Renewable and hydrophilic carbon quantum dots derived from human hair as the filler in Nafion composite membrane for vanadium redox flow battery application

Renewable and environmentally benign hydrophilic carbon quantum dots (CQDs) were synthesized using a hydrothermal method. Subsequently, composite membranes of Nafion/CQDs, demonstrating outstanding performance metrics for vanadium redox flow batteries (VRFBs), were developed. Employing a straightforward solution-casting technique, these membranes exhibited superior proton conductivity and reduced vanadium ion permeability. Tested at an elevated current density of 120 mA/cm², the single cell VRFB integrated with the optimized Nafion/CQDs composite membrane outperformed its commercial counterparts, achieving a high coulombic efficiency of approximately 96.13 % and an energy efficiency of nearly 85.46 %. Moreover, it demonstrated significant cycle life, retaining about 17.1 % of its capacity after 100 cycles, compared to 27.2 % capacity retention for the N-recast membrane over the same period. These results position the Nafion/CQDs composite membrane as a formidable contender in the VRFB domain, emphasizing its potential for broader commercial applications.