bluuebunny/crossref_metadata_2025 huggingface dataset:
Graphite Anodes for Electroreduction of Uranium Oxide
Authors: Motsegood Perry , Willit James , Williamson Mark A.
Published: February 2020

Recycling of used nuclear oxide fuel is under investigation using pyrochemical methods, which involve a series of molten salt processes performed at elevated temperatures and result in the separation of actinides from fission products. During this process, used fuel oxides are electrochemically reduced to metals prior to electrochemical separation of the actinides from fission products in a subsequent process step. This electroreduction is typically performed at 650°C in LiCl-Li2O. Reduction of UO2, the primary component of used nuclear fuel, has been successfully demonstrated at the kilogram-scale using platinum anodes1-2, but progression toward larger scales presents different requirements for anode materials.

Carbon (graphite) is commonly used in commercial molten salt processes within the ore refining industry. It is cost effective, readily available, and a logical choice for scale-up needs. However, different chemistries in molten LiCl-Li2O result from this change of anode material in both the salt and off-gas streams. Instead of forming oxygen at a platinum anode, the byproduct gas becomes CO and CO2. Although slightly soluble, these species can react with Li2O to form Li2CO3 as a result of residence time within the salt. The carbonate concentration can build up in the salt during the reduction process, which is problematic because of potential reaction between actinides and carbonate ions to form undesired byproducts in the reduced product.

This report will discuss use of carbon as an anode material for the electroreduction of UO2 to uranium metal in molten LiCl-Li2O at 650°C. We will present design challenges and a discussion of salt chemistry with respect to carbonate formation in the system, along with results on reduction efficiency.

References:

Laszlo Redey and Karthick Gourishankar, “Direct Electrochemical Reduction of Metal-Oxides” US Patent US6540902 B1, Granted April 1, 2003

S. D. Herrmann, S. X. Li, M. F. Simpson and S. Phongikaroon, Separation Science and Technology
2006, 41, 1965-1983.

The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government.
Importance of Polymer Backbone Stability of Anion Exchange Polymer Electrolytes
Authors: Kim Yu Seung , Lee Kwan-Soo , Choe Yoong-Kee , Fujimoto Cy
Published: February 2020

Anion exchange membranes have received attention for solid-state alkaline membrane water electrolysis. However, the harsh operating condicitions of alkaline membrane water electrolysis require good chemical stability of the membrane. Chemical degradation of anion exchange membranes can occur in the cationic functional group, cationic functional group-polymer linkage, and polymer backbone. The alkaline stability of cation-functionalized polyaromatic membranes has mainly been discussed in the context of cation stability. Thus far, lifetime studies of cation-fucntinalized polyaromatics indicate that cation stability is of paramount importnace for stable operation of alkaline membrane water electrolysis. However, equally important is the stability of the polymer backbone which may impact the key membrane properties such as mechanical toughness, hydroxide conductivity and water uptake.[1]

In this study, comparative studies on cationic group vs. polymer backbone stabilities of cationic group functionalized polyaromatic membranes were made by computational modeling and experimenatal method. The computational modeling study suggests that the facile backbone degradation of anion exchange membranes is not only due to the electron deficincy of the polymer backbone but also due to the low bond dissociation energy of the molecular stucture. The relatively lower bond dissociation energy of heteroatom substitutuents in the polymer backbone of anion exchange membranes caused facile backbone degradation before cationic functional group degradation. For example, benzyl trimethyl ammonium has very high electonegativity but the degradation occurs after aryl-ether degradation due to the high bond dissociation energy of carbon-carbon or carbon-nitrogen bonds.

Experimental study on degradation of benzyl trimethyl ammonium functionalized fluoirnated poly(arylene ether) membranes suggests further insight regarding polymer backbone degradation. The C-N stretching peaks of the poly(arylene ether) membranes is shifted to the higher wave number (blue shift) due to the cationic group degradation of the cationic group attached to the phenolic structure occurs before that of the cationic group attached to the un-degraded polymer backbone. This inidcates accessibility of water molecules also play a critical role in polymer backbone degradation. We will provide some other evidences on facile backbone degradation of polyaromatic polymers and their impact on membrane properties at the meeting. This presentation emphasizes on the importance of polymer backbone stability.

[1] Fujimoto, C.; Kim, D. S.; Hibbs, M.; Wrobleski, D.; Kim, Y. S. J. Membr. Sci. 2012, 423, 438−449.
Conductivity and Mechanical and Thermal Stability of Polyelectrolyte-Functionalized Anion Exchange Membranes
Authors: Rodriguez-Silva Allen , Movil-Cabrera Omar , Staser John A
Published: February 2020

Recent studies have shown that anion exchange membranes (AEMs) surpass cation exchange membranes (CEMs) in that they reduce fuel crossover and facile electrochemical kinetics in alkaline solution which makes possible the use of non-precious metal electrocatalysts. However, the chemical and mechanical stability of AEMs is generally poor compared to CEMs. Our research has focused on developing porous AEMs utilizing a stable, nonconductive polymer (polysulfone) as the structural matrix functionalized with an ion-conducting polyelectrolyte filling the pores. We have synthetized these membranes via a simple phase-inversion process. Preliminary results using electrochemical impedance spectroscopy (EIS) indicate that the membrane conductivity is not always proportional to the quantity of polyelectrolyte in the phase inversion solution, which has led us to believe that non-homogeneous distribution of the polyelectrolyte may be taking place due to the polarity difference of these molecules. These results are shown in Figure 1 [1].

Continuous analysis and study of the conductive properties as a function of the amount of polyelectrolyte will be performed. Surface and cross-sectional images to identify the porous structure of these AEMs, as well as thermal gravimetric analysis (TGA) investigating thermal stability of these membranes will be presented. Finally, water diffusion anisotropy data will be collected by nuclear magnetic resonance (NMR) technique.

Figure 1: Rodríguez. A., Staser, J. (2015). “Synthesis of polyelectrolyte-functionalized anion exchange membranes and conductive, mechanical and thermal properties study”. (Manuscript is currently in progress)

Figure 1
Status of Vertical Electroplishing at Cornell University
Authors: Furuta Fumio
Published: February 2020

Cornell's SRF group has continued R&D on vertical electropolishing (VEP) of Niobium SRF Cavity with electrolyte of HF(40w%):H2SO4(96w%) in Volume proportions 1: 9. Compared with conventional horizontal EP system for SRF cavities, VEP could eliminate rotary acid seals, sliding electrical contact, cavity vertical/horizontal position control fixtures. And also, the acid plumbing/containment could be simplified. So, the cost reduction of capital equipment is highly expectable. Many of single- and multi-cell cavities have been processed with VEP and performed RF test at Cornell. VEP’ed multi-cell cavity performance was limited by too much Qo degradation above 25MV/m before. But in the analysis of removal vs. field gradient against previous VEP’ed cavity tests, we have found a tendency that small removal as final etches could provide high gradient without Qo degradation. The ILC 9-cell cavity “ACCEL9” with TESLA shape processed by VEP at Cornell achieved Eacc of about 40MV/m by minimizing final removal. This is the first 9-cell cavity that achieved ILC base-line specification (Qo=1.0e10 at 31.5MV/m, Qo=8.0e9 at 35MV/m) by VEP in the world. We have also fabricated demountable half-cell coupon cavity. This cavity consists of Nb half-cell and dummy cavity assemblies. This coupon cavity provides us more information about VEP process details, such as the difference of I-V curve between cell orientations.  Four demountable Nb coupons with diameter of 11mm are attached on half-cell and processed. These coupons are very strong tool for further surface analysis to optimize process parameters. We will present our current status of VEP R&D, cavity test results, and fundamental study results with Nb coupons.
(Invited) Operating Mechanisms of Organic Bulk-Heterojunction Solar Cells
Authors: Garcia-Belmonte Germa
Published: February 2020

Bulk-heterojunction solar cells contains an interpenetrated blend of donor-acceptor molecules that assists photogeneration and carrier transport. We show for thinner films in which transport or outer interface extracting limitation is not severe that carrier recombination is easily accessible from impedance analysis, and permits evaluating losses in (Fermi level) voltage. As a result reconstruction of the current-voltage characteristics in any required conditions based on a restricted set of measurements is possible. The analysis highlights carrier recombination current as the determining mechanism of organic solar cell performance. In addition the influence of the electronic density-of-states (DOS) caused by the inherent energy disorder on open-circuit voltage and fill factor is highlighted. The connection between DOS and the capacitive response is also addressed.

A discussion of impedance analysis in the much less studied case of collection-limited solar cells is discussed. Recent experimental analyses of transport processes are presented. We show how by incorporating blocking electrodes into the cell structure transport mechanisms can be understood in terms of diffusion-recombination models. Impedance spectra reveal carrier diffusion signature when blocking or extracting cathode contacts are employed. Finally contact effects are also addressed. The energy level alignment at the contacts is of primary importance in establishing the contact extracting ability and carrier selectivity. Several characterization techniques of the contact properties are explored.
(Invited) Unexpected Molecular Interfaces: SAMs on Cobalt
Authors: Pookpanratana Sujitra , Richter Curt A. , Hacker Christina A.
Published: February 2020

Molecular-based materials are appealing for many applications due to their diverse composition, which in turn impacts physical and electronic properties. Often, the interaction between an organic layer and an inorganic substrate is unpredictable once the interface is formed. We use a holistic approach to investigate the molecular interfaces – photoelectron spectroscopies and electrical characterization to probe the interface and buried junction, respectively. Thus, molecular-based interfaces provide a unique platform to investigate the ensemble-scale impact molecules which provide basic physical insights and ideas for potential applications.  

An emerging field is to combine the flexibility of organic materials into spin-based electronics. Most research in this field implement organic semiconductors as the non-magnetic spacer in a spin-valve device configuration.  While there are many proposed mechanisms regarding spin-transport in organic materials, there is no doubt that the interface between the magnetic electrode and organic material is an important aspect for the success of an organic spintronic device. In addition to potentially altering the electronic structure at the interface, SAMs could serve as a tunneling barrier for spintronics due to their insulating nature and discrete thickness. Inorganic tunnel junctions have improved spin-injection into organic spin-valve devices.

We have explored self-assembled monolayers (SAM) on a template-stripped and oxidized cobalt surface to understand the molecular-metal interface from a structural, chemical, and electronic point of view. We find that the self-assembly of the bifunctional molecule is profoundly different than the thiol-alone species.  In particular, the cobalt surface exhibits a very different interface following self-assembly of a carboxylic acid-bearing species. We find that a thiol-carboxylic acid monolayer reacts with oxidized Co surface atoms in such a way that metallic Co atoms are detected at the surface. We propose two different models of the interface formation based on the results, and suggest that the MHA/ethanol removes the cobalt oxide during the self-assembly as the prevailing model. We also discuss the impact of this Co/molecule interface on electron transport through Co/molecule/Si molecular junctions. Our results provide insight into ex-situ modification and functionalization of ferromagnetic interfaces impacting an important aspect of spin-based devices. Interfaces are not always straight forward – they can have unforeseen impact and influence.

Figure 1
(Invited) Considerations for Materials, Processes, and Characterization of Flexible Electronics
Authors: Wong William S.
Published: February 2020

Conventional methods of monolithic integration are reaching a practical limit for large-area electronics where miniaturization is not the major constraint for scaling the technology. An overview of novel printing approaches to fabricate thin-film transistors (TFTs) on flexible polymeric substrates for displays and image sensor applications will be presented. The effect of low-temperature processing of Si-based device characteristics will be discussed along with long-term device stability of organic and inorganic semiconductor TFTs under both electrical bias and mechanical strain. Finally, a comparison of the advantages and disadvantages between organic/polymeric and Si-based semiconductor devices on flexible platforms will be reviewed.
Synthesis, Characterization, Electrochemical and Optoelectronic Properties and LED Device Fabrication of Low Band-Gap Donor-Acceptor Organic Semiconducting Small Molecules
Authors: Dhamodharan Ragavachari , Ramachandran Elumalai
Published: February 2020

Organic fluorophores that exhibit efficient emission in the NIR region, especially in the solid state, are scarce. The design of organic materials towards efficient solid state emission has gained immense importance [1] due to their applications in various fields, such as organic light emitting devices (OLEDs), flat panel displays, organic solid-state lasers and fluorescent sensors [2]. Among the various fluorophores, red emitters have acquired a great deal of importance since red is one of the three primary colors used for white light emission [3]. The development of p-conjugated systems emitting in the NIR region is of great importance as they are often used in bio-imaging, laser printers, optical disks, plasma panel displays and heat absorbers [4]. For low energy emission such as red and NIR, planar molecular architecture with extended conjugation is inevitable for lowering the band-gap. But this extended planar architecture often leads to a strong intermolecular p-p interaction, a detrimental phenomenon by which the molecule loses its excitation energy through a non-radiative emission, resulting in weak emission. In the light of these facts it is a challenging task to design molecules that would exhibit efficient emission in the solid state, especially in the red to NIR region.

This presentation will discourse upon the synthesis, characterization, electrochemical, optoelectronic properties and LED device fabrication of low band-gap donor-acceptor organic semiconducting small molecules that exhibit solid state emission in the yellow to NIR region.

References

a) Shimizu, M.; Hiyama, T. Chem. Asian. J.
2010, 5, 1516; b) Sreejith, S.; Divya, K. P.; Ajayghosh, A. Chem. Commun. 2008, 2903; c) Zhang, Z.; Xu, B.; Su, J.; Shen, L.; Xie, Y.; Tian, H. Angew. Chem.
2011, 123, 11858; d) Zhou, Y.; Kim, J. W.; Kim, M. J.; Son, W. J.; Han, S. J.; Kim, H. N.; Han, S.; Kim, Y.; Lee, C.; Kim, S. J.; Kim, D. H.; Kim, J. J.; Yoon, J. Org. Lett.
2010, 12,1272.

a) Kulkarni, A. P.; Tonzola, C. J.; Babel, A.; Jenekhe, S. A. Chem. Mater. 2004, 16, 4556; b) Justel, T.; Nikol, H.; Ronda, C. Angew. Chem.
1998, 110, 3250; c) Samuel, I. D. W.; Turnbull, G. A. Chem. Rev. 2007, 107, 1272; d) Zhang, S. W.; Swager, T. M. J. Am. Chem. Soc.
2003, 125, 3420.

a) Adhikari, R. M.; Duan, I.; Hou, L.; Qiu, Y.; Neckers, D. C.; Sha, B. K. Chem. Mater. 2009, 21, 4638; b) Park, M. J.; Lee, J.; Park, J. H.; Lee, S. K.; Lee, J. I.; Chu, H. Y.; Hwang, D. H.; Shim, H. K. Macromolecules. 2008, 41, 3063.

Qian, G.; Wang, Z. U. Chem. Asian  J. 2010, 5, 1006.

Figure 1
Photoelectrochemical Studies and Capacitance Measurements during the Nitride Passivation of InP in Liquid Ammonia (-55°C)
Authors: Njel Christian , Bakas Idriss , Aureau Damien , Gonçalves Anne-Marie , Etcheberry Arnaud
Published: February 2020

This work presents a fundamental photo-electrochemical process at the interface SC/electrolyte. The photoelectrochemical passivation of n-InP is reported in liquid ammonia (-55 °C) during an anodic treatment[1]. The extraction of InP sample from the solvent is successfully performed at ambient temperature. Thanks to XPS (X-ray Photoelectron Spectroscopy), a reproducible polyphosphazene like film is reported on InP (-[(H2N)-P=N]n-)[2]. A soft anodic electrochemical treatment under illumination is applied at the interface to provide a gradual controlled coverage ratio of the surface by the film. This quantitative study requires a chronopotentiometry process with a constant anodic current of 1µA.cm-2 under illumination. An anodic charge around 0.3 mC.cm-2 is enough to ensure a complete coverage of the surface by the film. According to the anodic charge a gradual striking flat band potential shift is observed (Fig. 1). A flat C-2 = f(V) is extended over 1 volt leading to a high interfacial capacitance (» 2µF.cm-2). From the analysis of capacitance-potential curves, the interface appears to be under accumulation conditions after the film formation. A significant drop of the resulting photo potential is then observed (Fig. 2). However, under a strong positive overvoltage (» 1V), a stationary anodic photocurrent is recovered.

[1] A-M. Gonçalves, N. Mézailles, C. Mathieu, P. Le Floch, A. Etcheberry, « «Fully Protective yet functionalizable monolayer onto InP” Chemistry of Materials.22(2010) 3114-3120.

 

[2] A-M. Gonçalves, C.Njel, C. Mathieu, D.Aureau, A. Etcheberry.
« Phosphazene like film formation on InP in liquid ammonia (223K)  . Thin Solid Films 538 (2013) 21–24.

Figure 1
An Attractive Wet Route for Nitriding III-Vs
Authors: Njel Christian , Aureau Damien , Gonçalves Anne-Marie , Etcheberry Arnaud
Published: February 2020

The control of surface quality or interface chemistry is one of the key steps for a lot of new advanced industrial products with high added value. This is particularly true in the case of III-V semiconductors (III-Vs) technology for which surface passivation plays a key role in device performances, low temperature and low damage processes having been developed over time to reduce surface effects.

With the introduction of III-V’s on large scale Silicon platforms and device scaling to nanometer range, passivation question will be on the front page again
[1]
. Phosphorus nitride insulating films as passivation layers on InP seem to be very attractive to realize MISFETs with high channel electron mobilities and low interface state densities. This paper presents an original electroless approach of polyphosphazen film formation on InP in liquid ammonia (-55 °C). The chemical surface modifications are closed to those observed by electrochemistry[2],[3]. These findings are protected by a CNRS patent filed by us in 2013
[4]
. Moreover, the chemical stability of the surface is also demonstrated by XPS analyses. Indeed no air ageing of the surface is observed after three months of air exposure. The electroless mode is attractive to the industry since it avoids any electrical (potential and current) control at the interface.

This paper proposes a novel electroless passivation route in liquid ammonia through a “Polyphosphazen like” film formation which could be adapted to a large scale production since no electrical contact is involved at the interface to provide a full and efficient chemical passivation.

 

[1]“Interface engineering and chemistry of Hf-based high-k dielectrics  on III–V substrates”, G. He, X. Chen, Z. Sun, Surface Science Reports 68 (2013) 107.

[2] A-M. Gonçalves, N. Mézailles, C. Mathieu, P. Le Floch, A. Etcheberry, « «Fully Protective yet functionalizable monolayer onto InP” Chemistry of Materials.22 (2010) 3114-3120.

[3] A-M. Gonçalves, C.Njel, C. Mathieu, D.Aureau, A. Etcheberry.
« Phosphazene like film formation on InP in liquid ammonia (223K). Thin Solid Films 538 (2013) 21–24.

[4] “Polyphosphazène electroless sur semiconducteurs III-P”, réf CNRS 03024-01 BFF100427CG

A. Etcheberry, A-M. Gonçalves, C. Mathieu, J. Vigneron, N. Mézailles, P. Le Floch
(Invited) Use of the Doping Dependence of Collection Efficiencies for Dye Sensitized Photocurrents to Demonstrate Physical Models for Charge Transfer at Single Crystal Oxide Semiconductor Surfaces
Authors: Spitler Mark T , Parkinson Bruce A , Watkins Kevin
Published: February 2020

The different physical limits of an Onsager-based model for charge collection at a semiconductor electrode are revealed through an experimental examination of the doping density dependence of photocurrents at single crystal ruitile TiO2 electrodes sensitized with the N3 chromophore and a trimethine cyanine dye. As the doping density of the electrodes was varied from 1015 cm-3 to 1020 cm-3, three different regimes of behavior were observed for the magnitude and shape of the dye sensitized current-voltage curves. Low-doped crystals produced current-voltage curves with a slow rise of photocurrent with potential. At intermediate doping levels, Schottky barrier behavior was observed producing a photocurrent plateau at an electrode bias in the depletion region. At highly doped electrodes tunneling currents played a significant role, especially in the recombination processes. The fitting revealed the role of the various physical parameters that govern photoinduced charge collection in sensitized systems.
Pseudocapacitive Charge Storage at Nanoscale Silicon Electrodes
Authors: McSweeney William , Geaney Hugh , Glynn Colm , McNulty David , O'Dwyer Colm
Published: February 2020

Current lithium-ion battery anode research involves significant investigations of semiconducting materials, particularly Si as its theoretical specific capacity is >4000 mAh/g1.  Previous theoretical studies showed that porous Si with a large pore size and high porosity can maintain its structure after Li ion induced alloying and swelling. Metal-assisted chemical (MAC) etching is shown here to form internally mesoporous nanowires in the form of a layer, etched from highly doped Si2-4. Some porous materials are well known to exhibit pseudocapacitive behaviour in aqueous electrolytes5,6. Maintaining the structure without stress-induced cracked caused by volumetric changes in material is crucial in achieving a high capacity and long cycle retention. Almost all investigations of nanoscale Si involve their deposition onto a metallic current collector electrode within the battery cell. Here, we demonstrate that pseudocapacitive behaviour can be harnessed when Si nanowires are etched to maximum mesoporosity, forming an electrically dead layer on silicon current collector electrodes. This limits insertion or alloying processes to form Li-Si phases7and charge is stored within the electric double layer, even in Li-ion containing electrolytes. Measurements using cyclic and linear voltammetry supported by Raman scattering spectroscopy and electron microscopy confirm surface charge storage mechanisms; pseudocapacitance is not observed when the same nanowires are used on stainless steel current collectors.  In such cases, the rate of lithiation is shown to be related to the degree of porosity and the net surface electronic density of the porous silicon in accumulation mode during charging.

References

C. K. Chan, H. Peng, G. Liu, K. McIlwrath, X. F. Zhang, R. A. Huggins and Y. Cui, Nat. Nanotechnol.
3, 31 (2008).

W. McSweeney, O. Lotty, N. Mogili, C. Glynn, H. Geaney, D. Tanner, J. Holmes and C. O'Dwyer, J. Appl. Phys.
114,034309 (2013).

A. I. Hochbaum, D. Gargas, Y. J. Hwang, P. Yang, Nano Lett.
9, 3550 (2009).

W. McSweeney, O. Lotty, J. D. Holmes and C. O'Dwyer, ECS Trans., 35, 25 (2011).

P. Simon and Y. Gogotsi, Nat. Mater.
7, 845 (2008).

T. Brezesinski, J. Wang, S. H. Tolbert and B. Dunn, Nat. Mater.
9, 146 (2010).

W. McSweeney, O. Lotty, C. Glynn, H. Geaney, J. D. Holmes and C. O'Dwyer, Electrochim. Acta, 135, 356 (2014).
(Invited) Integrated Semiconductor/Catalyst Assemblies for Sustained Photoanodic Water Oxidation
Authors: Yang Jinhui , Cooper Jason K. , Toma Francesca M. , Sharp Ian D.
Published: February 2020

Photoelectrochemical conversion of solar energy to chemical fuel relies on the availability of semiconductors that are stable under aqueous conditions, possess bandgaps suitable for harvesting light from the sun, and can be integrated with active catalysts. Regardless of the desired reduced product, water oxidation is necessary to provide an abundant source of protons and electrons for fuel formation. However, semiconductor (photo)corrosion under oxidizing conditions is a central challenge. Here, we provide an overview of different approaches to achieving durable semiconductor photoanodes and highlight two specific examples of how catalyst integration can be used to improve chemical stability. In the first example, we show that plasma-assisted atomic layer deposition (PE-ALD) of cobalt oxide onto silicon enables efficient photoelectrochemical water splitting. These integrated assemblies are stable under aqueous conditions, including at pH 14. Structure and composition, which play crucial roles in performance, are investigated via a combination of X-ray absorption spectroscopy, X-ray photoelectron spectroscopy, grazing incidence wide angle X-ray scattering, and transmission electron microscopy. Together, these methods reveal that amorphous catalyst coatings are beneficial for enhancing stability and improving catalytic activity. In the second example, semiconductors that possess at least a modicum of native stability are investigated. These semiconductors are often polycrystalline thin film metal oxides possessing lateral inhomogeneities, poorly understood interactions with electrolyte environment, and relatively unknown optoelectronic properties. One such material is bismuth vanadate (BiVO4), a 2.4-2.5 eV bandgap n-type semiconductor. We have utilized a suite of spectroscopic and microscopic methods to probe local compositional non-uniformities, understand the role of catalyst integration on chemical stability, and determine electronic structure and photocarrier dynamics that govern charge extraction efficiency. These measurements provide valuable insight into basic properties – often defined by local nonuniformities – that affect ultimate performance of functional photoanodes. The examples presented here highlight that, although few materials are inherently stable under conditions required for artificial photosynthesis, conformal catalyst deposition provides a viable approach to sustained operation in harsh environments.
Enabling Overall Water Splitting By Iron Oxide and Silicon
Authors: Wang Dunwei
Published: February 2020

Photoelectrochemical water splitting promises a large-scale solar energy storage solution.  Its development has been impeded by poor performance of photoanodes, particularly in the capabilities of photovoltage generation.  Using the prototypical photoanode material of hematite as a study tool, we show that structural disorders on or near the surfaces are an important reason for the low photovoltages.  A facile re-growth strategy was developed to readily alter the surfaces for reduced disorders.  A record-low turn-on voltage of 0.45 V (vs. reversible hydrogen electrode) was measured.  The result permitted us to construct devices made of three most abundant elements on the Earth crust (O, Si, and Fe) to split water with only sunlight as the energy input at an overall efficiency of 0.91%.
Deformation of Lithium-Ion Battery Anodes during SEI Formation: a Probe for the Structure of the SEI
Authors: Jones Elizabeth M. C. , White Scott R. , Sottos Nancy R.
Published: February 2020

Lithium-ion batteries are ubiquitous in small, portable electronics, where the lifetime of the battery now exceeds the expected lifetime of the device (ca. 2 years).  Capacity fade over time, however, remains a significant challenge hindering the use of lithium-ion batteries in more demanding applications with long life-time requirements, such as in electric vehicles.  One of the primary contributors to capacity fade is lithium trapping within the solid-electrolyte interphase (SEI) on the anode, making understanding the SEI critical to the design of more reliable lithium-ion batteries.  The size-scale (tens of nanometers) and reactivity of the SEI, though, make characterization of the SEI difficult. 

In this presentation, we present a new method to probe the structure of the SEI that is formed on lithium-ion battery anodes.  A custom battery cell employs an unconstrained (i.e. not on a current collector) graphite composite electrode and allows optical access to the electrode during electrochemical cycling.  Electrolyte is reduced on the electrode surface potentiostatically, and the resulting deformation of the electrode is measured using digital image correlation (DIC), an optical, full-field strain measurement technique.  The amount of deformation of the electrode induced during SEI formation is related to the structure of the SEI layer.  The strain measurements are then compared to galvanostatic cycling results, and the effects of different electrolyte salts, solvents, and additives on the SEI structure and battery capacity retention are evaluated.

Figure 1
The Limited Effect of VC in Graphite / NMC Cells
Authors: Deshpande Rutooj , Ridgeway Paul , Fu Yanbao , Zhang Wei , Cai Jinshu , Battaglia Vince
Published: February 2020

Degradation at the electrode surfaces is one of the major reasons behind capacity fade in a well-constructed battery. The presence of electrolyte additives is known to alter the electrode particle surface which may in turn lead to changes in rates of intercalation as well as side-reactions. In particular, VC has been studied extensively for different lithium-ion chemistries and been shown to improve columbic efficiency of some electrodes. In the present study, the effect of vinylene carbonate (VC) as an electrolyte additive in a graphite/NMC 333 (lithium-nickel-manganese-cobalt oxide) cell is investigated. The study shows that the addition of VC improves the rate performance especially at moderately high rates. A new three-electrode cell design with Li as a reference electrode was used in this study. The three-electrode cell was particularly useful in studying the effect of VC on the rate performance of each electrode. The rate of side reactions is found to decrease with the addition of VC. Despite these important performance improvements, no significant improvement in the capacity retention is observed. This suggests that the side reactions in Gr./NCM cells consist of two types, those that go to repair cracked SEI on the anode and results in a net consumption of Li from the cathode and those that reform SEI components that dissolve from the anode and are oxidized at the cathode.  The VC appears to reduce the second type but have negligible effect on the first.   This also indicates that columbic efficiency measurements are not a reliable indicator of cell life with regard to short term capacity fade.
N-Doped Graphene-CNT Cathode Composites for High-Performance Li-S Batteries
Authors: Noorbehesht Nikan , Hollenkamp Anthony F. , Church Tamara L. , Harris Andrew T. , Minett Andrew I.
Published: February 2020

Reaching beyond the horizon of Li-ion batteries is a formidable challenge, as energy storage will be more important in the future than at any time in the past. This requires the exploration of new chemistry, especially electrochemistry, and new materials. Among the available choices, lithium-sulfur (Li-S) batteries are attractive because of their low cost, environmental friendliness, and superior energy density (theoretically 2500 Wh/kg). Despite their great promise, the commercialization of Li-S batteries is hindered by low cycle stability, fast capacity fading, and low efficiency; these problems are induced by the polysulfide shuttle reaction that occurs through dissolution into electrolyte, the loss of active sulfur material, and the electronically insulating nature of sulfur. To tackle these issues, we synthesized a novel nanostructured composite consisting of Graphene and Carbon Nanotubes (CNT), each pre-doped with Nitrogen (N), as a host material for sulfur impregnation. In this unique composite, not only do CNTs act as the spacer units between the graphene sheets, avoiding losses in performance through restacking and agglomerate formation, but they also contribute to the material activity, overall surface area/nanoporosity, and the composite conductivity over the effective doping method strategy. In the next step, a new method of sulfur impregnating into the composite structure was implemented to effectively confine the sulfur into graphitic clusters, voids, and defects in N-doped graphene–CNT composite. The carbon nanostructured framework serves not only as a conductive layer for encapsulating sulfur and polysulfides without direct contact with electrolyte, but also as a nano-electrochemical reaction chamber. Cyclic voltammetry (CV) of the sulfur-impregnated N-doped graphene-CNT in high-dielectric solvent behaved similar to low-dielectric solvent, indicating that the material was not solvent dependent. Strong interaction between N-doped composite and sulfur or polysulfides enabled us to demonstrate Li–S cells

with a high reversible capacity (1005-1592 mAh/g), outstanding cycling stability, and great Coulombic efficiency (~97.5%). The results indicate that the sulfur-impregnated N-doped graphene-CNT nanocomposite is a very promising cathode material for high-performance lithium–sulfur batteries.

Figure 1
Strong Lithium Polysulfide Chemisorption on Electroactive Sites of Nitrogen-Doped Carbon Enables High-Performance Lithium-Sulfur Battery Cathodes
Authors: Song Jiangxuan , Yu Zhaoxin , Huang Qingquan , Gao Yue , Wang Donghai
Published: February 2020

Lithium-sulfur (Li-S) batteries have attracted great of interest due to their high theoretical capacity of 1672 mAh/g and low cost.1 Unlike batteries with intercalation chemistries, Li-S batteries experience dissolution and diffusion of reaction intermediated (lithium polysulfides, Li2Sx, 2<x≤8) in the electrolyte. This behavior can lead to loss of active material from the cathode and to a polysulfide shuttle phenomenon, resulting in capacity fading and poor coulombic efficiency.2
,
3

Here, we report a novel functional carbon composite (carbon-nanotube-interpenetrated mesoporous nitrogen-doped carbon spheres, MNCS/CNT) as a sulfur host which can strongly adsorb lithium polysulfides. The nitrogen functional groups of this composite enable effective trapping of lithium polysulfides on electroactive sites within the cathode, leading to much improved electrochemical performance (1200 mAh/g after 200 cycles). The enhancement in adsorption can be attributed to chemical bonding of lithium ion with nitrogen functional groups in the MNCS/CNT framework. In addition, the micron-sized spherical structure of the material yields a high areal capacity (~6 mAh/cm2) with a high sulfur loading of ~5 mg/cm2, ideal for practical applications of Li-S batteries.

Acknowledgements

This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy (DOE) under Contract No. DE-EE0005475.

References

1.         A. Manthiram, Y. Fu, S.-H. Chung, C. Zu and Y.-S. Su, Chem. Rev., 2014.

2.         J. Song, T. Xu, M. L. Gordin, P. Zhu, D. Lv, Y.-B. Jiang, Y. Chen, Y. Duan and D. Wang, Adv. Funct. Mater., 2014, 24, 1243-1250.

3.         J. Song, Z. Yu, T. Xu, S. Chen, H. Sohn, M. Regula and D. Wang, J. Mater. Chem. A, 2014, 2, 8623.

Figure 1
Composite Prussian Blue Analogues Utilized As Cathode Materials in a Sodium Ion Battery
Authors: Sawicki Monica , Shaw Leon
Published: February 2020

Increased environmental pollution and the inherent reliance of foreign import for fossil fuels and lithium have made the need for research towards alternative electrical energy storage systems. In this context, research in sodium ion batteries (NIBs) has become more prevalent since the price in lithium has increased due to its demand and reserve location.  Sodium is an abundant resource that is low cost and safe which makes it an attractive alternative to lithium. Its chemical properties are similar to that of Li which makes the transition into using Na chemistry for ion battery systems feasible.

In light of the requirements for grid scale energy storage: ultra-long cycle life (>20,000 cycles and calendar life of 15 to 20 years), high round trip efficiency (>90%), low cost, sufficient power capability, and safety, the need for a suitable cathode material with excellent capacity retention such as Na2MnFe(CN)6/K2MnFe(CN)6 composite will be investigated. Prussian blue (A[FeIIIFeII (CN)6], A=Na+ or K+) and its analogues have been investigated as alkali ion hosts for use as a cathode material. They have a cubic face-centered structure in which two different metal centers Fe3+ and Fe2+ are bridged by C≡N- groups which provides large ionic channels along the <100> direction enabling facile insertion and extraction of alkali ions.  This material is also capable of more than one Na ion insertion per unit formula which holds great promise in increasing the energy density of the NIB. Electrochemical impedance spectroscopy will be used to determine the conductivity of the composite Na2MnFe(CN)6/K2MnFe(CN)6 material.  The electrochemical performance of the cathode material will be analyzed using cyclic voltammetry, and galvanostatic charge/discharge investigation.
Conductive Additive for Si/Mesoporous C Anode in Li-Ion Batteries: Conductive Graphite Vs Carbon Black C65
Authors: Rezqita Arlavinda , Trifonova Atanaska
Published: February 2020

Silicon exhibits the highest theoretical capacity of 4200 mAh g-1, which is 10 times more than the capacity of graphite. Therefore, Si is a promising candidate for anode in lithium-ion batteries. However, Si has low electrical conductivity (theoretical: 6.7 x 10-4 S cm-1). To reach the high performance anode, the proper conductive additives are still needed in order to improve the electrical conductivity of Si-based anode. Here we investigated the effects of conductive nano-graphite and Carbon Black (CB65) on electrochemical performance of silicon-mesoporous carbon composite anode (Si/MC). The material has been synthesized by pyrolysis of polymer aerogel with embedded Si nanoparticles. The electrode was made by 75% active material, 15% conductive additive, and 10% polyacrylic acid (PAA) binder. The electrochemical characterization using impedance spectroscopy, voltammetry, and galvanostatic charge/discharge tests were conducted for both samples. Impedance spectroscopy showed that Si/MC anode with conductive graphite exhibited lower charge-transfer resistance (Rct ≈ 150 Ω), compared to those with carbon black (Rct ≈ 380 Ω). The collected results showed that the graphite additive improved significantly the electrochemical performance of Si/MC anode. In addition, the thermal and long cycling tests will be demonstrated.
Electrochemical Performance of Gas-Atomized Si-Alloy Anode for Lithium-Ion Battery
Authors: Kimura Yuta , Matsuoka Masashi , Tago Yuichiro
Published: February 2020

Introduction

 Si is focused as high capacity active anode material of lithium-ion battery. However, the large volume changes that occur during charge-discharge cycles cause cracking and falling conductivity of electrode. In order to prevent from these problems, various materilas that have structure covering Si surface by some substances such as SiOx have been studied1,2.

 We have improved conductivity of Si anode material by fabricating the unique microstructure that crystalized alloy-matrix phases around Si phases3.Here, the Si-alloy powder was prepared by gas atomization. One of the important features of gas atomization process is to be able to produce quenched powder in large volume.

 In this study, we investigated influence of Si composition and paticle size of gas-atomized Si-alloys on electrochemical properties for anode material such as cycle stability, initial clulombic efficiency, swelling of electrode during charge-discharge cycles.

Experiment

 Si-alloy powder (d50 = 18 µm) was prepared by gas atomization. Fine powder (d50 = 2~5 µm) was obtained by planetary ball mill. An electrode was prepared by coating slurry of 80 mass% Si-alloy powder, 5 mass% ketjen black and 15 mass% polyamic-acid on SUS foil. The electrode was tested in a 2032-type coin cell assembled using a lithium foil anode, a separator and electrolyte (1M LiPF6 in EC/DEC (1:1 volume ratio)). The charge-discharge performance was evaluated at 25 degrees C and the current density of 0.2 mA (1st cycle), 0.2C-rate (from 2nd cycle to 50th cycle) in the potential range of 0.002-1.0 V vs. Li/Li+.

Results and Discussions

 Fig.1 shows SEM image of Si-Sn-Fe-Cu alloy powder. The microstructure of the powder is composed of three phases (Si, Si-Fe and Sn-Cu phases). It can be seen that the Si phase is surrounded by Si-Fe and Sn-Cu phases.

 Fig.2 shows cycle life performance of Si-alloy powder anodes having different particle size. When patricle size is large (d50 = 18 µm), the discharge capacity dropped with increasing cycle number. On the other hand, cycle stability of the fine powder (d50 = 2 µm) was drastically improved.

 Fig.3 shows the relationship between the initial columbic efficiency and the Si composition of the Si-alloy. The initial coulombic efficiency decreaced by the particle size reduction and improved by increasing of the Si contens in the Si-alloy.

 It was clarified that the particle size and the Si contents in the Si-alloy powder affected the electrochemical performance.

References

1.T.Morita, N.Takami, J.Electrochem. Soc., 153(2), A425(2006)

2.M.Miyachi et al., J.Electrochem. Soc., 152(10), A2089(2005)

3.Y.Tago et al., The Electrochemical Society in Japan 80th Spring meeting proceedings,1H22(2013)

Figure 1
Enabling High-Energy Battery Performance of 4.8 V Li-Rich Layered Oxide Cathode with a High-Voltage Additive
Authors: Pham Hieu Quang , Hwang Eui-Hyeong , Kwon Young-Gil , Song Seung-Wan
Published: February 2020

Li-rich layered oxide of xLi2MnO3.(1−x)Li(Mn,Ni,Co)O2 is an attractive cathode material for high-energy density Li-ion batteries because of a possible attainment of high capacity as much as or higher than 250 mAhg−1 on the operation above 4.6 V vs. Li/Li+.1 Its performance however has been limited by high-voltage operation (> 4.3 V), due to anodic instability of conventional electrolyte and interfacial instability of the cathode. Here we report high performance of half-cell and full-cell with Li1.2Mn0.525Ni0.175Co0.1O2 cathode and fluorinated linear carbonate (di-(2,2,2 trifluoroethyl)carbonate, DFDEC) as a novel high-voltage electrolyte additive, on the high-voltage operation to 4.8 V.2 The full cell consisting of Li1.2Mn0.525Ni0.175Co0.1O2 cathode and graphite anode in the electrolyte of 1M LiPF6/EC:EMC only experiences a rapid capacity fade when being operated at 2.5- 4.75V, resulting in just 32 % capacity retention after 60 cycles. Although the performance improves with the use of DFDEC, a notable performance improvement is achieved when using the blended additives of DFDEC and VC, which is a well-known SEI-forming agent for graphite anode,3 delivering high discharge capacities of 231 − 189 mAhg−1 with the capacity retention of 82 % at the 60th cycle. The full-cell demonstrates doubled energy density (~278 Whkg−1) compared to ~136 Whkg−1 of a commercialized cell of graphite//LiCoO2. Spectroscopic surface chemistry studies indicate that DFDEC plays a critical role in stabilizing the SEI and inhibiting the interfacial degradation of cathode. The details of interfacial reaction (SEI formation) mechanisms, SEI composition and stability, and their relation to high-voltage cycling performance at room and elevated temperatures would be presented in the meeting.

References

1) M. M. Thackeray, S.-H. Kang, C. S. Johnson, J. T. Vaughey, S. A. Hackney, Electrochem. Commun., 8, 1531 (2006).

2) H. Q. Pham, K.-M. Nam, E.-H. Hwang, Y.-G. Kwon, H. M. Jung, S.-W. Song, J
.
Electrochem
.
Soc
., 161, A2002 (2014).

3) L. El Ouatani, R. DedryveÌre, C. Siret, P. Biensan, S. Reynaud, P. Iratçabal, D. Gonbeau, J. Electrochem. Soc., 156, A103 (2009).

Acknowledgement
s

This research was financially supported by the Korean Ministry of Trade, Industry & Energy (A0022–00725) and by the Ministry of Education (2012026203).
Orientation-Controlled Growth of LiNi0.5Mn1.5O4 Layers Directly Deposited on Current Collectors By Using Flux Coating and Their Electrochemical Properties
Authors: Zettsu Nobuyuki , Mizuno Yusuke , Teshima Katsuya
Published: February 2020

Newly developed cathode structures are strongly required for the improvement of LIB properties, including energy and power density, lifetime. Conventionally used cathodes consist of micrometer sized polycrystals of active materials, and additives that facilitate Li ion and electron transportation. Use of nanosized single crystals is expected to make huge improvements because those nanostructures might provide shorter diffusion pathways for ionic transportation. Here, we proposed fabrication of densely-packed orientationaly-controlled LiNi0.5Mn1.5O4 (LNMO) crystal layers directly onto a current collector using flux-coating. As shown in Figure 1, SEM observations revealed that those crystals have octahedral shape with well-developed facets. This shape reflected well the crystal structure of LiNi0.5Mn1.5O4, which belongs to cubic system with Fd-3m space group. Even though the filling rate of the LiNi0.5Mn1.5O4 crystal in the positive electrode reached more than 95% without any additives, the crystal layer exhibited excellent LIBs properties as same as conventionally used powdered electrode with an assistance of many additives. The first charge and discharge capacities of the LIB, containing 14 mm-thick LiNi0.5Mn1.5O4 crystal layer as a cathode were 111 and 105 mA∙h∙g-1 at 1 C. The retention rate after 30 cycles was 97% for each cycle at 0.3C. These results proved that the flux-coating offered growth of seamlessly connected layers of LNMO crystals on current correctors. Further detail crystallographic natures and electrochemical characteristics of other active material crystals will present in the ECS 227th Meeting.