For a PEMFC, other than inherent qu

For a PEMFC, other than inherent qualities depending on materials and manufacture, the operating conditions can also affect its performance to a large extent because they can alter the shape and position of the polarization curve [18]. During the operation,the fuel cell efficiency generally depends on mean cell potential as a function of current density. As current density is changed by load and operation parameters including pressure, relative humidity and stoichiometery, the PEMFC efficiency eventually takes place the corresponding change. Through the analysis of experimental results, a conclusion can be drawn that temperature has a more significant influence in the performance of the PEMFCthan other operation variables [41,42]. Fig. 5b shows that the polarization curves of the PEMFC shift upwards as temperature increases from 20 ◦C to 60 ◦C under control of the cooling water. This phenomenon indicates the improvement of electrical efficiency as temperature increases. It can be explained in that the rise of the temperature increases proton mobility in the membrane and improves catalyst activity and gas diffusion [42]. Amuch higher temperature is beneficial for the PEMFC to reduce inner resistance and improve electrical performance. However, according to the experimental data, it can also be concluded that the influence of temperature is limited, the voltage having only