Zn metal organic framework tailored cellulose acetate/PVdF-co-HFP based proton conductive composite membranes: performance enhancement in direct methanol fuel cells

A low-cost proton-conductive composite membrane composed of cellulose acetate (CA)/poly(vinylidene fluoride-co-hexafluoropropylene) incorporating ZIF-8 (ZPHC) was fabricated via solution casting for direct methanol fuel cell applications. Structural and physicochemical characterization, including FTIR, XRD, TGA, SEM, EDX, BET, and AFM, confirms that the introduction of ZIF-8 increases porosity, amorphous character, water uptake, and hydrogen-bonding interactions, thereby reinforcing the polymer network. Proton conductivity rises sharply from 0.08 × 10^-3 S cm^-1 for the pristine CA to 2.73 × 10^-3 S cm^-1 upon ZIF-8 incorporation, while methanol permeability drops from 18 × 10^-7 to 2.25 × 10^-7 cm² s^-1, notably below that of Nafion® 117, as a standard (21.31 × 10^-7 cm² s^-1). Mechanical strength is also enhanced, yielding more than a 2-fold improvement over neat CA. As a result, the composite exhibits markedly higher selectivity (10.31 × 10³ S s cm^-3) than both pristine CA (0.04 × 10³ S s cm^-3) and Nafion® 117 (6.43 × 10³ S s cm^-3). A single DMFC using the ZPHC₄₀-2.5 membrane delivers a peak power density of ∼38 mW cm^-2 and a current density of 126.5 mA cm^-2 at 30 °C, indicating slightly lower maximum power than Nafion® 117 but promising fuel efficiency and durability for DMFC. The results demonstrate the feasibility of engineering an economically promising proton exchange membrane with potential applicability in DMFC systems.