Intermetallic Pd3Pb nanocrystals with controlled size and cubic geometry exposing (100) facets are synthesized and tested as electrocatalysts for ethanol oxidation in alkaline media. We observe the ...ethanol oxidation activity and stability to be size-dependent. The 10 nm Pd3Pb nanocrystals display the highest initial current densities, but after few hundred cycles, the current density of smaller nanocrystals becomes much larger. All of the catalysts exhibit a pronounced current decay during the first 500 s of continuous operation, which is associated with the accumulation of strongly adsorbed reaction intermediates, blocking reaction sites. These adsorbed species can be removed by cycling the catalysts or maintaining them at slightly higher potentials for a short period of time to oxidize and later reduce the Pd surface. Such simple cleaning processes, that can be performed during operation breaks without cell disassembly, is sufficient to effectively remove the poisoning species adsorbed on the surface and recover the electrocatalytic activity.
•Interfacial mass transfer was accelerated by optimizing gradient porosity.•Water management efficiency was improved by optimizing structural design.•Hydraulic barrier is dominated by the direction ...of gradient hydrophobicity.•Self-humidifying property bases on balance of hydrophobicity and permeability.
Proton exchange membrane fuel cells (PEMFCs) are expected to reveal high adaptability at different operating conditions. One of the key challenges is interfacial water management of microporous layer (MPL) at dry condition. In this paper, MPLs with different structure were prepared for self-humidifying PEMFCs. It was found that when hydrophilic and hydrophobic carbon powder were respectively applied near catalyst layer (CL) and macroporous substrate (MPS), the membrane electrode assembly (MEA) revealed a stable performance at varying humidity condition. When carbon powder employed in the opposite structure, a hydraulic barrier formed at the interface of CL and MPL. These results were demonstrated by a three-dimensional numerical modeling that the intrusion of product water into the hydrophobic pore was decelerated. The gradient-porous MPLs were also prepared to evaluate their practicability at dry condition. Significantly, the MEAs containing gradient-porous MPL revealed a high response on humidity condition. It is attributed that the high pore volume provided more space for gas permeation, and the gradient-porous structure accelerated the water removal. Hence, this work reveals the relation between structural design and performance of MPL at relatively dry conditions. The findings in this study provide a promising strategy for the optimization of self-humidifying PEMFCs.
Gradient structural design of microporous layer (MPL) is useful to improve the interfacial water management efficiency of self-humidifying PEMFCs at varying humidity condition. Display omitted
This paper proposes a theory based on stereovision to estimate the relative position and attitude between non-cooperative spacecrafts. Good performance of the scheme can be presented even with ...outliers in real time observation. As the information of non-cooperative spacecraft in space is not accessible, a full consideration to the target freely tumbling in space is given. Firstly, relative position and orientation equation is derived from target's dynamics model. The extended Kalman filter (EKF) is designed to estimate the relative position and relative attitude by using the observation data provided by stereovision system. In addition, the full-dimensional state estimator is used to improve the precious of the relative position estimation. Furthermore, M-estimation is applied to improve the robustness and reliability of the previous mentioned algorithms. Simulation results demonstrate the effectiveness and convergence of the proposed algorithm. The filtering algorithms with M-estimation can effectively improve the accuracy of relative navigation for non-cooperative spacecraft when the images data is affected by outliers.
The barium hexaaluminate (BHA) supported Co3O4 catalysts (XCo/BHA) with varied mass loading of Co (X = 10%, 20%, 30%, 35% and 40%) were prepared by impregnating Co3O4 nanoparticles (NPs) onto BHA ...support that synthesized through urea combustion method. The catalyst was characterized by high-resolution transmission electron microscope (HRTEM), temperature programmed reduction (TPR), temperature programmed desorption (TPD) and valued the ammonia decomposition performance by fixed-bed reactor. The results showed that Co3O4 NPs were dispersed densely on the BHA surface, with the strong alkaline support that could adjust the binding energy of the active sites and the nitrogen, which was conducive to the ammonia decomposition reaction. Among the synthesized catalysts, 35Co/BHA achieves 87.2% ammonia conversion at 500 °C with a space velocity of 30000 ml gcat−1 h−1, corresponding to a hydrogen production rate of 29.2 mmol H2 gcat−1 min−1, and also shows excellent catalytic stability.
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•BHA supported Co3O4 is highly active toward ammonia decomposition.•35Co/BHA presents the optimal ammonia conversion rate.•BHA acts as electron donor to promote ammonia decomposition.•Co3O4 NPs are densely dispersed on BHA with increased pore volume.
Electrolysis of water has been one of the most promising approaches for renewable energy resources while the efficient oxygen evolution reaction (OER) remains challenging. Herein, a series of ...different ratio of Se doped Co3O4 nanoparticles XSe-Co3O4 are prepared by hydrothermal method and applied as OER electrocatalysts. Se2− is doped into the Co3O4 crystal lattice by substituting of O2− and a large number of oxygen vacancies are generated, which provides more available activity sites for OER. Se doping increases the surface ratio of Co2+/Co3+ and accelerates the electron transport that favors OER activity promotion. The optimized doping ratio of 6%Se–Co3O4 presents low overpotential of 281 mV at 10 mA cm−2, as well as a low Tafel slope of 70 mV dec−1 in 1 M KOH solution, which has great advantages compared to the recently reported Co3O4-based OER electrocatalysts. This work provides new ideas for the development of efficient Co3O4-based OER electrocatalysts.
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•Se2− was doped into the Co3O4 and oxygen vacancies were generated.•Se doping increases the ratio of Co2+/Co3+ and accelerates electron transport.•Se doped with Co3O4 increases the charge transfer efficiency in the OER process.•The 6%Se–Co3O4 presents high OER activity with 281 mV@10 mA cm−2.
Lymphaticovenous anastomosis (LVA) is an effective surgical treatment for lymphorrhea. However, the traditional indocyanine green (ICG) fluorescent lymphography mapping for lymphatic vessels has ...limitations, it can only depict the initial capillary lymphatic network localized in the dermis of the skin, which cannot visualize lymphatics deeper than 1.5 cm. A new mapping technique, microbubbles and contrast-enhanced ultrasound (CEUS) can address the problem. In one case of lymphocutaneous fistula, for the first time, we used microbubbles and CEUS technique for preoperative localization for LVAs. Microbubbles and CEUS can identify deep lymphatic vessels and better evaluate the function of lymphatic vessels. The patient's symptoms of edema and lymphorrhea improved clinically. Microbubbles and CEUS is an effective methods for identifying lymphatic vessels in lower limbs.
Chemosensory proteins (CSPs) can bind and transport odorant molecules and play important roles in insect chemoreception. In this study, we focused on the roles of a chemosensory protein (BodoCSP1) in ...perception of host plant volatiles in Bradysia odoriphaga. The expression of BodoCSP1 was significantly higher in adults than in larvae and pupae, without a significant difference between male and female adults. Recombinant protein BodoCSP1 exhibited relatively high binding affinities to 9 out of 10 tested ligands (K i < 10 μM). Behavioral assays revealed that adults of B. odoriphaga showed a significant preference for five compounds. The predicted three-dimensional (3D) structure of BodoCSP1 has the typical six α-helices that form the hydrophobic ligand-binding pocket. Molecular docking and site-directed mutagenesis combined with ligand-binding assays indicated that Val48 and Thr66 may be the key binding site in BodoCSP1 for host plant volatiles. RNAi results indicated that dsBodoCSP1-treated adults showed significant reductions in response to diallyl disulfide, dipropyl disulfide, and allyl methyl disulfide. These results indicated that BodoCSP1 plays essential functions in the perception of host plant volatiles in B. odoriphaga.
The structure majorization called Water Guide optimizes both the output performance and durability of PEMFCs.
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•The structure majorization is designed on the surface of microporous ...layer (MPL).•The special structure called Water Guide has certain size and regular shape.•Structure majorization improves the efficiency water management and mass transfer.•Durability is tested under Worldwide Harmonized Light Duty Test Cycle condition.•MPL with proper size of Water Guides has the best performance and durability.
Proton exchange membrane fuel cell (PEMFC) is regarded as a potential future power source for automotive applications. Microporous layer (MPL) enhances the output performance and durability of PEMFCs by regulating water management. In this study, the structure majorization on the surface of MPL is investigated for the first time. Polymethyl Methacrylate (PMMA), a kind of pore agent that can form specific size and regular shape, is used in this paper to create the special structure. Worldwide Harmonized Light-duty Test Cycle (WLTC) operating condition is used in durability tests, which is in line with the actual application conditions of PEMFC. The sample with smaller PMMA (MPL-S) exhibits predominant performance, maximum power density reaching 1.30 W/cm2 under the humidification of 100%RH (relative humidity). After online durability test, MPL-S best maintains its performance. The maximum power density of MPL-S only drops by 10.6% after 100 h durability test. Results can prove that water is uniformly guided into the structure and then discharged, not hindering the contact between the gas and active sites of the catalyst. The mass transfer resistance is reduced and the drainage capacity is improved. The majorization is instructive for water management research on MPL in PEMFCs and the durability under WLTC operating condition can be used as a reference for practical applications.
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