Manipulating the electronic configuration of Fe–N4 sites by an electron-withdrawing/donating strategy with improved oxygen electroreduction performance†‡
Abstract
Fe–N4 sites anchored on carbon (Fe–N–C) materials have drawn increasing interest on account of their remarkable electrocatalytic activity for the oxygen reduction reaction (ORR). Nevertheless, the Fe–N4 sites with a symmetric electronic configuration exhibit too strong binding energy between the Fe center and oxygen intermediates toward the ORR. Herein, we report a facile boron induced electron-withdrawing/donating strategy for manipulating the electronic configuration of Fe–N4 sites, and constructed Fe single-atoms anchored on B and N co-doped carbon (Fe-SA/BNC). Compared to the Fe single-atoms anchored on the N doped carbon (Fe-SA/NC) counterpart, the adjacent boron atoms induce more electrons to accumulate at Fe–N4 sites and optimize the absorption/desorption of oxygen intermediates in Fe-SA/BNC. Besides, Fe-SA/BNC features a large specific surface area, hierarchical porous architecture and low electrochemical impedance, which contribute to fast charge/mass transport. Thus, Fe-SA/BNC displays exceptional ORR activity with a half-wave potential of 0.910 V, surpassing those of Fe-SA/NC (0.889 V) and Pt/C (0.870 V). Furthermore, liquid and flexible solid-state Zn–air batteries equipped with Fe-SA/BNC achieve a high peak power density of 308.3 and 62.9 mW cm−2, respectively. This work not only offers an effective strategy to modify the electronic structure of Fe–N4 sites with improved ORR activity, but also paves the way for preparing high-performance single-atom catalysts.