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.

Automated summary

A novel air cathode for rechargeable zinc-air batteries (ZABs) is designed and synthesized by finely tuning the fluorinated nanopores of a covalent organic framework (COF). The COF nanosheets decorated with fluorinated alkyl chains provide well-defined O-2-transport channels and significantly enlarge the area of three-phase boundaries, promoting mass-transfer. The ZABs based on the COF-modified air cathode exhibit a small charge/discharge voltage gap, high peak power density, and stable cyclability. This work provides a feasible approach for the design of high-performance ZABs and expands the new application of COFs.