Artificial Photo Synthesis

By tony leather, 16th Aug 2012 | Follow this author | RSS Feed | Short URL http://nut.bz/1nkqy_ru/
Posted in Wikinut>News>Technology

Individual nano-trees are grown in a liquid, a silicon nano-wire placed into a zinc solution, in which the wire undergoes a chemical reaction, growing zinc oxide branches. To give a real idea of the scale here, 10,000 nano-trees could fit on the cross-section of a human hair.

Artificial Photo Synthesis

Nano-trees

For humanity ever to be able to artificially copy the unique way in which nature converts sunlight into energy, then science will need to need to create some very extraordinary pseudo-plants or trees indeed.

Californian electrical engineers have been trying to do just that, an amazing new nano-tree device created out of cheap, abundant materials. Incredibly, these creations use sunlight to split H2O - water molecules - into the base elements of oxygen and hydrogen, freeing them up for use in fuel cells.

Car technology already envisages the use of Hydrogen fuel cells, but they could equally be used to power houses, and since, in nature, hydrogen never exists alone, atoms must be separated out in order that they can be put to use.

Such extraction of course requires energy and with around 90% currently created via the use of fossil fuels - causing CO2 emissions - U.C. San Diego PhD student Ke Sun, and professor of electrical and computer engineering Deli Wang, collaborated to bring the nano-tree to fruition.

These could, potentially, employ sunlight to generate electrical currents without greenhouse gas emissions in controlled conditions, acting just as real trees would. In August 2009, Sun approached Wang with the idea to engineer branched nano-structures for solar cells, knowing that vertical nano-wires would be very good light harvesters.

Individual nano-trees are grown in a liquid, a silicon nano-wire placed into a zinc solution, in which the wire undergoes a chemical reaction, growing zinc oxide branches. To give a real idea of the scale here, 10,000 nano-trees could fit on the cross-section of a human hair.

One sq cm holds one million nano-trees, forming a single photo-electro-chemical cell, or PEC. This array is placed in another solution and exposed to sunlight, where silicon nanowire tree-trunk absorbs most of the light, transferring electrons through the zinc oxide branches to the surrounding water, generating hydrogen gas, which bubbles up through the solution to be harvested.

As yet no efficient way for collecting the hydrogen has been thought up, though a special two-compartment cell could be used to collect the hydrogen and ultimately produce electricity. Thing is that since conventional technologies for splitting water are expensive, nano-trees look like a bargain.

This method is thought to be 100 X cheaper than current systems, but is much less efficient at only 3% hydrogen generation efficiency against the world record 12.8%.
Wang and Sun are currently testing different nano-tree materials because Zinc oxide does have some drawbacks, only absorbing UV light and not being very stable, so they want to find a more chemically robust oxide to use.

The goal, Over the long-term, is to integrate more materials, including catalysts for the development of artificial photosynthesis, which would entail developing an ultra-efficient process. Though they are still some way off succeeding, they have made an excellent start.

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Meet the author

tony leather
mainly non-fiction articles, though I do write short stories, poetry and descriptive prose as well. Have been writing for over ten years now