Diffusion Layers with Localized Hydrophilic Domains: Influence of Electron Energy on Spatial Resolution

Abstract

The development of advanced water management strategies for polymer electrolyte fuel cells (PEFCs) could enable further improvements in power density, and therefore decrease the cost. A recently developed approach, consisting on electron radiation grafting using masks, has been utilized to fabricate gas diffusion layers with patterned wettability [1]. These novel materials feature hydrophilic, straightforward pathways for the transport of liquid water; and hydrophobic, low-resistance domains for the transport of reactant gases [2]. It has been recently demonstrated that PEFCs performance can be improved by employing the modified gas diffusion layers on the cathode side, due to the segregated distribution of liquid water that leads to reduced mass transport overpotentials [3]. However, further improvements in resolution are required to fabricate advanced porous materials with localized properties for various applications [4]. Pursuant to this goal, simulations can be used, in tandem with experiments, to elucidate the dominating parameters that influence the resolution (e.g. electron energy, mask-to-sample separation). Moreover, simulations can be utilized in a predictive fashion to calculate the electron beam parameters required to fabricate a given material. In this presentation, we will discuss the influence of electron beam energy on the spatial resolution of porous materials typically used in PEFCs. A combination of experiments and Monte-Carlo simulations was employed to advance the fundamental understanding of mask-assisted through-volume modifications of thick porous substrates. Interestingly, we found that an energy of, at least, 140 keV was required to modify throughout the complete thickness and that the use of energies lower than 300 keV results in a blurring in the adjacent regions. Additionally, we will discuss the influence of housing materials on the back-scattered radiation. Finally, and due to its practical relevance, we will discuss the possibility of selectively modifying one layer out of a bi-layered material (i.e. GDL-MPL arrangement). [1] Forner-Cuenca, A. et al., Adv. Mater. 27, 6317–6322 (2015). [2] Forner-Cuenca, A. et al., J. Electrochem. Soc. 163, F1038–F1048 (2016). [3] Forner-Cuenca, A. et al., J. Electrochem. Soc. 163, F1389–F1398 (2016). [4] Forner Cuenca, A. et al., Radiat. Phys. Chem. 135, 133–141 (2017). Acknowledgments AFC gratefully acknowledges the financial support of the Swiss National Science Foundation (P2EZP2_172183).