Cubic silicon carbide in water. Photo: Thor Balkhed/LiU.
Cubic silicon carbide in water. Photo: Thor Balkhed/LiU.

One prospective source of renewable energy is hydrogen gas produced from water with the aid of sunlight. Researchers at Linköping University in Sweden have now developed a novel material – nanoporous cubic silicon carbide – that exhibits promising properties for capturing solar energy and splitting water to produce hydrogen. The researchers report this novel material in a paper in ACS Nano.

"New sustainable energy systems are needed to meet global energy and environmental challenges, such as increasing carbon dioxide emissions and climate change," says Jianwu Sun, senior lecturer in the Department of Physics, Chemistry and Biology at Linköping University, who led the new study.

Hydrogen has an energy density three times that of petrol. It can be used to generate electricity in a fuel cell, and hydrogen-fuelled cars are already commercially available. When hydrogen gas is used to produce energy, the only product formed is pure water. But carbon dioxide is still created during hydrogen production, as hydrogen is mainly generated from fossil fuels, with 9–12 tonnes of carbon dioxide emitted for every 1 tonne of hydrogen gas produced.

Producing hydrogen gas by splitting water molecules with the aid of solar energy is a sustainable approach that doesn't generate carbon dioxide. In addition, it offers a way to convert solar energy into a fuel that can be stored.

"Conventional solar cells produce energy during the daytime, and the energy must either be used immediately, or stored in, for example, batteries," says Sun. "Hydrogen is a promising source of energy that can be stored and transported in the same way as traditional fuels such as petrol and diesel."

Spitting water using the energy in sunlight is not an easy task, however, and requires cost-efficient materials that have the right properties for catalyzing the reaction in which water (H2O) is split into hydrogen (H2) and oxygen (O2) through photo-electrolysis. The energy in sunlight that can be used to split water is mostly in the form of ultraviolet and visible wavelenths. Any material must thus be able to absorb these wavelengths to create charges that can be separated and have enough energy to split the water molecules into hydrogen and oxygen gases. Most materials that have been investigated up to now are either inefficient in the way they use the energy in sunlight (titanium dioxide, for example, absorbs only ultraviolet wavelengths), or do not have the properties needed to split water (such as silicon).

In their search for an efficient material, Sun's research group investigated cubic silicon carbide (3C-SiC), producing a form with many extremely small pores. This material, which they call nanoporous 3C-SiC, has promising properties that suggest it can be used to produce hydrogen gas from water using sunlight.

In the ACS Nano paper, the researchers show that this new porous material can efficiently trap and harvest both ultraviolet wavelengths and the majority of visible wavelengths in sunlight. Furthermore, its porous structure promotes the separation of charges with the required energy, while the small pores provide a large active surface area. This enhances charge transfer and increases the number of reaction sites, thus further boosting the material's water splitting efficiency.

"The main result we have shown is that nanoporous cubic silicon carbide has a higher charge-separation efficiency, which makes the splitting of water to hydrogen much better than when using planar silicon carbide," says Sun.

This story is adapted from material from Linköping University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.