Boosting Oxygen Reduction Catalysis Through Electronic Reconfiguration of Fe–N–C Induced by P Doping

Regulating the electron distribution is proved to be an effective strategy for improving the catalytic activity of catalysts. In this work, we proposed a new strategy to synthesize ORR catalysts by phosphorous (P) doping to reconfigure the distribution of electronic cloud in the atomically dispersed Fe–N–C complex. Three-dimensional hierarchical porous graphitic carbon catalyst (Fe/P–N–C) was synthesized by using green tea leaves as a source of carbon and nitrogen (N) and NaH2PO2 as P source. The synthesized catalyst (Fe/P–N–C) displays exceptional ORR activity with equivalent half-wave potential (E1/2 = 0.902 V vs. 0.866 V), onset potential (Eonset = 1.02 V vs. 1.04 V), and limiting current density (jL 5.61 mA cm−2 vs. 5.34 mA cm−2) compared with commercial Pt/C. Moreover, in the acidic medium, the catalyst showed reliable ORR activity with E1/2 = 0.70 V vs. RHE, jL = 4.23 mA cm−2, and Eonset = 0.91 V. This enhanced performance is due to the increase in the number of active sites by heteroatom doping, which helps for controlling the electron distribution of the carbon skeleton. Furthermore, phosphorus functionalities were used to boost the catalytic activity of atomically dispersed Fe–N active sites. Besides, by chemical activation with KOH results in highly porous (micro-mesopores) structure with increased surface area, which provides more exposed active sites for the reactants to react and give product, hence, the rate of catalytic reduction increases. Besides, this green tea–derived Fe/P–N–C catalyst reveals promising performance as the cathode in a zinc-air battery device. Green tea was used as precursor to obtain a three-dimensional (3D) hierarchically porous graphitic carbon catalyst intrinsically doped with N and extrinsically doped with P and Fe with high catalytic activity for ORR.