Hydrogen fuel made from a tiny forest of nanotreesElectrical engineers at the University of California-San Diego have built a forest of nanowire trees that use solar energy to turn water into  hydrogen  fuel.   The team recently reported their findings in the Nanoscale.	
	      
		

Hydrogen fuel is considered a clean fuel because it doesn't generate carbon emissions. However, the conventional method of producing hydrogen gas relies on energy from fossil fuels to separate the atoms from other molecules like water.
Deli Wang, professor in the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering, and his team sought out a way to cleanly capture solar energy without using fossil fuels and harvest it for hydrogen fuel generation.
Their creation: a silicon-based nanowire that grows zinc oxide branches when placed in a chemical reacting zinc solution, Alyssa Danigelis of  Discovery News recently reported. These nano-structures, like the name suggests, are tiny. One of these nanowire trees can reach up to a couple of microns in length. Ten thousand of these suckers could fit on the cross-section of a human hair.
The scientists took more than one million nanotrees to form a square centimeter-sized photoelectrochemical cell. From here, the nanotree forest is placed in another solution and exposed to sunlight. The vertical silicon structure absorbs the most of the light and then transfers electrons through the zinc oxide branches to the surrounding water. That reaction produces hydrogen gas, which bubbles up through the solution.
The world won't be teaming with nanowire-producing hydrogen forest anytime soon. Scientists have yet to develop an efficient method for collecting the hydrogen. They plan to try building a two-compartment cell, with a cathode on one side and an anode on the other -- to collect the hydrogen, Discovery News reported. The nanowire trees also have an efficiency problem. The device the team created has 3 percent hydrogen generation efficiency compared to the world record of 12.8 percent, Wang told Discovery News.
The nanowire trees have managed to crush the cost-effectiveness of conventional technologies that separate hydrogen from water. According to Wang, their method is 100 times cheaper than what's currently being used.
The end goal for Wang's team is artificial photosynthesis. Specifically, a device that can mimic a plant's ability to not only absorb sunlight, but to collect carbon dioxide from the atmosphere and convert it into a hydrocarbon fuel.

Photo: Flickr user MWolstenholme, CC 2.0