Biaxially-Strained Phthalocyanine at Polyoxometalate@Carbon Nanotube Heterostructure Boosts Oxygen Reduction Catalysis

Iron phthalocyanine (FePc) with unique FeN4 site has attracted increasing interests as a promising non-precious catalyst. However, the plane symmetric structure endows FePc with undesired catalytic performance toward the oxygen reduction reaction (ORR). Here, we report a novel one-dimensional heterostructured ORR catalyst by coupling FePc at polyoxometalate-encapsulated carbon nanotubes (FePc-{PW12}@NTs) using host-guest chemistry. The encapsulation of polyoxometalates can induce a local tensile strain of single-walled NTs to strengthen the interactions with FePc. Both the strain and curvature effects of {PW12}@NT scaffold tune the geometric structure and electronic localization of FeN4 centers to enhance the ORR catalytic performance. As expected, such a heterostructured FePc-{PW12}@NT electrocatalyst exhibits prominent durability, methanol tolerance, and ORR activity with a high half-wave potential of 0.90 V and a low Tafel slope of 30.9 mV dec-1 in alkaline medium. Besides, the assembled zinc-air battery demonstrates an ultrahigh power density of 280 mW cm-2, excellent charge/discharge ability and long-term stability over 500 h, outperforming that of the commercial Pt/C+IrO2 cathode. This study offers a new strategy to design novel heterostructured catalysts and opens a new avenue to regulate the electrocatalytic performance of phthalocyanine molecules. Iron phthalocyanine (FePc) is a promising non-precious molecular catalyst toward the oxygen reduction reaction (ORR). To enhance its catalytic activity and long-term durability, a host-guest self-assembly strategy is employed to fabricate one-dimensional ternary heterostructure of FePc-polyoxometalate@carbon nanotubes. The polyoxometalate-encapsulated nanotubes are able to tune the structure and ORR performances of FeN4 centers.+image

Automated summary

A novel one-dimensional heterostructured ORR catalyst, FePc-{PW12}@NTs, was fabricated through the host-guest self-assembly of FePc and polyoxometalate-encapsulated carbon nanotubes. The heterostructure exhibits enhanced ORR catalytic performance due to the strain and curvature effects of {PW12}@NT scaffold, which tune the geometric structure and electronic localization of FeN4 centers. The FePc-{PW12}@NT electrocatalyst demonstrates excellent durability, methanol tolerance, and ORR activity in alkaline medium, surpassing the performance of the commercial Pt/C+IrO2 cathode.