Origin of Enhanced Efficiency of Tin-doped Ultrathin Hematite Photoanodes for Water-Splitting

Hamidreza Hajiyani^a, Alexander G. Hufnagel^b, Siyuan Zhang^c, Thomas Bein^b, Dina Fattakhova-Rohlfing^d^,^e, Christina Scheu^c, Rossitza Pentcheva^a

^aDepartment of Physics, Theoretical Physics and Center of Nanointegration (CENIDE), Universität Duisburg-Essen, Lotharstraße 1, 47057 Duisburg, Germany

^bUniversity of Munich (LMU), Department of Chemistry and Center for Nanoscience (CeNS), 81377 Múnich, Alemania, Múnich, Germany

^cMax-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, 40237 Düsseldorf, Germany

^dInstitut für Energie- und Klimaforschung, Forschungszentrum Jülich GmbH, Germany, Wilhelm-Johnen-Straße, Jülich, Germany

^eUniversität Duisburg-Essen, Germany

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting 2018 (NFM18)

S2 Light Driven Water Splitting

Torremolinos, Spain, 2018 October 22nd - 26th

Organizers: Wolfram Jaegermann and Bernhard Kaiser

Oral, Hamidreza Hajiyani, presentation 096
DOI: https://doi.org/10.29363/nanoge.nfm.2018.096
Publication date: 6th July 2018

Using a combination of experimental and theoretical methods we explore the beneficial effect of Sn(IV) doping in ultrathin hematite photoanodes for water oxidation. A series of hematite photoanodes with tailored Sn-doping profiles were prepared by alternating atomic layer deposition. Using data from spectrophotometry and intensity-modulated photocurrent spectroscopy we deconvoluted the overall efficiency and obtained the individual process efficiencies for light harvesting, charge separation and charge transfer. Photoanodes with Sn-doping both on the surface and in the subsurface region show the best performance with enhanced charge separation and charge transfer efficiency. Density functional theory calculations with a Hubbard U parameter were performed to investigate the causes of the efficiency improvement considering both Fe₂O₃ (0001), as well as Fe₂O₃ (11-26) surface orientation, as identified from micrographs at atomic resolution. The energetics of surface intermediates during the oxygen evolution reaction reveal that while Sn-doping decreases the overpotential on the (0001) surface, the Fe₂O₃ (11-26) orientation shows a significantly lower overpotential, one of the lowest reported for hematite so far. Electronic structure calculations demonstrate that Sn-doping on the surface also enhances the charge transfer efficiency by elimination of surface hole trap states (passivation). Moreover, the subsurface Sn-doping introduces a band bending that helps to improve the charge separation efficiency.

We acknowledge funding by SPP1613 and computational time at MagntUDE.

[1] A. G. Hufnagel, H. Hajiyani, S. Zhang, T. Li, O. Kasian, B. Gault, B. Breitbach, T. Bein, D. Fattakhova-Rohlfing, C. Scheu and R. Pentcheva, Adv. Funct. Mater. (accepted).

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