Ladder-type π-conjugated metallophthalocyanine covalent organic frameworks with boosted oxygen reduction reaction activity and durability for zinc-air batteries

Abstract

π-Conjugated two-dimensional covalent organic frameworks (COFs) represent a family of rising oxygen electrocatalysts due to their controllable architectures, outstanding electrical conductivity and highly exposed molecular active sites. Herein, we report a novel ladder type π-conjugated two-dimensional benzoimidazobenzophenanthroline-linked iron-phthalocyanine COF (denoted as FePc-BBL COF) via solvothermal synthesis between 2,3,9,10,16,17,23,24-octacarboxyphthalocyaninato iron (Fe-OCAP) and 1,2,4,5-tetramino-benzoquinone (TABQ). Due to the robust fused aromatic backbone, the porous framework structure, and the natural Fe-N4 high active sites, the newly developed FePc-BBL COF exhibits unusual oxygen reduction reaction (ORR) activities and fast kinetics with a remarkable half-wave potential of 0.933 V and an ultralow Tafel slope of 24.8 mV dec-1 in alkaline media. In addition, the FePc-BBL COF also exhibits an ultrahigh turnover frequency (TOF) of 78.1 e- site-1 s−1 at 0.85 V vs. RHE and mass activity of 26.5 A mgFe-1, represents 16.4- and 57.2-fold enhancements compare to Pt/C. Furthermore, when employed as a cathode electrocatalyst for zinc-air batteries, FePc-BBL COF delivered superior maximum power density (181.4 mW cm−2), specific capacity (773 mAh g−1), and long-term durability compared with Pt/C as air electrodes. This work provided a promising strategy in engineering reticular materials to design highly stable and efficient pyrolysis-free electrocatalyst for practical value sustainable energy conversion and storage devices.