  High-resolution porous structures of catalyst layer (CL) with multicomponent
in proton exchange membrane fuel cells are reconstructed using a reconstruction
method called quartet structure generation set. Characterization analyses of
nanoscale structures are implemented including pore size distribution, specific
area and phase connectivity. Pore-scale simulation methods based on the lattice
Boltzmann method are developed and used to predict the macroscopic transport
properties including effective diffusivity and proton conductivity. Nonuniform
distributions of ionomer in CL generates more tortuous pathway for reactant
transport and greatly reduces the effective diffusivity. Tortuosity of CL is
much higher than conventional Bruggeman equation adopted. Knudsen diffusion
plays a significant role in oxygen diffusion and significantly reduces the
effective diffusivity. Reactive transport inside the CL is also investigated.
Although the reactive surface area of non-precious metal catalyst (NPMC) CL is
much higher than that of Pt CL, the oxygen reaction rate is quite lower in NPMC
CL compared with that in Pt CL, due to much lower reaction rate. Micropores (a
few nanometers) in NPMC CL although can increase reactive sites, contribute
little to enhance the mass transport. Mesopores (few tens of nanometers) or
macropores are required to increase the mass transport rate.
