No abstract

Hydrophobicity is generally believed to be key to water management in polymer electrolyte fuel cells (PEFCs). However, we reported that the membrane electrode assembly (MEA) using a hydrophilic micro porous layer (MPL) showed much better performance in a wide range of pressure and humidity conditions than that using a hydrophobic MPL. When operating an MEA, it usually needs to be humidified in order to maintain conductivity of the membrane. Operation without humidification is critical to the commercialization of PEFCs for backup power and automotive applications. We, therefore, evaluated MEAs at 60 • C, at the H 2 /air stoichiometric ratio of 1.4/5.0, without humidification, in addition to the normal conditions of 80 • C, 100 & 30%RH. We found that the MEA employing a gas diffusion electrode (GDE) method on the hydrophilic MPL showed the best performance under a very dry condition, suggesting that the firm interface between the catalyst layer and the MPL plays a crucial role in determining MEA performance, particularly under dry conditions

For better water management in polymer electrolyte fuel cells (PEFCs), microporous layers (MPLs) are generally used. In this paper, hydrophilic MPLs having various pore volumes and diameters were prepared using a range of carbon materials, and the effect of the MPL on the membrane electrode assembly (MEA) performance was investigated under dry and wet conditions. Under the dry condition (80 • C, 30%RH), the MEA employing an MPL with a larger median pore diameter showed higher cell voltage, suggesting that the MPL with a larger pore diameter has better gas diffusivity, leading to better MEA performance. Under the wet condition (80 • C, 100%RH), it was confirmed that pore volume of the MPL has a significant impact on the MEA performance and that the hydrophilic MPL with a large pore volume was effective in reducing water flooding in the cathode catalyst layer. When used in an MPL, VGCF-H (carbon fiber with a fiber diameter of 150 nm) gives the largest pore diameter and pore volume. This MEA with a hydrophilic MPL (made of VGCF-H and ionomer) showed the best MEA performance under both dry and wet operating conditions.

The gas diffusion layer (GDL) is a critical component for water management in PEFCs (Polymer Electrolyte Fuel Cells). The impact of anode GDLs and the hydrophobic/hydrophilic nature of GDLs were studied in order to determine the effect of water transport on membrane-electrode assembly (MEA) performance. Anode GDLs, regardless of their hydrophobic or hydrophilic nature, are of minimal bearing on the MEA performance, as long as they are thick enough to prevent flooding at the anode side. MEA performance largely depends on the combination of hydrophobic and hydrophilic anode and cathode GDLs. The best performance was obtained for the MEA using a hydrophilic GDL for both anode and cathode. In the case of an MEA with a non-hydrophobic anode GDL, use of a hydrophobic cathode GDL instead of a hydrophilic cathode GDL increased flooding of the anode, suggesting that water produced in the cathode catalyst layer was pushed across the membrane to the anode side by a pressure barrier created by the hydrophobic cathode MPL. The MEA using a hydrophilic MPL for both cathode and anode GDLs has proven to be advantageous by demonstrating stable performance for 200 hours, operating at 2.0 A/cm 2 , at 64 o C and 100%RH.

Perfluorosulfonic acid (PFSA) ionomer is one of the key materials used in polymer electrolyte fuel cell (PEFC). Most of the membranes used in high performance and high durability PEFC are made from PFSA ionomers. The ionomer for the membrane is required to perform well at high temperatures up to 120 °C at low relative humidity (RH). The ionomer for the electrode, besides transporting the protons to the membrane, its function in cathode of delivering the oxygen to the Pt surface is highlighted in the recent progress of high activity catalyst enabling low Pt loading. Asahi Glass Co., Ltd. (AGC) is also proposing the PFSA ionomer to be used for creating hydrophilic microporous layer (MPL) in between the gas diffusion media (GDM) and the catalyst layer to achieve better performance in low RH conditions. The monomer structures and their copolymer properties as well as their cell performance examined are presented in this paper.