Performance Evaluation and Durability Enhancement of FEP-Based Gas Diffusion Media for PEM Fuel Cells

Gas Diffusion Layer for Proton Exchange Membrane Fuel Cells: A Review

Proton exchange membrane fuel cells (PEMFCs) are an attractive type of fuel cell that have received successful commercialization, benefitted from its unique advantages (including an all solid-state structure, a low operating temperature and low environmental impact). In general, the structure of PEMFCs can be regarded as a sequential stacking of functional layers, among which the gas diffusion layer (GDL) plays an important role in connecting bipolar plates and catalyst layers both physically and electrically, offering a route for gas diffusion and drainage and providing mechanical support to the membrane electrode assemblies. The GDL commonly contains two layers; one is a thick and rigid macroporous substrate (MPS) and the other is a thin microporous layer (MPL), both with special functions. This work provides a brief review on the GDL to explain its structure and functions, summarize recent progress and outline future perspectives.

Greenhouse Gas Implications of Extending the Service Life of PEM Fuel Cells for Automotive Applications: A Life Cycle Assessment

A larger adoption of hydrogen fuel-cell electric vehicles (FCEVs) is typically included in the strategies to decarbonize the transportation sector. This inclusion is supported by life-cycle assessments (LCAs), which show the potential greenhouse gas (GHG) emission benefit of replacing internal combustion engine vehicles with their fuel cell counterpart. However, the literature review performed in this study shows that the effects of durability and performance losses of fuel cells on the life-cycle environmental impact of the vehicle have rarely been assessed. Most of the LCAs assume a constant fuel consumption (ranging from 0.58 to 1.15 kgH2/100 km) for the vehicles throughout their service life, which ranges in the assessments from 120,000 to 225,000 km. In this study, the effect of performance losses on the life-cycle GHG emissions of the vehicles was assessed based on laboratory experiments. Losses have the effect of increasing the life-cycle GHG emissions of the vehicle up to 13%. Moreover, this study attempted for the first time to investigate via laboratory analyses the GHG implications of replacing the hydrophobic polymer for the gas diffusion medium (GDM) of fuel cells to increase their durability. LCA showed that when the service life of the vehicle was fixed at 150,000 km, the GHG emission savings of using an FC with lower performance losses (i.e., FC coated with fluorinated ethylene propylene (FEP) instead of polytetrafluoroethylene (PTFE)) are negligible compared to the overall life-cycle impact of the vehicle. Both the GDM coating and the amount of hydrogen saved account for less than 2% of the GHG emissions arising during vehicle operation. On the other hand, when the service life of the vehicle depends on the operability of the fuel cell, the global warming potential per driven km of the FEP-based FCEV reduces by 7 to 32%. The range of results depends on several variables, such as the GHG emissions from hydrogen production and the initial fuel consumption of the vehicle. Higher GHG savings are expected from an FC vehicle with high consumption of hydrogen produced with fossil fuels. Based on the results, we recommend the inclusion of fuel-cell durability in future LCAs of FCEVs. We also advocate for more research on the real-life performance of fuel cells employing alternative materials.

The Role of Fluorinated Polymers in the Water Management of Proton Exchange Membrane Fuel Cells: A Review

As the hydrogen market is projected to grow in the next decades, the development of more efficient and better-performing polymer electrolyte membrane fuel cells (PEMFCs) is certainly needed. Water management is one of the main issues faced by these devices and is strictly related to the employment of fluorinated materials in the gas diffusion medium (GDM). Fluorine-based polymers are added as hydrophobic agents for gas diffusion layers (GDL) or in the ink composition of microporous layers (MPL), with the goal of reducing the risk of membrane dehydration and cell flooding. In this review, the state of the art of fluorinated polymers for fuel cells is presented. The most common ones are polytetrafluoroethylene (PTFE) and fluorinated ethylene propylene (FEP), however, other compounds such as PFA, PVDF, PFPE, and CF4 have been studied and reported. The effects of these materials on device performances are analyzed and described. Particular attention is dedicated to the influence of polymer content on the variation of the fuel cell component properties, namely conductivity, durability, hydrophobicity, and porosity, and on the PEMFC behavior at different current densities and under multiple operating conditions.

Optimization of Perfluoropolyether-Based Gas Diffusion Media Preparation for PEM Fuel Cells

A hydrophobic perfluoropolyether (PFPE)-based polymer, namely Fluorolink® P56, was studied instead of the commonly used polytetrafluoroethylene (PTFE), in order to enhance gas diffusion media (GDM) water management behavior, on the basis of a previous work in which such polymers had already proved to be superior. In particular, an attempt to optimize the GDM production procedure and to improve the microporous layer (MPL) adhesion to the substrate was carried out. Materials properties have been correlated with production routes by means of both physical characterization and electrochemical tests. The latter were performed in a single PEM fuel cell, at different relative humidity (namely 80% on anode side and 60%/100% on cathode side) and temperature (60 °C and 80 °C) conditions. Additionally, electrochemical impedance spectroscopy measurements were performed in order to assess MPLs properties and to determine the influence of production procedure on cell electrochemical parameters. The durability of the best performing sample was also evaluated and compared to a previously developed benchmark. It was found that a final dipping step into PFPE-based dispersion, following MPL deposition, seems to improve the adhesion of the MPL to the macro-porous substrate and to reduce diffusive limitations during fuel cell operation.

Bridging the Gap between Automated Manufacturing of Fuel Cell Components and Robotic Assembly of Fuel Cell Stacks

Recently demonstrated robotic assembling technologies for fuel cell stacks used fuel cell components manually pre-arranged in stacks (presenters). Identifying the original orientation of fuel cell components and loading them in presenters for a subsequent automated assembly process is a difficult, repetitive work cycle which if done manually, deceives the advantages offered by either the automated fabrication technologies for fuel cell components or by the robotic assembly processes. We present for the first time a robotic technology which enables the integration of automated fabrication processes for fuel cell components with a robotic assembly process of fuel cell stacks into a fully automated fuel cell manufacturing line. This task uses a Yaskawa Motoman SDA5F dual arm robot with integrated machine vision system. The process is used to identify and grasp randomly placed, slightly asymmetric fuel cell components, to reorient them all in the same position and stack them in presenters in preparation for a subsequent robotic assembly process. The process was demonstrated as part of a larger endeavor of bringing to readiness advanced manufacturing technologies for alternative energy systems, and responds the high priority needs identified by the U.S. Department of Energy for fuel cells manufacturing research and development.