Neutron radiography analysis of water management in a passive proton-exchange membrane fuel cell with superhydrophobic catalyst layers

Abstract

Water transport in proton-exchange membrane fuel cells (PEMFCs) with superhydrophobic catalyst layers (CLs) has been studied with neutron radiography. Superhydrophobic CLs were deposited by electrospray on the membrane to be tested on the cathode and anode sides of the cells. The cells are operated under passive conditions without applying convective forces for gas inlets. Operando water thickness images show that electrosprayed CLs accelerate water elimination by natural forces. Water management shows three stages characterized by different transport processes: 1) surface diffusion of bound water (associated to the ionomer), followed by 2) free water transport (liquid phase) by capillary diffusion towards the gas diffusion layer pores, and 3) evacuation of free water from the surface of the cathode by natural forces. A vertical cell, with cell plane parallel to gravity field, favors the action of evaporation and the dragging of water drops and slugs over the cathode surface leading to higher passive performance during the second and third stages. In this orientation, a superhydrophobic CL on one electrode and a hydrophilic CL on the other doubles the power generation with respect to a standard cell. In the horizontal position, superhydrophobic CLs can alleviate transport hindrances due to less effective natural forces.