Durability test with fuel starvation using a Pt/CNF catalyst in PEMFC

In this study, a catalyst was synthesized on carbon nanofibers [CNFs] with a herringbone-type morphology. The Pt/CNF catalyst exhibited low hydrophilicity, low surface area, high dispersion, and high graphitic behavior on physical analysis. Electrodes (5 cm2) were prepared by a spray method, and the durability of the Pt/CNF was evaluated by fuel starvation. The performance was compared with a commercial catalyst before and after accelerated tests. The fuel starvation caused carbon corrosion with a reverse voltage drop. The polarization curve, EIS, and cyclic voltammetry were analyzed in order to characterize the electrochemical properties of the Pt/CNF. The performance of a membrane electrode assembly fabricated from the Pt/CNF was maintained, and the electrochemical surface area and cell resistance showed the same trend. Therefore, CNFs are expected to be a good support in polymer electrolyte membrane fuel cells

Thermal Mathematical Modeling of a Multicell Common Pressure Vessel Nickel-Hydrogen Battery

A two-dimensional and time-dependent thermal model of a multicell common pressure vessel (CPV) nickel-hydrogen battery was developed. A finite element solver called PDE/Protran was used to solve this model. The model was used to investigate the effects of various design parameters on the temperature profile within the cell. The results were used to help find a design that will yield an acceptable temperature gradient inside a multicell CPV nickel-hydrogen battery. Steady-state and unsteady-state cases with a constant heat generation rate and a time-dependent heat generation rate were solved

Comparison of Heat-Fin Materials and Design of a Common-Pressure-Vessel Nickel-Hydrogen Battery

A two-dimensional, axisymmetric, and time-dependent thermal model was developed to study the temperature behavior of the cylindrically shaped common-pressure-vessel nickel-hydrogen cell. A differential-energy-balance equation was used as the governing equation. A finite-element software package called PDE/Protran was used to solve this model. Different materials such as copper, copper beryllium, silver, and sterling silver were compared as heat-fin materials. The heat-fin geometry (thickness and height) and spacing were tested to find a design that yielded an acceptable temperature gradient inside a nickel-hydrogen cell. Pulse heat-generation rates were tested and correlated with the time-dependent heat-generation cases

Thermal Characteristics of a Nickel-Hydrogen Battery

The maximum allowable temperature difference inside a nickel-hydrogen battery to avoid water relocation was calculated by using a graphical method together with a vapor pressure vs. temperature correlation equation for water vapor over potassium hydroxide solution. An equation was developed for this maximum allowable temperature difference for vessel-wall temperatures from 0 to 30°C and potassium hydroxide concentrations from 20 to 32%. A heat-generation equation for the nickel-hydrogen battery was used to investigate the effect of the location of heat generation on the maximum temperature in the cell and the temperature distribution in the cell

Ordered mesoporous carbon-carbon nanotube nanocomposites as highly conductive and durable cathode catalyst supports for polymer electrolyte fuel cells

Ordered mesoporous carbon-carbon nanotube (OMC-CNT) nanocomposites were prepared and used as catalyst supports for polymer electrolyte fuel cells. The OMC-CNT composites were synthesized via a nanocasting method that used ordered mesoporous silica as a template and Ni-phthalocyanine as a carbon source. For comparison, sucrose and phthalocyanine were used to generate two other OMCs, OMC(Suc) and OMC(Pc), respectively. All three carbons exhibited hexagonally ordered mesostructures and uniform mesopores. Among the three carbons the OMC-CNT nanocomposites showed the highest electrical conductivity, which was due to the nature of their graphitic framework as well as their lower interfacial resistance. The three carbons were then used as fuel cell catalyst supports. It was found that highly dispersed Pt nanoparticles (ca. similar to 1.5 nm in size) could be dispersed on the OMCs via a simple impregnation-reduction method. The activity and kinetics of the oxygen reduction reaction (ORR), measured by the rotating ring-disk electrode technique revealed that the ORR over the Pt/OMC catalysts followed a four-electron pathway. Among the three Pt/OMC catalysts, the Pt/OMC-CNT catalyst resulted in the highest ORR activity, and after an accelerated durability test the differences in the ORR activities of the three catalysts became more pronounced. In single cell tests, the Pt/OMC-CNTbased cathode showed a current density markedly greater than those of the other two cathodes after a high-voltage degradation test. These results were supported by the fact that the Pt/OMC-CNT-based cathode had the lowest resistance, which was probed by electrochemical impedance spectroscopy (EIS). The results of the single cell tests as well as those of the EIS-based measurements indicate that the rigidly interconnected structure of the OMC-CNT as well as their highly conductive frameworks are concomitantly responsible for the OMC-CNT nanocomposites exhibiting higher current density and durability than the other two carbons.close17

Thermal modeling of a nickel-hydrogen battery

Typescript (photocopy).The maximum temperature difference allowed inside a nickel-hydrogen battery to avoid water relocation was calculated by a graphical method using the vapor pressure versus temperature correlation equation for water and potassium hydroxide solution. The equation for the maximum temperature difference allowed was developed for vessel wall temperatures between 0°C and 30° C and potassium hydroxide concentrations between 20% and 32%. The heat generation equation for the nickel-hydrogen battery was used to investigate the effect of the heat generation location on the maximum temperature and temperature distribution. A thermal model of a multicell common pressure vessel nickel-hydrogen battery was developed. A finite element software package called PDE/Protran was used to solve this model. A differential energy balance equation was used as the governing equation. The physical and thermal properties of each cell region were averaged using the porosity. Conduction is assumed to be the only heat transfer mechanism in calculating the temperature behavior inside the cell. The model was used to investigate the effects of various design parameters on the temperature profile within the cell. These parameters include the number of modules between heat fins, heat generation rate, heat fin geometry (thickness and height), and the heat fin material. The results were used to help find a design that will yield an acceptable temperature gradient inside a multicell common pressure vessel nickel-hydrogen battery. Steady state with constant heat generation rate, unsteady state with constant and pulse heat generation rate, and unsteady state with time dependent heat generation rate were also studied

Thermal modeling of a nickel-hydrogen battery

Typescript (photocopy).The maximum temperature difference allowed inside a nickel-hydrogen battery to avoid water relocation was calculated by a graphical method using the vapor pressure versus temperature correlation equation for water and potassium hydroxide solution. The equation for the maximum temperature difference allowed was developed for vessel wall temperatures between 0°C and 30° C and potassium hydroxide concentrations between 20% and 32%. The heat generation equation for the nickel-hydrogen battery was used to investigate the effect of the heat generation location on the maximum temperature and temperature distribution. A thermal model of a multicell common pressure vessel nickel-hydrogen battery was developed. A finite element software package called PDE/Protran was used to solve this model. A differential energy balance equation was used as the governing equation. The physical and thermal properties of each cell region were averaged using the porosity. Conduction is assumed to be the only heat transfer mechanism in calculating the temperature behavior inside the cell. The model was used to investigate the effects of various design parameters on the temperature profile within the cell. These parameters include the number of modules between heat fins, heat generation rate, heat fin geometry (thickness and height), and the heat fin material. The results were used to help find a design that will yield an acceptable temperature gradient inside a multicell common pressure vessel nickel-hydrogen battery. Steady state with constant heat generation rate, unsteady state with constant and pulse heat generation rate, and unsteady state with time dependent heat generation rate were also studied