Numerical Investigation of Membrane Dehydration Based on PEM Stack Transient Simulation

In this work, a three-dimensional, serpentine channel, four-cell PEM Stack model including current collector, gas diffusion layer, catalyst layer and membrane has been developed and is used to investigate the effects of membrane dehydration on PEM Stack performance. This numerical study is conducted using finite element method and computational fluid dynamics (CFD) code. To characterize the effects of membrane dehydration, the settings of operating and boundary conditions are not uniform throughout the whole period of simulation. The simulation condition is originally preferable, indicating a normally running stack in healthy status. Further transient simulation has been conducted under four failure conditions with different reactant humidity to monitor the variation of membrane water content and PEM Stack output voltage. The relatively drier reactants carry away more production water, causing the dehydration of membrane and reducing the protonic conductivity. Under a specific demand current, the output voltage of the stack decreases with the process of membrane dehydration, curtailing the maximum power that can be derived from the stack. Based on the simulation results, it is noticed that inlet reactants humidity has a great impact on the water management of stack. An improper operation on reactants supply can cause failures in PEM Stack, even components material degradation. Meanwhile, the simulation of stack output voltage and interior characteristics, as well as comparison of different levels of drying are prepared for further model-based study of identification and diagnosis of failures caused by improper water management and reactants starvation.