A Fluorinated Covalent Organic Framework with Accelerated Oxygen Transfer Nanochannels for High-Performance Zinc-Air Batteries.

ABSTRACT

The establishment of abundant three-phase interfaces with accelerated mass transfer in air cathodes is highly desirable for the development of high-rate and long-cycling rechargeable zinc-air batteries (ZABs). Covalent organic frameworks (COFs) exhibit tailored nanopore structures, facilitating the rational tuning of their specific properties. Here, by finely tuning the fluorinated nanopores of a COF, a novel air cathode for rechargeable ZABs is unprecedentedly designed and synthesized. COF nanosheets are decorated with fluorinated alkyl chains, which shows high affinity to oxygen (O2 ), in its nanopores (fluorinated COF). The fluorinated COF nanosheets are stacked into well-defined O2 -transport channels, which are then assembled into aerophilic "nano-islands" on the hydrophilic FeNi layered-double-hydroxide (FeNi LDH) electrocatalyst surface. Therefore, the mass-transport "highway" for O2 and water is segregated on the nanoscale, which significantly enlarges the area of three-phase boundaries and greatly promotes the mass-transfer therein. ZABs based on the COF-modified air cathode deliver a small charge/discharge voltage gap (0.64 V at 5 mA cm-2 ), a peak power density (118 mW cm-2 ), and a stable cyclability. This work provides a feasible approach for the design of the air cathodes for high-performance ZABs, and will expand the new application of COFs.