In this study, proton exchange membranes (PEMs) based on chitosan (CS), sulfonated polystyrene (SPS), and pristine or modified nanosilica were fabricated for direct methanol fuel cell (DMFC) applications. Membranes containing different SPS contents were prepared, and polystyrene was sulfonated to an optimal degree of sulfonation determined by evaluating its hydrolytic stability. Proton conductivity and methanol permeability were measured to determine the membrane selectivity parameter (defined as the ratio of proton conductivity to methanol permeability), which was used to optimize the CS/SPS blend composition to achieve an optimal balance between proton conductivity and methanol crossover resistance. Among the prepared membranes, the membrane containing 40 wt% SPS exhibited the highest selectivity parameter (39,908 S s cm− 3) and was therefore identified as the optimal composition. This was attributed to strong acid–base interactions between the amino groups of chitosan and the sulfonic acid groups of SPS, which enhance proton conductivity and reduce methanol crossover. To improve membrane performance, nanocomposite membranes containing 2 wt% silica nanoparticles (SiO2) or sulfonated silica nanoparticles (S-SiO2) were separately prepared using the optimal chitosan/SPS blend. The incorporation of SPS increased the glass transition temperature and decreased the crystallinity of the chitosan matrix due to electrostatic interactions between the –SO3H groups of SPS and the –NH2 groups of chitosan. Furthermore, the nanocomposite membranes exhibited higher proton conductivity and lower methanol permeability compared with the optimal blend membrane. The S-SiO2 nanoparticles provide additional –SO3H groups that expand proton transport pathways while simultaneously reducing methanol permeability via tortuous diffusion pathways. The membrane containing S-SiO2 nanoparticles showed the highest selectivity (54,010 S s cm− 3), representing a 35% improvement over the optimal blend membrane, indicating its strong potential as a cost-effective alternative proton exchange membrane for DMFC applications. Graphical abstract The graphical abstract depicts proton transport within the chitosan–sulfonated polystyrene–sulfonated nanosilica nanocomposite membrane. Acid–base interactions between chitosan (–NH2) and sulfonated components (–SO3H) form ionic pairs (–NH3+/–SO3−), creating interconnected ionic domains. Hydrophilic groups enhance water retention and enable proton conduction via vehicle (H3O+ diffusion) and Grotthuss (proton hopping) mechanisms, while restricting methanol crossover.

Development of chitosan–sulfonated polystyrene–sulfonated nanosilica nanocomposite proton exchange membranes for direct methanol fuel cells

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2026年8月2日

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Shayan Navabi,
Mahdi Tohidian

摘要

In this study, proton exchange membranes (PEMs) based on chitosan (CS), sulfonated polystyrene (SPS), and pristine or modified nanosilica were fabricated for direct methanol fuel cell (DMFC) applications. Membranes containing different SPS contents were prepared, and polystyrene was sulfonated to an optimal degree of sulfonation determined by evaluating its hydrolytic stability. Proton conductivity and methanol permeability were measured to determine the membrane selectivity parameter (defined as the ratio of proton conductivity to methanol permeability), which was used to optimize the CS/SPS blend composition to achieve an optimal balance between proton conductivity and methanol crossover resistance. Among the prepared membranes, the membrane containing 40 wt% SPS exhibited the highest selectivity parameter (39,908 S s cm^− 3) and was therefore identified as the optimal composition. This was attributed to strong acid–base interactions between the amino groups of chitosan and the sulfonic acid groups of SPS, which enhance proton conductivity and reduce methanol crossover. To improve membrane performance, nanocomposite membranes containing 2 wt% silica nanoparticles (SiO₂) or sulfonated silica nanoparticles (S-SiO₂) were separately prepared using the optimal chitosan/SPS blend. The incorporation of SPS increased the glass transition temperature and decreased the crystallinity of the chitosan matrix due to electrostatic interactions between the –SO₃H groups of SPS and the –NH₂ groups of chitosan. Furthermore, the nanocomposite membranes exhibited higher proton conductivity and lower methanol permeability compared with the optimal blend membrane. The S-SiO₂ nanoparticles provide additional –SO₃H groups that expand proton transport pathways while simultaneously reducing methanol permeability via tortuous diffusion pathways. The membrane containing S-SiO₂ nanoparticles showed the highest selectivity (54,010 S s cm^− 3), representing a 35% improvement over the optimal blend membrane, indicating its strong potential as a cost-effective alternative proton exchange membrane for DMFC applications.

Graphical abstract

The graphical abstract depicts proton transport within the chitosan–sulfonated polystyrene–sulfonated nanosilica nanocomposite membrane. Acid–base interactions between chitosan (–NH₂) and sulfonated components (–SO₃H) form ionic pairs (–NH₃⁺/–SO₃⁻), creating interconnected ionic domains. Hydrophilic groups enhance water retention and enable proton conduction via vehicle (H₃O⁺ diffusion) and Grotthuss (proton hopping) mechanisms, while restricting methanol crossover.