Effect of Microporous Layer (MPL) and Carbon Fiber Paper (CFP) Properties on PEMFC High Current Density Performance

Abstract

The effect of microporous layer (MPL) and carbon fiber paper (CFP) properties on high current density cell performance is investigated in this work. Two types of carbon black (Denka Li-400 and Soltex AB50-HC) were used with the same MPL ink formulation using FEP as hydrophobic agent, and the inks were coated on two types of wetproofed CFP substrates. The resulting GDLs (CFP + MPL) have different, contrasting through-plane thermal conductivities – for the MPLs coated on Toray TGP-H-060, k = 0.310 – 0.390 W/mK but for those coated on Freudenberg H2312, k = 0.170 – 0.210 W/mK (under 2 MPa compression).The MPL coatings were characterized by mercury porosimetry and scanning electron microscopy (SEM) (top-down and cross-section). The two MPLs show contrasting peak pore sizes – the AB50-HC MPL peak pore size is at 60 nm while the Li-400 MPL peak pore size is at 300 nm, consistent with recent MPL studies using Li-400 in the MPL [1]. Single cell membrane electrode assemblies (MEAs) were made in a catalyst-coated membrane (CCM) configuration at both 5 cm2 (for testing under differential flow conditions) and 38 cm2 (non-differential cell) active areas. Polarization curves at different operating conditions were obtained in addition to limiting current experiments (on 5 cm2 differential cells) to determine the total oxygen transport resistance.At dry operating conditions (Tcell = 80°C, RH = 32%, pabs = 150 kPa), the cell performance of all four (4) samples (2 MPLs coated on 2 different CFP substrates) are comparable, but under wet operating conditions, (Tcell = 80°C, RH = 100%, pabs = 150 kPa), the 2 MPLs (AB50-HC and Li-400) coated on TGP-H-060 have significantly lower cell performance (38 cm2 non-differential cells, but the same trends were observed when testing under differential flow conditions (5 cm2 CCM MEAs)). These results reiterate the importance of GDL through-plane thermal conductivity as the main GDL property that influences water management and controls cell performance at high current densities (> 2.0 A/cm2) [2].