Direct growth of ordered N‐doped carbon nanotube arrays on carbon fiber cloth as a free‐standing and binder‐free air electrode for flexible quasi‐solid‐state rechargeable Zn‐Air batteries

Abstract

The development of an air electrode that is flexible in physical property and highly active and durable at different geometric status for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of crucial importance for the rational design of flexible rechargeable Zn‐air batteries (ZABs). Considering their good elasticity, high conductivity, and superior thermal and chemical stability, carbon nanotubes have been widely used as a catalyst support in various electrocatalysts, while oxide or metal nanoparticles have been frequently deposited on the carbon nanotube substrate to perform as the active materials. Considering the poor contact between active materials and carbon nanotubes may introduce a challenge for long‐term operating stability, in particular in flexible devices, pure carbon electrocatalyst is highly appreciated. Herein, a free‐standing air electrode with cobalt nanoparticles encapsulated N‐codoped carbon nanotube arrays uniformly grown on the surface of carbon fiber cloth is developed by a two‐step in situ growth method. Such a carbon‐based electrode shows outstanding activity for both ORR and OER. The flexible ZAB with such air electrode shows superior flexibility and stability working under extreme bending conditions. Moreover, the polarization and round‐trip efficiency for the flexible battery is 0.67 V and 64.4% at 2 mA/cm2, respectively, even after being operated for 30 hours. This study provides a feasible way to design all carbon‐based free‐standing and flexible electrode and enlightens the electrode design for flexible energy conversion/storage devices.

Facilitating Oxygen Redox on Manganese Oxide Nanosheets by Tuning Active Species and Oxygen Defects for Zinc‐Air Batteries

“…A typical alkaline Zn‐air battery is comprised of an air cathode, a Zn anode and an aqueous electrolyte [9,10] . Because of the slow kinetics of oxygen redox reactions on the air cathode, a bifunctional catalyst which can facilitate both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is required to obtain low overpotentials of discharging/charging and high energy efficiency [7,11–13] . In the past few decades, different types of catalysts have been developed, including precious metals, transition metal compounds, functional carbon‐based materials [14–23] .…”

A Function‐Separated Design of Electrode for Realizing High‐Performance Hybrid Zinc Battery

“…The transfer number of ≈4 indicates the predominant 4‐electron transfer process for OH − yielding. [ 51–53 ] MnS also shows a fair OER activity with a potential of 1.813 V at 10 mA cm −2 ( E j =10 ). While the ORR activity of Ni x Co 1− x S 2 ( E 1/2 = 0.710 V) is inferior to MnS, Ni x Co 1− x S 2 material shows a more favorable OER activity indicated by a E j =10 of 1.610 V. It suggests that the introduction of Ni x Co 1− x S 2 into the MnS will realize a significant improvement of the OER activity.…”

Flexible and Wearable Power Sources for Next‐Generation Wearable Electronics

“…According to these requirements, carbon-based materials (e. g., carbon particles, carbon nanotubes (CNTs), graphene, carbon fiber, carbon paper, and carbon cloth), conductive polymers, metal and metal oxide sheets (or foils) have been used and investigated as the flexible substrates for electrodes. [49][50][51][52][53][54][55][56][57][58][59] Carbon-based materials are attractive owing to the relatively high electrical conductivity (10 4 S cm À 1 ), good mechanical property, environmental stability and low-cost. [49] Polymer-based materials are intrinsically flexible, which are capable of withstanding bending, folding, twisting, or other deformations.…”

“…The specific flexible materials are supposed to be electric conductive (electrode materials) or ionic conductive (electrolyte materials). According to these requirements, carbon‐based materials (e. g., carbon particles, carbon nanotubes (CNTs), graphene, carbon fiber, carbon paper, and carbon cloth), conductive polymers, metal and metal oxide sheets (or foils) have been used and investigated as the flexible substrates for electrodes [49–59] . Carbon‐based materials are attractive owing to the relatively high electrical conductivity (10 4 S cm −1 ), good mechanical property, environmental stability and low‐cost [49] .…”