## 3 Results and Discussion
### Effect of Rib Groove Designs  
Figure 5 illustrates the polarization and power density curves of the conventional design and the different rib groove designs. Figure 5 shows that, when the operating voltage of the fuel cell was less than 0.8 V, as the voltage decreased, the current density and power density under the rib grooving (1/3 of the rib groove, 2/3 of the rib groove, and full rib groove) were greater than the same values under the conventional design. Furthermore, we also found that when the rib groove rate increased from 0 to 1, the performance of the fuel cells continued to improve. However, when the rib groove rate was greater than 2/3, there was less improvement of the fuel cell performance. When the operating voltage was lower than 0.6 V, the performance of the 2/3 rib groove was almost the same as that of the full rib groove. This was because as the operating voltage decreased and the current density increased, more oxygen on the cathode side was consumed, so the diffusion of oxygen in the cathode gas diffusion layer and catalyst layer became a key factor affecting the output performance of the fuel cell. The grooving  
Figure 4: Polarization and power density curves at different temperatures.  
Figure 3: Comparison between the simulation data and the experimental data.  
ribs improved the flow consistency of the reactant and product behavior in the flow fields, and then enhanced the current density in the ohmic resistance loss and mass transport loss regions [25]. Figure 6 shows the oxygen concentration at the interface of the cathode GDL and catalyst layer (CL) when the voltage was 0.6 V. Figure 6 shows that, in the case of rib grooving designs, the concentrations of oxygen in the GDL and CL on the cathode side were significantly greater than in the conventional design, thereby showing an improvement in both the utilization rate of catalyst and the output performance of the fuel cell. While the oxygen concentration was almost the same when the rib groove rate was 2/3 and 1, the phenomenon of the similar output performance between the two cases was further explained.  
Figure 7 shows the membrane current density of the middle surface of the proton exchange membrane under the conventional design and different rib groove designs when the cell voltage was 0.6 V. As can be seen in Figure 7, in all four cases, the current density decreased gradually along the gas flow direction, because the reactants were consumed gradually. However, in general, the membrane current density of the rib grooving flow fields of the PEM fuel cells was more uniform than in the conventional design. With the increase of the rib groove rate from 0 to 1, the minimum membrane current densities were 20, 30, \(1.72\times 10^{3}\), and \(3.66\times 10^{4}\) A/m\({}^{2}\) for the conventional design, 1/3 of the rib groove, 2/3 of the rib groove, and the full rib groove, respectively. As a result, the overall performance of the PEM fuel cell was improved when the rib grooving designs were applied.  
Figure 5: Polarization and power density curves of conventional and different rib groove designs.  
Figure 6: Oxygen concentration at the interface of the cathode gas diffusion layer (GDL) and catalyst layer (CL).