bluuebunny/crossref_metadata_2025_split huggingface dataset:
Oxidation of CuSn Alloy Nano-Tree and Application for Gas Sensors
Authors: Kaneko Naoto , Shimizu Tomohiro , Ito Takeshi , Tada Yoshihiro , Shingubara Shoso 
Published: February 2020

We have found nano-tree of CuSn alloy by DC electroplating with a constant potential mode [1,2]. Nano-tree is a true 3-D structure having many branches which separate from trunk perpendicularly, and sub-branches grow perpendicular from them also. It is well known that SnOx as well as CuOx are good materials for gas sensors. It is of great interest to evaluate gas sensor properties of the Cu-Sn Nano-tree oxide, because it has a very high ratio of surface to volume, and is expected to exhibit excellent properties as sensors. In this study, we carried out oxidation of CuSn nanotrees in air, and also measured resistance change properties by intoducing various reactive gases.
The Cu-Sn nanotrees were grown on Pt thin film electrode with the plating bath containing SnCl2, Cu(NO3)2, ((NH4)2C2O4) and Poly-ethylene glycol (PEG1000).
The oxidation of CuSn nanotrees was carried out in the atmosphere at temperature between 200 to 350 oC. Change in electrical resistance of CuSn nanotrees oxide was measured concomitant with introducing various gases in the chamber.
Figure 1 shows SEM images of the electrodeposited CuSn alloy. It is remarkable that nanotrees with many perpendicular branches were formed. Each branch has a one-dimensional structure with a diameter of around a few tens of nm, and grows perpendicularly from the branch. The nanotree structure is almost stable at annealing temperature below 350 oC, however, it is thickened due to volume expansion by oxidation.
Figure 2 shows the gas sensing property of the CuSn nanotree oxide. It turned out that the CuSn nanotree oxide reistance is sensitive against the introduction of H2, the resistance change increased with increasing amount of H2 gas. It is strongly suggested that the CuSn nanotree oxide has a high potential as a gas sensor material with a high sensitivity.
[1] T.Shimizu, et al., Surface and Coating technologies
[2] N. Kaneko , et al, Jpn.J.Appl.Phys. (2016) accepted for publication.

Figure 1
Identification of Polarization Losses in High-Temperature PEM Fuel Cells by Distribution of Relaxation Times Analysis
Authors: Schindler Stefan , Weiß Alexandra , Galbiati Samuele , Mack Florian , Danzer Michael A. , Zeis Roswitha 
Published: February 2020

In recent years phosphoric acid doped PBI-type fuel cells have drawn much attention as a promising candidate for energy storage and conversion applications at relatively high temperatures (100 – 200 °C). The elevated operating temperature of HT-PEMFCs (high-temperature polymer electrolyte membrane fuel cells) simplifies water and thermal management. In addition, it greatly enhances the fuel cell’s tolerance against impurities (e.g. CO) in hydrogen, which is critical for operation with reformate hydrogen. However, durability and stability of high-temperature PEM-MEAs still need to improve for widespread commercialization [1], and better tools for identifying performance-loss related mechanisms are desirable. A very useful in-situ technique for performance analysis of HT-PEMFCs is electrochemical impedance spectroscopy (EIS). As previously reported, EIS can be used to characterize the impact of different parameters (e.g. stoichiometry, temperature, etc.) on cell kinetics [2, 3]. Equivalent circuit models are usually used to analyze the EIS data and identify the performance-loss related mechanisms.
A major drawback of this approach is that the assumptions for the model equivalent circuits are sometimes ambiguous or even misleading due to the lack of priori knowledge about the electrochemical system under study. Furthermore, a clear separation of various physiochemical processes is difficult if the time constants of these processes overlap significantly in the frequency domain. To overcome these drawbacks, advanced mathematical methods such as Distribution of Relaxation Times (DRT) can be applied. DRT relies on the representation of the polarization impedance by its characteristic time constants and is numerically approximated by a discrete distribution function. This method has been successfully demonstrated for process identification and separation in solid oxide fuel cells (SOFC) [4].
In this study, we applied this technique on high temperature PEM-MEAs for the first time. Electrochemical processes were identified and analyzed by varying cell parameters such as temperature and stoichiometry. The results offer a refined understanding of loss mechanisms and provide valuable guidance for fuel cell improvement and optimization.

[1] A. Chandan, M. Hattenberger, A. El-kharouf, S. Du, A. Dhir, V. Self, B.G. Pollet, A. Ingram, W. Bujalski, J. Power Sources 231 (2013) 264

[2] J. L. Jesperesen, E. Schaltz, S.K. Kær, J. of Power Sources 191 (2009) 289-296

[3] F. Mack, R. Laukenmann, S. Galbiati, J. A. Kerres, R. Zeis, ECS Transactions 69 (17), 1075-1087 (2015)

[4] A. Leonide, V. Sonn, A. Weber, and E. Ivers-Tiffée, Journal of the Electrochemical Society 155 (1) B36-B41 (2008)

Figure 1 Typical Nyquist plot of a phosphoric acid doped PBI-type HT-PEMFC at different current densities (a) and the corresponding distribution function (b).

Figure 1
Electrochemical Performance of Thin-Film Pt3y Electrodes in PEMFC
Authors: Eriksson Björn , Lindahl Niklas , Wickman Björn , Lindstrom Rakel Wreland , Lindbergh Göran , Lagergren Carina 
Published: February 2020

In current polymer electrolyte fuel cells (PEMFC), high amounts of platinum catalysts is required due to the sluggish kinetics of the oxygen reduction reaction (ORR). As such it is important to find ways to increase the activity of the ORR catalyst. Previous studies have shown that alloying platinum with yttrium results in a catalyst which is more than six times as active as sole Pt in half cell rotating disk electrode measurements [1].
The model electrodes in this study are prepared by sputtering a well-defined layer of alloy catalyst onto a gas diffusion layer (GDL). In this manner the composition and thickness of the film can be controlled. These electrodes are studied with single cell PEMFC measurements to characterize the materials, similar to previous work done with these types of electrodes [2]. Using these methods the electrochemical surface area (ECSA), ORR activity, and stability are evaluated. The effects of different MEA preparations will also be investigated.
Scanning electron microscopy (SEM) with energy dispersive X-ray (EDX) analysis as well and X-ray photoelectron spectroscopy (XPS) are used to characterize the structure of the alloy catalyst as well as the bulk and surface compositions, i.e. platinum to yttrium ratio. This characterization is performed on both as-prepared samples and electrodes after being used in the PEMFC.
The main focus is to determine the role of yttrium in platinum thin-film platinum electrodes, and if the excellent activity in half cell experiments will also be seen in real PEMFC measurements.

References

[1] J. Greeley, I. E. L. Stephens, A. S. Bondarenko, T. P. Johansson, H. A. Hansen, T. F. Jaramillo, J. Rossmeisl, I. Chorkendorff and J. K. Nørskov , Nature Chemistry, 2009, 1, 552-556
[2] M. Wesselmark, B.Wickman,C.Lagergren,G.Lindbergh, Electrochimica Acta, 2013, 111, 152-159
Exploring the Lanthanide Contraction to Tune the Activity and Stability of Pt
Authors: Escudero-Escribano María , Malacrida Paolo , Hansen Martin Hangaard , Vej-Hansen Ulrik Grønbjerg , Velázquez-Palenzuela Amado Andrés , Tripkovic Vladimir , Schiøtz Jakob , Rossmeisl Jan , Stephens Ifan E. L. , Chorkendorff Ib 
Published: February 2020

The high platinum loadings required to compensate for the slow kinetics of the oxygen reduction reaction (ORR) impede the widespread uptake of polymer electrolyte membrane fuel cells. In order to improve the ORR kinetics and reduce the Pt loading, we can tailor the electronic properties of the Pt surface atoms by means of alloying Pt with other metals. Researchers have intensively studied alloys of Pt with late transition metals such as Ni and Co during the last decades. However, these compounds typically degrade under fuel cell reaction conditions, due to dealloying. In contrast, alloys of Pt and lanthanides present very negative enthalpy of formation [1,2], which should increase their resistance to degradation.
Herein we present eight novel Pt-lanthanide and Pt-alkaline earth ORR electrocatalysts: Pt5La, Pt5Ce, Pt5Sm, Pt5Gd, Pt5Tb, Pt5Dy, Pt5Tm and Pt5Ca [3]. All the materials are highly active, presenting a 3 to 6-fold activity enhancement over Pt. Pt5Tb is the most active polycrystalline Pt-based catalyst reported in the literature. A Pt overlayer with a thickness of few Pt layers is formed onto the bulk alloys by acid leaching [1-3]. Notably, the experimental ORR activity as a function of the bulk lattice parameter and the Pt-Pt distance follows a “volcano” relation [3], with Pt5Tb presenting the highest initial activity while Pt5Gd is the most active after 10 000 cycles stability test between 0.6 and 1.0 V versus the reversible hydrogen electrode. We use the lanthanide contraction to control strain effects and tune the electrocatalytic activity, stability and reactivity of Pt [3].

References

[1] M. Escudero-Escribano, A. Verdaguer-Casadevall, P. Malacrida, U. Grønbjerg, B.P. Knudsen, A.K. Jepsen, J. Rossmeisl, I.E.L. Stephens, I. Chorkendorff, J. Am.
Chem. Soc. 2012, 130, 16476.
[2] P. Malacrida, M. Escudero-Escribano, A. Verdaguer-Casadevall, I.E.L. Stephens, I. Chorkendorff, J. Mater. Chem. A
2014, 2, 4234.
[3] M. Escudero-Escribano, P. Malacrida, M.H. Hansen, U.G. Vej-Hansen, A. Velázquez-Palenzuela, V. Tripkovic, J. Schiøtz, J. Rossmeisl, I.E.L. Stephens, I. Chorkendorff, Science
2016, 352, 73.
Impact of Pressure and Temperature on Hydrogen Permeation in PEM Water Electrolyzers Operated at Asymmetric Pressure Conditions
Authors: Trinke Patrick , Bensmann Boris , Reichstein Sven , Hanke-Rauschenbach Richard , Sundmacher Kai 
Published: February 2020

Water electrolyzers are predominantly operated at elevated pressures. This is especially favorable in the context of the subsequent utilization of the produced hydrogen e.g. due to the more efficient, electrochemical and isothermal hydrogen compression or less afford for hydrogen drying. However, higher pressures lead to higher cross-permeation of the product gases in electrolysis cells.
In the present contribution, hydrogen permeation across a fumea EF-40 membrane is systematically investigated for pressure differences between 5-35 bar and for four different temperatures between 22 °C and 60 °C. The measured permeation fluxes show a quadratic dependency on the pressure difference. A permeation model combining a diffusive and convective transport can describe the experimental data quantitatively. For the investigated membrane, the diffusive as well as the proposed convective permeability coefficient and their temperature dependencies are obtained.
The diffusive permeability coefficient and its temperature dependency agrees very well with published data for Nafion membranes. The slightly lower value for the EF-40 can be explained by the lower water volume fraction. The obtained convective permeability coefficient indicates a high hydraulic permeability, especially in comparison to recently reported values for Nafion membranes. However, the reported values of the hydraulic permeability show high variations of about two orders of magnitude, with strong dependence on investigated materials, that show the importance of this parameter with regard to convective hydrogen permeation.
The present work discusses two potential reasons for the high obtained hydraulic permeability. The first one is related to the membrane properties. In particular, the lower equivalent weight of the fumea EF-40 membrane could cause the higher hydraulic permeability. Second the electrolysis conditions, in particular the applied small current, might increase the hydraulic permeability due to wider membrane water channels and a change to a hydrophilic membrane surface.
Figure: Parameterized equation in comparison to the experimental results.

Figure 1
Overpotential Analysis in High Pressure Water Electrolysis
Authors: Suermann Michel , Schmidt Thomas J. , Büchi Felix N 
Published: February 2020

To store or transport hydrogen (and optionally oxygen) in high pressure tanks or pipelines pressures up to 1000 bar are needed. Pressurized polymer electrolyte electrolyzers are typically operated at around 30 bar to reduce downstream mechanical compression and gas drying stages. Interestingly, often the cell voltage does not show the expected thermodynamic voltage increase [1,2]. Consequently beneficial influences are compensating the compression work, at the expense of higher faradaic losses due to increased gas crossover.
In this work we analyze cell voltages at gas pressures up to 100 bar as function of temperature up to 70 °C and current densities up to 4 A/cm2, considering the three main overpotentials (ohmic, kinetic, mass transport) using a zero-order analysis based on the Tafel kinetics model.
As expected, the ohmic overpotential is mainly a function of temperature and almost independent from pressure. Therefore the overpotential gains with increasing pressure, observed for current densities above about 0.8 A/cm2, stem from the kinetics and/or the mass transport. Both overpotentials decrease with increasing pressure, but over a wide current density region kinetics contribute about two thirds to the voltage gain. The improved kinetics can be attributed to an increased apparent exchange current density, whereas the increased mass transport might be related to smaller gas volumes or velocities resulting in an improved two-phase flow in the porous structures.
Literature:
[1] S.A. Grigoriev, V.I. Porembsky, V.N. Fateev, Pure hydrogen production by PEM electrolysis for hydrogen energy, Int J of Hydrogen Energy, 31 (2006) 171-175.
[2] P. Millet, R. Ngameni, S.A. Grigoriev, N. Mbemba, F. Brisset, A. Ranjbari, C. Etiévant, PEM water electrolyzers: From electrocatalysis to stack development, Int J of Hydrogen Energy, 35 (2010) 5043-5052.
(Invited Plenary) Honda Fuelcell Vehicle Development and Toward the Hydrogen Society
Authors: Moriya Takashi 
Published: February 2020

Honda launched new fuel cell vehicle "CLARITY FUEL CELL" in March 10, 2016. In this presentation, I explain the fuel cell vehicle (FCV) development status of Honda including the various main technologies of "CLARITY FUEL CELL". Honda does not only develop the FCV but also small hydrogen station and mobile inverter for power output from FCV. Honda has efforts toward the hydrogen society with concept of "Produce" "use" and "Connect". I explain the small hydrogen station named Smart Hydrogen Stration (SHS) and mobile inverter named "Power Exportor 9000". This explanation will be explained technical conceopts and actual demonstration test resylts. In terms of FCV development, I will explain the FCV development history and future technology direction. Of courese, FCV is not expanded without prepareation of hydrogen infrastructure (Hydrogen Refueling Station : HRS). So this presentation will be explained the situration of HRS preparation and recent direction of movement. Especially, I will introduce the most aggressive Japanese situation. And I expain the future strategy of Honda.
Iridium Nanoparticles Supported on Magneli Phase Ti4O7 for PEM Water Electrolyzers
Authors: Ioroi Tsutomu , Yasuda Kazuaki 
Published: February 2020

PEM water electrolysis is one of the promising technologies for hydrogen production from renewable energy sources. Iridium and their oxides are recognized as the most suitable catalyst showing high activity and stability for oxygen evolution reaction (OER) in acidic media [1], however, overpotential is still high and its scarcity and price are also drawbacks. To overcome these problems, a number of studies concerning particle size reduction, catalyst compositions, and utilization of catalyst support have been reported [2]. Among them, use of corrosion-resistant and highly electro-conductive oxides, especially Magneli phase Ti4O7 as catalyst support would be beneficial for reducing Ir loading and increasing durability. We have developed Ti4O7-supported Ir catalyst and examined activity and durability as an anode catalyst of PEM electrolyzer.
Titanium oxide support was prepared by UV laser technique [3]. Ir/Ti4O7 catalysts obtained by using H2IrCl6 precursor showed conductivity comparable with that of commercial Pt/C. MEAs with the Ir/Ti4O7 anode can be operated up to 4 A cm-2 at low cell voltage < 2.0 V (with DuPont NR212 membrane) with very low Ir loadings (0.25 mg-Ir cm-2). Considering fluctuating nature of the renewable energy inputs, catalyst stability against voltage change should be another important issue. To simulate and accelerate such degradation modes, potential sweep between 1.0 V and 2.0 V at a sweep rate of 500 mV s-1 was applied up to 10,000 cycles. The Ir/Ti4O7 MEA shows limited degradation even after 10,000 cycles. Stability of the cell performance and the catalyst structure will be discussed at the Meeting.

References

1. M. H. Miles and M. A. Thomason, J. Electrochem. Soc.,
123, 1459 (1976).
2. M. Carmo, D. L. Fritz, J. Mergel, D. Stolten, Int. J. Hydrogen Energy, 38, 4901 (2013).
3. T. Ioroi, H. Kageyama, T. Akita, K. Yasuda, Phys. Chem. Chem. Phys., 12, 7529 (2010).
Nanoporous IrO2 catalyst with Ultrahigh Specific Surface Area Synthesized through an Ammoniating Method for Acidic Oxygen Evolution
Authors: Li Guoqiang , Li Songtao , Liu Changpeng , Xing Wei , Ge Junjie 
Published: February 2020

The development of highly active and stable electrocatalysts for OER is urgent due to the slow kinetics and high overpotential of oxygen evolution reaction (OER) [1]. To date, the most promising catalysts for OER are IrO2 based catalysts with ordered porous structures, where a templating method was generally used to ensure the high utilization of the catalysts. However, the synthesis route for such catalysts is generally of high technique complexation, where the templates need to be effectively removed after synthesis [2,3]. Hence, a simple template-free method that leads to the formation of highly porous IrO2 catalysts with high surface area is highly attractive.

Herein, a satisfactory template-free ammoniating method was developed in which NH3 ligand was successfully kept until pyrolysis treatment, thus acting as the pore-forming agent to achieve highly porous IrO2. The specific and electrochemical surface areas of as-prepared IrO2 catalysts increased with the increasing quantity of NH3·H2O additive. Specifically, IrO2 (1:100)-450 °C catalyst synthesized with the highest ratio of NH3 ligand exhibited high specific surface area of 363.3 m2 g-1 as metal oxide. Furthermore, IrO2 (1:100)-450 °C showed remarkable electrocatalytic activity for acidic OER in the whole potential window, which can be ascribed to the high catalysts utilization. As shown in Figure 1, the over-potential for the IrO2 (1:100)-450 °C catalysts to attain current at 10 mA cm-2 was only 282 mV, which was shifted negatively by 31 mV and 46 mV in comparison to the home-made IrO2 (without NH3) and commercial IrO2 (CM) catalysts, respectively. Thus, the NH3 mediating method was found a superior method for increasing catalysts utilization, where the IrO2can be conveniently synthesized in large scale.
Figure 1. CV curves (Left, the inset shows the specific surface area) and LSV curves (Right, the inset shows the TEM of IrO2 (1:100)-450°C) of IrO2 (1:100)-450°C, IrO2 (1:10)-450°C, IrO2-450°C, and IrO2(CM) catalysts.

Acknowledgments

This work is supported by National Basic Research Program of China (973 Program, 2012CB932800), National Natural Science Foundation of China (21433003, 21373199), the Science & Technology Research Programs of Jilin Province (20150101066JC, 20160622037JC).

References

[1] S. Park, Y. Shao, J. Liu, and Y. Wang, Energy Environ. Sci., 5, 9331 (2012).
[2] W. Hu, Y. Wang, X. Hu, Y. Zhou, and S. Chen, J. Mater. Chem., 22, 6010 (2012).
[3] E. Ortel, T. Reier, P. Strasser, and R. Kraehnert, Chem. Mater., 23, 3201 (2011).

Figure 1
Mechanistic Insights into Electrochemical Oxidation of Small Alcohol Molecules
Authors: Dewan Shalaka , Raciti David , Wang Chao 
Published: February 2020

Small alcohol molecules such as methanol and ethanol represent promising fuels to power fuel cells for mobile electronic devices, transportation and stationary applications. Ethanol is of particular interest due to its renewability by generation from biomass feedstocks, large energy density and compatibility with existing infrastructures for fuel storage and delivery. Although substantial progress has been made in the recent years for the development of direct ethanol fuel cell (DEFC) technology, obstacles are still present for the practical implication, largely in the lack of efficient and selective electrocatalysts for complete oxidation of ethanol to CO2.
Platinum (Pt) is commonly used as electrocatalyst in fuel cells, including DEFCs. However, ethanol oxidation on Pt is found to be incomplete and produces undesired partial oxidation products such as acetaldehyde and acetic acid. It is thereby considered that Pt itself cannot cleave the C-C bond in ethanol molecules and a second transition metal such as Rh and Ir is needed to facilitate this rate- and selectivity-limiting step. However, evidences are also present in the literature for the formation of strongly binding adsorbates, such as -CO and -CH
x
, at low potentials (<0.5 V vs. RHE), from both in situ molecular spectroscopy (e.g., Infrared (IR) and surface enhanced Raman spectroscopy (SERS)) and differential electrochemical mass spectroscopy (DEMS) studies. These results suggest that oxidative removal of these C1 species, instead of C-C bond cleavage, is the sole rate-limiting factor on Pt catalysts.
In attempt to resolve this controversy, we have performed systematic studies of methanol, ethanol and ethylene glycol oxidation on polycrystalline Pt electrodes. In particular, surface-specific sum frequency generation (SFG) spectroscopy is combined with electrochemistry to determine the reaction intermediates and evaluate their dependence on electrode potentials. It is found that C1 adsorbates form at low potentials, and the coverages increase as the electrode potential is raised from 0.1 V to ~0.4 V. While the -CO feature drops above 0.4 V for methanol and ethylene glycol oxidation, it persists up to 0.5 V and then drops for ethanol oxidation. Our results confirm the presence of active Pt sites for C-C bond cleavage and underline the role of -CH
x
species generated from the β-carbon in governing the kinetics of alcohol oxidation reactions. It is proposed that the slow transition from -CH
x
to -CO gives rise to the higher overpotentials for ethanol oxidation compared to methanol and ethylene glycol oxidation.