Nanowires that efficiently split water into oxygen and hydrogen could be an important step toward affordable chemical storage of solar power according to US scientists.  

Water and sunlight are highly abundant and nature uses these to make energy through photosynthesis. Despite intensive studies on artificial photolysis, making it as efficient as nature is proving difficult. 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 amount of light converted to energy is low. 

Now, Hongkun Park and colleagues, at Harvard University, have synthesised TiO₂ nanowires with high surface areas, deposited them on an electrode and found that chemically crosslinking 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, says Park. 

Doping the nanowire network with gold or silver nanoparticles allows the water splitting reaction to take place under visible light, adds Park. This could lead to a ten fold improvement in the catalysts ability to split water, he says. 

'Our work shows that the performance of a material can be enhanced by putting it in a nanostructured network, and this design can potentially be extended to many other materials to achieve the goal of highly efficient solar water-splitting,' says Park. 

Steve Dunn, an expert in materials chemistry, at the Centre for Materials Research, Queen Mary University of London comments, 'This work is very interesting with the most significant new finding being the morphological change from using more traditional titania powders to using nanorods. The advantages of using titania, over other more exotic systems, is that the chemistry is well known, it is highly photostable, it is cheap and is also non-toxic.' 

The group now plan to study water photoelectrolysis with other metal oxides, such as iron oxide, that can absorb visible light and to study how their efficiency is enhanced in a similar nanowire networks. 

Carl Saxton 

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