The effects of operational conditions on the mixing behavior of a rotary energy recovery device have been systematically investigated through the combined methods of computational fluid dynamics and validating experiments in this paper. The sliding mesh technique and species transport equations were applied in the simulation process. An innovative parameter of inflow length was defined to express the moving distance of a mixing section in rotor ducts. A theoretical formula between the inflow length and operational conditions was first established on the basis of the mass balance and computational fluid dynamics analysis. Simulation results revealed that the mixing has a polynomial relation with dimensionless inflow length, which was in good agreement with the experimental results. The obtained formulas between mixing and dimensionless flow length provide a simple way to calculate and predict the mixing behavior of the device, which will be beneficial to design and operate the rotary energy recovery device in a lower mixing level.
The free radicals produced during the long-term operation of fuel cells can accelerate the chemical degradation of the proton exchange membrane (PEM). In the present work, the widely used free radical scavenger CeO 2 was anchored on aminofunctionalized metal−organic frameworks, and flexible alkyl sulfonic acid side chains were tethered onto the surface of inorganic nanoparticles. The prepared CeO 2 -anchored bifunctionalized metal−organic framework (CeO 2 -MNCS) was used as a promising synergistic filler to modify the Nafion matrix for addressing the detrimental effect of pristine CeO 2 on the performance and durability of PEMs, including decreased proton conductivity and the migration problem of CeO 2 . The obtained hybrid membranes exhibited a high proton conductivity up to 0.239 S cm −1 , enabling them to achieve a high power density of 591.47 mW cm −2 in a H 2 /air PEMFC single cell, almost 1.59 times higher than that of recast Nafion. After 115 h of acceleration testing, the OCV decay ratio of the hybrid membrane was decreased to 0.54 mV h −1 , which was significantly lower than that of recast Nafion (2.18 mV h −1 ). The hybrid membrane still maintained high power density, low hydrogen crossover, and unabated catalytic activity of the catalyst layer after the durability test. This study provides an effective one-stone-two-birds strategy to develop highly durable PEMs by immobilizing CeO 2 without sacrificing proton conductivity, allowing for the realization of improvement on the performance and sustained durability of PEMFC simultaneously.
The
approach to constructing proton transport channels via direct
adjustments, including hydrophilia and analytical acid concentration
in hydrophilic domains, has been proved to be circumscribed when encouraging
the flatter hydrophilic–hydrophobic microphase separation structures
and reducing conductivity activation energy. Here, we propose a constructive
solution by regulating the polarity of hydrophobic domains, which
indirectly varies the aggregation and connection of hydrophilic ion
clusters during membrane formation, enabling orderly self-assembly
and homogeneously distributed microphase structures. Accordingly,
a series of comb-shaped polymers were synthesized with diversified
optimization, and more uniformly distributed ion cluster lattices
were subsequently observed using high-resolution transmission electron
microscopy. Simultaneously, combining with density functional theory
calculations, we analyzed the mechanism of membrane degradations caused
by hydroxyl radical attacks. Experimental results demonstrated that,
facilitated by proper molecule polarity, beneficial changes of bond
dissociation energy could extend the membrane lifetime more than the
protection from side chains near ether bonds, which were deemed to
reduce the probability of attacks by the steric effect. With the optimal
strategy chosen among various trials, the maximum power density of
direct methanol fuel cell and H2/air proton exchange membrane
fuel cell was enhanced to 95 and 485 mW cm–2, respectively.
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