• Title, Summary, Keyword: Flat electrode method

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Design Analysis/Manufacturing /Performance Evaluation of Curved Unsymmetrical Piezoelectric Composite Actuator LIPCA (곡면형 비대칭 압전복합재료 작동기 LIPCA의 설계해석/제작/성능평가)

  • Gu, Nam-Seo;Sin, Seok-Jun;Park, Hun-Cheol;Yun, Gwang-Jun
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.25 no.10
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    • pp.1514-1519
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    • 2001
  • This paper is concerned with design, manufacturing and performance test of LIPCA ( Lightweight Piezo- composite Curved Actuator) using a top carbon fiber composite layer with near -zero CTE(coefficient of thermal expansion), a middle PZT ceramic wafer and a bottom glass/epoxy layer with high CTE. The main point of this design is to replace the heavy metal layers of THUNDER by thigh tweight fiber reinforced plastic layers without losing capabilities to generate high force and large displacement. It is possible to save weight up to about 30% if we replace the metallic backing material by the light fiber composite layer. We can also have design flexibility by selecting the fiber direction and the size of prepreg layers. In addition to the lightweight advantage and design flexibility, the proposed device can be manufactured without adhesive layers when we use epoxy resin prepreg system. Glass/epoxy prepregs, a ceramic wafer with electrode surfaces, and a graphite/epoxy prepreg were simply stacked and cured at an elevated temperature (177 $^{circ}C$ after following an autoclave bagging process. It was found that the manufactured composite laminate device had a sufficient curvature after detached from a flat mold. The analysis method of the cure curvature of LIPCA using the classical lamination theory is presented. The predicted curvatures are fairly in agreement with the experimental ones. In order to investigate the merits of LIPCA, a performance test of both LIPCA and THUNDE$^{TM}$ were conducted under the same boundary conditions. From the experimental actuation tests, it was observed that the developed actuator could generate larger actuation displacement than THUNDERT$^{TM}$.

Interfacial Layer Control in DSSC

  • Lee, Wan-In
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.75-75
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    • 2011
  • Recently, dye-sensitized solar cell (DSSC) attracts great attention as a promising alternative to conventional silicon solar cells. One of the key components for the DSSC would be the nanocrystalline TiO2 electrode, and the control of interface between TiO2 and TCO is a highly important issue in improving the photovoltaic conversion efficiency. In this work, we applied various interfacial layers, and analyzed their effect in enhancing photovoltaic properties. In overall, introduction of interfacial layers increased both the Voc and Jsc, since the back-reaction of electrons from TCO to electrolyte could be blocked. First, several metal oxides with different band gaps and positions were employed as interfacial layer. SnO2, TiO2, and ZrO2 nanoparticles in the size of 3-5 nm have been synthesized. Among them, the interfacial layer of SnO2, which has lower flat-band potential than that of TiO2, exhibited the best performance in increasing the photovoltaic efficiency of DSSC. Second, long-range ordered cubic mesoporous TiO2 films, prepared by using triblock copolymer-templated sol-gel method via evaporation-induced self-assembly (EISA) process, were utilized as an interfacial layer. Mesoporous TiO2 films seem to be one of the best interfacial layers, due to their additional effect, improving the adhesion to TCO and showing an anti-reflective effect. Third, we handled the issues related to the optimum thickness of interfacial layers. It was also found that in fabricating DSSC at low temperature, the role of interfacial layer turned out to be a lot more important. The self-assembled interfacial layer fabricated at room temperature leads to the efficient transport of photo-injected electrons from TiO2 to TCO, as well as blocking the back-reaction from TCO to I3-. As a result, fill factor (FF) was remarkably increased, as well as increase in Voc and Jsc.

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Fuel Cell End Plates: A review

  • Kim, Ji-Seok;Park, Jeong-Bin;Kim, Yun-Mi;Ahn, Sung-Hoon;Sun, Hee-Young;Kim, Kyung-Hoon;Song, Tae-Won
    • International Journal of Precision Engineering and Manufacturing
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    • v.9 no.1
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    • pp.39-46
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    • 2008
  • The end plates of fuel cell assemblies are used to fasten the inner stacks, reduce the contact pressure, and provide a seal between Membrane-Electrode Assemblies (MEAs). They therefore require sufficient mechanical strength to withstand the tightening pressure, light weight to obtain high energy densities, and stable chemical/electrochemical properties, as well as provide electrical insulation. The design criteria for end plates can be divided into three parts: the material, connecting method, and shape. In the past, end plates were made from metals such as aluminum, titanium, and stainless steel alloys, but due to corrosion problems, thermal losses, and their excessive weight, alternative materials such as plastics have been considered. Composite materials consisting of combinations of two or more materials have also been proposed for end plates to enhance their mechanical strength. Tie-rods have been traditionally used to connect end plates, but since the number of connecting parts has increased, resulting in assembly difficulties, new types of connectors have been contemplated. Ideas such as adding reinforcement or flat plates, or using bands or boxes to replace tie-rods have been proposed. Typical end plates are rectangular or cylindrical solid plates. To minimize the weight and provide a uniform pressure distribution, new concepts such as ribbed-, bomb-, or bow-shaped plates have been considered. Even though end plates were not an issue in fuel cell system designs in the past, they now provide a great challenge for designers. Changes in the materials, connecting methods, and shapes of an end plate allow us to achieve lighter, stronger end plates, resulting in more efficient fuel cell systems.

Effects of Al2O3 Coating on BiVO4 and Mo-doped BiVO4 Film for Solar Water Oxidation

  • Arunachalam, Maheswari;Yun, Gun;Lee, Hyo Seok;Ahn, Kwang-Soon;Heo, Jaeyeong;Kang, Soon Hyung
    • Journal of Electrochemical Science and Technology
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    • v.10 no.4
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    • pp.424-432
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    • 2019
  • Planar BiVO4 and 3 wt% Mo-doped BiVO4 (abbreviated as Mo:BiVO4) film were prepared by the facile spin-coating method on fluorine doped SnO2(FTO) substrate in the same precursor solution including the Mo precursor in Mo:BiVO4 film. After annealing at a high temperature of 450℃ for 30 min to improve crystallinity, the films exhibited the monoclinic crystalline phase and nanoporous architecture. Both films showed no remarkably discrepancy in crystalline or morphological properties. To investigate the effect of surface passivation exploring the Al2O3 layer, the ultra-thin Al2O3 layer with a thickness of approximately 2 nm was deposited on BiVO4 film using the atomic layer deposition (ALD) method. No distinct morphological modification was observed for all prepared BiVO4 and Mo:BiVO4 films. Only slightly reduced nanopores were observed. Although both samples showed some reduction of light absorption in the visible wavelength after coating of Al2O3 layer, the Al2O3 coated BiVO4 (Al2O3/BiVO4) film exhibited enhanced photoelectrochemical performance in 0.5 M Na2SO4 solution (pH 6.5), having higher photocurrent density (0.91 mA/㎠ at 1.23 V vs. reversible hydrogen electrode (RHE), briefly abbreviated as VRHE) than BiVO4 film (0.12 mA/㎠ at 1.23 VRHE). Moreover, Al2O3 coating on the Mo:BiVO4 film exhibited more enhanced photocurrent density (1.5 mA/㎠ at 1.23 VRHE) than the Mo:BiVO4 film (0.86 mA/㎠ at 1.23 VRHE). To examine the reasons, capacitance measurement and Mott-Schottky analysis were conducted, revealing that the significant degradation of capacitance value was observed in both BiVO4 film and Al2O3/Mo:BiVO4 film, probably due to degraded capacitance by surface passivation. Furthermore, the flat-band potential (VFB) was negatively shifted to about 200 mV while the electronic conductivities were enhanced by Al2O3 coating in both samples, contributing to the advancement of PEC performance by ultra-thin Al2O3 layer.

Electrochemical Properties of Lithium Secondary Battery and the Synthesis of Spherical Li4Ti5O12 Powder by Using TiCl4 As a Starting Material (TiCl4를 출발원료로한 구형 Li4Ti5O12 분말합성 및 리튬이차 전지특성)

  • Choi, Byung-Hyun;Ji, Mi-Jung;Kwon, Yong-Jin;Kim, Eun-Kyung;Nahm, Sahn
    • Korean Journal of Materials Research
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    • v.20 no.12
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    • pp.669-675
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    • 2010
  • One of the greatest challenges for our society is providing powerful electrochemical energy conversion and storage devices. Rechargeable lithium-ion batteries and fuel cells are among the most promising candidates in terms of energy and power density. As the starting material, $TiCl_4{\cdot}YCl_3$ solution and dispersing agent (HCP) were mixed and synthesized using ammonia as the precipitation agent, in order to prepare the nano size Y doped spherical $TiO_2$ precursor. Then, the $Li_4Ti_5O_{12}$ was synthesized using solid state reaction method through the stoichiometric mixture of Y doped spherical $TiO_2$ precursor and LiOH. The Ti mole increased the concentration of the spherical particle size due to the addition of HPC with a similar particle size distribution in a well in which $Li_4Ti_5O_{12}$ spherical particles could be obtained. The optimal synthesis conditions and the molar ratio of the Ti 0.05 mol reaction at $50^{\circ}C$ for 30 minutes and at $850^{\circ}C$ for 6 hours heat treatment time were optimized. $Li_4Ti_5O_{12}$ was prepared by the above conditions as a working electrode after generating the Coin cell; then, electrochemical properties were evaluated when the voltage range of 1.5V was flat, the initial capacity was 141 mAh/g, and cycle retention rate was 86%; also, redox reactions between 1.5 and 1.7V, which arose from the insertion and deintercalation of 0.005 mole of Y doping is not a case of doping because the C-rate characteristics were significantly better.