The water management in PEFCs is a rather complex issue. On one hand side, some water is needed in order to hydrate a proton conductive membrane and ionomer in the catalyst layers. Therefore, humidified gases are fed into the cell. On the other hand, excessive amounts of water in the porous layers lead to blockage of available pores for gas transport and consequently increased mass transfer limitations, especially at high current densities when large amounts of water are produced. The gas diffusion layers (GDLs) are highly porous carbon fiber materials which are sandwiched between electrodes and flow fields and provide several functionalities: conduction of electricity and heat, mechanical integrity of the membrane, distribution of reactant gases and removal of the liquid water produced. These functions imply a triple set of contradictory requirements: high diffusivity of the gas phase, high permeability of the water phase, and high thermal and electrical conductivity of the solid phase.

The creation of artificial pathways for water removal within the porous material would permit the development of advanced water management strategies; however none of the existing approaches proposed a method to produce such materials in a way compatible with mass productions. To tackle this issue, we invented a method to produce GDLs with patterned wettability based on radiation grafting [1]. The method permits creating hydrophilic patterns throughout the complete material thickness while the remaining areas remain hydrophobic [2]. The first part of the talk will focus on the synthetic method details [3] and particularly on the effect that electron beam energy has on the achievable resolution of the hydrophilic patterns [4].

In the second part, the capillary pressure characteristic of the modified materials will be shown and the influence of various material parameters (substrate type, pattern width, coating load, etc.) will be discussed. The water distribution was imaged at various capillary pressures using neutron radiography (NR) and X-ray tomographic microscopy [5]. Finally, electrochemical characterization of operando cells combined with NR will demonstrate the potential of these materials to improve power density at various conditions [6].

[1] P. Boillat et al., 2014 European Patent 15165515.6.

[2] A. Forner-Cuenca et al., Adv. Mater. 2015, 27, 6317-6322.

[3] A. Forner-Cuenca et al., J. Electrochem. Soc. 2016, 163 (8), F788-F801.

[4] A. Forner-Cuenca et al., Radiat. Phys. Chem., Submitted.

[5] A. Forner-Cuenca et al., J. Electrochem. Soc. 2016, 163(9), F1038-F1048.

[6] A. Forner-Cuenca et al., J. Electrochem. Soc. 2016, 163 (13), F1389-F1398.