A Numerical Study On The Impacts Of Catalyst Layer Thickness On Proton Exchange Membrane Fuel Cell (PEMFC)

Catalyst layer is the place where electrochemical reactions take place. It is the vital subassembly in Proton exchange membrane fuel cell(PEMFC). Owing to sluggish kinetics of electrochemical reactions, cathode catalyst layer(CCL) makes great contributions to cell polarization. In this study, we calculate the PEMFC power density polarization curve on the whole range of current densities. The oxygen concentration, oxygen reduction reaction(ORR) rate and cathode overpotential distributions in different CCLs are also compared. We investigate the effects of ionomer volume fraction, the phase behavior of water in the pores, ionomer distribution, and the roughness of the interface between CCL and gas diffusion layer(GDL) on the cell performance.The CCL thickness is a parameter which has a close relationship with the cell activation polarization, ohmic polarization and concentration polarization. It not only affects the material and charge transfer process in the CCL, but also affects the catalytic active area in the catalyst layer. Thus, with the intention of keeping the proportions of all constituents in the CCL invariant,we optimize the CCL thickness by two methods. One is to alter the Pt mass loading per unit area of CCL, the other one is to vary the Pt mass fraction on Pt/C catalyst particles.The effects of CCL thickness on cell performance is investigated by changing the Pt mass loading per unit area of CCL. And the different ionomer fractions and water phase behaviors in CCL pores are also considered. The liquid water in the pores makes mass transport, instead of catalytic active area in the CCL, limit the cell performance. The increasing ionomer fraction decreases the ohmic polarization, but increases the concentration polarization.When CCL thickness is varied by changing the Pt mass percentage upon Pt/C catalyst particles, ionomer fraction has no effects on optimal results. The thinnest CCL makes the cell power output highest during the whole range of current densities, because of its smallest mass transport resistance and largest catalytic active area. While if the pores in the CCL has no liquid water, the CCL with medium thickness makes cell performance best, due to its reasonable mass transport resistance and activation polarization.