Tetraiodo Fe/Ni phthalocyanine-based molecular catalysts for highly efficient oxygen reduction reaction and oxygen evolution reaction: Constructing a built-in electric field with iodine groups

In this paper, we report on the preparation and catalysis of a bifunctional molecular catalyst (Fe[Pc(I)4] + Ni[Pc(I)4]@NCPDI) for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in rechargeable Zn-air batteries. This catalyst is prepared by self-assembling tetraiodo metal phthalocyanines (Fe[Pc(I)4] and Ni[Pc(I)4]) on a 2D N-doped carbon material (NCPDI) through π-π interactions. The introduction of iodine groups in the edge of phthalocyanines controls the density of electron cloud and electrostatic potential around Fe-N/Ni-N sites and constructs a built-in electric field that facilitates directional transport of charges, enhancing the catalytic activity of the catalyst. Density functional theory (DFT) calculations support this mechanism by showing a reduced energy barrier for the ORR rate-determining step (RDS). The Fe[Pc(I)4] + Ni[Pc(I)4]@NCPDI exhibits excellent performance outperforming 20 wt% Pt/C and single-molecule self-assembled Fe[Pc(I)4]@NCPDI and Ni[Pc(I)4]@NCPDI, with a half-wave potential of E1/2 = 0.940 V in the ORR process under alkaline condition. During the OER process, Fe[Pc(I)4] + Ni[Pc(I)4]@NCPDI exhibited a low overpotential of 298 mV at 10 mA cm−2 under the alkaline condition, which is much better than RuO2, Fe[Pc(I)4]@NCPDI and Ni[Pc(I)4]@NCPDI. The catalyst also demonstrates excellent catalysis and durability in rechargeable Zn-air batteries. This work provides a simple and specific method to develop efficient multifunctional molecular electrocatalysts.