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The performance on a polymer electrolyte membrane (PEM) fuel cell is evaluated based on the relationship of thermal and electrical resistances to its electrical and thermal power output. An analytical method by which the electrical resistance is evaluated based on the polarisation curve and the thermal resistance from the mass balance, was applied to a 72-cell PEM fuel cell assembly. In order to evaluate the effect of resistances at elevated stack temperatures, the cooling system was operated at half of its maximum cooling effectiveness. The increase in current and resistance due to a unit change in temperature at a particular density was evaluated and it was found that the stack has a ratio of thermal resistance rise to current rise of 1.7, or equal to 0.00584 A/W of current increase per stack heat increase. These values suggest that the internal resistance of the stack components, most probably the electrode assemblies, are very high, which should be addressed in order to obtain lower resistances to current flow.

A Polymer Electrolyte Membrane (PEM) fuel cell is an electrical power generator utilizing a hydrogen-based fuel reactant and oxygen in a reversed electrolysis reaction, with byproducts of water and heat. The application is sensitive to temperature; more power is generated at elevated operating temperatures, but excessive cell temperature causes dehydration to the membrane electrolyte and subsequent power decline as well as cell deterioration. The power-to-weight ratio and reduced parasitic load, which are the main advantages of an air-cooled system, pushes the research tendency to replace water cooling with air cooling. This work analyzes the heat transfer characteristics, using analytical and Computational Fluid Dynamics (CFD) tools, of a 3 kW PEM fuel cell stack which is equipped with a single cooling channel on each bipolar plate. The base stack design consisting of 73 bipolar plates refers to an industrial water-cooled PEM fuel cell stack available at the Faculty of Mechanical Engineering, University of Technology MARA. From the results of the coolant flow over the base stack design, extended surfaces (fins) was added at an optimized geometry to enhance the heat transfer. Both designs were subjected to a heat flux magnitude of 1.6 times greater than theoretically required, and showed excellent simulated cooling capability of 100% cooling effectiveness when subjected to flows at Reynolds number of 800 and above. Addition of extended cooling surfaces further improves the thermal gradient reduction within the plate by 30%. Though still requires practical evidence, the simulation analysis has provided the groundwork of air cooling applicability in replacing water cooling for a 3 kW PEM fuel cell stack.