Highly dispersed ultrasmall iron phthalocyanine molecule clusters confined by mesopore-rich N-doped hollow carbon nanospheres for efficient oxygen reduction reaction and Zn-air battery

Iron phthalocyanine (FePc) has attracted extensive attention due to its unique planar symmetric Fe-N4 sites, which are considered to be the ideal active sites for oxygen reduction reaction (ORR) catalysis. However, the electrocatalytic performance of FePc is still unsatisfactory due to its low intrinsic activity, inadequate exposure and low utilization rate of Fe-N4 active sites. Herein, we synthesize a novel hybrid catalyst (FePc-NHCS-500) by coupling dispersed FePc molecule clusters into the defect-rich nitrogen-doped hollow porous carbon spheres (NHCS). Benefiting from the confining effect of mesopores in the NHCS, the well dispersed ultrasmall FePc molecule clusters exhibit excellent ORR performance with Tafel slope of 41 mV dec- 1, half-wave potential (E1/2) of 0.94 V and kinetic current density (Jk) of 25.39 mA cm-2 at 0.9 V. Moreover, the as-assembled Zn-air battery (ZAB) using the FePc-NHCS-500 electrocatalyst as air electrode exhibits excellent performance, with open circuit voltage (OCV) of 1.524 V, peak-power density of 230 mW cm-2 and specific capacity of 808.7 mAh g-1. This work not only designs a non-noble metal catalyst with excellent ORR performance, but also makes reasonable guidance for the practical application of the catalyst in renewable energy storage and conversion.