Microenvironment engineering of Fe-single-atomic-site with nitrogen coordination anchored on carbon nanotubes for boosting oxygen electrocatalysis in alkaline and acidic media

Developing cost-effective and high-performance non-precious electrocatalysts for ORR in acidic and alkaline media is an urgent need for clean energy generation. A significant improvement in the ORR performance has been realized by the single-atom catalysts (SACs). However, activity deterioration caused by the dissolution of catalyst structure is still a lingering challenge. Herein, we report a simple strategy for protecting the structure of SAC by implanting/decorating Fe-ZIF-derived carbon nanotubes with Fe-N4, denoted as FeSA@CNTs. The as-developed FeSA@CNTs catalyst exhibits an outstanding ORR activity in an alkaline medium with onset potential (Eo) = 0.998 V and half-wave potential E1/2 = 0.898 V, which are 28 mV and 29 mV higher than commercial 20% Pt/C, respectively. Moreover, FeSA@CNTs in an acidic medium show an impressive high half-wave potential (E1/2 = 0.8290 V) comparable to Pt/C (E1/2 = 0.8292 V) which is better than most recently reported ORR catalysts. The density functional theory (DFT) validates that the smaller difference in the energy orbitals of Fe in Fe-N4 and O2 improved the electron transfer onto the reaction intermediate (OH*) in the rate-determining step, which provides the higher catalytic activity for FeSA@CNTs' in both acidic and alkaline media.