Next Generation Cathode Catalyst Layer Design with High Oxygen Permeable Ionomer – Benefits, Challenges, and Prospects for Heavy Duty Fuel Cell Applications
Authors: PAUL Devproshad K , Young Alan , Hu Jingwei , Bellerive Julie 
Published: December 2024

Proton Exchange Membrane Fuel Cell (PEMFC) has a growing demand to power zero emission fuel cell applications. Ballard is the fuel cell industry leader, developing the next generation core technology to fulfill such demand and giving continuous efforts on cost reduction. Key requirements in fuel cell market applications include high power density and long-life operation, while maintaining high efficiencies and reducing costs. This places a high demand on improving catalyst performance and electrode layer transport, which can be sustained over the duration of the product lifetime. To reduce fuel cell membrane electrode assembly (MEA) cost, the push for high performance catalyst layers (CLs) with low platinum (Pt) loadings results in new challenges for the cathode material selection and electrode design. The increased oxygen transport resistance that occurs at lower catalyst loadings with reduced available catalyst electrochemical active surface area (ECSA), causes two very closely related challenges: 1) greater performance losses at high current density increases the difficulty to achieve the power requirements for the heavy duty market, and 2) the loss of catalyst ECSA via platinum dissolution over time puts additional demands on the design to achieve the end of life (EOL) performance requirement. Therefore, a combination of material solution, design choice and processing parameters are the key to optimize next generation cathode design for fuel cell applications1.

One material solution to achieve high performance while reducing catalyst loadings is the development of high oxygen permeable ionomer (HOPI) that mitigates oxygen transport limitations at the Pt surface. Chemours has developed a HOPI with a bulky, sterically rigid monomer group in the ionomer backbone, which disrupts the packing density, improving oxygen permeability on the catalyst surface2. One of the key challenges of HOPI integration and the scale-able fabrication of the catalyst layer is high crack density of CL due to the rigid nature of the ionomer. Ballard has integrated HOPI in the cathode CL overcoming scale-able fabrication challenges through appropriate process parameter selection and evaluated CL performance. The use of accelerated testing and modeling approach developed by numerous product iteration, has been applied for lifetime estimation for HOPI technology introduction. In this talk, we will discuss details about benefit of High Oxygen Permeable Ionomer (HOPI) in next generation cathode CL design.

Recently, key requirements in heavy-duty market applications are placing more importance on high efficiency rather than high power density to reduce fuel cost rather catalyst cost. Reaching the target lifetime, catalyst overloading to 0.45 mg/cm2 total Pt in anode and cathode, and 44% active membrane area oversizing are suggested3. Therefore, to achieve high efficiency target, high catalyst activity is more desired. Interestingly, HOPI also showed high specific activity due to the mitigation of catalyst poisoning by sulfonate anion groups4. We will also discuss the catalyst layer design prospect with HOPI for such transition on heavy duty market application.

Acknowledgement: US Department of Energy (DOE) funded heavy duty MEA development project (DE-EE0008822).

References

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S. Litster et al. 2020 Durable High-Power Density Fuel Cell Cathodes for Heavy-Duty Vehicle. DOE AMR 2020

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