Currently, intense work is being done on the creation of new materials to exploit renewable, virtually inexhaustible sources of energy. The photoelectrochemical decomposition of water is developing rapidly and represents a good approximation for transforming solar energy into hydrogen, a source of clean energy that can be stored. In this regard, tungsten oxide (WOx, also known as tungsten oxide) has been investigated as a material for the photoelectrochemical generation of hydrogen, that is, by an electrochemical reaction induced by a photoelectric effect.

In these devices, which offer a good enough performance to be used in the generation of hydrogen effectively, the surface of the nanostructured semiconductor material absorbs solar energy and acts as an electrode for the electrolysis of water, its decomposition into oxygen and hydrogen. In spite of everything, with a capacity to absorb 12% of the solar spectrum and with a relatively low theoretical limit for the photocurrent generated under solar illumination, the material seems far from offering the necessary features for a practical application.

Two groups of tungsten oxide nanocolumns with different radius and height (70/700 nm on the left and 13/130 nm on the right). The large nanocolumns are more effective in the photoelectrochemical separation of water since the photogenerated charges do not recombine rapidly as it happens in the small ones.

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In this framework, researchers from the group Microsystems and Nanotechnologies for Chemical Analysis (MINOS) of the Rovira I Virgili University (URV) and the Technological University of Brno, in the Czech Republic, bring to light new three-dimensional nanomaterials with photoelectrochemical properties for the generation of energy.
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In the study, self-organized clusters of tungsten oxide columns have been developed using the anodization technique (a protective treatment applied to metals through which a larger surface oxide layer is created that would be formed naturally ) assisted by titanium oxide and porous anodic alumina, an aluminum oxide prepared by electrochemical means.

Using different anodization conditions, different nanostructures have been obtained in the form of columns (with different diameters and heights). By varying the conditions of the subsequent treatment, at 500-550 ° C in vacuum or air, together with the selective dissolution of the porous anodic alumina, it has allowed controlling the composition of the nanocolumns of tungsten oxide, its crystalline structure, and the electrical properties.

Excellent performance in the largest nanostructures.

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In particular, the larger diameter structures treated in air show an excellent behavior in the photoelectrochemical decomposition of water: a low start potential, a high photocurrent generated and the absence of signs of photocorrosion.

These promising results are likely to improve, if higher and more densely clustered columns are used so that the efficiency in capturing solar radiation and separating the charges generated can be increased.
With this research, then, new nanomaterials have been created, the characteristics of which allow the photoelectrochemical decomposition of water and facilitate the generation of hydrogen. Therefore, this technique uses a form of renewable, virtually inexhaustible energy that does not produce greenhouse gases.

In conclusion.

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The appearance of these new experiments with nanomaterials constitutes a giant advance in the early generation of renewable energies, which can be called synthetic and that is almost inexhaustible. All this would mark a before and after for the energy industry.

For more information visit:

• https://www.sciencedirect.com/science/article/pii/S1748013217302426
• http://www.sciencedirect.com/science/article/pii/S2211285517300368
• http://www.sciencedirect.com/science/journal/22112855
• https://en.wikipedia.org/wiki/Nanomaterials
• Nanostructures and Nanomaterials, Guozhong Cao (University of Washington, USA)