## 4 Results and Discussion  
In Figure 4, the pressure variation in the anode and cathode sides of the fuel cell is displayed. The pressure drop across the anode channel is 2 bars, and throughout the cathode channel is higher than 9 bars. Although the pressure has decreased both in the cathode and anode, the pressure drop in the cathode is larger than the anode. Since the oxygen velocity in the inlet of the cathode channel is 2.5 times the speed of the hydrogen velocity in the input of the anode channel, a higher pressure drop in the cathode is obtained. Figure 5 shows the effect of pressure changes on the performance of the fuel cell. In this graph, 5 different operating pressures were investigated. According to the figure, with increasing pressure, the performance of the fuel cell is improved and the fuel cell generated power is increased; at different pressures and at a constant voltage, an increase in the fuel cell generated current can be detected, as the pressure increases, penetration of the reactive gases in the catalyst layer is augmented, which leads to an increment in the flow density. Figure 4: Pressure distribution at the cathode and anode channels at T = 180 \({}^{\circ}\)C, P = 1 atm, \(\mathrm{st_{a}}=1.2\), \(\mathrm{st_{c}}=2\) and V = 0.4 V.  
The concentration of reactive species, namely, hydrogen (Figure 6a) and oxygen (Figure 6b), are shown in Figure 6 at 180 \({}^{\circ}\)C and at a voltage of 0.4 V. As can be seen, the highest concentration is at the channel entrance, and the concentration of species decreases towards the channel outlet, as the species entering the anode and cathode channel, the reaction is started and species are consumed to generate current density According to figure, the oxygen concentration along the cathode channel reached from 1.26 to 5.43 mol/m\({}^{3}\) and the hydrogen concentration along the anode channel reached from 25.8 to 25.2 mol/m\({}^{3}\) that indicating a higher concentration of oxygen comparing to hydrogen. In Figure 7, the distribution of water concentration in the anode (Figure 7a) and cathode (Figure 7b) is shown at 180 \({}^{\circ}\)C and at a voltage of 0.4 V. Regarding the figure, it can be seen that the behavior of water dispersion in the cathode and anode channels is different from the dispersion behavior of the species concentration according to Figure 6. In contrast to species concentration, the lowest concentration of water is observed at the entrance of the channels, and the highest concentration of water is observed in the channel outputs. Because with moving of reactants from the entrance to the outlet, the species is consumed and more water will be generated by the reactions. Water management in fuel cell is critical,  
Figure 5: Pressure effect on the current density at T = 180 \({}^{\circ}\)C, \(\text{st}_{\text{a}}=1.2\), \(\text{st}_{\text{c}}=2\). Figure 6: Concentration of (**a**) the hydrogen along the anode flow channel and (**b**) the oxygen along the cathode flow channel operating at 180 \({}^{\circ}\)C and 0.4 V (mol/m\({}^{3}\)). so that a substantial decrease in humidity content of the inlet gas causes the membrane to dry and its ionic conduction decreases and, as a result, decreases its performance; in contrast with an excessive increase of the water level in the fuel cell, water droplets create a critical condition that blocks the pores of the porous layers and subsequently prevents the transfer of reactive gases. The effect of porosity coefficient of the GDL at 180 \({}^{\circ}\)C is shown in Figure 8. This graph is depicted for three porosity coefficients of 0.3, 0.4, and 0.5. According to this figure, the porosity coefficient has its most impact on the performance of the fuel cell at low voltages, which, with its increase, the fuel cell generated power will be enhanced. But at high voltages, there is no noticeable change, as the species consumption rate is lower at high voltages.