The average particle of metal dM, 4. It can be seen from the synthesized in this study. Part a in the upper-left corner shows polarization curves between 0. Figure 4. Catalyst loading was controlled at 0. No backpressure was applied during fuel cell operation. The observed in a decrease of the fuel cell performance. ORR on palladium maximum power density varied with the cathode electro- metal has been studied, and yet, Pd shows rather poor catalytic catalysts and demonstrated the following trend: activity in comparison with Pt metals.
Crooks et al. Pt loading, since TiO2 has a 2-fold higher density than carbon. Furthermore, the fuel cell results suggested that Pt70Pd30 electrocatalyst displayed substantially enhanced performance as compared with that of PtPd0 electrocatalyst. All electrocatalysts exhibited a reduction in the hydrogen under- potential deposition area with repeated potential cycling. The Figure 7. Series of CV plots obtained at room temperature after 0. Cyclic voltammetry was conducted in the potential range peaks.
By polarizing the catalyst in sintering Figure 8a. A variety of mechanisms for Pt dissolution and Periodic measurement of ORR activity was performed redeposition on the catalyst surface and Pt migration through initially and after every cycles during the ADT. Figure 8b the surface have been suggested34 to explain the increase in the compares the ORR activities at 0. The activities were catalyst particle size over exposure time.
One such mechanism calculated from the experimental data using the mass-transport is the Pt dissolution into the electrolyte from the supported Pt correction for rotating disk electrodes using eq 4. Table 2.
This material is E-mail: equation: popov cec. Related Papers Benchmarking Pt-based electrocatalysts for low temperature fuel cell reactions with the rotating disk electrode: oxygen reduction and hydrogen oxidation in the presence of CO review article By Kevin Calle Maldonado. Electrocatalytic activity and stability of niobium-doped titanium oxide supported platinum catalyst for polymer electrolyte membrane fuel cells By Wolfgang Schuhmann.
After ion exchange, the zeolite Y nanocrystals were centrifuged 3 times with relative centrifugal force of 48, g for 2 hours. After the third centrifugation, the zeolite Y nanocrystals were dispersed in ethanol proof. The resulting zeolite Y suspension contained 1. The resulting Nafion in ethanol suspension consisted of 7. The final suspension contained 1. The casting vessel was then covered with a watch glass and then put on a level surface in a vacuum desiccator operating at room temperature.
The casting vessel was removed when the solvent was completely removed from the casting suspension. Solvent removal required days. After ion exchange, the zeolite BEA nanocrystals were centrifuged 3 times with relative centrifugal force of 48, g for 2 hours. After the third centrifugation, the zeolite BEA nanocrystals were dispersed in ethanol proof. The resulting zeolite BEA suspension contained 0. After ion exchange, the acidified zeolite BEA nanocrystals were centrifuged 3 times with relative centrifugal force of 48, g for 2 hours.
After the third centrifugation, the acidified zeolite BEA nanocrystals were dispersed in ethanol proof. The resulting acidified zeolite BEA suspension contained 0. N,N-DMF acts as a high boiling aprotic cosolvent that helps cast homogenous membranes when using raw Nafion solutions. The Liquion solvent composition led to good membrane casting with acidified zeolite BEA nanocrystals.
The final suspension contained 0. After mixing of the Liquion, acidified zeolites, and N,N-DMF, and prior to pouring in the casting vessel, the mixture was titrated to a pH of 7 with ethanol solution saturated with NaOH.
After the membrane formation in the oven, the casting vessel was then removed from the oven and allowed to cool if it was heated to obtain the membrane. Then it was boiled in a 0. Finally, the membrane was boiled for 1 hour in DDI H 2 O, then allowed to cool, after which the membrane was ready for testing.
The proton conductivity of the membrane was determined using 4-electrode AC impedance spectroscopy similar to the technique in Sone, Y. Ekdunge, and D. Simonsson, Proton conductivity of Nafion as measured by a four - electrode AC impedance method. Journal of the Electrochemical Society, , 4 Methanol crossover was determined using a 2-compartment diffusion cell, similar to the technique in Tricoli, V. Journal of the Electrochemical Society, , 11 The anode and cathode were prepared according to the procedures reported by Wilson U.
In-situ methanol crossover, proton conductivity membrane resistance and polarization curve were electrochemically investigated for plain Nafion and zeolite modified membranes. The 2M methanol solution was fed to the anodic side of the MEA with 0 psig back pressure while the cathodic side was kept in an inert humidified N 2.
The true crossover current at open circuit is further obtained after the correction of back electro-osmotic drag. The anode, where hydrogen evolution took place, served as the counter electrode as well as dynamic hydrogen reference electrode DHE.
The experiments were conducted at different temperatures and concentrations to determine their influence on the limiting current density. The tables below summarize the results for the methanol crossover and proton conductivity measurements for DMFCs. Nafion N 0. Both the 2. Resistance Ohm N 0. The 2. Significant cell performance improvement is observed for acid functionalized zeolite modified membrane as shown in FIG.
The enhanced proton conductivity and lowered methanol crossover compared with Nafion are observed for the zeolite-modified membrane. To explain these, a better understanding about the structure of Nafion is required. Nafion membrane consists of hydrophobic PTFE backbone and hydrophilic pendant side chains terminated by sulfonate ionic groups.
The protonated solvent species within the connected clusters or channels serves as the major charge carrier in the membrane via hopping mechanism or vehicle mechanism. Water or methanol transport through the membrane is accomplished by moving through the ion-cluster pores and the connecting ion channels, or in more general way, through the hydrophilic network, while in the hydrophobic PTFE region both methanol and water have negligible solubility.
When zeolite particles are incorporated in the membrane, due to the hydrophilic property, they have a tendency to stay in the hydrophilic region of the membrane, which would affect the structure of the Nafion.
Nafion is a random copolymer of perfluoroethylene units and ionomeric units. One possible reason for the enhanced proton conduction is that the introduction of the acid functionalized zeolite nanocrystals causes an increase in ordering during the casting process or allows more ionic groups located within the vicinity of the hydrophilic particle surface to be exposed, instead of being buried underneath the PTFE backbone, which results in the acid groups of the Nafion polymer being more accessible for proton transport.
The lowered methanol crossover can be explained by the blocking of the hydrophilic channel with the zeolite particles. It should be mentioned that the sulfonic acid functionalized zeolite has a porous structure. Although the pore size is not small enough to physically exclude the transport of methanol or water, it is believed the transport rate of these small molecules through the porous structure is drastically reduced. The reason is that the motion of the water initially existing in the pores is restricted and the water is actually trapped inside the pores which blocks the transport of small molecules.
However, the proton conduction is not impeded by the existence of zeolite particles. Under such circumstance, it is believed that hopping mechanism is the predominant working mechanism, where the proton conduction is realized by the proton jumping from hydronium ion to the proton accepting water molecule adjacent to the sulfonic groups without the bodily drift of the hydronium therefore no net water movement through the pores.
The vehicular mechanism that requires the existence of mobile bulk-like water molecules to travel along with protons is unfavored because of the lack of mobile water molecules. The bounded movement of the methanol with proton due to the electro-osmotic drag is also mitigated with the introduction of zeolite.
The above bases can be used for the explanation of the slight improvement of proton conductivity when the membranes are subject to insufficient hydration at high temperature. At such condition, it is known that the membrane is in lack of mobile bulk-like water molecules. The introduction of sulfonic acid functionalized zeolite may allow the proton transport surrounding the zeolite to proceed more preferentially via the hopping mechanism than the vehicular mechanism as it adsorbs water or place restriction on the motion of water molecules.
The overall effect is the mitigated dragging of the water by the proton and therefore the improved proton conductivity. With a 2. As will be understood by those skilled in the art, the present invention may be embodied in other specific forms without departing from the essential characteristics thereof.
For example, steps may be combined or expanded during the synthesis of the nanocomposite membranes. These other embodiments are intended to be included within the scope of the present invention, which is set forth in the following claims. A proton exchange membrane fuel cell, comprising: an anode;.
The fuel cell of claim 1 wherein said polymer membrane has a methanol permeability of less than between 0. The fuel cell of claim 1 wherein said polymer membrane has a proton conductivity to permeability ratio of more than between 0.
The fuel cell of claim 1 wherein said cell functions in the absence of an external reformer to convert fuels to hydrogen. The fuel cell of claim 1 wherein said membrane is formed by a process, comprising: forming a zeolite nanocrystal suspension;. The fuel cell of claim 6 wherein the size of the zeolite nanocrystal particles match the polymer-network dimensions of the host polymer. The fuel cell of claim 7 , wherein the zeolite nanocrystal particles are between about 32 nm and 45 nm.
The fuel cell of claim 6 wherein the polymer is a film forming fluorinated sulfonic acid containing polymer. The fuel cell of claim 6 wherein the polymer is selected from the group consisting of a TEFLON polytetrafluoroethylene type polymer, perfluorinated polymer, and perfluorinated polymer with sulfonic groups. USP true Polymer-zeolite nanocomposite membranes for proton-exchange-membrane fuel cells.
USB2 en. Self-humidifying proton exchange membrane, membrane-electrode assembly, and fuel cell. WOA2 en. Extended two dimensional metal nanotubes and nanowires useful as fuel cell catalysts and fuel cells containing the same. At the peak point, the internal resistance of the cell is equal to the electrical Activation polarization is present when the rate of an resistance of the external circuit. Designer must be electrochemical reaction at an electrode surface is selected the desire operating range according to whether controlled by sluggish electrode kinetics.
In other words, high efficiency or high power are require for application. There is a close similarity the power curve drops off. The dominant Ohmic losses, through the electrolyte, are reduced by decreasing Fig.
Because both the electrolyte and fuel cell electrodes obey Ohm's law, the 3. That is, a decreases with the pressure of reactant gases.
But higher concentration gradient is formed. But the accumulation of water in oxidant stream limits the Where, iLis the limiting current operating temperature bellow o c i. At the boiling point of water the water boil and resulting steam severely reduce the partial pressure of 3. The optimum temperature is obtaining 80o c where the two affect balance each other. Typically operating temperature is 70 to 90o c with increases the boiling point of water by increasing the pressure.
Higher stochiometry ratio increases the chance that sufficient number of hydrogen and oxygen interact with electrolyte thus polarization curve increase with increase the stochiometry ratio and decrease with decrease in stochiometry ratio.
The optimum value of stochiometry Fig. Humidification is essential for the operation of PEM fuel cell because the water molecule moves with the hydrogen ion during the ion exchange reaction. Insufficient humidification of the membrane leads the cracks and holes in the membrane resulting chemical short circuit, hot spot, local gas mixing and possibility of fire occur. Excessive humidification leads the condensation and flooding within the flow field Fig. By proper humidification of reactant gases can improve the performance of fuel cell.
PEM fuel cell has the spatial dimensions so it is not possible to easily measured internal quantities. In the past starts in Literature Review D. Jeon et al. Researchers have taken two operating temperature, pressure and reactant flow rate evaluated conditions with high relative humidity and low relative researchers found that the performance of the fuel cell was humidity and evaluated over potential, Current density distribution, water content at different cell voltage.
PilHyong Lee et al focused on numerical Earlier Serpentine flow field of channels give better simulation of the effects of operating conditions, performance because it create high pressure drop compare especially cathode humidity, with simple micro parallel to the parallel flow field which help in effective water flow channels.
It evaluated water concentration, Oxygen draining inside the unit cell. Relative humidity of anode concentration was moderately high while maintaining high and cathode side also effect the performance of fuel cell ion conductivity at a membrane for obtain the good performance of the fuel cell the HyeYeon Park et al investigated the three- reactant gases must be humid.
By use of the split dimensional numerical computations have been carried out serpentine flow channel and external humidifier the to investigate the dynamics inside proton exchange performance of the fuel cell improve. It fuel cell also improves by selecting the proper range of evaluates Relative humidity, stoichiometric ratio at anode operating parameter pressure, temperature, relative and cathode channels, and cell configuration.
It find that humidity and stoichiometric ratio. Cell voltage is a little more affected by humidity change at cathode in comparison to results at C.
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