Study on the performance of a proton exchange membrane fuel cell related to the structure design of a gas diffusion layer substrate

•The relatively large macro-pores in the substrate act as water removal passages.•The relatively small macro-pores work as water retaining passages.•Size variation in macro-pores must be present to enhance water management.•Capillary pressure gradient through the GDL is a key parameter for water balance.

Although characteristics of the gas diffusion layer (GDL) affect the performance of a proton exchange membrane fuel cell (PEMFC), mass transfer mechanisms inside the GDL and the performance of the PEMFC have not been directly correlated. To determine the design parameters of the GDL, the effects of substrate design of the GDL on performance of a PEMFC are investigated. By adding an active carbon fiber (ACF), which has a high surface area, the substrate is designed to have a different pore size structure. The results show that steady-state and transient responses are determined by capillary pressure gradient characteristics of the GDL made by pore size distribution of the substrate. The small macro-pore functions as water-retaining passage and the large macro-pore functions as water-removal passage. It is concluded that both small and large macro-pore must be present on the substrate to facilitate its function in a wide range of operating conditions.