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.

Interface engineering of bifunctional oxygen electrocatalysts for rechargeable Zn–air batteries

“…2,24 Reasonable construction of the surface structure of a bifunctional electrocatalyst to optimize the triple-phase interface is particularly useful for accelerating oxygen transfer and exposing more catalytic active sites, thereby promoting efficient and durable operation. 22,48,93,94…”

“…For RZABs, both the ORR and OER at the cathode mainly occur at the solid-liquid-gas triple-phase interfaces where the oxygen reactant/evolution, electronic transportation, and the ionic conductor intersect. 48,93 The performance of the reaction interface is deeply dependent on the microenvironment of the electrocatalysts in the actual working environment. 2,22 The half-cell test generally employs a rotating disc electrode (RDE) or rotating ring-disc electrode (RRDE) to evaluate the catalytic properties, and these electrodes are conducive to enhancing mass transfer and eliminating concentration polarization for maximizing the inherent catalytic activity.…”

“…2,24 Reasonable construction of the surface structure of a bifunctional electrocatalyst to optimize the triple-phase interface is particularly useful for accelerating oxygen transfer and exposing more catalytic active sites, thereby promoting efficient and durable operation. 22,48,93,94 Recently, inspired by the bionics of diving flies, Tang et al developed a hybrid electrode based on a PTFE layer coated on the surfaces of Co 3 O 4 nanosheets (NSs)/carbon cloth (CC), which created a hydrophobic surface to promote the exposure of abundant triple-phase reaction interfaces and increase the rate of oxygen transfer. 32 In contrast with the untreated Co 3 O 4 NSs/CC electrode, the assembled Zn-air battery employing the hydrophobic-Co 3 O 4 NSs/CC exhibited a greater energy density (171 mW cm À2 ), higher open circuit voltage (1.42 V), and better cyclic durability (500 cycles) (Fig.…”

Regulating the Electron Structure of Covalent Organic Frameworks by Strong Electron‐Withdrawing Nitro to Construct Specific Li+ Oriented Channel

“…The Li + transfer environment will be improved under the regulated electronic states, which can further elevate the electrochemical performance of LMB. [41,42] Thus, effectively optimizing electron structure by the D-A effect will provide a better platform to understand Li + migration. [43] Herein, nitro-modified COF is introduced and served as an ASEI to realize the target of dendrite-free, long-life LMBs.…”

Design, Preparation, and High Intrinsic Proton Conductivity of Two Highly Stable Hydrazone-Linked Covalent Organic Frameworks

“…in 2011, with its higher stability than imine-linked COFs and the chelating sites provided by abundant polar functional groups (amides), , hydrazone-linked COFs have gained popularity among researchers, mainly in the field of catalysis − and heavy metal ion adsorption and detection − or I 2 uptake . Recently, the applications of some new hydrazone-linked COFs in the field of sensing , and energy storage , have also been discovered, showing great application prospects. For instance, Yang and co-workers found that a series of macrocycle-derived COFs have highly photocatalytic activity .…”