Impact of Microporous Layer Pore Properties on Liquid Water Transport in PEM Fuel Cells: Carbon Black Type and Perforation

Abstract

The oxygen and water transport through various microporous layers (MPLs) is investigated by fuel cell tests in a 5 cm 2 active area cell under differential-flow conditions, analyzing polarization curves, the associated high-frequency resistance, and the oxygen transport resistance extracted from limiting current density measurements. In this study, MPLs with two different carbon blacks are prepared and compared to a commercial material, all coated on the same GDL-substrate (Freudenberg); furthermore, perforated MPLs with large pores produced by a thermally decomposable polymeric pore former with a particle diameter of ≈30 μm are examined. The materials are characterized by mercury porosimetry, nitrogen adsorption and scanning electron microscopy. While at dry conditions (T cell = 80 • C, RH = 70%, p abs = 170 kPa) the performance of all materials is similar, at conditions of high water saturation (T cell = 50 • C, RH = 120%, p abs = 300 kPa), MPLs with larger pores or perforations exhibit a performance improvement due to a ≈30% reduction in oxygen transport resistance. The results indicate that liquid water is transported exclusively through these large pores, while the oxygen transport occurs in the small pores defined by the carbon black structure.

Investigating Electrode Flooding in a Flowing Electrolyte, Gas‐Fed Carbon Dioxide Electrolyzer

“…To this end, densely‐packed partially‐hydrophobized microporous layers (MPLs) coated onto carbon‐fiber substrates (CFSs) serve both as high‐surface‐area, electronically‐conductive contacts to the CL and as effective media for water management . Studies focused on water transport in PEFCs, enhanced by advanced operando imaging techniques, have motivated engineering both GDL microstructure and surface chemistry to achieve high power operation under water‐saturated conditions …”

Interfacial transport characteristics between heterogeneous porous composite media for effective mass transfer in fuel cells

“…Furthermore, straight‐cylindrical carbon fibers with uniform diameters of 6 μm that extended from boundary to boundary were randomly placed layer by layer in the domain. Moreover, the bulk densities of the carbon fiber and PTFE ( ρ carbon = 1.9 g cm −3 and ρ PTFE = 2.16 g cm −3 ) were used to convert the mass‐based parameters of the GDLs into the equivalent volume‐based compositions, to match the predetermined average porosities according to the following equations: where ϕ PTFE and ϕ carbon are the volume fractions of the PTFE and carbon, respectively. m PTFE and m carbon represent the masses of PTFE and carbon in a unit volume of the porous domain.…”

Ditch-structured microporous layers fabricated by nanosecond-pulse laser ablation for enhancing water transport in polymer electrolyte membrane fuel cells

“…In addition, the liquid water pressure is augmented at the CL/MPL interface due to the hydrophobicity of the MPL, which is the driving force for capillary transport of liquid water through the MPL or water back flow. 15 Perforated pores are known to be a preferred liquid water transport channel; 42 however, the hydrophilic perforated sites in D5-MPL do not have the above-mentioned positive functions of a hydrophobic MPL, in contrast to D1-and D3-MPL, resulting in the inferior water management. Further experimental results support that the ablated MPL exhibits better water management compared to the perforated MPL.…”