Ultrafine Mo2C nanoparticles embedded in an MOF derived N and P co-doped carbon matrix for an efficient electrocatalytic oxygen reduction reaction in zinc–air batteries

Exploring high-activity electrocatalysts for an oxygen reduction reaction (ORR) is of great significance for a variety of renewable energy conversion and storage technologies. Here, ultrafine Mo₂C nanoparticles assembled in N and P-co-doped carbon (Mo₂C@NPC) was developed from ZIF-8 encapsulated molybdenum-based polyoxometalates (PMo₁₂) as a highly efficient ORR electrocatalyst and shows excellent performance for zinc-air batteries. The well distribution of the PMo₁₂ in ZIF-8 results in the formation of ultrafine Mo₂C nanocrystallites encapsulated in a porous carbon matrix after pyrolysis. Significantly, from experimental and theoretical investigations, the highly porous structure, highly dispersed ultrafine Mo₂C and the N and P co-doping in the Mo₂C@NPC lead to the remarkable ORR activity with an onset potential of ∼1.01 V, a half-wave potential of ∼0.90 V and a Tafel slope of 51.7 mV dec^-1 at 1600 rpm in 0.1 M KOH. In addition, the Mo₂C@NPC as an ORR catalyst in zinc-air batteries achieved a high power density of 266 mW cm^-2 and a high specific capacity of 780.9 mA h g^-1, exceeding that driven by commercial Pt/C. Our results revealed that the porous architecture and ultrafine Mo₂C nanocrystallites of the electrocatalysts could facilitate mass transport and increase the accessibility of active sites, thus optimizing their performances in an ORR. The present study provides some guidelines for the design and synthesis of efficient nanostructured electrocatalysts.