A one-dimensional, dynamic proton exchange membrane fuel cells stack model is developed in this paper, where the transports of reactant and water (in both liquid and vapor phase) are described by partial differential equations (PDEs) in gas diffusion layers (GDLs) of both anode and cathode, and the lumped model is applied to channels and MEA. The boundary conditions needed for PDEs in GDLs are provided by the lumped model. In addition, the convection term is considered in PDEs for GDLs to describe the convection effect on hydrogen gas purge process on the anode side. As a result, the purge effect under medium current density (corresponding to ohmic polarization dominated region) can be simulated in an efficient manner by improving the mass transfer and reducing the effect of water back diffusion from cathode to anode. The presented gas purge model is validated by the experimental data obtained from our laboratory as well as other research group. The influence factors to the gas purge schedule on the anode side, such as the purge interval and purge time, are investigated as well.

The performance of a fuel cell stack is affected by the operating temperature of the stack. The thermal management subsystem of a multi-stack fuel cell system (MFCS) is particularly significant for the operating temperature control of each stack in the MFCS. To study the influence of different topologies of a MFCS thermal management subsystem, this paper proposes and establishes two different topologies. Firstly, the integrated topology is proposed. Secondly, seven component models, namely the mixer, thermostat, radiator, tank, pump, bypass value, and proton exchange membrane fuel cell stack temperature models, are described in detail. Finally, the performance of the two topologies of the MFCS thermal management subsystem under two working conditions, steady (200 A) and variable (China heavy-duty commercial test cycle, C-WTVC), is compared. Furthermore, there are two evaluating indicators, including the stability duration and deviation of the operating temperatures of the single stack in the MFCS. Results show that when the MFCS operates under steady working conditions, the integrated topology is superior in operating temperature control accuracy ($\Delta T<0.5 \mathrm{K}$), while the distributed topology is superior in the adjustment process ($\mathrm{t} \le 100 \mathrm{s}$). Moreover, when the MFCS operates under variable working conditions, the distributed topology is superior in operating temperature control accuracy.

In this paper, a fully coupled non-isothermal, electrochemical, and transport 3D model for a 10-cell PEMFC stack with coolant channels is constructed and implemented to examine and compare the influence factors to the stack performance. The first case to be considered is under different thermal operation conditions, including thermostatic, adiabatic, and heat exchange operation. The corresponding results show that a better uniformity and the largest stack output power density can be obtained under heat exchange operation. The other case is to compare the effects of heat transfer coefficients for different materials (ranging from 5 W/(m2 $·K$) to 50 W/(m2 $·K$)) on the spatial non-homogeneity of stack voltage and output power density. Numerical results indicate that the degree of the non-uniformity of individual cell voltage can be minimized, and the output power density can be elevated to a certain degree when the heat transfer coefficient is set as 25 W/(m2 $·K$). In addition, an attempt is carried out to investigate the changes of some important variables due to the tolerance stacking or performance degradation, where we assume some cells’ contact resistance increases. We observe that a large jump of cell voltage and temperature occurs, which can be used as a detection signal for stack safety operation.

To describe the degradation of proton exchange membrane fuel cells (PEMFCs), empirical degradation models of different indexes of PEMFCs are established. Firstly, the simulation process and assumptions of PEMFC degradation are proposed. Secondly, the degradation simulation results including the performance and distribution indexes under the different degradation levels are conducted by AVL FIRE M. Finally, the empirical degradation models of performance and distribution indexes are established based on the above simulation results and experimental data. The results show that the relationship between the experimental and simulation results is established by the index of current density. The empirical degradation models of current density, average equilibrium potential on the cathode catalyst layer (CL), average membrane water content, average oxygen molar concentration on the cathode CL, and average hydrogen crossover flux are the linear function. The empirical degradation models of average exchange current density on the anode CL, average hydrogen molar concentration on the anode CL, and average oxygen crossover flux are the quadratic function. The empirical degradation model of average activation overpotential on the cathode CL is the quintic function.