Abstract:
First-principles calculations based on density functional theory (DFT) were carried out to
study the energetic stability and electronic properties of a bimetallic-doped α-Fe2O3 photoanode
surface with (Zn, Ti) and (Zn, Zr) pairs for enhanced PEC water splitting. The doped systems
showed negative formation energies under both O-rich and Fe-rich conditions which make them
thermodynamically stable and possible to be synthesised. It is found that in a bimetallic (Zn, Ti)-
doped system, at a doping concentration of 4.20% of Ti, the bandgap decreases from 2.1 eV to
1.80 eV without the formation of impurity states in the bandgap. This is favourable for increased
photon absorption and efficient movement of charges from the valance band maximum (VBM) to the
conduction band minimum (CBM). In addition, the CBM becomes wavy and delocalised, suggesting
a decrease in the charge carrier mass, enabling electron–holes to successfully diffuse to the surface,
where they are needed for water oxidation. Interestingly, with single doping of Zr at the third layer
(L3) of Fe atoms of the {0001} α-Fe2O3 surface, impurity levels do not appear in the bandgap, at both
concentrations of 2.10% and 4.20%. Furthermore, at 2.10% doping concentration of α-Fe2O3 with Zr,
CBM becomes delocalised, suggesting improved carrier mobility, while the bandgap is altered from
2.1 eV to 1.73 eV, allowing more light absorption in the visible region. Moreover, the photocatalytic
activities of Zr-doped hematite could be improved further by codoping it with Zn because Zr is
capable of increasing the conductivity of hematite by the substitution of Fe3+ with Zr4+, while Zn can
foster the surface reaction and reduce quick recombination of the electron–hole pairs.
