Charge-enhanced porous graphene oxide nanosheets-embedded membrane with improved ion conduction and capacity retention for aqueous organic flow battery

Aqueous organic flow battery (AOFB), a promising energy storage technology, owned low self-discharge rate, cost-effective merit and non-dependence on metal resources. However, membranes with high ion-selective transport are urgently required to alleviate capacity degradation of AOFBs. Herein, charge-enhanced porous graphene oxide (CPGO) nanosheets were created by ultrasonic-assisted acid etching and embedded in polymer membrane to realize fast ion-selective transport by multiple ion channel construction and electrostatic repulsion synergistic strategy. Acid etching exposed more oxygen-containing groups on the porous surface, facilitating uniform dispersion of CPGO and connectivity of pore-assisted ion channels and interfacial water-bridged ion channel. Furthermore, carboxyl groups on CPGO in alkaline electrolyte also provided transfer sites for K + transport. On the other hand, the stronger interfacial interaction further effectively reduced ion cluster dimension, leading to a 2.1-fold enhancement in ion selectivity. As a consequence, the optimized membrane endowed the AOFB with excellent coulombic efficiencies of 98.9-99.9% and high voltage efficiencies of 94.8-77.9% at 20-100 mA cm -2 . Notably, the AOFB still keep more than 99% capacity for 1000 cycles (0.0002% capacity decay per cycle), which is greatly superior to that of pure polymer membrane (0.02% capacity decay per cycle).