Introducing Microporous Layer (MPL) Attached Catalyst Coated Membrane for PEFCs

Abstract

A brand-new membrane electrode assembly (MEA) fabrication method was conceived. The performance of the MEA by using an MPL attached catalyst coated membrane (CCM) was equivalent to that by using the gas diffusion electrode (GDE) method, indicating that the coated interface between the catalyst layer and the MPL plays a significant role in achieving better MEA performance. For the last few years, we have been doing research on hydrophilic MPLs. We have already reported (1, 2) that the MEA using a hydrophilic MPL showed much better performance in a wide range of pressure and humidity conditions than that using a conventional hydrophobic MPL. We also found that the MEA using the GDE method on the hydrophilic MPL showed the highest cell voltage compared to the MEAs using the decal method and the membrane coating method. In the case of the MEA using the GDE method on the hydrophilic MPL, the catalyst layer (CL) is integrated into the MPL to form a firm interface between the CL and the hydrophilic MPL. We suggested that this interface allows product water and oxygen gas to transport more smoothly (3).In order to examine the significance of the interface between the CL and the MPL in this work, we used an MPL attached CCM as illustrated in Fig.1, which was fabricated by hot-pressing a cathode CL coated hydrophilic MPL to the membrane with an anode CL. The hydrophilic MPL consists of carbon fiber and ionomer. The MEA employing the MPL attached CCM showed equivalent performance to that by using the gas diffusion electrode (GDE) method as shown in Fig. 2. This result clearly indicates that the coated interface between the CL and the MPL is more favorable than the hot-pressed interface. The MPL attached CCM is easy to handle because it shows little dimensional change despite employing a non-reinforced membrane. As any GDL substrate is applicable to this MPL attached CCM, this is a unique and promising method for MEA fabrication.