Sulfonated poly (ether ether ketone) (SPEEK) membranes with various degrees of sulfonation (DS) were prepared. Their proton conductivity and methanol permeability as a function of temperature were investigated. It was found that the proton conductivity of SPEEK membranes exceeded 10-2S/cm above 80℃, which is close to that of Nafion® 115 membrane under the same condition. The methanol permeability of SPEEK membranes was about an order of magnitude lower than that of Nafion® 115 membrane. The direct methanol fuel cell (DMFC) performance of the SPEEK membranes was better than that of Nafion® 115 membrane at 80℃

The effect of hydrostatic pressure on the swelling of temperature-sensitive gels was studied by measuring the volume change of the beads of poly (N-isopropylacrylamide) gel, poly (N-n-propylacrylamide) gel, and poly (N, N-diethylacrylamide) gel under pressure up to 120atm. The excess enthalpy and the excess volume of the gel-water systems during the volume phase-transition of the gels were measured. These measurements are helpful in understanding that the pressure sensitivity of these gels originates from their temperature sensitivity and is the consequence of the increase of their LCST with pressure. An equation relating the LCST of the temperature-sensitive gel to the pressure was obtained through thermodynamical analysis. These efforts contribute to reveal the interdependence between the pressure sensitivity and the temperature sensitivity of hydrogel. Copyright.

The enzymeβ-galactosidase was entrapped in poly (N-isopropylacrylamide) gel. The gel swelled or collapsed sharply upon the rise or fall of environmental pressure. The gel beads, prepared by reverse suspension polymerization, were placed in a stirred batch reactor filled with a solution of the substrate o-nitrophenol β-D-galactopyranoside. Operations under constant or cycling pressure were performed. A considerable increase in conversion rate was observed under pressure cycling operation, compared with isobaric operations at either atmospheric or high pressure. This result could be explained by the enhancement of mass transfer inside the gel beads during the pressure cycling operation.

The membranes in direct methanol fuel cells must both conduct protons and serve as a barrier for methanol. Nafion, the most common fuel cell membrane, is an excellent conductor but a poor barrier. Polyvinyl alcohol pervaporation membranes are good methanol barriers but poor conductors. These and most other pervaporation membranes offer no significant advantages over Nafion in methanol fuel cell applications. However, polybenzimidazole membranes have demonstrated characteristics that suggest up to a 15-fold improvement in direct methanol fuel cells. This improvement may be due to an alternate form of proton conduction in which protons travel via a Grotthus or "hopping" mechanism.

A novel composite membrane based on poly (vinyl alcohol) (PVA) with embedded phosphotungstic acid (PWA) were prepared and their proton conductivity and methanol permeability were studied. Infrared (IR) and UV spectrographic measurement indicates that the Keggin structure characteristic of the PW12O403- anion presents in the PVA membranes. Highest proton conductivity of 6.27

A mathematic model is established to simulate the effects of methanol crossover on the DMPC. The transport and reactions of both oxygen and methanol at the cathode are described and the theory of "parallel electrode reactions" is applied to calculate the cathode over-potential caused by methanol crossover. The influence of methanol conentration, fuel cell temperature, oxygen pressure, and membrane properties on the cathode over-potential is evaluated. Simulation results show that methanol crossover considerably increases the cathode over-potential at low current density, but its effect is significantly reduced when the current density is increased to reasonable values. It also shows that of the two parameters characterizing a polymer electrolytemembrane, proton conductivity and methanol permeability, the former has more impact on the performance of a DMPC.

A highly ionic conductive solid-gel membrane based on polyacrylamide hydrogels with a K2CO3 additive was investigated. The polymer-based gel was prepared by adding ionic species K2CO3 to a monomer solution followed by polymerization. After polymerization, the ionic species was embedded in the polymer-based gel, where it remained. The ionic species behaved like a liquid electrolyte, whereas the polymer-based solid-gel membrane provided a smooth impenetrable surface that allowed for the exchange of ions. The gel membranes were obtained in the form of thin films of reasonable mechanical strength. Their ambient temperature conductivities were in the range 10-2 to 10-1S/cm. The effect of K2CO3 concentration on the conductivity of the gels prepared was examined in the temperature range from 0 to 100℃. The microstructure and chemical composition of the gels studied were characterized by environmental scanning electron microscopy and FTIR, respectively.

A successful membrane for direct methanol fuel cell (DMFC) must not only conduct proton, but also prevent methanol crossover. With such an aim, membranes of polyvinyl alcohol (PVA)-blend-polystyrene sulfonic acid (PSSA) were prepared. The effects of curing temperature, methanol concentration and membrane composition on the ionic conductivity and the methanol permeability of the membranes were investigated. A membrane with 17% PSSA showed ionic conductivity σof 3x10−3S/cm and methanol permeability P of 2x10-8cm2/sec. The membrane would perform about 40 times better than NafionTMmembrane, if the ratio (σ/P) is adopted to characterize the performance of a membrane for DMFC.

Proton conducting membranes composed of phosphotungstic acid (PWA) and poly (vinyl alcohol) (PVA) were prepared. Conductivity and Fourier transform infrared spectrometer (FTIR) measurements show that most of the acid embedded are stable in the PVA matrix when the membrane is immerged in water or methanol solution at room temperature. Conductivity of the composite membranes scatters around 10-3 S-crn-1 at room temperature. The methanol crossover through the membranes is about an order of magnitude lower than that through Nafion 117 membrane.