Multi‐objective optimization of temperature uniformity in cathode catalyst layer and performance of PEMFC with an ionomer‐gradient design

Temperature uniformity (TU) of the cathode catalyst layer (CCL) and the power density are two key parameters to describe a fuel cell durability and performance. To achieve desired TU and output performance, a one-dimensional, non-isothermal, two-phase model coupled with a CCL agglomerate submodel is developed and validated in terms of the polarization curve, ohmic impedance and total oxygen transport resistance. Then, the ideal ionomer-gradient distribution across the triple-layer CCL is attained by a combination of Non-dominated Sorting Genetic Algorithm II (NSGA II) and TOPSIS. The results present that the gradient-decline distribution of ionomer towards the microporous layer (MPL) contributes to the larger power density and effective utilization of ionomer. The fuel cell can also operate at higher power with a top voltage range (TVR). After optimization, the ideal ionomer-gradient distribution affects the distribution of the total heat source by affecting the local oxygen transport resistance across the ionomer film and the volumetric current density ( J c ). As a result, the maximum temperature point in CCL is more likely to occur near the MPL and the CCL temperature becomes more uniform. Besides, the optimum ionomer-gradient values tend to be different in various operating voltages and RH cases. However, low voltage and high RH conditions are more highly sensitive to the ionomer-gradient design. It is possible to maintain a proper TU and desired output performance by optimizing the CCL gradient structure, especially for the stationary PEMFC that operates with a particular condition for a long time. Research Highlights A 1D, non-isothermal, two-phase model is validated from multiple aspects. Multi-objective optimization is performed by combining the NSGA II and numerical model. More uniform CCL temperature and higher power density are achieved after optimization.