Morphology and overpotential analysis of cathode catalyst layer with different ink compositions in low Pt-loaded membrane electrode assembly

Abstract

The effects of solvent composition and catalyst concentration in ink on the structure and properties of the catalyst layer are investigated. Catalyst layers (CLs) are prepared by slurry with different concentrations and compositions. Catalyst layer's morphology and cell performance are measured. The evaporation rate of the catalyst ink affects the pore structure of the catalyst layer (CL). When the volatilization rate is fast, the pore structure of CL is dense, and large cracks appear on the surface, which increases the mass transfer resistance of the CL. When CL is prepared from water-rich solvents (the mass fraction is 70%), the solvent volatilization rate is relatively slow, and the Marangoni flow effect exists in the local area volatilization, which makes the interior of the CL more porous and the surface forms a protruding structure. Finally, the polarization curve is fitted by semi-empirical formula, and three voltage losses (activation overpotential, ohmic overpotential, and concentration overpotential) are distinguished. When the solvent component ratio is 7/3 (water/iPA), the maximum power density is 0.897 W/cm2. The ink composition mainly affects the mass transfer loss of the membrane electrode assembly (MEA).