Modeling analysis of polymer electrolyte membrane fuel cell with regard to oxygen and charge transport under operating conditions and hydrophobic porous electrode designs

Abstract

Increasing the power density of polymer electrolyte membrane fuel cells (PEMFCs) is vital for their commercial application but requires detailed knowledge of the charge, oxygen, and water transport mechanisms. In this study, an improved multi-phase non-isothermal PEMFC model coupled with a detailed catalyst-layer (CL) agglomerate model is developed to investigate the performance characteristics under different operating conditions and hydrophobic porous electrode designs. During the parametric analysis, the oxygen and charge transport behaviors on cell performance are analyzed, the contributions of bulk and local oxygen transport to the entire oxygen transport process are revealed, and the corresponding water retention, drainage, and transport are evaluated to clarify the internal mechanisms of oxygen transport and membrane hydration. It is found that an increase in temperature can accelerate the membrane water back diffusion and hence improve the sluggish charge transport. Increasing the relative humidity (RH) enhances the cell performance. The local oxygen and charge transport resistances decrease with an increase in the RH owing to the higher membrane hydration. The presence of microporous layer (MPL) improves the liquid-water retention capacity, deteriorating the bulk oxygen transport due to liquid-water blockage but leading to more rapid local oxygen transport and charge conduction. The optimum performance improvement obtained using an MPL occurs in the moderate cathode humidification scheme (50%). A low-hydrophobicity CL tends to induce a large bulk oxygen transport resistance due to severe water flooding. An optimum hydrophobic electrode design is recommended to realize a tradeoff of oxygen and charge transport, which consist of a super-hydrophobicity gas diffusion layer (contact angle 120°), low-hydrophobicity MPL (contact angle 105°), and middle-hydrophobicity CL (contact angle 95°). • Detailed CL model considering more complex physic and geometry is proposed. • Dominating role of local oxygen, bulk oxygen, and charge transport is revealed. • MPL improves cell performance significantly at middle cathode humidification. • An optimum matching design for hydrophobic porous electrodes is recommended.