Two‐Step Activated Carbon Cloth with Oxygen‐Rich Functional Groups as a High‐Performance Additive‐Free Air Electrode for Flexible Zinc–Air Batteries

• Published in: Advanced energy materials Vol. 9; no. 4
• Main Authors: Kordek, Karolina, Jiang, Lixue, Fan, Kaicai, Zhu, Zhengju, Xu, Li, Al‐Mamun, Mohammad, Dou, Yuhai, Chen, Shan, Liu, Porun, Yin, Huajie, Rutkowski, Piotr, Zhao, Huijun
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 24.01.2019
• Subjects: Activated carbon; bifunctional air electrodes; Carbon; carbon cloth; Cloth; electrocatalysis; Electrocatalysts; Electrodes; Flexibility; flexible Zn–air batteries; Functional groups; Metal air batteries; metal‐free; Open circuit voltage; Oxidation; Oxygen evolution reactions; Rechargeable batteries; Zinc; Zinc-oxygen batteries
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201802936

A flexible air electrode (FAE) with both high oxygen electrocatalytic activity and excellent flexibility is the key to the performance of various flexible devices, such as Zn–air batteries. A facile two‐step method, mild acid oxidation followed by air calcination that directly activates commercial carbon cloth (CC) to generate uniform nanoporous and super hydrophilic surface structures with optimized oxygen‐rich functional groups and an enhanced surface area, is presented here. Impressively, this two‐step activated CC (CC‐AC) exhibits superior oxygen electrocatalytic activity and durability, outperforming the oxygen‐doped carbon materials reported to date. Especially, CC‐AC delivers an oxygen evolution reaction (OER) overpotential of 360 mV at 10 mA cm−2 in 1 m KOH, which is among the best performances of metal‐free OER electrocatalysts. The practical application of CC‐AC is presented via its use as an FAE in a flexible rechargeable Zn–air battery. The bendable battery achieves a high open circuit voltage of 1.37 V, a remarkable peak power density of 52.3 mW cm−3 at 77.5 mA cm−3, good cycling performance with a small charge–discharge voltage gap of 0.98 V and high flexibility. This study provides a new approach to the design and construction of high‐performance self‐supported metal‐free electrodes. An exceptionally simple two‐step activation method, mild acid oxidation followed by air calcination, is implemented to create a low‐cost flexible air electrode for zinc‐air batteries from commercial carbon cloth. This two‐step‐activated carbon cloth exhibits superior bifunctional oxygen electrocatalytic activity and durability. The corresponding flexible zinc‐air battery achieves a small charge‐discharge voltage gap, remarkable peak power density and good cycling performance.