bluuebunny/crossref_metadata_2025 huggingface dataset:
Water Electrolysis Using Water Absorbing Porous Electrolyte Cell
Authors: Terayama Yuki , Haji Takamasa , Mori Kouhei , Matsumoto Hiroshige
Published: February 2020

We have reported so far water electrolysis by use of a water absorbing porous electrolyte that works under similar conditions to a polymer electrolyte electrolysis cell (PEEC) [1]. This cell consist of a surface-proton conducting metal oxide nanoparticles as proton-conducting electrolyte, a controlled-hydrophobic electrocatalytic layer, and fully hydrophobic gas diffusion layer (GDL) to generate pressurized hydrogen and oxygen gases. In this presentation, we will discuss the optimized preparation condition for membrane electrode assembly (MEA), which consist of electrolyte, electrode, and GDL layers. We also show that the hydrogen gas generation rate depend on the supplied water pressure (ΔP).

MEA of the water electrolysis cell is prepared as follows: The GDL films were formed by compressing of acetylene black/poly(tetrafluoroethylene) (PTFE) (=1/6, weight ratio) composite powder using Newton Press under 6 kN cm-2 for 1 min and successive heat treatment at 360 °C for 15 min. Electrode part with Pt loading of 2.0 mg cm-2 on top of the GDL films was formed using hot-press at 300 °C for 3 min under 300 kgf cm-2, which is consisted of consisted of platinum carbon (Pt/C) / PTFE / titanium phosphate ionomer composite. Finally, electrolyte layer on top of electrode layer was prepared by coating of titanium sulfonate/Nafion (=9/1, weight ratio) slurry and hot-pressing at 140 °C under 100 kgf cm-2 for 1 min. The fabricated MEAs were different sizes with diameters of 30 mm and 12 mm for anode and cathode sides, respectively. The current-voltage characteristic and generation hydrogen gas is measured by putting the fabricated MEA into the cell as shown Figure 1. The distilled water is supplied from cathode side and is pressurized using nitrogen gas in the ΔP range from 0 MPa to 0.25 MPa. The gas evolution rates of hydrogen during water electrolysis were evaluated by gas chromatography to be determined by 1% hydrogen/argon calibration curve.

The gas evolution rate of hydrogen increased with increasing ΔP from 0 MPa to 0.10 MPa, and reaches a maximum value at 0.15 MPa. At ΔP higher than 0.15 MPa, the rates decreased to almost the same value at 0 MPa. We supposed that the generated gas was leaked to outside of the cell in lower pressure region than 0.15 MPa. On the other hand, in higher region than 0.15 MPa, the generated gas in the water phase by water electrolysis was not completely separated to gas phase.

The obtained evolution rate was compatible with the theoretical value calculated by Faraday’s law. However, electrolysis voltages were high compared with conventional PEEC. Possible reason is inhomogeneous state of electrode layer and electrolyte layer with lower electrical conductivity.

Acknowledgements

 This work was supported by CREST in JST.

References

(1) S.-J. Kim, T. Sakai, H. Oda, J.-I Hamagami, Y. Okuyama, M. Matsuka, S. Ohta, Y. Shimizu, T. Ishihara, H. Matsumoto Electrochem.
2012
80(4), 246.

Figure 1
Progress and Accomplishment in Development of High Performance Pcfcs at Kist
Authors: Lee Jong-Ho , An Hyegsoon , Choi Sung Min , Hong Jongsup , Yoon Kyung Joong , Kim Hyoungchul , Son Ji-Won , Kim Byung-Kook
Published: February 2020

Despite of numerous intensive studies for the protonic ceramic fuel cell (PCFC) for last decade, general PCFC performances were relatively lower than expected, more likely poor than those of oxygen ion conducting SOFCs. Among the many technical reasons for such lower performance, non-optimization of cell fabrication condition owing to incredibly high sintering temperatures of electrolyte has been recognized as the most critical one. KIST also has tried to develop viable PCFC (Protonic Ceramic Fuel Cell) fabrication techniques for last ten years and improved its performance by utilizing the advanced electrolyte and electrode materials and optimization of their microstructure. Whilst from the period of investigation, we could acquire strong experience in the optimization of cell fabrication condition as well as overall cell configuration for higher performance and reliability (thermomechanical and thermochemical stability). Here we introduced the progress and main achievements at KIST for the development of high performance PCFC by utilizing all these accumulated experience and know-how to date.
Fabrication and Characterization of Strontium-Doped Lanthanum Manganite Cathode Supports for Micro-Tubular Solid Oxide Fuel Cells
Authors: Panthi Dhruba , Choi Bokkyu , Tsutsumi Atsushi
Published: February 2020

Strontium-doped lanthanum manganite (LSM) is a preferred cathode material for solid oxide fuel cells (SOFCs) owing to its good electrocatalytic properties for oxygen reduction reaction, high electronic conductivity, and thermal/chemical stability in oxidizing environments. However, for fabricating cathode-supported SOFCs, co-sintering of the electrolyte layer with the LSM support is a challenging step. Although LSM is compatible with the most common zirconia-based electrolytes at SOFC operating temperatures, it reacts with zirconia at higher temperatures to form electrically insulating secondary phases, namely lanthanum zirconate and strontium zirconate. Thus, to avoid the reaction between LSM and zirconia, the co-sintering temperature must be below 1250 °C, which is relatively low for obtaining a dense electrolyte layer. Additionally, it is important to maintain a good porosity of the LSM support to minimize gas diffusion losses through it. In the present work, we attempted to optimize the fabrication process of micro-tubular LSM supports by controlling several parameters such as the slurry composition, pre-sintering temperature, and sintering/co-sintering profiles. The mechanical and electrical properties of the fabricated LSM supports were characterized. Our results are expected to be helpful for achieving high-performance cathode-supported micro-tubular SOFCs with conventional materials.
(Invited) Engineering Electronic and Electrochemical Nanoscale Oxides
Authors: Tuller Harry L. , Kim Jae Jin , Bishop Sean R. , Chen Di
Published: February 2020

Oxides are playing an increasing critical role as functional components in the fields of energy conversion/storage, microelectronics, displays, sensors/actuators and catalysis. In turn, their electrical (ionic & electronic), optical, magnetic and catalytic properties depend sensitively on their defect structure and oxygen nonstoichiometry, typically frozen in during processing, and rarely well defined. This is particularly true for thin films and nanoparticles/wires, where conventional methods, appropriate to bulk materials, do not apply. In this presentation, we review in-situ optical, electrochemical and dilatometric methods, developed or refined in our laboratory, to monitor, analyze and control nonstoichiometry, defect equilbria, transport and optical properties of oxide thin films and nano-sized particles. Examples will include materials of interest as electrodes in fuel cells, and as components of chemical sensors, oxidation catalysts and electronic memory devices.
Innovative Approach on Nano-Structuring of Electrode for Solid Oxide Cells
Authors: Myung Jaeha , Neagu Dragos , Irvine John T. S.
Published: February 2020

Solid oxide cells (SOCs) are electrochemical systems capable of operating reversibly and therefore may serve as versatile energy converters. Electrolysis mode, electricity can be converted to fuels or other valuable chemicals, on the other hand, fuel cell mode converts efficiently fuel to electricity on demand. Due to their severe operating conditions, the ideal fuel electrode materials has not been found yet to accomplish of its requirements such as electronic and ionic conductivity, and catalytic activity with strong stability in redox condition, while several high performance air electrode materials -have been identified. For a long time, Ni-YSZ cermet has been regarded as the embodiment of this functional trinity. However, even though degradation associated with reversible operation can be mitigated, the cermet electrodes still suffered from agglomeration during redox condition. Recent electrode designs have been developed to microstructures consisting of a porous mixed ionic electronic conductor backbone decorated with metallic nanoparticles (typically Ni) by impregnation method. However, these are still hindered by the lack of cost and time-effective methods to produce both robustness and high-performance from their nanostructured electrodes. Here, a simpler alternative, will be introduced, exsolution whereby the catalytically active metal is substituted in the crystal lattice of the backbone in oxidizing conditions and exsolved on the surface as designed metal particles under reduction condition. Here we demonstrated a simple and highly effective in situ method for producing nanostructured electrodes capable of delivering high performances in both fuel cell and electrolysis mode. Both the nanostructures and corresponding electrochemical activity show no degradation over 150 hours of testing.
Enhancement of Thermal Stability of Sputtered Nanoporous Pt Thin Film Using Oxygen Plasma Treatment in Low Temperature Solid Oxide Fuel Cells
Authors: Liu Kang-Yu , Su Pei-Chen
Published: February 2020

Sputtered nanoporous platinum (Pt) thin films are common choices as catalytic cathodes for low temperature (300~500°C) solid oxide fuel cells (LT-SOFCs) for its high catalytic activity towards oxygen reduction reaction. However, the nanoporous pure Pt is vulnerable to thermal coagulation during high temperature operation, which often causes irreversible deterioration to the cell performance. In our earlier work, physical confinement of the nanoporous Pt with a few nanometers of zirconia (ZrO2) conformal coating by atomic layer deposition (ALD) improved the thermal stability of Pt significantly, with more than 50% of the cell power density retained after 80 hours of operation. Still, around 29.5% of cell power density degradation was observed in cells using ALD-ZrO2 capped nanoporous Pt cathode. It is likely that the poor adhesion between the Pt cathode and the yttria-stabilized zirconia (YSZ) electrolyte that caused the triple phase boundaries to be unstable under high temperature operation and therefore a significant thermal degradation is still observed.

In this work, we studied the effect of adhesion between Pt and YSZ on the morphological stability of nanoporous Pt at the Pt/YSZ interface. The surface of YSZ electrolyte was treated with oxygen plasma to modify the wettability between ALD-ZrO2 capped Pt and YSZ. The contact angle of a water droplet on the untreated YSZ surface was 80˚, while it dropped to 16˚ on the oxygen-plasma treated YSZ surface, meaning a more hydrophilic YSZ surface was obtained. The oxygen-based functional groups may have formed after the oxygen plasma treatment and increased the YSZ-water interfacial energy. The additional chemical bonding may exist if the nanoporous Pt films are deposited on surface-treated YSZ to stabilize the morphology of nanoporous Pt at the Pt/YSZ interface. The surface confined nanoporous Pt thin film cathodes were annealed at 600°C to induce the agglomeration, followed by delamination of the Pt cathode film from the YSZ substrate using double cantilever beam (DCB), in order to investigate the morphological stability of the nanoporous Pt at the Pt/YSZ interface after oxygen plasma treatment. The interfacial morphology observation showed that the Pt agglomeration at the Pt/YSZ interface remained significantly severe for Pt cathode with only ALD-ZrO2 surface capping. For Pt cathode deposited on YSZ substrate treated with 5 minutes of oxygen plasma at 18 watts showed improved interfacial thermal stability. A fuel cell with ALD-ZrO2 capped nanoporous Pt cathode thin film deposited on the oxygen-plasma treated YSZ electrolyte was tested. It was observed that the performance degradation was effectively hindered by the oxygen plasma treatment after 75 hours of operation at 450°C.

Figure 1
Secondary Phases at Cathode/Electrolyte Interfaces
Authors: Szász Julian , Wankmüller Florian , Joos Jochen , Wilde Virginia , Störmer Heike , Gerthsen Dagmar , Ivers-Tiffée Ellen
Published: February 2020

Understanding the nature of a cathode/electrolyte interface in solid oxide fuel cells (SOFC) is still a challenge, especially if this interface is composed of a mixed conducting cathode, i.e., La1-xSrxCo1-yFeyO3-
δ (LSCF), and a bilayer electrolyte, i.e., Gd-doped Ceria (GDC) interlayer and Y2O3 stabilized ZrO2 (YSZ) electrolyte. The interface resistance can vary over more than two orders of magnitude [1], resulting from variable volume and local distribution of the poorly ionic conducting secondary phase SrZrO3(SZO) [2] and GDC-YSZ interdiffusion (ID) [3].

This contribution will introduce a COMSOL Multiphysicsmodel, which simulates the performance characteristics of such heterogeneous cathode/electrolyte interfaces. The model is based on 3D-reconstruction data of an interface region, which was characterized (i) electrically by in-situ electrochemical impedance spectroscopy and (ii) by ex-situ elemental analysis using TEM/EDXS. Our model calculations quantify the contributions of both secondary phases, SZO and ID to the cathodic polarization resistance, but also a contribution of ID to the ohmic resistance, corresponding well to the performance measurements. Our results further reveal that interface morphology, i.e. volume and local distribution of secondary phases, plays a significant role. When GDC is sintered at high temperatures (see Fig.1 at 1300°C) to a continuous and dense ID layer (green color), SZO formation is still significant (turquoise color), but a comparatively small area of “free” pathways for oxygen ions from LSCF→GDC→ID→YSZ can reduce the polarization resistance up to two orders of magnitude. On the contrary; when GDC is sintered at lower temperatures, a much thicker and continuous SZO layer blocks the diffusion of oxygen ions, corresponding to the highest polarization resistance.

From our investigation we conclude that because secondary phases are inherently present and their local contribution overshadows every high-performing material property, it is of particular interest to deepen the understanding of functional cathode/electrolyte interfaces by using high-resolution analysis techniques.

References 

[1] J. Szász, F. Wankmüller, V. Wilde, H. Störmer, D. Gerthsen, N. H. Menzler, E. Ivers-Tiffée, ECS Transactions, 66 (2) (2015) 79-87.

[2] H. Yokokawa, N. Sakai, T. Horita, K. Yamaji, M.E. Brito, H. Kishimoto, J. Alloys Compd., 452 (2008) 41-47.

[3] A. Tsoga, A. Naoumidis, A. Gupta, D. Stöver, Mater. Sci. Forum, 308-311 (1999) 794-799.

Figure 1
Materials Diffusion Stability at Interface Between Stabilized ZrO2 Electrolyte and CeOx Interlayer in Model SOFC Cell
Authors: Ozawa Masakuni , Imura Kensuke
Published: February 2020

We observed the solid state reaction at the interface between ZrO2 electrolyte and CeOx interlayer in a model SOFC. At that interface, ZrOx and CeOx diffuse each other and the Zr-CeO solid solution lowers the cell performance. In this report, diffusion coefficient which enables to predict how much the reaction occurs is derived by using the ZrO2 / CeOx diffusion couples, simulating the long time operation. Stabilized ZrO2 powder and Gd-added CeO2 powder were laminated into two layers and pressed. To measure more practical interface, we chose the material powders used for cell production. Then the pressed powder was sintered at tempertures of 1350 to 1600 oC for 24 hours. The sintered blocks were cut into 3mm thick samples and polished. The ZrOx / CeOx interface were observed by scanning electron microscope (SEM) and analyzed about composition and their amount by Energy-dispersive X-ray spectroscopy (EDS).
Design and Fabrication of a Flat Tubular SOFC Stack
Authors: Xie Bin , Ji Weijie , Ming Li , Jiang Yousong
Published: February 2020

SOFC is now considered to be a most promising power generating technique for its high energy conversion efficiency and no pollution. To accelerate the commercial application of SOFcs, flat tubular stacks combining tubular and planar cell structures, show high performance and low cost fabrication techniques. To reduce the cost, metallic materials are applied as interconnects and supports and Ag-Cu braze is applied as ceramic-metallic seal.

In this work, we design and fabricate a 600W anode supported flat tubular SOFC stack. The stack is composed of 36 replaceable flat tubular cassettes made by FeCrAl alloy. Cells composed of NiO-YSZ (anode)/ YSZ (electrolyte)/LSM-YSZ (cathode) are sealed on cassettes by Ag-Cu braze.
Rapid Structure Degradation of Silver Under SOFC Conditions with a Ni-YSZ Anode and Methane-Oxygen Mixed Gas
Authors: Wang Zhihong , Lü Zhe
Published: February 2020

The structure stability of solid silver (Ag), is widely used current collectors for solid oxide fuel cells (SOFCs), is examined in methane-oxygen mixed gas at a furnace temperature range of 650-750 ℃. A rapid porosity formation is observed for solid Ag samples, especially with a Ni/yttria-stabilized zirconia (YSZ) anode, which is mainly attributed to simultaneous diffusion of oxygen, hydrogen and carbon monoxide into Ag bulk, followed by subsequent interaction resulting in the formation of H2O and CO2 gas. The obtained results indicate that the catalytic of Ni-YSZ anode plays an important role in the quick structure degradation of Ag under this condition. Furthermore, methane-oxygen-ration (R
mix) and operated temperature have significant influence on its structure stability. It indicates that Ag may not be a good choice to be employed under SOFC conditions with hydrocarbon-air mixed gas, especially on the anode side.
Effect of the WO3/Lipon Solid Electrolyte Interface on the Performance of All Thin Film Inorganic Electrochromic Devices
Authors: Oukassi Sami , Poncet Séverine , Giroud-Garampon Cédric , Salot Raphaël
Published: February 2020

In this work we report on the realization of an all solid state thin film electrochromic device and the effect of WO3/LiPON (lithium phosphorus oxynitride) interface on the cycling performance.

An icon-type device representing a 1 cm² QR code design was fabricated on glass substrate with the following architecture: ITO/WO3/LiPON/LixV2O5/AZO-Ag-AZO (Fig.1). Cross-sectional FIB-SEM observation showed layers with uniform thicknesses and interfaces free of delamination, voids or interdiffusion defects. The lithium in-depth distribution measured by ToF-SIMS showed a uniform and almost constant profile at the insertion electrodes (Fig.2)

The device bleaching and coloring was observed upon +/-2V voltage application with switching time of 60 s. Constant voltage bleaching/coloration cycles have been carried out, the icon type devices exhibited a moderate capacity fading during the first 1000 cycles with an average loss of 0.01% per cycle followed by an almost stable capacity up to 3000 cycles (Fig.3).

Furthermore, electrochemical impedance spectroscopy (EIS) carried out at different state of charges on ITO/WO3/LiPON/Li cell revealed the existence of an important charge transfer resistance at the WO3/LiPON interface (Fig.3). After comparison with EIS data obtained from the full electrochromic device, the charge transfer resistance at WO3/LiPON interface was identified as the predominant limiting step for fast switching times of considered devices.

Figure 1
Pathway Selection in Wet-Chemical Reaction for Hierarchical High Surface Nano-Ceria
Authors: Kim Hanbit , Shin Tae Ho
Published: February 2020

Ceria has been received great attention owing to its unique optical, electrical and magnetic properties that make it valuable material for solid oxide fuel cells, chemical mechanical polishing, gas sensors, UV-adsorbents and automotive three-way catalysts. We study to find the right pathway in low-cost synthesis processing for nano-ceria with tremendous high surface reactivity and redox/thermal stability. Wet chemistry needs to be designed in fastidious details in order to obtain the nano-ceria with anticipated properties by the control of hierarchical surface structure of the nano-ceria. Each cerias we make has been showed poor repeatability resulted from the final architectures of it, albeit, it is synthesized from the same reactant concentration. It would be the thermodynamic differences of the pathways lead to crucial distinction in structure of nano-ceria depending on reaction time, the moment concentration and the temperature. The Hierarchically well-constructed nano-ceria shows high thermal stability in consequence of sufficient space to avoid the agglomerating among the crystals could maintain its structure at high temperature. Thus, to determine the relation between the pathway and result thermodynamically is one of the crucial part of design the right wet-chemical reaction, in order to get the nano-ceria with high surface reactivity and the redox/thermal stability with good repeatability. Furthermore, hierarchical high surface nano-ceria could be used for electrochemical device operating in extreme condition.

Figure 1
Synthesis of Gadolinium Doped Cerium Oxide at Low Temperature for Ion Transport Membrane
Authors: Jin Yun Ho , Song Chul-Han , Jang Dae Hwan , Yang Jae-Kyo
Published: February 2020

Recently, Ion transport membrane (ITM) or solid oxide membrane (SOM) technologies have been developed for new metal reduction technology because traditional extraction process emitted massive CO and CO2 gas and consumed large amount of electricity. The membrane based extraction process is now a promising candidate for resolving previous problems. Using high oxide ion conductivity such as yttria-stabilized zirconia (YSZ) or gadolinium-doped cerium oxide (GDC) for solid electrolytes between the anode and liquid electrolyte.

Here we successfully were synthesized gadolinium doped ceria (GDC) below 100oC by urea-mediated routes in two steps. Gadolinium nitrate hydrates and Cerium nitrate hydrates were used as reagents. Hydrolysis reactions were induced by various concentration of Urea. The Collected powders were calcined to transform from cerium carbonate hydrates to cerium oxide at 700oC for 2 hours in air.

The GDC powders were analyzed by X-ray diffractometer (XRD) for reveal its phases. The amount of Gadolinium dopants were measured by X-ray fluorescence (XRF) and Energy dispersive X-ray spec troscopy (EDX). Scanning Electron Microscopy (SEM) and Transmission electron microscopy (TEM) were exhibits its size and morphology. Finally, its ion conductivity were measured by electrochemical impedance spectroscopy in various temperature for comparison with commercial YSZ.

Figure 1
Effects of Trace Copper on Shrinkage and Low-Temperature Co-Firing of Solid Oxide Fuel Cells
Authors: Shul Yong Gun , Jeon Oksung , Lee Jin Goo , Hwang Ho Jeong , Jeon Yukwon , Park Myeonggeun , Lee Gicheon , Ji Yunseong , Jang Jeongseok , Kwon Oh Chan , Hwang Jusoon
Published: February 2020

Solid oxide fuel cells (SOFCs) are an attractive power generation due to their high energy efficiency and possibility of waste heat recovery with operating at high temperature. SOFCs were fabricated by commonly three steps with pre-sintering of anode, dip-coating electrolyte and screen printing cathode materials cause of different shrinkages. It is hard to commercialize with these high manufacturing costs of multi-step process. SOFCs have been focused on low-cost materials and process for commercializing with high efficiency and performance. 8 mol % yttria-stabilized zirconia (8 YSZ) has been considered as one of the most conventional material for SOFC electrolyte. The 8 YSZ electrolytes doped with Cu contents which used as a sintering aid leads to densify the electrolyte and increase the shrinkage and performance. So we attempted to fabricate with one step co-firing process with 8 YSZ electrolytes at low temperature as 1250 oC. First of all, we found addition of trace Cu is effective to improve the sinterability of the YSZ electrolytes. The YSZ electrolyte with 100ppm CuO shows better sinterability and ionic conductivity than the pure YSZ electrolyte. The YSZ electrolyte with 100ppm CuO was densified below 1300 oC and the increased oxygen vacancy concentration leads to have higher ionic conductivity. Furthermore, the performances of the single-layer YSZ cells with 100ppm CuO were about 1.5 times higher(0.51 W cm2) than the cell with the pure YSZ electrolyte (0.36 W cm2) at 800 oC. The GDC/YSZ (100 ppm CuO) bi-layer cells also showed higher cell performance at 700 oC which shows similar tendency to the single-layer YSZ cell tests. These show that addition of 100 ppm CuO into the YSZ electrolyte is greatly effective for improvement of SOFC performance with energy saving during sintering process. According to these results of enhancing the sinterability and ionic conductivity, co-firing process was developed by addition of 5000 ppm Cu to the YSZ electrolytes and anodes at 1250 oC which is seriously lower than conventional multi-step fabrications with the sintering temperature above 1500 oC. The sinterability of the YSZ electrolyte was significantly improved 1250 oC by the 5000 ppm Cu. The co-fired cells with one- and two-step exhibited reasonable OCV value of 1.016 V and 1.011 V, respectively. Maximum power density of two-step cell with 0.71 W cm-2 at 850 oC which was similar value compared to conventional cell but the one-step cell has low maximum power density with 0.14 W cm-2. Above 1200 oC as sintering temperatures, the LSM/YSZ cathode produces insulating phases at the interfaces and low porosity makes cathode polarization. As a result, the cathode should be improved to be stable at 1250 oC, or the co-firing temperatures should be reduced below 1200 oC.
Reduced Temperature Sintering of GDC Electrolyte for IT-SOFCs
Authors: Woo Sang-Kuk , Choi Hyun-Jong , Seo Doo-Won , Kim Sun-Dong
Published: February 2020

Lanthanide material- (gadolinium or samarium) doped ceria (GDC or SDC) is considered one of the most advanced electrolyte materials for intermediate temperature (below 700 oC) SOFC (IT-SOFC) because of its high ionic conductivity at these temperatures. However, a high sintering temperature (above 1400 oC) is a disadvantage of the doped ceria. Metal oxides such as Fe oxide, Co oxide, Mn oxide, Li oxide, Ga oxide and Cu oxide were used as sintering aids to obtain the fully sintered electrolytes at a lower sintering temperature. In this study, the effect of a copper additive as a sintering aid to lower the sintering temperature for the construction of solid oxide fuel cells (SOFCs) was investigated. Gd-doped ceria (GDC) electrolyte with 0.25-10 mol% CuO sintering aid was prepared by reacting GDC power and copper nitrate solution followed by heating at 600 oC. The sintering of CuO-coated GDC powder was optimized by investigating linear shrinkage, microstructure, grain size, ionic conductivity, and activation energy of CuO-GDC electrolytes at temperatures ranging from 1100 to 1400 ¢ªC. The addition of Cu additive in GDC powder led to a decrease in the sintering temperature from 1400 to 1100 oC, which can result in the reduction of SOFC fabrication costs. For the GDC powder with 0.25 mol% Cu additive, linear shrinkage rates over the range of 1100 to 1400 oC were the highest (ca. 16.79-17.34 %). Regarding ionic conductivity, the 0.25 and 0.5 mol% Cu-added samples showed a higher value than the untreated GDC powder in the range of 550 to 750 oC, while the value for the 0.75 mol% Cu-added sample was lower. This result was evidenced by the occurrence of mechanical defects in body of the GDC samples with higher Cu contents (≥ 0.75 mol%). In addition, the activation energy of the CuO-GDC prepared in this work remained unchanged significantly. These results obtained in this study suggest that further investigations of proper sintering aids with the combination of different metal oxides and the optimization of GDC-electrolyte synthesis conditions may enable more stable and efficient SOFCs based on GDC.

Figure 1
Electrophoretically Deposited Copper Manganese Spinel Coatings for Interconnections in Solid Oxide Fuel Cells
Authors: Sun Zhihao , Gopalan Srikanth , Pal Uday Bhanu , Basu Soumendra Nath
Published: February 2020

Chromium poisoning of the cathode due to oxidation of metallic interconnections and subsequent formation of vapor phase chromium containing species is a well-known problem. The application of ceramic coatings on the interconnections to prevent this deleterious phenomenon is currently being extensively investigated.

Copper manganese spinel coatings of different compositions were deposited on Crofer 22 APU substrates containing grooves, by electrophoretic deposition (EPD). Thermo-gravimetric measurements under oxidizing conditions at 800°C were carried out to study the effectiveness of the coatings as diffusion barriers. Special attention was paid to coating thickness variations and adhesion around corners and the vertical walls of the grooves. Chromium diffusion into the spinel coatings as well as area specific resistance of the coatings at 800°C are reported.
The Correlative Approach of 3D Imaging Techniques, Simulation and Diffusion Experiments to Explore Transport Properties in Porous Otm Support Material
Authors: Tjaden Bernhard , Brett Daniel J.L , Lane Jonathan , Shearing Paul R.
Published: February 2020

Solid state electrochemical energy devices such as batteries, fuel cells and oxygen transport membranes (OTMs) have the potential to revolutionize distributed low-carbon power supply. However, in order to accelerate their commercialization across a range of applications, a much improved understanding of the underlying material microstructure is required.

In particular, the rate limiting step of an OTM membrane applied for syngas production is found in concentration losses caused by mass transport limitations. In this field, microstructural parameters, such as tortuosity, porosity and average pore diameter, play a vital role in characterising, comparing and evaluating porous materials. However, unlike the latter two parameters, tortuosity cannot be measured directly which is why different methods have been developed for this purpose. These differ considerably from each other in terms of calculation approach and data preparation techniques.

Here, we utilise X-ray nano computed tomography (CT) techniques to reveal the complex microstructure and resolve geometric features affecting mass transport of tubular porous support layers of OTMs to examine the relationship between the pore structure and mass transport (Figure 1). This is achieved via image based tortuosity calculation methods: a fast marching computational technique and a Laplace solver using MATLAB is employed to examine the geometrical tortuosity, and StarCCM+ and COMSOL software packages are used to model the heat flux and effective transport parameters of the porous phase, respectively.

In turn, the results are validated using diffusion cell experiments to evaluate the bulk transport properties of the same samples for different binary gas mixtures at different temperatures. Tortuosity is then extracted by applying equimolar and equimass diffusion models [1].

We conclude, that image based calculation methodologies arrive at lower tortuosity values in comparison to diffusion cell experiments (Figure 2). Even the widely used Bruggeman [2] and Maxwell relations prove to be unfit to estimate tortuosity values in the analysed microstructure. The observed difference may stem from Knudsen diffusion effects which are not accounted for in the entirety of tomography based modelling techniques. Secondly, tortuosity values extracted via diffusion cell experiments are a function of gas mixture, temperature and microstructural characteristics rather than a constant value. Consequently, care must be taken in applying purely continuum interpretations of diffusion processes in these complex porous media.

References

[1] B. Tjaden et al., Solid State Ionics, 2016.

[2] B. Tjaden et al., Curr. Opin. Chem. Eng., 2016.

Figure 1
Beyond Pretty Pictures to Useful Quantities: The Next Step in 3D Quantification of SOFC Electrodes
Authors: Tariq Farid , Yufit Vladimir , Kareh Kristina , Ruiz-Trejo Enrique , Bertei Antonio , Cohen Ed , Kishimoto Masashi , Brandon Nigel P.
Published: February 2020

Global demands for energy storage, supply and portability has seen continual increase. Meeting these demands in a clean efficient manner will be expedited through an ability to directly image energy devices such as SOFC electrodes, in 3D, at high resolutions. Tomographic techniques allow for the 3D imaging and characterisation of complex electrode microstructures down towards tens of nanometers; which are inadequately described in 2D. The performance of the electrode is dependent on nano/micro-structure as the electrochemical reactions and transport phenomena are strongly affected by the complex porous structure. Furthermore, during processing or operation microstructural evolution may degrade electrochemical performance.

However, although many studies have utilised 3D imaging, there is a need to understand the information beyond common metrics .e.g. porosity and tortuosity and pretty pictures. Increasingly large quantities of 3D or time-resolved 3D electrode data are simultaneously acquired and yet poorly understood, simply in favour of more 3D data acquisition.

Here we use tomographic techniques (X-ray & FIBSEM) to probe the 3D SOFC electrode structure at nanometer to micrometer length scales. Advanced characterisation of particle specific attributes e.g. necks, interfaces and particle clustering within SOFC electrodes is derived; the electrode is not treated as three monolithic phases. The electrode is quantified as the interaction of particles of three phases. Micro/nano structural changes are followed to facilitate understanding the differences which occur with shape, structures and morphology at high resolution. Results reveal clustering behaviour of particles. The results are also correlated with measured experimental values to provide insight into microstructure-property relationships. We correlate models and this advanced 3D quantitative analysis. In doing so, altogether this work provides important insights for electrode design, enabling 3D optimised structures to be created and understanding sources of performance degradation.

Figure 1
Garnet Based Li-Metal Batteries
Authors: Hu Liangbing
Published: February 2020

Metallic lithium metal is considered the “Holy Grail” for high-energy density batteries. However, using lithium metal in organic liquid electrolyte systems faces many challenges in terms of both battery performance and safety. A fundamental strategy is to develop a solid-state electrolyte (SSE) to mechanically suppress lithium dendrites and intrinsically eliminate SEI formation. Meanwhile, numerous solid-state inorganic Li+ electrolytes are being investigated to replace liquid organic LIB electrolytes and enable Li metal anode. Due to their high ion conductivity and excellent stability, Li-stuffed garnets are particularly attractive, which exhibit the most promising physical and chemical properties for SSEs. However, major challenges still exist in garnet based electrolytes, including: (1) Being either too thick with corresponding high ASR or too mechanically fragile when thin (~20 μm); (2) High temperature processing that is incompatible with most anode/cathode materials; and (3) High interfacial impedance for cell operations.

In this talk, I will discuss our recent research progress on Li metal batteries with garnet electrolytes, including:

(1) interface layer treatments to improve the wetting between Li metal anode and garnet electrolytes, and stabalize Li metal-garnet interface;

(2) Garnet nanofibers that allows the development of flexible, all solid state electrolyte.

I will also breiflydiscuss cell integrations and performance.
(Invited) Correlating Ion Transport with Structure in Interstitial Containing Oxides:Potential for New Electrolytes?
Authors: Skinner Stephen J.
Published: February 2020

Development of oxide ion conducting devices such as sensors, fuel cells and permeation membranes, has traditionally relied on the optimisation of materials with lattice vacancies through substitution, increasing the vacancy content and consequently conductivity. Whilst the ionic conductivity is a key parameter it is also essential to understand the surface exchange kinetics, stability and compatibility with other functional components. For many of the perovskite and fluorite based ion conductors the process of increasing vacancy content through substitution induces chemical instabilities, including cation segregation, that leads to reactivity and ultimately degradation in lifetime. In an effort to address some of these issues and to extend the compositional space available to materials developers we have considered the use of materials with inherent oxygen interstitial content.

A range of materials have been considered, mainly based on the scheelite framework, in which significant interstitial content can be accomodated. Two main series of oxide niobates are the subject of this study: CeNbO4+d and LaNbO4. In the first series of oxides the oxidation of the Ce3+ species on increasing temperature induces ordering and results in a fast ion transport pathway through these phases. Unusually these materials are also structurally modulated, and anisotropic in nature. The oxidation of the Ce species also induces electronic transport. Substitution of the Ce species with divalent cations did not significantly affect the ion transport. For the second series of oxides we have focused on hexavalent substitution of the Nb site to incorporate interstitials, modulate the structure and reduce the electronic transport.

Here we will discuss the potential of these modulated scheelite oxides as ion conductors, demonstrate effective electrolyte performance and correlate the ion transport with the structure of the materials, using a suite of advanced characterisation techniques.
(Invited) Advanced Electrolytes for Lithium Metal Electrode
Authors: Lee Hoogil , Jeon Hyunkyu , Ryou Myung-Hyun , Lee Yong Min
Published: February 2020

Advanced electrolyte containing functional additives as well as dissolved lithium salts in organic solvents has greatly upgraded the performance and reliability of lithium-ion batteries (LIBs). For example, a small amount of vinylene carbonate (VC) or fluoroethylene carbonate(FEC) is still indespensable to state-of-the-art LIBs to control solid electrolyte interphase (SEI) upon graphitic carbon anodes. However, due to the energy density limitation of conventional LIBs, post LIBs having lithium metal anodes have been extensively investigated for lithium metal secondary batteries, Li/S, Li/Air, etc. during the last ten years. But, without controlling lithium dendrite formation, post LIBs may end in an empty talk. Thus, there are a variety of previous works to suppress the lithium dendrite formation by placing organic/inorganic protection layers upon lithium metal, modifying the surface morphology, or adding some functional additives. In particular, since the last approach is the most facinating method owing to simplicity, we cannot help finding new additives for electrolytes. Herein, we intoduce recent researches on advanced electrolytes for lithium metal electrode first. And then, we apply a few good candidates to micropatterned lithium metals, which could deliver much more stable cycling performance than bare ones. Finally, some optimized advanced electrolyte and micropatterned lithium metal systems are proposed in more detail.
A New Technique for Measuring the Diffusion Coefficient of Electrolytes for Lithium-Ion Batteries
Authors: Schoenleber Michael , Weber André , Ivers-Tiffée Ellen
Published: February 2020

The electrolyte is a crucial component in modern Lithium-Ion batteries. It is responsible for the transport Lithium-Ions not only through the separator but also within the porous structure of the electrodes. A small diffusion coefficient of the electrolyte leads to an increased voltage drop due to depletion of Lithium-Ions and thus limits the performance of a battery for high currents. While the diffusion coefficient is mostly measured by potentiostatic or galvanostatic intermittent titration techniques (PITT or GITT), also an evaluation of the diffusion impedance of the electrolyte should yield according values. However, standard impedance measurement techniques like Electrochemical Impedance Spectroscopy (EIS) suffer severe disadvantages: Due to the sinusoidal excitation a current is permanently flowing and, in case of beneficially used metallic Lithium electrodes, Lithium is continuously being deposited and stripped. This causes a continuously changing surface area during the measurement and hence a time-variant and thus invalid impedance spectrum. Moreover, the diffusion impedance needs to be measured down to very low frequencies, which results in very long measurement times for regular Electrochemical Impedance Spectroscopy. As an adequate solution for both issues we suggest computing the diffusion impedance from time-domain measurements [1]: By choosing an appropriate excitation signal, changes within the system during measurement can be prevented and, as all frequencies are excited simultaneously, measurement time can be minimized. By experimentally shifting the diffusion process to lower frequencies we are further able to clearly separate it from other, surface reaction related processes and thus to isolate the diffusion impedance. For an example see Figure 1, where repeated measurements of the diffusion impedance of LiPF6 in EC/DMC (1:1) are shown. From the time constant of the diffusion impedance, the diffusion coefficient of the electrolyte is finally obtained.

Caption Figure 1:

Repeated measurement of the diffusion impedance of LiPF6 in EC/DMC (1:1), as it is commonly used in Lithium-Ion batteries (real-parts shifted to origin).

References:

[1] D. Klotz, M. Schönleber, J. P. Schmidt and E. Ivers-Tiffée, "New approach for the calculation of impedance spectra out of time domain data", Electrochimica Acta 56, pp. 8763-8769 (2011)

Figure 1
Electrochemical Characterization and Interfacial Chemistry of Tin-Based Anode Materials for Mg-Ion Batteries
Authors: Nguyen Dan Thien , Tran Xuan Minh , Song Seung-Wan
Published: February 2020

Magnesium-ion batteries have received a particular attention as one of the beyond-lithium ion batteries for next-generation energy storage system applications. Magnesium is earth abundant and low cost compared to lithium, and environment-friendly, and provides higher theoretical volumetric capacity (3833 mAhcm-3) than lithium.1 The use of magnesium metal anode is often limited due to the formation of surface blocking layer in conventional electrolyte such as magnesium salts (TFSI-, ClO4
-, BH4
-) in ether-based solvents. To overcome these problems, recently insertion-type materials such as Sn, Sb, Pb and Bi, which is based on the alloy reaction with magnesium, have been proposed as a new class of anode materials for magnesium-ion batteries.2,3 However, studies on the materials’ intrinsic electrochemical characteristics and the interfacial chemistry between alloy anode and electrolyte are yet to be reported.

In the present study, we have investigated on the electrochemical and interfacial reaction behavior of tin-based anode materials in magnesium cells. Changes with cycling in their structure, surface property and particle morphology would be discussed in the meeting.

Acknowledgements

This work was supported by National Research Foundation of Korea (2015062107).

 

References

1. D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich and E. Levi, Nature, 407, 724 (2000).

2. N. Singh, T. S. Arthur, C. Ling, M. Matsui, and F. Mizuno, Chem. Commun. , 49, 149 (2013).

3. F. Murgia, L. Stievano, L. Monconduit, and R. Berthelot, J. Mater. Chem. A,

3, 16478 (2015).
Preferentially Ordered Solid Electrolytes for Fuel Cell and Lithium Battery
Authors: Fang Yu-shin , Wang Robin Chih-Hsing , Chang Alice Yi-han , Chu Peter Po-Jen
Published: February 2020

Electric field induces temporary polarization on molecular segment. In polymer solution or polymer melt, applying electric field induces self assembly that cannot be established otherwise. This preferentially ordered morphology is preserved after drying out solvent to form polymer membrane. The ordered nano structure delivered favorable ion transport behavior, raised ion conductivity, and improved membrane mechanical properties.

In one example given for fuel cell membrane composed of poly(ether sulfones)(PES) with sulfonated poly(ether ether ketone)(sPEEK, degree of sulfonation=50%) prepared with e-field poling, extremely high ion conductivity (7.43x10-2 S/cm) is observed. The hydrophilic dimension is found to be reduced which restricted methanol permeability (3.17x10-7 cm2/s). Due to more densely packed hydrophobic domain, membrane mechanical property is also improved. DMFC power output at 150mA/cm2 (80 oC, 1M Methanol) can be realized.

A second example is given for lithium battery membrane: Poly(vinylidenefluoride-co-hexafluoropylene)[PVDF-HFP] blending either with PMMA polymer, or with surface functionalized mineral clay containing ionic liquids. E-field has improved PVDF and PMMA miscibility, gave rise to more organized and more polar beta crystallite formation with denser amorphous region. The clay is homogeneously dispersed and oriented to form ordered and preferentially aligned nanostructure. As a result, the solvent free membrane delivered Li+ conductivity surpassing 10-3 S/cm at room temperature, and shows reduced interface resistance between electrodes. Coin cell (R2032) using this SPEs and LiFePO4cathode displayed 140 mAh/g discharge capacity and stable over 300 cycles, with 0.5C rate.

Membrane bearing preferentially ordered morphology induced by E-field is able to balanced high ion conductivity; low fuel/gas permeation and strong mechanical strength, simultaneously. This approach in preparing high performance membrane holds great promises to apply to future energy devices such as Li-S, Li-Air, and thin film battery.
Nanohybrid Polymer Electrolytes with Enhanced Safety and Electrochemical Performance
Authors: Wei Weifeng , Zhang Jinfang , Ma Cheng
Published: February 2020

Rechargeable Li/Na-ion batteries have been studied extensively for the electric and energy industries, but currently used liquid electrolytes have serious safety risks (combustion and explosion). Besides, nonuniform ion (Li+/Na+) deposition on the negative electrode upon cycling would eventually cause the cell to fail. Hence, the development of safe, stable, and long-life Li/Na-ion batteries is being intensively pursued to enable high-energy-density storage system applications. Solid polymer electrolyte (SPE) is attracting considerable attention to handle potential safety risk and regarded as a safer alternative to satisfy the needs for high-performance batteries. However, low conductivities and insufficient electrode-electrolyte interfaces still hinder the potential applications of SPEs.

Here we have been targeting poly(ethylene glycol) methyl ether methacrylate (PEGMEM) and devoted a large amount of research to modifying the polymer matrix, including copolymerization of PEGMEM and SMA (stearyl methacrylate), OV-POSS based graft polymer electrolyte with star-shaped structure and construction of cross-linked branching nanohybrid polymer electrolyte by functionalized nanoparticles with polymer chains. We focus on the exploring the interfacial design to enhance interaction between nanoparticles and the polymer matrix, and utilize microscopic and spectroscopic analyses to better understand the interfacial chemistry between particles and polymeric chains.