Improving the performance of polyvinylidene fluoride (PVDF)-based proton exchange membranes with the addition of cellulose acetate for direct methanol fuel cells

Abstract

In this work, a poly (vinylidene fluoride) (PVDF) and cellulose acetate (CA) blend membrane is developed using the solution casting method for a direct methanol fuel cell (DMFC). The CA addition in PVDF polymer reduces the dense structure of the polymer and creates a porous surface by increasing the amorphous region that is confirmed by surface morphology and crystallinity examination tests. The high glass transition temperature of CA boosts the protection from the melting of PVDF membrane and increases the thermal shrinkage that reduces the probability of a short circuit. PVDF and CA with abundant hydroxyl groups and carboxylic groups enhance the water uptake, also the hydrogen bonding in between them promotes the mechanical strength and develops a tortuous structure that allows protons to pass through them and block the methanol crossover. The 60% PVDF and 40% CA blend membrane shows an ion exchange capacity value of 0.91 and a methanol permeability value of 4.21 × 10^–7 cm² s⁻¹, which is lower than that of the conventional Nafion 117 membrane (19.5 × 10^–7 cm² s⁻¹). A direct methanol fuel cell with this membrane represents a power density value of 16.5 mW cm⁻² with a voltage and current density values of 0.178 V and 165 mA cm⁻² at 1 M methanol concentration and room temperature. Moreover, it shows a 70% voltage retention after 20 h of testing of the cell at room temperature that is superior to that of the commercial Nafion 117 membrane (48% voltage retention).