Surface-engineered Nafion membranes with an ion-sieving layer for high-performance vanadium redox flow battery

Area of Science:

• Materials Science
• Electrochemistry
• Chemical Engineering

Background:

• Nafion membranes in vanadium redox flow batteries (VRFBs) suffer from excessive swelling, leading to vanadium ion permeation and reduced performance.
• Addressing the conductivity-selectivity trade-off is crucial for advancing VRFB technology.

Purpose of the Study:

• To develop a straightforward and scalable surface modification strategy for Nafion membranes to mitigate vanadium ion permeation.
• To enhance the selectivity and stability of membranes for improved VRFB performance.

Main Methods:

• Sequential layer-by-layer (LbL) assembly of polyethyleneimine (PEI) and sodium lignosulfonate (SL) on Nafion 115 membranes.
• Chemical cross-linking of the assembled layer using glutaraldehyde (GA).
• Characterization of membrane properties including ion permeation, proton conductivity, and electrochemical performance in VRFBs.

Main Results:

• The modified N115-(PEI/SL)2 membrane demonstrated a 92.8% decrease in vanadium ion permeation with 80% proton conductivity retained.
• Achieved a peak energy efficiency of 85.14% at 80 mA cm⁻², compared to 81.77% for the pristine Nafion membrane.
• Exhibited excellent long-term stability with only a ~2% decay in energy efficiency over 350 cycles (>400 h) at 200 mA cm⁻².

Conclusions:

• The PEI/SL selective layer effectively suppresses vanadium ion crossover through synergistic size-sieving and Donnan exclusion effects.
• The modified membrane offers a promising solution to the conductivity-selectivity challenge in VRFBs, enhancing both efficiency and durability.
• This surface modification strategy is simple, scalable, and commercially viable for next-generation VRFB applications.