bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanostructured Steel Susceptibility to Sulfide Stress Cracking
Authors: Shadravan Arash , Case Raymundo , Rumann Argie
Published: February 2020

The susceptibility of a high strength low alloy nanostructured steel to sulfide cracking resistance (SSCC) is assessed. Notch Tensile Slow Strain Rate (NTSSRT) method is used to evaluate the threshold stress intensity values (KISSCC)). The objective is to understand the effect of the microstructure on the susceptibility to SSCC, the control condition is a conventional low alloy carbon steel with a tempered martensite micro structure.

The tests were performed in a brine with 1% NaCl buffered at pH 4.5 with H2S gas with 1% to 100% (mol %) balance N2 at room conditions. The nanostructured steel results of the KISSCC parameter are: 107 Ksi in0.5 at 1% H2S to 42 Ksi in0.5 at 100% H2S. The control condition exhibited 22 Ksi in0.5 at 100% H2S. The evaluation of the relative crack propagation energy suggest that the nanostructured ferrite grains exhibit a much lower susceptibility to SSCC than the tempered martensitic microstructure
Effect of Cr/Mo on the Protectiveness of Corrosion Scales on Carbon Steel in Sweet Medium Under Hydrodynamic Condition
Authors: Sk Mobbassar Hassan , Abdullah Aboubakr Moustafa , Ko Monika , Laycock Nick , Ingham Bridget , Ryan Mary P , Williams David E
Published: February 2020

In combating CO2 corrosion, literature suggests specific micro-alloying (< 2 wt. %) of plain carbon steel to be the best choice in consideration of durability to cost ratio. In order to achieve optimized steel chemistry, the effects of number of alloying elements on the corrosion behaviour and protectiveness of the corrosion scale have been studied over the years. Amongst the various alloying elements, Cr has been found to be most effective. However, to date, no convincing mechanistic interpretation for the protective effect of Cr of the corrosion scale has been developed. A further question is whether a combination of alloying elements can yield superior behaviour, and if so what are the mechanistic determinants of behaviour.

In the present study, we investigated the effects of the micro-alloying of plain carbon steel with Cr and Mo on the corrosion behaviour and scale formation and protective nature in a CO2 saturated (sweet) brine (0.5 M NaCl) environment, under controlled hydrodynamic conditions (0-1000 RPM), at 80oC in a slightly acidic environment (pH 6.6). Materials were low alloy steels fabricated by incorporating small amounts of Cr (~ 1 wt. %) and/or Mo (~ 0.7 wt. %) in base plain carbon steel. Corrosion behaviour was investigated by chronoamperometric type current-transient characteristics, as well as by initial current measurement at various flow conditions under different anodic over-potentials with respect to the open circuit potential (Eoc + 20 to + 70 mV) and initial current measurement at various anodic over-potentials under low (100 RPM) and high (1000 RPM) flow conditions.

Potentiostatic current transients indicated that the presence of Cr induced an obvious decrease in the overall current flux throughout transient whilst the presence of Mo appeared to induce faster crystallization. Qualitative observation of the scale morphology using SEM indicated that the corrosion scales formed on Cr/Mo micro-alloyed steels are comparatively thinner and yet they render better protectivity and lead to faster passivation, especially under higher flow conditions (e.g. 1000 RPM). Although, in general the higher flow rates caused higher current-flux passing through the scales at the beginning of the transient, the final stage of the current transients for Cr/Mo micro-alloyed steels indicated quicker passivation at high flow rate (1000 RPM) compared to low flow rate (100 RPM). From the mechanistic perspective, we suggest that the addition of small amounts of Cr/Mo modulates the current due to dissolution of iron, as well as the current due to growth of a crystalline layer, by modifying the local environment at the steel surface, in terms of pH and degree of supersaturation. Modeling of this hypothesis is currently in progress.

Figure 1
Self-Healing of Precoated AISI 441 for Solid Oxide Fuel Cell Interconnects at Intermediate Temperatures
Authors: Berger Robert , Lundberg Mats W , Westlinder Jörgen
Published: February 2020

Sandvik Materials Technology develops nanocoatings for SOFC stainless steel interconnects. The properties of cerium cobalt coated AISI441 (EN 1.4509) have previously been studied extensively (1-4). However, the trend in SOFC have been to decrease working temperatures from above 800°C and today commercial systems are sold that operate below 650°C. The lower operating temperature opens up new possibilities in selection of component materials. In this study we have examined precoated AISI 441 used in solid oxide fuel cell interconnects at 650°C and compared to previous studies at 800°C. The coating characteristics after different oxidation times were studied by SEM. Also, the variation of cobalt coating thickness and the development of the surface oxides were examined by SEM.

By using the double trench approach (3) samples with and without priming at 900°C for 5 hours followed by heat treatment at 650°C, were compared. These samples were also compared to the results from (3) with a sample prepared at 800°C for a total of 504 hours.

Figure 1. Mass gain of pre-coated cerium cobalt AISI441 (EN 1.4509) from cyclic oxidation at 650°C and 800°C in ambient air. The mass gains are not corrected for Cr evaporation, which shows for the 650°C as it displays flat or negative mass gains.

References

J. Froitzheim, S. Canovic, M. Nikumaa, R. Sachitanand, L.G. Johansson and J. E. Svensson J. of Power Sources, 220, 217 (2012)

J.G. Grolig, J. Froitzheim, J.E. Svensson, J. of Power Sources, 248 1007 (2014)

R. Berger, M. W. Lundberg, J. Westlinder, H. Holmberg, ECS Trans. 68 1649 (2015)

H. Falk-Windisch, J. Claquesin, M. Sattari, J.-E. Svensson, J. Froitzheim, J. of Power Sources, 343 1 (2017)

Figure 1
Structural Reliability of Cathode Contact Materials in Planar SOFCs
Authors: Karri Naveen K , Koeppel Brian J , Nguyen Ba N , Lai Kevin
Published: February 2020

One of the key issues hindering the commercial success of solid oxide fuel cells (SOFCs) is their long term mechanical reliability. While significant progress has been made in the electrode materials development, cell and stack manufacturing technologies, as well as large-scale system level assemblies, the operating thermal gradients in the cell or stack still remains a challenge. The thermal gradients combined with mechanical loading can lead to glass seal or other ceramic component (anode, electrolyte, and cathode) failure in SOFCs. Apart from these components that can affect the stack reliability, another weakest link identified in the assembled planar stacks is the contact between electrodes and interconnects, especially on the cathode side. While these contacts not only provide the needed mechanical support for electrodes, they also provide the necessary electrical current path in the SOFC and their failure typically results in significant loss of performance. Hence, the electrode-interconnect contact strength and bond reliability is one of the key aspects of SOFC stack mechanical reliability. One way to ensure the reliability of cathode contact materials is by experiments; however, such experiments are expensive and may not be feasible for large stacks using current generation planar SOFCs. An alternative to experiments is computational modeling of contact material mechanics and bond reliability assessment based on available experimental data. The latter method though may not quantify reliability as accurately as design-specific experiments; it does provide significant insights on the contact mechanics and parameters affecting contact reliability of planar SOFCs in general.

This paper presents recent efforts on SOFC cathode contact modeling and reliability evaluations. For this work a continuum viscous sintering model was incorporated into a commercial FEA code to simulate contact paste sintering and evaluate the cathode contact reliability. The data required for the model implementation and contact reliability assessments were obtained from literature as well as experiments conducted in-house. Sensitivity studies were conducted to assess the influence of contact sintering parameters such as contact material thickness, sintering temperature, sintering pressure etc. using a generic planar SOFC design. The reliability evaluations of SOFCs were conducted at operating as well as shutdown states using commercial software based on Weibull statistics. The realistic operating temperatures of the generic stack were obtained from the in-house multi-physics code SOFC-MP. The sintering parameter sensitivity studies indicated that of all the parameters, sintering temperature has the most significant influence on the contact densification and associated stresses. The reliability evaluations indicated that cathode contact materials still require improved sintering and higher strengths to avoid failure under shutdown conditions.

Figure 1
Dynamic Sub-Thermoneutral Voltage Operation of Solid Oxide Electrolysis with Alternative Heat Addition
Authors: McVay Derek , Zhao Li , Brouwer Jack
Published: February 2020

In this study, we experimentally evaluated electrolysis of water using a short stack of six solid oxide electrochemical cells (SOEC) at temperatures ranging between 700 °C and 800 °C. A model of the SOEC stack was verified and then used to evaluate thermal management of the stack operating below the thermoneutral voltage, which at these temperatures requires additional heat input into the stack to maintain the operating temperature of the stack. High quality heat supplied from two different sources were evaluated in this work. Heat generated from concentrated solar power (CSP) can reach the required SOEC operation temperature and, when scaled properly, can provide enough heat to sustain sub-thermoneutral voltage operation of an SOEC. CSP output follows a diurnal pattern and the peak output generally coincides with the time of day when solar photovoltaic power may need to be curtailed. Heat generated from nuclear power was also considered and offers a relatively constant supply of heat to an SOEC stack. The SOEC model is spatially and temporally resolved and was used to evaluate the performance of a system operating at sub-thermoneutral voltages with CSP and nuclear heat as two separate and distinct heat inputs to maintain the stack temperature and temperature gradients. Dynamic performance of the system was evaluated with respect to thermal management and the simulation results of various system configurations are presented.
A High Performance Low Temperature Direct Carbon Fuel Cell
Authors: Wu Wei , Ding Dong , Fan Maohong , He Ting
Published: February 2020

Direct carbon fuel cells (DCFCs) are one of the most efficient and cleanest energy technologies, especially when using the existing solid oxide fuel cell (SOFC) configurations. However, the conventional SOFC has issues of high cost and rapid degradation associated with high operating temperatures (> 750oC). Reduction in operating temperatures would mitigate degradation, reduce sealing problems, enable less expensive materials, and improve response to prompt start-up and repeat thermal cycling. In the present presentation, we report our research progress about DC-SOFCs operating at 400-650oC. A variety of cell configurations, material selections, fuel considerations and novel electrode optimization approaches are investigated and implemented for high-performing DC-SOFCs.
The Role of Interlayer on the Catalytic Activity and Performance Stability of (Pr1-xNdx)2NiO4 as Cathodes for Solid Oxide Fuel Cells
Authors: Dogdibegovic Emir , Alabri Nawf Saif , Tenny Kevin , Wright Christopher J. , Hardy John S , Coyle Christopher A , Horlick Sam , Guan Wanbing , Stevenson Jeffry W , Zhou Xiao-Dong
Published: February 2020

The use of doped ceria as an interlayer in solid oxide fuel cells (SOFCs) is ubiquitous, which provides better thermal expansion match and prevents interaction between the cathode (e.g. LSCF) and electrolyte (e.g. YSZ). However, the role of ceria interlayer on the cathode phase durability and catalytic activity remains obscure. This is particularly true in nickelate cathodes (e.g. Pr2NiO4). Here, we report that traditional Gd-doped ceria (GDC) interlayer substantially accelerates the phase transition in Pr2NiO4. Two new interlayer designs were investigated in order to circuvent the phase evolution by using (1) a thin Pr6O11 film deposited on the surface of GDC, and (2) a Pr-doped ceria interlayer. The latter design not only suppresses the phase transition, but also results in a 48% increase in cathode performance; and more importantly, it leads to a zero degradation over long-term measurements. Systemetic in situ and post analyses were carried out to understand the mechanism, by which the interlayer affects the cathode durability and activity.

This material is based upon work supported by the U.S. Department of Energy under Award Number DE-FE0023475.
Long Term Performance Stability Tests of Ba-Fe-O Infiltrated LSM/YSZ Solid Oxide Fuel Cells under High Steam and High Current
Authors: Fan Yueying , Song Xueyan , Abernathy Harry , Chen Yun , Pineault Richard , Liu Jian , Gerdes Kirk , Lee Shiwoo , Kalapos Thomas , Hackett Gregory A
Published: February 2020

Commercial LSM/YSZ cells infiltrated with a solution containing salts with barium and iron cations in a 1:2 ratio were evaluated for their performance and long term stability under high steam, high current and high temperature. Ba-Fe-O-infiltrated cells showed higher performance and lower degradation than the uninfiltrated LSM/YSZ baseline cell, which demonstrates that appropriate nanomaterial infiltration could improve the performance and mitigate the degradation of solid oxide fuel cells under steam. The uninfiltrated baseline cell showed a sharp voltage drop after exposure to steam, while infiltrated LSM/YSZ cells showed a smaller voltage drop that recovered in the first 3-4 h right after exposure to steam. TEM analysis showed no BaFe2O4-infiltrated nanoparticles, the anticipated composition and phase, near the functional layer in cathode before and after testing. However, three different morphologies (nanoribbons, nanoparticles and nanolayers) were found using TEM in the original pore region near the cathode functional layer. EDS showed significant reaction between infiltrated nanomaterials and the LSM/YSZ backbone for the infiltrated cells before and after test. Cells infiltrated with solutions containing different ratios of Ba and Fe cations were also tested to gauge the interaction of Ba and Fe with the LSM/YSZ backbone. Humidity in cathode air can cause an immediate increase in the polarization resistance of LSM/YSZ cathodes, and infiltration is a possible means of mitigating the effects of humidity on LSM/YSZ cathodes.
Novel Approaches to Prepare the High Performance Dense Electolyte and Interconnect Applicable to SOFC by Atmospheric Plasma Spraying
Authors: Li Chang-Jiu , Chen Xu , Zhang Shan-Lin , Li Cheng-Xin , Yang Guan-Jun
Published: February 2020

Plasma spraying has been widely applied to deposit ceramic coatings and is also considered as promising cost-effect manufacturing process to deposit electrolyte and ceramic interconnect for solid oxide fuel cells. However, it is generally difficult to deposit highly dense electrolyte and interconnect which can be directly applied to SOFC operation in the as-prepared state following the conventional process routine. In this paper, a novel approach based on the critical bonding temperature concept is presented to prepare dense electrolytes by plasma spraying. YSZ and LSGM are used as typical electrolytes, and LaxSr1-xCrO3 and LaxSr1-xTiO3 are used as typical interconnect. The individual ceramic functional layers are deposited at a deposition temperature higher than the critical bonding temperature. The compositions, microstructure, electric properties and gas permeability of different ceramic deposits are characterized. It is revealed that both plasma-sprayed electrolytes and interconnects present a gas permeability less than 1x10-7 cm4gf-1s-1 and can be directly applied to SOFC high temperature operation. Moreover, the deposited electrolytes present an ionic conductivity of over 80% sintered bulk materials. Along with the composition control approach during plasma spraying, high performance electrolyte and ceramic interconnect are deposited by atmospheric plasma spraying. Moreover, the excellent performance of the electrolyte and interconnect is also demonstrated by the output performance of assembled SOFC cells with the APSed functional layers.
Anode Concentration Polarization in Solid Oxide Cells as a Dissipative Process
Authors: Virkar Anil
Published: February 2020

Part of the voltage of a fuel cell is used up as a loss in irreversible processes that convert potential useful work into heat. This voltage loss is called overpotential or polarization. Voltage loss associated with the transport of gaseous species through the porous electrode is called concentration polarization. This manuscript examines voltage loss associated with anode concentration polarization as a dissipative process and determines its spatial dependence through the thickness of the anode. Background on the origin of this loss is given using analogies of transport of electrically charged and neutral species.
Effect of Mg/Mo Ratio in Stoichiometric Sr2MgMoO6-δ (SMM) Redox-Stable Anode
Authors: Thomas Tony , Qi He , Liu Xingbo , Zondlo John W. , Sabolsky Edward M. , Hart Richard
Published: February 2020

The state-of-the-art Ni/YSZ anode experiences a linear expansion of up to 1% when oxidized causing an irreversible microstructural change. Hence there is a need to develop redox stable anode materials with multifunctional properties like internal reforming, low temperature operation, and poison resistance. In this work, SMM, an oxygen-deficient, mixed valent perovskite has been studied to exploit its potential as a viable anode material in the SOFC application. The mixed valance of Mo (6+ and 5+) supports the electronic conductivity while losing oxygen. It also provides platform for catalytic activity for the oxidation of hydrogen and other hydrocarbon. It has been found that SMM experiences a volumetric reduction of only 0.03% in reducing atmosphere at 800oC compared to GDC and Ni/YSZ which experiences a volumetric expansion of about 0.2 and 1% respectively.

Stoichiometric SMM has a conductivity of 50 S/cm in the reducing atmosphere and with consecutive redox cycling, the conductivity decreases. Effort has been made to understand the reason for the drop in electrical conductivity with increasing redox cycling. It has been found that SMM loses Mo with time at 800oC, accounting for the drop in conductivity. To improve the electrical performance of SMM, Mg/Mo ratio in stoichiometric SMM has been varied to compensate for Mo loss and its effect on thermal stability and electrical conductivity will be discussed in this work. Above all, these compositions will be tested as an anode in an electrolyte supported SOFC and the performance data will be compared with Mo rich SMM compositions. The change in microstructure of the anode after many operating hours will be examined and discussed in this topic. Also EIS analysis of the tested cells will be discussed in this work.
Use of a Reduced Order Model (ROM) to Simulate SOFC Performance in System Models
Authors: Koeppel Brian J , Lai Canhai , Iyengar Arun K.S. , Xu Zhijie , Wang Chao , Hackett Gregory A
Published: February 2020

Use of SOFC-based hybrid power generation systems has the potential to reduce emissions while producing electricity from conventional fossil energy sources at costs that are competitive with other technologies. The numerical models used to perform predictive design analysis and optimization of the power generation system require an accurate representation of the SOFC stack performance over a varying range of operating conditions. Detailed stack models may contain the required information necessary for design purposes, but are often too computationally expensive for use in the overall system model. However, other desirable information about the state of the stack, such as the internal temperature gradient, is generally not available from simple performance or thermodynamic models often used to represent the SOFC. Such additional information can be important in system optimization studies to preclude operation under off-design conditions that can adversely impact overall system reliability.

Response surface techniques were used with detailed SOFC stack model results to create a computationally efficient reduced order model (ROM) of the stack. A tool was developed to randomly sample selected input parameters over the expected range of interest, perform stack solutions for these sampled points using the SOFC-MP 2D software, use regression to obtain response surfaces for the stack performance and other output metrics of interest, and export the response surfaces as a ROM. The procedure is shown in Figure 1. The ROM was then successfully implemented in an Aspen Plus® system model for a natural gas fuel cell (NGFC) power system. Additional work is in progress to improve the tool’s implementation by including the fuel/oxidant recirculation loops and to better characterize the expected approximation error of the ROM. The developed modeling approach, results of the system model integration, and ongoing efforts to improve the ROM accuracy will be presented.

Figure 1. Overview of ROM Generation Procedure and Usage

Figure 1
Degradation of SOFCs by Various Impurities: Impedance Spectroscopy and Microstructural Analysis
Authors: Kikuchi Yuhdai , Matsuda Junko , Tachikawa Yuya , Shiratori Yusuke , Taniguchi Shunsuke , Sasaki Kazunari
Published: February 2020

Introduction

SOFC is considered as a promising power generation system due to high electric efficiency and fuel flexibility. However, coal gas, for example, contains various impurities. In this study, siloxane, poisoning effect of siloxane to Ni-ScSZ cermet anodes is analyzed by applying Electrochemical Impedance Spectroscopy (EIS). Spectroscopy data are analyzed by the distribution of relaxation times (DRT) method[1] to investigate details of electrode resistance. Furthermore, microstructural analysis was made by electron microscopy.

Experimental

Electrolyte-supported cells with ScSZ (10 mol% Sc2O3
- 1 mol% CeO2-89 mol% ZrO2) plate (20 mmφ×0.2 mmt) were used in this study. Mixture of 56 wt.% NiO and 44 wt.% ScSZ was used for the anode and was sintered at 1300 oC for 3 h. Mixture of (La0.8Sr0.2)0.98MnO3 (LSM) and ScSZ with a weight ratio of 1:1 was used for the cathode. Electrode area was 8×8 mm2 and Pt mesh was used as the current collector. Figures 1 and 2 describe the experimental setup. Siloxane (decamethylcyclopentasiloxane) was supplied to the fuel cell using the bubbler setup. The fuel consisted of 97% H2 and 3% H2O. Cell temperature was 800oC. Table 1 shows the EIS conditions. EIS data analyzed by DRT enable the identification of electrode processes. FESEM-EDX was applied to investigate changes in the anode microstructure and composition after the cell performance tests.

Results and discussion

Figure 3 shows EIS spectra measured after 0h and 100h. Figure 4 shows the DRT result of the Fig. 3 data. Impedance semicircles, especially at the lower frequency, DRT peaks became larger with time. The DRT peak with relaxation time around 102~103 sec at 0h became wider, but the DRT peak around the 10-1~100 sec did not change. DRT peak around 10-1~100 sec may originate from the diffusion of H2 gas, that around 102~103 sec for charge transfer reaction and ionic transport[2][3]. Figure 5 shows EDX mapping of zirconium, silicon and oxygen. Ni particle on the anode surface is covered by silica. This reaction is considered as [4]:

[(CH3)2SiO]5+25H2O→5Si(OH)4(g)+10CO+30H2

(1)

Si(OH)4(g)→SiO2(s)+2H2O
(2)

Silica was formed under SOFC operating conditions at high temperature and high water vapour partial pressure. Therefore, cell performance degraded by inhibiting gas diffusion and covering by Ni particles with silica in the siloxane poisoning of Ni-based anodes.

References

[1] A. Leonide et al., Journal of The Electrochemical Society, 155(2008) B36-B41.

[2] T.H. Wan et al., Electrochimica Acta, 184 (2015) 483-499.

[3] V. Sonn et al., Journal of the Electrochemical Society, 155 (2008) B675-B679

[4] K. Haga et al., Journal of the Electrochemical Society, 155 (2008) B1233-B1239.

Figure 1
Synthesis and Characterization of CeO₂ for Use in Solid Oxide Fuel Cells
Authors: Mendoza Muñiz Diego Armando , Grishin Andrey , Cassir Michel , Ringuedé Armelle , Hinojosa Rivera Moisés , Chavez Carvayar José Álvaro
Published: February 2020

Due to the problems with greenhouse gas emission, fossil fuels consumption and air pollution, solid oxide fuel cells (SOFC) are a promising power generation technology, because of its good efficiency and low emissions. The key challenge is to achieve a competitive balance between cost, efficiency and durability. The aim of this work is to develop capabilities in order to acquire state-of-the-art knowledge on the chemical compatibility between stainless steel AISI 316 that was used as a substrate and CeO₂ as interconnector coating, as well as exploring the relationship between the electrolyte and the interconnector. The aim of this work was to synthesize and characterize materials by different techniques in order to have more information about of microstructure and electrochemical properties that may eventually lead to performance improvements.

In this work we report the synthesis and characterization of CeO₂ and Yttrium oxide (Y2O3) the materials were obtained by chemical bath deposition (CBD) and atomic layer deposition (ALD) techniques. The crystalline structures were analyzed by X-ray diffraction, the elemental composition of these materials was obtained by Energy-dispersive X-ray spectroscopy, and the microstructure was analyzed by scanning electron microscope (SEM) we also performed the study of the electrochemical properties by impedance measurements over a wide temperature range of 200-900°C. A mud-cracking pattern was observed in the samples obtained by chemical bath deposition whereas this pattern was not present in the ALD samples.
Towards Quantification of Local Electrochemical Parameters in Microstructures of Solid Oxide Fuel Cell Electrodes using High Performance Computations
Authors: Hsu Tim , Mahbub Rubayyat , Epting William K , Abernathy Harry , Hackett Gregory A , Rollett Anthony D , Litster Shawn , Salvador Paul A
Published: February 2020

Recent progress in micro-scale three-dimensional (3D) characterization techniques such as focused ion beam – scanning electron microscopy (FIB-SEM) and X-ray nanotomography has brought unprecedented opportunities in linking material microstructure to performance and properties. The link between solid oxide fuel cell (SOFC) electrode microstructure and performance is sometimes established by effective medium theory, where effective performance parameters are calculated from a representative volume element (RVE), an adequate volume that statistically represents global microstructure. However, different from performance, degradation and failure have not been addressed by mean parameters from effective medium theory. With the advent of modern 3D characterization techniques, there are new approaches in linking microstructure and degradation. This work aims to emphasize distributions (and outliers), rather than the mean, in better establishing the link between microstructure and degradation, failure, and performance. Using an open source finite element framework (MOOSE, Idaho National Laboratory) on a high performance computing platform (Joule, National Energy Technology Laboratory), a numerical transport and reaction model is applied to microstructural meshes to compute local distributions of electrochemical parameters. The microstructural meshes are obtained from the plasma sourced FIB-SEM characterization of a commercial SOFC electrode. The RVE size with respect to the computed distributions is determined based on examining the distributions from a series of microstructural meshes with various sizes. To validate the distributions, the averaged numbers from the distributions are compared with the effective medium theories in the literature. Finally, features such as the tails of the distributions and the local gradients of the electrochemical parameters are highlighted and discussed.
Numerical Analysis of Ammonia-Fueled Planar Solid Oxide Fuel Cells
Authors: Kishimoto Masashi , Kume Tatsuya , Iwai Hiroshi , Yoshida Hideo
Published: February 2020

Ammonia is receiving attention as a hydrogen carrier because of a number of advantages over other hydrogen carriers, such as greater hydrogen content, easy liquefaction and no carbon emission. Mass production process of ammonia has also been established and well-known as the Haber-Bosch process. Among the energy systems operated with hydrogen and hydrogen-containing fuels, solid oxide fuel cells (SOFCs) are one of the candidates that can be operated with ammonia-based fuels because they can decompose ammonia on their Ni-based anodes and produce hydrogen inside the systems; this can simplify the whole system configuration and realize cost reduction. In addition, the excess heat generation from the electrochemical reaction can be effectively utilized for the ammonia decomposition reaction.

Because the ammonia decomposition reaction is endothermic, temperature distribution on the cells is likely to be altered compared with the hydrogen-fueled SOFCs. Also, charge-transfer current distribution will be affected by the temperature distribution. To understand unique characteristics of ammonia-fueled SOFCs and to propose their appropriate operation conditions, numerical analysis is indispensable because of the difficulty in the direct measurement of physicochemical properties inside the cells. However, there are not many studies found in open literature where the characteristics of ammonia-fueled SOFCs are analyzed in detail by numerical analysis.

In this study, a numerical model of ammonia-fueled planar SOFCs has been developed. The model consists of a planar SOFC cell and fuel/air supply channels. Mass, momentum, energy and charge conservation equations are considered and coupled with the electrochemical reaction of hydrogen and the ammonia decomposition reaction. The ammonia decomposition rate per unit Ni-pore contact area in the Ni-YSZ anodes was developed in the authors’ group and implemented in the numerical model.

Distributions of the physicochemical properties, such as gas concentration, temperature and charge-transfer current, are analyzed and compared between the ammonia-fueled SOFCs and the hydrogen-fueled SOFCs. It was found that in the ammonia-fueled SOFCs the cell temperature first decreased in the upstream region by the endothermic decomposition reaction and then gradually increased towards the downstream, whereas in the hydrogen-fueled SOFCs the cell temperature monotonically increased in the flow direction. Also the peak in the charge-transfer current distribution was shifted towards the downstream in the ammonia-fueled SOFCs because of the altered temperature distribution.
Group IVA Oxide Surface Modification of LSCF Cathode Powders by Atomic Layer Deposition
Authors: Roeder Jeffrey F , Golalikhani Maryam , Zeberoff Anthony F , Van Buskirk Peter C , Torabi Alireza , Barton Joseph , Willman Carl , Ghezel-Ayagh Hossein , Wen Yeting , Huang Kevin
Published: February 2020

La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) powders have been modified by atomic layer deposition (ALD) with Group IVA based oxides, including zirconia, hafnia, and cobalt doped compositions. Amide (tetrakis(dimethylamido)zirconium and hafnium) and amidinate (bis-(N,N-disopropylacetamidinato)cobalt) precursors were used to treat 0.3 mm nominal diameter LSCF powders at 240°C using water as a co-reactant. The effect of the number of ALD cycles and level of Co additions have been examined up to 30% Co. The morphology and physical properties of sintered samples were similar to untreated powders with a modest shift to lower porosity and pore volume, but well within the desired range of microstructural properties. Cobalt additions lowered overall polarization in symmetrical electrochemical cells for zirconia based compositions. Hafnia based compositions also had significantly improved electrochemical performance.
Preparation and Properties of PrBa0.5Sr0.5Co1.5Fe0.5O5+δ as Novel Oxygen Electrode for Solid Oxide Electrolysis Cells
Authors: Tian Yunfeng , Yan Dong , Chi Bo , Chen Jing , Li Xi , Li Jian
Published: February 2020

A novel double perovskite oxide PrBa0.5Sr0.5Co1.5Fe0.5O5+δ (PBSCF) was prepared by a sol–gel method and then characterized by X-ray diffraction. The pure PBSCF as oxygen electrode for solid oxide electrolysis cells (SOECs). Electrochemical impedance spectra and voltage-current curves of the electrolysis cell with the configuration of PBSCF/GDC/YSZ/Ni-YSZ were measured as a function of operating temperature and steam concentration to characterize the electrolysis cell performances. The current density increased from 1.445 A/cm2 at 700℃to 1.735 A/cm2 at 800℃with 90vol% absolute humidity (AH) under an applied electrolysis voltage of 2V, The polarization resistance was 0.13Ω/cm2 at 800℃with 90% absolute humidity (AH). The hydrogen generation rate of the cell can be up to 978 mL/(cm2⸳h) with 90vol% AH at 800℃calculated from the Faraday’s law. Further, the electrolysis cell has showed very stable performance during a120 h short-term electrolysis testing, indicating that PBSCF can be a very promising candidate material for the oxygen electrode of SOECs.
Evaluation of the Influence of Gadolinium Doped Ceria Particle Size on the Electrochemical Performance and Microstructure of Nickel-Gadolinium Doped Ceria Anodes
Authors: Miyahara Kazuki , Sciazko Anna , Shimura Takaaki , Jiao Zhenjun , Shikazono Naoki
Published: February 2020

Last years, composite anodes consisted of nickel-gadolinium doped ceria (Ni-GDC) cermet gained a lot of attention as they have potential to be a beneficial solution for the intermediate temperature solid oxide fuel cells. In the range of temperatures below 700oC, a GDC cermet is characterized by a higher ionic conductivity compared to conventionally used yttria-stabilized zirconia (YSZ) cermet. Moreover, with the use of GDC as the mixed ionic-electronic conductivities (MIEC) material, electrochemical reaction sites are not restricted to triple phase boundaries (TPBs), but also extended to the double phase boundaries (DPBs) which consist of GDC/pore interfaces. Therefore, microstructure of electrodes has the crucial effect for the performance of the SOFCs and the evaluation of its changes are required to predict the deterioration of cell performances. Moreover, the precise mechanism behind observed microstructural reaction kinetics has not been fully revealed yet. For the further understanding of the electrochemical reaction kinetics, evaluation of the influence of TPB and DPB reaction for the overall electrochemical performance of MIEC anodes is required.

In this paper, the influence of the initial microstructure of Ni-GDC anode on the electrochemical performance and its deterioration after 100-h operation are investigated using electrolyte supported cells. The initial microstructure of anode is determined by the different aspect ratios and sizes of GDC powder used in the fabrication of cells. Four types of SOFC anodes were fabricated with the initial composition of NiO:GDC=60:40vol%.

The microstructural parameters of the fabricated anodes have been investigated by the focused-ion-bean – scanning electron microscopy tomography and 3D reconstruction of the representative structures. The parameters such as TPB length, surface area, porosity, tortuosity factor and connectivity have been quantitatively evaluated. From the observed microstructural changes and cell performances, contribution of the Ni-GDC microstructure and electrochemical reaction kinetics on anode performance are discussed.
Operando Vibrational Studies of Ni Electrode Degradation and Restoration in SOFCs Operating with Steam Reformed Methane
Authors: Walker Robert A , Owrutsky Jeffrey C. , Eigenbrodt Bryan C.
Published: February 2020

Two primary mechanisms responsible for Ni-based anode degradation in SOFCs are carbon accumulation (or coking) and reduction/oxidation cycling. Numerous strategies have been developed to suppress carbon formation on SOFC anodes including steam reforming and doping the anodes themselves with materials intended to prevent carbon growth. Once coking begins, however, removing carbon can cause even more anode degradation due to partial oxidation of the Ni anode itself. In experiments described below, operando Raman spectroscopy coupled with EIS and voltammetry measurements examine the propensity of carbon deposits to form from both methane and steam reformed methane in electrolyte supported SOFCs operating at temperatures between 700˚C and 800˚C. Vibrational spectra acquired from functioning cells shows that steam reformed methane limits but does not eliminate carbon accumulation. Changes in the mid- and low-frequency EIS data correlate closely with the spectroscopic observations and suggest that carbon accumulation affects both fuel oxidation activation energies as well as mass transport through the anode. Removing carbon electrochemically also induces Ni oxidation as reported directly in vibrational Raman experiments. Subsequent ex-situ experiments show a heterogeneous distribution of species throughout the anode and evidence of irreversible material degradation at the electrolyte/anode boundary. Steam by itself, however, proves to be remarkably effective at removing carbon while leaving the Ni anode largely intact. The ability of steam to remove carbon, presumably through solid carbon gasification, while allowing the Ni to remain in its elemental state shows microscopic reversibility of Ni oxidation and Ni reduction by H2O/H2 strongly favors reduction. Taken together these studies present a clear roadmap for restoring Ni-based SOFC anodes to their original operational state without forcing repetitive redox cycling that ultimately results in cell failure.
Modified LSCF Anode for Direct Conversion of Propane to Propylene in Proton Conducting Fuel Cell
Authors: Xu Yunjie
Published: February 2020

Using impregnation method to modified anode material LSCF(LaSrCrFe) to make it has PDH(propane dehydrogenation) catalytic activity and it can direct cogenerate electricity and propylene in proton conducting fuel cell.

LSCF is highly modified and has high surface area. And using PtGa and PtCo solution to treat anode material provides LSCF highly catalytic activity. Under Miro-reactor test, it shows that modified LSCF has very high propane conversion and propylene selectivity and it also has very promising stability and can keep catalyst stable more than 10 hours without steam treat. Different characterization methods are used. From TEM-EDX, it shows that PtGa nanoparticle cover on surface of LSCF and particle size is less than 10nm, and from EDX, it shows that even in nano-sclale, each element of LSCF is uniform distribution. And it shows in XRD pattern that LSCF doesn’t have any other phase. This modified material and method to treat anode material can highly improve anode material performance and give a promising future of directly convert fuel to electric.
Electrochemcial Performances of La-Doped SrTiO3 Anode Materials for Intermediate Temperature-Solid Oxide Fuel Cells
Authors: Jo Suyeon , Yang Jayoon , Park Jun-Young
Published: February 2020

Anode plays a very important role in the performance of solid oxide fuel cells (SOFCs) [1, 2]. In order to improve the cell performance proper anode materials should be selectd with suitable cell fabrication techniques. La-doped SrTiO3 (La0.4Sr0.6TiO3, LST) has received many attentions as an alternative anode material to state-of-art Ni-cermets anode for solid oxide fuel cells (SOFCs), because of its high redox stability, good electrical conductivity, and similar thermal expansion properties of yttria-stablized zirconia (YSZ) elecrolytes [3, 4]. Nowdays, decreasing the operating temperature of SOFCs down to intermediate temperature (IT) range (less than 800) is required to improve long-term durability and operational stability with economical advantages [5]. Hence, in this work, LST anode materials are fabricated with the highly conductive Nd0.1Ce0.9O2 (NDC) electrolytes and characterized to investigate the feasibility of SOFCs at the IT. In addition, LST is composited with the NDC to improve the ionic conductivity and decrease the thermal expansion mismatch of anode materails to the electrolyte. The Electrochmical impedance spectra (EIS) analysis shows that the polarization resistance of LST-NDC composite anode decreases with increasing of NDC concentrations, and 60:40 (LST:NDC in weight fraction) exhibits the lowest polarization resistance value at 650. The maximum power density of LST-NDC composite anode-cell is 143 mW cm-2 at 650, and thus we confirm the possbilty of LST as an anode material for the application of IT-SOFCs.

References

[1] S. Park, J.M. Vohs, R.J. Gorte, Nature 404 (2000) 265.

[2] S. Tao, J.T.S. Irvine, Nat. Mater. 2 (2003) 320.

[3] Ahmed D. Aljaberi and John T. S. Irvine. J. Mater. Chem. A. 1 (2013) 5868.

[4] Azra Yaqub, Cristian Savaniu, Naveed K. Janjuab and John T. S. Irvine, J. Mater. Chem. A, 1 (2013) 14189

[5] K.T. Lee, E.D. Wachsman, Science 334 (2011) 935.

Keywords:
anode-supported solid oxide fuel cells, Ni-free anode material, redox stability, La-doped SrTiO3, Nd0.1Ce0.9O2 electrolyte.

*
Corresponding author: Tel.: +82-2-3408-3848; Fax: +82-2-3408-4342

E-mail address: jyoung@sejong.ac.kr (J.-Y. Park)
Influence of Operating Parameters and System Design on Efficiency of Biomass and Biogas Based SOFC Systems
Authors: Herrmann Stephan , Hauck Maximilian , Geis Michael , Fendt Sebastian , Gaderer Matthias , Spliethoff Hartmut
Published: February 2020

With the recent COP 21 declaration many countries have dedicated themselves to a clear path towards decarbonization. This requires major installation of wind and solar power. However, these only provide intermittent electricity. Thus, balance power has to be provided, ideally from renewable resources. Currently only biomass seems to be available in large enough quantity to provide significant balancing power. A wide range of biomass feedstocks can be made available for power generation for example via anaerobic digestion or thermo-chemical gasification. However, resources are still limited. Hence, in order to maximize its potential the biomass has to be used at the highest possible efficiency. Electrochemical conversion, especially in SOFC, in general offers very high efficiency. However, also in SOFC systems the choice of the optimal system design and operating parameters can make a big difference.

The presented work investigates utilization of biogas and syngas from biomass gasification in different system designs. This is done using a thermodynamic SOFC model built in Aspen Plus, which has been validated against literature data. A comparison to cell and stack performance of the well known manufacturers Fuel Cell Energy and Forschungszentrum Jülich is presented. It is shown that at identical operating conditions the model shows slightly worse performance than the real stacks.

With the model, the influence of different fuel pre-treatment and pre-reforming options are compared at a fixed stack size. Furthermore the effect of anode offgas recirculation, as well as the choice of fuel utilization, oxidant, operating temperature and pressure are investigated. During the analysis operating conditions prone to the risk of carbon deposition are excluded. Also the impact on the balance of plant is taken into account. Results show, that depending on the fuel, system design and parameters the electrical efficiency of the fuel cell alone can vary between 35 and 71%. From this, depending on the system parasitic consumption and losses of up to 8% points have to be subtracted. Thus, net AC efficiencies reach 30 to 63%.

Finally a new system design and operating regime is proposed, which can significantly raise the DC efficiency while reducing the parasitic consumption by adjusting the gas treatment and operating parameters. Modelling results of new design show net AC system efficiencies of up to 72%.
Solid State Li-Garnet Batteries: On New Phase-Discoveries, Interface Engineering and Playing with Device Electrochemistry
Authors: Rupp Jennifer L.M.
Published: February 2020

Society requires innovative approaches to match the demand for cheap, non-abundant and high capacity energy storage, while also meeting efficient energy conversion demands to best capitalize on renewables or waste products. Through the research new concepts for ceramic interface processing in oxides based electrode/electrolyte arrangements to implicate the Li-transferrence and electrochemical storage capability for solid state batteries based on garnets are reported for whole oxide cell arrangements and performances are discussed. A second significant challenge of solid state battery is to develop strategies avoiding Li-dendrites at ceramic grain boundaries with potential for battery failure in solid state cells; currently Li-garnets are reported to exist in crystalline ceramic phase only. Here this challenge is tackled by the discovery of "polyamorphic" phases in Li-garnet electrolytes which can lead, based on the fundamentals on structure-transport-processing gained, to new design principles of glassy (grain boundary free) solid state battery architectures to avoid Li-dendrites for safe operation. As an extension to the existing application field using Li-garnets as battery electrolytes it is also demonstrated that one may apply those as future electrolyte components in new environmental CO2 tracker devices for electrochemical potentiometric sensor concepts. Ultimately, research contributes to new material phase discoveries, processing and engienering concepts of efficient solid state battery assemblies based on Li-garnets for safe energy storage and new application fields such as garnet-type potentiometric electrochemical sensors.
Crystal Plane Effects on Charge Storage in Cerium Oxide Nano Structures
Authors: Jeyaranjan Aadithya , Sakthivel Tamil Selvan , Sayle Dean C , Seal Sudipta
Published: February 2020

Nano cerium oxide (CeO2) is gaining a lot of attention as an electrochemical energy storage material. However, the crystal plane effects of CeO2 on energy storage remain largely unexplored. In this regard, two different CeO2 nano structures: nanoparticles (CNPs) and nanocubes (CNCs) with specifically exposed crystal planes were synthesized by a simple hydrothermal process. Structural characterization using TEM revealed CNPs were enclosed by {111} and {100} surfaces, and CNCs were enclosed by six {100} surfaces. The specific surface areas analyzed estimated by BET for CNPs and CNCs were 44 m2/g and 38.3 m2/g, respectively. The electrochemical properties of the nanostructures were evaluated using cyclic voltammetry and galvanostatic charge-discharge techniques with 3M KOH electrolyte. The experiments revealed that the exposed crystal planes have a more profound effect on the supercapacitance of the nanostructures than the surface area. Despite the slightly lower specific surface area, CNCs dominated by the high energy surface {100} showed considerably higher (69%) specific capacitance than the low energy {111} dominated CNPs. The difference in charge storage between CNCs and CNPs was increasingly wider with the decrease in scan rate. This suggested that the charge storage in CNCs took places both surface and bulk, but was restricted to the surface in CNPs. The difference in charge storage at the surface and bulk were also quantified using electrochemical analysis. Reactivity maps of the nanostructures, generated using molecular dynamics simulation, were in good agreement with our experimental findings. Thus, this study demonstrates how charge storage in supercapacitors can be improved by selecting redox active nanomaterial with highly exposed redox active crystal planes.