Millisecond activity modulation of atomically-dispersed Fe–N–C catalysts

Precious-metal-free transition metal–N–C catalysts containing atomic MeNx centers are promising candidates for the oxygen reduction reaction (ORR) in rechargeable zinc-air batteries. In this study, we present a highly efficient synthesis method and activity modulation of Me–N–C (Me = Fe, Co, Ni, and Cu) catalysts utilizing the flash Joule heating technique, accomplished within a mere 200 milliseconds. The instantaneous high temperature (∼3535 K) and rapid heating and cooling rates (above 104 K s–1) induce the formation of atomically-dispersed MeNx sites on the surface of carbon nanotube matrices. This ultrafast thermal shock process not only prevents the aggregation of isolated metal atoms but also achieves catalytic activity modulation through heteroatom engineering. Typically, phosphorus atoms play a crucial role in suppressing nitrogen loss and regulating the local coordination environment of FeNx centers, thereby facilitating the 4e– electrocatalytic reduction of oxygen. As expected, the phosphorus-doped Fe–N–C catalyst exhibits excellent ORR activity with a high half-wave potential of 0.904 V and a low Tafel slope of 23.1 mV dec–1 in a 0.1 M KOH medium. The assembled zinc-air battery demonstrates a prominent power density of 236.3 mW cm–2 and desirable long-term durability over 400 hours, surpassing that of the Pt/C+IrO2-based battery.