For more information on our ongoing investigations, please check out our publications and research projects pages!
Ionic Liquids in Polymer Electrolyte Fuel Cells: New State-of-the-art in the Oxygen Reduction Reaction and Durability
Lab Researchers: Arezoo Avid, Jesus Ochoa Lopez, Ying Huang and Iryna V. Zenyuk
Summary: Ionic liquids (ILs) have shown to be promising additives to the catalyst layer to enhance oxygen reduction reaction in polymer electrolyte fuel cells. However, fundamental understanding of their role in complex catalyst layers in practically relevant membrane electrode assembly environment is needed for rational design of highly durable and active platinum-based catalysts. Here we explore three imidazolium-derived ionic liquids, selected for their high proton conductivity and oxygen solubility, and incorporate them into high surface area carbon black support. Further, we establish a correlation between the physical properties and electrochemical performance of the ionic liquid-modified catalysts by providing direct evidence of ionic liquids role in altering hydrophilic/hydrophobic interactions within the catalyst layer interface. The resulting catalyst with optimized interface design achieved a high mass activity of 347 A g-1Pt at 0.9 V H2/O2, power density of 0.909 W cm-2 under H2/air and under 1.5 bar and had only 0.11 V potential decrease at 0.8 A cm-2 after 30 k accelerated stress test cycles. This performance stems from substantial enhancement in Pt utilization, which is buried inside the mesopores and is now accessible due to ILs addition.
Publication: Nature Communications, 2022
Highly Durable Fluorinated High Oxygen Permeability Ionomers for Proton Exchange Membrane Fuel Cells
Lab Researchers: Yongzhen Qi, Andrea Perego and Iryna Zenyuk
Summary: For proton exchange membrane fuel cells to be cost-competitive in light- and heavy-duty vehicle applications, their Pt content in the catalyst layers needs to be lowered. However, lowering the Pt content results in voltage losses due to high local oxygen transport resistances at the ionomer–Pt interface. It is therefore crucial to use ionomers that have higher oxygen permeability than Nafion. In this work, novel high oxygen permeability ionomers (HOPIs) are presented, with up to five times higher oxygen permeability than Nafion, synthesized by copolymerization of perfluoro-2,2-dimethyl-1,3-dioxole (PDD) with perfluoro(4-methyl-3,6-dioxaoct-7-ene) sulfonyl fluoride (PFSVE). PDD is the source of higher permeability due to its open ring structure, while PFSVE provides ionic conductivity. Optimization of PDD content and equivalent weight enables increased fuel cell performance, mainly at high current densities, where HOPIs can achieve power densities >1.25 W cm−2 and exceed the 0.8 A cm−2 U.S. Department of Energy durability target by losing only 4.5 mV, which is over six times less than 30 mV. The interactions between HOPI and SO3− groups with a PtCo/C catalyst are also elucidated here at a fundamental level.
Publication: Advanced Energy Materials, 2022
Correlating the morphological changes to electrochemical performance during carbon corrosion in polymer electrolyte fuel cells
Researchers: Prantik Saha, Kaustubh Khedekar, Iryna Zenyuk
Summary: A mechanistic understanding of carbon corrosion in polymer electrolyte fuel cells (PEFCs) is required to design durable catalyst layers. Uncontrolled startup and shutdown of PEFCs cause electrochemical oxidation of carbon, which leads to several degradation phenomena, such as loss in electrochemical surface area (ECSA), pore structure collapse or increase in mass transport resistance. In this study, the chronology of morphological changes in the cathode catalyst layer due to carbon corrosion was identified and correlated with electrochemical performance degradation. PEFCs were subjected to the Department of Energy carbon corrosion accelerated stress test (AST) protocol. The study revealed two phases: in the initial phase (∼500 AST cycles), amorphous carbon in contact with Pt nanoparticles oxidized fast. Rapid carbon loss and catalyst layer thinning occurred, but pore structure did not change significantly. Pt nanoparticles detached from the support and ECSA decreased drastically. In the second phase (∼1500 AST cycles), carbon corrosion slowed down, but severe pore structure collapse was observed. Porosity and pore connectivity within the cathode catalyst layer decreased considerably. Electrochemical diagnostics corroborated this finding by showing significantly higher O2 mass transport resistance. Lastly, no significant change was observed in the concentration of oxides on the carbon surface after AST. But overall water management in the cathode catalyst layer deteriorated as the pore structure collapsed. This study provides an in-depth understanding of morphological changes during PEFC carbon corrosion AST protocol and motivates novel material design strategies to enable durable PEFCs.
Publication: Journal Materials Chemistry A, 2022