Improving gas diffusivity with bi-porous flow-field in polymer electrolyte membrane fuel cells

•Porous metal with a novel pore structure for flow-field has been developed.•The porous flow-field exhibited higher current density operation at high humidity.•Smaller gas diffusion resistance was obtained by changing the pore structure.

The performance of polymer electrolyte membrane (PEM) fuel cells highly depends on their mass transport property at high current density operation. To improve the mass transport property, various types of flow-fields have been developed, such as serpentine, straight, grid, and porous flow-fields. Because of the limits of thin land and channel width, the authors have developed a porous type flow-field with unique pore diameter distribution. Unlike general types of porous flow-fields, it has a double peak in the pore diameter distribution; in this paper, it is called a “bi-porous flow-field”. The structure was intended to have organized flow paths for liquid water and gas. The paper investigates its performance and impedance characteristics compared with those of the conventional flow fields. The results of the analysis on the polarization and electrochemical impedance spectrometry revealed that the bi-porous flow-field exhibits the smallest gas diffusion resistance at a high current density operation regardless of humidity conditions. These results indicate that the bi-porous flow-field conducts water management well at high current density. In low humidity conditions, however, dry-out tends to occur and must be prevented.