Solar Water Splitting

Hydrogen Formation from Water and Sun Light

Schematic representation of overall photoelectrocatalytic solar water splitting (SWS). The photoanode produces oxygen and the cathode hydrogen. Image: Dr. Stefan Kilper and Dr. Marc Widenmeyer.
Schematic representation of overall photoelectrocatalytic solar water splitting (SWS). The photoanode produces oxygen and the cathode hydrogen. Image: Dr. Stefan Kilper and Dr. Marc Widenmeyer.

Hydrogen (H2) is considered as one of the future fuels. However, currently most of the hydrogen is produced from natural gas. A possible alternative is the generation via solar water splitting using water, photocatalysts, and sun light. We are developing new visible-light active photoabsorber materials on the basis of perovskite-type oxynitrides AB(O,N)3. These can be used as photoanodes to generate oxygen and hydrogen in another half-cell reaction. Therefore, the materials need a band gap of ca. 2 eV and to the redox potential of H2O aligned band edges of valence and conduction band. To do so, we use the chemical and structural flexibility of the perovskite materials towards substitution with other elements.

https://www.solarh2.tu-darmstadt.de/solarh2/index.en.jsp

A crucial bottleneck is the control over defects and charge compensation during the incorporation of nitrogen while forming the oxynitride. Defects can influence the conversion performance of the solar water splitting reactions in multiple ways by e.g., forming recombination centers or charge traps favoring loss of charge carriers before reaching the semiconductor-electrolyte interface and photooxidation of the material, respectively. All defect formation energies can be linked to a common energy scale, the Fermi level (chemical potential of the electrons). To allow for a description of the defect energies and finally the prediction of the dominating charge compensation mechanisms in a given or newly designed material is the key goal of the Collaborative Research Center 1548 “FLAIR”.

https://www.mawi.tu-darmstadt.de/flair/forschung_12f8byrr61ao2/projects_flair/A04.en.jsp