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Proton exchange membrane fuel cells (PEMFCs) with a dead-ended anode and cathode can reach high hydrogen and oxygen utilization by a relatively simple system. Nevertheless, the accumulation of the water in the anode and cathode channels can lead to a local fuel starvation deteriorating the performance and the durability of PEMFCs. In this study, a novel design for a polymer electrolyte membrane (PEM) fuel-cell stack was presented which could achieve higher fuel utilization without using hydrogen and oxygen recirculation devices such as hydrogen pumps or ejectors that consume parasitic power and require additional control schemes. The basic concept of the innovatively proposed design was to divide the cells of a stack into several stages by conducting the outlet gas of each stage to a separator and reentering it into the next stage; thereby, a multistage anode and cathode system was prepared. In this relatively ingenious design, a higher gaseous flow rate was maintained at the cell outlet, even under dead-end conditions resulted in a reduced purge-gas emission by avoiding the accumulation of liquid water in the cells. The results revealed that proposed design had the same polarization curve as the open-end mode, leading to an enhanced PEMFC performance. [ABSTRACT FROM AUTHOR]

The distribution of reactant gases in polymer electrolyte membrane fuel cells (PEMFCs) plays a pivotal role in current density distribution, temperature distribution, and water concentration. Problems such as flooding or drying of the membrane are caused by the non-uniformity of the above mentioned parameters resulting in a reduced membrane electrode assembly (MEA) life time. In this study, a new cascade type serpentine flow field is introduced and the concept of design is explained. The simulation results are in good agreement with the literature. The optimal channel to rib ratio is obtained using simulation results. The results show that the proposed flow field produces a uniform current density and local stoichiometry as well as an improved water management. It is also determined that the two phase numerical method can estimate experimental results correctly. [ABSTRACT FROM AUTHOR]

Efficient operation of a proton exchange membrane fuel cell (PEMFC) is hugely dependent on an effective cooling system. Non-uniformity of temperature causes a varying rate of electrochemical reaction at different places leading hot spot formation which decrease the lifetime of PEM fuel cell. The most part of heat generated in the PEM fuel cell is removed by cooling fluid (forced convection) while the remainder is dissipated by natural convection, radiation and temperature difference between the inlet and outlet of reaction gases. The reaction rate and current density are related to temperature distribution on flow field, therefore it has to be kept uniform at the surface of active area to achieve a uniform current density. Designing a cooling system requires significant challenges in regard to the narrow range of operating temperatures. In this study, new cooling flow fields are numerically investigated in order to clarify the sufficient design for the heat removal. Numerical simulation is employed to investigate the coolant flow distribution, pressure drop and thermal behavior of different designs. The temperature contours represent the temperature uniformity for the assessed case. [ABSTRACT FROM AUTHOR]

Contact pressure distribution over the active area of proton exchange membrane fuel cell (PEMFC) has significant effects on the performance of PEMFCs. Even clamping pressure over the membrane electrode assembly (MEA) affects contact resistance, characteristics of porous media and sealing task. This paper develops a PEM fuel cell model to study the contact pressure distribution over the membrane electrode assembly using finite element model. At first, the three-dimensional model of a single cell was reduced to a two-dimensional model to decrease the calculation time. After validation of the obtained results via the pressure sensitive films, the effect of some parameters such as thickness and material of the end plates, sealant hardness, number of the stack's cells and position of the cell on the contact pressure distribution over the MEA were investigated. The results reveal that optimizing mentioned parameters leads to design PEM fuel cells with proper contact pressure distribution over the MEA. [ABSTRACT FROM AUTHOR]