Concurrently Realizing Geometric Confined Growth and Doping of Transition Metals within Graphene Hosts for Bifunctional Electrocatalysts toward a Solid-State Rechargeable Micro-Zn-Air Battery.

The simultaneous realization of confined growth and doping of transition metals within carbon hosts promises to deliver unusual bifunctional catalytic activity but still remains challenging due to the difficulty in achieving synchronous nucleation and diffusion of metallic ions in a single synthesis step. Herein, we present a simple synthesis strategy capable of concurrently realizing geometric confined growth and doping of transition metals within graphene hosts, demonstrated in Co,N-codoped graphene-confined FeNi nanoparticles (Co,N-GN-FeNi). The obtained Co,N-GN-FeNi can take full advantage of the hierarchy of interactions between the confined-grown FeNi nanoparticles (for high oxygen evolution reaction (OER) activity) and the Co,N-codoped graphene hosts (for high oxygen reduction reaction (ORR) activity). The overall structure is a rationally designed synergy that simultaneously realizes (i) adequate exposure of electroactive sites, (ii) effective protection against corrosion/aggregation of FeNi nanoparticles, and (iii) rapid transport of ions/electrons between the interfaces. As a result, Co,N-GN-FeNi exhibits excellent bifunctional electrocatalytic activity relying on a low ORR/OER subtraction (ΔE = 0.81 V). Subsequent combination with a planar electrode configuration and a solid polymer electrolyte further demonstrates the utilization of Co,N-GN-FeNi as air cathode bifunctional electrocatalysts in a solid-state rechargeable micro-Zn-air battery (SR-MZAB), which exhibits a large open-circuit voltage of 1.39 V, a high power density/specific capacity of 62.3 mW cm-2/763 mAh g-1, excellent durability (126 cycles/42 h), and mechanical flexibility. This work demonstrates an effective synthesis strategy for concurrently realizing geometric confined growth and doping of transition metals within carbon hosts, for enhanced bifunctional catalytic activity toward novel SR-MZABs with high energy efficiency, security, and flexibility for wearable micropower sources.