L-tyrosine grafted palladium graphite oxide and sulfonated poly(ether ether ketone) based novel composite membrane for direct methanol fuel cell

This work involves synthesis of amino acid grafted palladium graphite oxide based nanocomposites as proton exchange membranes for direct methanol fuel cell applications (DMFC) and determination of their selectivity. Membrane synthesis includes grafting of L-tyrosine on palladium decorated graphite oxide (Pd-GO-L-Tyr) in a polymeric substrate viz. sulfonated poly(ether ether ketone) (SPEEK) by solution casting. Pd-GO-L-Tyr composites were characterized by FT-IR and XPS to analyze the functional groups and constituent elements to confirm successful functionalization of amino acid. The surface morphology was studied by scanning electron microscopy (SEM), atomic force microscopy (AFM) and transmission electron microscopy (TEM). The physicochemical properties of the SPEEK/Pd-GO-L-Tyr membranes such as ion exchange capacity (IEC), water uptake, methanol permeability and proton conductivity were measured. The results include significant improvement in blocking of methanol upon modification of Pd-GO-L-Tyr. On one hand, presence of Pd and GO inhibits the methanol permeability, while on the other L-Tyr significantly increases the conductivity of the membrane. Both these factors result in higher selectivity of the Pd-GO-L-Tyr-SPEEK composite membrane for DMFC applications, compared to that of benchmark Nafion-117 membrane.