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

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 (O 2 ), in its nanopores (fluorinated COF). The fluorinated COF nanosheets are stacked into well-defined O 2 -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 O 2 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.