Sources of Current Density Distribution in the Land-Channel Direction of a PEMFC

Abstract

A proton exchange membrane fuel cell (PEMFC) was segmented to measure local current density, electrochemical surface area, and high frequency resistance (HFR) distribution in the land-channel direction at resolution of 350 μm. An in-house catalyst coated membrane of 3 mm × 3 mm active area was prepared to represent a small area in a larger scale cell with 1 mm land and channel widths. This design was employed to measure current density and HFR distribution at 60 • C with several different operating conditions. Local electrical resistance was also measured separately so that local protonic resistances can be discerned from local HFR. To analyze the effect of the land-channel geometry a method was developed to quantify the sources of current distribution, such as distributions of oxygen concentration at the electrode, oxygen transport resistance, cathode catalyst layer resistance, and membrane water content. Current density distribution is strongly correlated with the distribution of membrane water content and electrode resistance in dry condition, and oxygen concentration distribution in wet condition, while in moderate condition both oxygen concentration and water content in membrane are critical to the local current density distribution. The results imply the limitation of uniform condition assumption used in a differential cell study. Proton exchange membrane fuel cell (PEMFC) is an electrochemical reactor with three geometrical directions: flow channel (length scale 1 to 100 cm), land-channel (length scale 100 to 1000 μm), and through-plane (length scale 10 to 100 μm) directions. Because of the geometry of a PEMFC the distribution of reactants and products in these directions are highly inhomogeneous, as a result making current generation non-uniform. In order to study the local non-uniformities in the flow-channel direction, segmentation of a PEMFC to many differential cells is widely used. Here the differential cell means a fuel cell with small enough active area so that various conditions within the cell can be considered uniform along the flow channel direction. On the other hand, because of its relatively smaller length scale, variations in the land-channel direction are often neglected in most of such studies. However, due to the non-uniform transport length distribution from channel to catalyst layer in the land-channel direction, the differential cells aligned in the flow direction give only the averaged values over each differential cell, and therefore the local information in the land-channel direction cannot be captured.In a wet condition, for example, due to the land-channel geometry liquid water tends to distribute non-uniformly in gas diffusion layer (GDL). Many modeling studies present in literature have predicted liquid water distribution in land-channel direction.1-4 One example of such study is numerical investigation of liquid water saturation distribution in the land-channel direction of a flow field with 1 mm wide land and channel presented by Wang et al. 5 According to their findings, li...

Hydration and dehydration cycles in polymer electrolyte fuel cells operated with wet anode and dry cathode feed: A neutron imaging and modeling study

“…The 2D-distributions of variables Γ i = ch,a , RH ach/acl , RH cch/ccl , mem and acl/ccl , as well as the 2D-distributions of current density and membrane ionic resistance, were calculated as: Sánchez et al [19], the pressure drop along the anode channel, ∆ g,ach , increases from 0.96 kPa to 1.44 kPa during current ignitions due to the blockage exerted by liquid water on the hydrogen flow. In contrast, the cathode stream remains undersaturated in both performance states, as shown by the neutron visualizations (see, e.g., the absence of water in the cathode channel in Figure 1(b RH a in = 50%, RH c in ≈ 0%), they found that higher current densities are generated under the ribs due to the better membrane hydration achieved in this region [100].…”

Visualization of the Oxygen Partial Pressure on the Gas-Diffusion-Layer Surface under the Single-Serpentine Flow Channel and the Ribs in a Polymer Electrolyte Membrane Fuel Cell during the Power Generation

“…3, p (O2) was seen to decrease from the inlet to the outlet, but not always monotonically along the flow channel because of the cross flow through the GDL as reported previously. 33) p (O2) under the ribs was clearly observed, and the value was lower than that under the neighboring flow channel because of the lower gas diffusivity under the ribs 3) ,5) , 8) The insufficient diffusivity should have lowered the oxygen concentration and increased the water vapor pressure. As the Uo2 increased, p (O2) near the inlet was also seen to increase.…”

Transport and Electrochemical Interface Properties of Ionomers in Low-Pt Loading Catalyst Layers: Effect of Ionomer Equivalent Weight and Relative Humidity

“…Decal transfer method was used to prepare an MEA. Nafion membrane (25 μm, NRE-211, DuPont, Wilmington, DE, USA) was hot-pressed in between the anode (0.2 mg Pt /cm 2 ) and the cathode decals at 150 °C and 2 MPa pressure for 3 min [ 44 , 45 ]. The MEAs had an anode and cathode active area of 1.44 and 1 cm 2 , respectively.…”