Graded Structure Design of the Microporous Layer for Improving the Mass Transfer Performance of Proton-Exchange Membrane Fuel Cells

The microporous layer (MPL) in membrane electrodes is critical for mass transfer in proton-exchange membrane fuel cells (PEMFCs). The mass transfer loss in electrodes is very serious when operating in high-current-density and high-humidity environments, which greatly reduces the output performance and durability of fuel cells. To address these challenges, we designed an MPL with a graded pore structure. By controlling the content of the pore former in the MPL slurry, conventional MPLs with uniform pores are constructed, and then structural MPL with ordered gradient pore distribution is formed through layered coating and sintering. The capillary driving force provided by such a gradient structure can effectively improve the cathode water management capability. In this study, the MPL with the graded pore structure (G-MPL) shows the highest output performance of 2.28 W cm–2 at a high relative humidity of 100%. This is mainly due to its gradient pore structure, which significantly facilitates water discharge and gas diffusion, thereby upgrading the mass transfer capacity of fuel cells. In addition to its outstanding electrochemical performance, G-MPL also has the advantages of low production cost and a simplified preparation process, making it an exceptional candidate to promote the practical application of PEMFCs.