The development of a novel approach to achieve high-performance and durable fuel cells is imperative for the further commercialization of proton-exchange (or polymer electrolyte) membrane fuel cells (PEMFCs). In this work, multifunctional dendritic Nafion/CeO 2 structures were introduced onto the cathode side of the interface between a membrane and a catalyst layer through electrospray deposition. The dendritic structures enlarged the interfacial contact area between the membrane and the catalyst layer and formed microscale voids between the catalyst layer and gas diffusion medium. This improved the PEMFC performance through the effective utilization of the catalyst and enhanced mass transport of the reactant. Especially, under lowhumidity conditions, the hygroscopic effect of CeO 2 nanoparticles also boosted the power density of PEMFCs. In addition to the beneficial effects on the efficiency of the PEMFC, the incorporation of CeO 2 , widely known as a radical scavenger, effectively mitigated the free-radical attack on the outer surface of the membrane, where chemical degradation is initiated by radicals formed during PEMFC operation. These multifunctional effects of the dendritic Nafion/CeO 2 structures on PEMFC performance and durability were investigated using various in situ and ex situ measurement techniques.

The physical and chemical degradations of a state-of-the-art proton exchange membrane (PEM) composed of a perfluorinated sulfonic acid (PFSA) ionomer and polytetrafluoroethylene (PTFE) reinforcement are induced through the repeated expansion/shrinkage of the ionomer and free radical attacks. Such degradations essentially originate from the loose structure of the materials and the low interactive binding force among the PEM constituents. In this study, the need for simplified design principles of adhesives led to the use of mussel-inspired polydopamine (PD) as an interfacial modifier for the fabrication of highly durable PEM. Indeed, a self-polymerized dopamine layer acts as an interfacial glue, and enables efficient impregnation of a hydrophilic PFSA ionomer into porous hydrophobic PTFE with high packing density, resulting in strong adhesion between the PTFE and the PFSA polymers in the membrane. In addition, the redox property of the PD end groups spontaneously reduces the partial Ce salts in the ionomer solution and anchors them to the PD@PTFE substrate as defective cerium oxide (CeO x ) nanoparticles, reducing the dissolution and subsequent migration under cell operations. Finally, a CePD@PTFE membrane shows outstanding durability in fuel cells under an accelerated humidity cycling test with a reduction in the degree of physical and chemical failures.

Cerium oxide nanoparticles (CNPs) are investigated as radical scavengers to increase the durability of polymer electrolyte membrane fuel cells (PEMFCs). However, the practical application of CNPs in PEMFCs is hindered by the low stability of the CNPs during cell operation and the low compatibility of the CNPs with PEM. In this study, as effective antioxidants for PEMs, surface‐engineered CNPs, passivated with dopamine‐based copolymer ligands containing multidentate catechol pendant groups (CNP@DPLs), are reported. The DPLs provide enhanced colloidal and chemical stability in acidic and radical environments, thanks to the robust catechol binding groups and polymer backbone shielding. It is highlighted that they also improved the redox cycling ability of the CNPs, with catechol's additional radical scavenging. Using the CNP@DPLs as a model system, the effect of surface charge is also examined. Negatively charged sulfonic acid‐functionalized CNPs (CNP@DSAs) exhibit the highest compatibility with PEMs. Coherently, the CNP@DSA‐based reinforced composite membrane (CNP@DSA‐RCM) shows the lowest disintegration rate in Fenton's test. The PEMFC based on the CNP@DSA‐RCM outperforms previously reported antioxidant‐based PEMFCs. Importantly, while the pristine PEMFC and Ce salt‐based one undergoes degradation after 40 h, the CNP@DSA based PEMFC retains its performance even after 100 h.

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