Abstract
Proton exchange membrane fuel cells (PEMFCs) powered by green hydrogen (H2) have become a promising alternative to conventional hydrocarbon-fueled power generators. Despite technological advancements, further improvements in efficiency, durability, and low-cost production are required for the widespread adoption of PEMFCs. Though numerous approaches to improve PEMFC electrodes have been reported, most strategies utilize a single material set (e.g., one combination of catalyst and ionomer) to improve performance. Alternatively, anisotropic (graded) electrode structures with locally tunable properties may yield superior electrode performance due to improved ionic and gas phase transport. In this work, graded cathode catalyst layers (CCLs) incorporating different ionomers (Nafion D2020, Aquivion D79-25BS, and HOPI) were designed and prepared. Performance screening shows that some of these graded electrode structures have comparable performance to optimized single-ionomer electrode structures (D2020) suggesting some synergistic benefit. Additionally, we show that electrodes with lower equivalent weight (EW) D79 ionomer near the membrane and D2020 ionomer near the gas diffusion media outperformed electrodes with the inverted configuration. Finally, EIS analysis shows some graded ionomer structures (e.g. D79/D2020) have better than expected H+ conductivity, generally leading to better electrode performance. However, further optimization of ionomer content and catalyst ink formulations is needed to improve overall PEMFC performance.
| Original language | English |
|---|---|
| Article number | 232530 |
| Journal | Journal of Power Sources |
| Volume | 556 |
| DOIs | |
| State | Published - Feb 1 2023 |
Funding
Examining the cyclic voltammograms shown in Fig. 3c and d, it's clear that Pt loadings are slightly different, but these differences in measured electrochemical surface area (summarized in Table 2) can't explain the dismal performance of HOPI and low I/C D79 electrodes. Instead, these results suggest ionic conductivity and gas transport of these electrode structures likely play a role in the performance at high potentials. These kinetic losses also manifest in H2/Air polarization curves shown in Fig. 4a–d (more information can be found from supporting information (SI) of Fig. S1 S2, and Table S1). Very similar performance trends are observed across the two operating conditions that were investigated. Among the single ionomer electrodes, D2020 exhibited superior performance across the entire voltage range, with more noticeable improvements in the higher current density region where ionic and mass transport limitations dominate. HOPI (I/C = 0.6) and D79 (I/C = 0.9) exhibit similar performance above 0.1 A cm−2, suggesting improved O2 transport may have overcome its kinetic limitations observed in Fig. 3a. In fully humidified H2/air at 80 °C, both D2020/HOPI and D79(0.5)/D2020 slightly outperform D2020 electrodes, possibly due to slightly higher loading as is the case for D79(0.5)/D2020. At slightly drier 90 °C, 65% RH conditions, only the D2020/HOPI outperformed D2020.This manuscript has been authored in part by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the U.S. Department of Energy (DOE), and by Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. This material is based on work performed by the Million Mile Fuel Cell Truck (M2FCT) Consortium, technology manager Greg Kleen. Funding was provided by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO). While we do not recommend or endorse the use of any materials, we appreciate the collaboration with Chemours and specifically Andrew Park in obtaining the HOPI ionomer utilized in portions of this study. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes. This manuscript has been authored in part by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the U.S. Department of Energy (DOE), and by Alliance for Sustainable Energy, LLC, the manager and operator of the National Renewable Energy Laboratory for the U.S. Department of Energy (DOE) under Contract No. DE-AC36-08GO28308 . This material is based on work performed by the Million Mile Fuel Cell Truck (M2FCT) Consortium, technology manager Greg Kleen. Funding was provided by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office (HFTO). While we do not recommend or endorse the use of any materials, we appreciate the collaboration with Chemours and specifically Andrew Park in obtaining the HOPI ionomer utilized in portions of this study. The views expressed in the article do not necessarily represent the views of the DOE or the U.S. Government. The U.S. Government retains and the publisher, by accepting the article for publication, acknowledges that the U.S. Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for U.S. Government purposes. This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for US government purposes. DOE will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ).
Keywords
- Cathode catalyst layer
- Fuel cell
- Graded MEA
- Heavy duty fuel cell truck
- M2FCT
