Electronic Structure of Cobalt Phosphates Co1 – xMxPO4 Doped with Iron and Nickel Atoms

Abstract

In this research, the electronic states, band structures, and bond properties of the framework compounds of CoPO₄, Co_{1 – x}Fe_xPO₄, and Co_{1 – x}Ni_xPO₄ were investigated by the density functional theory calculations. The potential capabilities of these systems in the photocatalytic water splitting to produce hydrogen were analyzed. The spin-up electron densities of states for the CoPO₄, Co_{1 – x}Fe_xPO₄, and Co_{1 – x}Ni_xPO₄ systems have band gaps of 2.7, 3.4, and 3.45 eV, respectively. The band of spin-down electron states has several energy gaps above the Fermi level. The density of states of electron with spin up near the Fermi level is obviously greater than that of electrons with spin down. In this case, localized states of electrons appear in the band gap of doped semiconductors due to impurity atoms. The calculated value of the energy at the lower edge of the conduction band for CoPO₄ was –0.7 eV, which is more negative than the energy required for water splitting. Meanwhile, the calculated value of the energy at the upper edge of the valence band was 2.01 eV, which is more positive than the oxygen evolution energy of 1.23 eV.