Hierarchical Carbon Micro/Nanonetwork with Superior Electrocatalysis for High-Rate and Endurable Vanadium Redox Flow Batteries

Vanadium redox flow batteries (VRFBs) are receiving increasing interest in energy storage fields because of their safety and versatility. However, the electrocatalytic activity of the electrode is a pivotal factor that still restricts the power and cycling capabilities of VRFBs. Here, a hierarchical carbon micro/nanonetwork (HCN) electrode codoped with nitrogen and phosphorus is prepared for application in VRFBs by cross‐linking polymerization of aniline and physic acid, and subsequent pyrolysis on graphite felt. Due to the hierarchical electron pathways and abundant heteroatom active sites, the HCN exhibits superior electrocatalysis toward the vanadium redox couples and imparts the VRFBs with an outstanding energy efficiency and extraordinary stability after 2000 cycles at 250 mA cm−2 and a discharge capacity of 10.5 mA h mL−1 at an extra‐large current density of 400 mA cm−2. Such a micro/nanostructure design will force the advancement of durable and high‐power VRFBs and other electrochemical energy storage devices.