Atomically dispersed Fe sites on hierarchically porous carbon nanoplates for oxygen reduction reaction

Developing cost-effective, robust and stable non-precious metal catalysts for oxygen reduction reaction (ORR) is of paramount importance for electrochemical energy conversion devices such as fuel cells and metal-air batteries. Although Fe-N-C single atom catalysts (SACs) have been hailed as the most promising candidate due to the optimal binding strength of ORR intermediates on the Fe-N4 sites, they suffer from serious mass transport limitations as microporous templates/substrates, i.e., zeolitic imidazolate frameworks (ZIFs), are usually employed to host the active sites. Motivated by this challenge, we herein develop a hydrogen-bonded organic framework (HOF)-assisted pyrolysis strategy to construct hierarchical micro/mesoporous carbon nanoplates for the deposition of atomically dispersed Fe-N4 sites. Such a design is accomplished by employing HOF nanoplates assembled from 2-aminoterephthalic acid (NH2-BDC) and p-phenylenediamine (PDA) as both soft templates and C, N precursors. Benefitting from the structural merits inherited from HOF templates, the optimized catalyst (denoted as Fe-N-C SAC-950) displays outstanding ORR activity with a high half-wave potential of 0.895 V (vs. reversible hydrogen electrode (RHE)) and a small overpotential of 356 mV at 10 mA cm−2 for the oxygen evolution reaction (OER). More excitingly, its application potential is further verified by delivering superb rechargeability and cycling stability with a nearly unfading charge–discharge gap of 0.72 V after 160 h. Molecular dynamics (MD) simulations reveal that micro/mesoporous structure is conducive to the rapid mass transfer of O2, thus enhancing the ORR performance. In situ Raman results further indicate that the conversion of O2 to *O2− the rate-determining step (RDS) for Fe-N-C SAC-950. This work will provide a versatile strategy to construct single atom catalysts with desirable catalytic properties.