bluuebunny/crossref_metadata_2025_split huggingface dataset:
Ionomer Thin Films for PEM Fuel Cells
Authors: Kusoglu Ahmet 
Published: February 2020

Ion-conductive polymers (ionomers) such as perfluorosulfonic-acid (PFSA) have been widely adopted in polymer electrolyte fuel cells (PEFCs) as a polymer-electrolyte membrane (PEM) due to their ability to conduct ions in hydrated conditions without losing stability. The role of ionomers in PEFCs, however, is not limited to PEM as it also extends to the porous catalyst layers (CL) where ionomers exist as nanometer-thick electrolyte thin films binding the catalytic agglomerates and facilitating proton transport. Moreover, the ionomer’s properties differ from the bulk (PEM) when it is confined to these nanometer thicknesses where its behavior is influenced by its interfaces with the air and the catalytic sites, such as carbon/platinum. In particular, this phenomenon of confinement onto Pt sites could have important implications for the mass-transport limitations observed in fuel-cell catalyst layers, which have been related to the transport resistances at the ionomer thin-film. Thus, despite an ever-growing number of studies on ionomer membranes for PEM, for desired next-generation PEFCs, it is important to characterize catalyst ionomers and elucidate factors controlling their transport properties. In particular, if is of great interest to develop model systems for thin films that can mimic catalyst ionomer behavior and establish their structure/functionality to optimize ionomer interfaces and improve CL performance.
This tutorial talk will present an overview of PFSA ionomer thin films and their current state of understanding with a focus on recent developments in advanced diagnostics and the information they can provide to establish their structure/function relationship. In addition, applicability of the various diagnostics techniques in the thin-film regime (5 to 500 nm) will be discussed, including the use of state-of-the-art techniques, such as Grazing-Incidence X-ray scattering (GIXS). First, thin films of dispersion-cast ionomers on model substrates will be explained in relation to catalyst ionomers. Swelling and water uptake behavior as well as various transport properties of these thin films will be examined. Then, it will be discussed how an ionomer’s phase-separated nanostructure and properties are correlated and impacted by film thickness (i.e., confinement effect) and substrate interactions, especially below 50 nm. Lastly, it will be explored how EW and side-chain chemistry influence the nature of ionomer-substrate interactions and thus the structure and properties of PFSA thin films. The collected data set will be analyzed to illustrate the bulk-to-film transition of ionomers of various equivalent weights used in fuel-cells. The results will be elucidated to highlight the key aspects of ionomer thin films, provide insight into optimization of their structure and functionalities for fuel-cell catalysts, and discuss implications for PEFC performance.
(Invited) Electrochemical Fuels Production Using High Temperature Alkaline Electrolytes
Authors: Xu Hui 
Published: February 2020

Anion exchange membranes (AEMs) have potential applications in a variety of energy conversion technologies (e.g. fuel cell, electrolyzer), due to enabled adoption of non-precious metal catalysts. However, these polymer-based AEMs generally have poor stability, particularly at elevated temperatures (> 80 ℃), limiting their viable applications. On the other hand, operating electrochemical cells at higher temperature can improve the electrode kinetics, simplify heat management, and increase the system efficiency. Here we report an alkaline system that utilizes molten alkaline (e.g., lithium, sodium, or potassium hydroxide) impregnated into a porous metal oxide (MO) matrix as the electrolyte. The operating temperature can vary from 250 to 500 °C, depending on the category and ratio of each individual electrolyte. A key factor that will influence the success of this technology is the microstructures of the porous oxide matrices. Their thickness, porosity, pore size and structure largely determine whether they can successfully retain molten hydroxides in their pores, particularly over extended period of time.
The single and binary hydroxide with 25 wt% (e.g., MO-LiOH-25 and MO-LiOH-NaOH-25) electrolyte showed OH- conductivity of 0. 15 S.cm-1 and 0.5 S.cm-1, respectively, at 500 ℃, demonstrating significant advantage of this alkaline electrolyte. As two applications, water electrolysis and electrochemical synthesis of ammonia using this composite electrolytes are being tested and will be reported. Cell components and process conditions will be optimized to maximize the performance of the electrochemical cells.

Acknowledgements

Financial support from DOE EERE Fuel Cell Technology Office under award # DE-EE0007644
Electrochemical Reduction of Carbon Dioxide at Alloy Systems: Cu-In and Cu-Bi
Authors: Zangari Giovanni 
Published: February 2020

The ability to maintain high efficiencies while simultaneously tuning the selectivity of the electrochemical reduction of CO2 (ERC) using low cost electrodes has proven to be one of the greatest obstacles to the widespread commercialization of this technology. In this study, we prepare dendritic copper-indium and copper-bismuth alloys of various compositions and investigate their catalytic activity and selectivity towards the reduction of CO2. The Cu-In electrocatalysts are increasingly dendritic with higher In fraction and, depending on composition, consist of mixed phases of Cu, In and Cu-In intermetallic phases. ERC at these electrodes produces formate at high efficiencies (up to 62% with a 80 at% alloy, -1 V)) while also tuning the CO/H2 ratio to achieve an ideal syngas composition with a 40 at% In alloy, -1 V. The observed product distribution as a function of alloy composition and applied potential is rationalized in terms of the relative adsorption strengths of CO and COOH intermediates at Cu and In sites, and their distinct variation with applied potential may be induced by the differences in electronic structure.
We also studied dendritic Cu, Bi, and Cu-Bi alloys with various compositions. The dendritic structures exhibit a high density of defect sites such as grain boundaries and twins, with these defects being increased at alloy dendrites. While the pure metals exhibited high H2 production and relatively high formate formation, the alloys exhibit a lower overall current density and a much higher selectivity towards formate, up to about 90%. Most importantly we show in this work that a combination of a d metal (Cu) with a p-block metal (In, Bi) with intimate contact between the two components is capable to tune the relative adsorption strength of the intermediates, thus steering the product distribution towards formate. The relatively purity of this product would be of interest for the direct feed of a direct formate fuel cell. Differences between In and Bi will be discussed in terms of the affinity for oxygen.
This study highlights the opportunities of using alloys to enhance control over the product distribution and suggests that suitable alloys could be promising catalysts for the inexpensive and efficient production of fuels.
In-Situ XRD during Electrochemical CO Reduction on Cu
Authors: Bertheussen Erlend , Scott Søren B. , Hogg Thomas , Hahn Christopher , Higgins Drew Christopher , Lin John , Landers Alan Taylor , Jaramillo Thomas F , Chorkendorff Ib , Seger Brian 
Published: February 2020

Almost all-successful CO2 and CO reduction catalysts to higher chain carbons are based on copper,1 however various facets and pre-treatments of copper have shown to give a wide variety of product selectivity.2, 3 Currently there are many unanswered questions regarding active sites and mechanisms thus fundamental studies are essential for this reaction. This talk will focus on in-situ monitoring the copper-copper oxide crystal structure at a variety of oxidative and reductive potentials. Using the synchrotron facilities at the SLAC national laboratory we were able to achieve an in-depth understand both of how deep the native oxide layer penetrates and how this oxide becomes reduced as we shift towards more cathodic potentials. This talk was also discuss under what conditions there is an amorphous copper oxide layer and what conditions lead to a crystalline copper oxide surface. This will be followed by a discussion of how the copper oxide effects the crystal structure of the metallic copper at the operating conditions.
The in-situ work focused on a preferentially oriented <111> thin film, however there were other facets to a lesser extent. This talk will discuss the degree to which these facets are modified during in-situ operating conditions at various potentials.

Hori, Y.; Wakebe, H.; Tsukamoto, T.; Koga, O., Electrocatalytic Process of CO Selectivity in Electrochemical Reduction of CO2 at Metal-Electrodes in Aqueous Media. Electrochimica Acta
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39 (11-12), 1833-1839.

Li, C. W.; Ciston, J.; Kanan, M. W., Electroreduction of carbon monoxide to liquid fuel on oxide-derived nanocrystalline copper. Nature
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508 (7497), 504-+.

Hori, Y.; Takahashi, I.; Koga, O.; Hoshi, N., Electrochemical reduction of carbon dioxide at various series of copper single crystal electrodes. Journal of Molecular Catalysis a-Chemical
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199 (1-2), 39-47.
Electrodeposition of Ag Catalysts for Electrochemical CO2 Reduction
Authors: Ham YuSeok , Kim Myung Jun , Lim Taeho , Kim Soo-Kil , Kim Jae Jeong 
Published: February 2020

The electrochemical reduction of CO2 to useful products has been considered as a promising technology for reducing the greenhouse gas [1]. Among the various products, CO has been targeted in this study since it can be directly used in Fischer-Tropsch process [2]. For CO production, Ag has received the great attention due to its electrocatalytic performance and moderate price compared to other noble metals [3, 4].
To improve the performance of the catalysts, structure engineering to enlarge the surface area have been widely investigated [4, 5]. In particular, fabrication of nano catalysts with large surface area on the carbon paper is required for MEA-type CO2 electrolyzer for large scale production. For this purpose, electrodeposition is efficient method to fabricate the catalyst on the carbon paper for various gas reduction reactions. In addition, the morphologies and coverage of catalyst layer could be easily controlled using various deposition method such as pulse electrodeposition [6, 7].
In this research, a galvanostatic pulse electrodeposition method was used to fabricate the Ag catalyst on the carbon paper. Increasing the off-time value during the galvanostatic pulse deposition, large surface area was developed. Using the optimized deposition conditions, high current density of CO production was achieved with large surface area of Ag catalysts. The CO production was further enhanced by removal of produced gases bubbles with surfactant.
References
[1] B. Endrődi et al., Progr. Energy Combust. Sci., 62, 133-154 (2017).
[2] Q. Lu et al., Nano Energy, 29, 439-456 (2016).
[3] J. Rosen et al., ACS Catal., 5, 4293-4299 (2015).
[4] Q. Lu et al., Nat. Commun., 5, ncomms4242 (2014).
[5] A. S. Hall et al., J. Am. Chem. Soc., 137, 14834-14837 (2015).
[6] G. Adilbish et al., Int. J. Hydrogen Energy, 42, 1181-1188 (2017).
[7] A. Egetenmeyer et al., Int. J. Hydrogen Energy, 42, 13649-13660 (2017).
*Corresponding author E-mail: jjkimm@snu.ac.kr, Tel: +82-2-880-8863
**Corresponding author E-mail: sookilkim@cau.ac.kr, Tel: +82-2-820-5770
(Invited) Low Temperature Electrolysis for Hydrogen and Oxygen Generation - a Tutorial on Catalyst and Electrode Development for Proton and Anion Exchange Membrane-Based Systems
Authors: Ayers Katherine E 
Published: February 2020

Hydrogen generation via electrolysis is rapidly gaining international interest for energy storage applications due to the carbon-free chemical cycle and response characteristics of the technology. At the same time, the need for a sustainable source of hydrogen has been widely recognized, not just as a potential transportation fuel, but to limit CO2 production and fossil fuel consumption from existing industrial processes such as ammonia generation. Currently over 95% of hydrogen is made from fossil fuels through natural gas reforming or coal gasification. Significant growth has therefore occurred in recent years in water electrolysis research, especially in catalyst research for the hydrogen (HER) and oxygen (OER) evolution reactions.
Commercial proton exchange membrane (PEM)-based electrolysis has reached scales of several hundred kg/day, providing a relevant pathway for industrial scale hydrogen generation. PEM electrolysis also has tremendous potential for continuing cost reduction, leveraging system and manufacturing scaling laws as well as leveraging advancements in PEM fuel cell materials, manufacturing, and analysis tools. Order of magnitude improvements in some of the highest cost elements are easily achievable. Many of the technology elements are known, but need to be refined and validated in a manufacturing environment, including modifications in materials and methods of fabrication. At the same time, alternate pathways based on anion exchange membranes (AEMs) are showing promise, as membrane chemistry has advanced and understanding of electrode processing has developed. The basic environment of the AEM electrolysis cell enables a broader range of catalyst materials and the potential to eliminate the highest cost materials such as platinum group metals and commercially pure titanium from the stack.
However, in both the AEM and PEM case, there are complex interactions at the electrode level which need to be considered in catalyst and membrane development. First, the liquid electrolyte environment used for catalyst activity screening, where all of the catalyst surface is accessible to the reactant is often not comparable to a complex, 3-dimensional, ionomer-based electrode. Also, similar to automotive fuel cells, the operating environment is highly important and should be considered when claiming improvements over state of the art. For example, catalyst performance at very low current densities may indicate inherent activity but may not represent capability at typical device operating currents. Similarly, a membrane which cannot operate at differential pressure may be highly limited in utility even if more efficient than current commercial solutions. This talk will describe some of the complex interactions that need to be considered, typical operating requirements, and stages of development where relevant conditions should be introduced.
Model-Supported Analysis of Degradation Phenomena of a PEM Water Electrolysis Cell Under Dynamic Operation
Authors: Frensch Steffen Henrik , Simon Araya Samuel , Olesen Anders Christian , Kær Søren Knudsen 
Published: February 2020

PEM water electrolysis for large-scale energy storage may also serve as an actor for grid stability in energy grids with a high share of fluctuating, renewable energy sources. The major challenge the technology is facing is to reduce the system cost. In that context, acceptable lifetime under variable operation conditions has yet to be proven. Degradation studies are still scarce, but considered crucial for a further market implementation.
In this study, a small single cell set up is utilized to extract information about degradation mechanisms. The major parameters of interest are the operational conditions. Therefore, long term tests are performed with electrochemical characterization through polarization curves and EIS while changing the input signal.
Preliminary results of the study show a high reversible share of the voltage increase, which can be recovered through a short interruption of cell operation (see figure). That is particularly interesting for grid service applications, since the data suggests that dynamic operation may be beneficial.
However, the voltage profiles alone do not reveal enough information about what causes the degradation. Periodically performed EIS experiments on the operational cell support the analysis of which part of the cell causes performance loss. It was found that the purely ohmic contribution to cell impedance is mostly affected in the initial period and stabilizes afterwards. Other contributions on the other hand influence cell aging throughout the whole investigated timespan of 1000h so far.
Furthermore, a model-based analysis of the changes in polarization curves over time is carried out as in previous studies on cell performance. The extracted parameters are linked to activation processes and ohmic contributions that stem from the membrane and the contacts resistances.

Figure 1
Non-Precious Electrocatalysts for Anion Exchange Membrane Water Electrolysis Cell
Authors: Choi Sung Mook , Choi Woo-Sung , Seo Min Ho , Jang Myeong Je , Park Yoo Sei , Lee Kyu Hwan 
Published: February 2020

The hydrogen has been recognized as a clean, nonpolluting and unlimited energy source that can solve fossil fuel depletion and environmental pollution problems at the same time. Water electrolysis has been the most attractive technology in a way to produce hydrogen, because it does not emit any pollutants compared to other methods such as natural gas steam reforming and coal gasification etc. In order to improve efficiency and durability of the water electrolysis, comprehensive studies for highly active and stable electrocatalysts have been performed. The platinum group metal (PGM; Pt, Ru, Pd, Rh, etc.) and its oxide catalysts showed a higher activity and stability compared with other non-precious catalysts in operating condition. It is necessary to develop non-precious catalysts with high activity and durability because the PGM catalysts are expensive materials with insufficient it’s reserves. In the water electrolysis field, the numerous researchers have been focused on the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) because the OER and HER are a key process (slow kinetics) compared with other resistances such as bubble, electrolyte, diaphragm, membrane, etc. On a point of view of a catalyst, slow kinetics and the use of precious metal (PGM) for high performance should be solved to popularize water electrolysis.
The target of this study is the development of non-precious catalysts with high activity via simple and efficient synthesis method that is a wet-chemical based method. The Ni-LaCeO/C (HER catalysts) and CuCoO (OER catalyst) were synthesized through the co-precipitation with oxidation and reduction heat treatment. The catalysts were characterized by various physicochemical analyses such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). To investigate electrocatalytic properties of prepared catalysts, we carried out electrooxidation activity measurements such as cyclic voltammetry (CV), linear sweep voltammetry (LSV), long-term stability test, and electrochemical impedance spectroscopy (EIS). The relationship between their physicochemical properties and electrocatalytic activities will be explored and discussed.
Role of Surface Area on the Performance of Iron Nickel Nanoparticles for the Oxygen Evolution Reaction (OER)
Authors: Acharya Prashant , Burrow James , Greenlee Lauren F 
Published: February 2020

Iron nickel based bimetallic catalysts have recently emerged as one of the best candidates for oxygen evolution reaction (OER) in alkaline conditions [1]. It is crucial to understand the composition and morphology of iron nickel nanoparticles to optimize the catalysts for enhanced performance [2]. One key aspect to understand in the study of OER performance, in addition to the function of composition and morphology, is the physical surface area and the electrochemically active surface area (ECSA) of the catalysts. In this study, three different iron nickel nanoparticles will be synthesized. The three nanoparticles will be varied based on morphology (alloy vs core-shell) and composition (high vs low amount of stabilizer). Brauner-Emmett-Tellet (BET) surface area analysis will be conducted on the as synthesized iron nickel nanoparticles using Autosorb-iQTM to calculate the physical surface area while electrochemical impedance spectroscopy (EIS) will be employed to quantify the ECSA [3]. In addition, electrochemical performance will be measured using techniques such as cyclic voltammetry (CV), chronopotentiometry (CP), and chronoamperometry (CA).
[1] M. W. Louie and A. T. Bell, J. Am. Chem. Soc., 135, 12329 (2013)
[2] S. L. Candelaria, N. M. Bedford, T. J. Woehl, N. S. Rentz, A. R. Showalter, S.
Pylypenko, B. A. Bunker, S. Lee, B. Reinhard, Y. Ren, S. P. Ertem, E. B. Coughlin, N. A.
Sather, J. L. Horan, A. M. Herring and L. F. Greenlee, ACS Catal., 7, 365 (2017).
[3] C.C. McCrory, S. Jung, J. C. Peters, and T. F. Jaramillo, J. Am. Chem. Soc., 135, 16977
(2013)
Carbon-Free Perovskite Oxide Oxygen Evolution Reaction Catalysts for AEM Electrolyzer
Authors: Chung Hoon T , Lee Albert Sung Soo , Kim Yu Seung , Fujimoto Cy , Wang Lin-Wang , Teeter Glenn , Bender Guido , Zelenay Piotr 
Published: February 2020

In alkaline electrolysis of water, kinetic limitations account for up to 85% of the total efficiency losses [1]. In particular, the efficiency of water electrolysis is largely limited by the high overpotential of the oxygen evolution reaction (OER). Therefore, reducing the reaction overpotential at the OER catalysts is critical for the overall efficiency improvement of alkaline water electrolysis.
Perovskite oxides are promising non-precious metal OER catalysts showing high activity in oxygen evolution in alkaline electrolytes, comparable to that of the state-of-the-art IrO2 catalysts [2], but their stability is in need of improvement. As these oxides exhibit relatively low electronic conductivity carbon, typically acetylene black (AB), is added to enhance their conductivity. However, the thermodynamic potential of carbon oxidation (C + 4OH- → CO2 + 2H2O + 4e-) is 1.03 V vs. RHE at pH 14, much below the OER onset potential. Carbon oxidation causes an increase in the electrode resistance and weakens the carbon-catalyst interaction, eventually limiting the electrolyzer lifespan. Consequently, improving the stability and electronic conductivity of the perovskite-oxide OER catalysts with further enhancement of the OER activity is critical to the application of perovskites as OER catalysts for anion exchnange membrane (AEM) electrolyzer.
In this work, perovskite (La1-xSrx)CoyFe1-yO3-δ (LSCF) was chosen to study the OER activity, stability, and electronic conductivity. In typical ABO3 perovskites, the valance state of cations, i.e., the sum of A and B, should be +6 to balance the overall oxygen valence of -6. The non-stoichiometry caused by the change in the ratio of La/Sr and Co/Fe in the LSCF will affect the OER activity, stability and the electronic conductivity. The effect of this non-stoichiometry of LSCF on the OER performance in alkaline electrochemical cells and AEM electrolyzer, in conjunction with DFT calculations, will be presented in this talk.

Acknowledgements

This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the HydroGEN Consortium.

References

[1] J. Greeley, N. M. Markovic, Energy Environ. Sci., 5 (2012) 9246-9256.
[2] J. Suntivich, K. J. May, H. A. Gasteiger, J. B. Goodenough, Y. Shao-Horn, Science, 334 (2011) 1383-1385.