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Performance and Stability of Membrane–Electrode Assemblies Using a Carbon-free Connected Pt–Fe Catalyst and Polyphenylene-Based Electrolytes for Direct Formate Anion-Exchange Membrane Fuel Cells
journal contributionposted on 2022-10-21, 01:43 authored by Hidenori Kuroki, Shoji Miyanishi, Takanori Tamaki, Sasidharan Sankar, Gopinathan M. Anilkumar, Masazumi Arao, Junichi Shimanuki, Masashi Matsumoto, Hideto Imai, Takeo Yamaguchi
A major challenge in direct formate anion-exchange membrane fuel cells (DF-AEMFCs) is the low chemical durability of membrane–electrode assemblies (MEAs). Here, we developed MEAs that combined polyphenylene-based electrolytes and a carbon-free cathode catalyst layer (CL). The polyphenylene-based electrolytes with a three-dimensionally twisted spirobifluorene (SBF) backbone possess excellent chemical stability. The carbon-free catalyst formed by a nanonetwork of connected Pt–Fe nanoparticles showed four–five times higher specific activity for oxygen reduction reaction than a conventional Pt/C catalyst in an alkaline electrolyte solution. The carbon-free structure in the connected Pt–Fe catalyst enhanced the durability against potential cycling. The MEA using SBF-based electrolytes and a connected Pt–Fe catalyst achieved a high power density of 219 mW cm–2 for DF-AEMFCs through MEA testing under different conditions. Notably, the high performance was retained even after 150 h of operation at 0.2 A cm–2 and 80 °C. Detailed structural analysis of the catalyst and polyelectrolyte materials used in the MEA indicated minor chemical degradation after long-term DF-AEMFC operation. The anode and cathode CLs were not delaminated and the membrane/CL interfaces were bonded properly after the MEA stability test. The cathode catalyst retained the connected Pt–Fe nanonetwork and hollow capsule structures. A small amount of Fe leached out from the catalyst; however, a chemically ordered fct phase was maintained in the catalyst. Cryo-transmission electron microscopy observations showed a swollen SBF-based ionomer layer with a coating thickness of ∼50 nm on the catalyst surface, which remained unchanged after the stability test. This study successfully demonstrated that carbon-free connected nanoparticle catalysts are more advantageous than Pt/C for AEMFCs and that MEAs for DF-AEMFCs with both high performance and stability can be developed, providing design guidelines for the development of advanced MEAs.
∼ 50 nmstudy successfully demonstratedproviding design guidelinespolyelectrolyte materials usedoxygen reduction reactionhollow capsule structuresdirect formate aniondimensionally twisted spirobifluorenedetailed structural analysisalkaline electrolyte solutionhigh power densitybased ionomer layerlow chemical durability80 ° c219 mw cmfree catalyst formedmea using sbfcathode catalyst retainedmea stability testmea testingstability testretained evenfree structurecathode clsbased electrolytescatalyst surfacec catalystswollen sbfsmall amountremained unchangedpotential cyclingmajor challengehigh performancefe leacheddifferent conditionscoating thicknesscl interfacescl ).bonded properly150 h