structure also maximizes hydrogen gas output. For example, on the flat wide surface of a pot of boiling water, bubbles must become large to come to the surface. In the nanotree structure, very small gas bubbles of hydrogen can be extracted much faster.
“With this structure, we have enhanced, by at least 400,000 times, the surface area for chemical reactions,” says Ke Sun, an electrical engineering Ph.D. student who is leading the project.
If hydrogen fuel cells were cheap enough they would be ideal for energy storage for buildings, the grid, and in fuel cell vehicles.
In the long run, the team is aiming for a holy grail of energy production: artificial photosynthesis. It would also capture carbon from the atmosphere, reducing emissions and converting it to hydrocarbon fuel.
The research is published in Nanoscale, and will be presented at the annual Research Expo, in April at the Jacobs School of Engineering.
[source: University of California, San Diego]
