Three-dimensional multi-phase model of PEM fuel cell coupled with improved agglomerate sub-model of catalyst layer

© 2019 Elsevier Ltd An improved agglomerate sub-model of catalyst layer (CL) involving actual agglomerate size and oxygen local transport characteristics is developed and incorporated into a three-dimensional (3D) multi-phase model of proton exchange membrane (PEM) fuel cell. This makes it capable to consider the effect of platinum (Pt) loading on oxygen transport and fuel cell performance more accurately. Oxygen local transport resistance near the catalyst surface is divided into three parts caused by liquid water blockage, ionomer coverage and Pt/carbon agglomeration, respectively. The resistances caused by ionomer coverage and Pt/carbon agglomeration are two major sources of oxygen local transport resistance. They have opposite variation trends as Pt loading changes. However, the ionomer resistance increases dramatically when Pt loading is lower than 0.1 mg cm−2 because of the much harder transport process through a relatively heavier ionomer coating. The simulation results agree with the experimental data reasonably under different cathode Pt loadings (from 0.3 to 0.025 mg cm−2), for both polarization curves and local transport resistance. In addition, a transport dominance parameter is defined to judge whether the concentration loss predominates the electrochemical reaction. A value greater than 10% can be seen as a symbol of local oxygen starvation. Using this model, fine channel geometry with extremely small channel and rib widths is investigated, and the highest net output power in this study is corresponding to 0.2 and 0.6 mm for channel (rib) width and height

Reduced MVD and perfusion in animals treated with VAE compared with rHSV, Endostar, and PBS.

<p>Mice with subcutaneous GSC-derived tumors were treated with a single dose (1×10⁷ plaque-forming units) of rHSV, VAE, PBS, or Endostar 10 d after tumor cell implantation. (A) Representative pictures of immunohistochemical staining for CD31 in tumors isolated from mice 10 d after therapy with PBS, VAE, r-HSV, or Endostar. Scale bar: 10 µm. (B) The quantification of MVD in tumors treated with PBS, VAE, r-HSV, or Endostar. Data are shown as the mean MVD ± SEM for each group (n = 2 to 4 sections/tumor and n = 10 tumors/group). Note the significant difference in MVD for VAE versus r-HSV (*P<0.001), PBS versus VAE (**P<0.001), and Endostar versus VAE (***P<0.001).</p

Expression of the exogenous endo–angio fusion gene and the activity of the fusion protein in vitro and in vivo.

<p>(A) RT–PCR results indicated that a significant induction of endo–angio mRNA expression existed after VAE infection in vitro and in vivo. By contrast, only the internal standard control, GAPDH, could be detected in the r-HSV-, Endostar-, and PBS-treated groups. (B) Cell lysates and ECM were harvested 48 h after infection, and the orthotopically implanted tumors were harvested 10 d after injection, as described in the Materials and Methods section. The temporal pattern of the expression of endo–angio was investigated via western blot analysis of cell lysates and ECM for the in vitro experiments, and proteins extracted from the tumors for the in vivo experiments. Western blotting results indicated that a 58 kDa fusion protein recognized by the endostatin antibody was present in the VAE group, but not in the r-HSV group or the Endostar group. β-actin was detectable in all samples.</p

In Operando Probing of Sodium-Incorporation in NASICON Nanomaterial: Asymmetric Reaction and Electrochemical Phase Diagram

NASICON-type materials are one of the most promising cathodes for sodium-ion batteries (SIBs) due to their stable structure and the three-dimensional framework for the migration of Na⁺. During the usage of SIBs, they should hold the ability to endure sudden changes in temperature and current density, which have a profound impact on battery life. However, little research focused on the reaction mechanism under the above situations. Here, the phase transformation processes of NASICON-type material, Na₃V₂(PO₄)₃, are investigated by applying high-resolution in situ X-ray diffraction and Raman coupled with electrochemical tests under different temperatures (273 and 293 K) and scan rates (0.5, 2, and 5 mV s^–1). The results demonstrate that the phase evolution process is one-phase solid solution during the desodiation process rather than the traditionally two-phase reaction at a high scan rate or low temperature. An electrochemical phase diagram is also drawn based on thein situ results, which can be used to explain the asymmetric result. This work can help with understanding the phase evolution process of NASICON-type cathodes, as well as guiding the application of SIBs in various working conditions

High-Performance Na–O₂ Batteries Enabled by Oriented NaO₂ Nanowires as Discharge Products

Na–O₂ batteries are emerging rechargeable batteries due to their high theoretical energy density and abundant resources, but they suffer from sluggish kinetics due to the formation of large-size discharge products with cubic or irregular particle shapes. Here, we report the unique growth of discharge products of NaO₂ nanowires inside Na–O₂ batteries that significantly boosts the performance of Na–O₂ batteries. For this purpose, a high-spin Co₃O₄ electrocatalyst was synthesized via the high-temperature oxidation of pure cobalt nanoparticles in an external magnetic field. The discharge products of NaO₂ nanowires are 10–20 nm in diameter and ∼10 μm in length, characteristics that provide facile pathways for electron and ion transfer. With these nanowires, Na–O₂ batteries have surpassed 400 cycles with a fixed capacity of 1000 mA h g^–1, an ultra-low over-potential of ∼60 mV during charging, and near-zero over-potential during discharging. This strategy not only provides a unique way to control the morphology of discharge products to achieve high-performance Na–O₂ batteries but also opens up the opportunity to explore growing nanowires in novel conditions

Facile Synthesis of Hierarchical Cu₂MoS₄ Hollow Sphere/Reduced Graphene Oxide Composites with Enhanced Photocatalytic Performance

We present a controllable synthesis of ternary hierarchical hollow sphere, assembling by numerous particle-like Cu₂MoS₄, via a facile hydrothermal method. By adding graphene oxides (GO) in the reaction process, Cu₂MoS₄/reduced graphene oxide (RGO) heterostructures were obtained with enhanced photocurrent and photocatalytic performance. As demonstrated by electron microscopy observations and X-ray characterizations, considerable interfacial contact was achieved between hierarchical Cu₂MoS₄ hollow sphere and RGO, which could facilitate the separation of photoinduced electrons and holes within the hybrid structure. In comparison with the pure Cu₂MoS₄ hollow sphere, the obtained hybrid structures exhibited significantly enhanced light absorption property and the ability of suppressing the photoinduced electron–holes recombination, which led to significant enhancement in both photocurrent and efficiency of photocatalytic methyl orange (MO) degradation under visible light (λ > 420 nm) irradiation

Multifield-Modulated Spintronic Terahertz Emitter Based on a Vanadium Dioxide Phase Transition

The efficient generation and active modulation of terahertz (THz) waves are strongly required for the development of various THz applications such as THz imaging/spectroscopy and THz communication. In addition, due to the increasing degree of integration for the THz optoelectronic devices, miniaturizing the complex THz system into a compact unit is also important and necessary. Today, integrating the THz source with the modulator to develop a powerful, easy-to-adjust, and scalable or on-chip THz emitter is still a challenge. As a new type of THz emitter, a spintronic THz emitter has attracted a great deal of attention due to its advantages of high efficiency, ultrawide band, low cost, and easy integration. In this study, we have proposed a multifield-modulated spintronic THz emitter based on the VO2/Ni/Pt multilayer film structure with a wide band region of 0–3 THz. Because of the pronounced phase transition of the integrated VO2 layer, the fabricated THz emitter can be efficiently modulated via thermal or electric stimuli with a modulation depth of about one order of magnitude; the modulation depths under thermal stimulation and electrical stimulation were 91.8% and 97.3%, respectively. It is believed that this multifield modulated spintronic THz emitter will provide various possibilities for the integration of next-generation on-chip THz sources and THz modulators