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:

• Commercial Nafion membranes in vanadium redox flow batteries (VRFBs) suffer from excessive swelling, leading to critical vanadium ion permeation and performance limitations.
• Addressing the conductivity-selectivity trade-off in VRFB membranes is essential for improving battery efficiency and lifespan.

Purpose of the Study:

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

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 performance, including vanadium ion permeation, proton conductivity, and battery cycling stability.

Main Results:

• The modified N115-(PEI/SL)₂ membrane demonstrated a 92.8% reduction in vanadium ion permeation with 80% proton conductivity retained compared to pristine Nafion 115.
• The modified membrane achieved a higher energy efficiency of 85.14% at 80 mA cm^-2 compared to the pristine membrane (81.77%).
• Excellent long-term stability was observed, 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 strategy successfully resolves the conductivity-selectivity trade-off, offering a scalable and commercially viable solution for VRFB membranes.
• This approach significantly enhances VRFB performance and durability, paving the way for advanced energy storage systems.