Pyrazine-linked Iron-coordinated Tetrapyrrole Conjugated Organic Polymer Catalyst with Spatially Proximate Donor-Acceptor Pairs for Oxygen Reduction in Fuel Cells.

ABSTRACT

Nitrogen-coordinated iron (Fe-N4 ) materials represent the most promising non-noble electrocatalysts for the cathodic oxygen reduction reaction (ORR) of fuel cells. However, molecular-level structure design of Fe-N4 electrocatalyst remains a great challenge. In this study, we develop a novel Fe-N4 conjugated organic polymer (COP) electrocatalyst, which allows for precise design of the Fe-N4 structure, leading to unprecedented ORR performance. At the molecular level, we have successfully organized spatially proximate iron-pyrrole/pyrazine (FePr/Pz) pairs into fully conjugated polymer networks, which in turn endows FePr sites with firmly covalent-bonded matrix, strong d-π electron coupling and highly dense distribution. The resulting pyrazine-linked iron-coordinated tetrapyrrole (Pz-FeTPr) COP electrocatalyst exhibits superior performance compared to most ORR electrocatalysts, with a half-wave potential of 0.933 V and negligible activity decay after 40,000 cycles. When used as the cathode electrocatalyst in a hydroxide exchange membrane fuel cell, the Pz-FeTPr COP achieves a peak power density of ≈210 mW cm-2 . We anticipate the COP based Fe-N4 catalyst design could be an effective strategy to develop high-performance catalyst for facilitating the progress of fuel cells.