Current Collector Layer Research Articles

Electrochemical properties of graded and homogeneous Ce0.9Gd0.1O2−δ–La0.6Sr0.4Co0.2Fe0.8O3−δ composite electrodes for intermediate-temperature solid oxide fuel cells

Graded and homogeneous CGO–LSCF composite electrodes deposited by Electrostatic Spray Deposition on an YSZ substrate have been studied with and without screen-printed LSCF current collector. Impedance spectroscopy measurements have been performed in air at open circuit potential between 450 °C and 700 °C; and during isothermal treatments at 600 °C for 200 h; and at 800 °C for 12 h to estimate the relevance of such oxygen electrodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). A thin and dense CGO layer is firstly deposited to avoid any chemical reaction between LSCF and YSZ. No significant increase of the polarization resistance has been evidenced during isothermal test at 600 °C for 200 h, proving good stability of the electrode. Using a LSCF current collector layer (CCL), the polarization resistance decreases by a 1.5 order of magnitude compared to samples with single cathode functional layer (CFL). The electrochemical results do not conclusively indicate which composition presents lower polarization effects.

Fabrication and electrochemical characterizations of Nd2NiO4+δ-Ce0.8Gd0.2O2−δ composite cathodes for anode-supported intermediate temperature solid oxide fuel cells

Nd2NiO4+δ (NNO)-Ce0.8Gd0.2O2−δ (CGO) composites were investigated as cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). Planar NiO-YSZ anode-supported cells in size of 50 mm×50mm were fabricated with YSZ as the electrolyte. The effects of sintering temperature and the relative proportions of NNO and CGO on the cell performance were investigated in combination with chemical reactivity tests of NNO-YSZ and NNO-CGO. NNO-CGO composite cathodes were successfully sintered on YSZ electrolyte at 1000°C. By using La0.6Sr0.4CoO3−δ (LSC) as current collector, the cell with 70NNO-30CGO composite cathode sintered at 1000°C exhibited the highest power density of 620mWcm−2 (at 0.7V) and the lowest polarization resistance of 0.302Ωcm2 at 800°C. Short-term durability studies revealed that the degradation of cell performance was attributed to the crack formation on the LSC current collector layer and the delamination between NNO-CGO cathode layer and LSC current collector layer.

Regularities of high-temperature oxidation of current collectors of solid oxide fuel cells due to diffusion processes in subsurface regions

A complex study of regularities of oxidative reactions is carried out in subsurface layers of current collectors of solid oxide fuel cells manufactured of Crofer 22APU or Crofer 22H stainless steel. The methods of scanning electron microscopy, energy dispersive X-ray analysis, and Raman spectroscopy are used to study the distribution of the main steel elements in subsurface layers of current collectors as dependent on the operation time under the conditions of a cathodic chamber of solid oxide fuel cells. A mechanism of the process is suggested and contact resistance between the current collector and LSM cathode is calculated using the model of a Schottky barrier for a metal–semiconductor junction.

Preparation of membrane-electrode assemblies of solid oxide fuel cells by co-sintering of electrodes

The results of the development of procedures for forming membrane-electrode assemblies (MEAs) of solid oxide fuel cells (SOFCs) by co-sintering of electrodes and electrochemical tests of MEAs were described. Plates of Hionic™ material (Fuel Cell Materials, United States) with an area of 50 × 50 mm2 were used as a solid electrolyte membrane. The cathode layers were prepared from cation-deficient lanthanum-strontium manganite and the anion conductor 89 mol % ZrO2–10 mol % Sc2O3–1 mol % CeO2 (10Sc1CeSZ) with a carbon black addition for control over the microstructure. The anode layers were formed from the composite NiO/10Sc1CeSZ and by introducing rice starch as a pore-forming agent in the anode current-collecting layer. The thermal treatment mode was optimized based on thermogravimetry and scanning electron microscopy data and the results of testing the electrochemical characteristics of SOFCs to provide the formation of electrochemically active electrodes using one thermal cycle.

Synthesis and Characterization of Nanocrystalline La0.65Sr0.3 MnO3 and La0.8Sr0.2MnO3 Cathode Powders by Auto-ignition Technique for Solid Oxide Fuel Cells (SOFC)

Solid Oxide fuel Cells (SOFCs) are considered to be one of the most promising energy conversion devices that have several advantages such as high efficiency, system compactness and low environmental pollution. In the present investigation La0.65Sr0.3MnO3 (LSM-1) and La0.8Sr0.2MnO3 (LSM-2) nanoceramic powders were prepared by citrate-nitrate route of auto-combustion with citrate to nitrate (c/n) ratio 0.50 to see the effect of these cathode powders on the performance of SOFC cells. The as prepared powder were calcined at 900oC for 4hrs using the Thermolyne 47900 furnace to remove carboneous residues and characterized them using SEM / EDS, XRD, TGA techniques and their results are presented . From calculations using Debye Scherrer’s equation, the average crystallite size of the powders were found to be around 16nm. The SEM indicates the particle sizes are within the range of around 200nm.The surface area of the calcined LSM-2 powder was found to be ~21m2/g. The TGA studies indicate the completion of combustion since there was no further weight loss after reaching temperature of ~ 650oC.
 Also, Electrochemical characterization of LSM cathode powders were carried out by coating these powders (as cathode functional layer CFL-Bottom and current collector layer CL- Top) using Screen printing on the SOFC half cells (NiO-YSZ+YSZ) procured from CGCRI, Kolkata, India with a cell size of 16mm dia x1.6mm and tested these cells with H2-O2 at 750-800oC with the flow rates of 100-200 sccm. The results of the performances of single cells are presented in this paper. The Current density and powder density values obtained are 0.80A/cm2 (at 0.7V) and 0.55 W/cm2 at 800oC with 200 sccm of hydrogen and oxygen respectively. The area surface resistance (ASR) values obtained were ~0.50 Ωcm2 at 0.7V at 800oC.

The Influence of the Substituting Element (M = Ca, Sr, Ba) in La1.7M0.3NiO4+δ on the Electrochemical Performance of the Composite Electrodes

<p>The actual work focuses on the development of electrochemically active and stable electrodes for a high temperature proton-conducting electrolyte with a perspective of application in intermediate temperature electrochemical devices. The comparative study of the electrochemical performance of the La<sub>1.7</sub>M<sub>0.3</sub>NiO<sub>4+</sub><sub>δ</sub> – based (M = Ca, Sr, Ba) composite cathodes with proton-conducting BaCe<sub>0.89</sub>Gd<sub>0.1</sub>Cu<sub>0.01</sub>O<sub>3</sub> or oxygen-ion-conducting Ce<sub>0.8</sub>Sm<sub>0.2</sub>O<sub>1.9</sub> ceramic components in contact with the proton-conducting electrolyte BaCe<sub>0.89</sub>Gd<sub>0.1</sub>Cu<sub>0.01</sub>O<sub>3</sub> was performed by an impedance spectroscopy in wet air during 1500 h. The composites were used as functional layers in bi-layered electrodes with current collector layers made of 98 wt.% LаNi<sub>0.6</sub>Fe<sub>0.4</sub>O<sub>3</sub> + 2 wt.% CuO or 99.4 wt.% La<sub>0.6</sub>Sr<sub>0.4</sub>MnO<sub>3</sub> + 0.6 wt.% CuO.</p>

Modeling the Nucleation and Growth of Li at Metal Current Collector/Lipon Interfaces

Li metal has a much greater theoretical capacity (3860 Ah kg–1) than rechargeable anodes in the present lithium-ion batteries (graphite, 372 Ah kg–1). Controlling Li plating/stripping reactions is thus important for next-generation-battery technologies with Li metal anodes such as Li-air battery, Li-S battery, and all-solid-state-lithium battery (SSLB). A great advantage of using an inorganic-solid-state electrolyte is that the Li dendrite growth can be blocked without any specific separators, which is always a critical problem in charging/discharging Li metal anodes in organic liquid electrolytes. Amorphous electrolyte especially plays a key role in suppressing the Li growth from the anode surface toward the cathode because there are no grain boundaries. Previous work studied the Li plating/stripping reactions with lithium phosphorous oxynitride (LiPON) electrolyte layers coated with Cu current collector (CC) films [1]. Fundamental studies on metal electrodeposition in solid electrolyte systems have hardly been reported in literature compared to liquid electrolyte systems. Nucleation sites are located at solid/solid interfaces for metal nucleation with a solid electrolyte. Hence, the nuclei must push either electrode or electrolyte to create their own spaces. This process is associated with generation of strain energies and the unique aspect of solid electrolyte systems. This study investigates how Li nucleates, grows, and dissolves across solid-electrolyte/metal-CC interfaces. We also in-situ observe Li electrodeposition and dissolution using a field-emission-scanning-electron microscope (FE-SEM). The top and bottom surfaces of a Li1+x+y Al x (Ti,Ge) 2-x Si y P 3-y O12(LATP) sheet (1.25 cm × 1.25 cm, Ohara Co.) were coated with 2.5-μm-thick LiPON layers by magnetron sputtering. A current collector film (Cu, Ni, W, Pt, Au) was deposited on the top LiPON surface by pulsed laser deposition (PLD). Only a 1.0-μm-thick Cu CC film was deposited by magnetron sputtering. The CC area was controlled to be 5.0 mm in diameter. A several-μm-thick Li film with a diameter of 9.0 mm was deposited on the LiPON surface on the bottom by vacuum evaporation deposition. A fabricated all-solid CC/LiPON/LATP/LiPON/Li cell was sandwiched with Cu and brass plates. The Cu plate has a viewport with a diameter of 3.0 mm in the center. Electrochemical impedance measurements were performed with amplitude of 20 mV in the frequency range from 3×106 to 1 Hz. Li electrodeposition was performed under galvanostatic conditions (50 μA cm−2). Applied current densities were estimated for the whole area of a CC film with a diameter of 5.0 mm. The contribution of the CC deformation to the overpotential for the Li nucleation and growth at CC/LiPON interfaces is expressed by the following equation in previous work [2]. η s = εθEM{ρF(1–ν}/{3(r i+t)3/[2{(r i+t)3–r i 3]–ν/(1– ν) } This model is based on an elastic process that a dome-shaped Li nucleus initially pushes and deforms a CC layer. The calculated voltage profiles consistently explain the initial stages of the experimental voltage profiles. Figure 1 shows a high-resolution SEM (SU8030, Hitachi) image of a single Li island electrodeposited under a 90-nm-thick Cu CC and a voltage transient during Li dissolution of the Li island at 50 μA cm−2. Our observed results support the above model that deformations of a CC are associated with the Li nucleation and growth on LiPON. The excellent spatial resolution of a FE-SEM allowed us to observe transient behaviors of single Li island growth and dissolution. We will present in-situFE-SEM movies showing how Li islands gradually dissolve back to a solid electrolyte under a metal CC at high magnifications by the help of a SEM. We will further discuss the mechanisms of Li deposition and dissolution on a LiPON electrolyte based on the observed results. Acknowledgements The authors gratefully acknowledge JST-ALCA and JSPS, 26870272 for the financial support. Reference [1] M. Motoyama, M. Ejiri, and Y. Iriyama, Electrochemistry, 82,364 (2014). [2] M. Motoyama, M. Ejiri, and Y. Iriyama, J. Electrochem. Soc., 162, A7067 (2015). Figure 1

Optimizing Energy Density of Li-Ion Batteries Using Thick Electrodes

Low-cost, high energy density lithium-ion batteries (LIBs) have been consistently pursued in consumer electronics, electrical vehicles (EVs) and stationary (grid) energy storage. Modern Li-ion cells can have an energy density of up to 550 Wh/L, compared to only 200 Wh/L in the late 1990s [1]. The gradual energy density improvement over the last 15-20 years was mostly due to the improved engineering of the electrode coatings and, to some extent, some improvement in active material development and manufacturing. The former has significantly increased the volume ratio of active materials (which provides the capacity of the battery) from ~20% at early stages to ~45% in the state-of-art LIBs [2,3]. Thickening the cathode and anode is one effective approach to further increase the active material content, enabled from reducing current collector and separator layers in the stack, which further improves the energy density and lowers the cost of LIBs. It has been estimated that significant reduction in pack cost can be realized when compared to conventional manufacturing if electrode thickness is doubled and aqueous slurry processing is utilized [4]. However, thicker electrodes lead to poor kinetics and electrolyte salt depletion and thus underutilization of active materials. The major concern of thick coatings is electrolyte salt depletion, which results in fewer lithium ions available in the liquid phase for reaction at the active material surface. Therefore, there is an optimum thickness for maximum energy and power density. To maximize energy and power density, the effect of various coating parameters on the reaction kinetics and thus battery performance must be considered during electrode design. The operation of LIBs follows porous electrode theory and electrochemical reaction thermodynamics, and the governing equations have been summarized by Newman et al. [5]. Thus, the porous electrode model is used in the present work to investigate the effect of manufacturing parameters such as electrode thickness and porosity. In the present study, the following will be discussed: (1) The effect of thickness on active material utilization, areal capacity, voltage and energy density. (2) The effect of porosity on active material utilization, areal capacity, voltage and energy density. (3) Possible solutions to further increase the energy density of thick-electrode battery. Acknowledgement This research at Oak Ridge National Laboratory (ORNL), managed by UT Battelle, LLC, for the U.S. Department of Energy under contract DE-AC05-00OR22725, was sponsored by the Office of Energy Efficiency and Renewable Energy Vehicle Technologies Office (VTO) Applied Battery Research (ABR) subprogram (Program Managers: Peter Faguy and David Howell).

Integral-Type Porous Cobalt@Cobalt Oxide Anode with Micro/Nano-Sized Pores for Lithium-Ion Battery

The integrated porous Cobalt@Cobalt oxide anode was prepared by facile processes including freeze-casting and thermal-oxidation for use as high-capacity anode material of lithium-ion battery. The three-dimensional Co foam with elongated, aligned micropores was synthesized by a freeze-casting process. Subsequently, it was heat-treated in order to form cobalt oxide material with nano-structure on the surface of the Co foam. In this electrode design, the hierarchical three-dimensional Co foam was used as current collector and nanowall-like cobalt oxide layer acted as anode that reacts with lithium ions during discharging and charging. The integrated porous Cobalt@Cobalt oxide anode exhibits highly reversible capacity of 1200 mAhg-1 even after 45 cycles with an initial coulombic efficiency of 79.1%, which is much higher than that of the conventional cobalt foil anode (259 mAhg-1). The integrated porous Cobalt@Cobalt oxide anode, which was fabricated in this study, has promising potential applications as a self-supporting advanced anode architecture with high capacity for lithium-ion battery.

Polydopamine-Coated Current Collector: Improving the Electrochemical Performance of Si Anode By Raising the Interfacial Adhesion Strength

The high theoretical capacity of Si has made it a promising candidate for high energy density and large-scale lithium ion battery (LIB) anode. However, this system exhibits rapid capacity decay and hence poor cycling performance due to huge volume expansion of about 300% when Li-ion inserts into the Si particle during charging. Experimental observations suggest the formation of cracks at the early stages of cycling due to this volume expansion. The continuous mechanical stressing and fracturing of Si particles lead to the pulverization of the electrode and formation of dead Si particles. In particular, dead particles detached from current collector can mainly occur decay of electrochemical performance of lithium ion batteries.[1,2] Hence, we tried to improve the interfacial adhesion between the Si electrode layer and the current collector by making a hydrophilic layer on the current collector through polydopamine coating and induce cross-linking of polydopamine (PD) and polyacrylic acid (PAA) binder. The contact angle and the interfacial adhesion between the electrode and the PD coated and bare current collector were analyzed using Phoenix 300 Touch and the Surface And Interfacial Cutting Analysis System(SAICAS), respectively. From the SAICAS analysis, the adhesion strength between PD-coated current collector and Si electrode layer was improved comparing to the bare system. (Bare current collector: 0.2455 kN m-1 and PD-coated current collector: 0.3532kN m-1). The PD-coated current collector showed a higher hydrophilicity to the electrolyte than the bare current collector. The cycle performance of the cell was greatly enhanced by the PD coating on the anode current collector. The present studies suggest that, the coating of PD and induced cross-linking of PD and PAA improves the electrochemical performance of the Si anode. Acknowledgement This work was supported by the Human Resource Training Program for Regional Innovation and Creativity through the Ministry of Education and National Research Foundation of Korea(NRF-2014H1C1A1066977)

Analysis of diffusion induced elastoplastic bending of bilayer lithium-ion battery electrodes

Bilayer electrode, composed of a current collector layer and an active material layer, has great potential in applications of in-situ electrochemical experiments due to the bending upon lithiation. This paper establishes an elastoplastic theory for the lithiation induced deformation of bilayer electrode with consideration of the plastic yield of current collector. It is found that the plastic yield of current collector reduces the restriction of current collector to an active layer, and therefore, enhances in-plane stretching while lowers down the rate of electrode bending. Key parameters that influence the elastoplastic deformation are identified. It is found that the smaller thickness ratio and lower elastic modulus ratio of current collector to an active layer would lead to an earlier plastic yield of the current collector, the larger in-plane strain, and the smaller bending curvature, due to balance between the current collector and the active layer. The smaller yield stress and plastic modulus of current collector have similar impacts on the electrode deformation.

Electrochemical and Mechanical Properties of a Newly Designed Anode Supported SOFC

In an SOFC stack, the interface between the cathode and the interconnect plays an important role on the measured performance of a single cell. A contact between cathode/interconnect and cathode/current collecting cathode was designed to investigate mechanism of cathodic current collector on cell performance. The cell covered with Ag paste on the cathode side exhibits slightly higher power density than that of the cell partially covered with Ag paste. The Ag paste was applied on the cathode side at the corresponding position in contact with the punctuate structure of the interconnect as current-collecting layer. The difference in power densities between the two unit cells was mainly due to the electron transverse transfer on the cathode surface. When the structure of the interconnect was changed from a convex punctuate structure to contentious liner strips. It is found that the cell performance is driven by both gas flow and electron transverse transfer. The effect of electron transverse transfer on cell performance was more significant than that of gas flow rate. The cumulative effect of the transverse electron cannot be neglected. Furthermore, we will report a newly cell structure, so-called “hollow symmetric anode-supported planar solid oxide fuel cell”. The cell remains flat before and after reduction. The pressure of anti-failure load was about 20 times larger than that of conventional anode supported substrates. Meantime, its performance is nearly identical as that of the traditional anode-supported cell. The designed cell can be scaled easily and is cost effective.

Direct formation of a current collector layer on a partially reduced graphite oxide film using sputter-assisted metal deposition to fabricate high-power micro-supercapacitor electrodes

When a reduced graphite oxide (RGO) freestanding film is fabricated on a supercapacitor cell via compression onto a current collector, there are gaps between the film and the current collector, even if the cell is carefully assembled. These gaps can induce increases in the electrical series resistance (ESR) of the cell, resulting in degradation of the cell's electrochemical performance. Here, to effectively reduce the ESR of the supercapacitor, metal sputtering deposition is introduced. This enables the direct formation of the current collector layer on a partially reduced GO (pRGO) film, the model system. Using metal sputtering, a nickel (Ni) layer with a thickness <1 μm can be created easily on one side of the pRGO film. Good electrical interconnection between the pRGO film and the current collector can be obtained using a Ni layer formed on the pRGO film. The pRGO film sustains its film form with high packing density (∼1.31 g cm−3). Furthermore, the Ni-sputtered pRGO film with optimized Ni thickness exhibits remarkable enhancement of its electrochemical performance. This includes a superior rate capability and semi-permanent cycle life compared with the untreated pRGO film. This is due to the significant decrease in the ESR of the film.

Cross-stacked carbon nanotube film as an additional built-in current collector and adsorption layer for high-performance lithium sulfur batteries

Cross-stacked carbon nanotube (CNT) film is proposed as an additional built-in current collector and adsorption layer in sulfur cathodes for advanced lithium sulfur (Li-S) batteries. On one hand, the CNT film with high conductivity, microstructural rough surface, high flexibility and mechanical durability retains stable and direct electronic contact with the sulfur cathode materials, therefore decreasing internal resistivity and suppressing polarization of the cathode. On the other hand, the highly porous structure and the high surface area of the CNT film provide abundant adsorption points to support and confine sulfur cathode materials, alleviate their aggregation and promote high sulfur utilization. Moreover, the lightweight and compact structure of the CNT film adds no extra weight or volume to the sulfur cathode, benefitting the improvement of energy densities. Based on these characteristics, the sulfur cathode with a 100-layer cross-stacked CNT film presents excellent rate performances with capacities of 986, 922 and 874 mAh g−1 at cycling rates of 0.2C, 0.5C and 1C for sulfur loading of 60 wt%, corresponding to an improvement of 52%, 109% and 146% compared to that without a CNT film. Promising cycling performances are also demonstrated, offering great potential for scaled-up production of sulfur cathodes for Li-S batteries.

3D Microstructure Effects in Ni-YSZ Anodes: Prediction of Effective Transport Properties and Optimization of Redox Stability.

This study investigates the influence of microstructure on the effective ionic and electrical conductivities of Ni-YSZ (yttria-stabilized zirconia) anodes. Fine, medium, and coarse microstructures are exposed to redox cycling at 950 °C. FIB (focused ion beam)-tomography and image analysis are used to quantify the effective (connected) volume fraction (Φeff), constriction factor (β), and tortuosity (τ). The effective conductivity (σeff) is described as the product of intrinsic conductivity (σ0) and the so-called microstructure-factor (M): σeff = σ0 × M. Two different methods are used to evaluate the M-factor: (1) by prediction using a recently established relationship, Mpred = εβ0.36/τ5.17, and (2) by numerical simulation that provides conductivity, from which the simulated M-factor can be deduced (Msim). Both methods give complementary and consistent information about the effective transport properties and the redox degradation mechanism. The initial microstructure has a strong influence on effective conductivities and their degradation. Finer anodes have higher initial conductivities but undergo more intensive Ni coarsening. Coarser anodes have a more stable Ni phase but exhibit lower YSZ stability due to lower sintering activity. Consequently, in order to improve redox stability, it is proposed to use mixtures of fine and coarse powders in different proportions for functional anode and current collector layers.

Effect of Microstructure on Performances of Hydrogen and Oxygen Electrodes for Reversible SOEC/SOFC

Solid oxide fuel cells (SOFCs) are, in principle, able to be operated in reverse as solid oxide electrolysis cells (SOECs) to generate pure hydrogen from water vapor with the highest efficiency. Since the pioneering work in late 1960s (1) and HOT-ELLY (hot-electrolysis) project in 1980s (2), the materials and system for the SOECs have been extensively investigated (3). We have engaged in the research and development of high-performance electrodes with novel architecture for the SOEC/SOFC reversible system (4-9). The essential factors to improve the electrode performance are a high electrocatalytic activity and an extended effective reaction zone (ERZ: effective transport of gas, ions, and electrons). In the present work, we demonstrate that the microstructure of both hydrogen and oxygen electrodes plays an important role in reducing the ohmic and polarization losses under reversible SOFC/SOEC operations. Figure 1 shows cross-sectional SEM images of double-layer (DL) hydrogen electrodes (6) prepared on YSZ electrolyte. The DL electrodes consisted of a mixed conducting samaria-doped ceria, (CeO2)0.8(SmO1.5)0.2 (SDC), with highly dispersed Ni0.9Co0.1 catalysts (8 vol%-Ni0.9Co0.1) as a catalyst layer (CL, thickness = 14 to 16 μm), on top of which a Ni-SDC cermet (60 vol%-Ni) was attached as a current collecting layer (CCL) with a thickness of 5 to 20 μm. A SEM image of the single CL without CCL is also shown for comparison in Fig. 1 (a). The porosity of the CCL has to be high to increase the gas-diffusion rate. The CCLs formed on the CL were found to be uniform in the thickness and the apparent porosity was 69 to 70%, irrespective of the thickness. A test cell was prepared with the following configuration: DL H2 electrode│YSZ (0.5 mm)│SDC interlayer│O2electrode The oxygen electrode employed was a composite of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) with 40 vol% SDC. A detailed analysis of the oxygen electrode microstructure is given elsewhere (8). As a Pt/air reference electrode, a Pt wire was wrapped along the lateral of the YSZ electrolyte disk and fixed with Pt paste. Figure 2 shows steady-state IR-free I−E curves of the DL hydrogen electrodes, which were measured by the current interruption method, in the reversible SOFC/SOEC operation mode with H2 + H2O (p[H2O] = 0.4 atm) at 800ºC. The thickness of the CCL showed a significant effect in reducing the polarization loss. The test cell with 5 μm-CCL exhibited the highest performance in both SOFC/SOEC operations, i.e., the IR-free cathode potential at j = −0.5 A cm−2(SOEC operation) was −1.16 V vs. air reference electrode, which corresponds to an overpotential of −0.20 V. We also expect that the thin CCL with high electronic conductivity can act as a micrometer-size current collector to minimize the ohmic loss between the separator (interconnect) and the CL in stacks. The ohmic resistance of the test cells R cell was indeed smaller than that without the CCL, and reached the minimum value with the 5 μm-CCL. This suggests that the whole Ni0.9Co0.1/SDC of the catalyst layer can work effectively. A further increase in the CCL thickness (≥ 10 μm) increased the R cell (additional ohmic resistance of the cermet). The gas diffusion rate through the CCL is presumably slowed down with increasing the CCL thickness. In summary, the 5 μm-CCL provides the best balance in enlarging the ERZ by an effective transport of gases (H2O and H2) and an effective conductive network for electrons and oxide ions. This work was supported by the funds for “Advanced Low Carbon Technology Research and Development Program” (ALCA) from Japan Science and Technology Agency (JST).

Development of Electrochemical Methanation Reactor with Co-Electrolysis of Humidified CO2

Solid oxide fuel cells (SOFCs) have received a great deal of attention recently, due to in part to their high energy conversion efficiency and environmental compatibility. Recently, an electrochemical cell with the same components as SOFCs has also been used as a solid oxide electrolysis cell (SOEC) for Power-to-Gas process. The use of alternative high performance electrolytes and electrodes materials means that the input power for electrolysis can be reduced. Co-electrolysis of CO2 and H2O with SOEC is considered to be one of the effective technologies to convert CO2 and H2O into CO and H2 gases [1]. Typical operation temperature of SOEC above 600ºC prevents further methanation reaction of CO and H2, while CO and H2 gases (syngas) are useful raw material for CH4 at lower reaction temperatures around 400ºC. Very recently, various researchers reported the excellent electrochemical performances and durability of heat-cycles for SOEC designs. Most of the cells are supported by a porous fuel-electrode tube. Therefore the tubular fuel-electrode support works as a current collector and gas diffusion layer as well as support medium of SOEC. Thus, the aim of this study is to realize the electrochemical reactor development with a reliable electrolyte layer on the excellent gas permeation, conductivity and mechanical strength for direct methanation process using co-electrolysis of CO2 and H2O at lower cell operation temperatures. In this presentation, we will report SOEC reactor fabrication technologies and the methanation properties.This research is partially supported by CREST program of the Japan Science and Technology Agency (JST).Ref 1. Energy and Environmental Science, 7 (2014) 4018-4022

A New Method for Fabrication of Solid State Batteries

Commercially available solid-state lithium and lithium-ion batteries with inorganic electrolytes are typically low capacity, low energy density and high cost devices. This paper discusses a new manufacturing technology with the potential to enable the development of high capacity solid-state batteries with very high energy density at very low cost. The process is called Battery-on-Wire (BoW) and is shown in Fig. 1. It consists of a single, cylindrical vapor phase reactor with multiple reactor zones. A metal wire, which acts as the cathode current collector, is continuously fed into the top of the reactor and cathode, electrolyte, anode and anode current collector layers are sequentially deposited on the wire. The result is a complete solid-state cell in the form of a thin flexible wire. A wide variety of anode, electrolyte and cathode materials can be deposited by judicious selection of reactants. Electrode and electrolyte morphology and chemical composition can be modified by controlling the reactor temperature and the partial pressures of the reactants. The various reactor sections are isolated to prevent cross contamination and the deposition rates are usually several orders of magnitude higher than those in the processes typically used to fabricate solid-state batteries with inorganic electrolytes. Fig. 2 shows SEM images of anode, cathode and electrolyte deposits. The anode and cathode coatings exhibit some porosity and surface roughness with surface features on the order of 1-2 μm. The electrolyte coating is smooth and non-porous. Fig. 3 shows initial cycle life data for a Si-based anode. There is some capacity fade in the early cycles but the discharge capacity is almost constant after cycle 5 and the coulombic efficiency is near 100% after cycle 10. The specific capacity of the anode material is estimated to be between 2500 and 3000 mAh/g. Additional data for anode, cathode and electrolyte materials and complete cells will be shown in the presentation. Figure 1

Effect of Microstructure on Performances of Hydrogen and Oxygen Electrodes for Reversible SOEC/SOFC

We have developed high performance electrodes for reversible SOEC/SOFCs. Double-layer hydrogen electrodes, consisting of a mixed conducting samaria-doped ceria (SDC) with highly dispersed Ni–Co catalysts as the catalyst layer (CL) and, on top of it, a thin Ni–SDC cermet as the current collecting layer (CCL), exhibited highly reversible performance at 800°C by controlling the microstructure. We have also succeeded in enhancing the reversible performances of LSCF–SDC composite oxygen electrodes accompanied by high durability.

Stationary 2D FEM Model Framework for SOFC Stack Performance Prediction

It is a well-known fact, that high-performing anode-supported cells (ASCs) undergo a significant power reduction when contacted in a stack by metallic interconnectors (MIC) with a specific flow field design (1,2). For profound investigations, a model framework has been presented in previous studies (3-5) which uniqueness is based on its strict use of in-house determined material parameters and validation measurements over broad range of operating conditions. Included are the physically coupled processes (i) electrical/ionic conduction in electrode/electrolyte material, (ii) electrochemical charge transfer at the electrode/electrolyte interfaces and (iii) porous media gas species transport in the porous electrodes [5]. It has become clear that O2 starvation underneath the MIC contact rips and/or electrical cross conduction limitations in the cathode material underneath the gas channel area creates performance losses, which add up additionally for each individual stack layer to the standard cell polarization losses. It will be shown in this work, why (i) by adding a current collector layer (CCL) losses are reduced, that (ii) the degree of loss reduction is highly dependable on CCL thickness and microstructure and that (iii) the overall performance can further be improved by a well-chosen MIC contact rip thickness.