A team of researchers from the Universitat Politècnica de Catalunya, the University of Aberdeen (Scotland) and the University of Auckland (New Zealand) uses ethanol and sunlight to generate hydrogen as an energy source.
The results of the study have been published in Nature Chemistry.
Jordi Llorca, director of the Institute of Energy Technology and researcher at the Universitat Politècnica de Catalunya's Nanoengineering Research Centre, is one of the authors of the study, which represents a major step towards using hydrogen as an alternative to fossil fuels. In the framework of the research, a fully scalable powder photocatalyst was created that makes the hydrogen production process simpler and cheaper as it takes place at ambient temperature and pressure.
A solid photocatalyst is placed in a container with ethanol and exposed to ultraviolet light by agitation, simulating the most energetic part of the solar spectrum. The device contains a titanium dioxide semiconductor that in contact with sunlight generates electrons captured by metallic gold nanoparticles, which react with the alcohol molecules to produce hydrogen. According to Llorca, the semiconductor's structure and the contact with the nanoparticles are crucial features in the design of the photocatalyst.
The amount of hydrogen and energy generated depends on the amount of catalyst used and the area exposed to solar radiation. Researchers have generated up to 5 litres of hydrogen per kilogram of catalyst in one minute. If 9 kg of catalyst were put in an ethanol tank and exposed to sunlight and the hydrogen generated were used to power a fuel cell, 3 kW of electricity would be obtained, an amount similar to that which is used in a home.
Llorca plans to design reactors with real-life applications such as providing electricity to the home, which he sees as an important step towards introducing hydrogen as an energy vector and gradually gaining independence from fossil fuels. One of the advantages of hydrogen compared with electricity is that it can be stored.
An economical process based on renewable resources Until now, solar-generated hydrogen techniques have largely relied on water. However, despite water being cheap and abundant, these techniques have garnered poor results and the materials they require are expensive. As an alternative, the researchers suggest using ethanol, a renewable and economical resource that is easily obtained from agricultural and forest waste (100 grams of glucose generate approximately 50 grams of ethanol).
The photocatalyst is also much cheaper and simpler to use than the materials employed in techniques with water as it uses very small gold particles, ranging in size from 2 to 12 nanometres (1 metre = 1 million nanometres). These nanoparticles capture the free electrons generated when titanium oxide -- used as a support base -- comes into contact with sunlight.
During the process, which is based on solar energy, the team also discovered that the size of the gold nanoparticles has no influence on the production of hydrogen, unlike what occurs during the more widespread processes in which the catalyst powder must be heated to reaction temperature (usually over 500ºC) and therefore incurs an energy cost. In addition, the catalyst is more durable because it works at ambient temperature and pressure.
- M. Murdoch, G. I. N. Waterhouse, M. A. Nadeem, J. B. Metson, M. A. Keane, R. F. Howe, J. Llorca, H. Idriss. The effect of gold loading and particle size on photocatalytic hydrogen production from ethanol over Au/TiO2 nanoparticles. Nature Chemistry, 2011; DOI: 10.1038/nchem.1048
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