bluuebunny/crossref_metadata_2025 huggingface dataset:
Highly Porous Carbon Nanospheres and Carbon Foams for Supercapacitors Using Facile Spray Pyrolysisand One-Pot Reaction
Authors: Wang Chengwei , O'Connell Michael J. , Chan Candace K.
Published: February 2020

Due to their unique properties, high surface area carbon nanomaterials such as carbon nanotubes and

graphene have been widely used in energy storage applications. However, it is still difficult and

expensive to synthesize carbon nanotubes and graphene at large-scales. Hence, there is still a need for

the development of low-cost and facile synthesis techniques for porous carbon materials with highly

accessible surface areas.

A facile and solution-based, spray pyrolysis synthesis technique which was used to synthesize individual

carbon nanospheres with specific surface area (SSA) up to 1106 m2/g using a novel ZnO catalyzed

reaction. The carbon nanosphere diameters were tunable from 10 nm to several micrometers by varying

the precursor concentrations. Solid, hollow, and porous carbon nanospheres were achieved by simply

varying the ratio of catalyst and carbon source without using any templates. When evaluated as

supercapacitor electrode materials, specific capacitances of up to 112 F/g at a current density of 0.1 A/g,

were observed, with no capacitance loss after 20,000 cycles. The performance of the carbon

nanospheres as electrodes in Li-ion batteries were also investigated.

The direct pyrolysis of sugar and zinc nitrate mixtures was employed to obtain foam-like carbons with

specific surface area (SSA) up to 2340 m2/g without using any hard templates. The role of the ZnO

nanoparticles formed from the decomposition of zinc nitrate and the effects of high temperature

annealing on the formation of the high SSA carbon foams were systematically studied. Due to the facile

and quick reaction conditions, these carbon foams carbons could be easily synthesized at a large scale.

When used as supercapacitor electrode materials, a specific capacitance up to 280 F/g was achieved at

current density of 0.1 A/g, and still remained as high as 207 F/g even at a high current density of 10 A/g.

References:

C. Wang, Y. Wang, J. Graser, R. Zhao, F. Gao, M.J. O’Connell, ACS Nano, 7, 11156-11165 (2013).

V. Etacheri, C. Wang, M.J. O’Connell, C.K. Chan, V.G. Pol, J. Mater. Chem. A, 3, 9861-9868 (2015).

C. Wang, M.J. O’Connell, C.K. Chan, ACS Appl. Mater. Interfaces, 7, 8952 (2015).
Structure-Directed CNT Arrays As Micro-Supercapacitor Electrodes and the Effect of Geometry on Electrolyte Selection
Authors: Nicol Katherine T , Hill Justin J
Published: February 2020

The demand for power-dense and energy-dense storage devices is growing rapidly. While supercapacitors offer high power density, improving the energy density can be obtained by precisely tuning the electrode nanostructure and pairing it with the appropriate electrolyte.  Multi-walled carbon nanotubes (MWNTs) are a promising electrode material for EDLCs because of their high electrical conductivity, chemical stability and exceptionally high surface area. Until single walled carbon nanotubes can be produced as solely conductive structures, low-diameter MWNTs offer the best properties with regard to carbon-based EDLC electrode materials. When MWNTs are fabricated in anodic aluminum oxide templates, a MWNT is grown within each nanopore, resulting in an ultra-high density vertically-aligned array. Vertically-aligned MWNTs offer numerous benefits, such as directed charge transport and high density packing, leading to a higher active surface area and better rate capabilities than observed with randomly-dispersed networks. We have demonstrated the fabrication and performance of these electrodes in non-pseudocapacitive supercapacitors with both organic and ionic liquid electrolytes. While these benefits are beneficial for all capacities of supercapacitors, they are increasingly important in the production of micro-supercapacitors, when it is essential to use all device volume efficiently. Despite the benefits, this highly oriented electrode design combined with the remnants of the template can lead to unique current distributions and behaviors in a coin cell test set-up. We will discuss the differences in electrochemical capacitive behavior of traditional and our anisotropic electrodes. There exists unique stability criteria in nanostructured domains that must be considered when designing this electrochemical system - specifically the current and potential distribution due to the MWNT curvature and constant phase element behavior. Through thorough characterization of the electrode structure and electrolyte behavior, we have successfully demonstrated cells with a projected energy and power density of 108 Wh/kg-carbon and 768 kW/kg-carbon.
Freestanding Graphene/Carbide Derived Carbon Films As High-Performance Electrodes for Electrochemical Capacitors
Authors: Alhabeb Mohamed , Beidaghi Majid , Van Aken Katherine L , Gogotsi Yury
Published: February 2020

Freestanding films of reduced graphene oxide (rGO) have attracted much attention as electrodes for electrochemical capacitor, especially for flexible device applications. However, graphene paper electrodes are usually limited in thicknesses to less than 10 μm, as increasing the electrode thickness hinders its performance due to restacking of rGO sheets and slow diffusion of ions  [1]. To prevent this problem, carbon nanoparticels such as carbon nanotubes (CNTs) are frequently used as nanospacers between the rGO sheets to increase the electrolyte accessibility and electronic conductivity of the films [2]. However, CNTs have a much lower capacitance compared to rGO and their addition limits the overall capacitance of the freestanding electrodes.

In this study, for the first time, we have used highly porous carbide derived carbon (CDC) nanoparticles as spacer between graphene sheets and fabricated thick rGO/CDC hybrid electrodes. The electrodes were made by thermal reduction of GO/CDC papers fabricated by vacuum-assisted filtration of aqueous solutions of GO and CDC containing 10, 20, and 30 wt. % of CDC. Utilizing the high surface area and conductivity of rGO and the accessible pores of the CDC [3], the hybrid electrodes showed specific capacitances as high as 200-210 F/g at a high scan rate of 100 mV/s in an aqueous electrolyte. The addition of CDC between the rGO layers increases the accessibility of active material to the electrolyte ions and we observed good performance of the electrodes with the thickness of 40-50 μm.

References:

1.  Oh, Y.J., et al., Oxygen functional groups and electrochemical capacitive behavior of incompletely reduced graphene oxides as a thin-film electrode of supercapacitor. Electrochimica Acta, 2014. 116: p. 118-128.

2.  Wang, Y., et al., Preventing Graphene Sheets from Restacking for High-Capacitance Performance. Journal of Physical Chemistry C, 2011. 115 (46): p. 23192-23197.

3.  Chmiola, J., et al., Anomalous increase in carbon capacitance at pore sizes less than 1 nanometer. Science, 2006. 313 (5794): p. 1760-3.
Environmental Friendly Electrode Preparation for Hybrid Battery-Supercapacitors Based on Li3V1.95Ni0.05(PO4)3/C and Activated Carbon
Authors: Meuser Carmen , Tran Hai-Yen , Secchiaroli Marco , Dsoke Sonia , Wohlfahrt-Mehrens Margret
Published: February 2020

In the last years, hybrid battery-supercapacitors have been a rising interest toward the improvement of both the energy density and power density in comparison to the classical systems [1]. By using Li-insertion materials and activated carbon it is possible to develop high energy and high power density Li-ion supercapacitors. Among the various numbers of Li-ion materials, Li3V1.95Ni0.05(PO4)3/C shows excellent performances at very high C-rates, with very high specific discharge capacity (93 mA h g-1 at 100 C) and a capacity retention of 97% after 1000 cycles [2]. Most of the currently used Li-ion battery electrodes are based on poly(vinylidene difluoride) (PVDF) due to its good electrochemical stability and binding capability within the electrode composite. However, the cost and the environmental impacts of these widely used PVDF based electrodes are still a concern in the battery industry. Thus, lot of effort has been put toward the pursuit of an environment-friendly, cost-effective binder for lithium-ion batteries, such as carboxymethyl cellulose (CMC) and polyacrylic acid (PAA) [3].In this study, the effect of CMC and PAA binders in the battery-like counter part on the mechanical and electrochemical behaviour in the hybrid battery-supercapacitor electrodes is explored (see Table 1). In particular, Li3V1.95Ni0.05(PO4)3/C has been studied both as high energy and high power anode and cathode, between 3.0-1.5 and 3.0-4.3 V vs. Li+/Li. Commercial activated carbon (AC) (Haycard) and LP30 (Merck) has been used as counter electrode and electrolyte, respectively. Furthermore, the functionalization of PAA during the electrode preparation will be investigated and shown during the presentation.

 

Table 1. Electrode compositions.

Compositions
Active material
LVNP / wt.%
Conductive agent
Super P / wt.%
Binder /wt.%

1
80
10
9% CMC + 1% SBR

2
85
5
9% CMC + 1% SBR

3
86
5
9% PAA

 

References

[1] D. Cericola, R. Kötz, Electrochim. Acta 72 (2012) 1–17.

[2] M. Secchiaroli, G. Giuli, B. Fuchs, R. Marassi, M. Wohlfahrt-Mehrens, S. Dsoke, DOI: 10.1039/c5ta00976f.

[3] J. Chong, S. Xun, H. Zheng, X. Song, G. Liu, P. Ridgway, J. Q. Wang, V. S. Battaglia, J. Power Sources 196 (2011) 7707– 7714.

Acknowledgments

Financial support from the German Federal Ministry of Education and Research (BMBF) under the grant 03EK3021 is gratefully acknowledged.
Solvothermal Synthesis of Copper Ferrite-Graphene Nanocomposite As a Supercapacitor Electrode Material
Authors: Piao Yuanzhe
Published: February 2020

In recent years, electrochemical supercapacitors have attracted great attention due to their advantages of short charging times, a long cycle, and high power density. In order to fullfill the market demand for further improved performance, the design of materials with a longer cycling lifetime, higher energy density and economic efficiency is imperative for supercapacitor electrode. Since the performance of electrode materials for supercapacitors is dependent on the accessible specific surface area and the pore structure, the control over structure and morphology of electrode materials is an effective strategy to render them high surface area and efficient paths for ion diffusion. Recently, the applications of graphene based nanocomposites for supercapacitor have attracted much research interest.

Here, a simple method to prepare a uniform sized copper ferrite nanoparticles attached graphene nanosheet is reported. A one-step solvothermal method featuring the reduction of graphene oxide and formation of copper ferrite nanoparticles was efficient, green, and controllable. The composite nanosheet was characterized by using X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy, which demonstrated that the copper ferrite nanoparticles with a diameter of approximately 100 nm were densely and compactly deposited on graphene nanosheet. To investigate the formation mechanism of the copper ferrite nanoparticles attached graphene nanosheet, the effects of a series of experimental parameters, including the concentrations of the precursor, precipitation agent, stabilizer agent, and graphene oxide on the size and morphology of the resulting products were discussed in detail. Furthermore, the electrochemical performances of the copper ferrite nanoparticles attached graphene nanosheet as electrode material for supercapacitor were studied by using cyclic voltammetry and galvanostatic charge-discharge measurements. The nanocomposite showed high electrochemical capacitance of 576.6 F/g at 1 A/g, good rate performance and cycling stability. These results demonstrated that the nanocomposite had a high specific capacitance and good retention. The versatile copper ferrite-graphene nanocomposite held great promise for a wide range of electrochemical fields due to the remarkable synergistic effects between copper ferrite nanoparticles and graphene.
Annealing-Induced Surface Segregation and SrSO4 Formation on La0.6Sr0.4Co0.2Fe0.8O3
-δ
Cathodes
Authors: Bagarinao Katherine Develos- , De Vero Jeffrey Centeno , Cho Do-Hyung , Kishimoto Haruo , Yamaji Katsuhiko , Horita Teruhisa , Yokokawa Harumi
Published: February 2020

La0.6Sr0.4Co0.2Fe0.8O3
-

δ
(LSCF) perovskite oxide is one of the most important cathode materials being developed for intermediate-temperature solid oxide fuel cells (IT-SOFCs); however, it is prone to surface segregation leading to the formation of undesirable secondary phases and reduction of active surface sites. In this study, dense LSCF thin films having controlled surfaces were epitaxially grown using pulsed laser deposition (PLD) on gadolinia-doped ceria (GDC) films with (100), (110), and (111) orientations, and then subjected to long-term annealing at 800°C and 900°C in air for 1-3 months. Detailed microstructural characterizations revealed preferential surface segregation for LSCF thin films which are predominantly (110)-oriented, conversely this appears to be mostly inhibited for (100)-oriented (pseudocubic) LSCF films, which exhibited extensive pore formation on the surface. Compositional and structural analyses revealed that the surface-segregated crystallites are SrSO4 in origin, which is attributed to the reaction of the segregated Sr cations from LSCF with SO2 present in the air. Furthermore, SrSO4 formation on LSCF surfaces was accompanied by drastic morphological changes as well as decomposition of the perovskite phase. These results have implications toward tailoring the performance of cathode surfaces by understanding the dependence of cation segregation on driving forces such as surface chemistry and microstructure.
Quantifying Chemical Expansion of Non-Stoichiometric Oxide Thin Films: Challenges and Opportunities
Authors: Swallow Jessica G. , Kim Jae Jin , Chen Di , Bishop Sean R. , Smith James F. , Tuller Harry L. , Van Vliet Krystyn J.
Published: February 2020

Non-stoichiometric oxides used for the electrodes and electrolytes of solid oxide fuel cells (SOFCs) typically exhibit chemical expansion behavior due to the large defect concentrations required for high ionic conductivity or gas reactivity. Robust SOFC design requires knowledge of how chemical expansion contributes to mechanical strains at interfaces, as such deformation promotes dislocation mobility, delamination, and fracture. Direct measurement of chemical expansion via X-ray diffraction or dilatometry typically requires long time scales (minutes to hours) to allow equilibration of gas atmospheres or bulk samples, or to allow adequate signal detection in the absence of synchrotron access. Here, we describe a new approach to directly and rapidly quantify dynamic chemical expansion of non-stoichiometric oxides in situ at elevated temperatures up to 650ºC, and demonstrate this method for the mixed-ionic-electronic conducting Pr0.10Ce0.90O2-δ (PCO) as a model SOFC electrode.  The activity of oxygen is modulated via sinusoidal electrical bias signal, while amplitude and phase lag of film expansion are detected with second-scale temporal resolution and sub-nanometer displacement resolution. These dynamic chemical expansion measurements are coupled with defect models of PCO to advance understanding of defect concentration and mobility under oscillating electrical potential. Extensions of this approach to estimate activation energies, lateral expansion differences, and breathing modes of multilayered electrodes are discussed. This approach provides facile access to dynamic chemical expansion under in operando conditions of SOFC electrodes, facilitating improved design of materials that withstand large chemomechanical changes during SOFC start-up, shut-down, and redox cycling.
Preparation and Characterization of Pr0.6Sr0.4CoO3-δ
Cathodes in IT-SOFC
Authors: Kanarbik Rait , Kivi Indrek , Tiirats Taavi , Möller Priit , Lust Enn
Published: February 2020

The Pr0.6Sr0.4CoO3-δ (PSC) and La0.6Sr0.4CoO3-δ (LSC) SOFC cathodes were prepared and deposited onto Ce0.9Gd0.1O2-δ | Zr0.85Y0.15O2-δ | Ni-Zr0.85Y0.15O2-δ anode supported half-cells for cyclic voltammetry, electrochemical impedance and chronoammetry analysis. The electrochemical analysis has been conducted under various working temperatures from 550 °C to 800°C and under various fuel and compositions. The performances of PSC and LSC based single cells at 800 °C were comparatively high with maximum power output 1.48 W/cm2 and 1.28 W/cm2, respectively. It was established that the power output under the same conditions for PSC based SOFC single cell showed slightly higher values comparing to LSC based cells. Short term stability tests show that the both materials have good stability at 700 °C and at cell potential 0.8 V and power output 540 mW/cm2.

Figure 1
Solid Oxide Fuel Cells Using Novel Cathodes in the BaO-Co2O3-Fe2O3 Composited withGDC10
Authors: Hing Peter , Sukleung Montri , Voo Nyuk Yoong , Lim L C , Atkinson Alan
Published: February 2020

Most current cathodes for SOFCs such as LSM, LSC and LSCF contain lanthanum oxide. The tendency for the lanthanum oxide to absorb moisture and degrade the materials make processing a critical issue. In this study, we have explored the fabrication of cathode materials free from lanthanum oxide. Compositions with high electrical conductivity in BaO-Y2O3-Fe2O3 and BaO-Y2O3-Co2O3-Fe2O3 systems have been obtained. Selected compositions with high electrical conductivities up to 600Scm-1 have been composited with GDC10 solid oxide electrolyte to form composite cathodes with matching thermal expansion to GDC10 for solid oxide fuel cells(SOFCs). Symmetrical cells with GDC10 between the experimental composite cathodes, and small SOFCs with GDC10 as electrolyte, GDC10.NiO as anode and experimental composites as cathodes have been constructed and evaluated up to 800oC. The electrical conductivity, thermal expansion, impedance and power densities have been studied. The power densities between 400oC and 800oC have been measured. The power density obtained at 800oC is found to be about 600mW/cm2. The results are presented and discussed in relation to the processing of the materials, properties, microstructures and performance of the solid oxide fuel cell. Ways to enhance the performance of the SOFCs are highlighted.
Development of a Novel Co-fired SOFC at Murata
Authors: Mori Naoya , Sato Yosuke , Nakai Hideaki , Iha Michiaki , Takada Takahiro , Konoike Takehiro
Published: February 2020

Murata Manufacturing Co., Ltd. has been developing planar-type solid oxide fuel cells (SOFCs) based on new design concept.  The cell is fabricated by a single-step co-firing process and consists of an electrolyte, electrodes, current collectors, gas-separators with manifolds, and gas-flow channels. The membrane electrode assembly (MEA) is sandwiched between ceramic gas-separators with via-hole electrodes providing electrical paths between cells. Murata’s new concept stack achieved volume power density higher than 0.5kW/L. By arranging gas manifolds in the central part of the cell, the temperature distribution in plane of the cell was moderated while keeping high volume power density. As a result, the stack operated stably at high efficiency. A long-term operation has been carried out at 750°C over 8000h under galvanostatic condition. The cell power degradation rate was less than 0.20%/kh after 2000h operation. Cr poisoning in the LSCF cathode after durability test was not observed. That is one reason of high durability of the cell.
Beyond the 3rd Generation of Planar SOFC: Development of Metal Foam Supported Cells with Thin Film Electrolyte
Authors: Han Feng , Semerad Robert , Constantin Guillaume , Dessemond Laurent , Costa Rémi
Published: February 2020

Manufacturing of thin and gas tight electrolyte is still a challenging issue for metal supported solid oxide fuel cells (SOFCs). In this work, we present a porosity graded multi-layer structure supporting thin film electrolyte. The substrate is made of NiCrAl metal foam impregnated with La-substituted SrTiO3 (LST) ceramic. Furthermore, a 20 µm thick composite anode functional layer with LST and gadolinium doped ceria (GDC) was deposited onto the substrate. The surface of the anode functional layer is later engineered with a suspension of nano-particles with 40 nm average particle size of yttria-stabilized zirconia (YSZ). This results in a mesoporous layer with smooth surface able to support a thin film GDC layers. Finally, a gas-tight GDC electrolyte was deposited by EB-PVD method. The thickness of the thin-film YSZ layer and the gas-tight GDC layer was approximately 1 µm and 2 µm, respectively. Button half cells with size up to 25cm² were successfully produced showing an air leakage rate down to 7.0*10-4 (hPa*dm3)/(s*cm2), satisfying the gas-tightness quality control threshold of the state of the art metal supported SOFCs at DLR. Full cells with LSCF cathodes were then produced and electrochemically tested presenting stable Open Circuit Voltage near to 1V. Results will be presented and discussed in this paper by confronting the performance with the cell microstructure.

Key Words: metal foam, thin-film, electrolyte

The research leading to these results has received funding from the European Union‘s Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement n° 303429
Small Scale Power Generation for Road Trucks with Planar SOFC System
Authors: Bossel Ulf
Published: February 2020

There is increasing interest in small SOFC generators for the conversion of commercial butane/propane fuel into DC electricity. However, with minor modification of the pre-reformer such units can also be used for the conversion of methane, natural gas, biogas or LNG.  A consortium of six groups form the UK, Spain, Poland and Switzerland is presently engaged in the development of a small SOFC power source for road trucks powered by LNG. The project “SAFARI” is funded by the FCH-JU Programme of the European Union.

Two different types of SOFC are simultaneously prepared for comparative evaluation. While the project leader “Adelan Ltd.” is optimizing its tubular SOFC design (see separate conference presentation), ALMUS AG is perfecting its planar approach for road truck applications. Stacks of 60 mm x 60 mm foot print are used. They are composed of metal bipolar plates and anode-supported cells. To match the generator output to the power demand, up to four such stacks can be arranged in line, each delivering up to 80 Watts at 24 VDC and 700°C operating temperature. For low heat losses and maximum conversion efficiency, the stack arrangement is surrounded by a 100 mm thick thermal jacket made of the best available insulation material (silica gel). The arrangement is contained in a metal box for safe handling and mounting on the truck platform. A partial oxidation methane reformer is part of the system. Start-up heat is generated by burning small amounts of fuel.    

Technical details and first test results will be presented.
Analysis of a Solid Oxide Fuel Cell System with Low Temperature Anode Off-Gas Recirculation
Authors: Engelbracht Maximilian , Peters Roland , Blum Ludger , Stolten Detlef
Published: February 2020

The daily growing global energy consumption has to be provided in the future by technologies which emit increasingly less greenhouse gases. This requires highly efficient energy systems. Methane fueled SOFC systems are already able to produce electricity with an efficiency up to 60 %. Through the combined use of produced electricity and thermal energy the overall efficiency can be above 90 %.

One possibility for a further improvement of the electrical efficiency is the implementation of an anode off-gas recirculation loop. Challenging is the high anode off-gas temperature of at least 700 °C, which prohibits the use of commercial components. Therefore, the use of ejectors and blowers with or without anode off-gas cooling are discussed in literature. At Forschungszentrum Jülich an anode off-gas recirculation loop operating at temperatures up to 200 °C is favored. To analyze the effect of anode off-gas recirculation, a dynamical model of the system including the recirculation loop was implemented in Matlab/Simulink®. The results show, that the recirculation rate has a huge effect on the electrical efficiency (both positive and negative). In principle, at constant current density high recirculation rates decrease the cell voltage and increase the power consumption of the recirculation blower. Therefore, the highest electrical efficiency can be reached with high systems fuel utilizations, low recirculation rates and in consequence high stack fuel utilizations. On the other hand less amount of steam is available for the reforming reaction at low recirculation rates, therefore the minimum recirculation rate is determined by the formation of carbon. An optimal operation range to avoid carbon formation and to ensure a high electrical efficiency requires recirculation rates between 65 and 70 % and system fuel utilizations above 90 %. This leads to acceptable stack fuel utilizations in the range of 70 to 75 % and electrical efficiencies above 60 %.
Thermodynamic Stability Assessment of MIEC Cathode Materials for Solid Oxide Fuel Cells
Authors: Cetin Deniz , Yu Yang , Luo Heng , Lin Xi , Pal Uday Bhanu , Basu Soumendra Nath , Gopalan Srikanth
Published: February 2020

Mixed ionic-electronic conductor (MIEC) cathode materials such as La(1-x)SrxCo0.2Fe0.8O3-δ (LSCF,where x=0.2, 0.3, 0.4), Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF 5582), Sr2Fe1.5Mo0.5O6-δ (SFMO), La2NiO4+δ (LNO), GdBaCo2O6-δ (GBCO), and PrBaCo2O6-δ (PBCO) exhibit excellent oxygen transport properties as well as high electronic conductivity at operational temperatures of SOFCs. Their promising electrochemical performance make these materials excellent candidates for potential application as SOFC cathodes. However, their long-term thermodynamic stability in the operating environment of SOFCs, including unexpected and uncommon situations such as CO2-leakage from the anodic side is of concern and should be thoroughly investigated prior to deploying them in cells and stacks.

This study investigates the thermodynamic stability of promising SOFC cathodes under operating conditions, in molten salt media, and through galvanic cell measurements. The cathode materials of interest are La(1-x)SrxCo0.2Fe0.8O3-δ (LSCF, where x=0.2, 0.3, 0.4), Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF 5582), Sr2Fe1.5Mo0.5O6-δ (SFMO), La2NiO4+δ (LNO), GdBaCo2O6-δ (GBCO), and PrBaCo2O6-δ (PBCO). The stability of these materials is studied in air and at various CO2 partial pressures.
Investigating the Relationship between Operating Conditions and SOFC Cathode Degradation
Authors: Pellegrinelli Christopher , Huang Yi-Lin , Taillon Joshua A. , Salamanca-Riba Lourdes G. , Wachsman Eric D.
Published: February 2020

High polarization losses associated with the oxygen reduction reaction (ORR) that occurs at the cathode and degradation of cathode materials under operating conditions remain serious issues for widespread implementation of solid oxide fuel cells (SOFC). Performance of the cathode is determined by the microstructural/interfacial relationship between the electrode and electrolyte, and the inherent materials properties. Rates of degradation depend significantly on the operating temperature, applied-potential, and environmental conditions, such as the presence of unwanted oxygen-containing compounds, namely H2O and CO2. Common degradation mechanisms can be categorized into three main groups: sintering, poisoning, and secondary phase formation. In this study we explore the effects of operating conditions on the above degradation mechanisms for two common cathode materials, (La0.8Sr0.2)0.95MnO3±δ (LSM) and (La0.6Sr0.4) (Co0.2Fe0.8)O3-δ (LSCF) using a multifaceted approach. Three-electrode cells have been aged under various temperatures, applied-potentials, oxygen partial pressures and contaminant conditions in order to observe changes through electrochemical impedance spectroscopy (EIS). In-situ EIS is a powerful tool that allows us to identify changes in conductivity for the reaction steps comprising the overall ORR. We have developed a powerful strategy for identifying the steps in the ORR that contribute to the overall impedance spectra, and how that contribution changes as a function of operating conditions and aging time. Our EIS results indicate a strong correlation between blocking effects caused by CO2 and H2O and the operating temperature for LSCF, while similar experiments performed on LSM show significantly less effect caused by the presence of these contaminants. Using EIS to de-convolute the overall cathode polarization helps us identify the mechanisms by which degradation occurs. In addition, focused ion beam-scanning electron microscopy (FIB-SEM) ex-situ analysis of the three-electrode cells has been performed to identify changes in the microstructure and composition of the electrodes, which are directly correlated to changes in the EIS response, and reveal specific regions where degradation has occured. Further, to investigate the fundamental kinetics of these materials, we have used a variety of gas-phase isotope exchange experiments on fresh and aged powder samples of the same cathode compositions to study the change in materials properties. Using impedance spectroscopy, supported by FIB-SEM and isotope exchange, we elucidate how changes in the conductivity, microstructure and kinetics of SOFC cathodes relate to their degradation.
Chromium Deposition and Poisoning of LSCF and LSM Oxygen Electrodes of Solid Oxide Electrolysis Cells
Authors: Chen Kongfa , Bo Wei , Hyodo Junji , Ishihara Tatsumi , Jiang San Ping
Published: February 2020

The degradation of solid oxide electrolysis cells (SOECs) is an issue of both scientific and technical importance. In this study, chromium deposition and poisoning at La0.8Sr0.2MnO3+
d (LSM) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) oxygen electrodes are studied under SOEC operation conditions. Significant performance degradation was observed for the reaction in the presence of Fe-Cr alloy metallic interconnect, indicating that presence of gaseous Cr species significnatly poisons and degrades the electrocatalytic activity of LSM and LSCF oxygen electrodes. In the case of LSM electrodes, XRD, XPS and SIMS analysis clearly identified the deposition of SrCrO4, CrO2.5 and Cr2O3 phases on the YSZ electrolyte surface and LSM electrode inner surface for the reaction under anodic polarization conditions. In the case of LSCF, Cr deposition occurs in the electrode bulk and on the electrode surface, forming SrCrO4. The results clearly indicate that the Cr deposition is closely related to the increased segregation of SrO species under anodic polarization conditions. The mechanism of the Cr deposition at LSM and LSCF electrodes under SOEC operation conditions is discussed.
Redox-Stable High-Performance Thin-Film Solid Oxide Fuel Cell
Authors: Keuter Thomas , Roehrens Daniel , Menzler Norbert H. , Vaßen Robert
Published: February 2020

An anode-supported Solid Oxide Fuel Cell (ASC) consists of a mechanically supporting, thick, and highly porous anode substrate, coated on top with thin films of a fine-structured porous anode, a dense electrolyte, and a fine-structured cathode. Both, the anode substrate and the anode are made of a cermet of nickel and yttria-stabilized zirconia (YSZ). An increase of the oxygen partial pressure at the anode side will lead to a reoxidation of the nickel and to microstructural changes. This may result in a macroscopic expansion of the anode substrate and in a complete cell failure, due to cracking of the YSZ electrolyte.

In this work, a redox-stable SOFC with a thin-film sol-gel electrolyte is presented. Using tailored suspensions and polymeric sols of varying target particle size, a 1 µm thick, three layer sol-gel electrolyte is coated on top of a tape cast anode substrate and a screen printed anode by spin-coating and dip-coating techniques. With this sol-gel electrolyte a power output larger than 1.25 W/cm2 at 0.7 V and an operating temperature of 600 °C could be demonstrated. In this study, half cells (anode substrate, anode, and electrolyte) are reoxidized in excess air, in order to test the redox stability of these SOFCs. Afterwards the electrolyte is investigated ex situ using optical microscopy and SEM. No cracks are found in the sol-gel electrolyte after reoxidation for 4 hours at 600 °C and 15 minutes at 800 °C, respectively, whereas a lot of cracks are visible in a standard ASC with a 10 µm thick, screen printed electrolyte for both reoxidation conditions. This means the sol-gel electrolyte can tolerate higher degrees of oxidation (DoO) of the anode substrate than the screen printed electrolyte. The residual compressive stresses of both electrolytes are measured to about 600 MPa using XRD and are therefore not responsible for the higher stability against reoxidation of the sol-gel electrolyte. In contrast, the energy release rate has to be larger than a critical value for the creation of cracks in a thin-film on a thick substrate. Due to the fact, that the energy release rate is proportional to the thickness of the thin-film, a thinner film is more stable against cracking than a thicker film at constant tensile stresses. After reoxidation of 8 hours at 600 °C and 60 minutes at 800 °C, respectively, cracks are also found in the sol-gel electrolyte. However, the SOFC with the thin-film sol-gel electrolyte can be considered as stable against reoxidation, because the long reoxidation time of 4 hours at an operating temperature of 600 °C is unlikely to happen under real conditions.
Coatings for SOFC Interconnects in Fuel Side Environments
Authors: Sachitanand Rakshith , Sattari Mohammad , Svensson Jan-Erik , Froitzheim Jan
Published: February 2020

Bipolar plates in solid oxide fuel cells operate under a significant oxygen potential gradient (0.2 to 10-18 bar pO2). For air side conditions (pO2 = 0.2 bar), a PVD technique has successfully been used to apply combination reactive element/Co coatings to inhibit the rapid oxidation of and Cr volatilization from Fe-Cr alloys such as Crofer22 APU and Sanergy HT. However, relatively little work has been done on developing similar coating strategies for fuel side conditions.

In this work, the ferritic steel Sanergy HT was coated with single element (Ce,La, Co and Cu) and duplex (Ce/Co, La/Co) coatings of varying thicknesses and exposed at 850°C in Ar-5%H2 charged with 3% H2O in a tubular furnace up to 500 h. Additionally, the effects of a ‘sealing’ step on corrosion mechanisms were also investigated by pre-oxidising the coated steel in air, prior to exposure in the fuel side environment. Chemical analysis on the samples was subsequently performed with SEM/EDX and XRD.

 It was established that:

(i)                 reactive element (Ce and La) coatings brought about a 2-4x reduction in oxidation rate

(ii)                Co and Cu coatings negatively affected oxidation performance due to their instability in fuel side conditions.

Figure 1
Properties of Spinel Protective Coatings Prepared Using Wet Powder Spraying for SOFC Interconnects
Authors: Hong Jong-Eun , Bianco Manuel , Van herle Jan , Steinberger-Wilckens Robert
Published: February 2020

Manganese cobalt spinel coatings have attracted much interest as a protective layer for stainless steel interconnects of solid oxide fuel cells (SOFCs) owing to their effectiveness of suppressing high temperature oxidation and Cr evaporation. In this study, a simple wet powder spraying (WPS) method was applied to prepare spinel layers on commercial stainless steels (Sanergy HT and K41/441) which were evaluated as protective coating of SOFC interconnects. A condition of heat treatment on spray coatings was optimised to achieve dense protective layers with microstructure analysis. Area specific resistance (ASR) and stability were measured in a humid atmosphere at 700 °C for 1000 hours. Post-test analysis was conducted on microstructure of measured samples using SEM-EDS. In addition, effect of a sublayer with spinel coatings was investigated on ASR and Cr retention. The implication for microstructure, ASR and stability of the evaluated coatings is discussed.
Evaluation of Protective Coatings for SOFC Interconnects
Authors: Tallgren Johan , Bianco Manuel , Himanen Olli , Thomann Olivier , Kiviaho Jari , van Herle Jan
Published: February 2020

Chromium poisoning is a widely recognized degradation mechanism in solid oxide fuel cells (SOFC). Stainless steel interconnects (IC), in a direct contact with the cathode, have been identified as the main chromium source. Chromium evaporation from the bulk steel may also cause break-away oxidation of the IC plate, which is equally deleterious for the stack. Thus, protective coatings are needed to prevent chromium from migrating from the steel. A low electrical resistivity and high chemical and physical stability are required of the coatings. This work compares manganese-cobalt and cobalt-cerium protective coatings. The evaluated coatings are fabricated on thin steel samples by commercial companies and research facilities with differing manufacturing methods. The chosen steels are Sandvik Sanergy HT and K41/441 as they are common in SOFC applications. Area specific resistance (ASR) and overall stability were determined with an innovative measurement setup. The steel samples were stacked in a sandwich structure adjacent to thin palladium foils with a screen-printed lanthanum strontium cobalt (LSC) layer. This setup offers two advantages. First, a realistic electrical contact with the cathode material is obtained since the LSC layer is manufactured with the same methods as real SOFC cathodes. Second, the adoption of palladium spacers instead of steel enables electron microscopy analysis on chromium migration into the LSC layer as well as on oxide scale growth. ASR measurements were conducted in a humid atmosphere at 700 °C for a period of 1000 hours. The paper compares the coating solutions in terms of ASR and stability and discusses their usability in SOFC applications.
Butane Steam Reforming: Comparison of Two Ni/MgO-Pd Catalysts with YSZ and GDC Supports
Authors: Seomoon Hee , Sung Jae Gi , Chung Yong Sik , Chung Jong Shik , Sammes Nigel Mark
Published: February 2020

Butane steam reforming with two different types of nickel magnesia catalysts is investigated. The catalytic and electrocatalytic properties of nickel magnesia with YSZ and GDC supports made using different calcinations temperatures; 673K, 873K, 973K, and 1073K are determined. A palladium doped catalyst sample is used to examine the effects of metals on the performance. Moreover, S/C ratio is also controlled from 4 to 6 to elucidate the mechanism of butane steam reforming. The effect of microstructural change and properties are observed using X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) to characterize the differences in reforming performance.
Sulfur Poisoning of the Reverse Water Gas Shift Reaction (RWGSR) on Anode Supported SOFCs
Authors: Madi Hossein , Singh Vaibhav , Diethelm Stefan , Van herle Jan
Published: February 2020

SOFCs have the advantage of being able to operate with fuels other than hydrogen due to their high operation temperatures. Among these, biogas from anaerobic digestion is considered to be carbon neutral and highly underused for power generation. Methane-free biogas, which can be produced by inhibition of the methanogenic process, is an alternative high quality fuel, consisting mainly of CO2 (70 to 50%), H2 (30 to 50%) and traces of CO and H2S. The impact of H2S in the ppm range on the performance of anode supported Ni-YSZ SOFC at 750°C is evaluated. An initial voltage drop is observed when the cell is exposed to H2S but the voltage recovers after a few hours of exposure to the impurity. Impedance spectroscopy revealed an increase in the polarization resistance even though the cell voltage was increasing.  Furthermore, it was found that this behavior is due to deactivation of the reverse water gas shift reaction (RWGSR); a mathematical model confirmed this conclusion. The poisoning effect is partly reversible under the applied operating conditions.

Figure 1
Understanding the Rheology of Screen-Printing Inks for the Fabrication of SOFC Thick Films
Authors: Somalu Mahendra R. , Muchtar Andanastuti , Brandon Nigel P.
Published: February 2020

Fabrication of solid oxide fuel cell (SOFC) components via a simple and economical technique is critical to lower the overall manufacturing cost of SOFCs. In this regard, screen-printing is widely used to fabricate SOFC components having thickness in the range of 10 to 100 μm. Fabrication of SOFC components by screen-printing using an optimized ink is very significant for the production of high quality films with improved performance. To realize this, the rheological properties of the ink, including static and dynamic properties, need to be understood deeply for the application of the ink at a specific printer setting. Understanding the relationship between the composition and rheology of the inks may enhance the properties and performance of the resultant screen-printed films. The effect of ink composition consisting of a solid, a binder, a solvent and a dispersant on the rheological properties and performance of resultant films must be understood for the fabrication of an optimized ink. These effects can be optimized by measuring the ink rheological parameters such as viscosity, yield stress, thixotropy and viscoelasticity. Furthermore, these parameters must be related to the particle network strength in the fabricated inks and mechanical, electrical and electrochemical performance of the resultant films. In this study, the rheological properties of NiO/ScSZ anode inks are studied and correlated to the particle network strength, screen-printability, microstructure, mechanical hardness, electrical performance and electrochemical performance. The initial study showed that inks having particle network strength and complex modulus in the range of 100-200 Pa and 500-4000 Pa, respectively, have been suggested suitable for screen-printing application. In addition, these inks showed suitable viscosity and thixotropy for screen-printing application. These range was exhibited by inks having binder and solids loading in the range of 1-3 wt% and 25-28 vol%, respectively (wt% refer to wt% of solids loading and vol% refers to vol% of final ink composition). The mechanical hardness, conductivity and electrochemical performance of screen-printed films produced using these inks also showed improved properties with increasing particle network strength in the fabricated inks. These properties were further confirmed by investigating the SEM images of sintered films.

Figure 1
Results for a New SOFC-Stack Design with Parallel-Connected Cells
Authors: Szepanski Christian , Immisch Christoph , Lindermeir Andreas , Faulstich Martin , Dörrer Lars , Schmidt Ute , Borchardt Günter , Hamje Jens , Wesling Volker
Published: February 2020

The TU Clausthal and CUTEC institute have teamed up to design, build and test a new stack architecture, based on repeating units with cells connected in parallel. This approach allows the use of electrically conducting seals like brazes and can be realized without any glass sealing.

Unlike conventional (serially connected) stacks, where all cells operate at the same current but individual voltage, in this setup each cell contributes as much current as possible at a common voltage. Thereby accelerated degeneration caused by undervoltage and the associated oxidation of the nickel catalyst can be completely overcome.

The concept uses two cells in electrical parallel connection with the anodes facing each other to form a repeating unit. Two designs have been realized:  An all ceramic housing made from 3YSZ, sealed with reactive air brazing (RAB) and a metallic one with a Crofer 22 APU housing, joined by laser beam welding. The housing materials have been chosen with respect to their thermal expansion coefficient (TEC) matching the TEC of the used ESC cells. Special interconnectors have been produced via hydroforming to create an even flow field while providing sufficient contact area.

The paper will focus on the test results of the repeating units under various operation conditions and the analysis of the degradation of components and joints.

Polarization curves for the twincell repeating unit and the individuell cells under H2 and air at 880°C are depicted in figure one.

Figure 1
Evaluation of Ni-YSZ Anode Degradation during Redox Cycling
Authors: Shimura Takaaki , Jiao Zhenjun , Hara Shotaro , Shikazono Naoki
Published: February 2020

Degradation of SOFC anode under redox cycling was evaluated by microstructure change measurements and overpotential calculations using a Lattice Boltzmann method (LBM). Microstructures were obtained by FIB-SEM reconstruction technique. In the overpotential calculation, exchange current density and YSZ ionic conductivity were considered as degradation factors. Numerical simulation reproduced well the decrease of overpotential just after each of the redox treatments. Then, overpotential increased after subsequent discharge process. This is consistent with the experimental result. However, simulation  showed lower overpotential values than the experiment after 10 redox cycles. Decrease of exchange current or YSZ ionic conductivity reduction are considered as the reason for the degradation after redox cycles.
Fabrication of Bimetallic (NiFe) Anode-Supported SOFCs with Direct Ceramic Inkjet Printing
Authors: Fakeeh A , Tomov R I , Kumar Vasant R , Glowacki B A
Published: February 2020

Anode-supported solid oxide fuel cells (SOFCs) based on nickel-iron supports were fabricated, and their performance evaluated at the intermediate temperatures. The ratio of NiO to Fe2O3 in the metal support was 7 to 3 on a molar basis. Fe2O3 and NiO powders and appropriate sintering aids were mixed in the desired proportions and discs were die-pressed. The goal of using sintering aids was to adjust the thermal expansion of the support and the electrolyte to a close match within the sintering temperature region. The functional coatings were sequentially applied on the metal support by the use of Direct Ceramic Inkjet Printing (DCIJP) of suspension inks. The use of DCIJP enables the formation of very thin electrolyte coatings (~10µm), which is challenging for the more conventional ceramic methods. It also allowed infiltration of the support composites into the porous scaffolding of the support, thus extending the active anode area. The reduction of utilised and wasted amounts of active materials can lead to significant cost reductions in the fabrication of the final cell. Two distinct cell structures were produced - first one consisted of four distinct layers- metal support (NiFe), anode functional layer (Ni/GDC), electrolyte (10Sc1CeSZ) and cathode (LSCF+ GDC) and the second one where the anode deposition was omitted and the anode was formed by infiltration of ink directly into the NiFe support during the printing of the electrolyte. Cells were tested with hydrogen as fuel and air as oxidant at temperatures up to 750oC. XRD and SEM examination indicated that the good performance of the button cells can be ascribed to the optimized composition and microstructure of the anode. The present work shows that high performance FeNi based cells can be successfully fabricated by the sole use of ceramic technology - DCIJP.

Figure 1