Fabrication of Catalyst Layers with Preferred Mass and Charge Transport Properties through Texture Engineering

Electrode structure strongly influences the charge and mass transport of energy conversion devices such as polymer electrolyte membrane fuel cells. Various studies have been carried out to optimize the nanoscale features and porosity of the electrode catalyst layer. The impact of large-scale texture, i.e., from several to tens of microns, was however much less investigated. In the present study, we demonstrated the fabrication of catalyst layers directly on the polymer electrolyte membrane with controlled texture by the ultrasonic spray coating technique. By controlling the droplet size of the catalyst ink as well as its drying behaviors, textured catalyst layers with enhanced mass or charge transport properties can be reproducibly obtained through the manipulation of micron-scale Marangoni flows. When the Marangoni effects are maximized, a heavily textured catalyst layer populated with large and deep pores exhibiting good mass transport properties is formed and shows a maximum current density of 1.75 A/cm2. With a slower drying rate of the catalyst ink, a much less textured but more loosely packed catalyst layer is obtained, which shows impressive charge transport properties even under low humidified conditions. With the mass transport resistance greatly alleviated, a maximum power density of 0.8 W/cm2 can be reached at a cathode humidity of 43% at 80 °C using a very low cathode Pt loading of 0.079 mgPt/cm2. Such high performance under low-humidity conditions can lead to significant cost reduction in fuel cell system and its operation.