Sulfonated NbS₂-based proton-exchange membranes for vanadium redox flow batteries.

Area of Science:

• Materials Science
• Electrochemistry
• Energy Storage

Background:

• Proton-exchange membranes (PEMs) are critical components in vanadium redox flow batteries (VRFBs).
• Sulfonated poly(ether ether ketone) (SPEEK) is a promising material for PEMs, but its performance can be limited by ion permeability and conductivity.
• Two-dimensional (2D) materials offer unique properties for enhancing membrane performance.

Purpose of the Study:

• To synthesize novel PEMs using SPEEK and 2D sulfonated niobium disulphide (S-NbS2) nanoflakes.
• To investigate the effect of S-NbS2 nanoflakes on the properties of SPEEK-based membranes.
• To evaluate the performance of these membranes in VRFBs.

Main Methods:

• Synthesis of S-NbS2 nanoflakes via liquid-phase exfoliation and chemical functionalization.
• Fabrication of SPEEK:S-NbS2 composite membranes using a solution-casting method.
• Characterization of membrane properties (conductivity, permeability, stability) and VRFB performance (efficiency, power density, cycling stability).

Main Results:

• Addition of S-NbS2 nanoflakes significantly reduced vanadium ion permeability (from 5.42 × 10⁻⁷ to 2.34 × 10⁻⁷ cm² min⁻¹).
• Proton conductivity (σ) and selectivity were enhanced, reaching 94.35 mS cm⁻² and 40.32 × 10⁴ S min cm⁻³, respectively.
• The optimized SPEEK:2.5% S-NbS2 membrane demonstrated high coulombic (98.7–99.0%), voltage (90.2–73.2%), and energy (89.3–72.8%) efficiencies, with a maximum power density of 0.83 W cm⁻² and stable cycling over 200 cycles.

Conclusions:

• The incorporation of S-NbS2 nanoflakes into SPEEK membranes effectively improves dimensional and chemical stability, proton conductivity, and fuel barrier properties.
• The developed SPEEK:S-NbS2 composite membranes show excellent performance and stability for VRFB applications.
• This study presents a viable strategy for creating advanced SPEEK-based membranes for next-generation energy storage systems.