bluuebunny/crossref_metadata_2025 huggingface dataset:
Changes in SOFC Cathode Crystallographic Structure Induced by Temperature, Potential and Oxygen Partial Pressure Studied Using in-Situ HT-XRD
Authors: Kivi Indrek , Aruväli Jaan , Kirsimäe Kalle , Heinsaar Alar , Nurk Gunnar , Lust Enn
Published: February 2020

Reversible changes in the lattice parameters of SOFC cathode were observed depending on the temperature (T), electrode potential (E) and oxygen partial pressure (p
O2) applied. At fixed T and p
O2, the cathode potential noticeably influences the unit cell volume, thus, the oxygen stoichiometry and concentration of vacancies.

The stabilization time of the XRD peak was in minute scale similarly with the plateau time on chronoculonometric curves. Relaxation time of the changes in crystal dimensions are correlated with electrochemical measurement data. The electrode structure (porosity) has strong influence to the shift time of XRD peak.

There was registered only slight influence of oxygen partial pressure and potential to the crystallographic parameters of LSM (La0.6Sr0.4MnO3
−
δ). At the same time for LSC (La0.6Sr0.4CoO3
−
δ) and GSC (Gd0.6Sr0.4CoO3
−
δ) the crystallographic unit cell volume was a function of electrode polarization and oxygen partial pressure. There is no remarkable vacancy formation detectable with HT-XRD in LSM cathode lattice caused by electrode polarizations applied.

Thermochemical crystallographic expansivity study of LSM, LSC and GSC cathodes with in situ HT-XRD method gives valuable experimental data about the crystallographic changes caused by changes in operating parameters like cell potential, temperature, and oxygen partial pressure in cathode compartment and therefore helps to understand thermomechanical and degradation behavior as a function of different conditions applied for  SOFC cathode.

Figure 1
High Durability Electrodeposition Painting for SOFC Metal Interconnector
Authors: Inoue Shuichi , Nonaka Hidemasa , Saito Tadashi , Yoda Masakazu , Nakao Tadayuki , Takuwa Yuya
Published: February 2020

Osaka Gas Co., Ltd. has been developing electrodeposition painting method for SOFC metal interconnector coating since 2010. Although the general electrodeposition painting was mainly consisted of resin with small amount of ceramics as a pigment, we have successfully increased the amount of ceramics in the coating and this method was adopted to SOFC metal interconnector coating. Generally, SOFC interconnector had the complex structure with the gas flow path. This method had the advantage of coating thickness uniformity regardless of the interconnector structure and mass productivity.

We have investigated to enhance the durability of the SOFC interconnector with this method.In addition, we aimed to reduce the cost of the metal interconnector by using the normal stainless steel, not stainless steel specially designed for the SOFC component.

The composition of Co-Mn spinel-type oxide widely used in this field was selected as the coating ceramics.

As is often the case with interconnector, the protective coating needed to be partially coated. The wet coating method like electrodeposition painting needed to be fired after coating to remove the resin and sinter the spinel-type oxide.

From the standpoint of processing cost, it was desirable to be fired in air, but non coated area was severely oxidized and Cr2O3 layer showing high ASR was formed on the surface of the stainless steel.

In order to prevent the oxidation of non-coated area and sinter the spinel powder enough, two steps of firing have been normally taken: the resin was removed in air first, then the Co-Mn spinel powder was sintered in the reduction atmosphere. This process cost tends to be high due to changing atmosphere.

However, our electrodeposition painting method did not need to be fired in two steps because its resin was acrylate resin which was removed completely even in the reduction atmosphere.

Cross section images of the post anneal coating showed the dense structure and the uniform layer thickness.

ASR test over 10,000hr showed excellent durability at the both of the continuous condition and thermal cycle condition.

The Cr diffusion from the stainless steel was also evaluated, it showed the high prevention of Cr diffusion.

The variability of coating weight were quite small, it was concluded that this electrodeposition painting method is suitable for mass production.
Manufacture of Solid Oxide Fuel Cells Using Electroless Co-Deposition: A Review of Work Carried out at Edinburgh Napier University
Authors: Davidson Alan , Wilson Callum , Shearer Neil
Published: February 2020

This paper reviews work carried out at Edinburgh Napier University on the manufacture of anodes and cathodes for solid oxide fuel cells (SOFCs) using electroless co-deposition of nickel and ceramic powders. Most of the work has been focused on anodes where the co-deposition of nickel and yttria stabilised zirconia (YSZ) negates the need for traditional manufacturing methods such as screen printing and removes the need for expensive and time consuming high temperature consolidation of the ceramic part of the composite.

Work has also been carried out manufacturing cathodes by electroless co-deposition replacing YSZ with lanthanum strontium manganite and lanthanum nickel ferrite. Anodes and cathodes of both planar and tubular designs of SOFCs have been successfully manufactured using this technique and process variables have included ceramic particle size, bath pH, ceramic loading, the inclusion of pore-formers and tubular orientation in the electroless bath.

Testing of the electrodes included impedance analysis, long term degradation testing at 850oC for 500 and 1000-hours, high temperature electrical conductivity measurements, scanning electron microscopy and energy dispersive X-ray analysis.

The cost benefits of the electroless co-deposition process compared with other conventional processes are also discussed.
Boundary Observation and Contrast Tuning of Ni/YSZ Anode by TEM and FIB-SEM
Authors: Liu Shu-Sheng , Matsumura Syo , Koyama Michihisa
Published: February 2020

The most widely used anode material in SOFC is Ni/yttria stabilized zirconia (Ni/YSZ). Its microstructure depends on the fabrication techniques, and determines its performance. Electron microscopy is often adopted to characterize the microstructure in wide scales. In this report, we focus on the microstructure observation of conventional Ni/YSZ anodes in two open issues: atomic structure of boundary by transmission electron microscopy (TEM) and phase contrast tuning by focused ion beam-scanning electron microscopy (FIB-SEM).

It is well-known that Ni/YSZ interface and Ni/YSZ/pore triple-phase boundary (TPB) play important roles in the stability and reaction activity of Ni/YSZ anodes. However, most of the microstructure researches related to interface and TPB lie in micro- or nano-scales. In atomic scale, few reports on the interfaces of conventional Ni/YSZ anode can be found. Moreover, there is no experimental study on the real atomic structures of TPB. So, high-resolution transmission electron microscopy (HRTEM) and scanning TEM (STEM) were adopted to observe the atomic structures at the interfaces and TPBs. Before observation, the pores of the porous electrode were infiltrated by low viscosity epoxy resin under vacuum, so that they could be easily distinguished in a microscopy and the bulk cell could be readily handled. The specimen for TEM was lifted out in a focused ion beam-scanning electron microscopy (FIB-SEM). After observation, high-index contact surfaces (e.g. Ni(15 13 1)/YSZ(4 4 10)) were found between Ni and YSZ. At TPB, YSZ(200) was found to be the contact surface while Ni(111) shows an included angle of ~13° with YSZ(200).

3D reconstruction is becoming popular with the help of several techniques, such as FIB-SEM and TEM. In case of FIB-SEM, many of previous works showed indistinct contrast among different phases, which will make the analysis difficult and the results distorted in some extent. Herein, we used a high-resolution machine (HITACHI MI4000L) and tuned many conditions to improve the contrast. The related mechanism will be discussed. For Ni/YSZ anode, distinct contrast was obtained among Ni, YSZ and pore (actually resin) by using InLens detector. The three phases could be automatically segmented by Avizo software. Then the 3D microstructure is reconstructed.
Performance and Redox-stability of La and Ni Co-doped SrTiO3 Anode of Solid Oxide Fuel Cell
Authors: Park Byung Hyun , Choi Gyeong Man
Published: February 2020

Conventional Ni-cermet anodes show problems for the stability due to carbon coking or Ni coarsening etc.. Perovskite oxides are good candidates as an alternative anode that can solve the problems. Electro-catalytic nanoparticles such as Ni, Ru or Pd can be produced in oxide anodes when exposed to reducing atmosphere. The Ni ex-solution in La0.2Sr0.8Ti0.9Ni0.1O3-δ (LSTN) was determined in our previous work. The electrochemical performances of electrolyte (ScSZ)-supported cells with LSTN anode was improved from that with La0.2Sr0.8TiO3 anode at 800oC in both H2 and CH4 fuels. However, the performance is limited due to poor ionic conductivity of LSTN. In this study, we have studied LSTN (La0.2SrxTi0.9Ni0.1O3-δ) anodes with different A-site composition (x=0.7 or 0.8). We have also studied the effects of Gd0.2Ce0.8O2 (GDC) and/or Ni addition in LSTN. In addition, the redox stability of the anodes was compared with conventional Ni-cermet anode. Impedance spectra and power measurement of the cells with the anodes have shown the redox stable and excellent performance of the cells when GDC and Ni were composited with LSTN.
Architectured Interfaces and Electrochemical Modelling in an Anode Supported SOFC
Authors: Geagea Maya , Ouyang Jian , Chi Bo , Delloro Francesco , Chesnaud Anthony , Ringuedé Armelle , Cassir Michel , Thorel Alain
Published: February 2020

The route for the increase in SOFC performances is many-fold: i/ in the low current density domain, through the enhancement of the catalytic properties of the electrodes, i.e. via a higher Triple Phase Boundary (TPB) density, hence a higher exchange current and a lower activation overpotential, ii/ in the ohmic loss region, through lower resistance, i.e. via thickness reduction, materials with a higher conductivity, iii/ in the high current density region, via the optimization of the electrodes microstructure, i.e. the control of the porosity, of the tortuosity and percolation of phases. Taking ideas from the batteries community, where the conceptual design of electrodes is much more mature, the present work proposes to explore how the corrugation of electrode/electrolyte interfaces impacts the performances.

This approach was applied to the anode/electrolyte interface of a SOFC based on standard compositions, YSZ (or YDC) for the electrolyte, and YSZ (or YDC) + nickel for the anode. The corrugation of surfaces was obtained through the patterning of this interface with different geometries (flat, pyramids, shallow and deep ellipsoids) at the 10-100 µm scale by cold pressing, templating or serigraphy. Thin electrolyte layers have been deposited on top of these architectures by Atomic Layer Deposition (ALD). In parallel, an electrochemical model was carried out and implemented by considering masses and charges conservation, gas transport and electrochemical reaction kinetics throughout the interface in FEM (finite element method) with COMSOL Multiphysics. The results showed a 25 % increase in the total current density for a certain ellipsoid geometry.
Electrochemical Performance of Plasma Sprayed Metal Supported Planar Solid Oxide Fuel Cells
Authors: Gupta Mohit , Weber André , Markocsan Nicolaie , Gindrat Malko
Published: February 2020

High material and production costs are key barriers to the widespread commercialization of solid oxide fuel cells (SOFCs). Thermal spray techniques are a low cost alternative for the production of SOFCs. The objective of this work was to fabricate single cells by thermal spraying and to evaluate the impact of electrolytes and anodes, differing in terms of thickness, composition and microstructure, on the cell performance.

In this work, the anode layer was deposited on a planar ferritic steel support with in-plane dimensions 50 mm X 50 mm, thickness of 550 µm and 35-40% porosity by atmospheric plasma spraying (APS). The anode material consisted of nickel, yttria stabilized zirconia (YSZ) and a pore former. The anode layer thickness was around 60 µm. The electrolyte layer was deposited by a low pressure plasma spray technique called plasma spray-thin film (PS-TF) which can produce dense coatings at high deposition rates. The electrolyte material consisted of 3YSZ and 8YSZ consisting of different powder morphologies such as fused and crushed and agglomerated and sintered. In order to ensure sufficient gas tightness, electrolytes thicknesses of 50-90 µm were deposited. The cathode layer was screen-printed and sintered in-situ during the start-up of the electrochemical tests. The cathode material was La0.58Sr0.4Co0.2Fe0.8O3-δ (LSCF). It must be noted that no diffusion barrier layer was deposited between the YSZ electrolyte and the LSCF cathode which will affect the performance and stability of the cells. The electrochemical tests were performed in a temperature range of 600-800°C at atmospheric pressure under various gas compositions of H2, H2O and N2 on the anode side and of O2 and N2 on the cathode side while keeping the total gas flow constant. Current-voltage characteristics and impedance spectra were measured.

Porous anodes and dense electrolytes were achieved in all cases. The measured open cell voltage indicated acceptable electrolyte gas tightness. Power density of produced cells at an operating voltage of 0.7 V were measured as high as 600 mW/cm2. In this work, the impact of spray parameters and applied layer thicknesses on the gas tightness of the electrolyte and the area specific resistance of the cell will be discussed.

Keywords: plasma spraying, solid oxide fuel cells, electrochemical characterization, impedance spectroscopy
Characterization of Cracks and their Effects on the Effective Transport Pathways in Ni-YSZ Anodes after Reoxidation Using X-Ray Nanotomography
Authors: Nakajo Arata , Kiss Andrew M. , Cocco Alex P. , Harris William M. , DeGostin M. B. , Greco Fabio , Nelson George J. , Peracchio Aldo A. , Cassenti Brice N. , Deriy Alex , Wang Steve , Chen-Wiegart Yuchen , Wang Jun , Van herle Jan , Chiu Wilson K. S.
Published: February 2020

Reduction-oxidation (redox) cycling of Ni-based electrodes for solid oxide fuel/electrolysis cell irreversibly alters their microstructure and can cause the fracture of the electrolyte. Non-destructive 3-D imaging techniques enable tracking the microstructural changes that occur during the cycling [1]. Despite the recent advances, the understanding of how local 3-D geometrical features in the heterogeneous electrode material contribute to the material degradation remains incomplete.

Absorption contrast X-ray nanotomography (XNT) of a same Ni(O)-yttria-stabilized zirconia (YSZ) sample was performed at the NiO K-edge white-line peak (8348 eV), before and after exposure to air at 800°C during 45 minutes. A complimentary XNT at 8376 eV confirmed a degree of oxidation in the range of 98%. The morphology of the Ni(O) phase was as expected completely different after re-oxidation. The spatial resolution in the range of 20 nm [2] further enabled the detection of cracks in the brittle YSZ phase. 3-D local curvature measurements were first performed to identify and characterize the crack initiation sites. Then, the capabilities of simple fracture mechanics models combined with curvature measurements were tested in the view of rapidly pinpointing the locations vulnerable to redox cycling. Finally, the detrimental effects of the cracks on the effective 3-D transport pathways in the Ni-YSZ anode under polarization was investigated using a skeleton-based discrete representation of the imaged volume and an analytical electrochemical fin model [3]. Topological properties, effective ionic conductivity and polarization resistance were calculated before and after oxidation. For the latter estimate, the effect of cracked YSZ network was considered first alone; that of the spatial re-distribution of triple-phase boundaries induced by re-oxidation will be included in the future.

 [1] A. M. Kiss, W. M. Harris, S. Wang, J. Vila-Comamala, A. Deriy and W. K. S. Chiu, Applied Physics Letters 102 (2013) 053902.

 [2] J. Vila-Comamala, Y. Pan, J. J. Lombardo, W. M. Harris, W. K. S. Chiu, C. David, Y. Wang, J. Synchrotron Rad. 19 (2012), 705–709.

[3] G. J. Nelson, A. Nakajo, B. N. Cassenti, M. B. DeGostin, K. R. Bagshaw, A A. Peracchio, G. Xiao, S. Wang, F. Chen, W. K. S. Chiu, Journal of Power Sources 246 (2014) 322-334.
Electrochemical Oxidation of CO/H2 Mixtures on Ni and Ceria Pattern Anodes
Authors: Tabish A.N. , Patel Hrishikesh C , Comelli Filippo , Aravind P.V.
Published: February 2020

In many proposed applications of SOFC, the syngas, primarily containing CO and H2, will be fed directly to the anode. Therefore, the understanding of electrochemical co-oxidation of CO/H2 fuel is very important for designing fuel cell systems and their long term operation. Pattern electrodes with well-defined geometrical electrode/electrolyte interface have been successfully applied as a tool to study the electrochemical oxidation mechanisms at triple phase boundary (TPB).

So far, Ni/YSZ cermet anodes have mostly been used to study CO/H2 co-oxidation and Ni pattern anodes to study elementary reaction mechanisms of CO and H2. Recently, ceria based anodes are becoming of potential interest because of their ability to suppress carbon deposition on electrodes besides other advantages of ceria over conventional Ni based anodes. Ceria has widely been used for preferential oxidation of CO in automotive industry. However, only limited experimental data is available for electrochemical oxidation CO/H2 mixtures on ceria.

In this study, electrochemical oxidation of dry CO/H2 mixtures on symmetrical Ni and ceria pattern anodes on YSZ electrolyte has been examined between 700-850 oC. Regardless of the mixed ionic and electronic (MIEC) nature of ceria, ceria patterns were prepared for comparison with Ni pattern anodes with the same geometrically defined TPB length. Dry environment was used to exclude the possible side reactions like water gas shift in case of CO and CO/H2 mixtures.

Spectra obtained from electrochemical impedance spectroscopy (EIS) of Ni and ceria anodes for different gas environments at 800 oC are shown in figure. EIS with Ni anodes revealed 2-3 times higher polarization resistance for pure CO as compared to pure H2. The addition of small quantities of H2 in CO decreased the polarization resistance drastically, indicating negligible contribution of CO oxidation for total current production.

With ceria electrodes the polarization resistance was 5-6 times higher in case of CO as compared to pure H2. For all considered CO/H2 mixtures the polarization resistance was closer to that of pure H2 indicating preferential oxidation of H2 which is contrary to the expected role of ceria catalyst for preferential oxidation of CO as observed in case of non-electrochemical oxidation.

Impedance spectra from both Ni and ceria pattern anodes were fitted to the equivalent circuit model [R(RQ)(RQ)]. In all impedance spectra with ceria patterns, a small arc at high frequency was observed as compared to main arc at low frequency. Relaxation frequency of small arc was much higher as compared to the main arc. Activation energies for both Ni and ceria anodes were also similar to that of pure hydrogen for all considered mixtures further indicating preferential oxidation of hydrogen.

Figure 1
Modelling and Prediction of the Deformation during Co-Sintering of a High Temperature Dual Membrane Fuel Cell
Authors: Masson David , Kuoh-Moukouri Joyce , Chesnaud Anthony , Thorel Alain
Published: February 2020

In the frame of a FP7 project (FET-Energy “IDEAL-Cell”, 2008-2011), we have developed with a European consortium a new type of high temperature fuel cell based on a dual membrane with mixed proton and oxygen ions conductivity. This dual conductivity porous membrane, made of a proton conducting phase (BCY15) and of an oxygen conducting phase (YDC15) was sandwiched between a dense BCY15 electrolyte and a dense YDC15 second electrolyte, forming a tri-layer itself sandwiched by a cathode (LSCF48) and an anode (BCY15 + Ni). In this configuration, water is formed neither at the cathode nor at the anode, minimizing electrodes concentration overpotentials, but rather within the dual membrane which interconnected porosity ensures water evacuation. The IDEAL-Cell project i) proved the concept, ii) showed that this new fuel cell was performing better at 750°C than PCFCs and SOFCs having equivalent thickness, iii) showed that the concept was fully reversible with a high dynamic when shifting from the fuel cell regime to the electrolyzer regime, iv) showed that BCY15 was also an excellent oxygen ions conductor when fed with oxygen, and then demonstrated that the cell could be fabricated by using solely BCY15 (replacing YDC15 in the dual membrane and for the oxygen electrolyte), leading to a drastic simplification of the concept, hence of the shaping process.

Today, this simplified cell is fabricated at the laboratory scale by a sequence of successive steps (1/ cold pressing, rolling and sintering of the porous dual membrane at 1350°C, 2/ deposition of both electrolytes by dip coating, and sintering at 1350°C, 3/ deposition of both cathode and anode by bar-coating, and sintering at 1150°C), which is hardly cost effective in view of stacking and further development. The present work proposes to demonstrate that co-sintering of the whole cell in a single step is possible, and to determine under what conditions of geometry, starting materials and sintering cycle a flat and stress-free cell in view of stacking, efficiency and durability can be produced via this simplified process. The research described in this paper was based on the thermomechanical modelling of the multilayer deformation occurring during sintering via a finite element numerical simulation, in which debinding, elastic and irreversible deformations, kinetics of grain growth and pores shrinkage are integrated. The thermomechanical parameters were obtained on a differential CTE measurement set-up, and the microstructural ones by image analysis on SEM images.
3D Multiscale-Multiphysics SOFC Modelling Status at the Institute of Electrochemical Process Engineering, FZ Jülich
Authors: Peksen Murat , Al-Masri Ali , Peters Roland , Blum Ludger , Stolten Detlef
Published: February 2020

The Institute of Electrochemical Process Engineering (IEK-3), SOFC modelling research group has been focusing on the 3D multiphysics modelling of SOFCs [1], auxiliary components [2-4], as well as whole fuel cell systems [5] during the last seven years; thereby giving particular attention to various geometrical scales including, micro, meso and macro level of solid oxide fuel cells [6-9], as well as cell, stack and system level high-end modelling.

                 Currently, emphasis of research has been given to the material, process and 3D design optimisation of APU fuel cell stacks, including the thermomechanical behaviour during the heating-up, operation and shut-down stages for safe SOFC operation. Micro modelling of cells, including the thermomechanical fatigue behaviour has been another research area to understand the cyclic durability of the critical fuel cell stack regions.

 The full scale 3D system level multiphysics modelling of the Forschungszentrum Jülich integrated SOFC system has been successfully continued and important results have been achieved and experimentally validated to improve the knowledge about the overall multiphysics system in full detail. Moreover, the interacting component behaviour of the fuel cell stack, afterburner, heat exchanger, pre-reformer and baffle plates have been intensively investigated to improve their design and thermofluid flow, thermomechanical performance. Coupled CFD/FEM is used to predict their thermofluid flow, heat radiation, electrochemical and chemically reacting species transport, creep, elastoplasticity and cyclic behaviour.

 

M. Peksen, Progress in Energy and Combustion Science, 48, 1-20 (2015)

M. Peksen, L. Blum and D. Stolten, Int. J. Hydrogen Energy,
37, 12540-12547 (2012)

Q. Fang, L. Blum, R.Peters, M. Peksen, P. Batfalsky, D.Stolten, Int. J. Hydrogen Energy
2, 1128-1136 (2015)

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, 6851-6861 (2011)

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38, 4099 (2013).
Effect of Non-Uniform Electrode Microstructure in Gas Diffusion Impedance
Authors: Bertei Antonio , Arcolini Giacomo , Nicolella Cristiano , Piccardo Paolo
Published: February 2020

Gas diffusion resistance represents a significant contribution to anode overpotential in anode-supported solid oxide fuel cells (SOFC). Gas diffusion limitations are often detected through the analysis of impedance spectra. Typically, equivalent circuits are adopted to fit the measured impedance data. However, equivalent circuits do not account for the non-uniform microstructure of SOFC anodes, which commonly consist of a fine functional layer and a thicker and coarser supporting layer.

In this study, the impedance response of gas diffusion phenomena in anodes with non-uniform microstructure is simulated by solving the dusty-gas model in frequency domain. The microstructural parameters are evaluated from the tomographic reconstruction of the two layers, as published in the literature. Simulations indicate that the non-uniform electrode microstructure affects the gas diffusion dynamics, thus producing an additional feature in the Nyquist plot at high frequency. Such an additional feature may be erroneously attributed to other phenomena (e.g., charge transfer processes) when phenomenological equivalent circuits are superimposed to fit the data.

The study shows that the gas diffusion fingerprint in impedance spectra can substantially differ from the expected finite-length Warburg response in electrodes with non-uniform microstructure. The paper highlights the potential misinterpretations that can arise when interpreting impedance spectra with phenomenological models, especially when the coupling between microstructural characteristics and electrode dynamics are not properly taken into account.
Computational Materials Design of Rare-Earth-Based Fast Oxygen Ion Conductors by First-Principles Simulation Based on Density Functional Theory
Authors: Sakaue Mamoru , Kasai Hideaki
Published: February 2020

Development of novel fast ion conductors is a crucial issue for realizing solid oxide fuel cells (SOFCs) which can operate in low temperatures. While yttria-stabilized zirconia (YSZ) had been well-studied both by experiments and theories, exploration of other types of materials retaining high ionic conductivities in lower temperatures is still desired. Experimental studies in the recent twenty years have found some rare-earth-based oxides having higher ionic conductivities to be promising for operation below 600°C [1-4], and first-principles simulation studies on the materials have begun [5-9]. As well as doping, introduction of strain by forming a laminate of nanoscale films was found to be an effective factor for controlling ionic conduction [3,5].

We studied atomic and electronic properties on oxygen-ionic conduction of LaGaO3-, La2GeO5-, Pr2NiO4- and CeO2-based materials by first-principles calculations based on density functional theory (DFT). We analyzed effects of doping and strain on stable structures, electronic densities of states, oxygen migration paths and activation energies in order to evaluate their capabilities in application to electrolytes. We focus on minimum energy paths of oxygen migration based on nudged elastic band analysis in order to figure out ion conduction properties in low temperatures. The obtained simulation results of the activation energies showed good agreements with experiments in several aspects. By analyzing the site dependencies of vacancy formation energies and activation energies, we inferred possible factors of preventing the oxygen ion conduction.

Based on the results, we practiced iterative materials design procedures that we deduced possibly more promising compositions for the oxygen ion conduction, confirmed the properties by simulation, inferred the desirable and undesirable factors, and went back to the deduction of possibly more promising compositions. In the presentation, we will propose the designed materials and predict their electronic, magnetic and ion conduction properties.

[1] T. Ishihara, H. Matsuda and Y. Takita, J. Am. Chem. Sot. 116, 3801 (1994).

[2] M. Yashima, N. Sirikanda and T. Ishihara, J. Am Chem. Soc. 132, 2385 (2010).

[3] J. Hyodo, S. Ida, J. A. Kilner and T. Ishihara, Solid State Ionics 230, 16 (2013).

[4] T. Ishihara, et al., J. Am. Chem. Soc. 123, 203 (2001).

[5] A. Kushima and B. Yildiz, J. Mater. Chem. 20, 4809 (2010).

[6] S. M. Aspera, et al., J. Phys.: Condens. Matter 24, 405504 (2012).

[7] T. P. T. Linh, et al., J. Phys.: Condens. Matter 26, 255503 (2014).

[8] M. Alaydrus, et al., J. Phys. Condens. Matter 25, 225401 (2013).

[9] T. D. K. Wungu, et al., ECS Transactions 57, 2715 (2013).
Evaluating the Behavior of CO/CO2 in Ni/GDC Solid Oxide Fuel Cell Anodes
Authors: Wang Lei , Jackson Gregory S
Published: February 2020

Ni/GDC anodes for solid oxide fuel cells have been reported to be more resistant to carbon deposition than conventional Ni/YSZ anodes. To facilitate understanding the nature of carbon chemistry in Ni/GDC anode functional layers, we have studied the behavior of CO oxidation and CO2 dissociation on thin-film Ni/GDC electrodes.  Sputtered thin-film GDC electrodes with open Ni sputtered overlayers provide an optically accessible and well-characterized electrode in which to study fundamental reactions of CO and CO2 in Ni/GDC systems for both dry and wet environments. To further separate out the behavior of the GDC surface chemistry from the Ni chemistry, Au overlayers were deposited on the thin-film GDC for an alternative electrode with the Au serving as a low-activity current collector. Results indicate that dry CO oxidation and CO2 dissociation are substantially slower than their H2 and H2O analogs on Ni/GDC with fitted exchange current densities for CO/CO2 approximately one order of magnitude lower than H2/H2O under similar partial pressures and temperatures ranging from 600 to 700 deg. C. By replacing the CO2 with H2O, exchange current densities associated with CO oxidation rise dramatically although still lower than H2 oxidation at similar conditions. By using our studies with ambient pressure XPS, we are able to obtain local overpotentials across the Ni/GDC for some test conditions and thereby extract fundamental information about the CO and CO2 chemistry in the Ni/GDC cell.

Although the CO/CO2 reactions are slow, they may play a vital role in the suppression of carbon formation in Ni/GDC cells.  Thus, to better understand this, we fit our experimental data for the thin-film electrodes to a microkinetic model that includes CO/CO2 chemistry on both the Ni and GDC.  By fitting these rates to match the model results to the performance of Ni/GDC and Au/GDC electrodes (and assuming the Au functions as an inert current collector), we have developed kinetic expressions for surface chemistry of CO and CO2 on the GDC surface. Coupling this surface chemistry to previous Ni surface chemistry and to our own developed mechanism for H2 oxidation on Ni/GDC provides a basis for exploring how the Ni and GDC surface chemistry interact with exposure to carbon-rich syngas.  The fitted model for the thin-film Ni/GDC performance suggests that the presence of surface hydrogen and hydroxyls on the Ni can have significant boosts to CO conversion to CO2 on both the GDC and Ni surfaces. These synergies may be critical for providing rapid CO conversion in lower temperature SOFCs which rely on GDC as part of the anode and electrolyte materials.
Enhancing the Stability of Infiltrated Ni/YSZ Anodes
Authors: Keyvanfar Parastoo , Hanifi Amir Reza , Sarkar Partha , Etsell Thomas H. , Birss Viola
Published: February 2020

One of the challenges related to Ni-based anodes in solid oxide fuel cells (SOFCs) is their dimensional instability, especially when they are exposed to air and then back to fuel, which is called redox cycling. One possible solution to this problem is the fabrication of a pre-sintered porous electrolyte matrix, followed by infiltration of 10-20 vol% of the active materials into this scaffold. However, this can lead to instability of the infiltrated particles as a result of sintering of the infiltrated phase at SOFC working temperatures. This problem is very severe when depositing nano-sized infiltrated metal particles on the oxide ceramic backbone.

In this study, Ni-containing solutions were infiltrated into a symmetrical tubular half-cell, fabricated by slip-casting, composed of two porous yttria-stabilized zirconia (YSZ) layers, separated by a 50 μm dense YSZ electrolyte. A combination of electrochemical impedance spectroscopy (EIS) and electron microscopy imaging has been used to determine long term stability of the cells.

It was found that the amount of infiltrated Ni has a significant impact on the long term stability of the Ni/YSZ anodes. This can be explained by the better connectivity between Ni particles even after long term testing when there is more Ni in the structure. It was also demonstrated that high temperature treatment of the infiltrated Ni/YSZ anodes just after the first few infiltrations, followed by several further Ni infiltration steps, has a significant effect not only on the stability of the anode at 800 C, but also on the anode performance. As the YSZ backbone has the ability to dissolve NiO at higher temperatures, the dissolved NiO can be ex-soluted in the form of nano-sized Ni particles at cell working temperatures and under reducing atmospheres. This effect was also investigated using electron microscopy, revealing the size and shape of the ex-soluted Ni particles, especially after long term testing.

Finally, the effect of infiltration of cerium oxide prior to Ni infiltration on the stability of the anodes was also investigated. As the wettability of Ni particles on a reduced ceria surface is different from non-reduced ceria, the sintering behaviour of Ni on these two surfaces was found to be different as well.
Direct Utilization of Methane in Microtubular-SOFC
Authors: Majewski Artur Jacek , Dhir Aman
Published: February 2020

Microtubular-SOFC (μSOFC) offer many advantages over planar SOFC systems.  They offer greater resistance to thermal shock, allow rapid startup and shut down.  They have high volumetric power density and the seals can be placed out of the high temperature zone.  Liquefied natural gas (LNG) is receiving increased interest as a fuel for trucks. This is an ideal fuel for SOFC. In this paper we examine the use of LNG in μSOFC in a truck APU application and the issues associated with LNG fuel. The work mainly focuses on solving issues with temperature distribution along and across the cell. 

The key problem in the proposed system is the temperature distribution (TD).  Despite the good resistance to thermal shock, the long-term operation with unequal TD can cause cell damage.  The TD was measured along the cell (internally and externally) under different operating conditions.  H2, CH4 and simulated LNG (individual gases mixed in the correct ratio of LNG) were used as fuels.  CH4 and simulated LNG were converted into syngas using semi-internal catalytic partial oxidation catalyst (CPOX) located at the entrance of the cell.  Different mixtures of fuel and air and several different catalysts were tested for the CPOX of hydrocarbons.  The figure shows a typical result during OCV using H2 as a fuel at 700oC furnace temperature.  It shows there was a difference of 200oC between the internal and external part of the tube at the fuel inlet, indicating research needs to be conducted into minimising this to ensure the durability of any SOFC APU system.  

Figure 1. Temperature distribution inside the μSOFC single cell.

The results are part of the SAFARI project funded under Europe’s Fuel Cell and Hydrogen Joint Undertaking (FCH JU), Grant Agreement No.325323. The Consortium gratefully acknowledges the support of the FCH JU.

Figure 1
A Novel Micro-Tubular Solid Oxide Fuel Cell with a Porous Zirconia Support for Intermediate-Temperature Operation
Authors: Panthi Dhruba , Choi Bokkyu , Tsutsumi Atsushi
Published: February 2020

To improve current collection efficiency and prevent cell degradation under reduction–oxidation (redox) cycling, we have proposed a novel micro-tubular solid oxide fuel cell (SOFC) with a configuration of inert support/current collector/inner electrode/electrolyte/ outer electrode/current collector. In this work, we applied multi-step dip coating and low-temperature co-sintering methods to fabricate a micro-tubular SOFC based on the proposed design using yttria-stabilized zirconia (YSZ), Ni, Ni-scandia-stabilized zirconia (ScSZ), ScSZ, strontium-doped lanthanum manganite (LSM)–ScSZ, and LSM as the inert support, anode current collector, anode, electrolyte, cathode, and cathode current collector, respectively. The electrochemical performance of the fabricated cell was characterized in an intermediate temperature range, which allows for the use of cheap stack materials and also slows down the performance degradation mechanisms. Our results indicate that the performance of the proposed micro-tubular SOFC can be improved considerably in the intermediate-temperature range using conventional materials when YSZ is substituted with ScSZ as the electrolyte and ion-conducting phase in the electrodes.
Performance Factors and Sulfur Tolerance of Metal Supported Solid Oxide Fuel Cells with Nanostructured Ni:GDC Infiltrated Anodes
Authors: Nielsen Jimmi , Sudireddy Bhaskar Reddy , Hagen Anke , Persson Åsa Helen
Published: February 2020

In recent years, there has been a growing interest in developing metal supported solid oxide fuel cells (MS-SOFCs). MS-SOFCs are interesting as they potentially offer some advantages compared to conventional electrode and electrolyte supported SOFCs, such as low materials cost, better thermal conductivity and ductility of the support. The two later aspects improve the shock resistance and lower internal gradients within the stacks. This enables fast start-up and provides higher tolerance towards operation under transient conditions that are particularly desirable for APU applications.

Today’s commercially available and relevant SOFC fuels such as natural gas and diesel etc.  contain trace amounts of sulfur. Thus, tolerance towards sulfur poisoning is desirable. Ceria and gadolinium doped ceria (GDC) have been reported in the literature to have a beneficial effect on the tolerance towards sulfur poisoning. The ceria can be incorporated as a Ni:GDC cermet anode, but also via infiltration of ceria and doped ceria into the conventional Ni:YSZ cermet anode. Both approaches have been reported to improve the tolerance towards sulfur poisoning [1-3]. In the present study we report the performance and sulfur tolerance of MS-SOFCs with two different microstructures of the support and the anode functional layer (AFL). The MS-SOFCs of the present study are based on ferritic stainless steel (FeCr) with an aimed operating temperature of 650ºC. This lower operating temperature compared to electrode and electrolyte supported SOFC (750ºC-850ºC) is expected to favor sulfur adsorption and hence increase the impact of sulfur poisoning. The AFL was infiltrated with Ni-GDC precursor solution and subsequent heat treated resulting in a nanostructured coating of the electrocatalyst. The two studied MS-SOFC single cells (active area 16 cm2) have initial area specific resistances (ASR) at 650ºC of 0.35 Ωcm2 and 0.7 Ωcm2 respectively. It was found that the porosity of the support and the AFL seems to have a pronounced effect on the resulting performance. The MS-SOFCs were subjected to technologically relevant H2S concentrations of 2, 5 and 10 ppm in hydrogen fuel, during galvanostatic operation at a current load of 0.25 Acm-2. The results are illustrated and compared with the conventional SOFC Ni:YSZ cermet anode in figure 1, where the relative increase in anode polarization resistance as a function of Ni sulfur coverage is shown. The comparison indicate the MS-SOFC anode of the present study to be more tolerant towards sulfur poisoning than the conventional Ni:YSZ cermet anode.   

[1] K. Sasaki et al., J. Electrochem. Soc., 153, A2023–A2029 (2006).

[2] L. Zhang et al., International Journal of Hydrogen Energy, 35, 12359–12368 (2010).

[3] C. Xu, P. Gansor, J. W. Zondlo, K. Sabolsky, and E. M. Sabolsky, J. Electrochem. Soc., 158, B1405–B1416 (2011).

Figure 1
Development, Manufacturing and Deployment of SOFC-Based Products at SOLIDpower
Authors: Bertoldi Massimo , Bucheli Olivier , Ravagni Alberto
Published: February 2020

SOLIDpower provides efficient energy solutions based on its proprietary planar SOFC technology. The first commercial product of the company is the EnGen™-2500. The company deploys the CE certified 2.5 kW combined heat and power generator within the FCH-JU project ene.field and with selected European partners. The EnGen™-2500 uses natural gas for combined heat and power generation (CHP) at high electrical and total efficiencies. The product targets multi-family houses and commercial applications. More than 60 units are to be installed within 2015 and field test results will be presented.

SOLIDpower operates a first “to scale” production cell in Northern Italy with a production capacity of 2MW/yr. Based on an ordering volume of 50 MW, the stack and balance of stack components match target market requirements, allowing selling and operating systems at grid parity prices.

Besides the micro-CHP generator deployment, SOFCpower also pursues strategic development activities to demonstrate biogas and waste-to-energy (WTE) applications on larger than 2.5 kW scale.

SOLIDpower progressed on the technological level for SO Electrolysis. Improved electrode materials and production technology open the door for lifetime for electrolysers stacks beyond 16’000 hrs. SOLIDpower expects that SOFC stack cost reductions stemming from SOFC volume manufacturing can be transferred to a large extend also to SOE stacks. In this field, SOLIDpower intends to work with integration partners on the systems level.

The paper provides an update of the stack and system development, including operational results of SOFC-based micro-CHP.

SOLIDpower comprises the companies SOLIDpower SpA Italy, SOLIDpower SA Switzerland and SOLIDpower GmbH Germany and unites under its new name the companies formerly known as “SOFCpower SpA” and “HTceramix SA”.
Dominant Factors Influencing the Electrochemical Performance of Plasma-Sprayed LSGM Electrolyte
Authors: Zhang Shan-Lin , Li Cheng-Xin , Li Chang-Jiu
Published: February 2020

Mg/Sr-doped lanthanum gallate (LSGM) is one of promising electrolyte materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) because of its high ionic conductivity. However, a main challenge in the application of LSGM is how to fabricate dense and thin LSGM electrolytes on electrode substrates at relatively low temperature since it is difficult to sinter LSGM to full density below 1500 °C. In this study, low-cost atmospheric plasma spraying (APS) is used to fabricate the thin and dense LSGM electrolyte. The effects of deposition temperature and particle size on the phase composition, microstructure, and electrochemical performance of LSGM electrolyte were investigated. It was found that the deposited LSGM presents a dense microstructure with well bonded lamellar interfaces with a porosity of ~2.3% when the deposition temperature is >300°C. Besides, the electrochemical performance depends sensitively on the particle size of LSGM powders because Gallium (Ga) may evaporate during plasma spraying. It was revealed that when the particle size is <30 μm, Ga evaporation loss increases rapidly with the decrease of particle size, which dramatically reduces the ionic conductivity of the LSGM deposits. The ionic conductivity of a dense LSGM deposit was only ~4.2% of the bulk conductivity. It was found that using LSGM powders with particle sizes >30 μm, plasma-sprayed LSGM reaches an ionic conductivity of ~0.075 S cm-1 at 800 °C, ~78% of the bulk value. Test cells based on the plasma-sprayed LSGM electrolyte show excellent performance. At 800°C, a maximum output power density of over 700W/cm2 was obtained with a APS ~60um thick LSGM under test condition of H
2
/Air, indicating that atmospheric plasma spraying is a promising approach for large-scale manufacturing of high-performance IT-SOFCs.
Synthesis of Pure La10-XSrxSi6O27-0.5x Apatites Using an Optimized Sol-Gel Process
Authors: Ma Yangzhou , Fenineche Nouredine , Moliere Michel , El-Kedim Omar , Briois Pascal
Published: February 2020

Apatite-type lanthanum silicates draw researcher’s attention due to their good performances as electrolyte materials for IT-SOFC (intermediate temperature solid oxide fuel cells) [1-5]. In this paper we present the synthesis and characterisation of Sr-doped La10Si6O27 prepared through an optimized, water-based sol-gel [6] process. The parameters involved in this process have been investigated to obtain high purity, high crystallinity powders. The mechanisms of the sol-gel reactions that underlie the quality of the sol are discussed. The optimized sol gel process enables obtaining pure apatite structures through a calcination step for 2 hours at a temperature as low as 800℃. They were characterized by scanning electron microscopy, X-ray diffraction and Energy-dispersive X-ray spectroscopy. Ionic conductivities have been measured after sintering at 1500℃ in order to investigate the effect of the Sr-doping. 

The electrical properties were measured as a function of temperature by complex impedance spectroscopy, using a Solartron 1260A frequency response analyzer (FRA) in the frequency range 5 Hz - 15 MHz, under static air. The measurements were performed at the open circuit voltage as well as with an applied AC voltage of 100 mV. The impedance diagrams were recorded from 673 K to 1273 K with thermal steps and stabilization times of about 25 K and 20 minutes respectively. The results show that the ionic conductivity is thermally activated and its value lies between 3×10-5 and 1×10-6 S.cm-1 at 873 K as function of the composition and powder preparation conditions.

Keywords: Sol-gel processes; SOFC; apatite type lanthanum silicates; Sr doping

References:

1. S. Nakayama, et al, Journal of Materials Chemistry 5 (1995) 1801-1805.

2. Claire Bonhomme, et al, Solid State Ionics 180 (2009) 1593–1598

3. Jun Xiang, et al, Electrochimica Acta 153 (2015) 287–294

4. R. Serra, et al, Journal of Alloys and Compounds 536S (2012) S480–S484

5. Janne Patakangas, et al, Journal of Power Sources 263 (2014) 315-331

6. Chieko Yamagata, et al, Materials Research Bulletin 48 (2013) 2227–2231