New Insights into Properties of Methanol Transport in Sulfonated Polysulfone Composite Membranes for Direct Methanol Fuel Cells

Methanol crossover through a polymer electrolyte membrane has numerous negative effects on direct methanol fuel cells (DMFCs) because it decreases the cell voltage due to a mixed potential (occurrence of both oxygen reduction and methanol oxidation reactions) at the cathode, lowers the overall fuel utilization and contributes to long-term membrane degradation. In this work, an investigation of methanol transport properties of composite membranes based on sulfonated polysulfone (sPSf) and modified silica filler is carried out using the PFG-NMR technique, mainly focusing on high methanol concentration (i.e., 5 M). The influence of methanol crossover on the performance of DMFCs equipped with low-cost sPSf-based membranes operating with 5 M methanol solution at the anode is studied, with particular emphasis on the composite membrane approach. Using a surface-modified-silica filler into composite membranes based on sPSf allows reducing methanol cross-over of 50% compared with the pristine membrane, making it a good candidate to be used as polymer electrolyte for high energy DMFCs.

Effect of Catalyst (de)activation on Reagent Diffusion in ZSM-5/alumina Extruded Pellet for the Methanol-to-hydrocarbons Conversion

A pelletized ZSM-5/alumina catalyst was prepared by the extrusion technique. The catalyst was activated by ion-exchange with NH4NO3 aqueous solution. The activated catalyst was trained in the methanol-to-hydrocarbons reaction which caused the catalyst deactivation due to coke deposition (6.5 % wt.). Coke deposition resulted in a two-time decrease in the micropore volume. The methane, benzene, and methanol transport through ZSM-5/alumina pellet were consequently studied prior to activation, after activation, and after catalyst deactivation. A slight decrease in the diffusion rate after catalyst activation is observed. After deactivation, the diffusion rate increases insignificantly. The diffusion regime remains unchanged with respect to either activation or deactivation procedure. Contrary, for the methanol, the diffusion rate through a deactivated catalyst pellet remarkably increases due to micropore blockage by coke deposition. The obtained results reveal that the micropores blockage during the catalyst deactivation enhances the methanol mass transfer.

An Investigation of Methanol Anomalous Diffusion in Mesoporous Silica

Methanol transport in mesoporous silica is investigated. It is demonstrated that usual approach based on the second Fick’s law fails describing the experimental kinetic data. Contrary, the solution of the time-fractional diffusion equation fits the experimental data in a fairly good manner. Obtained value of the fractional order reveals the presence of fast super-diffusive regime of transport.