Date: 11-27-2018 - Tuesday - 08:00 PM - 10:00 PM
Joseph Simfukwe1 2 Refilwe Mapasha1 Artur Braun3 Mmantsae Diale1

1, University of Pretoria, Gauteng, , South Africa
2, Copperbelt University, Kitwe, Copperbelt, Zambia
3, Empa–Swiss Federal Laboratories for Materials Science and Technology, Switzerland, , Switzerland

First principles studies of Zn doped {0001} and {012} surfaces of hematite for enhanced photoelectrochemical water splitting have been carried out. Doping was confined to planes in close proximity to the termination region, precisely from the top most layer to the third inner layer (plane P1, P2 and P3) of Fe atoms. The two surfaces and the three doped layers were found to be thermodynamically stable and would prefer exothermic formation under oxygen rich conditions. The analysis of electronic properties reveals that even with mono doping of Zn on the top most layer (P1) of the {0001} α-Fe2O3 surface, the band gap can be decreased without impurity states in the band gap which normally acts as recombination centres. The doping of Zn atom on P2 and P3 (second and third layer respectively) of the {012} surface narrowed the band gap from ~ 1.43 eV to ~1.0 eV for both systems, without any impurity states in the band gap. Furthermore, the conduction band minimum (CBM) of P2 and P3 of the {012} surface also become wavier and delocalised suggesting improved electron mobility of hematite, while the CBM of the {0001} surface shifted upward between ~0.05eV and ~0.3 eV. The observed upward shift in the CBM is likely to enhance photoelectrochemical splitting of water with a smaller application of external bias. Analysis of the charge density difference plots showed concentration of charge mainly at the top of the surface, which is the termination region. This suggests facile transfer of charges to adsorbed water molecules due to the closeness of the charges to the adsorbate. The concentration of the charges at the surface, the decreased band gap and the absence of recombination centres within the band gap suggest improved photocatalytic activity of the Zn doped α-Fe2O3 surface.

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