Project 6

High-troughput characterization of multinary transition metal oxide and oxynitridel ibraries. New materials for solar water splitting with improved properties

  • Prof. Dr. Sebastian Fiechter, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH
  • Prof. Dr.-Ing. Alfred Ludwig, Ruhr-Universität Bochum, Fakultät für Maschinenbau, Institut für Werkstoffe, Lehrstuhl Werkstoffe der Mikrotechnik (WDM)
  • Prof. Dr. Wolfgang Schuhmann, Ruhr-Universität Bochum Fakultät für Chemie und Biochemie Lehrstuhl für Analytische Chemie

Using a combinatorial approach we will push forward the discovery, characterization and optimization of multinary oxide and oxynitride electrodes for solar water splitting. The approach combines the fabrication of well-defined thin-film materials libraries with efficient automized characterization methodology, thus allowing to provide quantitative data at high throughput.

It is intended to substantially facilitate and speed up the discovery of new and more efficient materials for solar water splitting. By means of combinatorial reactive sputtering thin-film materials libraries will be deposited in two promising basic systems: Fe-Ti-W-O and Fe-Al-Cr-O. These basic systems will be extended by doping (B, N) and substitution (Ta, V, Zr). The obtained materials libraries will be investigated using automatic high-throughput characterization techniques such as x-ray diffraction, analytical electron microscopy and local conductivity measurements. The photoelectrocatalytic properties of the materials libraries will be investigated using an automatic scanning droplet cell with integrated light fiber. Potentiodynamic photocurrent and dark current measurements, photocurrent spectroscopy, determination of the open-circuit potential under illumination and in the dark will be performed.

In dependence from the material composition information about the photopotential, the photocurrent in dependence from the bias potential, the nature of the semiconductor, the band gap and the nature of the band gap, the amount of charge recombination, photocurrent spectra and IPCE values will be obtained. Stable materials compositions with promising photoelectrocatalytic properties and suitable band gap will be synthesized in a focused composition range and again investigated using the scanning droplet cell in order to identify the most suitable materials compositions.

The material libraries will be modified with nanoparticular co-catalysts for the oxygen evolution and the hydrogen eveolution reaction. Here, especially noble-metal free co-catalysts are in the focus. The co-catalyst material libraries will be again investiaged using the scanning droplet cell in order to in-depth evaluate and optimize the interface between the semiconductor and the co-catalyst and hence achieve a substantial decrease of the overpotentials. Based on the results of the high-throughput experiments the most promising oxide and oxynitride materials will be prepared as nanoparticles and layers or using sol-gel deposition and spray pyrolysis as nanostructured and porous layers in order to investigate the photoelectrochemical properties of the sputter-depsited materials compositions by means of a scalable synthesis process. The carrier life-time of photoexcited electron-hole pairs will be evaluated using sub-ps time-resolved THz photoconductivity and microwave reflectivity. The efficient charge carrier transport will be optimized by nanostructuring of the best identified material systems

In summary, the project addresses the search of new photoactive and/ or photoelectrocatalytically active multinary oxides/oxynitrides as well as composite of these phases characterized by band gaps < 2.3 eV to obtain an efficient light-induced separation of electron-hole pairs in the process of water oxidation.