Investigation On Catalyst Ink Evaporation And Dispersion Characteristics And Performance Of Fuel Cells

Proton exchange membrane fuel cells(PEMFCs)have very broad application prospects.The high cost and durability of catalyst layers(CLs)are still important factors restricting their commercialization.The heterogeneous microstructure of the CL is closely related to the catalyst utilization and durability of fuel cells.In this study,the evaporation process and deposition mode of catalyst ink droplets and their effects on the microstructure of CL and fuel cell performance are investigated experimentally.The relationship among the ink droplet dispersion characteristics,the microstructure of the CL and fuel cell performance is constructed.It is found that when commercial Pt/C used as catalyst and isopropanol/water used as solvents,the solvent with higher isopropanol content can make the ink droplets spread more on the substrate,and the internal flow of droplets is mainly radial outward;with the decrease of isopropanol content,the surface tension of the droplet gradually increases,creating a circulating flow inside the droplet,bringing particles at the edge back to the center of the droplet.The deposition patterns are divided into uniform disk mode,annular disk mode,"coffee ring" mode and point deposition mode.The more uniform the droplet deposition distribution and the smaller the surface roughness,the better the performance.The CL sprayed with the corresponding catalyst ink also has a denser structure and better performance.If bubbles remain in the evaporation process,the deposition pattern will be unevenly distributed,which will affect the uniformity of the CL spraying process,resulting in larger surface roughness of the CL and poorer performance of the fuel cell.Second,the effects of different evaporation conditions(temperature,relative humidity,and ambient atmosphere)and different substrates are investigated.As the substrate temperature increases,the deposition diameter of the droplets decreases slightly,but the deposition patterns are similar at different temperatures,and the microstructure of the CL and the fuel cell performance are also similar.Relative humidity significantly affects the transport of particles in droplets.Under high relative humidity,the catalyst particles are concentrated at the edge of the droplet,and under the condition of low relative humidity,the catalyst particles are more uniformly distributed and almost cover the deposition surface.The saturated ethanol atmosphere induces the generation of Marangoni flow,which is beneficial to the more uniform droplet deposition in the "coffee ring" mode.The catalyst ink droplets exhibit similar deposition patterns under different substrates.