كليدواژه :
Fuel permeation , Bio , polymeric membrane , Direct methanol fuel cell , Modeling 45 Figure 1 – RDFs , CN , and average number of H , bonds of water molecules with chitosan functional groups at different methanol concentrations.
چكيده فارسي :
Chitosan biopolymers have been recently employed in various forms as an alternative protonconducting
membrane to Nafion due to its considerably lower methanol crossover properties or
higher selectivity (i.e., the ratio of proton conductivity to methanol permeability) [1-3]. The ability
of water molecules to transport the proton from anode to cathode compartments relies upon the
network of hydrogen bonds emerged among them, which is influenced by the amount of methanol
uptake inside the DMFC membrane [4]. In the present research, the effects associated with the
methanol crossover on the water hydrogen bonding characteristics across the water/methanol
solvated chitosan membrane were examined by means of molecular dynamics (MD) simulation
approaches. To this purpose, a range of methanol concentrations (including 0, 10, 20, 40, 60, and
80 wt%) were taken into account. Intermolecular hydrogen bonding interactions of water with
chitosan functional fragments, namely, amine (-NH2), hydroxyl (-OH) as well as hydroxymethyl (-
CH2OH) were studied using radial distribution function (RDF), coordination number (CN), and
time evolution of the number of hydrogen bonds. The obtained simulation results for RDFs and
CNs (the insets in Figure 1) of water around each function group suggested that water interactions
with chitosan chains weakened against an increase in methanol concentration. Such an observation
was further confirmed by the reduced number of hydrogen bonds in increasingly methanol solvated
chitosan membrane. These findings propose that an increase in methanol sorption (and its
subsequent crossover) could significantly diminish the proton conductivity feature of DMFC
membranes fabricated from chitosan biopolymers.
