Exploring the stability and electronic properties of Zn-doped hematite surfaces for photoelectrochemical water splitting

First-principles calculations of Zinc (Zn) doped {0001} and {01 (1) over bar2} hematite surfaces for improved photoelectrochemical water splitting have been studied. The single Zn-doped systems were found to be energetically favourable (negative formation energies) and the stability increased with increasing concentration of Zn atoms. Our results show that even with mono-doping of Zn on the topmost layer L1 structure of the {0001} alpha-Fe2O3 surface, the band gap can be decreased without impurity states in the band structure which normally acts as recombination centres. At the doping concentration of 4.20% of Zn atoms on L1 of {0001} surface, the conduction band minimum (CBM) is shifted upwards by 0.23 eV as compared to the bulk. In addition to the decrease in the band gap, the CBM of the single doped layer 2 (DL21) and layer 3 (DL31) of the {01 (1) over bar2} surface become wavier and delocalised suggesting improved electron mobility of hematite surface. Charge density difference plots and Bader charge analysis showed the accumulation of charge at the top of the surface with more pronounced charge depleting from Zn atom and accumulating on O and Fe neighbouring atoms, implying that the photo generated charge carriers can efficiently diffuse to the surface for enhanced interfacial charge transfer to the adsorbates. The electronic properties exhibited by doping of Zn on the two hematite surfaces postulate that surface doping is likely to strengthen the electrocatalytic activity of hematite for water splitting.