NiO-Decorated rGO Functional Layer on the Graphite Felt as the Negative Electrode of Vanadium Redox Flow Batteries

Vanadium redox flow batteries (VRFBs) are prospective energy-storage medium owing to their flexible design and long lifetime. However, the problem of sluggish negative electrode dynamics of VRFBs has become a great resistance to their large-scale commercial applications. To solve this problem, we employed a facile and cost-effective approach to synthesize NiO/rGO composites using hydrothermal and calcination processes. The NiO/rGO nanocatalysts were evenly applied onto the heat-treated graphite felt (HGF) to prepare a high-performance negative electrode for VRFBs. This coating process was achieved using an ultrasonic spraying system, resulting in NiO/rGO-HGF. The NiO/rGO electrocatalysts provided enhanced adsorption characteristics of vanadium ions and sufficient redox-reactive sites, which improved electrochemical performance (9.41% higher energy efficiency of NiO/rGO-HGF compared with HGF at 160 mA cm⁻²) and high cycle stability (84.7% electrolyte capacity after 100 cycles) of the VRFB cells. In conclusion, our work with the NiO/rGO-HGF anode represents a promising direction for the development of highly efficient and stable VRFB anodes for broadening commercial applications.