Catalyst layers to enhance uniformity of current density in membrane electrode assemblies
Components that include catalyst layers used in membrane electrode assemblies (MEAs), and methods of making such components are described. The catalyst layers yield more uniform current distributions across the active area of the MEA during operation. The catalyst layers may have a uniform catalyst activity profile of a less active catalyst to achieve more uniform current density over the MEA active area. The catalyst layers may have a variable activity profile, such as an activity profile with a varying slope, to compensate for the inherent nonlinearities of catalyst utilization during operation of an electrochemical fuel cell. Desired variable catalyst activity profiles may be achieved, for example, by varying the catalyst loading across the MEA from inlet to outlet ports or by varying the surface area of the catalyst loading or by varying the surface area of the catalyst support elements.
1. An article, comprising a single catalyst layer having a width and a length, wherein the length is longer than the width, and wherein the single catalyst layer has a catalyst activity profile comprising at least one positive slope and at least one negative slope across the width of the single catalyst layer and having substantially zero slope along the length of the single catalyst layer.
2. The article of claim 1 , further comprising a substrate, wherein the single catalyst layer is formed on the substrate.
3. The article of claim 2 , wherein the substrate comprises a microtextured surface.
4. The article of claim 1 , wherein the single catalyst layer comprises a nanostructured thin film catalyst layer.
5. The article of claim 1 , wherein the single catalyst layer comprises a dispersion coating.
6. The article of claim 1 , further comprising an electrically conductive microporous layer, wherein the single catalyst layer is formed on the electrically conductive microporous layer.
7. The article of claim 1 , wherein the catalyst activity profile further comprises at least one zero slope across the width of the single catalyst layer.