Solar hydrogen: Photoanodes made of α-SnWO4 promise high efficiencies

Photoanodes made of metal oxides are considered to be a viable solution for the production of hydrogen with sunlight. α-SnWO4 has optimal electronic properties for photoelectrochemical water splitting with sunlight, but corrodes easily. Protective layers of nickel oxide prevent corrosion, but reduce the photovoltage and limit the efficiency. Now a team at HZB has investigated at BESSY II what happens at the interface between the photoanode and the protective layer. Combined with theoretical methods, the measurement data reveal the presence of an oxide layer that impairs the efficiency of the photoanode.

Hydrogen is an important factor in a sustainable energy system. The gas stores energy in chemical form and can be used in many ways: as a fuel, a feedstock for other fuels and chemicals or even to generate electricity in fuel cells. One solution to produce hydrogen in a climate-neutral way is the electrochemical splitting of water with the help of sunlight. This requires photoelectrodes that provide a photovoltage and photocurrent when exposed to light and at the same time do not corrode in water. Metal oxide compounds have promising prerequisites for this. For example, solar water splitting devices using bismuth vanadate (BiVO4) photoelectrodes achieve already today ~8 % solar-to-hydrogen efficiency, which is close to the material’s theoretical maximum of 9 %.

Read more on the HZB website

Image: TEM-Image of a α-SnWOfilm (pink) coated with 20 nm NiO(green). At the interface of α-SnWO4 and NiOx an additional interfacial layer can be observed.

Credit: HZB