A High-Performance Polyimide Composite Membrane with Flexible Polyphosphazene Derivatives for Vanadium Redox Flow...

Area of Science:

• Materials Science
• Electrochemistry
• Polymer Chemistry

Background:

• Sulfonated polyimides are key materials for proton exchange membranes.
• Enhancing proton conductivity and stability is crucial for advanced energy storage devices.
• Vanadium redox flow batteries (VRFBs) require membranes with high ion selectivity and durability.

Purpose of the Study:

• To design and synthesize novel composite membranes for VRFB applications.
• To investigate the effect of polyphosphonitrile (PFMPP) modification on sulfonated polyimide (S-F-abSPI) membranes.
• To evaluate the electrochemical performance and stability of the developed composite membranes.

Main Methods:

• Synthesis of S-F-abSPI with alkyl sulfonic acid side chains and PFMPP.
• Fabrication of S-F-abSPI/PFMPP composite membranes with varying ratios.
• Characterization of membrane properties including proton conductivity, surface resistance, and mechanical strength.
• Electrochemical testing of VRFB performance (voltage efficiency, energy efficiency, cycling stability).
• Computational analysis of electrostatic potential distribution to understand interactions.

Main Results:

• The S-F-abSPI membrane achieved a proton conductivity of 0.116 S cm⁻¹, surpassing the N212 membrane.
• The S-F-abSPI/1% PFMPP composite membrane showed optimal performance with low surface resistance (0.54 Ω cm²).
• High voltage efficiency (83.12%) and energy efficiency (81.95%) were achieved at 200 mA cm⁻².
• Excellent long-term cycling stability was demonstrated over 200 cycles.
• PFMPP incorporation enhanced mechanical strength, reduced vanadium ion permeability, and improved selectivity.

Conclusions:

• The S-F-abSPI/PFMPP composite membrane offers superior comprehensive performance for VRFBs.
• Alkyl sulfonic acid side chains contribute to enhanced proton conductivity.
• Strong interactions between PFMPP and S-F-abSPI improve membrane durability and ion selectivity.
• This novel composite membrane is a promising candidate for high-performance vanadium redox flow battery applications.