bluuebunny/crossref_metadata_2025 huggingface dataset:
X-Ray Micro-Tomography As a Diagnostic Tool for the Electrode Degradation in Vanadium Redox Flow Batteries
Authors: Trogadas Panagiotis , Taiwo Oluwadamilola O , Tjaden Bernhard , Neville Tobias P , Yun Sukhwan , Parrondo Javier , Ramani Vijay K , Coppens Marc Olivier , Brett Dan J. , Shearing Paul R.
Published: February 2020

The vanadium redox flow battery (VRFB) is an electrochemical device suitable for large-scale energy storage due to its fast response time, long cycle life, and high energy efficiency1. In VRFBs, the electrodes provide the sites to facilitate the redox reactions between V3+ / V2+ and V4+ / V5+ ions2.

Graphite felt is the most common electrode material employed in VRFBs due to its low cost, high stability and conductivity, and reasonable surface area3. Micro-tomograms of fresh graphite felt have already been obtained and used to extract detailed structural characteristics of electrodes4. Based on the acquired structural information, 3D pore scale models have been built to investigate the effect of electrolyte flow rate, vanadium ion concentration and electrode morphology on VRFB performance.

However, even though this model-based design approach has helped optimize the fresh felt material, pore scale models for VRFBs would be much more accurate and realistic if the structural information of used (voltage-cycled) felts were incorporated in the model to capture the changes in felt structure and properties during operation.

Using a combination of micro-tomography (CT) measurements of voltage-cycled graphite felts (over ca. 30 charge / discharge cycles), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS) measurements of the same felt electrode, the first description of micro-structural evolution processes occurring in VRFB felts during operation is provided.

Reconstructed 3D images of the VRFB electrodes reveal fiber agglomeration and carbon electrochemical oxidation during continuous battery operation (Fig. 1a and b). Key geometric characteristics of the graphite felt samples are extracted from these 3D images allowing the calculation of porosity, tortuosity and volume specific surface area for each sample. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) measurements have been also employed in order to verify the significant structural changes on voltage-cycled graphite felts observed by micro-CT.

References

1. A. Weber et al., J. Appl. Electrochem., 41, 1137 (2011).

2. A. Parasuraman et al., Electrochim. Acta, 101, 27 (2013).

3. B. Li et al., Nano Letters, 13, 1330 (2013).

4. G. Qiu et al., Electrochim. Acta, 64, 46 (2012).

Figure 1. 3D reconstructed image of the fresh (A) and voltage-cycled (B) graphite felt electrode respectively.

Figure 1
High Rate Capacity through Redox Electrolytes Confined in Macroporous Electrodes
Authors: Narayanan Rajaram , Bandaru Prabhakar R
Published: February 2020

The capacitive characteristics of a model macroporous electrode, comprised of vertically aligned carbon nanotubes, with a relatively large volume /unit mass (of∼40 cm3/g) are discussed. The faradaic characteristics of the capacity were evidenced through a voltage plateau in the galvanostatic discharge experiments. It is shown that the conﬁnement of electrolyte within the spacing between the nanostructures with respect to an appropriate choice of the voltage scan rate yields a regime where both high capacity and rate capability may be realized. Additionally, the absence of diffusional processes allows for large capacitance retention even at discharge current densities of the order of 200 mA/cm2. For 1M K3Fe(CN)6, the maximum observed capacity was found to be ∼26 mAh/cm3 (normalized to the pore volume) or 0.28 mAh/cm2 (normalized to the projected area of the electrode) and it was noted that the capacity could be cycled at very high rates for 5000 cycles.1

References:

1. R. Narayanan and P. R. Bandaru, J. Electrochem. Soc., 162, A86–A91 (2015)

Figure 1
A Disruptive Concept for a Whole Family of New Battery Systems
Authors: Roumi Farshid , Cid Clement , Roumi Jamshid , Hoffmann Michael R
Published: February 2020

We propose a radically new approach to the architectural design of batteries. The invention is a new geometry that replaces conventional cell and module designs and significantly reduces the weight, volume and cost of non-active materials, while increasing the thermal performance.  The new battery relies on an innovative architecture called an S-cell. The proposed cell geometry may increase the energy per cost or weight by a factor of 2, by significanlty reducing the manufacturing cost and by enabling high capacity electrode materials.
Can Radiolysis Help Understanding the Decomposition Products of the Electrolytes Used in Lithium-Ion Batteries?
Authors: Ortiz Daniel , Maître Philippe , Mostafavi Mehran , Le Caër Sophie
Published: February 2020

Lithium-ion batteries appear to be one of the most important advances in energy storage. Unfortunately, their performance declines gradually with their use and/or time. Nevertheless, their degradation products affect both the battery performance and its safety. Therefore it is of paramount importance to understand the reaction mechanisms involved in the ageing processes. Among those, redox processes are likely to play a critical role and radiolysis is an interesting approach in order to simulate the ageing phenomena.

One of the aims of our group is then to investigate the effect of ionizing radiation on the different solvents containing or not lithium salts used in batteries. We generate, thus, the decomposition products that are actually comparable to those formed by electrolysis. Moreover, the use of the “radiolysis approach” entails particularly two important benefits: the time needed to degrade the solvent is much shorter than in classical charge/discharge cycles and it offers the possibility to explore different time scales processes (from picoseconds to days).

Our work was first focused on linear alkyl carbonates diethyl and dimethyl carbonate (DEC and DMC) with/without LiPF6. At short-time scale, picosecond pulse radiolysis has been used in order to explore the primary radiation effects. These experiments reveal, for instance, an unambiguous reaction between the electron and the PF6
- anion. 

Then, the long-time decomposition products were analyzed both in the gas and liquid phase. To this end, a wide variety of analytical techniques has been used. Gas phase has been analyzed and quantified using Gas Chromatography-Electron Impact-Mass spectrometry (GC-EI-MS) whereas a combination of Electrospray-High Resolution Mass Spectrometry (ESI-HRMS) with both Ion Mobility Spectroscopy (IMS) and Infrared Multi-Photon Dissociation (IRMPD) spectroscopy has been used to characterize the decomposition products in the liquid phase.

In conclusion, we show that the “radiolysis approach” used herein can provide an unprecedented, quantitative and fast overview of the electrolyte decomposition phenomenon.
Ion Transport in Temperature-Resistant Ceramic-Based Composites
Authors: F. Rodrigues Marco-Tulio , Kalaga Kaushik , Gullapalli Hemtej , Arava Leela Mohana Reddy , Ajayan Pulickel M
Published: February 2020

Polymer-based membranes have been widely investigated as ion transport media for energy storage devices. However, they lack dimensional and mechanical stability at higher temperatures, limiting their operating range. Room Temperature Ionic Liquids (RTILs) are an attractive class of electrolyte with high thermal and electrochemical stability. Negligible values of vapor pressure and reasonable ionic conductivities suggest that they are serious candidates to feature as a role component in designing temperature-robust devices. The challenges for temperature-resistant technologies lie around properly immobilizing the liquid electrolyte. In the present work a temperature-stable ion-conductive composite membrane is designed by combining RTILs with ceramic supports, as bentonite clay. The role of the ceramic material is to effectively offer mechanical support while absorbing and retaining the electrolyte. The ionic conductivity of composites with different contents of ceramic and RTIL were investigated and they were found to be appropriate for operation between room temperature and at least 150 oC. Such composites are a good alternative for high temperature applications where ionic conductivity is required.
Optimization of MnO2 Cathodes for Aqueous Battery Applications
Authors: Hertzberg Benjamin Joseph , Phadke Satyajit , Davies Greg , Chamoun Mylad , Hsieh Andrew , Rus Eric D. , Moon Geon Dae , Erdonmez Can K. , Meng Shirley , Steingart Daniel A
Published: February 2020

Grid-level energy storage demands a low-cost, safe, long cycle life battery chemistry. The Zn-MnO2 alkaline battery chemistry hits the first two targets. This type of battery has high energy density (comparable to that of a Li-ion battery) and low cost per kilowatt-hour.  However, their rechargeability is limited by phase transformations which occur in the MnO2 cathode during discharge of close to one electron, which transforms it into an spinel phase, generally considered to be electrochemically inert. As a result, depth of discharge is limited to no more than 70% of the 1e- capacity of MnO2 at best, and in a large format cell typically no more than 0.5 e-.

We have extensively studied the MnO2 alkaline system and have developed a variety of techniques to extend this depth of discharge window, improving the capacity and cyclability of the cell dramatically. We have also developed novel nanostructured forms of MnO2 for use as a cathode material in this system. Using these techniques, we have achieved capacities of over 350 mAh/g (1.2 e-) for more than 150 cycles. In this presentation, we will discuss the various failure modes of the MnO2 alkaline system, and the techniques our group has developed to overcome them. We will describe the crystal structure and electrochemical performance of the nanomaterials we have synthesized, as well as the structural changes occurring during their use as an electrode material as characterized via synchrotron radiation and other techniques.  

With further development, this material, combined with either a zinc anode or an earth abundant, insoluble anode such as Fe or Cd, may allow for over 1000 cycles at a cost of less that $100/kWhr for a packed out cell. Figure: a) MnO2 electrode before cycling; b) MnO2 electrode after 1st-electron discharge; c) MnO2 electrode after full discharge; d) MnO2 electrode after full recharge; e) MnO2 electrode after 3 cycles (discharged state); f) MnO2 electrode after 15 cycles (discharged state)

Figure 1
Investigation of Electroplating Trivalent Cr-C on Copper Alloy As Bipolar Plates with Different Current Density in Pemfcs
Authors: Wang H.C. , Hou K.H. , Lu C.E. , Ger M.D.
Published: February 2020

In this study, the trivalent Cr-C coating was electroplated on copper alloy as bipolar plates because of their excellent electric conductivity and corrosion resistance.  The SEM images showed that the thickness of the coating was about 2 to 13 μm and increased with raised coating current density. The surface morphology at 10 A/dm2 is more smooth, no cracks and has high carbon content (46.65 at％). Moreover, the polarization curve with different coating current density (10, 30, 50 A/dm2) represented the coating prepared at 10 A/dm2 and 10 minutes possessing the lowest corrosion current density (Icorr=1.9 x 10-
7 A/cm2). At contact resistance measurement, we got value (3.2 mΩcm2) at 10 A/dm2 which less than the standard of DOE (20 mΩcm2). The results of single cell test showed better performance (about 338.0 mW/cm2) at 10 A/dm2.

Figure 1
Various Types of Applications with Double Perovskite Structure
Authors: Jun Areum , Kim Junyoung , Shin Jeeyoung , Kim Guntae
Published: February 2020

Perovskite oxides with variable oxygen non-stoichiometry play a prominent role in many fields, including fuel cells, catalysis and gas storage. One interesting class of materials for solid oxide fuel cells (SOFCs) are cation ordered layered perovskite oxides due to their mixed ionic and electronic conductivity and fast oxygen kinetics. Even though progress has been made in cathode materials to lower the cathodic polarization, still it is also important for fuel cell technology to achieve highly efficient anode that realize long term stability with enhanced tolerance to carbon buildup (coking) and sulfur contamination (poisoning) from hydrocarbon fuels. Here, we report identification of redox-stable cation layered perovskite anode, with superior electrochemical performance in both hydrogen and hydrocarbons. Further, double perovskite materials will have immediate and profound implications for a new generation of SOFCs, proton conducting SOFC, oxygen separation membranes, electrolyzers, as well as other processes involving oxygen/electron transport.
Rational Design of Three-Dimensional TiO2 for Use in Li-Ion Battery
Authors: Park Soomin , Baek Jayeon , Song Chyan Kyung , Kim Tae Yong , Nam Inho , Han Jeong Woo , Yi Jongheop
Published: February 2020

Although high surface area and short lithium ion diffusion of nano-structure have dramatically improved the performance as the Li ion battery until now, inevitably accompanying problems such as electrode side reaction or structural instability made one develop for rationally designed architecture. In this research, a rational design of TiO2 architecture is exploited in order to elicit its intrinsic Li storage performance. We proposed the 3D dendritic TiO2 sphere as an idealized architecture which comprised of specialized nanorods. When fabricated into an electrode, the 3D dendritic TiO2 sphere is capable of delivering an outstanding efficiency in conjunction with long cycle charge/discharge stability. This approach, which is based on theoretical studies and experimental validation, provides guidance for tailoring electrode materials for use in Li storage systems.
Research on Unitized Regenerative Fuel Cell Stack with Producing High Pressure H2 and O2 in WE Mode
Authors: Zhang Xinrong
Published: February 2020

A unitized regenerative fuel cell (URFC) is an electrochemical energy storage device that combines a fuel cell and a water electrolyzer in a single system. The URFC is an excellent clean, quite energy source and are promising energy storage systems for uninterrupted power supplies, solar powered aircraft, and satellites. In the paper, the high pressure unitized regenerative fuel cell was developed and validated with a capacity of producing hydrogen and oxygen at a pressure of up to 5MPa in the water electrolysis mode.

The bifunctional performance of URFC stack in the hydrogen and oxygen fuel cell (FC) and water electrolysis (WE) modes and the generated gases pressure influence on URFC stack were investigated. The main electrochemical element is bifunctional membrane electrode assembly (MEA) with an active area of 200cm2 which consists of polymer electrolyte membrane from Dupont and the electrode layer on both sides of the membrane by catalyst coated on membrane technique (CCM). Oxygen electrode layer was prepared by Pt/IrO2mixing catalysts. Hydrogen electrode layer was prepared by 40%Pt/C (J.M.). The diffusion layer of MEA was the porous sintered metal foil with corrosion resistance.

Primary test results illustrated that high pressure URFC stack exhibited the promising bifunctional performance. The static seal level of URFC stack was up to 10MPa and the dynamic gas pressure reached 5MPa in the water electrolysis mode. Figure1 showed that the stack output electric power was greater than 1.2kW at a current density of 1000mA/cm2in the fuel cell mode.

Figure 2 showed that the generated gases pressure had few influence on the performance of the stack in the water electrolysis mode under working conditions. The single cell voltage was 5~12mV higher at the generated gases pressure of up to 5MPa when the current density was less than 700mA/cm2. However the single cell voltage was 5~10mV lower at the generated gases pressure of up to 5MPa when the current density greater than 700mA/cm2. The stack showed good pressure adaptability. The round-trip energy conversion efficiency of high pressure URFC stack was greater than 45% at the current density of 500mA/cm2.

In addition, the cycling test of the stack during URFC operation was performed in both fuel cell and water electrolysis modes. The results indicated that high pressure URFC stack had the promising cycling stability. Further research and validation are still underway.

Figure 1
Improvement of Cycle Life of Lithium Air Batteries Using Ag and Mg Alloyed Li Anode
Authors: Algül Hasan , Tokur Mahmud , Uysal Mehmet , Cetinkaya Tugrul , Alp Ahmet , Akbulut Hatem
Published: February 2020

Lithium-air batteries have attracted great interest due to great theoretical specific energy of Li-air excluding oxygen is 11.5 kWhkg−1, the value of which is comparable with that of gasoline/air device. This high energy density battery has the potential to be the power source for the advanced electric vehicles.  However, there are a lot of challenges, one of which is low cycleability of lithium-air batteries because of formation dendrites on lithium anode and most significantly very high corrosion of lithium metal when room temperature ionic liquids (RTILs) are used. In this study, it was aimed to increase corrosion resistance therefore, cycleability of anode materials in Li-air battery cells by using mechanical alloying with silver and magnesium powders.

The effect of the silver and magnesium on the electrochemical behavior of lithium anode for lithium-air batteries were investigated.  Fine granules of Li metal and silver or magnesium were used as starting materials. At the first step the production of the Li-Ag and Li-Mg alloys was optimized in the mechanical alloying process. Subsequently, Li-Ag or Li-Mg powder alloys were synthesized as anode materials. The high energy ball milling was performed under argon atmosphere at room temperature. The alloys produced by mechanical alloying were cold pressed to produce dense lithium alloys. The physical characterization of the produced anodes was evaluated by X-ray diffraction (XRD) and scanning electron microscopy(SEM). Electrochemical analysis of the lithium and lithium alloys were carried out using a Swagelok-type cell with 1 M LiPF6 in TEGDME as electrolyte and GDL (gas diffusion layer) as cathode and prepared Li-Ag and Li-Mg powders as working anode. The electrochemical impedance spectroscopy (EIS) measurement of the lithium and alloys have been conducted to investigate the difference in the resistance of the cell before and after electrochemical cyclic test.
Improvement of Charge Transfer Resistitance of Cathode in Ni-MH Batteries Using Ni/Al-LDH Prepared By Liquid Phase Deposition Method
Authors: Mizuhata Minoru , Takigawa Masashi , Maki Hideshi
Published: February 2020

Much attention has been paid to the layered double hydroxides containing transition-metal elements for various electrochemical devices. Nickel-aluminum layered double hydroxide (Ni-Al LDH) is the promising materials for the positive electrode of Ni-MH battery because of its good electrochemical properties and high stability in strong alkaline keeping the structure of α-Ni(OH)2. Furthermore, α-Ni(OH)2 have higher capacity than β-Ni(OH)2 which is commonly used for the electrode materials of Ni-MH battery, but less stability in strong alkaline. Generally, electrode is prepared by painting colloidal active materials, however, the internal resistance in the electrode is high. Improvement of the adhesion between current collector and active materials contribute to reduce the internal resistance, especially charge transfer resistance (R
ct) of an electrode reaction. Previously, we reported the precipitation of Ni-Al LDH with high crystallinity and high purity by the liquid phase deposition (LPD) method. The LPD method is the syntheses method of metal oxides and hydroxides using the hydrolysis reaction of metal fluorine complexes. The merits of LPD method are easy operation and following capability for substrate surface shape. In this study, the Ni-Al LDHs were directly prepared on the surface of Ni foam as a current collector of Ni-MH battery, and investigated the reduction effect of the R
ct. From the cross-sectional SEM images of the sample, dense Ni-Al LDH was deposited on the Ni foam surface, and the thickness was up to 950 nm. The resistance of charge transfer, R
ct was measured by an ac impedance spectroscopy at 0.5 V vs Hg/HgO.  The apparent activation energy of chage transfer is calculated from Arrhenius plots of the temperature dependence of R
ct values.  The composition of LDH was determinded by ICP-AES spectroscopy for Ni and Al, and neutralization titration for OH, as Ni0.95Al0.05(OH)2·A
0.05 ,where A is exchangable anionic species.  Deposition of Ni-Al LDH on the surface of Ni foam directly reduced the R
ct because of the improving the adhesion between current collectors and active materials as shown in Figure 1. In this case of using the sample where the Ni/Al LDH layer is deposited, the value of R
ct decreased with the thickness of LDH layer on the Ni metal form from ca. 0.8 to 0.2 Ω cm-2, where those values for the sample using LDH power increase over 0.8 Ω cm-2.  Furthermore, the activation energy for the electrode reaction decreased from 22.3 to 17.9 kJ mol-1 . It is suggested that the ionic transport becomes easily in the LDH layer and are coupled electronic conduction from Ni form using deposited Ni/Al LDH on Ni form.  This Ni-Al LDH/ Ni foam composite will be able to provide a secondary battery electrode having high charge transfer efficiency.

Figure 1
Improved Electrochemical Performance of Lithium Air Batteries with N-Methyl-2-Pyrrolidone Based Composite Polymer Electrolytes
Authors: Tokur Mahmud , Algül Hasan , Cetinkaya Tugrul , Akkbulut Ahsen , Uysal Mehmet , Guler Mehmet Oguz , Akbulut Hatem
Published: February 2020

Lithium air batteries are able to have higher energy density because of the lighter cathode and the fact that oxygen is freely available in the environment. This causes a great interest on these type of batteries. However, the performance of Li-air batteries is affected by many factors such as type of catalysts and electrolyte composition. The stability of electrolytes is a significant limitation for cycle life performance in Li-air batteries. In recent years, most efforts have focused on the development of stable electrolytes to improve cycle life and capacity of rechargeable Li-air batteries. Therefore, stability of the polymer composite electrolytes against the reduced oxygen species generated during the discharge process was investigated. Since Li2O2 is generated at the cathode surface during cycling, an investigation of the thermal stability, conductivity and resistance of electrolytes with Li2O2 was conducted. The other challenge of the stability of Li-air batteries is degradation of lithium anode. For this reason, great efforts of this study focused on improving lifetime and recycleability through, obtaining stable electrolyte with polymeric and inorganic additives.

For this aim, 1 M LiPF6 and LiBF4 salts dissolved in N-methyl-2-pyrrolidone (NMP) aprotic solvent and selected amount of polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO), which is mostly used as binders for air electrodes in Li-air batteries and Al2O3 nanoparticles added into the electrolyte to improve thermal stability, provide highly reversible Li-O2 reaction during charging/discharging and prevent clogging of the porous structure of the cathode. In order to investigate electrochemical performance of the produced nanocomposite electrolytes, ECC-Air test cell was assembled in Ar-filled glove box. The lithium foil was used as anode, Sigracet 24BC gas diffusion layer (GDL) was used as the cathode and prepared nanocomposite solutions were used as the electrolyte. The anode and cathode was separated with a glass fiber separator. Differential scanning calorimetry (DSC) and derivative thermagravimetry (TG) measurements were used for thermal stability studies for the electrolytes. The cells were cyclically tested using 0.1 mA/cm2 current density over a voltage range of 2.15–4.1 V. Electrochemical impedance spectroscopy (EIS) measurements was carried out to investigate the effect of the PVDF, PeO and Al2O3 additives on the resistivity of the electrolyte. After the electrochemical cycling test, the surface of the cathode (GDL) was characterized using environmental scanning electron microscopy, X-ray diffraction patterns and Raman spectroscopy to investigate deposited lithium compounds such as LiO2, Li2O2 and Li2CO3 on the cathode during cycling test.
Metallic MoS2 Nanosheets As Electrodes with High Volumetric Energy and Power Densities
Authors: Acerce Muharrem , Voiry Damien , Chhowalla Manish
Published: February 2020

In the past few years, considerable effort has been devoted to the study of graphene as energy storage material for supercapacitors. More recently other 2D materials have emerged such as MXenes and transition metal dichalcogenides. In this study, chemically exfoliated and restacked nanosheets of metallic 1T phase MoS2 has been introduced as a supercapacitor electrode and its electrochemical charge storage mechanism has been investigated in aqueous and organic electrolytes. High volumetric capacitance values (650F/cm3) have been obtained with 1T phase MoS2 even at high scan rates. High volumetric energy density (0.1Wh/cm3) and power density (51W/cm3) values were measured with organic electrolytes. During chemical exfoliation and restacking process, structural, chemical and electronic properties of MoS2 change via phase transformation from semiconducting 2H MoS2 to metallic 1T MoS2. High charge storage performances can be explained with the distinct structural and electronic properties of metallic 1T phase MoS2.  The good electrical conductivity of the 1T phase enables thicker and binder free film fabrication. Interestingly the capacitance obtained from 1T MoS2 is surprisingly high comparing the modest surface area of MoS2. In order to understand the charge storage mechanism, ex-situ XRD measurements were conducted. Our results demonstrate that cations (Proton, Li+, Na+, K+, TEA+) intercalate to the two dimensional MoS2 flakes and enhance the accessible surfaces for the charge storage. Charge storage performance is stable over 5000cycles (97% capacitance retention). Our study provides insight into the electrochemical behavior of the phase engineered exfoliated and restacked nanosheets.
NiO Hybrid Nanoarchitecture Based Symmetric Supercapacitor in Non-Aqueous Electrolytes with Improved Rate Capability and Cycle Life
Authors: Narayanasamy Padmanathan , Selladurai S. , Rahulan K. Mani , O'Dwyer Colm , Razeeb Kafil M
Published: February 2020

A three dimensional hierarchical NiO nanostructures with combined microstructure of nanoflakes and nanoflowers have been fabricated on carbon fiber cloth (CFC). Unique nano-micro structural features of NiO electrode exhibit an excellent electrochemical activity as electrode material for symmetric supercapacitors in non-aqueous organic electrolyte (1 M TEABF4 in propylene carbonate). The NiO/CFC electrode showed an enhanced electrochemical activity in organic electrolyte in terms of rate capability, specific energy and power performance, as well as potential limit. The symmetric supercapacitor showed a specific capacitance of 34.9 F/g at 1 A/g current density in organic electrolyte. The hybrid electrode delivered a maximum specific energy density of 19.4 Wh/kg at a high power density of 1002.8 W/kg in 1 M TEABF4/PC at a constant current density of 1 A/g. The cell is also capable of good reversibility with a cycling efficiency of 58% after 25000 cycles. This superior electrochemical activity of the NiO electrode is due to their structural benefits of well-connected hybrid nano/mesoporous structure and rapid ion intercalation within the porous electrode surface.
Enhanced Charge Transport and Storage of Two-Dimensional Vanadium Pentoxide
Authors: Rhodes Christopher , Lambdin Nicole , Patel Radica , Zaleski Audrey
Published: February 2020

Atomically thin two-dimensional (2D) materials have a number of key features for electrochemical charge storage including significant available surface area, quantum confinement in two dimensions, and distinct local structures (e.g. surface states, edge sites).   Vanadium pentoxide (V2O5) is a useful charge storage material based on its multiple available oxidation states which allows the material to store multiple ions and electrons within its structure during electrochemical cycling.  V2O5 has a high theoretical specific capacity of 294 mAh/g based on the two-electron charge storage process, and this capacity is significantly higher than the capacity of current commercial cathode materials (~160 mAh/g). However, typical forms of V2O5 exhibit severe capacity fading upon cycling. We have explored 2D forms of V2O5 to provide cathode materials with high capacities and improved cycling stability.  Two-dimensional V2O5 nanosheets were prepared from drying suspensions of ion-exchanged sodium metavanadate solutions. The synthesis, structural characterization, and electrochemical testing of 2D V2O5 will be presented to show the effect of various parameters (e.g. composition, particle size, aggregation, orientation) on the electrical and electrochemical properties.  The ability to control the structure and properties of 2D materials allows the development of improved charge transport and storage materials for batteries, supercapacitors, and other electrochemical applications.
Ion-Transport Characteristics of Alkaline Battery Cathodes Containing Different Graphitic Additives
Authors: Forouzan M. Mehdi , Robertson Logan , Wray Michael , Wheeler Dean
Published: February 2020

Yearly demand for primary alkaline batteries is around US$5 billion. Even though it is a mature technology, continued performance improvement is still possible. In common with other types of batteries, the performance of alkaline batteries is strongly affected by the composition and microstructure of the electrodes, especially the cathode. Naturally, in trying to optimize an electrode there are trade-offs between the capacity or amount of active material, and the volume fractions of conductive additive (carbon) and pores, which are each needed to transport charge.

 This work builds on our prior work in directly measuring transport properties of electrodes [1-2]. We focus on understanding ion transport in the alkaline cathode, which is composed of EMD (electrolytic manganese dioxide), graphitic carbon, and electrolyte-filled pores. The effects of varying carbon type, carbon amount, and overall porosity on the ionic conductivity and tortuosity were studied. The correlations between ion transport and the microstructure and electronic conductivity were investigated as well. Tested carbons included a variety of common graphite additives from TIMCAL as well as graphene. Multiple analysis tools were used, including SEM/FIB determination of microstructure, ion-transport experiments, and multi-probe determination of electronic conductivities. It was found that highly compressible expanded graphites like BNB90 actually have a more deleterious effect on overall ionic conductivity that do other additives. This suggests a tradeoff between ionic and electronic conductivity performance in the choice of graphitic additive.

 Furthermore, the degree of anisotropy of ion transport in the cathode for different conditions was investigated for samples containing EMD and BNB90 additive. Anisotropy of the structure of the graphite, caused by pellet compression, was observed by SEM. It was found that tortuosity is lower and ionic conductivity is higher in the direction orthogonal to the direction of compression.

 [1] Zacharias et al., J. Electrochem. Soc. 160, A306-A311 (2013).

[2] Peterson and Wheeler, J. Electrochem. Soc. 161, A2175-A2181 (2014).

Figure 1
Investigating Novel Electrolytes to Suppress Dendrite Growth in Li-Air Batteries
Authors: Ryan Emily M , Tan Jinwang , Sokolinski Tatiana , Ferris Kim
Published: February 2020

This research focuses on improving the performance and durability of advanced lithium air (Li-air) battery technologies through computational modeling and materials informatics. In particular, the issue of dendrite growth at the anode-electrolyte interface was investigated through physical models and a materials informatics approach to identify novel electrolyte materials for Li-air batteries.

Dendrites form on the anode surface over multiple charge and discharge cycles, causing a decrease in performance and safety concerns due to short circuiting. Dendrite growth depends strongly on the reactive transport near the anode-electrolyte interface and heterogeneities on the anode surface. To reduce dendrite growth, we investigated increasing the mixing near the anode-electrolyte interface through novel electrolyte designs that directionally affect the transport properties of the electrolyte solution. The research was divided into two main tasks: physical modeling of dendrite growth and morphology, and development of a materials informatics approach for identifying novel electrolyte materials.

            Dendrite growth was investigated using the meso-scale smoothed particle hydrodynamics (SPH) method. SPH is a mesh-free technique that uses a Lagrangian framework to model the simulation domain as a discrete system of particles.  SPH particles are used as interpolation points to discretize and solve the governing partial differential equations of a system based on the SPH smoothing function. Due to its Lagrangian nature, SPH does not require explicit boundary tracking, which allows for simple implementation of complex geometries and moving boundaries, such as the dendrite formation at the anode-electrolyte interface.

A materials informatics approach was used in a discovery mode to identify promising material combinations for the electrolyte. Our research focused on developing the materials informatics framework for electrolyte solutions. The developed framework is general and is applicable to other materials systems for batteries and for other application areas. The informatics techniques have predictive capabilities based upon an electrolyte materials knowledge base, allowing us to evaluate materials based on their thermodynamic properties and the desired properties needed for a specific application.
Modeling Diffusivity in Catalyst Layer of a PEMFC Based on a Unit Cell Approach
Authors: Salari Sina , McCague Claire , Tam Mickey , Stumper Jürgen , Bahrami Majid
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFC) convert the reaction energy of hydrogen and air to electricity without harmful emissions. PEMFC rely on a membrane-electrode assembly (MEA) constructed from multiple layers of micro/nano porous materials and associated interfaces.  The MEA includes a polymer electrolyte membrane (PEM) that conducts protons, a composite nano-structured catalyst layer (CL), and a fibrous gas diffusion layer (GDL) that distributes reactant gases and collects current. The production cost and limited durability of the platinum catalyst layer is a significant challenge for the commercialization of hydrogen fuel cells. The greater the activity of the Pt nanoparticles, the lower the required Pt loading on the carbon support, and the lower the production costs for the catalyst layer. Hydrogen and oxygen reactants diffuse to the catalyst Pt particles. Existing models for the diffusivity of CL are either not accurate or computationally demanding, making them difficult to use for CL optimization. In this study, the CL is represented by unit cells based on porosimetry and analysis of SEM images of CL structure. The mass diffusion problem is analytically solved for the unit cell to calculate effective diffusivity of CL. Unlike other simple models which use porosity as the only input to calculate diffusivity the proposed model considers the pore size distribution as well as structure of CL, which improves the accuracy. The model presented in this study shows results within acceptable accuracy respect to published experimental data.
Hierarchical TiO2 Hollow Nanospheres: Ultra Stable Anode for Na-Ion Batteries
Authors: Su Dawei
Published: February 2020

Amorphous TiO2@C nanospheres were synthesized via a template approach. After being sintered at different condition, two polyphase TiO2 hollow nanospheres were obtained. The electrochemical properties of amorphous TiO2 nanospheres, and different phase TiO2 hollow nanospheres as anodes for the Na-ion batteries were characterized. It was found that all of them demonstrated the excellent cyclability, which can sustainable for thousands of cycles with tiny capacity fading. By comparison, the anatase TiO2 presented higher capability than that of rutile TiO2 and amorphous TiO2. Through the crystallography analysis, it was revealed that anatase TiO2 crystal structure supplies 2-dimension diffusion path for the Na ions intercalation and more accommodation sites. Density functional theory (DFT) calculation indicates lower energy barriers for Na+ inserting into anatase TiO2. Therefore, anatase TiO2 hollow nanospheres show the well-defined high rates performance. Via the ex-situ FESEM analysis, it was revealed that the TiO2 hollow nanospheres architecture can be maintained for thousands cycles, which is the main reason for its superior cyclablity.
First-Charge Instabilities of Layered-Layered Lithium-Ion-Battery Materials: Relationship of Oxygen Ion Displacement to Mn Migration
Authors: Croy Jason R. , Iddir Hakim , Gallagher Kevin G. , Benedek Roy , Balasubramanian Mahalingam
Published: February 2020

Layered-layered composites with composition xLi2MnO3•(1-x)LiMO2 enable high capacity and energy density Li-ion batteries, but suffer from degradation with cycling. Evidence of atomic instabilities during the first charge are discussed based X-ray absorption spectroscopy, first principles simulation, and existing literature. EXAFS measurements on 0.3Li2MnO3•0.7LiMn0.5Ni0.5O2 during the first charge were analyzed to determine the coordination number deficit of Mn and Ni.
Self-Assembly of Nanoparticle and Block Polymer Electrolytes
Authors: Villaluenga Irune , Inceoglu Sebnem , Jiang Xi , Chen Xi chelsea , Devaux Didier , Balsara Nitash P.
Published: February 2020

Electrolytes used in rechargeable lithium-ion batteries are mixtures of lithium salts and alkyl carbonate solvents. The high ionic conductivity of these electrolytes is well-suited for several applications including cellphones and laptops. Unfortunately, these electrolytes are flammable and this limits our ability to use lithium batteries in large devices like electric vehicles. Solid block copolymer electrolytes are inherently less flammable and thus better suited for large scale applications.1 The ionic conductivity of block copolymer electrolytes is governed by the tortuosity of the conductive pathways, which is related to the morphology of block copolymers.2,3 Therefore, the ionic conductivity can be controlled by tuning the morphology. One approach consists in the addition of nanoparticles to block copolymer electrolytes. The morphology of these systems depends on the arrangement and the location of the nanoparticles in the block copolymer.4

Here, we describe the effect of the addition of functionalized silsesquioxane nanoparticles on the morphology and electrochemical properties of polystyrene-b-poly(ethylene oxide) diblock copolymer electrolytes.

_______________________

[1] Parker, J. M.; Wright, P.V. Polymer
1973, 14, 589.

[2] Singh, M.; Odusanya, O.; Wilmes, G. M.; Gomez, E. D.; Patel, A. J.; Chen, V. L.; Park, M. J.; Eitouni, H. B.; Fragouli, P.; Iatrou, H.; Hadjichristidis, N.; Balsara, N. P. Macromolecules
2007, 40, 4578.

[3] Hallinan, D. T.; Balsara, N. P. Annu.
Rev. Mater. Res. 2013, 43, 503.

[4] Warren, S. C.; DiSalvo, F. J.; Wiesner, U. B. Nat. Mater.
2007, 6, 156.
Photosensitizing Properties of Thiolated Gold Clusters. Exploring Beyond Plasmonics
Authors: Chen Yong Siou , Kamat Prashant V
Published: February 2020

Metal nanoparticles possess unusual catalytic and optical properties. Specifically, larger size particles exhibit plasmonic effects as they interact with incident photons. However, the plasmon resonance activity ceases as the size of metal nanoparticles decrease. However, such small size nanoparticles with few atom metal clusters continue to exhibit photoactivity in the visible. The gold clusters containing 10-25 metal atoms exhibit molecular like properties with relatively long lived excited state (lifetime ∼ 800 ns). When a mesoscopic TiO2 film sensitized by Aux-GSH NCs was used as the photoanode in a photoelectrochemical cell, we can generate photocurrent under visible light irradiation with a photoconversion efficiency of 2%. The reversible reduction (E0= -0.63 V vs. RHE) and oxidation (E0= 1.51 V vs. RHE) potentials make them suitable as visible sensitizers for driving the water splitting reaction. Additionally, sensitizing Pt/TiO2 nanoparticles with Aux-GSH NCs has been explored in an aqueous slurry system and irradiating with visible light resulted in hydrogen production. These metal nanoclusters which serve as a new class of visible photosensitizers exhibit significantly higher photoactivity than the larger nanoparticles and thus offer new opportunities as light harvesting assemblies.
(Invited) Fabrication of Micro- and Nanostructures for High Efficiency Energy Conversion By Using Anodic Porous Alumina
Authors: Masuda Hideki , Kondo Toshiaki , Yanagishita Takashi
Published: February 2020

The fabrication of micro - and nanostructured materials with controlled geometrical structures has attracted increasing interest for the preparation of various types of energy conversion devices with high efficiencies.  The use of the material, which has naturally occurring ordered structures, is effective for the fabrication of the micro- and nanostructures of various kinds of materials.  Anodic porous alumina, which is formed by anodization of Al in acidic solution, is a promising candidate for the fabrication of micro- and nanostructured materials with controlled geometrical structures1,2.  One of commonly used process for the fabrication of micro- and nanostructures using anodic porous alumina is a template synthesis3,4.  This process can generate the micro- and nanostructures with controlled geometrical structures, which are useful for the fabrication of high efficient energy conversion devices.  However, the problem of the usual template synthesis is the low throughput due to the difficulty of the repeated use of the template.  To solve this problem, we have been studying the new types of processes, which allow the high throughput formation of micro- and nanostructures.  In the present report, recent results concerning the high throughput fabrication process for the micro- and nanostructures of metals and metal oxides, which can be applied to the energy conversion devices.  The processes include the molding fabrication process for metal nanowires, and the membrane emulsification for uniform sized nanoparticles of metal oxides5,6 by using anodic porous alumina.  These processes allow the high throughput fabrication of micro- and nanostructures because the starting structures of anodic porous alumina can be used many times.  The obtained micro- and nanostructures will be useful for the fabrication of energy conversion devices with high efficiency due to their precisely controlled geometrical fine structures. 

1. T. Yanagishita, K. Nishio, and H. Masuda, Appl. Phys. Express, 1, 067004 (2008).

2. H. Masuda and K. Fukuda, Science, 268, 1466 (1995).

3. K. Yasui, T. Morikawa, K. Nishio, and H. Masuda, Jpn. J. Appl. Phys., 15, L469 (2005).

4. T. Kondo, T. Fukushima, K. Nishio, and H. Masuda, Appl. Phys. Express, 2, 125001 (2009).

5. T. Yanagishita, R. Fujimura, K. Nishio, and H. Masuda, Langmuir, 26, 1516 (2009).

6. T. Yanagishita, Y. Maejima, K. Nishio, and H. Masuda, RSC Adv., 4, 1538 (2014).
Synthesis and Characterization of CdSe Quantum Dots for Photovoltaic Application
Authors: Dasari Mallika , Kohli Punit
Published: February 2020

Nanomaterials and nanotechnology attained remarkable importance in the recent years. Nanomaterials have applications in diverse fields including chemistry, physics, material science, medicine, and engineering. Quantum dots (QDs) are semiconducting nanoparticles with particle size in the nanometer scale. QDs have typical diameters ranging from 1 to 10nm possess exceptional optical and electrical properties that makes them useful in photovoltaic, laser and light emitting diode (LED) applications. The band gap of QDs can be tuned by controlling the growth size and so the optical properties can be tuned in the visible range with broad excitation range. In our paper we synthesized and characterized CdSe quantum dots using hot injection method. We have successfully synthesized QDs of three different sizes ranging from 1 to 10nm in three sampling steps emitting in green, yellow and red region of the visible spectrum. Growth characteristics of QDs were studied by growing them at different temperatures and for different times than typical standard growth parameters. We attempted to synthesize QDs with varying sizes in one sampling step. The varying sizes were formed at 175oC with multiple injections of Se in varying quantities. The fluorescence spectra showed three peaks at 482, 518 and 590nm respectively. The emission peaks indicating QDs of three different sizes, which was achieved by creating three nucleation steps by injecting controlled amounts of Se. Our QDs can be used in the photovoltaic application to improve the light absorption (broad wavelength) by the photo active material and to improve the charge carrier generation. We performed optical and electrical characterization using UV-Visible, fluorescence spectroscopy, cyclic voltammetry and Keithley. The crystallinity of QDs with different growth time was measured using X-ray diffraction (XRD) spectroscopy.
Polar Self-Assembled Subphthalocyanine Materials
Authors: González-Rodríguez David , Guilleme Julia , Torres Tomas
Published: February 2020

Subphthalocyanines (SubPcs)1 are singular cone-shaped molecules with unique physicochemical properties that render them promising light-harvesting and/or donor units for photovoltaic and light-emitting applications. We were very interested in studying if such molecules could be organized in columnar stacks, both in solution2 and liquid-crystalline phases3 by hydrogen-bonding and p-p stacking interactions. The columnar aggregation of these non-planar molecules with axial dipole moments represents in itself a challenging task. Our motivation comes from the possibility of obtaining supramolecular chiral nanofibers and condensed phases that can be aligned in the presence of electric fields, yielding nanomaterials with permanent polarization and unusual ferroelectric and piezoelectric properties.

Figure 1