Impact of Porosity Gradients within Catalyst Layer and MPL of a PEM Fuel Cell on the Water Management and Performance: A Neutron Radiography Investigation

Abstract

The influence of porosity modifications of either microporous layer (MPL) or the catalyst layer of a low temperature Polymer Electrolyte Membrane Fuel Cell (PEMFC) on the performance of the cell has been investigated in many studies. However, we have been focusing in our study on the interactive impact of this morphological modification of both cathode MPL and catalyst layer in the water distribution and transport inside the cell and consequently also on the performance of the cell. In this study, three types of cathode MPLs with different porosity distributions and three type of membrane electrode assemblies (MEA) with different porosity of the catalyst layer are manufactured. Five one-cell fuel cells are investigated using combinations of those in-house made layers. To modify the porosity of the cathode MPL polymer particle in two sizes of 30 µm and 1.5 µm from company Chemisnow ® are introduced into the carbon slurry, which are then evaporated out of the MPL during the sintering process. For the catalyst layers, 0.5 µm Polystyrene particles are mixed in the electrode slurry with variable weight fractions and then washed out of the dried MEA. A more detailed description of the production procedure of these layers will be demonstrated in the presentation. Performance of fuel cells using these five combination of cathode MPL and electrode are measured using a Fuel Cell with 25 cm² active area and 3 serpentine channel flow fields. Neutron Radiography is used to investigate the water distribution dynamics and water content of the fuel cell. For this purpose, a specially designed single cell with 8 cm² active area and 3 serpentine channel flow fields is used. The measurements are obtained at two different humidity values on both cathode and anode inlet gases of RH=70% and RH=120% and different current densities. With an exposure time of 10 s, images with 12.4 µm pixel size are achieved. The quantitative analysis of the water thickness in the cathode GDL and cathode electrode of 5 cells at RH=120% for an increasing current density is shown at an exemplary radiogram for water distribution inside the cell with our reference cathode MPL and electrode (without porosity modification). Also the Current (I Cell ) and Voltage (V Cell ) evolution of the same cell is shown in figure 1. All cells have reached a water content plateau even before reaching the highest current density of 1A/cm². The cell with a porous catalyst layer and a double layer cathode MPL shows the highest water content on the cathode side of the cell, whereas the cell with a highly porous catalyst layer and a porous MPL shows the lowest water content of all cells, comparable to the water thickness observed for the cell without modified layers. Further results of both water content and performance dependent on porosity changes will be provided in the presentation. Figure 1

Key findings

• ▸Porosity modifications in both MPL and catalyst layer affect water distribution and transport inside the cell.
• ▸Different porosity distributions in MPL and catalyst layer have varying effects on fuel cell performance.
• ▸The study uses neutron radiography to investigate the interactive impact of porosity modifications on water management and performance.

Keywords

Identifiers

DOI

10.1149/ma2019-02/32/1404

Journal

ECS Meeting Abstracts

Year

2019