Nano-Tree to store solar energy and convert water into hydrogen

Researchers at the University of California at San Diego have built a forest of small trees of nanowires to capture solar energy without using fossil fuels. Solar energy is then converted into hydrogen. The research presented in the latest issue of the journal Nanoscale.

Nano threads are produced from natural materials which plenty on earth, such as silicon and zinc oxide, which makes production technology for a cheap way to produce hydrogen on a large scale.

- This is a clean way to deliver a clean fuel, says Deli Wang, a professor in the Department of Electrical and Computer Engineering, University UC San Diego Jacobs School of Engineering.

The tree structure and vertical segments are crucial importance in order to be able to absorb as much of the solar energy as possible. This is because the vertical structures catch and absorb the light while the flat surfaces only reflects it. This is done in a similar way to the photoreceptor cells in the human retina of the eye catches the light.

Wang's team has mimicked this structure in its three-dimensional forest of branched nanowires. It uses a process called the photo-electrochemical decomposition of water ("photoelectrochemical water-splitting") to produce hydrogen.

The water disintegration is the process consisting in that water is separated into oxygen and hydrogen in order to extract hydrogen. The process uses clean energy without any greenhouse gases as byproducts. By comparison, builds current technologies to produce hydrogen on electricity, often generated from fossil fuels.

- Hydrogen is considered a clean fuel compared to fossil fuels because it produces no carbon emissions, but production is currently not in an environmentally friendly way, says Ke Sun, a graduate student in electrical engineering who attended the project.

The vertical tree structure also maximizes the production of hydrogen. One can liken this to a pot of boiling water. Is the pan on a flat surface, the bubbles must be pretty big to get up to the surface. The nano-tree structure can be very small gas bubbles of hydrogen is extracted more rapidly.

In the long term goal is more Wang's research goes way: to create artificial photosynthesis. In photosynthesis, plants absorb sunlight while storing carbon dioxide and water from the atmosphere to produce carbohydrates for its own growth. Wang's team hopes to simulate this process is also used to capture carbon dioxide from the atmosphere, reducing carbon dioxide emissions and convert it into fuel.

- We try to simulate what plants do to convert sunlight into energy. We hope that our "Nano tree" in the near future may become part of a device that works like a real tree for photosynthesis, says Sun.