Metal Mesh Gas Diffusion Layers for PEM Fuel Cells

Abstract

As fuel cells gain increased volumetric power density, there is a need for thinner GDLs that give increased thermal and electrical conductivity, and mechanical stiffness. This has been demonstrated by the introduction of advanced GDL/bipolar plate designs that have been implemented in commercial fuel cells such as that seen in the Toyota Mirai (1). The use of metal GDLs has been previously examined in ethanol and methanol fuel cells (2,3) but have been largely ignored in PEMFCs due to the corrosive conditions present in PEMFCs which considerably reduce the lifetime of cells with non-passive metals present. Spun carbon fibre GDLs, such as Toray and Avcarb, have previously been the main choice for PEMFC GDLs due to the passivity and gas and water transport properties of these materials. With increased power density in fuel cells however these materials can incur losses due to a lack of thermal and electrical conductivity as well as being relatively thick and brittle. In this study we have examined a number of metal meshes used in place of carbon paper GDLs in fuel cells. Meshes with different aperture sizes were examined with regard to fuel cell performance as well as flooding of the electrodes and performance under high mass transport conditions. The aperture sizes of these meshes played a significant role in performance in the cell, both in terms of electrical conductivity and water management. Surface passivation of the meshes by nitriding and using carbon and other passive coatings was also examined in order to increase their durability in the cell. The surface energy properties of these coatings was also examined ex situ via droplet shape analysis in order to achieve the best properties for use in a fuel cell. Adjustment of the hydrophilicity and hydrophobicity of these coatings was also used to improve water management. The performance of some of these meshes and foams was seen to exceed some of the commercially available carbon papers even without significant optimisation. These materials could soon replace carbon fibre GDLs in PEMFCs leading to much higher volumetric power densities and improved performance. References T. Yoshida, K. Kojima, Electrochemical Society Interface, 24 (2015), pp. 45–49.S. Arisetty, A. K. Prasad, S. G. Advani, Journal of Power Sources, 165, 1, (2007).W. Yuan, Y. Tang, X. Yang, Z. Wan, Applied Energy, 94 (2012). Figure 1 (a) Water droplet on metal mesh surface before surface treatment, and (b) after surface treatment. (c) PEM fuel cell performance of a metal mesh GDl compared with two common commercial carbon papers (Toray HGP-H-080 and SGL 24 BC). Figure 1