Potential Bifunctional Filler (CeO₂–ACNTs) for Nafion Matrix toward Extended Electrochemical Power Density and Durability in Proton-Exchange Membrane Fuel Cells Operating at Reduced Relative Humidity

Abstract

Cerium oxide–anchored amine-functionalized carbon nanotubes (CeO2–ACNTs) are applied as radical scavengers as well as solid proton conductors to realize hybrids with Nafion (Nafion/CeO2–ACNTs) for a proton-exchange membrane fuel cell (PEMFC) operating at low relative humidity (RH). Reinforcement due to the existence of ACNTs offers good mechanical strength and proton conductivity to hybrid, and addition of CeO2 mitigates the chemical degradation of hybrid. The proton conductivity of Nafion/CeO2–ACNTs at 20% RH is 12.2 mS cm–1, which is 4 and 5 times better than that of recast Nafion and Nafion-212, respectively. PEMFC integrated with Nafion/CeO2–ACNTs delivers a maximum power density of 174.25 mW cm–2 at a load current density of 334.66 mA cm–2 while operating at 60 °C under 20% RH. In contrast, under identical condition, the maximum power densities of 83.14 and 72.55 mW cm–2 are achieved by recast Nafion and Nafion-212, respectively. Additionally, PEMFC integrated with Nafion/CeO2–ACNTs exhibits a decay of only 0.21 mV h–1 over 200 h while keeping at 60 °C under 20% RH. Compared to Nafion/CeO2–ACNTs, the recast Nafion and Nafion-212 are experienced the accelerated decay (recast Nafion, 0.65 mV h–1; Nafion-212, 0.59 mV h–1). PEMFC performance, hydrogen crossover as well as morphology of specimens are probed before and after durability test; the Nafion/CeO2–ACNTs exhibits high stability than other specimens. Thus, Nafion/CeO2–ACNTs can be exploited to address various critical issues associated with commercial Nafion in PEMFC applications.

Carbon Nanocomposite Membrane Electrolytes for Direct Methanol Fuel Cells—A Concise Review

“…The tensile strength of CNTs is around 63 GPa, which is 50 fold higher than steel, while Young’s modulus is five-fold higher [82]. In addition to these remarkable mechanical properties, high surface area boost CNTs as reinforcing material in polymer matrices [34,44,83] CNTs are chosen as additive mainly to address the methanol permeability and mechanical strength issues of PEMs in DMFCs. However, the homogeneous dispersion of CNTs is difficult as they are held by Van der Waals forces, which limit the interfacial interactions with the polymer matrix [84].…”

The Multilevel Structure of Sulfonated Syndiotactic-Polystyrene Model Polyelectrolyte Membranes Resolved by Extended Q-Range Contrast Variation SANS

“…Moreover, free radicals such as hydroxyl and hydroperoxyl are produced during the operation of the PEMFC as a result of the reaction of hydrogen and oxygen on the electrodes or the decomposition of hydrogen peroxide with metal contaminants in the membrane. These radicals initiate processes of chemical degradation that affect the durability and the lifetime of the PEM [12,13]. Thus, the PSFI membranes seem not to be the ideal choice for the commercialization of PEMFC technology.…”

“…Several approaches have been proposed to overcome these issues, considering both the improvement of the properties of the Nafion membranes and the development of alternative membrane materials with similar or better performance. However, there is always a trade-off between improving one or another of these properties [12]. The ion-exchange capacity (IEC), and hence the conductivity, can be increased by adding ionic groups to the Nafion, but this may lead to deterioration of the mechanical properties of the membrane due to excessive swelling.…”

The Effects of Temperature and Humidity on the Microstructure of Sulfonated Syndiotactic–polystyrene Ionic Membranes

“…Moreover, free radicals such as hydroxyl and hydroperoxyl are produced during the operation of the PEMFC as a result of the reaction of hydrogen and oxygen on the electrodes or the decomposition of hydrogen peroxide with metal contaminants in the membrane. These radicals initiate processes of chemical degradation that affect the durability and the lifetime of the PEM [6,7]. Therefore, improvements in the Nafion properties by incorporating inorganic fillers (such as titania, zirconia, and silica) or carbon-based nanomaterials (carbon nanotubes, fullerenes, etc.)…”

“…Therefore, improvements in the Nafion properties by incorporating inorganic fillers (such as titania, zirconia, and silica) or carbon-based nanomaterials (carbon nanotubes, fullerenes, etc.) into the membranes [ 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 ] and alternative low-cost materials that present similar conductive and chemo-mechanical properties, such as the Nafion membranes [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ], are continuously searched for. Given the recent developments, which enable a controlled sulfonation of only the amorphous phase [ 26 ], preserving thus the crystallinity of the material, and an improved resistance to oxidation decomposition when fullerenes are added [ 27 ], the sulfonated syndiotactic polystyrene (s–sPS) is a good potential candidate for some PEMFC applications, as it presents a high proton conductivity comparable to Nafion [ 28 ], high chemical and thermomechanical stability, and a low cost.…”