Molecular Dynamic Simulation Approach to Understand the Physical and Proton Transport Properties of Chitosan/sulfonated Poly(Vinyl Alcohol) Composite Membranes

The physical and proton conduction properties of electrolyte membranes are crucial for the development of proton-exchange membrane fuel cells (PEMFCs). However, data on novel bulk polymers is lacking, which is detrimental to conveying their superiority for applications. Hence, molecular dynamics (MD) simulations could lead to understanding some important properties with great accuracy. In this work, MD simulations of chitosan/sulfonated poly (vinyl) alcohol (CS/SPVA) composite membranes produced in our previous experimental work are performed. First, the miscibility of the CS/SPVA composite is confirmed by simulating the Flory-Huggins interaction chi, which satisfies the condition chi < chi(critical). In terms of thermal stability, the glass transition temperature T-g of the CS/SPVA composite is simulated at a value of 430 K (with only 3.18% deviation from the literature data). This suggests that the composite membrane satisfied the fuel cell working condition of 353 K. The proton conductivity was quantified by the ability of hydronium ions to diffuse into the polymer matrix. The simulated data demonstrated a higher proton conductivity in the CS/SPVA15 composite membrane than in the single SPVA membrane, with a computed value of 11.15 mS/cm. In addition, the RDFs agree with the Grotthuss-type proton transfer mechanism proposed in the CS/SPVA15 polymer model. In addition, better mechanical properties are reported with CS/SPVA15 composite membranes, with an approximately 110% improvement in the average Young's modulus. This suggests that the composite membrane has a much more compact and rigid structure than the SPVA membrane. This is beneficial for achieving an electrolyte polymer with better dimensional stability, which could prevent potential membrane failure during fuel cell operation. It can be concluded that the CS/SPVA composite displays superior thermal and mechanical stability, as well as proton conductivity, compared to the SPVA membrane.