bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hodrogen Oxidation Reaction Mechanisms in Mixed Ionic and Electronic Conducting Oxide Anode for Solid Oxide Fuel Cells
Authors: Li Wenyuan , Liu Xingbo 
Published: February 2020

Ceramics anode offers certain advantages in terms of impurity tolerance and other properties, as compared to conventional Ni/YSZ anode for solid oxide fuel cells (SOFC). However, ceramic anodes typically have much lower electrochemical performance, and there is very few studies on the hydrogen oxidation reaction (HOR) mechanisms and kinetics in ceramic anodes. In this research, using Doped YCrO3 as baseline material, we systematically investigated the HOR mechanisms in mixed ionic and electronic conducting (MIEC) ceramic anodes, with the focus on the effect of electronic conductivity, electro-catalytic activity, triple-phase-boundary (3PB), and electrolyte, on the HOR kinetics.
It is found that both electrical conductivity and electrode performance of yttrium chromites have been enhanced after Co and Ni doping. Electrochemical impedance spectroscopy (EIS) results indicate that charge transfer process at high frequency and surface adsorption/diffusion processes at low frequency domain can be the dominant anode reaction steps. Ni doping accelerates the surface processes by reducing the related activation energy from 1.2 to 0.5 eV. It also substantially improves the charge transfer process probably by increasing the amount of adsorbed H on electrode surface. The resistance of high frequency is found to be dependent on H2 content. The observed reaction order is 1/4 for Co doped and 1/3 ~ 1/2 for Ni doped yttrium chromites. A model of H2
oxidation reaction is proposed, revealing this dependence stems from the reaction between adsorbed H and the lattice oxygen.
The influence of electrolyte to electrode performance was investigated by replacing YSZ electrolyte with scandium stabilized zirconium (SSZ). Smaller polarization resistances are observed on each electrode in both wet H2 and air atmospheres. Replacement of electrolyte can alter not only the rate of charge transfer process but also in some cases other surface processes not related to the electrolyte directly. It is proposed that the impact of the electrolyte on each electrode process is passed down as in a chain and the charge transfer step functions as the first ring in the chain.
Oxygen Activation and Dissociation on Transition Metal-Free Perovskite Surfaces. Isights on the Surface Reactivity of SrTiO3
Authors: Staykov Aleksandar , Akbay Taner , Druce John , Téllez Helena , Ishihara Tatsumi , Kilner John A. 
Published: February 2020

Density functional theory and low energy ion scattering spectroscopy were applied to study the mechanism of oxygen dissociation on the SrO-terminated surfaces of strontium titanate (SrTiO3) and iron-doped strontium titanate (SrTi1–x
FexO3−δ). Our study reveals that while O2 dissociation is not favored on the SrO-terminated perovskite surface, oxygen vacancies can act as active sites and catalyze the O–O bond cleavage. Electron transfer from lattice oxygen atoms to the O2 molecule, mediated by the subsurface transition metal cations, plays an important role in the resulting formation of surface superoxo species. The O2 molecule dissociates to produce oxygen ions, which are incorporated into the perovskite lattice, and highly active oxygen radicals on the perovskite surface, which further recombine to O2 molecules. Our focus on the SrO-terminated surface, rather than the TiO2 layer, which is presumed to be more catalytically active, was driven by experimental observation using low energy ion scattering spectroscopy, which reveals that the surface of SrTiO3 after high temperature heat treatment is SrO-terminated, and hence this is the surface that is technologically relevant for devices such as solid oxide fuel cells (SOFCs). Our study demonstrates that although the more active BO2-perovskite layer is not exposed at the gas–solid interface, the SrO-terminated surfaces also actively participate in oxygen exchange reaction. Further calculations were performed using the non-equilibrium Green's function method combined with density functional theory (NEGF-DFT) to study the ballistic electron transport through a few layers of iron-doped strontium titanate. This computational method can provide critical information for the surface reactivity and surface active sites which is comparable with the STM experiments. Our study shows that the electron transport is enhanced if oxygen vacancies are present in the surface layed and the electron transport is significantly suppressed by overlayers of SrO. We believe that this study provides useful information for the control over the surface activity of SrTiO3 and explains the mechanisms of the material degradation with SrO surface segregation. Finally, we investigate the properties of the SrTiO3 / SrO interface to elucidate the mechanism of oxygen ion transport between the perovskite and the oxide phase.

Figure 1
Chemical and Electrochemical Stability on Perovskite Oxides As a Function of Surface Reducibility
Authors: Lu Qiyang , Tsvetkov Nikolai , Sun Lixin , Crumlin Ethan J , Yildiz Bilge 
Published: February 2020

Segregation and phase separation of aliovalent dopants on perovskite oxide (ABO3) surfaces is detrimental to the performance of energy conversion systems such as solid oxide fuel/electrolysis cells and catalysts for thermochemical H2O and CO2 splitting. One key reason behind the instability of perovskite oxide surfaces is the electrostatic attraction of the negatively charged A-site dopants by the positively charged oxygen vacancies enriched at the surface. Here we show that decreasing the surface reducibility (oxygen vacancy concentration) improves the oxygen surface exchange kinetics and stability significantly. This appears contrary to the well-established understanding that surface oxygen vacancies facilitate reactions with O2 molecules. We take La0.8Sr0.2CoO3 (LSC) as a model perovskite oxide, and modify its surface with additive cations that are more and less reducible than Co on the B-site of LSC. By using ambient pressure X-ray absorption and photoelectron spectroscopy, we proved that the dominant role of the less reducible cations is to suppress the enrichment and phase separation of Sr while making the LSC more oxidized at its surface. Consequently, we found that these less reducible cations significantly improve stability, with up to 30x acceleration of the oxygen exchange kinetics, after 54 hours in air at 550 oC achieved by Hf addition onto LSC. Finally, the results revealed a “volcano” relation between the oxygen exchange kinetics and the oxygen vacancy formation enthalpy of the binary oxides of the additive cations. This volcano relation highlights the existence of an optimum surface oxygen vacancy concentration that balances the gain in oxygen exchange kinetics and the chemical stability loss.
(La,Sr)(Cr,Ni)O3/CeO2-Based Composite Anode with Various Ni Content and Mixing Ratio for SOFC
Authors: Fukunaga Hiroshi , Saito Makoto , Takei Yuta , Shimada Iori , Osada Mitsumasa , Takahashi Nobuhide 
Published: February 2020

Introduction
Fuel cells are being developed as one of the power sources in the near future. Among them, solid oxide fuel cell (SOFC) is known for its high efficiency due to its high operating temperature. On the other hand, because of the high temperature, problems such as sintering, material compatibility, and mismatch of thermal expansion occurs. Generally, a so-called cerment is used for the anode material, which is a composite of metals and ceramics. Ni-YSZ (Yttria Stabilized Zirconia) is the most common cermet, but metal particles such as Ni would show degradation due to the sintering of the particles and/or due to expansion and contraction by thermal or redox cycling. As an alternative to Ni-YSZ anode, perovskite-type oxide has been attracting attention. Some perovskite type oxide show deposition of metal particles on the surface of the oxides in a reducing atmosphere, which is expected to increase catalytic activity. The deposited metal particles would dissolved in the structure in an oxidizing atmosphere. We have reported this repeating deposition and dissolution would recover the degradation using Pd doped lanthanum-chromite based perovskite type oxide. In this study, LSCN with different Ni composition ratio (La,Sr)(Cr,Ni)O3 were prepared, and their performance was compared. The performance of anode with different ratio of LSCN and doped ceria was also investigated.
Experimental
LSCN was prepared by citrate process. Crystal structure of the sample was determined using X-ray diffraction. Mixture of LSCN and GDC was used as the anode. Sm0.5Sr0.5CoO3 was used for the cathode. Electrochemical performance was investigated by measuring current-voltage characteristic at 900 ˚C. Terminal voltage change over time was measured during power generation at constant current for 16 h, followed by oxidation treatment, and another 16 h of power generation.
Results
Fig. 1 shows current density vs. time during power generation at constant current using anode with different mixing ratio of La0.85Sr0.15Cr1-x
Ni
x
O3 (LSCNX , X = 100x). LSCN with higher Ni composition showed higher power generation performance, whereas LSCN with lower Ni composition showed higher resistance to degradation.
The performance of anode with different ratio of LSCN and doped ceria was measured. Anode with mixing ratio of 60 % LSCN and 40 % GDC showed highest performance and resistance to degradation.
References
1) Y. Nishihata et al, Nature, 418, 164 (2002)
2) H. Fukunaga et al, J. Chem. Eng. Jpn, 40, 1183 (2007)

Figure 1
Processing of Solid Oxide Fuel Cell Anodes for Enhanced Intermediate Temperature Catalytic Activity at High Fuel Utilization
Authors: Gasper Paul Joseph , Lu Yanchen , Basu Soumendra Nath , Pal Uday Bhanu 
Published: February 2020

Despite many years of research on solid oxide fuel cell (SOFC) electrolyte and electrode materials, the conventional anode formulation of nickel and yttria-stabilized zirconia (Ni-YSZ) cermet has not changed much, which highlights the effectiveness of nickel as a catalyst for the fuel oxidation reaction occurring at the triple phase boundaries (TPBs). However, most studies on single cells report results only under fuel rich atmospheric conditions in the anode, which is not representative of how fuel cell stacks are operated. SOFC stacks can easily reach fuel utilizations of 85%. High fuel utilization conditions result in lower hydrogen and higher water vapor partial pressures and an increase in anodic polarization, reducing the electrochemical performance of SOFC anodes. It is postulated that fuel oxidation reaction kinetics can be improved by increasing the TPB length via the deposition of sub-micron sized nickel particles in the cermet anode. This research analyzes the effects of various such nickel infiltration and deposition processes on the performance of anode-supported SOFC over a wide range of hydrogen and water vapor partial pressures at intermediate temperatures (600-800 Celsius). Infiltration and stability or coarsening of sub-micron nickel particles in Ni-YSZ cermets is a well-documented problem. So the impacts of various processing techniques derived from literature and developed internally were examined through long-term or accelerated testing. The cell performance was characterized using I-V and EIS techniques. The cell microstructure was characterized using SEM and image analysis techniques. Out-of-cell measurements on electrodes were also conducted to model its performance. The results were then all combined to identify the role of the sub-micron size nickel particles and the deposition process in enhancing the anode performance at high fuel utilization.
Novel Gradient-Porosity Structure Cathode for Intermediate-Temperature Solid Oxide Fuel Cells
Authors: Li Jin , Jia Lichao 
Published: February 2020

A-site cation ordered double perovskite cathode, especially LnBaCo2O5+δ series, have drawn great interests due to their faster oxygen ion diffusion and higher electrical conductivity[1-3].As a promising SOFC cathode with highest oxygen diffussion coefficient (D*) among the mixed ionic and electronic conductor (MIEC)[4], PrBaCo2O5+
δ exhibits great oxygen reduction reaction(ORR) catalytic activity and electrochemical performance[5] .Here we proposed a gradient-porosity PrBaCo2O5+
δ SOFC cathode. The top-layer of the cathode was highly porous while the sub-layer much denser. Gases’ adsorption plays important roles in ORR process, thus pores’ distribution has great influence on cathode’s performance[6]. Higher porosity means more ORR active regions but less ions paths, and vice versa. There is a trade-off between gases path and ions path. And gradient-porosity cathode aiming at increasing gases adsorption region at gas-contacted surface of cathode about 3-5um depth, at the meantime ensure ions’ fast transfer by enlarge cathode-electrolyte contacted regions. This targeted modification will enhanced cathode’s ORR activity and can be adopted in SOFC’s practical application.
[1] Q. Zhou, T. He, Y. Ji, J. Power Sources, 185,754-758 (2008) .
[2] A. Chang, S.J. Skinner, J.A. Kilner, Solid State Ion, 177,2009-2011 (2006) .
[3] S. Choi, S. Yoo, J. Kim, S. Park, A. Jun, S. Sengodan, J. Kim, J. Shin, H.Y. Jeong, Y. Choi, Sci. Rep, 3 (2013).
[4] A. Tarancón, M. Burriel, J. Santiso, S.J. Skinner, J.A. Kilner, J. Mater. Chem, 20,3799-3813 (2010) .
[5] D. Chen, R. Ran, K. Zhang, J. Wang, Z. Shao, J. Power Sources, 188,96-105 (2009) .
[6] S. Skinner, J. Kilner, Solid State Ion, 135,709-712 (2000) .
Effect of SrZrO3 Formation at Lscf-Cathode/GDC-Interlayer Interfaces on the Electrochemical Properties of Solid Oxide Fuel Cells
Authors: De Vero Jeffrey Centeno , Bagarinao Katherine Develos- , Ishiyama Tomohiro , Kishimoto Haruo , Horita Teruhisa , Yamaji Katsuhiko , Yokokawa Harumi 
Published: February 2020

Formation of oxide scales such as SrZrO3 (SZO) at the gadolinia-doped ceria (GDC)-interlayer/yttria-stabilized zirconia (YSZ) electrolyte interface during fabrication and operation negatively affects the electrochemical properties and long-term stability of La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode/GDC/YSZ based solid oxide fuel cells (SOFCs). In this work, we investigated the effect of SZO formation at LSCF-cathode/GDC-interlayer interfaces on the electrochemical properties of LSCF/GDC/YSZ using scanning electron microscopy and electrochemical impedance spectroscopy. The GDC interlayers were grown on YSZ by pulsed laser deposition and fired using a multi-step heat treatment in air at 1400ºC for 1.5 h followed by 1000ºC for 10 h. The obtained GDC interlayer is dense with minimal cracks and pores avoiding the complexity arising from the porosity of the interlayer and cation diffusion via gas phase. The porous LSCF cathode layer with 12.0 µm-thickness was then screen-printed on top of GDC surface and fired at 1080ºC for 3.5 h in air. Cells consisting of LSCF cathode/GDC interlayer/YSZ electrolyte/Pt electrode was tested under open-circuit voltage and -0.3A cathodic polarization conditions at 800ºC for 300 h in air. It has been found that both cells showed an initial formation of nanosized SrZrO3 (SZO) particles along the LSCF/GDC due to the fast Zr transport in PLD-grown GDC interlayers after the tests. However, the size and distribution of SZO differ between the OCV and cathodically polarized interface. The SZO particles on the LSCF/GDC interface are substantially smaller and are highly distributed across the GDC surface in OCV as compared to cathodically polarized interface characterized by larger localized SZO grains. From this result, we infer that the SZO grains may have impaired the O2 reduction and oxidation reactions at the O2/LSCF/GDC triple-phase boundary (TPB) areas responsible for the observed increase in polarization resistances as a function of time. However, the formation and subsequent growth of larger localized SZO grains on the cathodically polarized LSCF/GDC interface may have led to oxygen permeable TPB areas corresponding to no apparent cell performance degradation. Our results show that the morphology, size, and distribution of SZO along the LSCF/GDC interface influenced the electrocatalytic activity of LSCF cathode affecting electrochemical cell performance.
SrZrO3 Formation in SOFCs : Microstructural Characterization and Cell Performance
Authors: Kanae Shu , Toyofuku Yasuhiro , Kawabata Tsutomu , Inoue Yuko , Matsuda Junko , Chou Jyh-Tyng , Shiratori Yusuke , Taniguchi Shunsuke , Sasaki Kazunari 
Published: February 2020

One of the major phenomena to shorten SOFC durability is the formation of insulated phases, such as SrZrO3, between the cathode and the electrolyte. It is known that SrZrO3 is formed and grown during sintering processes as well as during long-term operation. A systematical study is therefore desired to clarify the SrZrO3 formation mechanisms and their influence on electrochemical properties.
In this study, four parameters are considered and systematically varied: sintering temperatures of cathode, electrolyte, and buffer layer, and buffer layer thickness. The cells tested consist of yttria stabilized zirconia (YSZ) as the electrolyte, Ni-yttria stabilized zirconia (Ni-YSZ) as the anode, La(Sr)Co(Fe)O3（LSCF）as the cathode, and Ce0.9Gd0.1O2 (GDC) as the buffer layer. The GDC layer was sintered at 1300oC with 5μm in thickness, while the YSZ electrolyte was sintered at 1400oC. Cathode sintering temperature and time were varied. The electrochemical performance of the cells was tested under various conditions of testing temperature, current density, and testing time by feeding humidified fuel: H2 (97 cc/min) and H2O (3 cc/min). Microstructure of model cells after sintering and testing was observed in details by FE-SEM (Field Emission Scanning Electron Microscope) and STEM (Scanning Transmission Electron Microscope).
Microstructural observation has been revealed (1) no SrZrO3 formation during sintering LSCF at 1000oC, and (2) a partial formation of SrZrO3 between the cathode and the electrolyte after sintering LSCF at 1100oC. (3) After the sintering of the LSCF cathode at 1200oC, the interface was fully covered by the SrZrO3 layer, clarified by the microstructural observation with EDX elementary mapping. This shows that cathode sintering temperature depends on SrZrO3 formation. Microstructure of model cells after sintering for (a) 0.5h, (b) 1h, (c) 2h, (d) 16h was observed in details by STEM. Figure 1 shows that sintering time of cathode depends on SrZrO3 formation. Figure 1 indicates SrZrO3 formation mechanisms that SrZrO3 was partially formed between the YSZ and the GDC by grain boundary diffusion or surface diffusion along pore walls and covered fully the interface. Such SrZrO3 formation led to a decrease in electrochemical performance (Figure 2). These results indicate the importance of the SrZrO3 formation controlling the SOFC performance.

Figure 1
Effect of the Stabilized Bismuth Oxide Interlayer on Oxygen Reduction Reaction at the Cathode/Electrolyte Interface
Authors: Joh Dong Woo , Kim Do Yeub , Park Jeong Hwa , Lee Kang Taek 
Published: February 2020

Solid oxide fuel cells (SOFCs) are one of the most efficient electric power generating technologies through electrochemical reactions. However, conventional SOFCs based on yttria-stabilized zirconia (YSZ) electrolytes operate at high temperatures over 800 ºC, leading to high system cost and insufficient long-term stability. Reducing the operating temperature below 700 ºC brings significant reduction of system cost via scope expansion of material’s availability for stacks and balance of plants (BOPs), faster start-up time, as well as higher mechanical and chemical stability. However, the cathodic polarization loss at the electrolyte and cathode interface is significantly increased at reduced temperatures, due to the thermally activated nature of oxygen reduction reactions (ORRs).
At below 700 oC, the erbia- stabilized bismuth oxide (ESB) is a promising electrolyte material due to exceptionally high oxygen ion conductivity. Moreover, recent studies showed that ESB improves the cathode performance via enhancing ORR rate at the electrolyte/cathode interface at lower temperatures (450 ~ 700 ºC)1,2.
In this study, we employed an ESB interlayer at the interface between LSM-ESB cathode and YSZ electrolyte. The effect of the stabilized-bismuth oxide phase on ORR at reduced temperatures was systematically investigated by electrochemical impedance spectroscopy. Furthermore, I-V characterization was carried out to evaluate the performance of YSZ/ESB bilayered electrolyte SOFCs.

Acknowledgement

This research was supported by (1) Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2014R1A1A2057681), (2) the DGIST R&D Program of the Ministry of Science, ICT and Future Planning of Korea (1501- HRLA-01) and (3) the Global Frontier R&D on Center for Multiscale Energy System funded by the National Research Foundation under the Ministry of Science, ICT & Future Planning, Korea (2014M3A6A7074784).

Reference

1. K. T. Lee, D. W. Jung, H. S. Yoon, A. A. Lidie, M. A. Camaratta and E. D. Wachsman, J. Power Sources, 220 (2012) 324–330.
2. K. T. Lee, A. A. Lidie, S. Y. Jeon, G. T. Hitz, S. J. Song and E. D. Wachsman, J. Mater. Chem. A, 1 (2013) 6199

Figure 1