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51.
《International Journal of Hydrogen Energy》2021,46(55):28078-28086
Interfacial hydrophobic/hydrophilic reaction fields significantly affect various reactions at the electrode surface. The hydrogen evolution reaction (HER) and the hydrogen oxidation reaction (HOR) have been investigated on single crystal Pt electrodes modified with hydrophobic/hydrophilic cations and anion-exchange copolymers in alkaline solutions. In alkali metal hydroxide solutions, Pt (110) exhibits the highest HER/HOR activity in the low-index planes of Pt. On the low-index planes of Pt, the hydrophilicity of the alkali metal cation in the supporting electrolyte activates the HER/HOR depending on its hydration energy. Hydrophilic cations at the interface facilitate the extraction of hydrogen from the hydrated water. The modification of anion-exchange copolymers with a hydrophobic skeleton on Pt (110) further enhanced the HER/HOR activity. The hydrogen bonding network formed around the hydrophobic species facilitated the mobility of water molecules and the OH− as the reactant/product of the HER/HOR. Appropriately forming hydrophilic and hydrophobic reaction fields at the interface improved the HER/HOR activity. 相似文献
52.
Gokce S. Avcioglu Berker Ficicilar Inci Eroglu 《International Journal of Hydrogen Energy》2018,43(23):10779-10797
Cathode catalyst layer has an important role on water management across the membrane electrode assembly (MEA). Effect of Pt percentage in commercial catalyst and Pt loading from the viewpoint of activity and water management on performance was investigated. Physical and electrochemical characteristics of conventional and hydrophobic catalyst layers were compared. Performance results revealed that power density of conventional catalyst layers (CLs) increased from 0.28 to 0.64 W/cm2 at 0.45 V with the increase in Pt amount in commercial catalyst from 20% to 70% Pt/C for H2/Air feed. In the case of H2/O2 feed, power density of CLs increased from 0.64 to 1.29 W/cm2 at 0.45 V for conventional catalyst layers prepared with Tanaka. Increasing Pt load from 0.4 to 1.2 mg/cm2, improved kinetic activity at low current density region in both feeding conditions. Scattering electron microscopy (SEM) images revealed that thickness of the catalyst layers (CLs) increases by increasing Pt load. Electrochemical impedance spectroscopy (EIS) results revealed that thinner CLs have lower charge transfer resistance than thicker CLs. Inclusion of 30 wt % Polytetrafluoroethylene (PTFE) nanoparticles in catalyst ink enhanced cell performance for the electrodes manufactured with 20% Pt/C at higher current densities. However, in the case of 70% Pt/C, performance enhancement was not observed. Cyclic voltammetry (CV) results revealed that 20% Pt/C had higher (77 m2/g) electrochemical surface area (ESA) than 70% Pt/C (65 m2/g). In terms of hydrophobic powders, ESA of 30PTFE prepared with 70% Pt/C was higher than 30PTFE prepared with 20 %Pt/C. X-Ray Diffractometer (XRD) results showed that diameter of Pt particles of 20% Pt/C was 2.5 nm, whereas, it was 3.5 nm for 70% Pt/C, which confirms CV results. Nitrogen physisorption results revealed that primary pores of hydrophobic catalyst powder prepared with 70% Pt/C was almost filled (99%) with Nafion and PTFE. 相似文献
53.
惯性约束聚变冷冻靶中氘氘(D2)冰层的质量对聚变实验的成功与否起重要作用。目前文献报道的制备冷冻靶D2冰层的方法并不具备好的可操作性,且技术、工艺不定型,制约了高质量冰层的形成。因此,本文采用将温度梯度、降温速率和温度冲击相结合的技术实现燃料冰层在靶丸内的均化。通过温度控制以及施加温度冲击可控地形成残留冰,并在残留冰的控制技术基础上,实现了高质量冰层的可控结晶生长。同时,研究了温度控制对靶丸内D2冰层品质的影响和D2冰层结晶生长的过程,并应用晶体生长动力学理论分析了D2冰层结晶生长行为。从背光阴影图像中的D2冰层亮环可知,D2冰层均匀度为85.2%、厚度为40.35 μm、内表面粗糙度为2.15 μm。本方法拓宽了超低温下D2冰籽晶控制、晶体生长技术,为DT冷冻靶中冰层均化打下了坚实基础,并形成了一定的技术储备。 相似文献
54.
通过对铝金属化纸领域专利技术的收集、分析、标引,介绍了铝金属化纸的制备方法及种类,包括铝粉涂布、铝箔纸以及可降解回收的真空镀铝纸等;并对其专利申请量、区域分布以及渡铝技术进行了分析,同时对各技术的发展历程和改进情况进行了梳理归纳。 相似文献
55.
Casey Jessop Johan Ahlstrm Christer Persson Yubin Zhang 《Fatigue & Fracture of Engineering Materials & Structures》2020,43(1):201-208
Rolling contact fatigue cracks and thermally induced defects are common problems in the railway industry especially as demands for increasing loads, speeds, and safety continue to rise. Often, the two types of defects are found together in the field, however, whether one causes the other to occur is not completely agreed upon. The effect of thermal damage, in the form of a martensite spot on pearlitic steel test bars, on the fatigue life in uniaxial low cycle fatigue experiments was investigated by the authors. However, the focus of the current work was to characterize the damage evolution from the low cycle fatigue (LCF) tests and correlate the crack initiation and propagation with the initial thermal damage. Residual stress measurements, digital image correlation, and X‐ray tomography were used to characterize the effects of the thermal damage before, during, and after fatigue testing, respectively. It was found that the thermal damage causes strain accumulation and crack initiation at the interface between the two materials. The strain evolution was visualized using digital image correlation (DIC), clearly showing the strain concentrations at the top and bottom of the white etching layers (WEL), where the residual stresses are also most tensile. X‐ray tomography confirmed the planar crack growth from the martensite spot. 相似文献
56.
57.
《Journal of the European Ceramic Society》2020,40(15):5634-5645
Na2AlTi(PO4)3 (NATP) and Na1.8Al0.8Ge1.2(PO4)3 (NAGP) NASICON (Na-Superionic Conductor) glass-ceramics are obtained by applying different single (SHT) and double (DHT) heat treatments on the respective precursor glass to evaluate its effect on the microstructure and in turn, on the total ionic conductivity. The grain and grain boundary contributions are also analyzed in the NATP composition. SHT with longer crystallization times favors the development of well-defined grains in both compositions and also promotes the grain growth in NAGP samples. This behavior causes a decrease in the activation energy of the grain boundary, which enhances the total ionic conductivity. Regarding DHT samples, microstructure with larger grains and higher ionic conductivity were obtained with shorter nucleation times for NATP and NAGP compositions. Finally, the microstructural variation generated by the different thermal treatments causes the total conductivity to increase up to two times. 相似文献
58.
《Ceramics International》2020,46(17):27219-27225
Designing double metal-dielectric (cermet) solar selective absorber coatings (SSACs) often requires complex co-sputtering techniques with multiple targets. This inevitably limits the simple and low-cost industrial fabrication. Here, we develop novel nano-multilayered MoOx-based SSACs by simple and stable one-step reactive magnetron sputtering process using single molybdenum target. The proposed multilayer SSACs exhibit good solar absorptance of 0.93 and low thermal emittance of 0.06. Owing to the temperature-induced oxygen diffusion and oxidation phenomenon the as-sputtered SSACs have a poor thermal tolerance under air atmosphere, and after annealing at 200 °C for 150 h, the resulting absorptance is diminished from 0.93 to 0.90. However, the optical performance of the annealed SSAC is relatively stable in high-vacuum environment, even after annealing at 450 °C for 200 h, it still displays an ideal spectral selectivity of 0.92/0.07. With above properties, the resulting MoOx-based SSAC is a promising absorber for enduring thermal harvesting in solar vacuum collectors. 相似文献
59.
《International Journal of Hydrogen Energy》2020,45(15):8094-8106
A titanium Porous Transport Layer (PTL) is usually used at the anode side of PEM water electrolyzers to ensure both the gas/water transport and the electric charges transfer. In this paper, four different sintered Ti powder PTLs were characterized to determine some properties, such as the pore size distribution, the porosity, and the permeability. Their influence on the electrolysis performance was investigated by using a 30 cm2 segmented cell which allowed measuring the current density distribution, while controlling temperature and pressure conditions. For a better understanding, in-situ techniques such as the Polarization Curves and the Electrochemical Impedance Spectroscopy (EIS) were used. A local characterization of mass transport limitations caused by oxygen saturation was carried out, paying special attention to the pressure influence when using a PTL with very small pores. The results showed that current density heterogeneities can be explained by microstructure changes along the PTL. The optimal geometric characteristics of the PTL depend not only on the operating conditions such as current density, pressure, and temperature but also on the catalyst layer properties. A new model for the constriction resistance between the catalyst layer and the PTL was proposed. 相似文献
60.
In this work, CuInS2/multiwalled carbon nanotube (MWCNT) layers are fabricated by the sol–gel spin-coating method. We introduce two forms of MWCNTs into a CIS2 solution, washed functional multiwalled carbon nanotubes (W-FMWCNTs) and unwashed-functional multiwalled carbon nanotubes (UW-FMWCNTs), in order to investigate the effects of MWCNTs and an acidic environment on the physical properties of the CIS2 absorber layers. The structure and morphology of the samples are investigated by X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM), respectively. The XRD study shows that all samples crystallize in a tetragonal structure. The results obtained from the optical, thermo-electric, and electrical measurements indicate that the two groups of CIS2 layers prepared using W- and UW-FMWCNTs show the opposite behaviors. The Seebeck coefficient (SC) measurements indicate possible formation of a p–n junction. 相似文献