Experimental study of contact pressure distribution for PEM fuel cell with metallic bipolar plates

One of the parameters that play an important role in the efficiency of fuel cells is the contact resistance between the fuel cell plates, which causes ohmic losses in the fuel cells. The ohmic resistance decreases with increasing compressive stress between the two plates and make full contact between them. On the other hand, with increasing pressure, the amount of porosity in the gas diffusion layer is reduced and the active area is reduced, thus reducing the efficiency of the fuel cell. In this research, contact pressure distribution on the Membrane Electrode Assembly in a three-cell fuel cell stack with metallic bipolar plates with an active area of ۱۰۰ cm۲ has been studied experimentally. To experimentally investigate the distribution of contact pressure on the Membrane Electrode Assembly, a pressure sensitive film of Fujifilm Company has been used. Due to the fact that the stack consists of three cells, Pressure film is used in the middle cell.Price and efficiency are two important factors that have a great impact on the use of fuel cell technology. Various parameters have been effective in the efficiency of PEM fuel cells that extensive research has been done in this field so far. One of the parameters that play an important role in efficiency is the contact resistance between fuel cell components. The contact resistance between the bipolar plates and the gas diffusion layer is the most important part of the ohmic losses in PEM fuel cells. Much research has been done on fuel efficiency as well as the effect of design and assembly parameters on the performance of PEMFC. In ۲۰۰۷, Chang examined the effect of clamping force on fuel efficiency [۱]. Their results showed that excessive increase in compressive force retains moisture and prevents its repulsion. Also, the amount of porosity and contact resistance decreased with increasing pressure. In ۲۰۰۹, Xie optimized the containment force [۲]. In this study, two objectives were studied, the first objective was to create a three-dimensional model and the second objective was to investigate the effect of the restraining force on the gas penetration layer and its properties and fuel cell performance. Ghadimi et al. investigated the effect of end plate thickness and material, washer stiffness and number of fuel cells on the distribution of contact stress applies to the membrane and electrode assembly [۳]. In ۲۰۲۰, Peng et al. proposed an efficient approach to improve the contact pressure on the GDL by optimizing the amount of restraint force as well as the position of the force applied to the end plates [۴].Manufacturing a complete sample of a metallic bipolar plate involves a variety of processes such as molding, welding and coating. The process of forming metal bipolar plates is done by stamping method. Prior to the forming process, the sheets are subjected to a cutting process to create holes required for the entry and exit of reactive gases and water. After forming, the metal bipolar plates are subjected to a welding process. Metallic bipolar plates are coated by physical vapor deposition to reduce contact resistance and increase corrosion resistance. To investigate the distribution of contact pressure on the GDL of fuel cell with metallic bipolar plates, pressure film of Fujifilm company has been used. The desired pressure film contains microcapsules that burst when pressed and turn red. The color density produced is directly related to the amount of pressure applied to the plates. The assembly model of the fuel cell stack with metallic bipolar plates as well as how to assemble the pressure film in the series is shown in Figure ۱. Figure ۱: (a) The assembly model of the fuel cell stack, (b) How to assemble pressure film in stack.Three cell fuel cell was initially assembled using a torque of each bolt at ۷ and ۱۰ N.m, which did not produce the desired result in terms of pressure distribution. By increasing the bolt torque of the set to ۱۳ Nm, the pressure distribution on the membrane and electrode set became uniform, which the result is shown in Figure ۲ (a). It should be noted that the temperature of the test site was measured at ۲۵ °C and the humidity of the site was measured at ۵۰%. In the continuation of the tests, in order to investigate the distribution of contact pressure on the membrane and electrode of the fuel cell, a control press was used for clamping the fuel cell instead of the bolts. In this way, the set is assembled on top of each other similar to the previous cases, but with the difference that a control hydraulic press machine has been used to apply pressure to the set. An example of a pressure film obtained by applying pressure to a press (۳.۷ Ton) and showing a uniform distribution of contact pressure over a membrane and electrode assembly is shown in Figure ۲(b).Figure ۲: (a) Pressure distribution under torque ۱۳ Nm, (b) Pressure distribution with the help of a press machine.In this study, the distribution of contact pressure on the membrane and electrode set in a fuel cell with metallic bipolar plates with an active area of ۱۰۰ square centimeters was investigated. The assembly was assembled in two modes of using a bolts and nuts mechanism and using a press machine, and the distribution of contact pressure on the membrane electrode assembly was investigated experimentally. The results reveal that the pressure distribution on the membrane electrode assembly is uniform in both cases

کلیدواژه ها:

Pressure distribution ، GDL ، Metallic bipolar