چكيده به لاتين
Nowadays fuel cell is known as a clean source of energy. In order to reduce costs and increase the operational life of the fuel cell, many experimental types of research have been conducted in the last decade. However, not all the details of the processes performed in the fuel cell can be well observed and measured in the laboratory. This problem justifies the necessity for a model to express fuel cell process in detail and accurately. In this study a membrane-electrode assembly(MEA) is modeled that is working with a sulfonated Poly-ether-ether-ketone(SPEEK) as proton exchange membrane. Poly-ether-ether-ketone shows the lack of mechanical and chemical stability despite the relative merits in comparison to the more expensive commercial membrane like Nafion regarding mechanical and chemical stability Nafion. For this reason, many empirical studies performed to enhance the mechanical and chemical stability of this membrane. But no model has not been reported in this area. In this study, a membrane electrode assembly of a fuel cell is modeled in which the sulfonated Poly-ether-ether-ketone is used. The model is one-dimensional and taking into account the presence and interaction of charge, mass, heat, and momentum transfer phenomena. The fact that the electrochemical reactions occurred once the chemical substances dissolved in the electrolyte phase is included in this model. Since not all of the properties is available for the sulfonated Poly-ether-ether-ketone membrane, two equations were obtained to use in the model which includes the equation between the humidity and the water content of the membrane, and also the equation between water uptake and proton conductivity of the membrane. Estimated average absolute related errors of these equations from experimental values are respectively 13 and 15% at 100 °C. The model was also compared with experimental values. Polarization graph that is taken from a model and is known as the main feature of the fuel cell performance showed 11% error comparing with Nafion experimental data and 19% error with SPEEK experimental data. Due to structural differences of SPEEK membrane with Nafion membrane and the importance of the presence or absence of water in the system, model results are computed using three operational conditions dry gas input, wet gas input and in the presence of liquid water. Due to the absence of water channels in the SPEEK membrane with dry feed gas, the least relative humidity of the feed gas which is needed for proper function of this MEA was 50%. To show the degradation of the membrane, the reduction of the average molecular weight and consequent increase in the free volume fraction of the polymer during the decomposition were inserted into the model. Results showed the amplification of the feed-gas crossover in the MEA.
