Metal-organic framework derived porous N, P co-doping carbon microcubes toward aqueous and flexible quasi-solid-state rechargeable Zn-air batteries

The sluggish kinetics of oxygen reduction and/or evolution reactions in air cathodes of Zn-air batteries (ZABs) limits their practical applications. Herein, a facile strategy of phosphating metal-organic framework is developed to fabricate porous defect-enriched nitrogen and phosphorus co-doing carbon microcubes (NPC) both toward efficient oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), as a cost-efficiency bi-functional electrocatalyst. With detailed regulation in annealing temperatures, the optimized NPC sample (NPC-10) with nitrogen (N, 1.0 at.%) and phosphorus (P, 1.6 at.%) co-doping possesses bi-model micro-/meso-pores, and large specific surface area of 1627.1 m2 g−1. Thanks to unique structural merits and N/P synergetic contribution, the NPC-10 is endowed with abundant active sur-/interfaces and rapid kinetics for efficient ORR (limited ORR current density of 5.4 mA cm−2, half-wave potential of 0.89 V at 10 mA cm−2, Tafel slope of 141.6 mV dec−1 and a four-electron selectivity of >94.7 %) and OER (overpotential of 220 mV at 10 mA cm−2 and Tafel slope of 57.3 mV dec−1). More encouragingly, the NPC-10 assembled aqueous and flexible quasi-solid-state (QSS) rechargeable ZABs both deliver high power density and long-cycle stability. The work provides highly efficient, durable, and low-cost ORR/OER electrocatalysts toward rechargeable aqueous and/or QSS ZABs.