Porous adsorbents such as MOF-5 have low thermal conductivities which can limit the performance of adsorption-based hydrogen storage systems. To improve the thermal properties of these materials, we ...have prepared a series of high-density MOF-5 composites containing 0–10 wt % expanded natural graphite (ENG), which serves as a thermal conduction enhancer. The addition of 10 wt % ENG to MOF-5 and compaction to 0.5 g/cm3 was previously found to increase the thermal conductivity relative to neat MOF-5 of the same density by a factor of 5. In this study, detailed measurements of the hydrogen storage behavior of MOF-5/ENG composites between 77 and 295 K are reported. We find that MOF-5 pellets with 0 wt % ENG and a density of 0.5 g/cm3 have a total volumetric hydrogen storage density at 77 K and 100 bar that is 23% larger than powder MOF-5 and 41% larger than cryo-compressed hydrogen. The addition of 10% ENG to 0.5 g/cm3 MOF-5 pellets produces only a small decrease (6%) in the total volumetric hydrogen storage compared to neat MOF-5 pellets of equal density. The excess, absolute, total, and deliverable hydrogen storage amounts by the MOF-5 composites are compared for ENG additions of 0–10 wt % and pellet densities of 0.3–0.7 g/cm3. Three adsorption models (Unilan, Tóth, Dubinin–Astakhov) are compared for their effectiveness in describing hydrogen adsorption isotherms of MOF-5 and MOF-5/ENG composites. The Unilan model provides the most accurate description of the experimental data, requiring only five temperature-invariant parameters to accurately fit the data across a wide temperature range.
•We assess the thermophysical properties of an industrial, pilot-scale version of MOF-5.•Assessed properties include: packing density, thermal conductivity, heat capacity, and stability against ...hydrolysis.•The data are essential ingredients in the development of MOF-based systems for catalysis, separations, and adsorption.
We present a comprehensive assessment of the thermophysical properties of an industrial, pilot-scale version of the prototype adsorbent, metal–organic framework 5 (MOF-5). These properties are essential ingredients in the design and modeling of MOF-5-based hydrogen adsorption systems, and may serve as a useful starting point for the development of other MOF-based systems for applications in catalysis, gas separations, and adsorption of other gasses or fluids. Characterized properties include: packing density, surface area, pore volume, particle size distribution, thermal conductivity, heat capacity, stability against hydrolysis, differential enthalpy of H2 adsorption, and Dubinin–Astakhov isotherm parameters. Hydrogen adsorption/desorption isotherms were measured at six temperatures spanning the range 77–295K, and at pressures of 0–100bar.
To address the issues of not accurately identifying ice types and thickness in current fiber-optic ice sensors, in this paper, we design a novel fiber-optic ice sensor based on the reflected light ...intensity modulation method and total reflection principle. The performance of the fiber-optic ice sensor was simulated by ray tracing. The low-temperature icing tests validated the performance of the fiber-optic ice sensor. It is shown that the ice sensor can detect different ice types and the thickness from 0.5 to 5 mm at temperatures of -5 °C, -20 °C, and -40 °C. The maximum measurement error is 0.283 mm. The proposed ice sensor provides promising applications in aircraft and wind turbine icing detection.
Acoustic metasurfaces, as two-dimensional acoustic metamaterials, are a current research topic for their sub-wavelength thickness and excellent acoustic wave manipulation. They hold significant ...promise in noise reduction and isolation, cloaking, camouflage, acoustic imaging, and focusing. Resonant structural units are utilized to construct acoustic metasurfaces with the unique advantage of controlling large wavelengths within a small size. In this paper, the recent research progresses of the resonant metasurfaces are reviewed, covering the design mechanisms and advances of structural units, the classification and application of the resonant metasurfaces, and the tunable metasurfaces. Finally, research interest in this field is predicted in future.
Amorphous carbon (a-C) film about 3
μm in thickness is coated on 316L stainless steel by close field unbalanced magnetron sputter ion plating (CFUBMSIP). The AFM and Raman results reveal that the a-C ...coating is dense and compact with a small size of graphitic crystallite and large number of disordered band. Interfacial contact resistance (ICR) results show that the surface conductivity of the bare SS316L is significantly increased by the a-C coating, with values of 8.3–5.2
mΩ
cm
2 under 120–210
N/cm
2. The corrosion potential (
E
corr) shifts from about −0.3
V vs SCE to about 0.2
V vs SCE in both the simulated anode and cathode environments. The passivation current density is reduced from 11.26 to 3.56
μA/cm
2 with the aid of the a-C coating in the simulated cathode environment. The a-C coated SS316L is cathodically protected in the simulated anode environment thereby exhibiting a stable and lower current density compared to the uncoated one in the simulated anode environment as demonstrated by the potentiostatic results.
In the present study, the effects of TiCl3 on desorption kinetics, absorption/desorption reversibility, and related phase transformation processes in LiBH4/CaH2/TiCl3 hydrogen storage system was ...studied systematically by varying its concentration (x = 0, 0.05, 0.15 and 0.25). The results show that LiCl forms during ball milling of 6LiBH4/CaH2/xTiCl3 and that as temperature increases, o-LiBH4 transforms into h-LiBH4, into which LiCl incorporates, forming solid solution of LiBH4 times LiCl, which melts above 280 degree C. Molten LiBH4 times LiCl is more viscous than molten LiBH4, preventing the clustering of LiBH4 and the accompanied agglomeration of CaH2, and thus preserving the nano-sized phase arrangement formed during ball milling. Above 350 degree C, the molten solution LiBH4 times LiCl further reacts with CaH2, precipitating LiCl. The main hydrogen desorption reaction is between molten LiBH4 times LiCl and CaH2 and not between molten LiBH4 and CaH2. This alters the hydrogen reaction thermodynamics and lowers the hydrogen desorption temperature. In addition, the solid-liquid nano-sized phase arrangement in the nano-composites improves the hydrogen reaction kinetics. The reversible incorporation/precipitation of LiCl at the hydrogen reaction temperature and during temperature cycling makes the 6LiBH4/CaH2/0.25TiCl3 nano-composite a fully reversible hydrogen storage material. These four states of LiCl in LiBH4/CaH2/TiCl3 system, i.e. "formed-solid solution-molten solution-precipitation", are reported for the first time and the detailed study of this system is beneficial to further improve hydrogen storage property of complex hydrides.
A nickel-rich layer about 100
μm in thickness with improved conductivity was formed on the surface of austenitic stainless steel 316L (SS316L) by ion implantation. The effect of ion implantation on ...the corrosion behavior of SS316L was investigated in 0.5
M H
2SO
4 with 2
ppm HF solution at 80
°C by potentiodynamic test. In order to investigate the chemical stability of the ion implanted SS316L, the potentiostatic test was conducted in an accelerated cathode environment and the solutions after the potentiostatic test were analyzed by inductively coupled plasma atomic emission spectrometer (ICP-AES). The results of potentiodynamic test show that the corrosion potential of SS316L is shifted toward the positive direction from −0.3
V versus SCE to −0.05
V versus SCE in anode environment and the passivation current density at 0.6
V is reduced from 11.26 to 7.00
μA
cm
−2 in the cathode environment with an ion implantation dose of 3
×
10
17
ions
cm
−2. The potentiostatic test results indicate that the nickel implanted SS316L has higher chemical stability in the accelerated cathode environment than the bare SS316L, due to the increased amount of metallic Ni in the passive layer. The ICP results are in agreement with the electrochemical test results that the bare SS316L has the highest dissolution rate in both cathode and anode environments and the Ni implantation markedly reduces the dissolution rate. A significant improvement of interfacial contact resistance (ICR) is achieved for the SS316L implanted with nickel as compared to the bare SS316L, which is attributed to the reduction in passive layer thickness caused by the nickel implantation. The ICR values for implanted specimens increase with increasing dose.
Nitrogen plasma immersion ion implantation (PIII), a non-line-of-sight surface treatment technique suitable for bipolar plates in polymer electrolyte membrane fuel cells, is conducted at low and high ...temperature to improve the corrosion resistance and conductivity of titanium sheets. X-ray photoelectron spectroscopy (XPS) shows that high-temperature (HT) nitrogen PIII produces a thick oxy-nitride layer on the titanium surface. This layer which provides good corrosion resistance and high electrical conductivity as verified by electrochemical tests, inductively coupled plasma optical emission spectroscopy, and interfacial contact resistance (ICR) measurements renders the materials suitable for polymer electrolyte membrane fuel cells. In comparison, the low-temperature (LT) PIII titanium sample exhibits poorer corrosion resistance and electrical conductivity than the untreated titanium control.
Recent efforts have been made to develop high-capacity complex hydride composites by combining alanates and amides. The hydrogen storage mechanisms in those composites are not unambiguously clarified ...because of chemical reactions during the sample preparation process. In this Article, we have studied the effects of sample preparation conditions on the phase stability of a mixture of 3Mg(NH2)2–2Li3AlH6 and identified that unlike high-energy ball-milling light mixing generates a physical mixture of the reactants without decomposition. Subsequently, the hydrogen storage properties, the desorption pathway, and the reversible reaction mechanism of the composite were investigated through a combination of kinetic measurements and phase and microstructure analyses. The results reveal that the first step of hydrogen release (initiated at 170 °C) involves decomposition of Li3AlH6 to LiH and Al. The second step of hydrogen release occurs as the temperature increases (to 230 °C) when Mg(NH2)2 reacts with LiH to form Li2Mg(NH)2. If desorption of the 3Mg(NH2)2–2Li3AlH6 mixture is limited to a temperature of 400 °C, then the reversible reaction takes place between Li2Mg(NH)2 (plus H2) and LiH and Mg(NH2)2. We find that the Al generated from the first hydrogen release step does not participate in the reversible hydrogen storage process and instead inhibits mass transfer that results in higher desorption temperatures (and low desorption rates) and lowers the overall reversible capacity (2.7 wt %) as compared with the neat reaction (i.e., ∼4.3 wt % without the presence of Al).
Contact resistance between the bipolar plate (BPP) and the gas diffusion layer (GDL) plays a significant role on the power loss in a proton exchange membrane (PEM) fuel cell. There are two types of ...contact behavior at the interface of the BPP and GDL, which are the mechanical one and the electrical one. Furthermore, the electrical contact behavior is dependent on the mechanical one. Thus, prediction of the contact resistance is a coupled mechanical–electrical problem. The current FEM models for contact resistance estimation can only simulate the mechanical contact behavior and moreover they are based on the assumption that the contact surface is equipotential, which is not the case in a real BPP/GDL assembly due to the round corner and margin of the BPP.
In this study, a mechanical–electrical FEM model was developed to predict the contact resistance between the BPP and GDL based on the experimental interfacial contact resistivity. At first, the interfacial contact resistivity was obtained by experimentally measuring the contact resistance between the GDL and a flat graphite plate of the same material and processing conditions as the BPP. Then, with the interfacial contact resistivity, the mechanical and electrical contact behaviors were defined and the potential distribution of the BPP/GDL assembly was analyzed using the mechanical–electrical FEM model. At last, the contact resistance was calculated according to the potential drop and the current of the contact surface. The numerical results were validated by comparing with those of the model reported previously. The influence of the round corner of the BPP on the contact resistance was also studied and it is found that there exists an optimal round corner that can minimize the contact resistance. This model is beneficial in understanding the mechanical and electrical contact behaviors between the BPP and GDL, and can be used to predict the contact resistance in a new BPP/GDL assembly.
