Study on the thermal transient of cathode catalyst layer in proton exchange membrane fuel cell under dynamic loading with a two-dimensional model

•A two-dimensional, two-phase, PEMFC transient thermal model is established.•Effects of operating&structure parameters on CCL thermal transient are studied.•CCL temperature overshoot and fluctuation are analyzed under dynamic loading.•Both electrochemical and two-phase flow transients cause temperature overshoot.•Optimal loading rate, operating temperature, and width ratio are suggested. The temperature variation of the cathode catalyst layer (CCL) inside the proton exchange membrane fuel cell (PEMFC) caused by dynamic loading will damage the material and consequently shorten cell lifetime. To address this problem, the thermal transient of CCL needs to be clarified first before further action is taken. In this work, the effects of current load, operating temperature, and channel to rib width ratio on the thermal transient of CCL are systemically investigated by a two-dimensional, two-phase transient PEMFC thermal model. At the same time, the action mechanisms of electrochemical and two-phase flow transients on the thermal transient are detailly described. We observe that the overshoot of CCL temperature will happen as the current steps from nearly zero to a certain level. Interestingly, under the action of local water and thermal evolution, the overshoot amplitude first increases and then decreases with the rise of the step current density. Moreover, with the increase in loading time and operating temperature, temperature overshoot significantly decreases. The former is attributed to the quasi-steady state operation of two-phase flow at a long loading time, while the latter is caused by the reduction of membrane water absorption with atmosphere drying. It is also found that the larger channel to rib width ratio will induce more uniform temperature fluctuation in CCL regions under rib and channel due to the more uniform electrochemical reaction caused by shorter O2 transport path length. The above model simulation results can guide cell operation and design for better thermal management under dynamic loading.