bluuebunny/crossref_metadata_2025_split huggingface dataset:
Accelerated Lifetime Tests for SOFCs
Authors: Weber André , Szász Julian , Dierickx Sebastian , Endler-Schuck Cornelia , Ivers-Tiffée Ellen 
Published: February 2020

Considering the expected lifetimes for Solid Oxide Fuel Cells of 5 to 10 years, durability is still a major issue. Even though quite a number of research institutions and companies have proven an acceptable degradation rate of cells, stacks and systems for periods ranging from a few hundred hours to several years, neither reliable degradation models nor methodologies to evaluate the durability in a short timeframe are available. Thus any kind of modification on the cell or stack level, which might affect the durability, requires an expensive and time consuming repetition of the durability test. Accelerated lifetime tests, which enable a rapid degradation analysis, and degradation models, that enable an extrapolation of the results, would be highly desirable.
In most durability investigations a cumulative degradation rate is evaluated from the cell voltage decrease in a galvanostatic operating mode. In addition, extensive post test analysis is performed to detect the failure causes. This approach does not reveal any quantitative information on the different underlying degradation mechanisms. If aggravated stress is applied by increasing operating temperature, current density or gas utilization, the degradation of cathode, electrolyte, anode, contact layers and interconnects is accelerated in different ways. Therefore the cell voltage alone is insufficient to understand the performance degradation and its acceleration due to aggravated stress.
To deconvolute the degradation of cathode, electrolyte and anode (i) electrochemical impedance spectroscopy, (ii) impedance data analysis by the distribution of relaxation times and, (iii) a subsequent CNLS-Fit to a physically meaningful equivalent circuit model is suggested. Cell tests were performed at different stress levels by varying temperature and current density as well as fuel and oxidant composition. Based on this extensive data set, the interplay between stress level and impact of the different stresses on degradation mechanisms in cathode, electrolyte and anode will be presented and guidelines for the design of accelerated tests will be discussed.
Towards the Design-Led Optimization of Solid Oxide Fuel Cell Electrodes
Authors: Kishimoto Masashi , Lomberg Marina , Ruiz-Trejo Enrique , Brandon Nigel P. 
Published: February 2020

Electrode microstructure plays an important role in determining the performance and durability of solid oxide fuel cells (SOFCs). It needs to be tailored towards a variety of requirement for the electrodes, such as transport properties and electrochemical activity. Long-term stability of the microstructure is also important to guarantee the durability of SOFC systems. In order to satisfy the growing demand for their performance and durability, an improved understanding of the microstructure-performance relationships is desired, along with optimization of the microstructure, through a design-led approach.
The focus of this study is on electrodes fabricated with the nano-particle infiltration techniques. Porous framework structures (scaffolds) were first fabricated with gadolinium-doped ceria (GDC), and then nickel metal particles were introduced into the structures in the form of nano particles. 3D microstructural analysis using focused ion beam and scanning electron microscope (FIB-SEM) was carried out and revealed that the infiltration technique has a greater potential, compared with the conventional approach based on powder mixing and sintering, to control the electrode microstructure, helping satisfy multiple requirements for the electrodes. Most notably, the triple-phase boundary (TPB) density in the infiltrated electrodes was found to be one order of magnitude larger than that typically found in the conventional electrodes.
A 1D numerical model for Ni-GDC electrodes was also developed assuming that the GDC phase has mixed ionic and electronic conductivity and hence that the electrochemical reaction takes place on the GDC-pore double-phase boundary (DPB), and successfully reproduced the overpotential characteristics obtained from the experiment. Sensitivity analysis was also conducted with the developed model at 700 °C to investigate the effect of electrode microstructure on electrode performance. This revealed that the electrochemical reaction on the DPB is the rate-determining process within the electrodes; therefore increasing the DPB density is recommended as the most effective route to improving performance of ceria-based electrodes, rather than improving species transport rate.
Using the insights from the experiment, microstructural analysis and numerical simulation, guidelines for further optimizing the electrode microstructure are proposed

Figure 1
Electrochemical Investigation of a Large SOFC Fed with n-Dodecane Reformate
Authors: Trocino Stefano , Lo Faro Massimiliano , Campagna Zignani Sabrina , Monforte Giuseppe , Aricò Antonino S. 
Published: February 2020

In recent years, solid oxide fuel cells (SOFCs) have been extensively studied because of its potential as clean and efficient electric generators. Recently, SOFCs coupled with an external reforming have been suggested for the utilization in marine on-board applications. Diesel marine is the conventional fuel actually used; however, the stability of a conventional SOFC fed with a diesel reformate is not yet proven. Furthermore, the testing of a large area SOFC has a specific importance with the aim of the subsequent scaling up to a stack.
This study deals with the investigation of the degradation effects occurring onto the anode of a large area cell in presence of n-dodecane reformate. A commercial anode supported SOFC (10 × 10 cm2) with planar configuration having the composition Ni-YSZ/YSZ/YDC/LSFC, has been investigated in-situ electrochemically. The test bench used for this experiment is the conventional ECN test station showed in Figure 1. The electrochemical experiments concerned I-V curves (Figure 2) and impedance spectroscopy (Figure 3) carried out at OCV and at 0.9 V. Ex situ tests were also carried out in order to evaluate morphological and and physico-chemical modification on the discharged cell.
In the case of anodes (Ni-YSZ cermets), the degradation phenomena are recognized due to Ni agglomeration and carbon deposition. These microstructural changes in anode is expected to be highly dependent on operating conditions, such as operating temperature, operating voltage and water content in the feed.

Figure 1: ECN test bench (a) and commercial large area cell (b)

Figure 1
Fabrication of a Ni/MgO Nanocomposite Catalyst by Exolution
Authors: Lim Ye Sol , Yoon Jong Seol , Choi Byung Hyun , Seo Won Seon , Hwang Hae Jin 
Published: February 2020

Methane steam reforming reaction is the most important chemical process to produce hydrogen or synthesis gas. Hydrogen is heavily consumed for ammonia production, the cryogenics industry and methanol production. Recently, the hydrogen demand is expected to increase as fuel cells become more widely accepted and are used more in the near future. For effective production of hydrogen or synthesis gas, the role of the reforming catalyst becomes more significant. Especially, highly active and stable catalyst is necessary for an on-site reformer for fuel cell systems.
In conventional technology, the methane steam reforming reaction is conducted on supported noble metals- (Pt, Pd, Rh, Ru, and Ir) or nickel-based catalysts at temperature up to 700~800°C and steam to methane rations between 2 and 4. However, these catalysts suffer from the deactivation by agglomeration and carbon deposition. Noble metal-based catalysts are less sensitive to carbon deposition than nickel-based catalyst. However, high cost and limited availability are major concern.
In this study, nickel-based nanocomposite catalysts were fabricated by exolution process. The exsolution means the process to precipitate particles from solid solution by means of the heat treatment in a specially-controlled atmosphere. This process is distinguished from the infiltration in which particles are precipitated from solutions by evaporation. First, Mg1-xNixO solid solution powders were synthesized from aqueous magnesium and nickel nitrate solution by precipitation technique and then the powder was heat-treated in reducing atmosphere at 600 to 900°C. SEM and TEM images revealed that the nano-sized nickel particles were homogeneously dispersed in the Mg1-xNixO solid solution matrix and the size and morphology of nano nickel particles can be controlled by the heat-treatment condition. Catalytic activity for the methane steam reforming or methane particle oxidation reaction and durability of the Ni/Mg1-xNixO was investigated in terms of nickel contents and sizes.

Figure 1
Numerical Assessment of SOFC Anode Polarization with Microstructure Evolution
Authors: Jiao Zhenjun , Shimura Takaaki , Shikazono Naoki 
Published: February 2020

A phase field method was introduced to simulate the microstructural evolution of nickel-yttria stabilized zirconia composite anode of solid oxide fuel cell in high temperature sintering based on three-dimensional microstructures reconstructed by focused ion beam-scanning-electron-microscopy technique. Nickel phase morphology and crystal structure evolutions and the change of nickel network percolation in operation were simulated simultaneously. In order to quantitatively study the correlation between anode microstructure change and the anode electrochemical performance degradation, the evolution of three-phase boundary density and nickel specific surface area were calculated. Corresponding degradation experiments have been conducted to compare with the simulation results. The experimental results showed good agreement to the simulation results.

Figure 1
Development of Robust SOFC Anode Materials Using La-Doped SrTiO3
Authors: Shen Xuesong , Sasaki Kazunari 
Published: February 2020

We utilize the very stable Sr0.9La0.1TiO3 (SLT) to fabricate robust anode for SSZ electrolyte-supported SOFC single cell. The anode consisted of three layers: a layer of 60wt% GDC-SLT or 40wt% SSZ-SLT as functional layer and two layers of SLT as current conducting layer. Cathode was composed of a layer of 50wt% SSZ-LSM as functional layer and a layer of LSM as current conducting layer. Impregnation method was employed to decorate nano-sized Ni and CeO2 into the ceramic anode. We measured electrochemical properties of the single cells in 3%-humidified H2at 800°C, and investigated redox stability of the nano-sized catalyst impregnated ceramic anodes by fuel interruption method described in our previous publication.
The homogeneously dispersed nano-sized catalyst provides sufficient catalytic activity for the conductive ceramic backbones, GDC-SLT or SSZ-SLT, to work as effective anodes, and remarkable improvement of cell performance could be achieved. Compared with the traditional Ni-SSZ cermet anode, the catalyst impregnated ceramic anodes have prominent advantage against the redox cycling test. Cell performance drops 0.52% and 0.45% when using catalyst impregnated 60wt% GDC-SLT and 40wt% SSZ-SLT as anode in the first 10 redox cycles respectively, whereas, the degradation rate of Ni-SSZ in the first 10 redox cycles is 14%. The excellent stability of the impregnated anodes against redox cycling test mainly comes from two aspects: firstly, the electronic conducting path provided by ceramic backbone maintains completely during redox cycling, whereas, conducting path in traditional Ni-SSZ, the connected Ni particles, will be dislocated when Ni particles suffer shrink and expansion during redox cycling. Moreover, CeO2used in the anode works as inhibitor preventing Ni particles from further agglomeration, meanwhile it supports Ni particles to maintain sufficient catalytic activity for fuel oxidation at constant current loading.
In conclusion, we have developed robust SLT-based ceramic anodes using impregnation method, which demonstrated excellent stability in redox cycling test compared with traditional Ni-Zirconia cermet.
Gas Composition Analysis on Ni-YSZ Anode in Direct Internal Reforming Solid Oxide Fuel Cell
Authors: Muroyama Hiroki , Ando Daiki , Okanishi Takeou , Matsui Toshiaki , Eguchi Koichi 
Published: February 2020

Solid oxide fuel cell (SOFC) is one of the most promising power generation devices. In Japan, the residential SOFC cogeneration systems have been commercialized since 2011. In this system, the supplied methane-rich fuel is reformed in an external reactor and the pre-reformed gas (hydrogen-rich fuel) is introduced to the anode chamber. In contrast, high operating temperature of SOFCs provides the possibility of a direct internal reforming operation, in which the anode material plays a role in the promotion of fuel reforming and fuel oxidation. Because the supplied fuel is reformed over anode catalyst, the concentration distribution of reactants and products appears along the direction of gas flow. Moreover, under discharge operation, the exothermic reaction of electrochemical oxidation as well as the endothermic reaction in the fuel reforming proceed simultaneously at the anode. In this case, the temperature distribution is more complicated than that in a supply of hydrogen fuel. Up to now, there are few reports on the direct evaluation of gas composition and temperature distributions over the anode although the theoretical calculation have been conducted.
This study, therefore, aimed to investigate the methane steam reforming and electrochemical oxidation over Ni–YSZ anode in an anode-supported cell. The distribution of gas composition over the anode surface along the direction of gas flow was examined by gas chromatograph under the open circuit and discharge conditions in a direct internal reforming SOFC.
The effect of total flow rate on the reaction process was studied under the open circuit condition. Regardless of total flow rate, the methane conversion remarkably increased at the upstream part. The extent of conversion enhancement was more significant at slower flow rates. In contrast, the correlation between the obtained methane conversion and the gas-catalyst contacting time agreed well in all flow rate conditions. The temperatures of anode surface at all measurement positions were lower than that under supplying only hydrogen due to the endothermic reaction in methane reforming process. The temperature variation against the direction of gas flow corresponded to the methane conversion. The surface temperature decreased at the upstream parts and then gradually rose toward the downstream parts.
During discharge, the enhancement of methane conversion and the decrement of CO concentration were accomplished with an increase in current density. This result suggests that the steam reforming reaction and water gas shift reaction were promoted by the consumption of hydrogen and the formation of steam in the electrochemical hydrogen oxidation.
Characterization and Stack Testing of Solid Oxide Fuel Cells with Cathodes Prepared by Infiltration
Authors: Küngas Rainer , Hertz Thomas B. , Heiredal-Clausen Thomas 
Published: February 2020

Recently, the use of infiltration as a method for SOFC electrode preparation has gathered significant scientific interest (1-6). The results thus far have been mostly obtained on button cells with electrode active areas on the order of 1 cm2 or less. Here, we report the physical characterization and stack testing of 12 x 12 cm2 planar cells with cathodes prepared by infiltration of a perovskite precursor solution into a stabilized zirconia backbone.
As the first step in the development of the new cell design, a stabilized zirconia backbone layer with high surface area and good mechanical compatibility with the rest of the cell was developed. After an optimized sintering procedure was introduced, batches of about 90 cells could reproducibly be manufactured with high yields. The optimized blank cells were infiltrated with a precursor solution of (La0.8Sr0.2)0.95FeO3 and the resulting cells were characterized thoroughly using XRD, van der Pauw in-plane conductivity, BET specific surface area, and electrochemical single-cell measurements. As the in-plane conductivity, the BET surface area as well as the pore-size distribution of the cathode are thought to play a key role in determining the long-term performance and stability of infiltrated cells in a stack, changes in these properties were mapped out as a function of the cathode sintering temperature.
Electrochemical testing on both cell and stack level confirmed the enhanced performance of cells with cathodes prepared by infiltration. Results on degradation testing will be reported separately.
This work was partly funded by EUDP project J 64012-0225, “SOFC Accelerated”.
References

S.P. Jiang, Mater. Sci. Eng. A, 418, 199 (2006).

J.M. Vohs, R.J. Gorte, Adv. Mater., 21, 943 (2009).

A.J. Samson, P. Hjalmarsson, M. Søgaard, J. Hjelm, N. Bonanos, J. Power Sources, 216, 124 (2012).

D. Ding, X. Li, S.Y. Lai, K. Gerdes, M. Liu, Energy Environ. Sci., 7, 552 (2014).

T.Z. Sholklapper, H. Kurokawa, C.P. Jacobson, S.J. Visco, L.C. De Jonghe, Nano Lett. 7, 2136 (2007).

M. Shah, S.A. Barnett, Solid State Ionics, 179, 2059 (2008).

Figure 1
Dusty-Gas Model with Uniform Pressure: A Numerical Study on the Impact of a Frequent Inconsistent Assumption in SOFC Electrode Modeling
Authors: Bertei Antonio , Nicolella Cristiano 
Published: February 2020

One of the most popular models adopted to describe the gas transport in porous electrodes is the dusty-gas model. Such a model is commonly applied in the literature under the assumption of uniform pressure. However, as we recently summarized in a short communication [A. Bertei, C. Nicolella, J. Power Sour. 279 (2015) 133-137], this assumption is incompatible with the dusty-gas model formulation and leads to serious inconsistencies, for example, fluxes that do not obey reaction stoichiometry. In such a case the model fails to predict partial pressure profiles, concentration overpotentials and limiting currents.
In this study, we report the quantification of the error in the prediction of partial pressure profiles and concentration overpotential due the inconsistent assumption of uniform pressure in a broad range of conditions, focusing mainly on SOFC anodes. Simulations show that an inconsistent use of the dusty-gas model may lead to relative errors in the prediction of concentration overpotential as large as 60%. In H2/H2O/N2 mixtures, the error increases as the molar fraction of the inert species decreases and is maximum in binary H2/H2O mixtures. In addition, the error increases as porosity, pore size and water molar fraction increase while it decreases as the current density and the electrode thickness increase. These results are helpful to quantify the impact of an inconsistent use of the dusty-gas model in the literature and to promote a coherent gas transport modeling.
Stability of Nickel-Infiltrated Anodes in Intermediate Temperature SOFCs
Authors: Miller Elizabeth C , Sherman Quentin , Gao Zhan , Voorhees Peter W , Barnett Scott A 
Published: February 2020

Solid oxide fuel cells (SOFCs) with a thin La1-xSrxGa0.8Mg0.2O3-
δ (LSGM) electrolyte plus Ni-infiltrated LSGM anode functional layer and Sr0.8La0.2TiO3 (SLT) anode support have shown high power density (> 1 W cm-2) at temperatures ≤ 650°C and good stability in short-term testing (< 100 h). However, the long term stability of these cells is still largely unstudied. In this work, ex situ studies on the evolution of aqueous infiltrated Ni(NO3)2 to NiO and finally to Ni metal nanoparticles on LSGM pellets determined that the size and number of Ni particles can be controlled by dehydrating the samples before calcination, which could be used to advantageously control the microstructure of infiltrated anodes. SOFCs with Ni-infiltrated anodes were tested in humidified hydrogen and air at open circuit voltage (OCV) to determine stability for durations up to 600 h. Scanning electron microscopy indicated that Ni nanoparticles coarsened over time, which negatively affected performance. The polarization resistance of the anode doubled in magnitude over the course of the test, and ohmic polarization was found to increase with time, which could result from coarsening Ni closing off active areas in the anode functional layer. OCV remained within ~0.05 V of the theoretical OCV by the end of the test. In all cases, the majority of the polarization resistance resulted from degradation of the La0.6Sr0.4Fe0.8Co0.2O3-δ-Ce0.8Gd0.2O1.95 (LSCF-GDC) cathode. To better understand the effect of Ni coarsening on cell performance, a model was developed to predict the changes in triple phase boundary (TPB) length during coarsening and its effect on cell performance. Additional testing is required to determine how these preliminary results will extend to operating lifetimes and how to use the ex situ test results to control microstructures in processed cells.
Morphological Modelling of a Metal Foam Supported SOFC Configuration
Authors: Masson David , Abdallah Bassam , Willot François , Jeulin Dominique , Mercadelli Elisa , Sanson Alessandra , Chesnaud Anthony , Thorel Alain 
Published: February 2020

The EVOLVE cell, named after a running FP7 project, is an innovative SOFC concept that integrates advanced materials, providing multiple functionalities (electrochemical activity, ion or/and electron conduction, gas diffusion…), and an inventive anode current collector made of a NiCrAl preoxidized foam impregnated with a conductive perovskite. Therefore, this anode combines the beneficial characteristics of MSC and ASC technologies, and strong improvements in terms of reliability and durability (inter-diffusion, Ni coarsening and agglomeration, sulphur tolerance, mechanical robustness and chemical stability under redox cycling in temperature) are expected.
In order to enhance the electrode efficiency, the 3D microstructure needs to be precisely described at the microscopic scale by a morphology model. An optimized microstructure (controlled pores size, morphology and connectivity, grains size distribution, 3D tortuosity and 3D percolation of phases, volume fraction of phases, final thickness of components …) is closely related to the starting parameters (nature and quantity of starting powder, binder, shaping aids…) and to the control of the shaping process parameters (sintering treatment and atmosphere). It should meet the best compromise between a good electrocatalytic activity and a low ohmic resistivity while ensuring a stisfactory long term thermomechanical stability on the life time of the device.
Based on a mathematical morphology approach applied on symmetrical LST/CGO anode layers, the present work aims at showing how a morphology model can be establised and 3D microstructural data relevant for shaping and performances can be derived from back-scattered electrons (BSE) SEM observations. For each sample, a series of images were used as input information for the microstructural modelling. All the original images were first filtered to remove the noise, thresholded and finally a series of morphological operators (openings, surface openings, closings and reconstruction with markers) were applied to remove artefacts. A 3D pluri-Gaussian model has been generated from 2D images, and then computed to predict volume fraction of the 3 phases, 3D tortuosity, gas permeation and ionic conductivities. These results were used for the optimization of the shaping process that includes the integration of the metal foam.