  The high cost of platinum-based catalysts has hampered the commercialization
of polymer electrolyte membrane fuel cells (PEMFCs). Hence, the electronic
structure and oxygen reduction ability of [Ti(IV)Pc]2+, Ti(II)Pc
titanyl-phthalocyanines, and their tailored peripheral and axial ligand
complexes were theoretically investigated to determine non-precious cathode
catalysts. Our results revealed that the peripherally substituted and
unsubstituted Ti(II)Pc triplet complexes can spontaneously reduce peroxide. The
singlet [Ti(IV)Pc]2+ parent complex has a 6.45 eV barrier. However, fluorine
substitution at peripheral positions reduced the energy barrier up to 0.45 eV.
In addition, chlorine substitution has shown spontaneous peroxide reduction as
in the case of triplets. The high catalytic activity of Ti(II)Pc complexes and
singlet chlorine substituted complex is attributed to the optimal charge
transfer between dioxygen molecule and the novel catalyst complexes. As a
result, Ti(II)Pcs and chlorine substituted singlet complexes are considered as
potential substitutions for the noble Pt-based catalyst for the PEMFCs.
