Pore-Scale Study of the Effect of Through-Plane Carbon Support Gradients on Catalyst Layer Performance in Proton Exchange Membrane Fuel Cells

The cathode catalyst layer (CL) is a key component governing the performance of proton exchange membrane fuel cells (PEMFCs), yet the trade-off between oxygen transport and electrochemical activity in conventional uniform CLs remains a critical limitation. This study presents a pore-scale numerical investigation into the effect of through-plane carbon support volume fraction gradients on oxygen transport and electrochemical performance in PEMFC catalyst layers. A lattice Boltzmann method (LBM) model, coupled with a stochastic reconstruction algorithm, was employed to simulate three gradient configurations, linear (LG), stepwise (SG), and hybrid stepwise (HSG), under varying gradient directions and magnitudes. The results demonstrate that positive gradients, with higher carbon fraction near the membrane, enhance oxygen diffusivity and electrochemical activity compared to negative and uniform configurations. Among all designs, the HSG with a positive large gradient achieves the highest peak current density of 694.11 mA cm−2, representing a 13.4% increase over the uniform structure. This improvement is attributed to the optimized oxygen concentration distribution and electrochemically active surface area, enabled by a broadened pore size distribution that facilitates gas transport while concentrating catalytic activity in the membrane-adjacent region. The findings establish a quantitative link between carbon support gradient design and CL performance, providing a simulation-based framework for the rational engineering of high-performance PEMFC electrodes.