project 16

Photoelectrocatalytic Anion Substituted Perovskites PAP

  • Prof. Dr. Anke Weidenkaff, Universität Stuttgart, Institut für Materialwissenschaft – Chemische Materialsynthese

Efficient photoelectrocatalytic water splitting with solar radiation requires suitable semiconductor materials. The process still shows poor performance as the commonly used active compounds – particularly TiO2 or Ta3N5 – either have a too large band gaps or are not sufficiently stable under reaction conditions. A possible approach is the combination of both material classes resulting in the formation of ternary, quaternary or higher complex perovskite-type oxynitrides AB(O,N)3 due to the extremely flexible perovskite structure tolerating diverse modifications both in the cationic (A, B) and the anionic (X) composition. Those (partial) substitutions enable the specific introduction of nitrogen and, thus, a precise adjustment of the band gap. This results in an increased quantum efficiency of the photocatalytic reaction. In addition, the morphology has to be controlled by appropriate reproducible synthesis processes because it is an important factor influencing the catalytic conversion efficiency of the material.

The objective of the project is to replace the currently used binary oxides and nitrides by more suitable, anion-substituted perovskites AB(O,N)3. The focus will be on titanium-based (B cation) compounds. In the course of the project, also chemically more stable zirconium compounds will be studied. In parallel, the influence and applicability of an additional anionic substitution with flour yielding oxynitridefluorids AB(O,N,F)3 will be evaluated. Knowledge on the influence of cationic substitutions at the A- und B-position as well as on the ammonolysis of the oxide precursors will be gained with modern materials chemistry methods. Morphology and defect concentration are additional factors to be controlled to improve the photoelectrocatalytic efficiency. Both will be systematically studied within the scope of the project. The morphology can be changed using flux, the defect concentration either by introducing cations with higher valence at the A- or B-position during ammonolysis or by the mentioned fluor substitution. A general task will be to develop efficient and repeatable synthesis protocols for all compounds to be studied in the project.

Photo-electrochemical cells based on the improved perovskite-type oxynitrides developed in this project will be manufactured in collaboration with partners within the SPP.