First-principle calculations study of the ORR/OER electrocatalytic activity of ruthenium polyphthalocyanine axially modified with aliphatic thiol groups

Abstract

In this study, the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalytic activity of ruthenium polyphthalocyanine axially modified with different aliphatic thiol groups, RuPPc–SR (SR = –SCH₃, –SC₂H₅, –SC₃H₇, –SC₄H₉, –SC₅H₁₁, and –SC₆H₁₃), in an acidic medium were simulated using DFT. All –SR groups can effectively enhance the ORR and OER catalytic activities of RuPPc. The ORR and OER overpotentials of RuPPc–SC₄H₉ are 0.237 V and 0.436 V, respectively, which are far lower than those of RuPPc (0.960 V and 0.903 V). For RuPPc–SC₄H₉, the four C and S atoms of the –SC₄H₉ chain and Ru atom are coplanar, and thus, conjugate effects and inductive effects exist between the –SC₄H₉ chain and Ru atom. This makes the Ru atom exhibit the least positive Bader charge and smallest spin density, and the anti-bonding orbitals of d_xz, d_yz, and d_z² of the Ru atom shift below the Fermi level (E_f). This makes the adsorption strength of RuPPc–SC₄H₉ toward ORR and OER intermediates the weakest, which accelerates the reaction process, thus resulting in better ORR and OER catalytic activity. Therefore, the introduction of the aliphatic thiol groups might effectively improve the OER/ORR catalytic activity of RuPPc.