▎ 摘　　要

Vanadium redox flow batteries areemerging as a promisinggridstorage solution. Unlike competing flow battery concepts, these utilizevanadium in both the catholyte and anolyte chambers which enableseasy regeneration and balancing of the cell upon crossover of speciesthrough the membrane during long-term use. To increase the time betweenregeneration cycles and to improve the overall efficiency of vanadiumflow batteries, we investigate the use of an ultrathin, graphene coatingon the surface of various Nafion membranes. Electrochemically exfoliatedgraphene (EEG) was dispersed at the air-water interface ofa Langmuir-Blodgett trough, compressed, and transferred toNafion 117 (180 mu m thickness) and Nafion 115 (127 mu m)membranes. Single-cell vanadium redox flow batteries assembled withthe coated membranes led to significantly higher energy efficiency(increased by 13%), power density (by 67%), and discharge capacity(by 17.5%) over 100 cycles compared to uncoated Nafion. The graphenelayer was stable over cycling, and electrochemical impedance spectroscopyand self-discharge experiments indicated that the improved batteryperformance is due to a combination of reduced vanadium crossoverand enhanced electrochemical activity provided by the graphene atthe electrode surface.