Cathode Thickness Research Articles

Augmentation Method of Triple Phase Boundary in Thin Film Solid Oxide Fuel Cell via Physical Vapor Deposition

Triple phase boundaries (TPBs) where electrode, electrolyte, and reactant meet altogether were augmented in thin film solid oxide fuel cell when Pt cathode was deposited on yttrium-doped barium zirconate electrolyte (BZY) via sputter. The augmented TPBs were observed to exist as three-dimensional structures, which is different from what are known to exist as two-dimensional planes or interfaces, by using energy dispersive spectroscopy (EDS). The permeating phenomenon of sputtered Pt into BZY was found to depend on dc sputtering power. Polarization curves showed increasing tendency of maximum powers in accordance with increasing thickness of Pt cathode and spectra of ac impedances showed decreasing tendency of faradaic resistances. If TPBs were located as an interfacial structure between electrode and electrolyte, oxygen could not diffuse well into TPBs, causing radius of semicircle in impedance spectra to decrease. The results are violating this expectation. As a result, as long as charge transfer resistance is a function of temperature, reactant concentration, activation barrier and TPB length, TPB must be only a factor to affect the results in this experiment.

Scale‐up design of a 300 kA magnesium electrolysis cell based on thermo‐electric mathematical models

Magnesium production process is highly energy intensive. Electrolysis provides an effective route to reduce energy consumption and greenhouse gas emission for the magnesium production. This paper concerns the scale‐up design of a 300 kA magnesium electrolysis cell using a three‐dimensional thermo‐electric mathematical model. The model provides information on the steady‐state thermoelectric fields thus allowing the evaluation of the effects of structure parameters (anode–cathode distance, anode thickness, cathode thickness, anode width, and anode number) on the current intensity, resistance voltage drop, and current density. Non‐dimensional analyses give a linear relation between the current intensity and a set of dimensionless numbers, which upon further comprehensive analyses, gives a criterion for the scale‐up. Such a scale‐up criterion is found to be able to predict, within 1%, the amperage of 300 kA magnesium electrolysis cells. The results suggest that the criterion could be used for the scale‐up design of magnesium electrolysis cells with a high current intensity.

Electrochemical properties related to the thickness control of the solid oxide fuel cell component layer using decalcomania paper

We fabricated anode-supported solid oxide fuel cells using decalcomania paper. To investigate the changes in thickness of the component layer and electrical properties in a unit cell, the number of layers of cathodes and the electrolyte decalcomania paper is changed. As a result, the thickness of the electrolyte and cathode layer regularly increases with an increase in the number of decalcomania papers attached. In addition, when only one electrolyte decalcomania paper is attached to an anode support, a tight and dense 8 μm electrolyte layer is obtained. A unit cell with a cathode thickness of 120 μm to which decalcomania paper is attached nine times is shown to have an open circuit voltage (OCV) of 1.08 V and a maximum power density (MPD) of 902 mW cm−2 at 800 °C.

Full Parametric Characterization of LSM/LSM-YSZ Cathodes by Electrochemical Impedance Spectroscopy

The contributions of the individual process steps of the cathode resistance were determined experimentally, directly from impedance spectra obtained from symmetrical cells. The symmetrical cells have architecture/structure consisting of YSZ electrolyte and a double layer cathode LSM-LSM/YSZ. The investigations were carried out in the temperature interval from 650 to 900 °C. The cathode processes steps activation energies obtained were 1.16 eV, 1.1 eV, and 0.09 eV (diffusion), respectively, which is in relatively good agreement with literature values. To understand the role of layer cathode thickness on electrochemical performance, electrical impedance spectra from symmetric LSM/YSZ/LSM cells were deconvoluted to obtain the key electrochemical components of electrode performance, namely ohmic resistance (RΩ), two low frequency processes related with chemical adsorption and dissociative reaction of O2 (Rp1 and Rp2), and bulk gas diffusion (W, finite warburg) through the electrode pores. The model used has Voight structure with three times constant. These parameters were then related to features, such as contact layer thickness, function layer thickness, and temperature. It was found that polarization resistance is highly dependent on the thickness of the contact layer (Rp1 and Rp2). All deconvoluted parameters are validated by using the appropriate physicochemical model.

Enhancing SOFC-Stack Performance by Model-Based Adaptation of Cathode Gas Transport Conditions

High performance anode–supported cells (ASC), contacted in a planar stack by metallic interconnectors (MIC), undergo a significant power density reduction. Performance limiting factors originating from the MIC-design were identified by detailed experimental data analysis and via a straightforward FEM simulation. Conclusively, gas diffusion polarisation contributes close to the sum of all ohmic losses to the overall polarization, both controlling stack performance. Based on this knowledge, a multiphysic-FEM-model was developed, considering coupled ohmic, gas diffusion and nonlinear polarization losses in the electrodes and ohmic losses in the electrolyte. Consequential ASC-performance depends over a broad range of operating conditions on i) an optimal MIC-design and ii) a well-chosen cathode thickness increases the overall power output.

Analysis of Residual and Operational Thermal Stresses in a Planar SOFC

A structural model has been developed for analysis of residual stresses for anode- and electrolyte-supported planar solid oxide fuel cells (SOFC). This model was also used for analysis of thermally induced stresses during operation for three different case studies with the electrolyte-supported geometry. Temperature distribution in the solid parts of the cell was modeled by means of an in-house electrochemical model, and the results were exported to the structural model. In the case studies, the impact of air and fuel inlet temperatures, steam reforming, and operation voltages on thermal stresses were studied. Weibull statistics were used for the prediction of failure probabilities and design considerations. Base case geometry for the electrolyte-supported cell was 50, 150, and 50 μm for anode, electrolyte, and cathode thicknesses, respectively, and for the anode-supported cell 1000, 20, and 50 μm, respectively. Analysis of residual stresses showed that, compared with the anode-supported cell, the electrolyte-supported cell experienced considerably higher stress levels in the anode and cathode due to the thick electrolyte, while the stress levels in the electrolyte were lower. For the anode-supported cell, maximum stress levels were 57, −12, and −678 MPa in the anode, cathode, and electrolyte, respectively, with negative values indicating compressive and positive values, tensile stresses. For the electrolyte-supported geometry, the corresponding levels were 282, 100, and −308 MPa, respectively. With a failure probability of 1E-6 and an electrolyte thickness of 10 μm, the minimum allowable anode thickness was estimated to be 1000 μm. For an electrolyte-supported cell, optimal thicknesses of electrolyte and anode were considered to be 100 and 100 μm, respectively, while the thickness of the cathode showed low impact. During operation, the stress levels were reduced considerably, since high operating temperatures reduce the temperature difference to the sintering temperature (1250 °C). Concerning the presence of methane in the fuel and the effect of steam reforming, small amounts of methane—as low as 10% of molar mass—were found to induce a cooling effect with correspondingly high gradients. With 45% methane in the fuel, the tensile stress level in the anode was about 130 MPa; the impact of thermal gradients was considered to be 40 MPa and the cooling effect also 40 MPa.

Elementary reaction modeling of CO2/H2O co-electrolysis cell considering effects of cathode thickness

A one-dimensional elementary reaction model of CO2/H2O co-electrolysis in solid oxide electrolysis cell (SOEC) coupled with heterogeneous elementary reactions, electrochemical reactions, electrode microstructure, and the transport of mass and charge is developed in this paper. This model, validated with the experimental performance of H2O electrolysis, CO2 electrolysis and CO2/H2O co-electrolysis at 700 °C, is demonstrated to be a useful tool for understanding the intricate reaction and transport processes within SOEC electrode and the electrode structure design and optimization. The simulation results indicate that the heterogeneous reactions reach the equilibrium near the cathode outside surface, and the electrochemical reactions mainly occur in the electrode near the electrode–electrolyte interface. The main zone of electrochemical reactions is far enough from the main zone of heterogeneous reactions, so that the two kinds of reactions almost don't influence each other when the cathode is thick enough (e.g. 700 μm). While, as the cathode thickness reduces, the zones of electrochemical reactions and the non-equilibrium heterogeneous reactions overlap each other, and the electrochemical performance of CO2/H2O co-electrolysis is affected by the variations of elementary species concentrations of O(Ni) and (Ni) due to the heterogeneous reactions. The model successfully explains the experimental phenomenon that the polarization curve of CO2/H2O electrolysis lies between that of H2O and CO2 electrolysis in a cathode supported SOEC, but almost the same as that of H2O electrolysis in a electrolyte supported SOEC.

BSCF계 혼합전도성 공기극의 두께에 따른 고체산화물 연료전지의 전기화학적 특성

In order to reduce the costs and to improve the durability of solid oxide fuel cell (SOFC), the operating temperature should be decreased while the power density is maintained as much as possible. However, lowering the operating temperature increases the cathode interfacial polarization resistances dramatically, limiting the performance of low-temperature SOFC at especially purely electronic conducting cathode. To improve cathode performance at low temperature, the number of reaction sites for the oxygen reduction should be increased by using a mixed ionic and electronic conducting (MIEC) material. In this study, anode-supported fuel cells with two different thicknesses of the MIEC cathode were fabricated and tested at various operating temperatures. The anode supported cell with <TEX>$32.5{\mu}m$</TEX>-thick BSCFZn-LSCF cathode layer showed much lower polarization resistance than that with <TEX>$3.2{\mu}m$</TEX> thick cahtode and higher power density especially at low temperature. The effects of cathode layer thickness on the electrochemical performance are discussed with analysis of impedance spectra.

Ultra Small Angle X-ray Scattering Studies of Solid Oxide Fuel Cell Cathode Powders

We demonstrate the feasibility of using Ultra Small Angle X-ray scattering to study cathode structures in solid oxide fuel cells (SOFC) under operating conditions. Cathode thickness has been optimized and symmetric SOFC test structures have been characterized. We also demonstrate that we can follow the evolution of microstructure on a La0.6Sr0.4Co0.2Fe0.8 infiltrated yttria stablized zirconia backbone structure under annealing, showing the viability of characterizing multi-scale cathode structures in real time.

Effect of LiCoO2 Cathode Density and Thickness on Electrochemical Performance of Lithium-Ion Batteries

Effect of LiCoO2 Cathode Density and Thickness on Electrochemical Performance of Lithium-Ion Batteries

Effect of LiCoO2Cathode Density and Thickness on Electrochemical Performance of Lithium-Ion Batteries

The consequences of electrode density and thickness for electrochemical performance of lithium-ion cells are investigated using 2032-type coin half cells. While the cathode composition is maintained by 90:5:5 (wt.%) with active material, Super-P electric conductor and polyvinylidene fluoride polymeric binder, its density and thickness are independently controlled to 20, 35, 50 um and 1.5, 2.0, 2.5, 3.0, 3.5 g , respectively, which are based on commercial lithium-ion battery cathode system. As the cathode thickness is increased in all densities, the rate capability and cycle life of lithium-ion cells become significantly worse. On the other hand, even though the cathode density shows similar behavior, its effect is not as high as the thickness in our experimental range. This trend is also investigated by cross-sectional morphology, porosity and electric conductivity of cathodes with different densities and thicknesses. This work suggests that the electrode density and thickness should be chosen properly and mentioned in detail in any kinds of research works.

Effects of the Thickness and Density of Cathodes on Electrochemical Performance of Lithium Secondary Batteries

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Dependence of Characteristics on Cathode Thickness for All-Solid-State Thin-Film Lithium Rechargeable Battery

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Model Prediction and Experiments for the Electrode Design Optimization of LiFePO4/Graphite Electrodes in High Capacity Lithium-ion Batteries

LiFePO4 is a promising active material (AM) suitable for use in high performance lithium-ion batteries used in automotive applications that require high current capabilities and a high degree of safety and reliability. In this study, an optimization of the electrode design parameters was performed to produce high capacity lithium-ion batteries based on LiFePO4/graphite electrodes. The electrode thickness and porosity (AM density) are the two most important design parameters influencing the cell capacity. We quantified the effects of cathode thickness and porosity (LiFePO4 electrode) on cell performance using a detailed one-dimensional electrochemical model. In addition, the effects of those parameters were experimentally studied through various coin cell tests. Based on the numerical and experimental results, the optimal ranges for the electrode thickness and porosity were determined to maximize the cell capacity of the LiFePO4/graphite lithium-ion batteries.

Manufacturing of Electrolyte and Cathode Layers SOFC Using Atmospheric Spraying Method and Its Characterization

The use of Solid Oxide Fuel Cell (SOFC) has created various interest in many parties, due to its capability to convert gases into electricity. The main requirement of SOFC cell components is to be produced as thin as possible to minimize the losses of electrical resistance, as well as able to support internal and external loads. This paper discusses the procedure of making a thin electrolyte layer, as well as a porous thin layer cathode using atmospheric spraying technique. The procedure of spraying was in room temperature with the process of sintering at temperature of 1350 0 C held for 3 hours. The SOFC characterization of electrolyte and cathode microstructure was determined by using the SEM, FESEM, XRD and impedance spectroscopy, to measure the impedance of SOFC cells. The results show that the thickness of thin layer electrolyte and porous cathode obtained of about 20 µm and 4 µm, respectively. Also the SOFC cell impedance was measured of 2.3726 x 10 6 Ω at room temperature. The finding also demonstrated that although the materials (anode, cathode and electrolyte) possess different coefficient thermal expansion, there was no evidence of flaking layers which seen the materials remain intact. Thus, the atmospheric spraying method can offer an alternative method to manufacturing of SOFC thin layer electrolyte and cathode. [ Key words: SOFC; spraying method; electrolyte; cathode ]

Optimization of Sm0.5Sr0.5CoO3−–Sm0.2Ce0.8O2− composite cathodes fabricated by electrostatic slurry spray deposition

Strontium doped samarium cobaltite (Sm 0.5 Sr 0.5 CoO 3− δ , SSC)–samarium doped ceria (Sm 0.2 Ce 0.8 O 2− δ , SDC) composite cathodes were fabricated using the electrostatic slurry spray deposition method for intermediate temperature solid oxide fuel cells (IT-SOFCs). To optimize the performance of the full cell containing the fabricated composite cathode, the effects of sintering temperature, composite ratio between SSC and SDC components, and film thickness of the composite cathode have been investigated through SEM, EDS and EIS analysis. As per the results, the best electrochemical performance was obtained from the SSC–SDC composite cathode sintered at 1000 °C in the weight ratio of 60:40 and with 20 μm in thickness. The cathode sintered at 1000 °C showed better performance than the cell sintered at 900 °C due to the well-developed connectivity between the SSC and the SDC particles. Also, the 60SSC–40SDC composite cathode showed an excellent percolating property and the lowest polarization resistance was obtained from the composite cathode with 20 μm in thickness due to its well developed microstructure in terms of gas diffusion and TPB area.

Experimental optimization of the optical and electrical properties of a half-wavelength-thick organic hetero-structure in a Micro-cavity

In the context of progress towards the organic laser diode, we experimentally investigate the optical and electrical optimization of an OLED in a vertical λ/2 microcavity. The microcavity consists of a quarter-wavelength TiO₂/SiO₂ multilayer mirror, a half-wavelength-thick OLED and a semitransparent aluminum cathode. The Alq3/DCM2 guest-host system is used as the emitting layer. This study focuses on the design and the fabrication of a half-wavelength thick organic hetero-structure exhibiting a high current density despite both the thickness increase and the cathode thickness reduction. The emission wavelength, the line-width narrowing and the current-density are studied as a function of two key parameters: the hetero-structure optical thickness and the aluminum cathode thickness. The experimental results show that a 125 nm thick cavity OLED ended by a 20 nm thick aluminum cathode exhibits a resonance at 606 nm with a full width at half maximum of 11 nm, and with current-densities exceeding 0.5 A/cm². We show that even without a top high-quality-mirror the incomplete microcavity λ/2 OLED hetero-structure exhibits a clear modification of the spontaneous emission at normal incidence.

Performance of microtubular SOFCs with infiltrated electrodes under thermal cycling

In this research, tubes consisting of a co-extruded dense YSZ electrolyte (∼10 μm) and porous NiO–YSZ anode (∼200 μm) were modified with different cathodes and anode infiltration to investigate the effects on both power and thermal cycling tolerance. Type of cathode (produced by infiltration of LSM into a porous YSZ matrix or by hand-painting of an LSM–YSZ ink), the type of pore former used in the cathode (graphite or poly (methyl methacrylate), PMMA) and the infiltration of the anode (no infiltration, or with infiltration steps using a co-precipitated SDC (Samaria doped ceria) mixture, or Ni–SDC mixture) were investigated as variables. The overall aim of this work is to produce cells that are more tolerant to thermal cycling, without sacrificing power density.Testing at 750 °C with 20 mL/min of dry hydrogen shows that anode infiltration has a particularly advantageous effect on performance, raising the peak power and reducing the degradation in peak power seen after aggressive cycling (100 °C/min heating and cooling rates). Cell power can be improved by LSM infiltration into a porous YSZ layer when the thickness of the YSZ layer is optimised and there is sufficient LSM. Infiltrated cells with cathode thicknesses of 20–40 μm functioned better than those 10–15 μm thick despite having a similar LSM/YSZ weight ratio. This may be due to the additional reaction zone available as a result of the higher LSM mass, suggesting that the reaction zone extends beyond 15 μm from the electrolyte. LSM and SDC infiltrated fine particles (50–100 nm) show good distribution and connectivity in the cathode and anode of the cells respectively. When PMMA is used as the pore former in the porous YSZ matrix, a slightly better cell performance is obtained compared with graphite as the pore former. Monitoring the power variation is found to be a more reliable tool than open circuit voltage (OCV) measurements for studying the effect of thermal cycling on cell stability.

A model for emission yield from planar photocathodes based on photon-enhanced thermionic emission or negative-electron-affinity photoemission

A general model is presented for electron emission yield from planar photocathodes that accounts for arbitrary cathode thickness and finite recombination velocities at both front and back surfaces. This treatment is applicable to negative electron affinity emitters as well as positive electron affinity cathodes, which have been predicted to be useful for energy conversion. The emission model is based on a simple one-dimensional steady-state diffusion treatment. The resulting relation for electron yield is used to model emission from thin-film cathodes with material parameters similar to GaAs. Cathode thickness and recombination at the emissive surface are found to strongly affect emission yield from cathodes, yet the magnitude of the effect greatly depends upon the emission mechanism. A predictable optimal film thickness is found from a balance between optical absorption, surface recombination, and emission rate.

Cathode Thickness Dependency of Oxygen Reduction Rate in PEFC

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