bluuebunny/crossref_metadata_2025 huggingface dataset:
Encapsulation of Supported Metal Nanoparticles with an Ultra-Thin Porous Shell for Size-Selective Reactions
Authors: Shang Zeyu , Patel Rajankumar L. , Liang Xinhua
Published: February 2020

Heterogeneous catalysts are widely used. However, heterogeneous catalysts cannot selectively convert specific molecules in the reactant mixture to catalyze only desired reactions. Size-selective catalysts with a metal core and porous oxide shell have a promising structure that can increase the reaction selectivity through reactant molecular discrimination. This paper describes a general method to create porous metal oxide films with well-defined porous structures and precisely controlled thickness down to several angstroms from dense organic/inorganic hybrid metal alkoxide films grown by molecular layer deposition (MLD). A novel nanostructured catalyst with an ultra-thin porous shell obtained from the thermal decomposition of an aluminum alkoxide film deposited by MLD for size-selective reactions was developed. The molecular sieving capability of the porous metal oxide films was verified by examining the liquid-phase hydrogenation of n-hexene versus cis-cyclooctene. The success of making these materials by MLD opens up a new method for preparing size-selective catalysts.
Carrier Transport in CdTe Nanocrystals and Coupled Films As Measured with Time-Resolved Microwave Conductivity
Authors: Callahan Rebecca , Crisp Ryan , Rumbles Garry , Luther Joseph
Published: February 2020

Solution-processable semiconducting CdTe nanocrystals are promising materials for solution processed inorganic photovoltaic technologies and other various technologies. Solution processed photovoltaic device performance is reliant on sufficient carrier transport between coupled nanocrystals. We use transient microwave conductivity experiments to measure charge carrier mobilities within isolated CdTe tetrapods nanocrystals in solution. We find that the (GHz) mobility and lifetime of photo-induced carriers are related to the tetrapod arm dimensions. Furthermore, carrier mobilities in nanocrystal films are highly dependent on the nanocrystal capping ligand. Recent advances in inorganic ligand exchanges have allowed for coupled yet quantum-confined nanocrystal films. The combination of these experiments allows us to report photo-induced charge generation to measure both inter- and intra-NC conductivity in a series of Metal Chalcogenide capped CdTe nanocrystal films. We identify specific Te-based ligands that show transport characteristics (diffusion lengths) improved over bulk CdTe films.
Surface-Enhanced Raman Scattering Biosenor for Detection of Hepatitis B Virus DNA
Authors: Wu Nick
Published: February 2020

Surface-enhanced Raman scattering (SERS) has received increasing attention in biological and chemical sensing because of its unique features. At first, the sandwich nanoparticles have been developed as the SERS Probe.1 And then the sandwich nanoparticles are coupled with a gold triangle nano-array chip to create spatially broadened plasmonic “hot spots”, which enables a large density of Raman reporters to experience strong local electromagnetic field enhancement. Such a quasi-periodic structure increases the intensity and area of the localized surface plasmon resonance, which enhances the SERS signal significantly. This nano-architecture has been used to construct a SERS sensor for hepatitis B virus DNA detection. This sensor exhibits the limit of detection as low as 47.6 aM and can discriminate single-base mutant of DNA.

References

[1] M. Li, S. K. Cushing, J. Zhang, J. Lankford, Z. P. Aguilar, D. Ma, N. Q. Wu, Nanotechnology, 23 (2012), 115501.

[2] M. Li, S. K. Cushing, H. Liang, S. Suri, D. Ma, N. Q. Wu, Analytical Chemistry, 85 (2013), 2072-2078.

Acknowledgement:

The resource and facilities used were partially supported by NSF (EPS 1003907), the West Virginia University Research Corporation and the West Virginia EPSCoR Office. The use of WVU Shared Facility was appreciated.
A Three-Dimensional Model for Thermal Analysis in a Vanadium Flow Battery
Authors: Zheng Qiong , Zhang Huamin , Li Xianfeng , Ma Xiangkun , Ning Guiling , Xing Feng
Published: February 2020

The development of vanadium flow battery (VFB) has expanded the possibilities for large-scale energy storage in confronting against the conventional energy’s challenges. With the development of commercialization of VFBs, more focuses should be switched to probe deeply into the fundamental processes inside a VFB and develop practical tools to aid controlling/monitoring the VFB system. Whereas, achieving the above objectives via extensive laboratory testing is time-consuming and costly. In pilot studies, modelling can be a promising substitute. Heat and temperature need to be considered seriously in the VFB design and control for an efficient and safe operation. In this regard, a three-dimensional model for thermal analysis in a VFB was proposed to provide a deep insight into heat source of heat generation and temperature in a VFB. The model is a combination of mass, momentum, charge, energy transport and electrochemical reactions involving all vanadium species. A quasi-static thermal behaviour and the temperature spatial distribution were characterized. The simulations indicate that the heat generation exhibits a strong dependence on the applied current density. The electrochemical reaction heat rises proportionally while the ohmic heat and activation heat increase at a parabolic rate with the increase of applied current density, resulting in the determining heat source’ varying from electrochemical reaction heat to ohmic heat if the applied current density is large enough. In addition, the electrochemical reaction heat and activation heat have a lack of sensitivity to the porosity and flow rate, whereas an obvious increase of ohmic heat can be observed with the rise of the porosity. Lower porosity or faster flow shows better uniformity of temperature distribution. Thus, the model proposed in this paper shows good prospect in heat and temperature management for a VFB aiming at eliminating any crisis of internal heat accumulation.

Keywords: Vanadium flow battery (VFB), Three-dimensional model, Thermal analysis, Heat generation, Temperature distribution
Low-Temperature, High Energy Density Non-Aqueous Redox Flow Battery
Authors: Herr Tatjana , Fischer Peter , Tübke Jens , Pinkwart Karsten , Elsner Peter
Published: February 2020

Redox flow battery (RFB) is a well-known storage technology. Commercial RFBs are based on aqueous electrolytes, but also several organic electrolytes are evaluated. Organic solvents provide a number of advantages due to their physicochemical properties, such as a wider operating temperature window and a wider stable potential window. Limiting factor in these systems is the solubility of the redox-active species.

In our study the solubility of vanadium(III) acetylacetonate as redoxactive species and tetrabutylammonium hexafluorophosphate as supporting electrolyte were investigated in a ternary solvent mixture containing acetonitrile, 1,3-dioxolane and dimethyl sulfoxide. The solubility could be almost doubled compared to the well-known acetonitrile system [1]. Furthermore the non-aqueous redox flow battery demonstrated good performance at -25°C (Figure 1).

Further studies to improve the solubility of redox-active species and to optimize battery tests are still under research.

Figure 1: Energy efficiency (EE) and coulombic efficiency (CE) of the V(acac)3 RFB in acetonitrile-1,3-dioxolane-dimethyl sulfoxid solvent mixture at -25°C.

Literature:

[1] Shinkle, A. A.; Sleightholme, Alice E. S.; Griffith, L. D.; Thompson, L. T.; Monroe, C. W., Journal of Power Sources 206 (2012) 490–496.
A Printed Carbon Nanotube Sensor on a Flexible Substrate
Authors: Tortorich Ryan P. , da Costa Tallis H. , Song Edward , Choi Jin-Woo
Published: February 2020

Printing becomes an emerging manufacturing technology for mechanics, electronics, and consumer products. Carbon nanotubes have recently been used as a material for sensors and electrodes due to their unique electrical and mechanical properties. Printed electrodes and conductive traces particularly offer versatility of fabricating low-cost, disposable, and flexible sensors and devices. While screen-printing has been a conventional method for printing conductive traces and electrodes, inkjet-printing recently attracts a wide attention due to its unique advantages including no template requirement, rapid printing at low cost, on-demand printing capability, and precise control of the printed material. Computer generated conductive trace or electrode patterns can simply be printed on a flexible substrate with proper conductive ink. However, for inkjet-printing of nanotubes to form conductive traces and electrodes, there are few challenges that need to be addressed. One is nanotube dispersion in an ink base solution while others include adjusting surface tension and controlling viscosity of the ink and treating the surface of the printing substrate. This work presents carbon nanotube ink preparation and its demonstration in chemical sensing along with our recent achievements.

It is essential to disperse carbon nanotubes to make a carbon nanotube ink. In our previous work, we have demonstrated an inkjet printed electrochemical sensor using an office HP inkjet printer and a carbon nanotube ink. Sodium dodecyl sulfate (SDS) was used as a dispersant and a surfactant in preparing the carbon nanotube ink. It should be noted that that a ratio of SDS concentration and carbon nanotube concentration would be an important factor determining the sheet resistance of a printed carbon nanotube pattern. A preliminary test result confirmed that there would be an optimum SDS:CNT ratio. For flexible sensor applications, sheet resistance change of the printed carbon nanotube patterns on a flexible substrate was measured for varying curvatures of the substrate. For a curvature up to 0.36 cm-1, the sheet resistance increase was less than 2.5% showing that the printed carbon nanotube patterns could be used for a flexible and printed sensor. Using the developed technologies, a fully printed carbon nanotube sensor on a flexible substrate will be demonstrated for chemical and biological sensing.
Application of a Methodology Combining Predictive and Descriptive Models to Describe the Influence of the Temperature on the Passive Film Steady State
Authors: Boissy Clément , Ter-Ovanessian Benoît , Normand Bernard
Published: February 2020

Passive materials are working in more and more severe conditions. By example, the development of the Proton Exchange Membrane Fuel Cell – PEMFC, leads to the used of stainless steel in higher temperature to improve the energetic efficiency. The main issue understanding the passivation process lies with the multiplicity of the phenomena modifying the behavior of the film. As describe into the Point Defect Model - PDM, the electrochemical reactions occurs at the metal/oxide interface and the oxide/solution interface. The reactivity is limited by mass transport through the oxide. Although, this phenomenon is slow because occurring into a solid phase, it could be observable by electrochemical impedance spectroscopy at regular frequencies because of a very thin oxide.

A methodology was developed to study this transport phenomenon combining the use of the PDM with a descriptive model to analyze experimental data from electrochemical impedance spectroscopy. The evolution of the main charge carrier density vs. the formation potential of the oxide is studied and according to the PDM the diffusion coefficient of the point defect through the oxide is determined. Knowing the thickness of the oxide, by means of X-ray Photoelectron Spectroscopy, the time constant of the transport is determined. Based on this value, a descriptive model is selected avoiding the over-parameterization of the EIS data.

In this way the combination of a predictive model and a descriptive one is used to objectively take into account the transport phenomena without using an over-parameterized model. This methodology is used in acidic solutions at several temperatures on two materials. Pure chromium is studied as model material and 316L as an industrial one. The conditions which leads to the consideration of the mass transport in the electrochemical impedance analysis are discussed. At higher temperature, the study of the mass transport seems to be necessary.
Considerations in the Internal Corrosion Mitigation
Authors: Pedraza Basulto Gabriela Karina , Ortega Dulce , Carrillo Irene , Cantó Jorge , Martinez Lorenzo
Published: February 2020

Corrosion is an important dominant contributing factor to failures and leaks in pipelines. It´s important that to deal with this issue, there is recommended practices to improve and maintain the mechanical integrity of upstream pipelines. They are intended to assist ups tream oil and gas producers in recognizing the conditions that contribute to pipeline corrosion incidents, and identify effective measures that can be taken to reduce the likelihood of corrosion incidents.

These factors could be low velocity and poor pigging practices allow water to stagnate in the pipelines, CO2 dissolves in water to form carbonic acid, Corrosion rates increase with increasing CO2 partial pressures for example.

This document addresses design, maintenance and operating considerations for the mitigation of internal corrosion in oil pipeline systems.
Evaluation at Pipeline Corrosion at Oil Field
Authors: Pedraza Basulto Gabriela Karina , Ortega Dulce , Carrillo Irene , Cantó Jorge , Martinez Lorenzo
Published: February 2020

It is important to know that the Petroleum industry contains a wide variety of corrosive agents . Some of these, many are unique to this industry. Thus it is opportune to group all these environments together. Corrosion problems occur in the petroleum industry in at least three general areas: production, transportation and storage, and refinery operations.

In spite of Internal corrosion of product pipelines can be controlled with coatings and inhibitor, such as amines and nitrites. The various aggressive agents shall be determined through monitoring of the physical and chemical characteristics of the fluid in contact with the system under study, providing aggressive conditions thereof. The most important elements to be determined are: Gases dissolved in water and gas (H2S, CO2 and O2), Bacteria sulfatoreductoras , Chlorides , pH.

The aim of this work is make the characterization of the fluid and determinate the corrosivity of them in a transportation pipeline. The results show us the scale of priorization of them as well as a results of the gravimetric tecniques.
Electrochemical Corrosion of 409 and 439 Ferritic Stainless Steels Employees in the Automotive Industry in NaCl and H2SO4 Solutions
Authors: Estupiñan Francisco , Robledo Patricia Zambrano , Calderón Facundo Almeraya , Tiburcio Citlalli Gaona , Miramontes Jose Angel Cabral , Garcia Ulises , Correa Paola
Published: February 2020

La industria automotriz a través del tiempo ha evolucionado en el empleo de los aceros en las diferentes partes de los vehículos, esto gracias a la tecnología de los materiales; propiedades de corrosión son a menudo, el factor decisivo entre autopartes aceptadas y rechazadas en el mercado. Debido a esto, se ha optado por la incorporación de aceros inoxidables, principalmente en aquellas partes que están expuestas al ambiente, como lo son los tubos de escape, en donde el acero inoxidable 409 encabeza la lista en producción y el cual, en algunos casos ya ha sido sustituido por el 439. En este estudio, se presenta una evaluación comparativa del desempeño entre los aceros ferríticos 409 y 439 en distintos medios ácidos de interés automotriz, salmuera al 5%, simulando ambiente salino, ácido sulfúrico (H2SO4) al 3.5% y agua como blanco; con el fin de identificar el comportamiento frente a la corrosión. Dadas las características de los acero inoxidables 409 y 439, se espera obtener corrosión por picaduras, por lo que se usaran técnicas electroquímicas mecanísticas, como curvas polarización cíclica y ruido electroquímico, y por último se contempló incluir resistencia a la polarización lineal, exclusivamente para obtener velocidad de corrosión y concordancia con las técnicas anteriores. La cinética de corrosión indica que en H2SO4 el inoxidable 439 presento la mayor velocidad de corrosión con 3.25 mm/año, en NaCl el 409 tuvo la mayor velocidad con 0.075 mm/año. Ambos materiales presentan un tipo de corrosión por picaduras en cloruro de sodio mediante las técnicas de curvas polarización cíclica y ruido electroquímico.
Evaluation of Corrosion T22 and 347H Steel Molten Salt By Electrochemical Techniques
Authors: Estrada Ariadna Trujillo , Miramontes Jose Angel Cabral , Robledo Patricia Zambrano , Tiburcio Citlalli Gaona , Calderón Facundo Almeraya
Published: February 2020

INTRODUCTION

The main applications of the SA213 and SA213-TP347H-T22 steels are in aggressive environments such as molten salts, the concentration of these along with the temperature increase generated in the corrosion rate [1-3].

METHODOLOGY

The electrochemical cell used consists of a working electrode WE1, a reference electrode and an auxiliary electrode RE AU in a molten salt electrolyte consisting of 50% V2O5 - 50% Na2SO4 at 700 ° C.

RESULTS

Current I [mA/cm2] and Potential time series [mV/cm2] were obtained to evaluate the behavior of both steels in time, and determine the type of damage caused by molten salts [1,2]. In Figure 1 two sets of time are shown in current for two types of steel.

CONCLUSIONS

Behavior TP347H SA213-SA213-T22 and corrosive attack at high temperature by means of electrochemical noise was evaluated.

The results of electrochemical noise are processed in the frequency domain [4] results acquiring noise impedance Zn.

REFERENCES

[1] Almeraya, F., A. Martinez-Villafañe, C. Gaona, M. A. Romero, and J. M. Malo. Revista de metalurgia 34, no. 1 (1998): 11-17.

[2] Tristancho, José Luis, Facundo Almeraya, and José Chacón. Scientia et Technica 3, no. 46 (2010): 163-167.

[3] Wood, Graham C. Oxidation of Metals 2, no. 1 (1970): 11-57.

[4] J. Botana-Pedemonte, A. Aballe-Villero, M. Marcos-Bárcenas. SEPTEM Ediciones, Oviedo España (2002).
Experimental Considerations in in Predicting Damage during Galvanic Corrosion
Authors: Lillard R. Scott , Haque Ziaul
Published: February 2020

Commercially available finite element software based on a solution of La Place's equation offers the opportunity for investigators to predict galvanic corrosion rates for engineering parts with complex geometries. In these routines, potentiodynamic polarization data are used to determine the current density at a given mesh point based on the solution for the potential distribution. However, stochastic processes, such as local initiation, can quickly complicate these models as they lead to deviations from the input polarization data. In this presentation we discuss these experimental considerations for two systems: the galvanic couple between Monel 500 and low alloy steel 9310 and the couple between copper and aluminum. For the case of Monel / steel in ASTM artificial sea-water, corrosion on the steel anode is relatively uniform and deviations from the polarization data are limited. However, in the case of Cu/Al in chloride solution the initiation of galvanic corrosion is localized and, more importantly, the current density at the initiation site can be orders of magnitude greater than the current density one would predict from the polarization curve for Al at the couple potential. We will present experimental data for both of these systems including measurements of damage evolution and local current density using several different techniques. These results are then compared to model predictions.
Effect of the Coating Deposition Technique on the Protective Properties of Hybrid Sol-Gel on AA2024-T3
Authors: Hernandez Miguel , Zamora Christian , Uruchurtu Jorge , Menchaca Carmina , Covelo Alba
Published: February 2020

The deposition technique effect on the corrosion properties of thin films applied on AA2024-T3 was evaluated. The deposition techniques were spin-coating, dip-coating, brush painting and spray painting. For each technique different parameters were varied in accordance to its nature of deposition. The coating synthesized by the sol-gel method carried out by a copolymerization of 3-Glycydoxypropyltrimethoxysilane (GPTMS) and tetra-n-propoxyzirconium (TPOZ) was deposited on AA2024-T3 substrate. Scanning electron microscopy (SEM) and roughness measurements revealed that the spin-coating method formed a more homogenous film. The time deposition and the surface finishing significantly modified the bond strength between substrate and sol-gel coating. The corrosion properties were assessed by Electrochemical Impedance Spectroscopy (EIS). These results revealed that the spin-coating technique not only provides better corrosion properties of the sol-gel but also a marked improvement of the corrosion resistance on aluminum at larger immersion times in saline media. The combination of ground finishing in conjunction with time deposition modifies significantly the dielectric properties of the sol-gel coating.
Investigating the Role of Electrolyte Composition and Oxide Structure in Galvanic Corrosion Susceptibility Under Atmospheric Electrolytes
Authors: Policastro Steven , Hangarter Carlos M , Martin Farrel J
Published: February 2020

The goal of this study is to develop a better mechanistic understanding of how electrolyte composition and surface oxides can influence corrosion kinetics in the electrolytes formed from atmospheric processes. It has been observed that galvanic couples between aluminum alloys and titanium or stainless steel fasteners exposed to electrolytes formed from atmospheric processes lead to very different corrosion rates (Z. Feng, G. Frankel, Corrosion, 70(2014) pgs 95-106).

In order to collect the data necessary to accomplish this goal, sixteen 2”x2” panels of AA2024, AA7075, CRES 13-8, CRES 17-4, Ti-6Al-4V, and Custom 465 were cut from panel or bar stock and polished to 600 grit SiC. The samples were then mounted in 300 mL Gamry Paracells and exposed for 18 hours to the following electrolytes: 0.6M NaCl at ambient aeration, 6M NaCl at ambient aeration, deoxygenated 0.6M NaCl saturated with nitrogen,0.6M NaCl + 0.01M HCl, 0.6M NaCl + 0.01M H2SO4, and 0.6M NaCl + 0.005M HNO3 + 0.005M H2SO4. The aluminum alloys were then anodically polarized at 0.167 mV/sec from -0.02V below EOC to + 1.5VSCE. The other alloys were polarized cathodically at 0.167 mV/sec from +0.02V above EOC to -1.4VSCE. Results for the cathodic polarization scans of the CRES 13-8PH stainless steel and the Ti-6Al-4V titanium alloy are shown in Figure 1.

The differences in cathodic current capacity for materials exposed to the same electrolyte at the same aeration level reinforces the fact that oxide microstructure plays a significant role in catalyzing reduction reactions, though the kinetics of the reaction rates may not be predicted from a simple galvanic series. Of more interest are the changes in reaction rates from acidification of the electrolyte. This suggests that the electrolyte is changing the the oxide microstructure or that new reduction reactions are supported. This is significant because overlays of the anodic polarizations of the aluminum alloys indicate that material loss rates can be orders of magnitude higher for acidified atmospheric electrolytes. These effects are being investigated using microelectrode experiments on droplets of the various electrolytes along with supporting experiments using Scanning Kelvin Probe techniques.

Acknowledgements

The authors gratefully acknowledge the financial support of the Office of Naval Research

Figure 1: Cathodic polarization curves for the titanium alloy Ti-6Al-4V and the stainless steel CRES 13-8PH in 0.6M NaCl and 0.6M NaCl + 0.005M H2SO4 + 0.005M HNO3, showing that materials with different surface oxides and in near-neutral to low-pH electrolytes can support very different cathodic reaction rates with potentially very deleterious consequences for galvanic couples with more active materials.
Hybrid Electrocatalysts of NiMo and Molybdenum Sulfide for Hydrogen Evolution Reaction
Authors: Lee Kyu Hwan , Chang Doyon , Lim Jae-Hong , Lim Dongchan , Choi Sung Mook , Lee Joo Yul , Myung Nosang Vincent
Published: February 2020

The best known catalysts for the hydrogen evolution reaction (HER) are platinum group precious metals, but the scarcity and high cost of these materials prohibit their wide-scale deployment.

As a alternatives, nickel-based alloy (NiMo, NiW, NiFe etc.) catalysts show high electrocatalytic activity for HER, but they often degrade in acidic solutions.

Recently, Molybdenum sulfides nanomaterials have drawn great attention due to their low cost, high chemical stability, and excellent photocatalytic and electrocatalytic properties in HERs. They are potentially useful if they can be tailored for the development of hydrogen energy devices. In order to enhance the efficiency of inorganic catalysts, many research efforts have been made toward the modification of material properties, the formation of composite catalysts, and the fabrication of the electrodes with nano-architecture.

In this paper, we will show the hybrid electrocatalysts of NiMo nanoparticles and molybdenum sulfide thin films for HER, showing high activity and stability. The main purpose of this work is to draw the synergetic effect of NiMo's high activity and high electrical conductivity and molybdenum sulfide's high activity and high chemical stability.

We synthesized NiMo nanoparticles and molybdenum sulfide thin films with various compositions. The electrodeposited molybdenum sulfide films had amorphous structure of MoSx and/or MoOSx. The electrochemical and spectroscopical analysis to understand the catalytic activity of hybrid catalysts will be discussed.
A Study of SOFC Cathode Degradation in H2O Environments
Authors: Pellegrinelli Christopher , Huang Yi-Lin , Taillon Joshua A. , Salamanca-Riba Lourdes G. , Wachsman Eric D.
Published: February 2020

An understanding of the degradation mechanisms of SOFC cathodes under operating conditions is essential for the development of commercial, low temperature (<700°C) SOFCs with high performance. Literature shows that the presence of H2O in the cathode impacts the performance of SOFCs. In this study, we attempt to determine the degradation mechanisms of two SOFC cathodes ((La0.8Sr0.2)0.95MnO3-x (LSM) and La0.6Sr0.4Co0.2Fe0.8O3-x (LSCF)) in H2O based on a multi-faceted approach. LSM-YSZ/YSZ/LSM-YSZ and LSCF-GDC/GDC/LSCF-GDC symmetric cells will be examined in the presence of the contaminant (H2O) under different cycling, polarization and working conditions. Symmetric cell performance will be measured by in-situ electrochemical impedance spectrometry (EIS), and directly compared to quantitative microstructural parameters obtained from FIB-SEM 3D reconstructions. FIB-SEM is a powerful technique that can help us visualize the complex cathode/electrolyte microstructure, and allow us to quantify important performance characteristics such as triple phase boundary (TPB) length and surface to volume ratio. EIS and FIB-SEM results will then be compared to kinetic rate data, determined by isotope exchange experiments, to determine correlations.
Understanding Compositional Segregations in Shaped Bimetallic Nanoparticles by Ex-Situ and In-Situ Aberration-Corrected STEM
Authors: Gan Lin , Cui Chunhua , Heggen Marc , Rudi Stefan , Strasser Peter
Published: February 2020

Compositional segregation is an important physical phenomenon in alloy materials and has significant influences on their physical and chemical properties. In particular, segregation at the surface or subsurface can drastically change the molecular adsorption properties of alloy surfaces and thus becomes a promising way to design highly active catalysts. Understanding segregations in alloy catalyst nanoparticles at atomic level is therefore crucial yet still challenging for future catalyst designs. In this talk, we will highlight some of our recent works on nano segregation effect in shaped Pt alloy catalysts for fuel cell technologies. Particular attentions will be placed on the atomic imaging of nano segregation by using state-of-the-art ex-situ and in-situ aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS). In particular, we discovered distinct compositional segregations in octahedral PtxNi1-x nanoparticles, which featured Pt-segregation at the edges/corners and Ni-segregation at the facets (Figure 1) . We explored the physical origin for these distinct segregation behaviors and their impact on the catalytic activities and stability for fuel cell reactions. This will be further complemented by in-situ STEM-EELS experiments to study the structural and compositional evolution of Pt alloy nanoparticles during nanoparticle synthesis, post thermal annealing and solution-phase electrocatalysis, shedding important light on catalyst designs with desired segregation patterns and chemical properties.
Computational Modelling of Cation Contamination in PEFCs
Authors: Uddin Md. Aman , Pasaogullari Ugur , Molter Trent
Published: February 2020

Polymer electrolyte membrane (PEM) is a key component of polymer electrolyte membrane fuel cell (PEFC). It is vulnerable to cationic impurities that are present in the air and fuel stream or that may have originated from the cell, stack or balance of plant components. Almost all foreign cations have higher affinity to sulfonic acid group than proton and the presence of foreign cation in the membrane or catalyst layers results in reduced ionic conductivity, increased electro-osmotic drag, and reduced water content (1).

In this study, a steady, one dimensional cation (Na+) contamination model of membrane electrode assembly (MEA) of PEFC (shown in figure 1) is developed by solving the coupled transport phenomena related to the foreign cation, water, and oxygen. Concentrated solution theory is utilized to solve the cation transport equation based on Serincan et al.’s model (2) and dilute solution theory for water, hydrogen, and oxygen transport. A spherical agglomerate model is considered in the cathode catalyst layer (CCL) to describe effects of foreign cations in the catalyst layer. To separate the effects of cations on different transport phenomena, first no contamination case is solved and then contamination effects are added one by one to the cation transport, water transport, and oxygen transport and finally to the Nernst equation.

Cation (Na+) contamination in the air stream found to cause several detrimental effects on the performance of PEFC. The main effects are: (a) cation replaces proton and occupies sulfonic acid sites in ionomer. It can occupy up to 96% sites in the cathode catalyst layer (CCL); (b) It causes serious water depletion in the ionomer due to decrease in water diffusivity; (c) It decreases the oxygen diffusivity causing a decrease in dissolved oxygen concentration in CCL; and (d) It decreases the open circuit voltage (OCV) in CCL due to reduction in proton concentration in the ionomer phase. These contamination effects on each parameter decrease the protonic current density and combined effects result in a reduction of current density from 0.72 A/cm2 to 0.25 A/cm2at a cell voltage of 0.7 V (shown in figure 2).

Acknowledgements

The authors are grateful for the financial support of the Department of Energy (DOE)-EERE, DE-EE00000467 (University of Hawaii, prime contractor, Jean St-Pierre, PI).

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. Hydrogen Energy,
35, 11 (2010).
Polymer Electrolyte Membrane Fuel Cells: Characterization and Diagnostics
Authors: Dhanushkodi Shankar , Schwager Maximilian , Mérida Walter
Published: February 2020

The normal operation of proton exchange membrane fuel cells (PEMFCs) can induce significant temperature, humidity, pressure or concentration gradients across the cell’s active area. The overall performance and stability can be affected negatively by these gradients. For example, localized transient changes in environmental conditions may contribute to material degradation, and ultimately, to cell failure.

We report on new diagnostic techniques and methodologies that have been developed to characterise PEMFC material properties, and the inhomogeneities across the active area of a working cell. Specifically, we will describe ex situ techniques for membrane electrode assembly (MEA) materials characterisation, and in situ techniques for the spatially resolved characterization of PEMFC performance. These techniques incorporate independent control over local potentials with concurrent membrane water content characterization (via high-frequency resistance measurements). Our testing hardware features sixteen fully isolated segments over a 42 cm2 active area, reference electrode capabilities, and individual segment control. This configuration enables the measurement of localised anode and cathode overpotentials separately.

The technique’s versatility will be illustrated by effective platinum surface area (EPSA) measurements across the active under accelerated stress tests (ASTs) conducive to platinum dissolution. Each segment in a membrane electrode assembly was exposed to 10,000 cycles of Pt dissolution AST separately. The beginning-of-life EPSA was calculated via cyclic voltammetry, and the catalyst layer morphology and properties were found to change during the AST. Impedance measurements were obtained in H2/N2 conditions in order to map the ionic conductivity and the polarization resistance of the catalyst layer across the segmented cell. Higher EPSA and performance loss were observed in segments near the fuel cell outlet compared to those near the reactant inlets.
Porphyrinic Carbon Electrocatalysts Decorated with Ultralow Active Metal for Oxygen Reduction Reaction (ORR)
Authors: Hwang Sun-Mi , Jeon Sang-Yeon , Cheon Jae Yeong , Joo Sang Hoon , Choi YongMan , Sohn Young-Jun , Yang Tae-Hyun , Park Gu-Gon
Published: February 2020

The high cost combined with limited performance and low durability of precious metal based-catalysts are major technical barriers to overcome for the commercialization of polymer electrolyte fuel cells (PEFCs). Therefore, exploring the cost effective electrocatalyst with enhanced activity focuses on (1) Pt-M alloy/dealloy with inexpensive transition metals and (2) non-precious metal based electrocatalysts. Unfortunately, the performance of non-precious metal-based materials is still inferior to that of Pt-based catalysts in respect of cell activity and lifespan. Recently, although we found that the self-supported ordered mesoporous porphyrinic carbon (M-OMPC) doped with transition metals, which revealed to have a comparable catalytic activity with Pt/C towards oxygen reduction reaction (ORR), a relatively large amount of catalyst (> 0.6 mg/cm2) is required to be loaded. The catalytic behavior of M-OMPC for ORR is depended on the morphology and mass of the catalyst on the electrode. Thus, a thick membrane electrode with a high catalyst loading is unfavorable for the cell performance in terms of cell resistance and conductivity. In this study we demonstrated an alternative catalyst combined with M-OMPC as a substitution for carbon supports generally used and a trace of Pt particles. The ultralow Pt (<5 wt%) loading on M-OMPC (Pt/M-OMPC) showed a 10-fold enhancement of ORR kinetic activity compared to that of M-OMPC at 0.9 V RHE. The Pt mass activity was also improved by two times compared to that of Pt/C at 0.85 V RHE.
Kinetics of Sodium Borohydride Hydrolysis at the Cobalt with a Fiber Structure Modified with Gold Nanoparticles
Authors: Norkus Eugenijus , Balciunaite Aldona , Lichusina Svetlana , Simkunaite Dijana , Stalnioniene Irena , Zieliene Albina , Vaiciuniene Jurate , Selskis Algirdas , Tamasauskaite-Tamasiunaite Loreta
Published: February 2020

Among chemical hydrides sodium borohydride is widely used as a source for a hydrogen generation during its catalytic hydrolysis. This attention is determined by its features such as a high hydrogen storage capacity, nontoxicity, good storability, easily controlled hydrogen generation rate. The development of new catalysts with high activity in the hydrolysis reaction of borohydride and durability plays an important role in the hydrogen generation for fuel cells.

This work presents the study of catalytic activity of cobalt with a fiber structure deposited on the copper surface and modified with gold nanoparticles towards the hydrolysis of borohydride. Cobalt coatings with the thickness of ~3 µm were deposited from the electrolyte described in Ref. [1]. Au crystallites were deposited on the Co/Cu surface (denoted as Au(Co)/Cu) via the galvanic displacement technique. The Co/Cu catalysts were immersed into the 1 mM HAuCl4 + 0.1 M HCl solution at 25 oC for 0.5, 1 and 5 min, respectively [2]. The morphology, structure and composition of the prepared catalysts were examined by means of Field Emission Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy, X-ray diffraction and Inductively Coupled Plasma Optical Emission Spectroscopy.

It has been determined that the Au loadings were 10.8, 22.4 and 84.4 µg cm-2 in the prepared Au(Co)/Cu catalysts after the immersion of Co/Cu into the gold-containing solution for 0.5, 1 and 5 min, respectively. The data of hydrogen generation from an alkaline sodium borohydride solutions using the Co/Cu and different Au(Co)/Cu catalysts under various conditions are presented.

It has been determined that the temperature and amount of catalysts have exceptional influence on the rate of hydrogen generation from alkaline sodium borohydride solutions.

References

[1] E. Juzeliunas, S. Lichusina. Patent of the Republic of Lithuania No. 5481 26.03.2008.

[2] L. Tamasauskaite-Tamasiunaite, A. Jagminiene, A. Balciunaite, A. Zabielaite, J. Vaiciuniene, A. Selskis, R. Juskenas, E. Norkus. Int. J. Hydrogen Energy 38 (2013) 14232-14241.
Study of Azoles as Bifunctional Additives for Proton Exchange Membranes Melt-Processing from LSC and SSC Perfluorosulfonic Acid Ionomers
Authors: Mokrini Asmae
Published: February 2020

This work investigates the potential use of azoles as bifunctional additives for proton exchange membranes (PEM) manufacturing through direct melt-processing of acidic ionomers. The development of high-volume manufacturing processes to prototype PEM fuel cell components with a reduced number of steps is vital to reduce system cost and complexity, and to meet the demands of high volume production and durability requirements especially for automotive applications.

The strong ionic associations in ionomers act generally as physical cross-links, increasing by several orders of magnitude both melt-viscosities and relaxation times, resulting in ionomeric materials that are very difficult to melt-process with high shear rate processes such as melt-casting or melt-blowing. The strength of the ionic interactions in ionomers, and hence their physical and mechanical properties, depends on the acidity of the pendent anion. Polymers modified with the stronger acid, such as sulfonic acid (pKa~1), exhibit more dramatic changes in thermal, viscoelastic, and rheological properties than those modified with the weaker carboxylic acid (pKa~4-5). However, most ionomers may be melt-processed in very low shear rate operations such as compression-molding, which reveals that these ionic associations are not permanent cross-links and can be reversibly disrupted under suitable conditions.

The approach investigated is based on the use of selected bi-functional additives that act as a SO3H groups protection and a melt-processing aid.[1] The additives selected are highly polar additives with relatively high boiling points that are expected to interact with the ion-rich aggregates that compose the nanophase separation in ionomers and act as plasticizers which expectantly improve the viscoelastic behavior during melt processing. Additives from the azole family, imidazole, 1,2,4-triazole and benzimidazole have been investigated as potential bifunctional additives. This presentation, will discuss the results obtained with four commercial PFSA ionomers Nafion® DE-2020 and NR-40 with long side chain (LSC), and Aquivion® D83-24B and D79-20BS with short side chain (SSC).

Figure 1. melt-processed samples of Aquivion® D79-20BS a) no additive, b) with 2 mol of imidazole/mol of SO3- and c) with 2 mol of 1,2,4-triazole/mol of SO3-

[1] US patent application 61/767,849 "PROCESS FOR PRODUCING ION EXCHANGE MEMBRANES BY MELT-PROCESSING OF ACIDIC PFSA IONOMERS"
Development of Hybrid Membranes Nafion-ZrO2 for PEM Fuel Cells
Authors: Gutiérrez Cynthia Karina , Montemayor Sagrario M. , Rivas Gandara Sandra , Pineda Jose Luis , Ledesma García Janet , Chavez Abraham Ulises , Arriaga Luis Gerardo
Published: February 2020

Six hybrid membranes were synthesized by the sol-gel process, Nafion was used as a polymeric matrix and it was modified with 1% wt. of N-HfO2, N-ZrO2, N-La2O3, N-(HfO2-ZrO2), N-(HfO2-La2O3) and N-(ZrO3-La2O3), with a thickness interval of 120-160μm. The proton conductivity (CP) was evaluated by four-electrode method using a commercial conductivity cell (Bekktech®), a potenciostat-galvanostat (Autolab PGSTAT 302) in connection with a Fuel Cell Test Station (PSCompuCell of Electrochem®) was used to evaluate the hybrid membranes in a fuel cell conditions, in which relative humidity and temperature were established at 50-100% and 30-120 ˚C respectively. The N-La2O3 and N-HfO2 membranes showed a CP of 0.12 S/cm-1 (100%RH-30˚C) and 0.13-0.11 S/cm-1 (100%RH-80˚C - 50%RH-120˚C) respectively, while the CP of Nafion 115 is 0.09 S/cm-1 (100RH-30˚C). Water up-take and swelling at 30-100 °C was also measured. First results show a promising incorporation of a N-HfO2 membrane for PEM Fuel Cells performance at high temperature and low relative humidity.
Invited: Electrochemical Hydrogen Compression
Authors: Bouwman Peter Jaime , Konink Jonne , Semerel Daniel , Raymakers Leonard , Koeman Menno , Kout Wiebrand , Dalhuijsen Wouter , Milacic Evan , Mulder Martijn J.J.
Published: February 2020

The company HyET pioneers Electrochemical Hydrogen Compression (EHC) with strong focus on advancing our rate capability and energy efficiency for compression and simultaneous purification. Additional advantages over mechanical pumping are: isothermal compression vs. adiabatic, no moving parts, instantaneous, variable pump rate, included metering, and bi-directional control (de-/compression).

Previously, HyET demonstrated a compression record showing pressures as high as 100MPa are feasible in one single stage using EHC. Simple scalability of the ‘active’ membrane area enabled us to produce stacks with a pumping capacity around 2 kg per day. Stand-alone systems are designed in ongoing JTI funded programs containing multiple parallel stacks and delivering up to 100 kg per day upon request.

Only hydrogen gas is transported through the solid, proton-conducting membrane through conversion at the catalysed membrane surface according to the following reaction equation: H2 = 2 H+ + 2 e-

Other gases that may be present in the mixture stay behind because these cannot follow this pathway.

Proprietary membranes have been developed at HyET to minimise passive permeation of all gases. The primary reason is the reduction of hydrogen back-diffusion, which goes at the expense of the energy efficiency. Secondary, our bespoke membranes automatically show better selectivity towards hydrogen and deliver enhanced purification ability, especially in combination with positive pressure differential.

This presentation will provide insight in EHC working principles, current abilities and potential solutions made available for building a viable hydrogen infrastructure, enabling market application such as:

Automotive (Home) refuelling

Distributed energy storage from sustainable supply

Harvesting from impure hydrogen gas sources

Hydrogen injection and selective extraction from natural gas pipelines
Can CO-Tolerant Anodes be Economically Viable for PEMFC Applications with Reformates?
Authors: Wang Jia X. , He Ping , Zhang Yu , Ye Siyu
Published: February 2020

Recent advances in removing carbon monoxide (CO) from about 1% to ~10 ppm level via preferential oxidation (PROX) of CO in hydrogen feeds[1] renewed the interest in developing CO-tolerant catalysts for using inexpensive reformates as the fuel other than pure hydrogen. The savings would be considerable since the 2015 price target for hydrogen produced by reforming natural gas is $2 per kg H2, viz., ~40% cheaper than pure hydrogen generated by water electrolysis at $3.5 per kg H2
[2].

RuPt alloy and Ru-Pt core-shell nanocatalysts have been studied as CO-tolerant anode catalysts for PEM fuel cells. However, dissolution of Ru occurs at occasional high potentials experienced at the anode, causing performance decay. To address this issue, we developed a surfactant-free and scalable synthesis method to produce ordered Ru(core)-Pt(shell) nanoparticles with tunable Pt shell thickness of 1 to 3 atomic layers. Commonly found disordering in Ru cores was attributed to defect-induced partial alloying, and was eliminated by annealing Ru cores before coating Pt shells. The single crystalline particles with a sharp Ru-Pt boundary and ordered transition from Ru’s hexagonal close-packed lattice to Pt’s face-centered cubic structure were confirmed by atomically resolved scanning transmission electron microscopy images coupled with density functional theory calculations[3].

We shall mainly show that a complete Pt bilayer shell protects Ru from dissolution during potential cycles up to 0.95 V while exhibiting enhanced CO-tolerance. The results demonstrate a promising anode with less than 0.1 mg cm-2 total metal loadings for operating PEM fuel cells with reformates. In order to find optimal Pt shell thickness and metal to carbon weight ratio, we developed an electrochemical testing method using standalone, gas-diffusion electrodes for evaluating the performance without and with CO in hydrogen. The findings will be discussed in comparison with the results of membrane electrode assembly tests under realistic conditions, shedding light on causes of deactivation effects and ways to alleviate them.

Acknowledgements

The work at Brookhaven National Laboratory was supported by U.S. Department of Energy under contract DE-AC02-98CH10886 and Power Bridge NY.

References

[1] K. Liu, A. Wang, T. Zhang, ACS Catalysis
2012, 2, 1165-1178.

[2] Satyapal, S. http://www.hydrogen.energy.gov/pdfs/htac_apr13_1_satyapal.pdf, Fuel cell technologies update. page 17 (2013).

[3] Y.-C. Hsieh, Y. Zhang, D. Su, V. Volkov, R. Si, L. Wu, Y. Zhu, W. An, P. Liu, P. He, S. Ye, R. R. Adzic, J. X. Wang, Nat Commun
2013, 4, 2466.