bluuebunny/crossref_metadata_2025_split huggingface dataset:
An FIB-SEM Study on Correlations between PEFC Electrocatalyst Microstructure and Cell Performance
Authors: Okumura Makito , Noda Zhiyun , Matsuda Junko , Nishihara Masamichi , Hayashi Akari , Sasaki Kazunari 
Published: February 2020

The electrocatalyst layer of the polymer electrolyte fuel cells (PEFCs) has a complicated porous microstructure. Since the structure allows gas, proton, and electron transport, and water management, cell performance depends strongly on their 3-dimensional microstructure. Understanding on the correlations between the electrocatalyst microstructure and the cell performance is therefore essential in improving the PEFC electrochemical performance. The purpose of this study is thus to clarify these correlations using focused-ion-beam coupled scanning electron microscopy (FIB-SEM).
We used the standard electrocatalyst (TEC10E50E) and varied the Nafion-to-electrocatalyst ratio (hereafter the Nafion ratio) for the electrocatalyst layer because the Nafion ratio affects the electrocatalyst microstructure and the cell performance[1],[2]. After model cell preparations, current-voltage (IV) performance was measured and thus each electrode overvoltage contribution was separated. We then considered FIB-SEM working condition and method of image processing to observe electrocatalyst microstructure by the FIB-SEM technique. In particular, because it was difficult to distinguish between solid and pore in SEM images due to the complicated porous microstructure, we solved this problem by separating solid and pore objectively by auto-image thresholding technique[3]. Then, we examined the correlations between the 3D microstructure and the cell performance.
According to the results of IV characteristics of several cells with different Nafion contents, in case Nafion ratio was 28 wt.%, IV performance was the highest. In case Nafion ratio was less than 28 wt.%, whilst IV performance was lower than that of 28 wt.%, the cells can still generate high current densities. On the other hand, in case Nafion ratio was higher than 28 wt.%, the cells can exhibit a lower cell voltage due to a much higher concentration overvoltage. In order to examine the correlations between the 3D microstructure and the cell performance, we observed electrocatalyst microstructure by the FIB-SEM. Figure 1 describes the observation process. According to the results of 3D analysis of samples with different Nafion contents, we could confirm that gas transport pathway in the electrocatalyst layer was filled with Nafion ionomer with increasing Nafion ratio. Details on the FIB-SEM observation conditions and the microstructure-performance correlations are presented at the symposium.
(1) S. Jeon, J. Lee, G.M. Rios, H.-J. Kim, S.-Y. Lee, E Cho, Intl. J. Hydrogen Energy 35 (2010) 9678-86.
(2) T. Suzuki, S. Tsushima, S. Hirai, Intl. J. Hydrogen Energy 36 (2011) 12361-12369.
(3) J. Bernsen, 8th ICPR (1986) 1251-1255.

Figure 1
Computational Modelling of Cationic Contamination in PEFCs: a Multiphase Mixture Approach
Authors: Banas Charles Joseph , Pasaogullari Ugur 
Published: February 2020

Cationic contamination in polymer electrolyte membrane fuel cells (PEFCs) can lead to accelerated degradation and loss of performance. There are several mechanisms to introduce these cationic impurities; including transport with the inlet fuel/air streams, or from degradation of the fuel cell and balance of plant components. Many common cations tend to have a higher affinity to the sulfonic acid side chains of the polymer electrolyte membrane (PEM) than protons, resulting in preferential uptake of these contaminants into the PEM. Once occupying these sites, the impurity cations contribute to the loss of performance by lowering the water content of the membrane and reducing the ionic conductivity.[1] To compliment experimental results, numerical studies have been performed[2,3] to understand the coupled impact of cation occupancy in the membrane with the water transport in the cell and the overall cell performance. Early generations of these models had assumed a constant cation occupancy in the cathode that was used as a boundary condition to solve the cation transport via a Stefan-Maxwell diffusion process. By coupling the contaminant occupancy to the water content of the membrane and electro-kinetics of the catalyst layers, cell performance has been shown to decrease down to as little as one third its non-contaminated levels.[3] This study builds off of previous models to develop a steady state, one dimensional, cation contamination model of a PEFC to examine the impact of cation transport to the membrane electrode assembly (MEA) via a water bridge across the gas diffusion layer (GDL) as shown in Figure 1. The multiphase mixture (M2) model, proposed by Wang and Cheng[4], is used to derive species transport equations for the reactant gases and water that permits two phase water transport in the GDL and catalyst layers. This resulting water distribution acts as to promote cation transport from the gas flow channels across the GDL, where the dissolved cations can evolve out of the liquid phase water and into the MEA, occupying the sulfonic acid sites of the membrane. A baseline non-contaminated case is presented to study the cell performance and species distribution normal operating conditions. Then, the model is employed to show how the saturation of the cathode effects cation distribution across the GDL and how the presence of dissolved cations in the catalyst layer impacts the contaminant occupancy and overall cell performance.
References
1. T. Okada, in Handbook of Fuel Cells, Cells– Fundamentals, Technology and Applications., W. Vielstich, H. A. Gasteiger, A. Lamm and H. Yokokawa. Editors, John Wiley & Sons, Ltd (2010).
2. M. F. Serincan, U. Pasaogullari and T. Molter, Int. J. Jydrogen Energy, 35, 11 (2010).
3. M. A. Uddin and U. Pasaogullari, J. Electrochem. Soc., 161, 10 (2014).
4. C. Y. Wang and P. Cheng, Int. J. Heat Mass Transfer, 39, 17 (1996).

Figure 1
Novel Anode Catalysis for Ammonia Solid Oxide Fuel Cell
Authors: Hashinokuchi Michihiro , Zhang Mengjia , Yokochi Ryuji , Doi Takayuki , Inaba Minoru 
Published: February 2020

Ammonia (NH3) is attractive as a hydrogen carrier and a suitable fuel for solid oxide fuel cells (SOFCs) because it has high hydrogen density 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.
There are many studies on the Ni-based anodes for NH3-SOFCs. However, the number of report on the bimetallic anode for NH3-SOFCs is limited. Previously, we have investigated the activity of Ni-M (M = Fe, Mo ,Ta, W and Nb) cermet anodes for NH3-SOFCs at temperature of 700 - 900 °C [2-5]. In these studies, we found that the anode polarization was greatly improved by transition metal additives, which favored the formation of metal (and/or alloy) nitrides in the anode under operation condition. Furthermore, the activation energy of NH3 oxidation at the anode was strongly dependent on the metal additive, suggesting that a metal-nitrogen biding energy of catalysis was related to the catalytic activity for NH3 oxidation. Among these anodes, Ni-Fe and Ni-Mo cermet anodes were highly active for the electrochemical oxidation of NH3 at 700 °C and expected for the active anode of NH3-SOFCs at intermediate temperature.
In this study, we further investigated the effects of Fe and Mo additives to Ni cermet anode on the cell performance at temperature of 500 - 600 °C. Fig.1 shows the current density versus voltage (I–V) curves for the electrolyte supported cells: Ni40-Fe60/SDC, Ni97-Mo3/SDC and Ni/SDC|LSGM|SSC at 600 °C. The thickness of LSGM electrolyte was 300 µm. The cell performance was significantly improved by the addiction of Fe and Mo as shown in Fig.1. The formation of alloy nitrides in both Ni-Fe and Ni-Mo anodes was observed under operation condition. The role of alloy nitrides in the NH3oxidation will be discussed.

Acknowledge

This work was supported by “Kyoto Regional Scientific Innovation Hub” from MEXT in Japan and by JSPS-KAKENHI Grant Number C16K05958.

Reference

[1] Q. Ma et al., J. Power Sources 161 (2006) 95.
[2] W. Akimoto et al., Solid State Ionics 256 (2013) 1.
[3] M. Hashinokuchi et al.,Solid state Ionics 285(2016) 222.
[4] M. Hashinokuchi et al., ECS Transactions 68 (2015) 2739.
[5] R. Yokochi et al., ECS Transactions 68 (2015) 2745.

Figure 1
Reduction of Thermal Stress during Soec Unsteady Operation
Authors: Watanabe Kentaro , Maeda Atsushi , Mizusawa Tatsuya , Araki Takuto , Mori Masashi 
Published: February 2020

In recent years, natural energy sources such as solar and wind power have been introduced into the electric grid. However, the wind and solar power suffer instability with respect to changes in the weather. As the proportion of these energies increases, a technique to store a surplus electric power is required. The hydrogen generation systems using solid oxide electrolysis cells (SOECs) are expected as large-capacity power storage facilities with the ability to stabilize the electrical power supply.
For the use of the SOEC, it is important to grasp the unsteady characteristics, especially temperature distribution which is the one of the biggest destruction factor of the cell. In this study, the unsteady, two dimensional, tubular numerical model of a cathode supported micro-tubular SOEC was developed to clarify the temperature distributions and its responses .The temperature of anode surface were measured directly by K-type thermocouples during the simultaneous electrochemical performance measurements. The operating condition of SOEC was controlled to reduce the unsteady temperature distribution in SOEC.
Rough description of the numerical model is shown in Fig.1. The model calculates heat-mass-charge transports and electrochemical reactions, simultaneously. The construction materials of SOEC cathode electrode was mixed materials of nickel (Ni) and yttria-stabilized zirconia (YSZ). The electrolyte was YSZ, and the anode electrode was mixture of lantern strontium manganite (LSM) and YSZ. The thicknesses of cathode electrode, electrolyte and anode electrode were 200 mm, 20 mm and 20 mm, respectively. The cell length was about 50 mm, with an outer diameter of about 2 mm. The flow rate of hydrogen and steam was set to be same. The operating temperature was 1123K. Experiments of SOEC were conducted in same conditions.
The calculated temperature distributions at steady states are shown in Fig.2. The temperature decreased at 1.1 V, 1.2 V and increased at 1.3 V, 1.4 V. The maximum temperature gradient was observed around z=0.042 at 1.4 V. This position was consistent with the point where a clack was observed during a measurement.
The maximum temperature gradients change during potential sweep with various intermediate voltage are shown in Fig.3. This shows that the maximum temperature gradient could be reduced by controlling the sweeping conditions.

Figure 1
Phase Evolution in (Pr1-xNdx)2NiO4+d Cathodes for Intermediate Temperature Solid Oxide Fuel Cell Applications
Authors: Dogdibegovic Emir , Wright Christopher J. , Zhou Xiao-Dong 
Published: February 2020

Fast kinetics of Pr2NiO4+δ cathode is counterbalanced by readily occurring phase transitions at operating conditions. Single phase (Pr1-xNdx)2NiO4+δ powders (x=0, 0.25, 0.50, 0.75, 1) were synthesized in an attempt to suppress the phase transitions, and in turn lead to stable long term performance. Rietveld refinement shows linear decrease in unit cell volume with increase in x. This volume contraction is mainly driven by decrease in the c lattice parameter. Thermal annealing on powders and electrodes show reducedphase transitions in a parent nickelate phase with increase in Nd content. Long term thermal annealing shows preserved (Pr0.25Nd0.75)2NiO4+δ and Nd2NiO4+δ phases at 750 °C, as confirmed by x-ray diffraction analysis. Phase transitions in electrochemical cells were also suppressed with increase in Nd content. TEM analysis confirmed multiple phases present in operated Pr2NiO4+δ electrodes, while Nd2NiO4+δ electrodes retained stable phase. SEM analysis showed reduced reaction with ceria buffer layer with increase in Nd content. Diffusion of Pr was decreased by twofold for x=0.25 and by sixfold for x=0.50, while the reaction was fully suppressed with higher Nd content.
Degradation Analysis of SOFC Stack Performance-Durability Test and Verification of Improved SOFCs-
Authors: Yoshikawa Masahiro , Yamamoto Tohru , Yasumoto Kenji , Mugikura Yoshihiro 
Published: February 2020

Central Research Institute of Electric power Industry (CRIEPI) has operated six types of SOFC stacks, which are developed by MITSUBISHI HITACHI POWER SYSTEMS (MHPS), KYOCERA, TOTO, NGK SPARK PLUG, NGK INSULATORS, and MURATA, to reveal their durability and find dominant degradation factor for each SOFC stack under NEDO’s project. The target of this NEDO durability project is set at 0.11%/1,000hr. In order to evaluate a performance degradation of the SOFC quantitatively and in order to quantify a performance change with time, the performance factor analysis method is required. We have been developed the electrode polarization models which is able to express SOFC performance factors such as Nernst loss (ηne), anode polarization (ηa), cathode polarization (ηc), and internal resistance IR drop (ηiR) with high prediction accuracy for six types of SOFCs. This gives us enable to make detail comparison among different type of SOFCs with the same performance analysis method inside the NEDO project. The MHPS’s stack which was operated until 16,000 hours, showed better stability and no further degradation factor has been identified. On the other hand, peculiar degradation behaviors arising from some impurities in air have been observed in our test for the stacks of Kyocera’s, TOTO’s, NTK’s, NGK’s, and Murata’s. For example, performance test exibited a rapid voltage drop within initial operation period for flattened tubular segment-in-series stack. The factor of this rapid voltage drop was increment of cathode overvoltage from a performance factor analysis result. One of possible reason for the negative effect to cathode overvoltage is sulfur contamination in the supply air from air compressor or thermal insulating foam on furnace.
In this study, we report our recent activities on the durability and the dominant performance factors, and the peculiar degradation behaviors.
Proton Conduction on YSZ Electrolyte Thin Films Prepared by RF Magnetron Sputtering
Authors: Takayanagi Makoto , Tsuchiya Takashi , Minohara Makoto , Kobayashi Masaki , Horiba Koji , Kumigashira Hiroshi , Higuchi Tohru 
Published: February 2020

Yttria stabilized zirconia (YSZ) is known as solid electrolyte materials with oxide ion conduction and is used for sensor and solid oxide fuel cells (SOFCs). Recently, Wagner et al. has reported proton conductivity in YSZ single crystals at high temperature. Furthermore, Scherrer et al. has also reported proton conduction in YSZ thin films prepared by various technique. However, the existence of proton conduction of YSZ thin film at intermediate temperature (IMT) region has not been clarified thus far. In this study, we present the structural and electrical properties at IMT region of YSZ thin films prepared by RF magnetron sputtering.
YSZ thin films were deposited on Al2O3 substrates at various temperatures by RF magnetron sputtering using ceramics target. The 8 mol % Y2O3-doped ZrO2 target was prepared by solid phase reaction. The flow rate of Ar gas and the deposition pressure were set at 0.67 sccm, 8.0 × 10-3 Torr. The structural property of the YSZ thin films were characterized as a function of film thickness by powder X-ray diffraction (XRD) analysis. The conductivity of the deposited thin film was measured by AC impedance method at the temperature region of 200-500 ℃. The measurement frequency region was from 0.1 Hz to 32 MHz. In order to probe conducting carriers, the conductivity was measured by changing oxygen gas partial pressure (P
O2). The electronic structure was characterized by photoemission spectroscopy (PES) and X-ray absorption spectroscopy (XAS).
The lattice constant of the (111)-oriented thin film increases with increasing film thickness due to relaxation of lattice distortion. The 80 nm thick film exhibits the oxide ion conduction with the activation energy of ~ 1.13 eV. Although the conductivity of 160 nm thick film dose not depend on atmosphere during measurement, the 80 nm and 120 nm thick films have higher conductivity in atmosphere than that in dry atmosphere. The activation energy of 80 nm thick film is ~ 0.76 eV and of 120 nm thick film is 0.82 eV. The electrical conductivity depends on film thickness. These results indicate that the thin film has proton conduction at the surface in the temperature region.
(Invited) Impact of Electrolytes on Li+ Charge Transfer Kinetics at the Electrolyte and Electrode Interface and Rate Performance in Li-Ion Batteries
Authors: Jow Taiguang Richard , Delp Samuel A. , Allen Joshua L. , Borodin Oleg , Allen Jan L. 
Published: February 2020

The rate performance of Li-ion batteries remains challenging, especially at temperatures below -20 oC. Apart from engineering improvements, the rate performance of the cell is determined by the rate of Li
+
ion transfer across the interface, so-called charge transfer kinetics and the rate of Li+ ion diffusion within the electrode. In this paper, we will focus on the Li
+
ion charge transfer kinetics as it is still poorly understood and can be improved by modifying the electrolyte. Examination of Li
+
charge transfer kinetics at both a graphite anode and a LiFePO4 cathode, revealed a much higher activation at the graphite anode/electrolyte interface than at the LiFePO4 cathode/electrolyte interface [1]. Values from 50 to 60 kJ mol-1 have been observed for the activation energy at the graphite/electrolyte interface [1-3] whereas, at the LiFePO4 cathode/electrolyte interface, an activation energy of 30 kJ mol-1 has been observed [1]. At either electrode, the solvated Li
+
ion needs to be de-solvated before diffusing into the electrode. The distinct difference between the graphite anode and the intercalating cathode is that there is a distinct presence of a solid electrolyte interphase (SEI) on the graphite anode while there is no SEI or no discretely defined SEI layer on the cathode. What is not clear is why the SEI on the graphite anode leads to a larger Li
+
charge transfer activation energy value. Is this due to diffusion through the SEI itself or the slow de-solvation process in the presence of the SEI?
Recent studies indicate that the electrolyte composition plays a vital role in determining the electrolyte solvation structure and furthermore the nature of the SEI formed on the graphite anode can be modified by changing solvents, salt concentrations and additives [3-5]. This paper will report our recent exploration of how changing the electrolyte composition can improve the Li
+
charge transfer kinetics.

References

T. R. Jow, M. B. Marx, J. L. Allen, J. Electrochem. Soc. 2012, 159 (5), A604-A612.

T. Abe, H. Fukuda, Y. Iriyama, Z. Ogumi, J. Electrochem. Soc. 2004, 151(8), A1120-A1123.

Y. Yamada, Y. Iriyama, T. Abe, Z. Ogumi, Langmuir, 2009, 25(21), 12766-12770.

M. Nie, D. P. Abraham, D. M. Seo, Y. Chen, A. Bose, and B. L. Lucht, J. Phys. Chem. C 2013, 117, 25381−25389.

K. Abe, M. Colera, K. Shimamoto, M. Kondo, and K. Miyoshia, J. Electrochem. Soc. 2014, 161 (6) A863-A870.
Carbon Nanostructures for the Electrochemical Conversion of CO2 to Fuels: Defect & Electrocatalytic Activity
Authors: Wu Jingjie , Yadav Ram Manohar , Liu Mingjie , Sharma Pranav P. , Sharma Pranav P. , Wright Christopher J. , Tiwary Chandra , Yakobson Boris I. , Lou Jun , Ajayan Pulickel M , Zhou Xiao-Dong 
Published: February 2020

The advantages of the electrochemical conversion of carbon dioxide to fuels using renewable energy sources are twofold: (1) it has the potential to accomplish a carbon-neutral energy cycle and (2) it can provide an approach to tackle the environmental challenges caused by anthropogenic carbon dioxide emissions. Although thermodynamically possible, the kinetics of carbon dioxide reduction to fuels remains challenging and therefore, an efficient and robust electrocatalyst is needed to promote the reaction. The ideal catalyst for the electrochemical CO2 reduction must be capable of mediating multiple proton-coupled electron transfer reactions at low overpotentials, suppressing the concurrent hydrogen evolution reaction, converting CO2 to desired chemicals with high selectivity, and achieving long-term stability. Extensive research has been carried out on metallic electrocatalysts during the past three decades; however, further studies are need to develop materials that are simultaneously efficient and stable for practical purposes.
The focus of this presentation is to report the use of N-doped carbon nanostructures as the electrocatalysts, which are highly efficient, selective and more importantly, stable catalysts to achieve CO2 conversion to CO. The catalytic activity of N-doped carbon nanotubes (NCNTs) was further benchmarked against other metallic catalysts reported in literature. Compared to noble metals Ag & Au, these NCNTs exhibited a lower overpotential to achieve similar selectivity towards CO formation. The dependence of catalytic activity, i.e., the overpotential and selectivity for CO formation on the defect structures (pyridinic, graphitic, pyrrolic-N) inside NCNTs will be discussed. The presence of both pyridinic and graphitic-N was found to significantly decrease the absolute overpotential and increase the selectivity towards CO formation. In addition, the electrocatalytic activity of two-dimensional materials will be presented. Overall, pyridinic-N defects exhibited the highest catalytic activity; thereby suggesting the directions for developing carbon nanostructures as metal-free electrocatalysts for CO2 reduction.