Hypercrosslinked polymer-mediated fabrication of binary metal phosphide decorated spherical carbon as an efficient and durable bifunctional electrocatalyst for rechargeable Zn-air batteries.

Bifunctional oxygen catalysts with excellent catalytic activity and durability towards both oxygen reduction and oxygen evolution reactions (ORR/OER) are pivotal for long-term rechargeable Zn-air batteries. Herein, we report a spherical carbon decorated with FeP and CoP nanoparticles (denoted as FeCoP/NPC) as an ORR/OER bifunctional electrocatalyst for rechargeable Zn-air batteries. HCTCz@Fe/Co-PA is first produced by the modification of phytic acid (PA) onto (into) a porous cross-linked polymeric sphere of poly(bis(-carbazolyl)-1,2,4,5-tetrazine) (HCTCz), followed by chelating with metal ions (, Fe and Co). The subsequent pyrolysis yields FeCoP/NPC, which shows prominent activity and reliability for the ORR and OER due primarily to the synergistic effect of FeP and CoP active sites and N/P co-doped carbon. The aqueous Zn-air battery assembled with FeCoP/NPC provides high specific capacity and peak power density. Notably, the constructed Zn-air battery can be repetitively charged and discharged for 1200 h at 5 mA cm. In addition, a flexible solid-state Zn-air battery made from FeCoP/NPC exhibits a power density of 74 mW cm and repeatedly works for 90 h at 2 mA cm. This work opens up an avenue for the preparation of highly efficient bifunctional electrocatalysts for Zn-air batteries considering the extensive N-rich polymer precursors and various metal phosphide nanoparticles.