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Nanowires for electrolyzer

An electrolyzer uses two different electrodes, one of which releases the oxygen atoms and the other the hydrogen atoms. Although it is the hydrogen that would provide a storable source of energy, it is the oxygen side that is more difficult, so that’s where many other research groups have concentrated their efforts. Nanowires are now used for efficiently splitting water into oxygen and hydrogen. Highly dense vertical arrays of nanowires made from silicon and titanium oxide and measuring 20 microns in height show promise for the efficient production of hydrogen through solar water splitting. Titanium dioxide electrodes are one way to split water under ultraviolet light but the efficiency is low as they are only able to absorb ultraviolet light and the conversion efficiency is low.
Metal oxide nanowires
Researchers at Harvard University have synthesized TiO2 nanowires with high surface areas, deposited them on an electrode and found that chemically cross linking them increases their optical density allowing more light to be absorbed. This allows the light to energy conversion to be doubled compared to previous TiO2 electrodes. Doping the nanowire network with gold or silver nanoparticles allows the water splitting reaction to take place under visible light and could lead to a ten fold improvement in the catalysts ability to split water. The advantages of using titania, over other more systems is highly photostable, it is cheap and is also non-toxic. Water photo electrolysis with other metal oxides, such as iron oxide which can absorb visible light is also possible.
Researchers at University of California have fabricated devices using dense and vertically aligned metal oxide nanowire arrays, such as TiO2 and ZnO, as photo anodes. They have explored different methods including elemental doping and quantum dot sensitization to improve the visible light absorption of these wide band gap metal oxides. They prepared dense and vertically aligned ZnO nanowires from a hydrothermal method, followed by annealing in ammonia to incorporate N as a dopant. Upon illumination at a power density of 100 mW/cm2 (AM 1.5), water splitting was observed in both ZnO and ZnO:N nanowires.
New Catalyst
Researchers at MIT have found a formulation based on inexpensive and widely available materials that can efficiently catalyze the splitting of water molecules using electricity. Nickel borate made from materials function as the oxygen-producing electrode that are even more abundant and inexpensive than those used earlier such as expensive platinum catalyst.

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