bluuebunny/crossref_metadata_2025_split huggingface dataset:
Estimation of 3D Effective Properties from 2D Cross Sections in Porous Electrodes
Authors: Ferrari Tommaso , Bertei Antonio , Nicolella Cristiano 
Published: February 2020

Nowadays tomographic techniques are used to reconstruct the 3D microstructure of Solid Oxide Fuel Cell (SOFC) electrodes from a sequence of 2D cross sections and to evaluate the effective properties of real samples. However, this approach involves expensive instrumentation and time-consuming procedures. Thus, there is the need of short-cut methods to infer 3D properties from a single 2D cross section for a rapid characterization of the electrode properties.
In this study, the correlation between 2D and 3D properties is studied through the numerical reconstruction of the electrode microstructure by using packing algorithms. 3D effective geometrical properties, such as the mean particle diameter, the pore size, the specific surface area and the three-phase boundary length per unit volume are calculated and correlated to 2D properties evaluated in a cross section, such as the mean diameter of the sectioned particles, the mean chord length, the particle perimeter exposed to the porous phase and the number of three-phase boundary points per unit area, respectively. A strong correlation is found between 2D and 3D properties in a wide range of porosity, particle size and electrode composition. A statistical analysis on the accuracy of the estimated properties as a function of the size of the cross section is also reported.
The results of this study provide practical indications that can be easily applied to Scanning Electron Microscope (SEM) images of real samples for a rapid estimation of the effective properties of the electrodes.
High Fuel Utilization Operation of Solid Oxide Fuel Cells - a Modeling Study
Authors: Monder Dayadeep S. , Pawar Vishal , Kumar Sanjay , Shekhar Rustam Singh 
Published: February 2020

High fuel utilization (Uf
) is desirable in fuel cells as it has a direct impact on efficiency – the higher the Uf

the higher the fuel cell efficiency. However, the Ni phase in Ni based SOFC anodes is susceptible to oxidation to NiO when the fuel cell is operated at high fuel utilizations. This phase transition is problematic because a) NiO is inactive to the fuel oxidation reactions, and b) the larger specific volume of NiO results in damage to the anode microstructure if this Ni to NiO transition is reversed and repeated a few times. The second problem listed above is known as Ni redox cycling. Thus, there are conflicting objectives where the designer/operator of a SOFC system desires a high fuel utilization Uf

while avoiding Ni oxidation.
Ideally, one would like to identify a safe operating zone where the fuel utilization Uf

can be maintained in a high enough range without risking Ni oxidation. In this presentation we will use simulation results from a detailed multiphysics model to outline some of the challenges of operating a SOFC at high fuel utilization and attempt to identify the above mentioned “safe operating zone”.
The multiphysics model used in this work is for a planar anode supported geometry and includes a fully coupled description of the flow and mass transfer in the air/fuel channels and the electrodes, and the current/potential distribution in the electrodes. One of the mechanisms for Ni oxidation is through reaction (1).
Ni + H2O ↔ NiO + H2 (1)
The favourability of reaction (1) at a particular location in the anode is dictated by the thermodynamics of the reaction and the local fuel composition. As the model is able to predict the fuel side composition as a function of position, the output of the model can be used to predict whether there is a risk of Ni oxidation in the anode at any given set of operating conditions.
We will present results from a parametric study over a wide range of different temperatures, cell voltage, as well as inlet fuel flow-rates and composition. An example set of results is given in Fig 1 where the inlet flow-rate is varied for a given cell voltage and temperature. The Ni oxidation reaction is thermodynamically favourable in the latter section of the anode where the partial pressure ratio PH2O/PH2 exceeds the threshold value given by the thermodynamics of the reaction and shown as a dot-dash line in the bottom plot. According to Fig 1, the threshold Uf

for these conditions is ~99%. This is a much higher value than the typical 80-85% used in most SOFC designs. Another noteworthy point is that at this high fuel utlization, the last 1/3 of the cell is producing a very small fraction of the total current.

Figure 1
A Thermo Fluid and Thermo Mechanical Modelling of a Microtubular Solid Oxide Fuel Cell Stack for Unmanned Aerial Vehicles
Authors: Hari Bostjan , Dhir Aman , Steinberger-Wilckens Robert 
Published: February 2020

This work presents a three-dimensional thermo fluid and thermo mechanical computational analysis of a microtubular solid oxide fuel cell (SOFC) stack as part of a microtubular SOFC generator. The latter powers a lithium-ion battery as a microtubular SOFC hybrid power system to extend the flight endurance of a mini unmanned aerial vehicle.
The microtubular SOFC stack and balance of plant components, comprising microtubular SOFC generator, were designed based on computational fluid dynamics (CFD) assumptions. The stack design process has been further upgraded with thermo mechanical finite element analysis (FEA) simulation to capture deformations and stresses in the stack due to thermal expansion of microtubular SOFCs and manifolds.
The developed microtubular SOFC stack will be built based on CFD and FEA predictions and tested to determine the suitability of the microtubular SOFC hybrid power system for this application.
Reversible Fuel Cells with Tri-Layer Electrolytes
Authors: Virkar Anil V. 
Published: February 2020

Reversible solid oxide fuel cells (SOFC) are operated as solid oxide fuel cells and as solid oxide electrolyzer cells (SOEC). In SOFC mode, hydrogen is consumed at the fuel electrode to convert chemical energy of fuel oxidation into water vapor. In SOEC mode, water vapor is decomposed at the fuel electrode to generate hydrogen under an applied DC voltage. Much of the reported work on reversible solid oxide cells is based on yttria-stabilized zirconia (YSZ) electrolyte, Ni + YSZ fuel electrode, and a perovskite-based oxygen electrode. At high operating voltages in the SOEC mode, cell degradation can occur which involves oxygen electrode delamination, formation of cracks within the electrolyte, and also reduction of the electrode near the fuel electrode. The higher the applied voltage, the greater is the propensity to degradation. These observations are consistent with the chemical potential of oxygen in the electrolyte exceeding both electrode bounds under an applied voltage. It has been shown that a small amount of electronic conductivity can minimize degradation. The principal role of electronic conductivity is to smoothen out the variation in oxygen chemical potential through the electrolyte such that it does not exceed electrode bounds. YSZ-based electrolyte if doped with sufficient amount of CeO2 can create significant electronic conductivity such that the electrolyte becomes a mixed ionic electronic conductor. Doping with ceria also lowers the ionic transference number of the electrolyte. A possible bi-layer electrolyte consists of a thin layer of YSZ (or another purely oxygen ion conductor) deposited on a mixed ionic electronic conducting material. As long as electronic conduction through the blocking layer is negligible, the overall ionic transference number of the bi-layer electrolyte can approach unity. In this paper, theoretical analysis of the bi-layer electrolyte for reversible cells is presented. Two configurations of the bi-layer electrolyte are investigated. (1) The electron blocking layer adjacent to the oxygen electrode. (2) The electron blocking layer adjacent to the fuel electrode. For both configurations, the spatial distribution of oxygen chemical potential through the bi-layer electrolyte in both the SOFC and the SOEC modes are evaluated. The ionic transference number of the MIEC part of the bi-layer electrolyte is varied over a wide range. Theoretical analysis shows that such bi-layer electrolyte cells should exhibit good performance characterstics and excellent stability. The net variation of the oxygen chemical potential through the bi-layer electrolyte is determined as a function of transport properties of both layers, electrode polarizations and interfacial resistances to electron transfer.
Effect of Bismuth Oxide as Sintering Aid for Gadolinia-doped Ceria at 1050°C
Authors: De Marco Vincenzo , Sglavo Vincenzo Maria 
Published: February 2020

Dense GDC electrolytes can work as high ion-conducting material for innovative IT-SOFCs. These electrolytes will be used as a base to develop sulfur resistant anodes using copper oxide and GDC, in order to avoid the use of nickel oxide. An aqueous tape casting process to produce dense gadolinia-doped ceria (GDC) electrolyte was developed. The study developed in three main steps. First, the dispersant concentration was idealized for slurries consisting of only distilled water, an ammonium polyacrylate (PAA) dispersant and ceramic powder (commercial Ce0.9Gd0.1O1.95). By examining the rheological behavior of the slurry, the ideal ratio between the active part of dispersant and powder surface was found to be between 0.15 and 0.30 mg/m2 . Second, starting with the dispersed slurry, fixed amounts of acrylic binder and plasticizer were added and the pH was varied in order to identify the optimum pH interval in which the suspension is stable and no agglomerates form. The ideal pH was found to be between 8 and 9. Finally, the amounts of binder and plasticizer were varied and the suspensions were tape casted (thickness 200 µm) to produce a defect free, smooth and high relative green density (about 50%) tape. SEM observations of samples sintered at 1500 °C showed satisfactory dense section profile (about 95%).

Figure 1
Oxygen Ion Adsorption Studies on La10Si6O27 (001) Surface with DFT Calculation for SOFC Electrolyte
Authors: Ma Yangzhou , Fenineche Nouredine , El-Kedim Omar 
Published: February 2020

The apatite-type material La10-xSi6O27-1.5x (LSO) has promising future as electrolyte in SOFC for its high ionic conductivity [1-3]. In this work, ab-initio calculation based on density functional theory (DFT) [4] has been used to investigate the oxygen ion adsorption mechanisms and energy at different sites on the LSO (001) surface. The oxygen ion migration channel can be predicted using the results of adsorption energies on various sites. The most stable adsorption is shown at the hollow between La and O (located away from O-Si Tetrahedron), thus it should be a candidate channel of oxygen ion migration. Furthermore, the electronic properties, including the Fermi energy level, bond strength and length, have been changed with the ion adsorption, and the electrons transition features were obtained by density of states analysis. The calculated results also imply that LSO could be employed as possible electrolyte material due to its low formation and migration energies for the oxygen ion.

Keywords: Apatite electrolyte, Ab initio calculations, DFT, SOFC, ion adsorption.

Reference:

1. H. Yoshioka, Y. Nojiri, S. Tanase, Solid State Ionics 179 (2008) 2165-2169
2. Guangchao Yin, et al, Journal of Alloys and Compounds 586 (2014) 279–284
3. Susumu Nakayama, et al, Ceramics International 40 (2014) 1221–1224
4. T.Q. Nguyen et al. Applied Surface Science, 288 (2014) 244–250

Figure 1
Performance Enhancement of LSM Cathode of SOFCs through Sequential Infiltration of Ag and Ceria
Authors: Babaei Alireza 
Published: February 2020

In this study, the effect of sequential infiltration and catalyst loading of metallic and ceramic catalysts on the performance and stability of La0.8Sr0.2MnO3 (LSM) cathode of solid oxide fuel cell was investigated. Small loading of catalytic silver nanoparticles along with ceria catalytic nanoparticles were sequentially infiltrated into the porous structure of LSM cathode and the electrochemical performance of the cells was evaluated at intermediate temperature range of 600-800°C. Cathode performance was investigated by electrochemical impedance spectroscopy (EIS) and Chrono potentiometery technique at dc bias of 200 mA/cm2 on cathode half cells. The results indicate that electrochemical performance of dually infiltrated cathode is significantly improved compared with those of LSM cathodes separately infiltrated with Ag and ceria. The results show that while individual infiltration of Ag and Ceria decreased the electrode polarization resistance of the cell by %56 and %79, respectively, dual infiltration of Ag and Ceria with equal total loading of catalyst decreased the polarization resistance of the electrode by %98 at open circuit potential and 700°C. Scanning electron microscopy (SEM) studies showed the random distribution of discrete nano catalysts in the vicinity of cathode/electrolyte interface which proves effectiveness of the infiltration technique for performance enhancement of cathode electrodes. Long term stability of cathode was also investigated and a stable performance was observed for dually infiltrated cathode which can be attributed to well distribution of catalyst nanoparticles.
High Temperature Metal / Metal Oxide Battery
Authors: Yildiz Saffet , Loll Isabelle , Vinke Izaak C. , de Haart L.G.J. , Eichel Rüdiger-Albrecht 
Published: February 2020

In future there will be a strong demand for large capacity rechargeable batteries to store electrical energy (e.g. from renewable power sources) in long-term stationary applications [1]. A high temperature metal / metal oxide battery can be built up by combining solid oxide fuel cell (SOFC) technology and a metal/metal oxide storage system [2]. Such a type of battery promises charging and discharging capacities of more than 250 W/cm2 [3]. Requirements for a reversible working solid oxide cell (SOC) are a high performance, minimum internal resistance of the cell, and long-term stability at operating conditions. In the present work the performance of solid oxide cells (SOC) operating in fuel cell and steam electrolysis mode over a temperature range of 650-900 °C and as a function of humidity were studied. Results presented were obtained from single SOCs, with an active area of 16 cm2 and button cells with an active area of 0.5 cm2. The SOCs investigated were anode substrate cells (ASC), with nickel-YSZ-cermet steam/hydrogen electrodes, yttria-stabilized zirconia (YSZ) electrolytes, and lanthanum strontium iron cobalt perovskite (LSCF) air electrodes. Current-voltage measurements were coupled with electrochemical impedance spectroscopy (EIS), in order to identify the different loss terms in cell behaviour during the fuel cell and electrolysis mode. EIS measurements are conducted under practical load conditions in SOCs in both modes. The cells show stable current-voltage curves during cycling between fuel cell and electrolysis mode at short cycling times between 2.5 h and 5 h. Measurements at different humidity show that high electrical-to-hydrogen energy conversion efficiencies are achieved and the amount of steam content is the limiting factor for the electrolysis mode. During electrolysis mode remarkable high current densities around -1.3 A/cm2 were achieved at a cell voltage of 1.3 V and a temperature of 800 °C. Below 50 % steam content, however, a strong efficiency loss was observed. It is also well known that the degradation of the SOC during steam electrolysis is still a limiting factor for the long term application [4]. Hence the focus of interest was also the degradation of the air electrode. Increasing the current density and elongating the duration of electrolysis experiments resulted frequently in a very fast delamination of the LSCF electrode.
Solid Oxide Cell and Stack Testing, Safety and Quality Assurance (SOCTESQA)
Authors: Auer Corinna , Lang Michael , Couturier Karine , Nielsen Eva Ravn , McPhail Stephen J. , Tsotridis Georgios , Fu Qingxi , Chan Siew Hwa 
Published: February 2020

The market penetration of fuel and electrolysis cell energy systems in Europe requires the development of reliable assessment, testing and prediction of performance and durability of solid oxide cells and stacks (SOC). To advance in this field the EU-project “SOCTESQA” was launched in May 2014. Partners from different countries in Europe and one external party from Singapore are working together to develop uniform and industry wide test procedures and protocols for SOC cell/stack assembly. In this project new application fields which are based on the operation of the SOC cell/stack assembly in the fuel cell (SOFC), in the electrolysis (SOEC) and in the reversible SOFC/SOEC mode are addressed. This covers the wide field of power generation systems, e.g. stationary SOFC µ-CHP, mobile SOFC APU and SOFC/SOEC power-to-gas systems. The paper presents the results which have been achieved so far in the SOCTESQA project. Besides a summary of existing test procedures a so called “test matrix” was created. This document includes generic test modules, e.g. current-voltage curves, electrochemical impedance spectroscopy, thermal cycling, electrical current cycling and long term tests both under steady state and dynamic operating conditions. The application specific test programs are created by combining several of these test modules. In a next step defined test modules will be applied for the initial test bench validation, which will be improved by several validation loops. The final test protocols will be confirmed by round robin tests.
Improved Performance and Durability of Anode Supported SOFC Operating on Biogas
Authors: Troskialina Lina , Dhir Aman , Steinberger-Wilckens Robert 
Published: February 2020

Performance curves for both Sn-doped Ni-YSZ and un-doped Ni-YSZ single cells are presented in Fig.1. The cell tests were carried out at 750oC under dry hydrogen flowing at 7mL/min Helium and 21mL/min H2 followed by biogas flowing at 7mL/min CO2: 14mL/min CH4: 7 mL/min He with the cathode side open to ambient air. The cells were allowed to reduce under H2 for a minimum of 3hrs in OCV mode before any initial data was obtained. Operation on hydrogen was run for 26 hours to stabilize cell performance before the fuel was switched to biogas. After stabilization on hydrogen the Sn-doped Ni-YSZ gave 390mA/cm2 at 0.7V compared to the un-doped Ni-YSZ cell which gave 100mA/cm2 at 0.7V.
Mechanism and Activity of Ni-Based (Ni-M: M = Fe, Mo, W, Ta) Cermet Anodes for Ammonia Oxidation in SOFCs
Authors: Hashinokuchi Michihiro , Yokochi Ryuji , Akimoto Wataru , Doi Takayuki , Inaba Minoru , Kugai Junichiro 
Published: February 2020

Ammonia (NH3) is attractive as a hydrogen (H2) carrier and a suitable fuel for solid oxide fuel cells (SOFCs) because it has high hydrogen density (17.6 %) and can be easily liquefied at an ambient temperature. However, the activity of conventional Ni cermet anodes of SOFCs for NH3 oxidation is much lower than that when H2 is used as a fuel [1]. It is necessarily to improve the anode activity for NH3 oxidation for realizing NH3-fueled SOFCs.
We have investigated the activity of anodes prepared with transition metals nickel(Ni), iron (Fe) and their alloy for NH3-SOFCs[2,3]. The Fe/Sm-doped ceria (SDC) cermet anode was more active for NH3 oxidation than Ni/SDC. We also found that the activity of the Ni40-Fe60//SDC for NH3 oxidation was highest by optimizing the metal composition. These results suggested that the rate limiting steps in a direct NH3 oxidation (or reforming NH3) at the anode were (i) NH3 adsorption and (ii) N2 desorption. We concluded that Fe and Ni atoms had the roles of accelerating reactions (i) and (ii), respectively, and the synergetic effect of Fe and Ni resulted in the enhancement of the anode activity for NH3oxidation.
On the basis of the mechanism of NH3 oxidation at the anode, we prepared the anode of Ni and Molybdenum (Mo) since Mo has the high ability of NH3 adsorption, and evaluated their performance for NH3-SOFCs. The Ni-Mo/SDC anodes were fabricated by impregnating a MoCl5 aqueous solution into a Ni/SDC pre-sintered cermet on an electrolyte. It was revealed that the optimum addiction of Mo enhanced the anode activity for NH3 oxidation. Our experimental results suggested that the anode activity for NH3 oxidation was determined by a balance between abilities of NH3 adsorption and N2desorption.

Acknowledge

This work was supported by “Kyoto Environmental Nanotechnology Cluster” and “Kyoto Regional Scientific Innovation Hub” from MEXT in Japan.

Reference

[1] Q. Ma et al., J. Power Sources 161 (2006) 95.
[2] W. Akimoto et al., Solid State Ionics 256 (2013) 1.
[3] W. Akimoto et al., ECS Transactions 57 (2013) 1639.
Understanding the Aging Degradation of Doped Barium Cerate Proton Conductor in Ambient Air at Room Temperature
Authors: Yan Ning , Gao Tong , Wang Wei , Luo Jing-Li 
Published: February 2020

As a promising alternative power generation technology, solid oxide fuel cells (SOFC) have been intensively studied during the past several decades [1]. Among all the solid electrolyte candidates, proton conducting materials, e.g., BaCeO3, exhibit relatively high ionic conductivity at intermediate temperature (< 750 oC). Particularly, Zr and Y doped cerate, e.g., BaZr0.1Ce0.7Y0.2O3 (BZCY) was widely reported to have excellent conductivity as well as adequate stability in resisting concentrated CO2 up to 30 % with moisture at elevated temperatures typical for SOFC operation [2,3].
Herein, via using a combinations of various electrochemical measurements together with materials characterization techniques including XRD, TEM, SEM, XPS, TG-MS and FTIR, we firstly report that BZCY was prone to a gradual degradation in ambient air at room temperature with considerably minor CO2 (~0.04%) and humidity (<45% relative humidity). The adsorbed H2O acted as an effective catalyst that promoted the decomposition of BZCY via reaction with CO2, subsequently leading to the formation of BaCO3 nanorods as the major impurity phase, presumably following a microcrucible mechanism. Yttrium (oxy)carbonate and amorphous CeO2 and ZrO2 were also produced. It is also confirmed that the doping elements of Ce and Y caused the degradation of BZCY. During the fuel cells tests, the formed impurities on BZCY significantly hindered the electrocatalytic reactions at the electrolyte/electrode interfaces. We also proposed the regeneration and appropriate storage method of the electrolyte materials.
Figure 1. TEM microscopic analysis of: (left) HAADF-STEM image of degraded BZCY with amorphous mixed oxides microcrucible and BaCO3 nanorods: (right) elemental mapping of Ba, Ce, Zr and Y.
[1] X. W. Zhou, N. Yan, K. T. Chuang, J. L. Luo, RSC Adv., 4(2014), 118.
[2] N. Yan, X. Z. Fu, K. T. Chuang, J. L. Luo, J. Power Sources, 254(2014),48.
[3] L Yang, et. al., Science 326 (2009), 126.

Figure 1