Mixed phthalocyanine-porphyrin-based conjugated microporous polymers towards unveiling the activity origin of Fe–N4 catalysts for the oxygen reduction reaction

Abstract

Mixed phthalocyanine-porphyrin-based conjugated microporous polymers (CMPs) are still rare, limited to one sole NN-bridged example. Developing new mixed phthalocyanine-porphyrin-based CMP compounds towards exploring their new functionalities and application potential is therefore of significant importance. In the present case, four ethynyl-linked mixed phthalocyanine-porphyrin-based 2D CMPs, including FePcZnPor-CMP, ZnPcFePor-CMP, FePcFePor-CMP, and ZnPcZnPor-CMP, were fabricated by utilizing a Sonogashira–Hagihara coupling reaction. A series of spectroscopic and electron microscopy methods confirmed the successful fabrication of the as-prepared CMPs with alternate distribution of phthalocyanine and porphyrin chromophores. The electrocatalytic activity of these CMPs for the oxygen reduction reaction (ORR) was evaluated by cyclic voltammetry, rotating disk electrode, and rotating ring-disk electrode tests. In alkaline media, the two FePc-containing CMPs exhibit excellent ORR catalytic activity with an E_1/2 as high as 863–866 mV, making them significantly superior to FePor-containing catalyst ZnPcFePor-CMP and comparable to commercial Pt/C. On the basis of the experimental results and theoretical calculations, the significantly higher ORR performance of the two FePc-containing CMPs than the FePor-containing catalyst ZnPcFePor-CMP originates from the stronger coordination field of the phthalocyanine macrocyclic ligand than porphyrin, which is more favorable for stabilizing Fe²⁺ species.