Water and Protons in a Pt-Loaded Carbon Mesopore: A Molecular Dynamics Study

Pt-loaded mesoporous carbon (Pt/MPC) is a representative unit of the cathode catalyst layer (CCL) in a proton exchange membrane fuel cell (PEMFC). However, the distribution and transport of water and protons in Pt/MPC, key to the electrochemical properties of the CCL, are largely unknown due to the lack of effective experimental probes at the mesoscale and the inadequacy of the homogeneity assumption within the volume-averaged modeling framework. The penetration of ionomers into mesopores also remains a controversial issue. Herein, molecular dynamics (MD) is employed to unveil the distribution of ionomers, water, and protons as well as the transport properties of water and protons in a Pt-loaded mesopore. The effects of functional groups and platinum oxide (PtO) are examined. The results indicate that ionomers do not penetrate into mesopores with a diameter of 4 nm. Both the quantity and connectivity of water and protons within the pore increase with the introduction of hydrophilic functional groups, as well as the PtO surface charge, which may be conducive to the performance. However, the presence of functional groups also restricts water and proton diffusion, which may be detrimental. These findings provide molecular insights for optimizing catalyst support materials in the PEMFC cathode.