Screening of catalytic oxygen reduction reaction activity of 2, 9-dihalo-1, 10-phenanthroline metal complexes: The role of transition metals and halogen substitution.

The sluggish kinetics of oxygen reduction reaction (ORR) restricts the employment of fuel cells, it is urgent to design ORR catalysts with excellent performance. The ORR performances of 2, 9-dihalo-1, 10-phenanthroline metal complexes (named as TM-X, X = Cl, Br, I) are comprehensively studied by the density functional theory methods. From the stability point of view, chlorine is more suitable for substitution. The adsorption free energy reveals that the liner relationship between adsorption free energy of *OOH and *OH is changed positively by the steric hindrance caused by the orthogonal TM-X structures. The Ni-Br stands out with the lowest overpotential of 0.34 V, and many other TM-X also show the promising ORR activity. Combining with the analysis of the Gibbs free energy diagrams and d-band center results, the substitution of halogen can improve the electronic structures of TM-X, thus enhancing their ORR activities and changing the ORR mechanism possibly.