bluuebunny/crossref_metadata_2025 huggingface dataset:
Hybrid Flow Battery/Mediator Supercapacitor Using Iron Cyanide Redox Materials
Authors: Zhou Xiangyang , Pape Marie , Narasimhan Swati , Zhang Chen
Published: February 2020

Flow batteries have very high specific energy but low specific power and slow response while mediator supercapacitors give high specific power and fast response but relatively low specific energy. A hybrid flow-battery/supercapacitor is fabricated and operated under different conditions in order to provide both high specific energy and power. The porous electrodes of the consisted of catalysts for redox reactions (Ni, Pt, Ru, etc.), mediators (NaI/I2, VOSO4, K4Fe(CN)6, etc.), and polymer electrolytes as binders. An ion exchange membrane was used as the separator. An array of complex iron cyanide compound were synthesized and used as the redox materials in slurry reservoirs. This investigation focuses on the effects of flow rate, temperature, pressure, and mediator concentration on the performance of the energy storage device. Cyclic voltammetry (CV) and galvanostatic charge/discharge (GCD) measurements were conducted under a wide range of flow rate and mediator concentration. The redox potential of the slurry was monitored using an electrochemical redox sensor. The electrochemical kinetics of the mediators and redox materials were evaluated using linear polarization methods. The results indicate that at a given scan rate for CV or current for GCD, both flow rate and mediator concentration greatly impact the charge/discharge behaviour, the total energy, and efficiency. There is a critical flow rate at which a capacitor-like behaviour transits to battery-like behaviour. A simple numerical model is created to analyse the experimental data and provide an explanation of the observations.
Asymmetric Growth of the Solid-Electrolyte Interphase on Carbonaceous Anodes
Authors: Attia Peter , Chueh William C
Published: February 2020

Growth of the solid electrolyte interphase (SEI) is the primary driver of capacity fade in lithium-ion batteries. Despite its importance to this device and intense research interest, the fundamental mechanisms underpinning SEI growth remain unclear. In this work, we measure the electrochemical growth of the SEI with precision coulometric measurements on different relevant carbon electrodes, including graphite and carbon black. For both materials, we report large, decaying lithiation capacities and smaller, constant delithiation capacities, implying the SEI grows primarily on lithiation. This observation is especially striking at low rates (C/10), rates at which most charging/discharging phenomena can be approximated as symmetric as they approach equilibrium. We determine the asymmetry in irreversible SEI growth is coupled to the asymmetries in reversibleintercalation and deintercalation of carbon. This work illustrates an interesting electrochemical coupling phenomenon and furthers our understanding of SEI growth in carbon anodes.
Electrochemical Reactions in Li-Ion Battery Electrodes and Their Interaction with Mechanical Stresses: Size Effects, Phase Segregation, and Crack Propagation
Authors: Stein Peter , Zhao Ying , Xu Bai-Xiang
Published: February 2020

Since their introduction 25 years ago, lithium-ion batteries have risen to become the primary power source for mobile devices such as electric tooth brushes and razors, but also for cellphones and tablet PCs. They have a high potential for wider application, e.g. in (hybrid) electric vehicles or for the storage of renewable energy. This is currently hindered by the gradual capacity fade over cycle lifetime. Main factors for this degradation are electrochemical side-effects such as SEI formation and mechanical damage. The cyclic insertion and extraction of Li ions results in high stress levels in and large deformation of the electrodes, leading to delamination of the electrode structure and to fracture of individual particles, respectively. The freshly cracked surface is then exposed to further chemical reactions. Experimental evidence however suggests, that nanostructured electrodes exhibit a higher resilience against this diffusion-induced mechanical degradation.

In this talk, we report on our efforts towards modeling the chemo-mechanical processes taking place in free-standing electrode particles at the micro- and the nano-scale. In particular, we describe two models used to study the interaction of phase segregation and crack growth, as well as the interaction of chemical reactions and surface tension in nanoparticles. Both models feature a direct coupling between diffusion and elasticity as well as concentration-dependent diffusivity. In particular, the Butler-Volmer relation for the description of electrochemical surface reactions has been modified to account for the effects of mechanical stress and phase formation.

We show that surface tension provides mechanical stabilization in nanoparticles, allowing, in principle, for higher charge/discharge rates. This effect is size-and shape-dependent. Due to surface tension, however, the usable capacity of a particle shrinks with its size. Regarding phase segregation, we demonstrate how the rate of surface reactions can determine the separation behavior, and that the evolution of the phase interface can drive the propagation of pre-existing cracks in an electrode particle.
A Study of Mediators As Ion Providers in Supercapactors
Authors: Zhou Xiangyang , Zhang Chen , Wang Yuchen , Qiao Xiaoyao
Published: February 2020

Doping mediators (soluble redox compounds) in polymer electrolyte contained in the porous electrodes is an effective method to increase the capacitance of supercapacitors. Mediators not only provide additional capacitance but also ions to electrolyte. The total capacity of a supercapacitor is dominated by the minor of the electrode capacity and the number of ions in electrolyte. In this research, we focused on revealing the effect of on the extra ions provided by the mediators during the charge/discharge processes. Two types of supercapacitors were fabricated. For the first type, the active electrode material consisted of 50 wt% mediators (in solid state) and 50 wt% high specific surface area active carbon (AC). For the other type of supercapacitor, the active electrode material consisted of AC only. Acetonitrile was used as liquid phase for both types. Under this circumstance, ions are provided by mediator only. The calculation of specific current was based on total weight of two electrodes and cyclic voltammetry (CV) curves. As shown in Figure 1, supercapacitor (a) (AC only) is unable to store any charges and energy without the ions in the solution. However, supercapacitor (b) can store ten times more energy with the mediator enhancement. In this situation, we can consider mediators as ‘charge harbor’. They can release ions into the liquid phase. These ions then participate in formation of electric double layers (EDLs) on AC. This capability of providing ions into the liquid phase can increase capacity of supercapacitor. CVs (b) and (c) also indicate that different mediators are different in the kinetics of providing ions. Taking supercapacitor (b) as an example, when we charge the supercapacitor, the K2CuFe(CN)6
can release K+ cation into the liquid phase and [CuFe(CN)6]- will still be hold on the solid phase because of the electrostatic force. On the other hand, we can use VOSO4 as a mediator too. V4+ can be reduced and releases SO4
2- anion. Thus, it is preferred to use K2CuFe(CN)6
 in the positive electrode while use VOSO4 in the negative electrode. An series of mediators were evaluated using the same method.

Figure 1
How to Enhance the Performance of Graphene/Metal Oxide Nanocomposite Supercapacitors
Authors: Shim Jae-Jin , Nguyen Van Hoa , Sahoo Sumanta , Mohamed Saad Gomaa , Hwang Jinho
Published: February 2020

Graphene/metal oxide nanocomposites have been developed for energy storage applications such as supercapacitors, catalysts, sensors, and batteries. Electrochemical performance of the nanocomposites has been improved so much due to the synergistic effect of excellent conductivities and mechanical properties of graphene sheets and the high pseudocapacitance of metal oxides. For the applications of these nanocomposites to the real supercapacitors, a huge enhancement in capacitance, cycling stability, energy density, and power density should be achieved, resulting in an excellent performance as an electrode material for supercapacitors.

In this study, we have tested several methods to enhance the supercapacitor performance, such as doping of graphene with other elements and using mixed metal oxides and conducting polymers. We have achieved high surface area, high conductivity, and remarkable electrochemical properties (specific capacitance of over 4,000 F/g). Cleaner synthetic methods have also been involved in the synthesis process.
Stable Electrolyte for High Voltage Electrochemical Double-Layer Capacitors
Authors: Ruther Rose Emily , Delnick Frank M. , Nanda Jagjit
Published: February 2020

Abstract

Virtually all state-of-the-art, non-aqueous electrochemical capacitors use the same electrolyte: tetraethylammonium tetrafluoroborate (TEABF4) in acetonitrile (ACN). ACN-based electrolytes have very high conductivity (>50 mS/cm), which minimizes resistive losses and enables capacitors to operate at very high power. However, these electrolytes are limited by a practical voltage window around only 2.5 – 3.0 V, beyond which the capacitor lifetime is significantly shortened. Since the energy stored in a capacitor increases quadratically with voltage, extending this electrochemical window could significantly boost energy density. In this contribution, we explore the possibility of using ether-based electrolytes to increase the voltage window of double-layer capacitors. Ethers such as dimethoxyethane (DME) do not passivate carbon electrodes at very negative potentials (near Na/Na+), extending the practical voltage window by about 1.0 V compared to standard, ACN-based electrolytes. A simple electrolyte of NaPF6 salt in DME enables a voltage window > 3.5 V in full cells with conventional, high-surface-area carbon electrodes. Electrolyte stability is evaluated in both two and three-electrode cells with EIS, charge-discharge cycling, float tests, and measurements of leakage current. The conductivity of NaPF6in DME (> 10 mS/cm) is comparable to commercial lithium-ion battery electrolytes and superior to most ionic liquids. Factors that limit the voltage window and energy density will be discussed, and strategies to further boost energy density will be proposed.

Acknowledgement

This work was sponsored by the Oak Ridge National Laboratory Technology Innovation Program using technology transfer license royalties. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U. S. Department of Energy under Contract No. DE-AC05-00OR22725.
An in-Depth Investigation of the Alucone Coating Impact on the Performance of the Silicon Anode
Authors: Son Seoung-Bum , Wang Yikai , Li Xuemin , Stokes Adam , Cheng Yang-Tse , Ban Chunmei
Published: February 2020

Si is one of the promising candidates that can replace the graphite, owing to its high theoretical capacity of 3,579 mAh g-1, which is greater than any other Lithium-ion battery anode materials including graphite (372 mAh g-1). However commercialization of Si has not been successful yet because of following issues: First, the Si experiences huge volume expansion up to ~ 300 % with lithiation (formation of Li15Si4) that can cause mechanical failure of Si with repeated lithiation and delithiation. And second, unstable and insulate solid electrolyte interface (SEI) layer forms on the surface of Si as a result of exposure to organic solvent in the electrolyte. Mechanical failure of Si during repeated lithiation/delithiation creates new Si surfaces and those surfaces are susceptible to formation of SEI layer that makes Si anode more insulated and leads to rapid degradation of cycling performance. Our previous work demonstrated, for the first time, the success in utilizing molecular layer deposition (MLD) to grow mechanically robust and flexible surface coatings to address the challenges associated with Si’s dramatic volume changes. In this work, we further investigate the advantages of MLD coating on thick electrodes in a mechanical point of view. The presence of MLD coating on the electrodes increases the mechanical properties such as elastic modulus and hardness, which makes thick electrode robust and resistant to volume changes. Scratch test also reveals the stronger bonding strengths of Si anode materials to the Cu current collector with MLD coating. Remarkably improved electrochemical performance of the Si electrode with MLD coating was observed and specific capacity of 1,490 mAh g-1 at 500 cycles is achieved while uncoated Si anode delivered negligible amount of specific capacity. And this study exactly states the advantages and limits of MLD coated Si-CB-PVDF system and motivate us further to investigate the novel system that is still unexplored.
Controlling the Surface Chemistry of Cathode Materials for High Energy Rechargeable Batteries
Authors: Lin Feng , Doeff Marca
Published: February 2020

Chemical evolution and structural transformations at the surface of an electrode material influence greatly the key performance metrics of lithium batteries, including energy density, power capability, safety and cycle life. This presentation will discuss how we bridge the design principles of surface chemistry in electrode materials with advanced characterization tools, in pursuit of safer and durable lithium batteries. A high-throughput analytical method, based on synchrotron X-ray spectroscopy and transmission electron microscopy, is developed to investigate the surface phase irreversibility of lithium ion battery materials, a phenomenon that has been widely observed yet poorly understood. It is found that, in layered cathode materials, surface reconstruction from a layered to a rock-salt structure is commonly observed under a variety of battery operating conditions, particularly in high energy Ni-rich NMC compositions. This phenomenon, together with electrolyte decomposition and formation of a cathode electrolyte interphase, result in poor high-voltage cycling performance, impeding attempts to improve the energy density by widening the potential window at which these electrodes operate. Subsequently, we propose three methods to improve the surface stability of cathode materials, including selective surface metal segregation, surface coating and electrolyte formulation. This presentation will demonstrate the great importance of controlling surface chemistry of cathode materials for the successful development of high-energy lithium batteries.
Local Variation in Microstructure Causes Heterogeneity in the Conductivity of Commercial Lithium-Ion Cathode Films
Authors: Vogel John E , Clement Derek V , Hardy Emilee , Mazzeo Brian A , Wheeler Dean R
Published: February 2020

The electrical conductivity of battery films is an important characteristic in how battery cells perform but is not very well understood on a µm scale. Although the macroscopic electrical conductivity of battery films has been explored, small-scale variations in the film have been shown to exist [1]. Factors that may affect this heterogeneity include film composition as well as manufacturing steps such as drying and calendering [2].

We show that in commercial quality battery electrode films there is not only expected variation on a micrometer scale, but that measured conductivity variation can occur on the order of millimeters. A modified micro-N-line probe [1] was installed in a high-resolution stage for taking local measurements of conductivity. Electrical conductivity of battery films was then mapped.

A key advance in this work is the correlation of local conductivities with the local microstructure. ”Hot”, ”average” and ”cold” conductivity spots were investigated by scanning electron microscopy (SEM) with focused ion beam (FIB) milling in order to produce planar cross sections. The SEM/FIB images were then segmented into 3 major domains: carbon-binder, active material, and large pores. We see a strong correlation between conductivity and both porosity and carbon volume fraction, consistent with macroscopic trends observed in our previous research [3].

Acknowledgements

This research is supported by the US Department of Energy through the Advanced Battery Material Research (BMR) Program.

References

[1] B. J. Lanterman, A. A. Riet, N. S. Gates, J. D. Flygare, A. D. Cutler, J. E. Vogel, D. R. Wheeler, and B. A. Mazzeo, “Micro-four-line probe to measure electronic conductivity and contact resistance of thin-film battery electrodes,” Journal of the ELectrochemical Society, vol. 162, no. 10, A2145–A2151, 2015.

[2] M. M. Forouzan, C.-W. Chao, D. Bustamante, B. A. Mazzeo, and D. R. Wheeler, “Experiment and simulation of the fabrication process of lithiumion battery cathodes for determining microstructure and mechanical properties,” Journal of Power Sources, vol. 312, pp. 172–183, 2016.

[3] S. W. Peterson and D. R. Wheeler, “Direct measurements of effective electronic transport in porous li-ion electrodes,” Journal of the Electrochemical Society, vol. 161, no. 14, A2175 –A2181, 2014.

Figure 1: (a) Shows a local map of resistivity taken on an NMC TODA 523 cathode with locations A, B, and C marked where further investigation was carried out. (b) Shows FIB/SEM investigation of point B. (c) Shows segmentation of the FIB/SEM image into 3 domains: carbon-binder (grey), active material (white), and large pores (black). (d) Shows volume fractions taken over a large range of samples for high-conductivity, average-conductivity and low-conductivity locations.

Figure 1
Crystalline Porous Materials and Their Applications in Electrochemical Energy Storage Devices: Lithium Batteries and Li-Sulfur Batteries
Authors: Zhang Zhongyue , Awaga Kunio , Wu Yang
Published: February 2020

The development of new electrochemically active materials towards the application of battery electrodes is still one of the most intriguing topics in energy-related science. A good electrode material requires not only a large energy storage density, but also high permeability to electrolytes and robustness during the electrochemical process. From the perspective of synthetic material science, we chose highly crystalline porous materials, including metal-organic frameworks (MOFs) and covalent-organic frameworks (COFs) as the target of research. The crystallinity of materials guaranteed the stability upon the electrochemcial treatment, while the porosity allowed the penetration of electrolytes and a high mobility of ions in the materials. Towards Li-ion batteries, we could achieve the electron accepting ability on both metal cation clusters and organic linkers of MOFs with proper design strategies and a total capacity that is comparable with major commercialized batteries has been obtained. A series of physical measurements were performed and resulted an insight to the mechanism of the electrochemical processes, hence the discovery of a "bipolar charging" mechanism that has not been observed for traditional Li-ion batteries. Such mechanism utilized the insertion of both Li-ions and anions from the electrolyte, which alternates the doping feature and the ionic conductivity of MOFs in electrochemical steps. We also examined the potential of these porous materials as the substrate of sulfur in the cathode of Li-S batteries, as they can easily separate sulfur into nanoparticles through a simple adsorption approach. We performed studies on a series of isoreticular MOFs, UiO-66-68, which adopt same structural topology and the only difference is pore size and pore volume. The C-rate dependent electrochemcial behavior of sulfur impregnated MOFs were analyzed and suggested the importance of pore size. Furthermore, we prepared MOFs and COFs with functionalized sulfur binding groups, and the linkage between the sulfur and porous frameworks generated a new type of polymer, namely MOF/COF-graft-polysulfides. These new type of polymers were applied as the cathode materials of Li-S batteries, and the binding groups sucessfully increased the cyclic performance of Li-S batteries referencing with non-functionalized MOFs/COFs.
In-Operando Investigation of Rechargeable Aqueous Sulfate Zn/MnO2 Batteries
Authors: Chamoun Mylad , Brant William Robert , Karlsson Gunder , Noréus Dag
Published: February 2020

Large-scale energy storage necessitates inexpensive, safe and long life batteries. Present battery development is rapid but based on insufficient materials for large scale power grid applications. The Zn/MnO2 battery has high energy density comparable to Li-ion batteries and delivers a lower price per kilowatt-hour. Nonetheless, the rechargeability of the battery is limited and the cathode suffers from an irreversible phase formed during cycling. In the traditional alkaline battery, the irreversibility arises from a spinel phase that is electrochemically inactive. In this work, we use a zinc sulfate electrolyte and thus the reaction mechanisms are different. The inactive phase corresponds to a basic zinc sulfate precipitate passivating the electrode surface. Noteworthy suppression of the inactive precipitate can be achieved by adding small amount of manganese sulfate into the electrolyte. Our current Zn/MnO2 cells have achieved stable capacity retention over 100 cycles by using commercially available materials. Specific capacity of 230 mAh/g and coulombic efficiency around 99.9% of the MnO2 electrode as well as a mid-point voltage of 1.35 V was achieved.

We describe the phase transformations and the failure mechanisms of the cathode in the aqueous zinc sulfate Zn/MnO2 battery, with and without the manganese sulfate. The phase transformations occurring in the cathode are directly observed with in-house in-operando X-ray diffraction using a Mo-source and 2D detector for rapid data acquisition. The manganese dioxide electrode is reversible over several charge and discharge cycles. The basic zinc sulfate dissolves and precipitates facilely if manganese sulfate is added. We discuss the factors of this reversibility in perspective of pH and surface area. Furthermore, we describe the structural changes and the electrochemical performance of the cathode using X-ray radiation, analytical and electrochemical techniques.

Our results can make it possible to further improve this battery to make it a worthy contender to the Li-ion battery in large-scale storage applications.

Figure (left): Charge and discharge curves of Zn/MnO2 cell at C/5. Figure (right): Specific discharge capacity and efficiency vs. cycle number of two Zn/MnO2 cells over 100 cycles.

Figure 1
Electro-Oxidation of Borohydride in a Molten Alkali Hydroxide Eutectic Mixture and a Novel Borohydride/Periodate Molten Electrolyte Battery
Authors: Gyenge Elod L. , Wang Andrew
Published: February 2020

The NaBH4 electro-oxidation kinetics in a molten NaOH-KOH eutectic mixture (0.585:0.415 mole fractions) is investigated on Ni, electrochemically oxidized Ni and Pt electrodes in conjunction with the performance of a novel NaBH4/KIO4 battery [1, 2]. The oxidized Ni shows excellent electrocatalytic activity towards BH4
- oxidation at 458 K, with apparent exchange current density, Tafel slope and electron transfer coefficient of 22.54 mA cm-2, 127 mV dec-1 and 0.7 respectively. The activation energy of the BH4
- oxidation reaction is 16.3 kJ mol-1. The BH4
- diffusion coefficient was determined using a chronoamperometric technique. X-ray photoelectron spectroscopy (XPS) analysis of the anodically oxidized Ni reveals the formation of NiO, which is responsible for the increased catalytic activity towards BH4
- oxidation compared to the untreated Ni electrode. A compact molten NaOH-KOH eutectic electrolyte battery with dissolved NaBH4 at the anode, immobilized KIO4 at the cathode and sintered Ni separator, was assembled and investigated for the first time. An oxidized Ni gauze served as the anode, whereas the cathode was Pt mesh containing the immobilized KIO4. Figure 1 a and b, show the NaBH4/KIO4 battery polarization curves as a function of NaBH4 molal concentration and the discharge cell voltage profile over time at 160 mA cm-2, respectively.

Fig. 1: a) Polarization curves of the NaBH4/KIO4 battery at 458 K in the NaOH-KOH eutectic mixture, b) Constant current discharge at 160 mA cm-2 with 500 milimolal NaBH4. Oxidized Ni gauze anode; Pt gauze cathode with 2.5 g cm-2 loading of KIO4; electrolyte: NaOH-KOH eutectic mixture with mole fractions 0.515:0.485.

Factorial design of experiments revealed the main and interaction effects influencing the power output of the NaBH4/KIO4 battery. Temperature and cathodic KIO4 loading have the most significant main effects on the power density, whereas the NaBH4 concentration in the molal concentration range of 50 to 500 milimolal, has a comparatively smaller effect. A maximum power density of 210 mW cm-2 is achieved at 458 K. With further research and development it is proposed that the NaBH4 – KIO4 battery could be used together with solar – thermal energy storage systems.

References:

A.Wang and E.L. Gyenge J.Power Sources 282 (2015) 169-173.

A. Wang and E.L. Gyenge, manuscript in preparation (2016).

Figure 1
Effect of Metal Complex Mediators on the Performance of Mediator Supercapacitor
Authors: Zhang Chen , Wang Yuchen , Qiao Xiaoyao , Zhou Xiangyang
Published: February 2020

Demand of electrical energy storages is increasing quickly with market expansion of cell phones, electrical vehicles, and stationary energy storage. Supercapacitor is an alternative choice of rechargeable batteries because of their low cost for fabrication and maintenance, high cycle life, high charge rate, and high specific power. Using mediators to enhance the performance of the carbon materials based supercapacitors is more effective than using conductive polymer or metal oxide materials. In this study, we improved the performance using metal complex mediators. Several different mediators were synthesized and compared in this work. The active electrode material consisted of 10% mediator, 90% high specific surface area active carbon (AC). An EDLC made by AC only was also fabricated as a reference. To qualify the industrial requirements, current collector, electrolyte and separator are all commercial. The prototypes were fabricated in the glove box and sealed under vacuum. The calculation of specific energy (SE) was based on total mass of both electrodes and cyclic voltammetry (CV) curves and glvanostatic charge/discharge curves (GCDs). Typical CVs were shown in Figure 1. The mediator supercapacitor exhibited high energy densities (˃40 Wh kg-1), high charge/discharge efficiency (˃99%) and high reversibility (˃90% after 10000 cycles). The effect of the rare earth and transition metals on the effectiveness of the mediators is investigated. As shown in Table 1, for mediators containing rare earth metals, Pr, La, Y are more effective than Ho. For mediators containing transition metals, Mn, Fe, and Co are more effective than Zn. The authors explain the phenomenon with the notions of molecular configurations, electronic structures, and interactions between charged mediators.

Figure 1
Cycling Life Prediction By Reaction Depth Index Analysis of Lead Acid Battery
Authors: Dai Changsong , Yang Shaoqiang , Li Ruhong , Cai Xianyu , Xue Kuiwang , Yang Baofeng , Hu Xinguo
Published: February 2020

The use of energy storage lead acid batteries in deeper discharge leads to a pronounced capacity fading and too short life. Now the analysis of positive active material (PAM) composition was the average content of plates. So exploring the influence of positive additives to PAM and cycle life in lead acid batteries was very limited. In addition, the cycle life test of lead acid batteries, especially at relatively high depth of discharge (DoD) could continue for months, even years. It’s always a challenge to the efficiency of research and development of new products. In our work, plates with different DoD have been divided into five layers from surface to center of section. The content of PbO2 in above samples have been characterized by X-ray diffraction (XRD). The reaction depth index of Plates has been obtained by Gaussian fitting of PbO2 content distribution curves of section direction. Addition of metallic sulfate and metallic oxide into the active mass of positive electrode clearly extended the cycle life of batteries. Through contrastive analysis of different lead acid batteries, it has been established that lower reaction depth index was beneficial for the cycle life of batteries. Upon the relationship between reaction depth index and cycle life of lead acid batteries, the cycle life of new battery could be predicted accurately.

Fig.1 the relationship of DoD, reaction depth index and cycle number

Figure 1
(Invited) Fullerene Cation-Mediated Demethylation/Cyclization to 5- and 7-Membered Cyclo[60]Fullerene Derivatives
Authors: Matsuo Yutaka , Ogumi Keisuke , Okada Hiroshi , Nakagawa Takafumi
Published: February 2020

This presentation reports on new cyclization reaction by using fullerene cation to obtain 5- and 7-membered cyclo[60]fullerene derivatives. In this talk, mainly we focused on development of methodology to obtain new fullerene derivatives utilizing cationic fullerene intermediate, and discussed reaction mechanism involving fullerene cation which can be coordinated by benzene rings or the oxygen atom, affording migration of the phenyl groups and activation of the methyl group of the methoxy group for demethylative cyclization.[1]

Single-bonded fullerene dimers, (C60R)2 (R = (2-methoxyphenyl)dimethylsilylmethyl, (isopropoxy)dimethylsilylmethyl, and 2-methoxy-5-methylphenyl), afforded fullerene derivative cations (RC60
+) in the presence of an oxidant (I2, CuCl2, or CuBr2), leading to 5- and 7-membered cyclo[60]fullerene derivatives such as cyclo[60]fullerenes containing a Si–O bond, cyclo[60]fullerenes containing a C60–O bond, and dihydrobenzofurano[60]fullerene. The reaction mechanism involved thermal homolytic cleavage to give fullerene radical, oxidation of the radical to generate fullerene cation, and then demethylative cyclization in which the fullerene cationic centers interact with an aromatic group or the oxygen atoms of methoxy groups to produce the cyclized products. Obtained cyclo[60]fullerene derivatives were used in bulk-heterojunctoin organic solar cells and showed moderate power conversion efficiency and respectable open-circuit voltage.

[1] Y. Matsuo, K. Ogumi, Y. Zhang, H. Okada, T. Nakagawa, H. Ueno, A. Gocho, E. Nakamura, J. Mater. Chem. A, in press.

Figure 1
(Invited) Efficient Electron Transport Layer-Free Solar Cells Based on Innovative Perovskite:Fullerene Blends
Authors: Delgado Juan Luis , Martín Nazario , Collavini Silvia , Tena-Zaera Ramón , Pascual Jorge , Kosta Ivet , Sandoval-Torrientes Rafael , García-Benito Inés
Published: February 2020

A variety of novel fullerene materials, showing different electron accepting capabilities, has been synthesized and used to prepare electron transport layer-free solar cells based on CH3NH3PbI3:fullerene blends. The photovoltaic study performed over a series of devices verifies the suitability of this electron transport layer-free strategy as a promising alternative to build efficient solar cells avoiding the use of TiO2. Furthermore, clear correlation between the LUMO of the fullerene material and the open circuit voltage of the solar cells is found.
Trends in Buckled and Planar Halogen-Doped Graphene for ORR Activity: A DFT Study
Authors: Geronia Reynaldo Marcelino , Serraon Ace Christian , Mora Joy Marie , Sua-an Desiree Mae , Padama Allan Abraham Bustria , Cervera Rinlee Butch , Ocon Joey Duran
Published: February 2020

Owing to the sluggish oxygen reduction reaction (ORR), high-performance catalysts like Pt-based alloys are widely used to render the reaction practically useful in systems like fuel cells. Nonetheless, high costs and technical complications associated with such catalysts have encouraged the exploration of alternative ORR catalysts like heteroatom-doped carbon nanomaterials. To improve the catalytic activity of carbon, earlier studies used boron, nitrogen, phosphorus, sulfur, and selenium as dopants. In this paper, we perform density functional theory (DFT) calculations to explore the potential of halogens (X = F, Cl, Br, I) substituted within the two-dimensional structure of graphene. We also validate some of the results of previous experimental and theoretical studies on halogen-doped graphene. For example, we compare halogen adsorption and band structures of the resulting halogen-doped materials, as well as the possible influence of atomic size and atomic interactions (e.g., Br2/Br interactions, polyiodide formation) on their experimentally observed properties. Based on the resulting electronic and structural information, we then identify which among the buckled and planar forms of halogen-substituted graphene show the most promise for ORR activity. Finally, we compare this method of doping with previously studied methods like adsorption and edge-halogenation to provide additional insight on halogen doping.
Tuning the Optical Band Gap of Graphene Oxide By Ozone Treatment
Authors: Hasan Md Tanvir , Senger Brian , Gonzalez-Rodriguez Roberto , Naumov Anton V
Published: February 2020

Graphene oxide (GO) inherits high transparency, substantial conductivity, high tensile strength from its parent materials graphene. Apart from these properties, it emits fluorescence which makes it a potential material to use in optoelectronics and bio-sensing applications. In this work, we have utilized systematic ozone treatment to alter the optical band gap of single-layered graphene oxide in aqueous suspensions. Due to controlled ozonation, additional functionalization takes place in GO graphitic sheet which changes GO electronic structure. This is confirmed by the increase in vibrational transitions of a number of oxygen-containing functional groups with treatment and the appearance of the prominent carboxylic group feature at c.a. 1700 cm-1. Albeit, timed ozone induction introduces only slight change in color and absorption spectra of GO samples, the emission spectra show a gradual increase in intensity with a significant blue shift up to 100 nm from deep red to green. This large blue shift suggests an increase in optical band gap with additional functionalization introduced by ozone treatment. We utilize a semi-empirical theoretical approach to describe the effects of functionalization-induced changes. This model attributes the origins of fluorescence emission to the quantum confined sp² carbon islands in GO encircled by the functional groups. As we decrease the graphitic carbon cluster size on the GO sheet, the optical bandgap calculated via HyperChem molecular modeling increases, which supports the experimentally observed blue shifts in emission. This theoretical result is further supported by the TEM of ozone-treated samples, which shows a decreasing trend of average ordered graphitic carbon cluster size on GO sheets with treatment time. Theoretical modeling, as well as the experimental results, indicate that the optical bandgap and emission intensity of GO are alterable with controlled ozone treatment, which allows tailoring the optical properties of GO for specific applications in optoelectronics and bio-sensing.
(Invited) Liquid-Exfoliated Transition Metal Dichalcogenides: A Story of Excitons, Spectroscopic Metrics and Functionalisation
Authors: Backes Claudia , Rashvand Farnia , Synnatschke Kevin , Knirsch Kathrin , Cieslik Patrick , Lafargue Paul
Published: February 2020

Liquid exfoliation has become an important production technique to give access to large quantities of two-dimensional nanosheets in colloidal dispersion.[1] Importantly, this is a highly versatile technique that can be applied to numerous layered materials beyond graphene such as transition metal dichalcogenides, III-VI semiconductors, black phosphorus, layered oxides to name just a few. These can be cast into films and composites and have proven useful in a number of application areas. However, as produced dispersions contain a nanosheets of various sizes and thicknesses making post-exfoliation size selection extremely important to tap the full potential in the future. We have previously developed a universal and efficient size selection technique termed liquid cascade centrifugation.[2] Optimisation of this centrifugation procedure allowed us to produce monolayer-rich dispersions with monolayer volume fractions up to 75%. This was made possible because we have realised that nanosheet size and thickness, as well as monolayer content can be quantitatively extracted from for example optical extinction spectra due to edge and confinement effects greatly facilitating and accelerating the characterisation.[2,3]

We now use this basic understanding and these improvements in sample quality to systematically investigate the effect of the chemical environment on the optical properties of the liquid-exfoliated nanosheets. For example, we show that the A-exciton energy depends on the layer number in a similar way for a number of different TMDs. Furthermore, dielectric screening from additives and solvents can be tracked via this A-exciton layer number dependence making this an ideal fingerprint for noncovalent functionalisation.[4] Last but not least, we show that the ability to dramatically increase the surface area of the layered materials on exfoliation can be used to explore new chemistry and to controllably functionalise either basal plane [5,6] or edge sites.

 

[1] Bonaccorso, F., Bartolotta, A.; Coleman, J.N., Backes, C., Adv. Mater.
2016, 28, 6136-6166.

[2] Backes, C.; Szydłowska, B.M.; … Coleman, J. N.,
ACS Nano
2016, 10, 1589-1601.

[3] Backes, C.; Smith, R. J.; … Coleman, J. N., Nature Communications
2014,
5, 4576.

[4] Vega-Mayoral, V.; Backes, C.; …. Coleman, J. N., Adv. Func. Mater.
2016, 7, 1028-1039.

[5] Backes, C.; Berner, N. C.; …. McDonald, A., Angew. Ch. Int. Ed..
2015, 54, 1-6.

[6] Knirsch, K.; Berner, N. C.; …. Backes, C., ACS Nano
2015, 9, 6018-6030.
Chemically Modified Graphene and Carbon Quantum Dots: Structural, Electronic and Chiroptical Characterization
Authors: Herranz Mª Ángeles , Ferrer-Ruiz Andres , Vázquez-Nakagawa Mikiko , Rodríguez-Pérez Laura , Martín Nazario
Published: February 2020

Graphene Quantum Dots (GQDs) and Carbon Quantum Dots (CQDs) are nanomaterials with rising popularity as an alternative to traditional semiconductor quantum dots and organic dyes.1 In addition to simple fabrication methods and low production costs, GQDs and CQDs exhibit a good chemical stability and solubility, unique photophysical properties, photochemical stability, and biocompatibility. These are remarkable properties for applications in fields such as catalysis, photovoltaic devices, bioimaging or medical diagnosis.2

With the objective of constructing versatile and functional ensembles for nanoelectronics and optoelectronics, we lately embarked in the synthesis of these carbon nanomaterials and their covalent or supramolecular modification with ligands that modify their fundamental properties. For instance, adding a chiroptical response to the semiconductor properties of GQDs will provide the extra value of their potential application in photonics. In this sense, we recently proof the concept that GQDs are able to become chiral and that this property can be transferred to a supramolecular structure built with pyrene molecules, where the chiral-GQDs/pyrene ensembles show a characteristic chiroptical response depending on the configuration of the introduced organic ligands.3

We have also combined GQDs and CQDs materials with p-quinonoid π-extended tetrathiafulvalenes (exTTFs)4 in the search for new electron donor-acceptor systems (Figure). The electronic interactions between the CQDs and exTTF have been investigated in the ground and excited states.

The characterization of the obtained GQDs and CQDs nanomaterials by a combination of analytical, microscopic and spectroscopic techniques will be presented and discussed, along with the photophysical properties of some of the aggregates formed.

References

[1]. (a) A. Cayuela, M. L. Soriano, C. Carrillo-Carrión, M. Valcárcel, Chem. Commun., 2016, 52, 1311. (b) X. T. Zheng, A. Ananthanarayanan, K. Q. Luo, P. Chen, Small,
2015, 11, 1620. (c) L. Li, G. Wu, G. Yang, J. Peng, J. Zhao, J.-J. Zhu, Nanoscale, 2013, 5, 4015.

[2]. (a) X. Wang, G. Sun, N. Li, P. Chen, Chem. Soc. Rev.,
2016, 45, 2239. (b) Y. Du, S. Guo, Nanoscale, 2016, 8, 2532. (c) Y. Wang, A. Hu, J. Mater. Chem. C, 2014, 2, 6921

[3]. M. Vázquez-Nakawaga, L. Rodríguez-Pérez, M. A. Herranz, N. Martín, Chem. Commun.,
2016, 52, 665.

[4]. J. Mateos-Gil, L. Rodríguez-Pérez, M. Moreno Oliva, G. Katsukis, C. Romero-Nieto, M. A. Herranz, D. M. Guldi, N. Martín, Nanoscale, 2015, 7, 1193.

Figure 1
(Invited) Probing the Dielectric Response of Exfoliated Black Phosphorous in Free Standing Conditions
Authors: Gaufres Etienne , Fossard Frederic , Favron Alexandre , Gosselin Vincent , Côté Michel , Martel Richard , Loiseau Annick
Published: February 2020

Ultra-thin Black Phosphorus (BP) is a 2D semiconductor characterized by a direct and tunable band gap associated to high carriers mobility (1-3). Studying suspended thin layers of pristine BP is however challenging due to its strong degradation through a thickness dependent and photo-assisted oxidation reaction by adsorbed moisture oxygen (4). Using a protective transfer procedure from glovebox to our TEM-EELS operating at 40kV, we probe the dielectric response of suspended BP down to the monolayer in the range 0.5-40 eV, that include band gaps thresholds and surface/volume plasmons energies for BP. The dispersion of the plasmons as a function of the momentum is also measured and simulated for both in-plane crystallographic directions.

(1)Liu et al, ACS Nano (2014)

(2)Qiao et al, Nature Comm. (2014)

(3) Long et al, Nano Letter (2016)

(4)Favron et al, Nature Mater. (2015)
Electrostatic Double Layer Flash Memory Based on Two-Dimensional Crystals
Authors: Fullerton Susan , Xu Ke , Liang Jierui , Lu Hao , Wang Weihua , Kim Hanchul , Kwak Iljo , Cho Kyeongjae , Kummel Andrew , Seabaugh Alan
Published: February 2020

A new type of flash memory will be presented based on the electrostatic doping of two-dimensional crystals using ions. The proposed device consists of two, 2D crystals separated by a 2D electrolyte through which the ions can pass. The top 2D crystal comprises the channel of a field-effect transistor (FET), while bottom 2D crystal is a backgate. When the ions are near the surface of the channel, they induce image charge in the channel and the device is the low resistance, or ON state. When the ions are pulled back to the backgate by an applied field, the device is in the high resistance or OFF state. The 2D electrolyte is cobalt crown ether phthalocyanine (CoCrPc) plus a salt, which can be deposited on the surface of 2D crystals simply by drop casting and annealing. The crown ethers solvate metal ions, and the ions can pass through the cavity of the crowns. Density functional theory (DFT) calculations show that the crown ethers present a small barrier to ion transport required for fast (nanosecond) switching, but the height of the barrier will be increased for long retention both by the image charge induced in the channel and by modulating the gate bias. The current-voltage characteristics of a simplified device architecture (monolayer CoCrPc:LiClO4 on graphene) will be presented. The graphene FET can be reconfigureably programmed by the 2D electrolyte, achieving sheet carrier densities of 4 x 1012 cm-2 at a low lithium concentration of 5 crown ethers to 1 Li+. Based on the geometric packing of the molecules, as determined by scanning tunneling microscopy, the doping density is predicted to increase to 5 x 1013 cm-2 at a crown ether to lithium ratio of 1:1. State retention measurements show that the two states can be retained for at least 30 minutes (maximum time measured to date) with a memory window of 10 uA. To increase the ON/OFF ratio and therefore the memory window, MoS2 FETs doped with the 2D electrolyte were also fabricated and similar bistable behavior is observed.

This work was supported in part by the Center for Low Energy Systems Technology (LEAST), one of six SRC STARnet Centers, sponsored by MARCO and DARPA, and NSF grant #ECCS-GOALI-1408425.

Figure 1
(Invited) Rare Earth Doped Light Emitting Thin Film Materials for Silicon Photonics
Authors: Bradley Jonathan D. B.
Published: February 2020

Silicon photonic technology is becoming ubiquitous for data center, sensing and advanced photonic applications. However, one of the key challenges for silicon photonic microsystems is integrating materials which can provide optical gain. The leading approach involves hybrid bonding of III-V materials to silicon chips, which is expensive and difficult to scale. Alternatively, rare-earth-doped materials are promising for active device applications on silicon. Rare earth doped oxide thin films can be deposited using standard, low-cost, and wafer-scale methods directly on silicon and emit light in important bands for communications and other emerging applications.

This presentation will cover recent progress on integrating rare-earth-doped materials into silicon photonic microsystems. It will focus on fabrication and integration methods, particularly reactive magnetron co-sputtering, which yields low-loss, high-gain thin films which can be deposited using a single post-processing step onto silicon photonic chips that have been fabricated in a silicon foundry. The fabrication challenges, spectroscopic properties, and device design requirements related to prospective materials, including ytterbium-, erbium- and thulium-doped oxides will be discussed. The talk will review the application of such films in light-emitting rare-earth-doped devices, including amplifiers and continuous-wave and pulsed lasers.
(Invited) Electrolysis with Plasma Cathodes: Modeling and Experiments to Understand the Electrochemical Interface
Authors: Go David B.
Published: February 2020

In the conventional picture of electrolysis, two metal electrodes are submerged into an electrolyte solution and an applied voltage drives redox reactions at the cathode and anode, respectively. Plasma electrolysis, also called glow discharge electrolysis, changes this convention by replacing one or both of the solid electrodes with a plasma or gas discharge. Reduction and/or oxidation reactions, therefore, are no longer mediated by a solid/liquid interface but by a gaseous/liquid interface, requiring that free charges traverse from the gas to liquid and vice versa. The plasma cathode configuration replaces the typical metal cathode with a plasma, such that free gaseous electrons in the plasma must be injected into the solution phase to initiate reduction reactions at the “cathode”. Recently, this approach to electrolysis has received significant attention for nanomaterials synthesis and emerging applications include the ‘catalyst-free’ electrochemical processing of carbon dioxide (CO2) into useful chemicals.

However, there are significant questions that persist about the nature of the electron reactions at the plasma-liquid interface. Recent studies have confirmed that the plasma electrons solvate in the solution before reacting with other dissolved species, and interfacial measurements of the absorption spectrum show that it is similar to, but different from, the standard solvated electron spectrum measured using radiolysis techniques. This anomaly suggests that the plasma-liquid interface is a wholly different environment for solvated electrons from that they experience in bulk radiolysis. To understand this interface, a model of the interfacial electrostatic Debye layer was constructed by considering both the electrostatic potential variation on the plasma side and the liquid side along with electron injection across the liquid interface. This analytical model predicts a non-linear scaling relationship between the plasma current density and electrolyte conductivity, and experimental measurements confirm the model. Extracted values from the model, including the interfacial electric field (~105 V/m) and the electrolyte cation concentration, offer insight into the electrochemical interface, but do not fully resolve questions regarding the anomalous absorption spectrum of plasma-injected solvated electrons.