Composition Dependant Charge Carrier Lifetimes in p-type Fe-Cr-Al Containing Oxides

Sönke Müller^a, Rainer Eichberger^a, Dennis Friedrich^a, Helge Sören Stein^b, Alfred Ludwig^c, Klaus Schwarzburg^d

^aRuhr-Universität Bochum, Chair for MEMS Materials, Institute for Materials, Universitätsstraße, 150, Bochum, Germany

^bRuhr-Universität Bochum, Materials Research Department, Universitätsstraße, 150, Bochum, Germany

Materials for Sustainable Development Conference (MATSUS)
Proceedings of September Meeting 2016 (NFM16)

Berlin, Germany, 2016 September 5th - 13th

Organizers: Marin Alexe, Enrique Cánovas, Celso de Mello Donega, Ivan Infante, Thomas Kirchartz, Maksym Kovalenko, Federico Rosei, Lukas Schmidt-Mende, Laurens Siebbeles, Peter Strasser, Teodor K Todorov, Roel van de Krol and Ulrike Woggon

Poster, Sönke Müller, 088
Publication date: 14th June 2016

Intermediate bandgap, p-type and stable photocathode materials for photoelectrochemical water splitting devices are hard to find. One promising oxide material containing Fe, Cr, and Al was discovered through a combinatorial outreach programme (SHArK – Solar Hydrogen Activity Research Kit) and subsequently confirmed by groups around the world. The most photoelectrochemically active region was confirmed to exist near a nominal composition of Fe_0.84Cr₁Al_0.16O_x^[1]. Reported hydrogen evolution onset potentials of 1.1 V vs. RHE and IPCE values of up to 28 % at 400 nm sparked widespread scientific interest in this material^[2]. There is however the open question why photocurrents and onset potentials are so unexpectedly high for this Cr containing oxide material. To this end charge carrier dynamics experiments may contribute to the clarification of processes.

Therefore an investigation of ultrafast time-resolved transient reflectance measurements on 24 measurement areas from a materials library in a narrow composition range around Fe_0.73Cr_1.11Al_0.16O_x is presented. As for this compositional region the highest photocurrent densities and IPCE values were found^[1,2,3] the materials library was designed for a controlled variation of the Fe:Cr ratio. The observed noticeable variation in the time constants of the transient signal is discussed by correlation to photoelectrochemical and structural properties. In addition, the reflectance signal is related to time-resolved microwave conductance measurements.

[1] Rowley, J. G., Do, T. D., Cleary, D. A., & Parkinson, B. A. (2014): Combinatorial Discovery Through a Distributed Outreach Program: Investigation of the Photoelectrolysis Activity of p-Type Fe, Cr, Al Oxides. In: ACS Appl. Mater. Interfaces 6 (12), S. 9046–9052. DOI: 10.1021/am406045j.

[2] Kondofersky, I., Müller, A., Dunn, H. K., Ivanova, A., Stefanic, G., Ehrensperger, M., et al. (2016): Nanostructured Ternary FeCrAl Oxide Photocathodes for Water Photoelectrolysis. In: J. Am. Chem. Soc. 138 (6), S. 1860–1867. DOI: 10.1021/jacs.5b08040.

[3] Sliozberg, K., Stein, H. S., Khare, C., Parkinson, B. A., Ludwig, A., & Schuhmann, W. (2015): Fe–Cr–Al Containing Oxide Semiconductors as Potential Solar Water-Splitting Materials. In: ACS Appl. Mater. Interfaces 7 (8), S. 4883–4889. DOI: 10.1021/am508946e.

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