Research News
At the HZB Institute for Solar Fuels, researchers now experiment with nano structures to efficiently use sunlight to produce hydrogen. Photo: HZB
Further Information:
Light for Refuelling
At the "Solar Fuels" institute of the Helmholtz-Zentrum Berlin (HZB), Prof. Dr Roel van de Krol and his team develop new material systems, which transform as efficiently as possible energy from sunlight into hydrogen. Hydrogen is a chemical storage for solar energy and is versatile as regards its application: within a fuel cell, it can produce electricity or it can be further processed to methane, methanol, petrol or diesel.
In an electrolytic process, water can be split into its components oxygen and hydrogen. In order for this to be achieved by sunlight, the light first needs to create voltage within the electrode, just as in a solar cell. In his work, van de Krol can draw from the HZB's vast experience in solar cell research. The electrode core consists of a multitude of differently doped semiconductor layers, which form several junctions. The researchers have demonstrated that one of these junctions can be replaced by a metal oxide layer. This would present one method of facilitating the production of these multilayered systems, of increasing their stability to resist corrosion and to improve their efficiency. Whereas semiconductor junctions predominantly use long-wave red light for charge separation, the metal oxide layer transforms light's blue components into voltage.
Van de Krol and his team already experiment with metal oxide nano structures. The reason for this is that the metal oxide layer needs to fulfil two contradictory requirements: On the one hand, it ought to be sufficiently thick to absorb enough light, whereas, on the other, it should be as thin as possible to allow easy discharge for charge carriers. Nano structures offer interesting solutions for this problem: A thin "carpet" of nanorods would provide short pathways for charge carriers and at the same time sufficient head way for light absorption. Or take the "hollow cup" structure made of iron oxide: the open hemispheres could capture almost all of the light. "We need solar energy storage solutions on a terawatt hour scale and chemical storage such as hydrogen could be part of the solution", says van de Krol with full conviction.
