Low temperature synthesized iron oxide photoanodes via vapour phase routes
Daniel Peeters, Inorganic Materials Chemistry, Ruhr-University Bochum, Bochum, GermanyLidong Wang, Institute of Electrochemistry, Ulm University, Ulm, GermanyRadim Beranek, Institute of Electrochemistry, Ulm University, Ulm, GermanyDetlef Rogalla, RUBION, Ruhr-University Bochum, Bochum, GermanyHans-Werner Becker, RUBION, Ruhr-University Bochum, Bochum, GermanyAnjana Devi, Inorganic Materials Chemistry, Ruhr-University Bochum, Bochum, Germany
Iron oxide thin films are generally fabricated by multiple techniques and incorporated in various devices, for instance in gas detection systems, Li-ion batteries or water splitting devices. All aforementioned applications are based on materials thin films and are therefore dependent on the availability of thin film deposition methods. Especially for the application of iron oxide as photoanodes in photoelectrochemical water splitting, several draw backs, i.e. short life time of charge carriers, low electron mobility and short hole diffusion length, have to be solved. Besides doping, two different approaches are discussed in research literature to enhance photocatalytic performances of the pure iron oxide.
On the one hand, nanostructuring of the photoactive material was found to enhance photocatalytic activities  and, on the other hand, very thin, conformal films were found to reduce the recombination of charge carriers. Even more, the deposition of nanometer sized films on complex nanostructures can compensate for the typically very smooth appearance. In this regard, metal organic chemical vapour deposition (MOCVD) and atomic layer deposition (ALD) are two suitable vapour phase techniques, which allow fabricating nanostructured, crystalline and several 100 nanometer thick deposits on the one hand and very smooth, mostly amorphous, conformal and nanometer thick thin films on the other hand.
Here, we report on the new precursor [bis(isopropyl ketoiminate) iron(II)], [Fe(ipki)2], and demonstrate the suitability for vapor phase depositions of iron oxide via MOCVD and ALD. Considering both deposition techniques, a temperature processing window of 100 – 800 °C was achieved to produce nano- to micrometer-sized iron oxide thin films suitable for photocatalytic applications.
 G. Rahman and O.-S. Joo, International Journal of Hydrogen Energy 2012, 37, 13989-13997.
 D. A. Wheeler, G. Wang, Y. Ling, Y. Li and J. Z. Zhang, Energy & Environmental Science 2012, 5, 6682-6702.