Balancing Proton and Mass Transfers in Cathode Catalyst Layer of High-Temperature Proton Exchange Membrane Fuel Cell Via Gradient Porous Structure Design

Abstract

The porous structure within the cathode catalyst layers (CLs) plays a crucial role in facilitating phosphoric acid (PA) invasion and oxygen diffusion, which are essential for establishing the triple-phase boundaries (TPBs) in high-temperature proton exchange membrane fuel cells (HT-PEMFCs). In this work, a gradient porous structure is deliberately constructed within the cathode CL by carefully controlling the microstructures of the double CLs. The effects of pore diameter distribution in the cathode CL and PA content in the membrane electrode assembly (MEA) on the single cell performance of HT-PEMFC are systematically investigated. By incorporating an appropriate amount of PA in the MEA, along with the optimized gradient porous structure, the inner pores effectively store acid and prevent its outward diffusion. Simultaneously, the pores in the outer CL provide additional pathways for oxygen transfer. Consequently, the optimized gradient porous structure enhances the peak power density of H2/Air fuel cells to 0.510 W/cm2 at a Pt loading of 0.5 mgPt/cm2, a notable improvement compared to 0.396 W/cm2 of the traditional single CL. The mechanism analysis further reveals that the cathode CL with gradient porous structure can successfully balance proton transfer and mass transfer, hence reducing the polarizations in fuel cell.

Keywords: high temperature proton exchange membrane fuel cell, cathode catalyst layer, gradient porous structure, phosphoric acid loading, reducing polarization