Battery and Fuel Cell Technology

We have already shown that membrane electrode assemblies (MEAs) with a hydrophilic microporous layer (MPL) work much better in a wide range of operating conditions. The hydrophilic MPL is made of carbon fiber and ionomer, and its functions are to remove excess water from the cathode catalyst layer under wet conditions and to prevent dehydration of the membrane under dry conditions. In addition to the typical MEA fabrication methods (gas diffusion electrode (GDE) and decal methods), a brand-new MEA fabrication method (M-CCM method) was conceived as shown in Fig. 1. Generally, an MPL is formed on the gas diffusion layer (GDL) substrate for water management. However, in M-CCM method, a hydrophilic MPL is attached to the cathode catalyst layer. If the CCM with an MPL attached (M-CCM) is used instead of a standard CCM using the decal method, the MEA performance will still improve even when using conventional GDLs with a hydrophobic MPL. Figure 2 compares the MEA performance of an M-CCM and a standard CCM, using commercially available hydrophobic GDLs. The M-CCM shows higher cell voltage in high current density region under a wet condition of 80oC, 100% RH. Under a dry condition of 80oC, 20% RH, M-CCM shows higher cell voltage through the whole current density region. The hydrophilic MPL is beneficial in distributing gas more effectively and keeping the membrane suitably wet. As any GDL substrate is applicable to this M-CCM, this is a unique and promising method for MEA fabrication.