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991.
A novel proton exchange membrane using phosphotungstic acid (HPW) as proton carrier and cubic bicontinuous Ia3d mesoporous silica (meso-silica) as framework material is successfully developed as proton exchange membranes for fuel cells. Meso-silica is functionalized by 80wt% HPW using a vacuum impregnation method. The HPW-functionalized meso-silica (HPW-meso-silica) nanocomposites are characterized by transmission electron microscopy (TEM), small angle X-ray scattering (SAXS), N(2) adsorption/desorption isotherms, thermogravimetric analysis (TGA), water uptake and four-probe conductivity. The results show that the mesoporous structure of silica hosts can be altered by the hydrothermal temperature. Conductivity measurements indicate that meso-silica host with pore diameter of 5.0 nm has the highest proton conductivity of 0.11 S cm(-1) at 80 °C and 100% relative humidity (RH) with an activation energy of ~14 kJ mol(-1) and better stability as compared to that with large mesopores. The proton conductivity and performance of HPW-meso-silica nanocomposites also increase with the RH, but it is far less sensitive to RH changes as compared to conventional perfluorosulfonic acid (PFSA) polymers such as Nafion. The maximum power density of the cell with HPW-meso-silcia nanocomposite membranes is 221 mW cm(-2) at 80 °C and 100% RH and decreases to 171 mW cm(-2) when RH is reduced to 20%, a 20% decrease in power output. In the case of a cell with Nafion 115 membranes, the decrease in power density is 95% under identical test conditions. The results demonstrate that the HPW-meso-silica nanocomposite has an exceptionally high water retention capability and is a promising proton exchange membrane material for fuel cells operating at reduced humidity and elevated temperatures. 相似文献
992.
The capacity of Ti-capped sp carbon atomic chains for use as hydrogen storage media is studied using first-principles density functional theory. The Ti atom is strongly attached at one end of the carbon chains via d-p hybridization, forming stable TiC(n) complexes. We demonstrate that the number of adsorbed H(2) molecules on Ti through Kubas interactions depends upon the chain types. For polyyne (n even) or cumulene (n odd) structures, each Ti atom can hold up to five or six H(2) molecules, respectively. Furthermore, the TiC(5) chain effectively terminated on a C(20) fullerene can store hydrogen with an optimal binding energy of 0.52 eV per H(2) molecule. Our results reveal a possible way to explore high-capacity hydrogen storage materials in truly one-dimensional carbon structures. 相似文献
993.
The wetting behavior of spherical nanoparticles at a vapor-liquid interface is investigated by using density functional theory, and the line tension calculation method is modified by analyzing the total energy of the vapor-liquid-particle equilibrium. Compared with the direct measurement data from simulation, the results reveal that the thermodynamically consistent Young's equation for planar interfaces is still applicable for high curvature surfaces in predicting a wide range of contact angles. The effect of the line tension on the contact angle is further explored, showing that the contact angles given by the original and modified Young's equations are nearly the same within the region of 60° < θ < 120°. Whereas the effect is considerable when the contact angle deviates from the region. The wetting property of nanoparticles in terms of the fluid-particle interaction strength, particle size, and temperature is also discussed. It is found that, for a certain particle, a moderate fluid-particle interaction strength would keep the particle stable at the interface in a wide temperature range. 相似文献
994.
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996.
In this paper, we analyze a cascadic multigrid method for semilinear elliptic problems in which the derivative of the semilinear term is Hölder continuous. We first investigate the standard finite element error estimates of this kind of problem. We then solve the corresponding discrete problems using the cascadic multigrid method. We prove that the algorithm has an optimal order of convergence in energy norm and quasi-optimal computational complexity. We also report some numerical results to support the theory. 相似文献
997.
Zhang Xiaoming Zeng Chao Li Denghui Xie Jianhua Grebogi Celso 《Nonlinear dynamics》2021,104(4):3467-3477
Nonlinear Dynamics - Mechanical systems with dry friction are typical Filippov systems. Such class of systems have complicated dynamical behaviors due to the existence of sliding motion. In this... 相似文献
998.
Ye Jane J. Yuan Xiaoming Zeng Shangzhi Zhang Jin 《Set-Valued and Variational Analysis》2021,29(4):803-837
Set-Valued and Variational Analysis - We study linear convergence of some first-order methods such as the proximal gradient method (PGM), the proximal alternating linearized minimization (PALM)... 相似文献
999.
The diffractive optical element (DOE) is widely used to generate various illumination modes in the projection lithography system. The working principle and design methods of the DOE are discussed in detail in this paper. A mixed multi-region design method is proposed to calculate the phase of DOE based on the poor spatial coherence of excimer laser, using the Gerchberg–Saxton (GS) algorithm. The DOEs generating circular, dipole and quadrupole illumination modes are designed and simulated by three different methods: single region design, repeated multi-region design and mixed multi-region design. The performance of these DOEs are compared and analyzed with these three design methods. The mixed multi-region design method is used to design the DOEs generating three illumination modes, the diffraction efficiencies are greater than 85%, and the non-uniformities of illumination are less than 3%. The analysis results indicate that the DOE designed by the mixed multi-region design can achieve higher diffraction efficiency and illumination uniformity of the far-field intensity distribution without modifying the GS algorithm. 相似文献
1000.
Nanocrystal samples (particle size about 90 nm) of Eu3+-doped rutile titanium dioxide (TiO2) nanocrystals (rutile Eu3+/TiO2 nanocrystals) were synthesized by the sol–gel method with hydrothermal treatment. The pressure effect on photoluminescence (PL) and Raman spectra of the rutile Eu3+/TiO2 nanocrystals was investigated with a diamond anvil cell under hydrostatic pressure condition. Raman spectra of the samples at high pressures indicated that the critical pressure for the transition from the rutile phase to a new baddeleyite-type phase was between 10 and 14.2 GPa. The position of Raman bands shifted to high wavenumbers and the PL intensity of 5D 0→7F 2 transition of Eu3+ decreased down to zero with the increase of pressure before the phase transition occurred. After releasing the pressure, the rutile phase was not recovered and a α-PbO2-type phase was observed at ambient pressure. 相似文献