The thermodynamics and electronic structure analysis of P-doped spinel Co₃O₄

The thermodynamics of phosphorus (P) doping to spinel Co₃O₄, for both bulk cases and (100) and (110) surface cases, is studied using first principles calculations. The doping energies of the P atom at different doping sites are carefully calculated and compared. It is shown that P doping at Co sites, at either tetrahedral or octahedral sites, is energetically favorable, while P doping and replacing O atoms are energetically unfavorable. The doping energy difference is large enough to conclude that P doping has a very strong preference to take the Co sites, rather than the O sites in spinel Co₃O₄. Even when O-vacancy is available, P doping and taking the O-vacancy site is thermodynamically unfavorable. The physical/chemical mechanism behind this phenomenon is carefully analyzed. Electronic structure analysis shows that P doping and replacing the Co atom brings excess electrons to the Co₃O₄ system, which is beneficial to enhance the electrochemical and catalytic performance of the spinel Co₃O₄. Our results clarified the misleading results of P doping and replacing O atoms in spinel Co₃O₄ reported in the literature.