bluuebunny/crossref_metadata_2025 huggingface dataset:
Nanoscale Engineering of Efficient Oxygen Reduction Electrocatalysts By Tailoring the Local Chemical Environment of Pt Surface Sites
Authors: Linic Suljo
Published: February 2020

The oxygen reduction reaction (ORR) is the major source of overpotential loss in low-temperature fuel cells. Expensive, Pt-based materials have been found to be the most effective catalysts, but exploration of alternatives has been hampered by stability constraints at the typical operating conditions of low pH and high potential.

I will discuss our studies of elementary mechanism of ORR on various metal electrodes using kinetic and micro-kinetic analysis of reaction pathways and quantum chemical calculations. These studies allowed us to identify the elementary steps and molecular descriptors that govern the rate of ORR. Using these performance descriptors we have been able to identify families of Pt and Ag-based alloys that exhibit superior ORR performance is acid and base respectively.

We have synthesized these alloys to demonstrate the superior ORR activity with rotating disk electrode experiments. We have also performed thorough structural characterization of the bulk and surface properties with a combination of cyclic voltammetry, x-ray diffraction, and electron microscopy with spatially resolved energy-dispersive x-ray spectroscopy and electron energy loss spectroscopy.

Xin, H.; Linic, S., J. Chem. Phys. 2016 144 (23), 234704

Van Cleve T, Moniri, S, Linic, S, 2016, ACS Catalysis 7 (1), 17-24

Moniri S., Van Cleve T., Linic S., Journal of Catalysis 345, 1-10

Holewinski and Linic. J. Electrochem. Soc. 159, (2012).

Adam Holewinski, Juan-Carlos Idrobo, Suljo Linic. Nature Chemistry
,
6, 828-834, 2014.
Hierarchical Nanoporous Gold with Engineered Architectures Via Dealloying of 3D Printed Alloys
Authors: Qi Zhen , Zhu Cheng , Chen Wen , Duoss Eric B , Ye Jianchao , Worsley Marcus A. , Spadaccini Christopher M , Biener Juergen
Published: February 2020

Nanoporous metals which have a continuous solid/void structure attracted great attention due to their low density, outstanding mechanical properties, large surface area and excellent electrical conductivity. However, it is difficult to shape these nanoporous metals, especially with hierarchical pores using conventional synthesis techniques. Besides, purely stochastic porous networks may limit their performance for specific applications compared with the potential use of an engineered architecture via proper design. Here we report the fabrication of hierarchical nanoporous gold with deterministic architecture using a combination of 3D printing and dealloying. The 3D printed hierarchical nanoporous gold shows designable three levels of pores and structures with the first level size from 10-1000 microns by controlling the printing nozzle size and spacing, the second level size around several microns adjusted via changing the portion of polymer, and the third level size from 30 nm to microns depending on post-annealing and dealloying conditions. This work widens the choice of materials for 3D printing and enables the creation of a shape-controllable hierarchical nanoporous gold, which has many potential applications in both industry and fundamental science.
Nano Gold- Carbon Nanotube Modified Sensor for the Determination of Diabetes Risk Biomarkers, 8-Hydroxydeoxyguanosine and 8-Hydroxyguanine
Authors: Goyal Rajendra N
Published: February 2020

Diabetes is a serious and one of the growing health care problems worldwide and is associated with the oxidative DNA damage resulting increased level of metabolites such as 8-hydroxydeoxyguanosine (8-OHdeGuo) and 8 – hydroxyguanine (8-OHGua) in biological fluids. In the present studies efforts have been made for the development of a simple, fast and reliable method for the analysis of these products formed by the oxidative DNA damage in body fluids. An electrochemical study at gold nanoparticles attached single walled carbon nanotubes modified pyrolytic graphite sensor has been employed for studying the oxidation of these compounds with an aim to develop a method for the self diagnosis of diabetes. The fabricated sensor was characterized by using FE-SEM, AFM and Impedance studies and the effective surface area of the sensor surface was found to enhance significantly in comparison to the bare surface. The oxidation of both the compounds occurred in a pH dependent process in square wave voltammetry and the electrode reaction followed adsorption controlled pathway. Under optimum conditions linear calibration curve for 8-OHGua is obtained over the concentration range 0.01 – 10.0 nM in phosphate buffer of pH 7.2 and detection limit and sensitivity of 5.0 (± 0.1) pM and 4.9 (± 0.1) μA nM−1, are observed respectively. Similarly 8-OHdeGuo exhibited linear dynamic range of 0.005 – 20 nM and detection limit of 1.0 (± 0.1) pM was observed. The electrode exhibited an efficient catalytic response with good reproducibility and stability. The common metabolites present in urine such as ascorbic acid, uric acid and dopamine did not interfere in the determination. The method has been found selective and successfully used for the determination of these compounds in urine samples of diabetic patients.
Enhanced Electrochemical Activity of Polyaniline-Ferricyanide Films in Neutral Electrolyte
Authors: West Ryan M , Marinelli Lucas
Published: February 2020

We have successfully developed a two-step chronopotentiometric routine for electropolymerizing a polyaniline-ferricyanide film with stable electroactivity in neutral pH electrolyte containing 1 M KCl. Here we present a spectroscopic, electrochemical, and gravimetric analysis of these films to determine the nature of doping and role of the ferricyanide ion. The experimental evidence currently supports the hypothesis that the presence of ferricyanide alters the electrochemical behavior of the films in 1 M KCl, specifically the films are found to be conducting in non-acidic media. The spectroscopic evidence suggests that the Fe(CN)6 interacts with the nitrogen atoms on the PANI chain, resulting in the increased presence of polarons (mostly localized) even while the film is in the emeraldine base form. Gravimetric measurements provide insight into the role of anion and proton exchange during voltammetric cycling.
Light-Driven Small Molecule Oxidation on Pd-Au Bimetallic Film-Coupled Electrodes
Authors: McClure Joshua P. , Grew Kyle N. , Boltersdorf Jonathan , Forcherio Gregory T. , Baker David R , Lundgren Cynthia A.
Published: February 2020

The ability to efficiently oxidize small molecules containing C-C bonds (e.g. ethanol and ethylene glycol) is challenging at low temperature (i.e., < 80°C). It was previously shown that bimetallic catalysts (e.g. Pd-Au systems) have enhanced electrocatalytic activities for various organic reactions.1 Moreover, an increased overall selectivity and turnover frequency for primary alcohol conversion to aldehydes has been reported after the addition of Au to Pd nanocrystals.2 However dissociation of the C-C bonds is often incomplete and only undergoes a partial oxidation to intermediate product(s). Therefore, a breakthrough technology is required to overcome this obstacle at low temperature. One strategy is to tailor bimetallic catalysts for photo-electrochemical oxidation reactions by engineering the plasmonic response. For example, bimetallic Pd-Au nanostructures have been tuned to the visible portion of the solar spectrum for use as plasmonic H2 sensors.3 We report the use of nanolithography patterned Pd-Au bimetallic catalysts for the photo-electrochemical oxidation of ethanol and ethylene glycol. We consider the effect of laser and solar-simulated excitations on nanostructured Pd-Au bimetallic electrodes fabricated on atomic layer deposited TiO2 films coupled to a back contact.4-5 The Pd-Au bimetallic electrodes with and without film-coupling are evaluated in parallel with discrete dipole approximation (DDA) modeling derived from doubly-periodic array simulations, which allows assessment of the absorption, scattering, and near-field enhancements. For select bimetallic configurations, we compare the selectivity and kinetics of the photo-electrochemical oxidation reactions and discuss the catalytic response driven by light excitation.

Lu, C.L.; Prasad, K. S.; Wu, H.L.; Ho, J.A.; Huang, M.H. JACS
2010,
132 (41), 14546-14553.

Enache, D. I.; Edwards, J. K.; Landon, P.; Solsona-Espriu, B.; Carley, A. F.; Herzing, A. A.; Watanabe, M.; Kiely, C. J.; Knight, D. W.; Hutchings, G. J. Science
2006,
311 (5759), 362-365.

Nugroho, F. A.; Iandolo, B.; Wagner, J. B.; Langhammer, C. ACS Nano
2016,
10 (2), 2871-9.

McClure, J. P.; Grew, K. N.; Das, N. C.; Chu, D.; Baker, D.; Strnad, N.; Gobrogge, E. MRS Advances
2017,
2 (55), 3397-3402.

Ciracì, C.; Chen, X.; Mock, J. J.; McGuire, F.; Liu, X.; Oh, S.-H.; Smith, D. R. Applied Physics Letters
2014,
104 (2), 023109.
Defect Chemistry and Lithium-Ion Transport in Doped Li2ZrO3: The Role of Oxygen Vacancies
Authors: Zhan Xiaowen , Shirpour Mona , Cheng Yang-Tse
Published: February 2020

Lithium zirconate (LZO) is an attractive material for many applications. For example, it has been extensively studied as a solid absorbent for reversible CO2 capture at elevated temperatures, as a ceramic breeder for nuclear reactors, and as a coating for high-capacity cathode materials in lithium ion batteries (LIBs).

The Li+ transport is critical to the functionality of LZO in these applications. For CO2 adsorption, Li+ diffusion is a critical factor affecting both surface absorption and high-temperature CO2 desorption processes. For LIBs, LZO can provide fast migration pathways for Li+ at the electrolyte-electrode interface when it is used as a coating for electrodes. For nuclear fusion, the Li+ migration through vacant sites inside LZO grains is closely related to its performance in tritium (3H) release. Therefore, understanding the Li+ migration mechanism and, more importantly, enhancing Li+ transport in LZO is important to many applications.

Control of dopant concentration is an effective way to tune the Li+ conductivity. However, the electrical conductivity of doped LZO and the relationship between defect chemistry and electrical conductivity in doped LZO have not been reported. In addition, the effect of oxygen concentration on Li+ diffusion has not been fully understood. Here, we study the defect chemistry and electrical properties of the undoped LZO and a series of cation-doped LZO samples. We establish a relationship between Li+ conductivities and doping-induced oxygen/Li nonstoichiometries. We demonstrate that the conductivity results can be understood by unveiling the critical role of oxygen vacancies in Li+ transport. An improved CO2 absorption performance of doped LZO materials will also be discussed.
Dielectric and Ferroelectric Properties of Rare Earth Doped Lead Zirconate Titanate Ceramics
Authors: Bhattarai Mohan K , Pavunny Shojan Pullockaran , Instan Alvaro A , Katiyar Ram S
Published: February 2020

We have synthesized La3+ and Sc3+ doped lead zirconate titanate electroceramics with the stoichiometric formula ( (PLZTS), where x = 0.1 and y = 0.2, 0.4, 0.6 & 0.8, by a conventional solid-state reaction method & investigated its structural, microstructural, dielectric, electrical and ferroelectric properties. X-ray diffractometry was used to probe the phase purity and to derive the crystallographic parameters. Furthermore, structural phase transition was investigated by analyzing Raman spectra recorded in the temperature window of 80-580 K. The size, shape, and the distribution of grains were examined through a scanning electron microscope (SEM) and the sample was subjected to energy dispersive spectroscopy (EDS) for elemental analysis.

We have carried out dielectric and electrical measurements on Pt/PLZTS/Pt metal-ferroelectric-metal capacitors using impedance analyzer and electrometer, respectively, as a function of temperature (100-600 K) and frequency (102-106 Hz). High dielectric constants (ɛ’) ~280, ~500, ~1800 & 1000 for y = 0.2, 0.4, 0.6 & 0.8 respectively were observed at room temperature. We measured hysteresis loops which proved the existence of ferroelectricity in all prepared samples of different compositions. These results provide insights into PLZTS ferroelectric capacitor for its potential applications in the future electronic devices.
Lithium Storage Behavior of Three-Dimensional Graphene-like Ordered Microporous Carbon Synthesized in a Zeolite Template
Authors: Ryoo Ryong , Kwon Yonghyun , Park Hongjun , Kim Kyoungsoo , Shin Jae Won
Published: February 2020

Nanostructured carbons with high porosity are of great interest as high-performance anode materials for lithium-ion battery (LIB) applications. In the present work, we investigated the Li storage behavior of three-dimensional graphene-like ordered microporous carbon, which was synthesized via a zeolite-templating route. The microporous carbon exhibited an extremely high initial Li storage capacity as an anode for LIBs. Approximately 60% of the initial capacity was reversible during the subsequent cycles, while 40% was irreversible. The reversible capacity was comparable to the highest value reported so far with carbon alone. In order to investigate the chemical state of the Li species (i.e., ionic or metallic), the charged and discharged zeolite-templated carbon sample was characterized with 7Li nuclear magnetic resonance spectroscopy. The location of lithium was investigated using a transmission electron microscope equipped with an electron energy loss spectrometer and an energy-dispersive X-ray spectrometer. The result indicated that most of the reversible and irreversible lithium existed in nonmetallic +1 oxidation state inside the carbon micropores. The huge amount of Li storage is attributed to the three-dimensionally ordered microporous structure with a large surface area built with the single-layer graphene-like framework. In this study, we provides insights on the Li storage behavior in narrow carbon pore environment.
(Invited) Soft Materials Approaches to Carbon Nanotubes: Gels and Composites
Authors: Islam Mohammad F.
Published: February 2020

Carbon nanotubes combine low density with exceptional mechanical, electrical, and optical properties. It is highly desired to harness these intrinsic nanoscale properties for macroscale applications. I will describe surface modification assisted self-assembly of single-walled carbon nanotubes into macroscopic, shape and size tunable, ultra-lightweight and electrically conducting networks – hydrogels and aerogels – with large surface area. The mechanical properties of these aerogels are dictated by free rotation and sliding of nanotubes about the junctions, which unfortunately make them fragile. Interestingly, coating the junctions and struts with various two-dimensional materials such as graphene and hexagonal boron nitride suppress rotation and sliding at the junctions and stiffen the struts, enhancing Young’s moduli and imparting emergent superelasticity, fatigue resistance and creep resistance that is preserved over a broad temperature range (-100–500˚C). Owing to their microstructure, both uncoated and coated aerogels are suitable for diverse applications. For example, we have used these aerogels to enhance elastic modulus of thermoplastic polymers by at least 40,000%. These materials also show high capacitance that remains stable over thousands of charge/discharge cycles even at high rates exceeding 1 V/s and under 90% compression, allowing us to construct supercapacitors with exceptional volumetric capacitance. Furthermore, the aerogels can be decorated with noble metals and metal oxides to fabricate electrodes for fuel cells with high current density and stability, highly visible-light photoactive composites using ultraviolet-active photocatalysts, and pseudocapacitors without compromising the mechanical properties of the underlying scaffolds. Finally, our fabrication process also allows densification of these aerogels to at least 400 mg/mL, reaching high Young’s moduli of 0.4 GPa, while maintaining the microstructure, thermomechanical responses, and ultralow loss (≈0.01–0.04) of low density aerogels.
SWCNT Photocatalysts for Hydrogen Evolution from Water
Authors: Izawa Takumi , Nishikawa Kakeru , Watanabe Ken , Tajima Tomoyuki , Miyake Hideaki , Takaguchi Yutaka
Published: February 2020

Visible and near-infrared (NIR) light-induced water splitting has received considerable attention in terms of solar energy conversion and hydrogen energy storage. Single-walled carbon nanotubes (SWCNTs) are potentially strong optical absorbers with tunable absorption wavelengths between 500 and 1350 nm depending on their chiral indices (n,m). However, their application for solar energy conversion is difficult because of the large binding energy (> 100 meV) of excitons. In order to make SWCNTs act as a H2-evolving photocatalyst, we have developed coaxial p-n heterojunction systems consisting of a SWCNT and fullerodendrons, such as SWCNT/fullerodendron, SWCNT/fullerodendron/SiO2, SWCNT/fullerodendron/Pt(II), SWCNT/fullerodendron/TiOx. This paper describes fabrication of several SWCNT photocatalysts and their photocatalytic activity for H2 evolution from water by the use of a three-component system and an interconnecting system including Z-scheme (Figure 1).

Figure 1
Electrochemical Responses of Graphene with Biofilm Formation on Various Metallic Substrates By Using Laboratory Biofilm Reactors
Authors: Kanematsu Hideyuki , Shindo Kodai , Barry Dana M. , Hirai Nobumitsu , Ogawa Akiko , Kuroda Daisuke , Kogo Takeshi , Ikegai Hajime , Mizunoe Yoshimitsu
Published: February 2020

We have confirmed that graphene is very sensitive to biofilm formation by environmental biota and by some special bacteria (E.coli and S.epidermidis). Therefore, graphene is not recommended for biomaterials used in the human body. Graphene’s high sensitivity could lead to infections. On the other hand, this high sensitivity might allow grapheme to serve as a sensor for detecting biofilm formation at a very early stage. To obtain more data, we investigated the change of electrochemical responses for graphene on various substrates (while biofilms were forming on these samples).

Biofilms were formed on metallic substrates. The procedure is briefly described. A mechanical exfoliation method was repeated by using scotch tape. For each final stage, the graphene on the scotch tape was transferred to the surface of a metallic sheet-type specimen. (Various specimens were used.) The graphene formed on the metallic specimens was confirmed by using Raman spectroscopy and by staining. For the staining, 0.1% crystal violet was used. We expected that the extent of graphene formation would increase with the repeated number of attachments between tapes. Therefore, some transferred specimens, with different repeated numbers than others, were prepared as specimens. Then they were immersed in culture liquids (LB culture liquids and HI ones) including E.coli and Staphylococcus epidermidis.

The specimens were also immersed into rotational-type reservoirs filled with culture liquids including bacteria. Each specimen was fixed with a special jig and the culture liquids were stirred continuously.

Two laboratory biofilm reactors (a static type and a flow type reactor) were used for this work. Measurements of electrochemical responses (Cyclic voltammetry, immersion potential etc.) were made for all samples, while the changes of Raman shifts with time on those specimens were observed too. Also the final states of the specimens were checked by using crystal violet.

Finally, behaviors were analyzed and the applicability to sensing biofilm formation was discussed.
Graphene Supported Manganese (IV) Oxide Nanoparticles As High-Performance Electrochemical Capacitor
Authors: Jablonskienė Jolita , Šlopšnys Justinas , Pakštas Vidas , Vaičiūnienė Jūratė , Selskis Algirdas , Drabavičius Audrius , Jasulaitienė Vitalija , Tamašauskaitė-Tamašiūnaitė Loreta , Norkus Eugenijus
Published: February 2020

The search for cleaner energy sources is required to shift focus to the generation of energy from electrochemical systems, batteries and fuel cells, solar cells, and super capacitors, among others. We report a simple one-step approach for microwave-assisted synthesis of manganese oxide nanoparticles deposited on the graphene (MnO2/GR) or carbon (MnO2/C) supports. The MnO2/GR and MnO2/C nanocomposites have been synthesized with different morphologies. The MnO2 nanoparticles were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). Electrochemical performance of the MnO2/GR and MnO2/C nanocomposites was evaluated using cyclic voltammetry (CV) and galvanostatic charge-discharge.

It was found that the graphene supported MnO2 nanoparticles has significant influence on the electrochemical performance of composites electrodes compared with that of the carbon supported MnO2 nanoparticles. The maximum specific capacitance of 108 F g-1 was achieved at the MnO2/GR electrode in the 1 M Na2SO4 aqueous solution at the scan rate of 10 mV s-1.

Acknowledgement

This research is funded by the European Social Fund under the No. 09.3.3-LMT-K-712-02-0142 “Development of Competences of Scientists, other Researchers and Students through Practical Research Activities” measure.
Unexpected Relation between Degradation Rate of Lithium Ion Battery and Stage Structure of Graphite Anode
Authors: Ito Yuki , Sato Kenji , Tamai Atsushi , Nakao Kazuhito
Published: February 2020

It is very important to understand the degradation behavior of lithium ion battery under various conditions (ex.; state of charge (SOC), temperature) in order to predict the lifetime of the battery. We performed long-term storage tests for lithium ion batteries which consist of layered rock-salt structure cathode and graphite anode on various conditions. During analyzing these test results, we found that the relation between the degradation rate and the SOC is not monotonous. In order to reveal the reason of this peculiar result, we paid attention to the stage structure of graphite. The electrochemical potential of graphite anode is determined by two-phase coexistence relation of stages of Li-graphite intercalation compound. Therefore we can specify the fractions of stages by using differential voltage analysis (dV/dQ). We adopted five stages to characterize the state of anode; stage1, stage2a, stage2b, stage3, and higher stage, and non-lithiated graphite [1]. We estimated the degradation rate of individual stage by solving simultaneous equations of the fraction of each stage and degradation rate. The degradation rate are expected to have negative correlation with the electrochemical potential of stage, however we revealed that the degradation rate of stage2a was much lower than expected rate, as shown in Figure 1. This result suggests that stage2a has high stability against the irreversible reaction accompanied by formation of solid electrolyte interface.

Figure 1
High Voltage Spinel LiNi 1/2Mn3/2O4 : Kinetics and Thermodynamics Properties
Authors: Dumaz Philippe , Rossignol Cécile , Bouchet Renaud
Published: February 2020

In order to increase the energy density of lithium-ion batteries, there are two levels; one is the increase of the specific capacity of both positive and negative active materials (i. e. in Li/S8 technology) and/or the increase of the battery voltage. The most simple solution a promising solution is theo use of positive active materials with high potential (up to 5V vs Li + / Li) [1] because it does not change the technology conception. Among the different materials, The spinel LiNi1/2Mn3/2O4 has a theoretical capacity of 147 mAh/g and a potential of 4.8 V vs Li+/Li, which enable a high energy density [2] (at least 20% more than standard LiCoO2). In the literature, a wide range of values for diffusion coefficient have been reported and only few studies reports values for exchange current density [3,4,5] . This work intended to highlight the impact of thermodynamic factor on the diffusion and to bring new values for the exchange current density, measured by impedance spectroscopy. The study of thin film of spinel LiNi1/2Mn3/2O4 enables to use simplified equations for extracting kinetics and thermodynamics values like exchange current density at the interface of the material, values of the diffusion in the thin electrode and thermodynamic factor that affect the mobility in the structure, depending on the state of charge. These results have then been compared to the ones obtained on composite electrodes. Very and good agreement were obtained even using a 1D model on composite electrodes.

[1] Tarascon et al. Nature Mater. 2011

[2] Yi et al. J. Power Sources, 2016

[3] Aurbach et al. Electrochim. Acta, 2005

[4] Amin et al. J. Power Sources, 2017

[5] Nishikawa et al. J. Electroanal. Chem. 2017
Improving High Rate Electrochemical Performance of Patterned Lithium Metal Anode for Lithium Secondary Batteries By Using Dual Salt Electrolyte System
Authors: Yoon Byeolhee , Kim Seokwoo , Jin Dahee , Park Jinkyu , Oh Jeonghun , Jo Hearin , Choi Junyoung , Ryou Myung-Hyun
Published: February 2020

Recently, demand for lithium (Li) secondary batteries has been increasing as the market for mid- to large-size batteries such as electric vehicles (EV) and energy storage systems (ESSs) is expanding. Especially in order to popularize EVs, it is essential to improve the energy density in order to secure mileage. However, using commercialized graphite as an anode material is difficult to increase energy density due to their limited capacity. Li metal is an ideal anode material due to its extremely high theoretical specific capacity (3860 mAh g-1), low density (0.59 g cm-3) and the lowest negative electrochemical potential (‒3.040 V vs. the standard hydrogen electrode). For instance, Li/air and Li/S batteries enable to increase dramatically energy density. However, Li metal has been proposed as a problem of deterioration of cell performance due to dendrite caused by charging / discharging process and battery short circuit. More importantly, Li dendrite-growth lead to safety issue, i.e., thermal runaway, causing a catastrophic satety failure accompanied by fire and smoke.

To overcome this problem, many efforts have been devoted to suppress lithium dendrite-growth. Recently, we demonstrated the possibility of using mechanically surface-patterned Li-metal for Li secondary batteries. In our previous work (J. N. Park et. Al), patterned Li-metal anode showed good cycle life at low current density cycling. Still, high current density cycling showed limited cycle life because of bulky Li dendrite formation in the micro-patterned Li-metal holes. These consume more amount of electrolytes during charging/discharging processes.

In this work, we applied dual salt system electrolyte on the micro-patterned Li metal to suppress mechanically bulky Li deposition in the micro-patterned Li-metal holes during charging/discharging processes. And then, their electrochemical properties are investigated in detail.
(Invited) Ion Irradiation Effects on Structural and Electrochemical Charge Storage Properties of Electroceramic Materials for Lithium-Ion Batteries
Authors: Smith Kassiopeia , Savva Andreas , Wharry Janelle , Xiong Hui (Claire)
Published: February 2020

Lithium-ion batteries are promising battery technologies to provide high energy and high power for applications such as electric vehicles or electrical grids. Recent studies have observed that lithium-ion battery

electrode materials (e.g. TiO2) containing intentional structural defects exhibit enhanced electrochemical charge storage capacity. In this work we investigate the irradiation effect on structure and electrochemical response of TiO2 nanotube electrodes through proton ion irradiation, because irradiation is known to produce an excess of defects in a material. In addition, we investigated heavy ion irradiation on TiO2 single crystals to elucidate the effects of irradiating species and crystallographic orientation on defect production and microstructure evolution. We have observed defect generation upon irradiation in both nanostructured and single crystal TiO2 samples and investigated the relationship between irradiation-induced defects and the electrochemical properties of the TiO2 samples.
Planar Lithium Battery Cell Development to Advance in-Operando Nano-CT Imaging of Graphite Electrodes
Authors: Li Yubai , Choi Paul , Love Corey T , Swider-Lyons Karen , Litster Shawn
Published: February 2020

In-operando nano-scale resolution X-ray computed tomography (nano-CT) imaging provides an excellent new possibility to investigate a wide variety of phenomena in the electrodes of Li-ion batteries. The 3D X-ray imaging provides direct observation of internal morphological changes in electrodes with up to 50 nm resolution regarding standard materials and electrolyte, which is difficult or impossible to achieve by electron microscopy. Such fine resolution enables the possibility to observe detailed structural changes like the deposition of electrolyte decomposition products within the electrode, transition from Li intercalation to electroplating on graphite, and lithium dendrite formation and growth. One task for applying in-situ nano-CT imaging on Li-ion battery imaging is to develop special lithium battery cells compatible with both the nano-CT instrument’s sample size constraint and X-ray attenuation length limits of higher atomic number materials. Herein, we have developed a planar cell design that allows us to use commercial electrode, separator, and electrolyte. Successful charging and discharging has been achieved with this planar cell design using commercial graphite, LiMn2O4, and lithium foil electrodes. In-operando nano-CT imaging is performed on planar cell lithium battery with focus on graphite anodes. The experimental methodology developed in this study has applicability to test wide ranges of electrolyte, separators and other electrode materials in Li-ion batteries.
Effect of Dispersing Solvents of Ionomer Binder Solutions in Catalyst Inks on Performance and Durability of Membrane-Electrode Assembly
Authors: Song Chan-Ho , Park Jin-Soo
Published: February 2020

Proton exchange membrane fuel cells (PEMFCs) is currently considered as a potential next-generation alternative energy technology because of the high energy density and high abundance of hydrogen in nature. However, many issues still exist to be improved in terms of performance and durability for the wide use of PEMFCs as a clean and efficient power system. One of the most important parts in PEMFCs is membrane-electrode assembly (MEA) which provides the electrochemical reactions at electrode where fuel/oxidant (gas), hydrated ions (liquid) and electron (solid) co-exist (so called triple phase boundary), the permeation of fuel and/or oxidant gas and the drainage of water product. In MEA, water and IPA based Nafion dispersion is the most widely used as the ionomer binder for conduction of hydrated ions, formation of pores and adhesion of solid catalyst. The structure of electrodes in MEA could be significantly determined by characteristics of ionomer binder solutions where polymer dispersion interacts with solvent. Upon the structure of the electrodes formed by agglomerates of catalyst and ionomer binder with different size, it has reported that MEA performance and durability would be highly affected. The former could be achieved by reducing overvoltages, and the latter by reducing electrode cracking (i.e., well adhesion of catalyst by ionomer). Electrode structure of MEA, including the Pt-ionomer interface, is determined when electrodes are solidified from catalyst inks during a drying step. Thus, the properties of the solvent system in catalyst inks play an important role in determining the electrode structure in MEA. A fundamental understanding of the phenomenological outcome from the relationship between morphology and property for perfluorosulfonic acid (PFSA) membranes is crucial in obtaining high power and durable MEA. In this study ion and liquid water behavior in PFSA membranes formed from different dispersing solvents were investigated with ionomer particle sizes, solvent viscosity, solvent dielectric constants and distribution which cause various morphology. In addition, MEAs with different electrodes prepared by different ionomer binder solutions were investigated in terms of I-V polarization, cyclic voltammetry, electrochemically-active surface area (ECSA), and chemical stability.

Acknowledgment

This work was supported by the New and Renewable Energy of the Korea Institute of Energy Technology Evaluation and Planning(KETEP) granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea (No. 20173010032100).
Advances in Electron Microscopy Methods to Evaluate Thin Ionomer Layers in PEM Fuel Cell Catalyst Layers
Authors: More Karren L. , Cullen David A.
Published: February 2020

The ability to characterize the thin ionomer films within the catalyst layers in membrane electrode assemblies (MEAs) at the nm-scale via analytical electron microscopy presents many challenges. The ionomer degrades rapidly during analysis with high-current electron beams, which can be mitigated to some extent when experiments are conducted using higher operating voltages and under cryogenic temperatures.1 These microscopy operational parameters have proven most useful for imaging, mapping, and analyzing ionomer aggregates that are typically tens-to-hundreds of nms in size, have not been particularly useful for understanding the nature of the thin ionomer films that percolate through the thickness of the catalysts layers.

Recently, Oak Ridge National Laboratory has acquired a new aberration-(probe)-corrected analytical scanning transmission electron microscope (STEM) that can be operated under conditions significantly more favorable for interrogating “soft matter” at very high resolution, e.g., structure and chemistry of the nm-scale thin ionomer films within intact catalyst layers. This new STEM, the JEOL-NEOARM, can be operated between 30kV-200kV at low-electron-dose and is equipped with state-of-the-art analytical capabilities for the simultaneous acquisition of electron energy loss spectroscopy (EELS) and energy dispersive X-ray spectroscopy (EDS). Most notably, the new STEM is equipped with a novel pixelated detector that enables ultrafast image/diffraction (ptychographic) data acquisition that will minimize exposure of the ionomer films to the electron beam, preventing damage accumulation, and allowing for complete data reconstruction following data collection.

We will present imaging and spectroscopic results obtained by varying the STEM operating conditions on the NEOARM (voltage, electron dose, sample temperature, ptychographic reconstruction methods) and exploiting its unique combination of ultrafast capabilities. The high-resolution structural and compositional information provided will provide new insight regarding thin ionomer films within MEA catalyst layers

Research supported by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy, as part of the Fuel Cell Performance and Durability (FC-PAD) Consortium. Microscopy research performed as part of a user project at the Center for Nanophase Materials Sciences, which is a U. S. Department of Energy, Office of Science User Facility.

References

D.A. Cullen, R. Koestner, R.S. Kukreja, Z.Y. Liu, S. Minko, O. Trotsenko, A. Tokarev, L. Guetaz, H.M. Meyer, C.M. Parish, and K.L. More, “Imaging and Microanalysis of Thin Ionomer Layers by STEM,” Journal of The Electrochemical Society
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Fuel Cell Electrodes Based on Functional Meso-Structured Arrays
Authors: Spendelow Jacob S , Komini Babu Siddharth , Mukundan Rangachary , Borup Rod L. , Cullen David A. , More Karren L.
Published: February 2020

State-of-the-art fuel cell catalyst layers consist of a random mixture of functional components (catalyst, ionomer, and pore) that are formed in an uncontrolled ink deposition process. The random nature of these structures makes it difficult to optimize the functional domains and hence causes severe mass transport limitations during high-power operation, resulting in a loss in performance and requiring that the fuel cell be oversized to maintain an acceptable level of performance. The ionomer binder adds an additional transport resistance and becomes significant at lower Pt loadings [1]. Decreasing this transport resistance would remove the main barrier to low-cost, ultra-high power density fuel cells. Rational design of the electrode structure in PEFCs could improve performance and reduce cost. By separating the different electrode functions into discrete electrode elements, each element can be optimized for specific functions. Arranging these optimized discrete elements in a controlled, low-tortuosity array configuration enables transport limitations to be reduced or eliminated.

We have demonstrated this approach through fabrication of freestanding arrays of vertically-oriented ionomer channels with different aspect ratios, and incorporation of these channels into fuel cell electrodes where they serve as non-tortuous proton-transport highways (Figure 1). Providing effective proton transport through these low-tortuosity percolating highways allows the catalyst domain to have a lower ionomer/catalyst ratio, reducing transport resistance. Proof of concept was demonstrated by achieving a 15% increase in performance with channels with an aspect ratio of 8. Further work is underway to increase channel aspect ratio and improve integration of channels with surrounding catalyst layer, leading to further transport improvements and increases in performance.

Fig. 1. Left: freestanding array of ionomer channels. Right: catalyst layer incorporating ionomer channels.

References

N. Nonoyama, S. Okazaki, A. Z. Weber, Y. Ikogi, and T. Yoshida, J. Electrochem. Soc., 158, B416 (2011).

Acknowledgments

This research is supported by DOE Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium.

Figure 1
Ionomer and Carbon Aggregate Structure in Catalyst Ink Using Coarse-Grained Molecular Dynamics Simulations
Authors: Mabuchi Takuya , Tokumasu Takashi
Published: February 2020

The cathode catalyst layer (CL) is one of the principal components for proton exchange membrane fuel cells. CL is typically prepared by drying a catalyst ink consisting of Pt-C (platinum on a carbon power support), ionomer, and solvents (water/alcohol mixtures). Under good solvent conditions for the polymer backbone, where solvents dissolve the backbone chains, ionomers exhibit polyelectrolyte-type behavior, forming loose ionic aggregates. The interaction between ionomer and solvents controls the ionomer conformations in the solutions, which determines the final microstructure of ionomer in CLs. The characterization of ionomer structures has been extensively studied using experimental measurements such as small-angle neutron scattering (SANS) and small-angle X-ray scattering (SAXS).1-2 They observed that hydrophobic backbones of Nafion form the cylindrical-like core of self-assembled ionomer structures while ionic groups are located at the periphery of this aggregates. Theoretically, while most of studies have primarily focused on the solid membrane state with water volume fraction significantly below 50%, ionomer and carbon aggregations in solutions are also an important phenomenon to understand the self-assembly behaviors of ionomers as key structure-forming elements in CL. In this study, ionomer and carbon aggregations in a mixture of 1-propanol (NPA) and water have been investigated using coarse-grained molecular dynamics simulations. To perform simulations of larger systems and longer time spans compared with atomistic simulations, the reduced spatial resolution of the bead representation based on the relative free energy difference was used as a coarse-grained model. The dependence of NPA content on the ionomer structures was studied by systematically changing the NPA content in the system. The self-assembly behavior of ionomers into cylindrical bundle-like aggregates was observed for all NPA content solutions (Figure 1). Ionomer aggregates showed different behavior of formation at different NPA contents. The radius of an ionomer bundle was found to become smaller as NPA content increases, which is in good agreement with the trend seen in experimental measurements.3 The effects of carbon particles on the ionomer aggregation for various ionomer concentrations will also be discussed in the presentation.

References

Gebel, G.; Loppinet, B.; Hara, H.; Hirasawa, E., Small-Angle Neutron Scattering Study of Polyethylene-Co-Methacrylate Ionomer Aqueous Solutions. J. Phys. Chem. B
1997, 101, 3980-3987.

Jiang, S.; Xia, K.-Q.; Xu, G., Effect of Additives on Self-Assembling Behavior of Nafion in Aqueous Media. Macromolecules
2001, 34, 7783-7788.

Yamaguchi, M.; Matsunaga, T.; Amemiya, K.; Ohira, A.; Hasegawa, N.; Shinohara, K.; Ando, M.; Yoshida, T., Dispersion of Rod-Like Particles of Nafion in Salt-Free Water/1-Propanol and Water/Ethanol Solutions. J. Phys. Chem. B
2014, 118, 14922-14928.

Figure 1
Effect of Hydrophobicity Gradients within MPL and MEA on PEM fuel cell performance
Authors: Mohseninia Arezou , Kartouzian Dena , Regnet Fabian , Scholta Joachim , Jörissen Ludwig
Published: February 2020

The water inventory of PEMFC components strongly influences the performance under two-phase operating conditions. Within this work, the influence of hydrophobicity variation within electrode and microporous layer (MPL) on cell performance will be presented. Different weight percentages of PTFE is used in the catalyst and MPL inks as an additive in order to increase the hydrophobicity. The fabrication method for the membrane electrode assembly (MEA) is based on spraying the catalyst ink onto the membrane and coating MPL ink onto the GDL substrate using a doctor blade method. Fuel cell tests are carried out with a 25 cm² active area single cell at different relative humidities (RH) and oxygen flow rates to investigate the effect of PTFE on the ability of MEA and MPL on water management. Electrochemical impedance spectroscopy is performed as a diagnostic tool to investigate the reaction kinetics and mass transport. In order to assess the wettability of MEAs contact angle measurements were carried out. The materials are characterized by mercury porosimetry and scanning electron microscopy.

Figure 1 shows the performance curve for cell 1 (conventional MEA +Conventional MPL), cell 2( MEA with 5 wt.% PTFE +Conventional MPL) and cell 3 (Conventional MEA+ MPL with 40 wt.% PTFE ) at different relative humidities. At dry conditions (RH=70%) cell 2 has a higher limiting current density compared to the other cells, which could be the indication that the hydrophobic electrode keeps the membrane material in the catalyst layer better hydrated. At over humidified conditions (RH=120%) the limiting current density value has decreased for cell 1 and 2 compared to the standard conditions (RH=100%) as a result of mass transport limitations. On contrary, Cell 3 shows an improved performance in high current density region at humid conditions, illustrating the ability of hydrophobic MPL to prevent the accumulation of liquid water at the interphase of MPL and catalyst layer at cathode side. In the presentation of the ongoing work, additional results, including HFR data will be reported.

Figure 1
Impact of Ionomer Dispersion on PEM Fuel Cell Performance
Authors: Xu Hui , Lei Chao , Kim Yu Seung , More Karren L.
Published: February 2020

Conventional polymer electrolyte membrane (PEM) fuel cell electrodes using aqueous ionomer dispersion suffer from high manufacturing costs and rapid performance degradation. We have investigated an innovative method of designing fuel cell electrodes to reduce manufacturing costs and extend the lifetime. Our approach to obtaining good fuel cell performance is to; 1) understand ionomer particle morphology in dispersion; 2) investigate the electrode morphology, catalyst, and ionomer binder distributions in the electrodes; 3) evaluate the electrode performance using various electrodes prepared from different dispersing agents.

First, laser diffraction particle size analysis was used to understand the various solvents’ impacts on catalyst ink structure. It can be seen that nPA/H2O and ethylene glycol (EG) solvent systems provide better ink structure, implied by much smaller agglomeration sizes. IPA/H2O and pentanediol based solvent systems exhibit large agglomerations in the ink, which may account for their poor quality. The laser diffraction particle size will be correlated with electrode structure and fuel cell performance later.

Low magnification transmission electron microscopy element mapping was then used to characterize the ionomer distribution in these cathode layers. The best ionomer distribution was found in the EG based sample, with ionomer aggregates <50 nm. The porosity and pore size distribution of the electrode layers were also obtained from transmission electron microscopy image analysis. The EG-based electrode shows the lowest porosity (i.e., 13%). It also contains the smallest pore sizes and the highest number of pores.

The effect of the dispersing agents on initial fuel cell performance was investigated. In this experiment, four ionomer dispersions were used and compared with nPA/H2O and IPA/H2O. All MEAs had a Pt loading of ~0.20 mgPt/cm2. The IPA/H2O baseline shows very low performance especially in the mass transport region, which is probably attributed to its poor coating quality. The ionomer dispersions have shown significant influence on the fuel cell performance, with a general ranking as: nPA/H2O > ethylene glycol > butanediol > pentanediol). The ethylene glycol based sample displays the best performance of all the non-aqueous samples, and its performance is very comparable to the nPA/H2O baseline.
Reducing Mass-Transfer Polarization By Surface Functionalization of Carbon Support of PEM Fuel Cells at Low Platinum Loadings
Authors: Fang Zhengyuan J , Lee Moo-Seok , Kim Jun Young , Kim Jung Ho , Fuller Thomas F
Published: February 2020

The cathode platinum loading has been significantly reduced from 0.4-0.8 mgPt/cm2 to about 0.1 mgPt/cm2, which meets the U.S. DOE’s target for 2020. However, at this low platinum loading, larger-than-expected mass-transfer polarization occurs at high current densities. Recent work proposed the enhancement of ionomer distribution via carbon support functionalization. In this study, two schemes of surface functionalization were investigated 1) diazotization of p-phenylenediamine and 2) amination of pre-oxidized carbon supports (Vulcan and Ketjen Black). N2 adsorption, XPS, and sessile-drop method were used to verify and characterize the functionalization. Improvements of cell performance at high current densities were observed using 5 cm2 MEAs. Scanning Transmission Electron Microscopy (STEM) coupled with Energy-dispersive X-ray Spectroscopy (EDX) were applied to characterize surface ionomer coverage.