In this theoretical study, first-principles calculations were carried out to explore the photocatalytic activity of cation (Ti or Zr) and anion (N) compensated codoped hematite based on density functional theory (DFT). For (Ti/Zr,N) codoped hematite, the band edges of the conduction band and the valence band move close to each other, leading to an obvious bandgap reduction. Compared with the pure hematite, the optical absorption coefficient of codoped hematite is significantly enhanced in the visible light region. The charge distribution at the conduction band minimum (CBM) and valence band maximum (VBM) is spatially separated after codoping, which is beneficial for extending the carrier lifetime. More interestingly, the CBM becomes electronically delocalized in (Ti,N) doped hematite, which indicates better carrier transport properties in the bulk system. Due to these special features of (Ti/Zr,N) codoped hematite, an improved photocatalytic performance can be expected.

To investigate the influence of the Morin transition on the photoelectrochemical (PEC) activity of hematite, electronic properties in different magnetic phases were studied on the basis of the first-principles calculations within the GGA+U approximation. The results show that the effective electron mass in the (0001) plane changes remarkably due to the spin−flop transition, while the effective electron masses in other Miller planes are not sensitive to the spin orientation around irons. The electronic structure calculations of Sn-doped hematite predict that the improved PEC activities of Sn-doped hematite are proved to arise from a shrinking of the band gap, decreasing of the effective electron mass, and thus enhanced electronic conductivity. More interestingly, the heavier doping of Sn (≥16.7 atom %) in hematite would induce a new level between the valence band maximum (VBM) and Fermi level E F , which facilitates its PEC activity of visible light water splitting.