Ultra-low Pt loading cathode catalyst layers with hierarchically mesoporous distribution modulation for high-performance proton exchange membrane fuel cells

Developing cathode catalyst layers (CCL) with efficient mass transport capability is crucial to developing ultra-low Pt loading (< 50 μg·cm⁻²) proton exchange membrane fuel cells (PEMFCs). Herein, CCLs with various pore distributions were constructed by depositing Pt onto the integrated carbonaceous films consisting of carbon nanoparticles (CNs), three-dimensional (3D) graphene nanosheets (GNs), and nanocomposites of CNs and GNs (CNs-GNs), respectively. The hierarchical mesoporous pore distributions of CCLs strongly affect the effective exposure of Pt active sites, proton-transfer resistance, and oxygen mass transport efficiencies related to Knudsen diffusion and local resistance at the Pt/ionomer interface. The CCL with Pt/CNs-GNs (50.0 μg_Pt·cm⁻²) features a unique tri-modal pore distribution concentrated at 10.2, 20.4, and 43.7 nm, providing efficient three-phase boundaries with a significantly higher active surface area of 49.67 m²·g⁻¹, lower oxygen transport resistance and proton resistance of down to 18.68 s·m⁻¹ and 0.0603 Ω·cm², compared with Pt/CNs (31.48 m²·g⁻¹, 41.17 s·m⁻¹, and 0.0702 Ω·cm²) with a single-modal pore distribution at 9.5 nm and Pt/GNs (38.21 m²·g⁻¹, 33.40 s·m⁻¹, and 0.0654 Ω·cm²) with a bi-modal pore distribution at 9.8 and 20.9 nm. Correspondingly, the cell with Pt/CNs-GNs delivers a high power output of up to 1.01 W·cm⁻² and presents a high durability that satisfies the 2025 targets set by the U.S. Department of Energy. This work provides new insights into the critical role of hierarchically mesoporous pore distribution of CCL for constructing high-performance PEMFCs with ultra-low Pt loading < 50 μg·cm⁻².