An experimental investigation of the feasibility of Pb based bipolar plate material for unitized regenerative fuel cells system

The unitized regenerative fuel cell (URFC) system has attracted significant attention and interests because of its round-trip energy conversion with high energy density. However, the identification of low-cost bipolar (BP) plate with higher corrosion resistance is required to produce a sustainable system. In this work, we investigated the possibilities of using cost-effective lead (Pb) metal-based plate as a BP plate material for URFC system. To further enhance the advantageous properties of Pb plate, silver (Ag) was coated onto the Pb plate. Different types of structural and microstructural analyses (XRD, XPS, SEM, EDAX, and mapping) were conducted to characterize the properties of Pb-based plate and the presence of Ag-coated layer on the surface of Pb plate. When compared with the Pb plate, the Ag-coated Pb plate exhibited a higher water contact angle. The obtained water contact angles of Pb and Ag-coated Pb plates were 77.83° and 92.21°, respectively. The obtained water contact angle of the Ag-coated Pb plate is quite acceptable in the URFC system because it offers exceptional advantages during the URFC operation. Furthermore, the interaction between Pb plate and Ag coated layer resulted in an efficient electrochemical performance. Based on these results, we could conclude that the Pb-based BP plate can be possibly considered for the URFC applications.     

Computation and investigation of mode characteristics in nonlinear system with tuned/mistuned contact interface

This study derived a novel computation algorithm for a mechanical system with multiple friction contact interfaces that is well-suited to the investigation of nonlinear mode characteristic of a coupling system. The procedure uses the incremental harmonic balance method to obtain the nonlinear parameters of the contact interface. Thereafter, the computed nonlinear parameters are applied to rebuild the matrices of the coupling system, which can be easily solved to calculate the nonlinear mode characteristics by standard iterative solvers. Lastly, the derived method is applied to a cycle symmetry system, which represents a shaft–disk–blade system subjected to dry friction. Moreover, this study analyzed the effects of the tuned and mistuned contact features on the nonlinear mode characteristics. Numerical results prove that the proposed method is particularly suitable for the study of nonlinear characteristics in such nonlinear systems.     

Improving performance of high-power indium gallium nitride/gallium nitride-based vertical light-emitting diodes by employing simple n-type electrode pattern

In this work, simple n-type electrode structures were used to enhance the electrical and optical performances of fully packaged commercially mass-produced vertical-geometry light-emitting diodes (VLEDs). The forward bias voltage of the VLED with a Y-pattern electrode increased less rapidly than that of VLEDs with a reference electrode. The VLEDs with the reference and Y-pattern electrodes exhibited forward voltages of 2.93±0.015 and 2.89±0.015 V at 350 mA and 3.77±0.015 and 3.53±0.015 V at 2000 mA, respectively. The VLEDs with the Y-pattern electrode resulted in a higher light output than the VLEDs with the reference electrode with increase in the drive current to 2000 mA. The emission images showed that the VLEDs with the Y-pattern electrode exhibited better current spreading behavior and lower junction temperatures than the VLEDs with the reference electrode. With increase in the current from 350 to 2000 mA, the VLEDs with the Y-pattern electrode experienced a 39.4% reduction in the wall plug efficiency, whereas the VLEDs with the reference electrode suffered from a 43.3% reduction.     

Direct and quantitative understanding of the non-Ohmic contact resistance in organic and oxide thin-film transistors

We explore the device physics of thin film transistors (TFTs) with non-Ohmic contacts and develop a simple and fast method for evaluating the contact properties TFTs through output characteristics. Using one single output scan, the quantitative relationship between contact resistances and drain voltage were evaluated, revealing the property of interfacial injection at non-Ohmic contacts. This is demonstrated and validated in both TFT simulations and experiments employing inorganic and organic TFTs. The approach can be applied to general TFTs with arbitrary materials and configurations conveniently and enables faster and improved understanding of TFT operation and device physics.     

Current–voltage and capacitance–voltage characteristics of Al Schottky contacts to strained Si-on-insulator in the wide temperature range

The electrical characteristics of Al/strained Si-on-insulator (sSOI) Schottky diode have been investigated using current–voltage (I–V) and capacitance–voltage (C–V) measurements in the wide temperature range of 200–400 K in steps of 25 K. It was found that the barrier height (0.57–0.80 eV) calculated from the I–V characteristics increased and the ideality factor (1.97–1.28) decreased with increasing temperature. The barrier heights determined from the C–V measurements were higher than those extracted from the I–V measurements, associated with the formation of an inhomogeneous Schottky barrier at the interface. The series resistance estimated from the forward I–V characteristics using Cheung and Norde methods decreased with increasing temperature, implying its strong temperature dependence. The observed variation in barrier height and ideality factor could be attributed to the inhomogeneities in Schottky barrier, explained by assuming Gaussian distribution of barrier heights. The temperature-dependent I–V characteristics showed a double Gaussian distribution with mean barrier heights of 0.83 and 1.19 eV and standard deviations of 0.10 and 0.16 eV at 200–275 and 300–400 K, respectively. From the modified Richardson plot, the modified Richardson constant were calculated to be 21.8 and 29.4 A cm⁻² K⁻² at 200–275 and 300–400 K, respectively, which were comparable to the theoretical value for p-type sSOI (31.6 A cm⁻² K⁻²).     

Effect of non-metallic inclusions on butterfly wing initiation,crack formation,and spall geometry in bearing steels

Non-metallic inclusions such as sulfides and oxides are byproducts of the bearing steel manufacturing process. Stress concentrations due to such inclusions can originate cracks that lead to final failure. This paper proposes a model to simulate subsurface crack formation in bearing steel from butterfly-wing origination around non-metallic inclusions until final failure. A 2D finite element model was developed to obtain the stress distribution in a domain subjected to Hertzian loading with an embedded non-metallic inclusion. Continuum Damage Mechanics (CDM) was used to introduce a new variable called Butterfly Formation Index (BFI) that manifests the dependence of wing formation on depth. The value of critical damage inside the butterfly wings was obtained experimentally and was used to simulate damage evolution. Voronoi tessellation was used to develop the FEM domains to capture the effect of microstructural randomness on butterfly wing formation, crack initiation and crack propagation. Then, the effects of different inclusion characteristics such as size, depth, and stiffness on RCF life are studied. The results show that stiffness of an inclusion and its location have a significant effect on the RCF life: stiffer inclusions and inclusions located at the depth of maximum shear stress reversal are more detrimental to the RCF life. Stress concentrations are not significantly affected by inclusion size for the cases investigated; however, a stereology study showed that larger inclusions have a higher chance to be located at the critical depth and cause failure. Crack maps were recorded and compared to spall geometries observed experimentally. The results show that crack initiation locations and final spall shapes are similar to what has been observed in failed bearings.     

基于康复训练中力信号的人体参与度建模

设计一种基于人机接触力的人体主动参与程度评估模型,用于康复机器人应用中的主动康复训练。通过人体的肌电信号得到肌肉活跃度,确定肌电信号与人体参与度的关系。分析这一过程中人机接触力的变化,将腿部力信号平均值以及腰部力信号方差作为模型输入,对基于肌电信号的参与度模型进行拟合,得到基于力信号的参与度模型,使用肌电信号参与度模型对力信号参与度模型进行验证,证明了该模型的有效性。该方法避免了肌电信号采集时干扰较大且准备工作繁琐等缺点,具有良好的实用性。     

Droplet behaviors on inclined surfaces with dynamic contact angle

Dynamic contact angle (DCA) is of crucial importance in the numerical investigation of water management problems in proton exchange membrane fuel cells (PEMFCs). In order to well predict the gas-liquid two-phase flow in the complex flow field in PEMFCs, first, it is very critical to build a robust DCA model that is capable of simulating droplet behaviors on a single surface under various conditions. In our previous research work, an advancing-receding DCA (AR-DCA) model is developed and has been successfully validated against a series of experiments from the available literature for droplet impact on surfaces. In this study, the AR-DCA model is further applied to simulate droplet behaviors on inclined surfaces with different droplet impact velocities, impact angles and viscosities. It is found that the droplet spreading and deformation from the simulations have excellent agreement with those captured in the corresponding experiments. The results also indicate that higher impact velocity and impact angle can facilitate the spreading trend at the droplet trailing edge and have no notable effects on the leading edge. In addition, the increase of droplet viscosity leads to a transition from droplet deposition phenomenon to partial rebound on the surface.     

橡塑往复密封性能参数数值求解流程与物理模型探讨

橡塑往复密封的密封寿命通常是通过膜厚、承载力、泄漏率、磨损率等参数以表征。为获取上述参数,佐治亚大学SALANT提出橡塑往复密封模型建立和数值计算求解流程。为更好地理解与应用该方法,从橡塑往复密封物理结构、数值求解流程、Reynolds方程建立、方程约束边界建立、GW接触模型建立、力载平衡等6个方面系统地分析其特点与不完备之处,并从6个方面探讨数值求解流程和数值模拟的修正方法;提出密封模型修正方法,给出修正后密封数值求解流程,使得计算结果更好地与实际工作性能相吻合,并能较好地揭示密封机制。     

Fabrication of multi-filler thermoset-based composite bipolar plates for PEMFCs applications: Molding defects and properties characterizations

The bipolar plate (BP) material should possess contradictory properties. They should also manufacture from low-cost methods and materials. In the current investigation, thermoset-based composite materials reinforced with conductive fillers, and the compression molding process is implemented. In addition to fabricating the bipolar plates (BPs) with and without the flowing channels, alleviating the defects during the molding process is performed. The channels are perfectly formed on the plates with the designed depth of 0.65 mm and 0.5 mm of width. In the meanwhile, we alleviate different molding defects, which spoil the surface appearance and part properties. Regarding the physical properties, the water contact angle is measured to be around 85°. The through-plane electrical conductivity of molded plates showed high values up to 38 S/cm, and the interfacial contact resistance measured to be 18–24 mΩ cm². The mean value of the flexural strength of the produced samples was equal to 47 MPa, which is almost twice the DOE target (>25 MPa).