bluuebunny/crossref_metadata_2025 huggingface dataset:
(Invited) Optical Signatures of Carbon Nanotube Excitons Coupled to Plasmonic Nanocavities and Metallo-Dielectric Antennas
Authors: Strauf Stefan
Published: February 2020

Single-walled carbon nanotubes (SWCNTs) have recently gained tremendous interest as a nanomaterial for next generation optoelectronics and quantum photonic devices, in particular through the demonstration of quantum light emission at room temperature in doped SWCNTs [1]. For further advances and to enable practical applications in quantum information processing light enhancement strategies are required. To this end plasmonic nanocavities such as bowtie antennas feature nanometer gaps that can support ultra-small mode volumes which are particularly attractive to enhance the exciton emission of single-walled carbon nanotubes (SWCNTs). In this talk we will discuss several technique to achieve the required spectral, spatial, and orientational resonance between SWCNT excitons and nanoplasmonic modes. Both time integrated and time-resolved measurements reveal characteristic signatures demonstrating pronounced coupling in the Purcell regime. As a test system we employ co-polymer wrapped carbon nanotubes for which we have recently shown that the polymer backbone can lead to efficient acoustic-phonon localization implying long exciton coherence times and ultra-narrow linewidth [2]. In addition, we will discuss SWCNT excitons coupled to metallo-dielectric antennas and evaluate the light collection efficiency enhancements achievable with this approach. Finally, we will discuss the prospects of achieving transform limited single photons in these systems.

[1] X. Ma, N.F. Hartmann, J.K.S. Baldwin, S.K. Doorn, and H. Htoon, “Room-temperature single-photon generation from solitary dopants of carbon nanotubes”, Nature Nanotech 10, 671–675 (2015).

[2] I. Sarpkaya, Ehsaneh D. Ahmadi, Gabriella D. Shepard, Kevin S. Mistry, Jeffrey L. Blackburn, and S. Strauf, “Strong Acoustic Phonon Localization in Copolymer-Wrapped Carbon Nanotubes”, ACS Nano 9, 6383 (2015).
A Low-Cost, High-Performance Polysulfide/Ferrocyanide Redox Flow Battery Using Highly Active Metal Pyrites Catalysts
Authors: Li Wenjie , Dong Yifan , Jin Song
Published: February 2020

Polysulfide is a promising redox couple employed in various aqueous redox flow batteries (RFB) for large scale electrochemical energy storage due to its high solubility and low cost. However, polysulfide has much lower rate constant in comparison with other commonly used redox couples in RFB. Therefore, efficient electrocatalysis is a key to achieving high performance for polysulfide-based RFB. Here we first systematically investigated the electrocatalytic activity of various pyrite phase metal disulfides (FeS2, CoS2, NiS2) as thin film electrodes towards polysulfide redox reactions under steady state condition. Then we further demonstrated a high-performance polysulfide/ferrocyanide RFB using optimized high surface area NiS2 nanostructures grown on carbon paper as the electrode. The NiS2/carbon paper electrode was able to achieve a high current density of 38.6 mA cm-2 at an over potential of 100 mV. An aqueous polysulfide/ferrocyanide RFB employing NiS2/carbon paper as anode and plain carbon paper as cathode was further evaluated by constant current cycling test and electrochemical impedance spectroscopy to demonstrate high charging-discharging cycling performance and low charge transfer impedance.
Miniaturized Ascorbic Acid Fuel Cells with an Ion-Exchange Films and Flexible Electrodes Made of Graphene-Coated Carbon Fiber Cloth
Authors: Doi Toshinari , Hoshi Kazuki , Muramatu Kazuo , Sumi Hisato , Nishioka Yasushiro , Imai Satomitsu
Published: February 2020

Ascorbic acid (AA), also known as vitamin C, is an environmentally biologically friendly compound and a stable and non-toxic powder. AA exists in many products such as sports drinks, fruit, and in human blood. Thus, AA is expected to be an alternative fuel for potable power supplies. Fujiwara et al. reported an ascorbic acid fuel cell (AAFC) without catalysts on the anode [1]. However, these AAFCs were not portable. Recently, Hoshi et al. reported a miniaturized AAFC with an area of 0.3 cm2 using a flexible graphene-coated carbon fiber cloth (GCFC) [2]. The AAFC exhibited lower power density of 34.1µW/cm2 in a buffer solution containing 100 mM AA at room temperature and the lifetime is not reported. Further improvement in their power density is needed for their application as portable AAFC and the lifetime should be investigated.

In this study, we optimized a miniaturized and flexible AAFC using a GCFC. The power density of the optimized AAFC in a mcllvaine buffer solution (MBS, pH 5.0) containing 100 mM AA at room temperature was 155.7 µW/cm2 at 0.375 V (Fig. 1a). Although this value is approximately five times greater than that of previous studies Hoshi et al. reported, the lifetime is substantially short. Since AA oxidizes on GCFC electrodes, ion-exchange films is needed for inhibiting crossover. We also fabricated a miniaturized and flexible AAFC incorporating ion-exchange films. The power density of the AAFC incorporating ion-exchange films in a MBS containing 100 mM AA at room temperature was 32.7 µW/cm2 at 0.221 V and the performance lasted about 50 % for 12 hours (Fig. 1b).

References

[1] N. Fujiwara, K. Yasuda, T. Ioroi, Z. Siroma, Y. Miyazaki, and T. Kobayashi: Electrochem. Solid-State Lett. 6, A257 (2003).

[2] K. Hoshi, K. Muramatsu, H. Sumi, and Y. Nishioka: Jpn. J. Appl. Phys. 55(4S), (2016).

Figure 1
Synthesis of NiMoS4 and Its Application for High-Performance Supercapacitors
Authors: Du Dongwei , Lan Rong , Tao Shanwen
Published: February 2020

Supercapacitors have attracted considerable attention due to the fast charge-discharge ability, excellent rate capability and long-time stability. Transition metal sulfides possess multiple oxidation states that enable rich redox reactions for pseudocapacitance, which have been investigated as promising electrode materials for high performance supercapacitors. Here, NiMoS4 is successfully synthesized by a facile chemical co-precipitation method and further heating in Ar atmosphere. The as-prepared NiMoS4 is firstly studied in a three-electrode system, it exhibits a specific capacitance of 707 F g-1 at a current density of 1 A g-1. Moreover, an asymmetric supercapacitor is fabricated using the NiMoS4 electrode as positive electrode and activated carbon (AC) as negative electrode. The asymmetric supercapacitor demonstrates high rate capability and good cycling stability. The operation voltage could expand to 1.6 V, at which the energy density can reach 35 Wh kg-1 with a power density at 400 W kg-1. The capacitance maintains around 82.4% after 10000 cycles at a current density of 5 A g-1. These high performances indicate NiMoS4 electrode is promising for applications in renewable energy storage in the future.

Fig. 1 Cycling performances of the asymmetric supercapacitor for 10000 cycles at 5 A g-1
.

References

[1] Stoller, M. D. & Ruoff, R. S. Best practice methods for determining an electrode material's performance for ultracapacitors. Energy & Environmental Science 3. (2010) 1294-1301.

[2] Guan, B. Y., Yu, L., Wang, X., Song, S., & Lou, X. W. D. Formation of Onion‐Like NiCo2S4 Particles via Sequential Ion‐Exchange for Hybrid Supercapacitors. Advanced Materials 29 (2017) 1605051.

[3] Dongwei Du, Rong Lan, Wei Xu, Richard Beanland, Huanting Wang and Shanwen Tao, Preparation of a hybrid Cu2O/CuMoO4 nanosheet electrode for high-performance asymmetric supercapacitors, Journal of Materials Chemistry A, 4 (2016) 17749–17756.

Figure 1
Planar-Type Na-Metal Halide Battery: Low Operating Temperature, Low Cost and Long Cycle-Life
Authors: Chang Hee Jung , Lu Xiaochuan , Jung Keeyoung , Sprenkle Vincent , Li Guosheng
Published: February 2020

Energy storage systems (ESS) have gained great attentions recently for grid-scale applications. Among various types of batteries, Na-beta alumina batteries (NBBs), which are based on a β"-Al2O3 solid electrolyte (BASE) and a molten sodium anode, have been considered as a promising technology due to their high energy density, high efficiency, and good cycle life. Two types of NBBs, sodium sulfur (Na-S) and sodium-metal halide (Na-MH) batteries, have been investigated and commercialized in the past. Despite of being considered as a relatively new and less popular technology compared to Na-S batteries, Na-MH battery can provide several advantages over a Na-S battery including lower operating temperature (280oC for Na-MH vs. 350oC for Na-S), safe cell-failure mode, higher output voltage and safe assembly in the discharged state without preloading metallic sodium in the anode.

Our Na-MH battery researches in PNNL are primarily focused on developing advanced planar-type Na-MH batteries operated at temperatures below 200oC. It was found that lowering operating temperature helps to retain the long-term stability and higher energy density by slowing down materials degradation. Lowering operating temperature also provides opportunities to deploy conventional high temperature polymers as sealing materials, which can greatly reduce cell manufacturing costs. In this presentation, we will present the important correlation between cathode formula and battery performances, and will discuss about the design and testing results of larger planar cells aiming practical applications.
Liquefied Gas Electrolytes for Electrochemical Energy Storage Devices
Authors: Yang Yangyuchen , Rustomji Cyrus Sam , Meng Ying Shirley
Published: February 2020

Electrochemical energy storage devices, such as Li-ion batteries and electrochemical capacitors, have seen little change in their electrolyte chemistry since their commercialization. These liquid electrolytes often limit the energy density and low-temperature operation of these devices, which hinder many potential applications. Our work uses electrolytes based on solvent systems which are typically gaseous under standard conditions and show excellent performance in electrochemical energy storage devices. It is demonstrated that these novel solvents have excellent performance over an extended temperature range and a wide potential window of stability. Fluoromethane based electrolytes demonstrate a high coulombic efficiency for cycling dendrite-free lithium metal anodes. Lithium batteries show excellent low-temperature operation down to -60 °C with high capacity retention. Electrochemical capacitors, using difluoromethane based electrolytes, show outstanding performance and a wide operation temperature range from -78 to +65 °C with an increased operation voltage.
Fast Charging of Chlorine Doped Amorphous TiO2 Reaching 1 Li per TiO2 for Sub-Micron Thick Films
Authors: Moitzheim Sébastien , Balder Ellis , Poodt Paul , Unnikrishnan Sandeep , De Gendt Stefan , Vereecken Philippe M
Published: February 2020

Negative electrodes from TiO2 remains an intriguing choice for lithium-ion batteries, as it could offer a high theoretical capacity (336 mAh/g) and excellent cycling stability. Unfortunately, due to its low electronic and ionic conductivity, state-of-the-art nanosized (< 20 nm) TiO2 electrodes still only achieve about 75% of this capacity at 1 C (or 336 mA/g). From submicron sizes on, TiO2 almost no accessible capacity is left at practical C-rates. In this work, submicron thick chlorine doped amorphous TiO2 (TiO2-xClx) films are investigated as a high-performance Li+-ion insertion electrode material. The TiO2-xClx films were fabricated by Spatial Atomic Layer Deposition (S-ALD), by which the chlorine content was controlled by varying the deposition temperature and gas precursor exposure time, as determined by Rutherford Backscatter Spectroscopy (RBS) and X-Ray Photoelectron Spectroscopy (XPS). Electrochemical tests revealed a maximum reversible Li+-ion insertion/extraction capacity of 362 mAh/g at 0.25 C for the TiO1.912Cl0.088 film (see Fig. 1), which is above the theoretical maximum and suggests that reduction of Ti(III) to Ti(II) is accessible in Cl-doped amorphous TiO2. At a rate of 1 C, still 90% (301 mAh/g) of the theoretical TiO2 capacity is achieved and even 27% (92 mAh/g) at 50 C (see Fig. 1). In addition, TiO2-xClx films deposited by S-ALD are demonstrated as three-dimensional (3D) thin-film electrodes for 3D solid-state batteries. Using 3D structuring, the footprint capacity increased 24 times, while the excellent rate-performance of the planar TiO2-xClx films is retained. The cycling stability of the 3D TiO1.912Cl0.088 electrode was tested for 1000 cycles at 10 C, and no degradation in capacity is observed. Finally, benchmarking our 3D thin-film TiO1.912Cl0.088 electrode shows that it outperforms all other 3D thin-film TiO2 electrodes previously reported.

Figure 1
Flow Batteries Containing Solid Dispersions of Lithium-Ion Active Material Redox Couples
Authors: Gupta Devanshi , Qi Zhaoxiang , Koenig Gary
Published: February 2020

Large scale flow battery energy storage has long been considered as a potential candidate for smart grid batteries because of their design flexibility, safety and high current densities. However, one limitation of flow batteries for certain applications is their relatively low power density, which is fundamentally due to limited solubility of active species in the electrolyte which leads to the formation of precipitates at high concentration and/or high temperature. To overcome energy density limitations several methods/improvements have been reported in the battery research literature, including: polymer based flow batteries, new active materials, ionic liquids, and hybrid flow batteries with multiple redox couples.

Semi-solid flow batteries, first reported using lithium-ion chemistry by Duduta et. al1 use high energy density lithium storage compounds within a suspension/slurry in a redox flow battery. This system also relies on a nanoscale conducting network of carbon particles to provide electronic contact between the active material particles and increase active material participation in the flow channel. Their reported energy density was an order of magnitude greater than conventional flow batteries; however, the carbon network resulted in a highly viscous electrolyte requiring high pumping energy. This poster will describe carbon-free redox flow couples with solid electroactive materials in electrolyte suspensions. LiCoO2 (LCO) and Li4Ti5O12 (LTO) were used as the active cathode and anode active materials, respectively.2 The use of solid active materials and lithium-ion battery materials and electrolytes expands both the voltage range and volumetric energy density of the electrolyte. Without carbon the dispersions with sub-micron LTO and LCO particles have reduced viscosity compared to semi-solid flow batteries due to the absence of carbon conducting additives. The lack of carbon results in dramatic decreases in power density due to lower active material participation. The impacts of active material loading on electrochemical and rheological behavior in multiple cell designs will be described.

1. Duduta, M., Ho, B., Wood, V. C., Limthongkul, P., Brunini, V. E., Carter, W. C., & Chiang, Y. M. (2011). Semi‐Solid lithium rechargeable flow battery. Advanced Energy Materials, 1(4), 511-516.

2. Qi, Z., Liu, A. L., & Koenig, G. M. (2017). Carbon-free Solid Dispersion LiCoO2 Redox Couple Characterization and Electrochemical Evaluation for All Solid Dispersion Redox Flow Batteries. Electrochimica Acta.
(Olin Palladium Award of the Electrochemical Society Address) Corrosion Mechanisms at the Atomic or Nanometric Scale
Authors: Marcus Philippe
Published: February 2020

In this Award Lecture I will emphasize a surface science approach that allows to reach a deep understanding of the mechanisms of corrosion at the atomic or nanometric scale. I will show the link between atomic/nanometric scale mechanisms and the macroscopic corrosion manifestations. The lecture will include the combined experimental approaches using advanced surface analytical and electrochemical methods with theoretical approaches based on atomistic modeling.

The high resolution techniques used in combination with classical electrochemical methods will be presented, high resolution meaning high space resolution, as achieved by near field microscopies (Scanning Tunneling Microscopy and Atomic Force Microscopy), high energy resolution in electron spectroscopy for chemical analysis, and high mass resolution for surface molecular analysis by Time-of-Flight Secondary Ions Mass Spectrometry.

The formation of the metal-water interface occurring when a metal surface is exposed to water, which has been investigated by in situ Scanning Tunneling Microscopy, will be presented.

A major part of this address will be devoted to passivity of metals and alloys, a central issue in corrosion science and engineering since the formation of ultra-thin surface oxide films is the best of all means for protection of metallic materials against corrosion. I will discuss the growth mechanisms, the nanostructure, and the electronic properties of passive films, as well as passivity breakdown and initiation of localized corrosion, with emphasis on atomic and nanoscale data.

Cathodic reactions on oxidized metal surfaces will then be discussed, with a theoretical approach of the di-oxygen reduction on surface oxide films on Al surfaces using DFT.

Finally I will mention recent work on corrosion inhibition by adsorbed organic molecules, an area in which progress has been recently achieved by combining quantum chemical calculations (DFT) with experiments.
Redefining the Electrochemical Kinetics of Redox Reactions on Passive Metals
Authors: Macdonald Digby D.
Published: February 2020

The kinetics of redox reactions are described by specifying a standard exchange current density and a transfer coefficient that locates the position along the reaction coordinate at which the activated complex (transition state) occurs. However, this formulation was originally developed to describe charge transfer reactions on bare metal surfaces. In the case of a passive metal, however, the barrier layer of the passive film represents a barrier to the quantum mechanical tunneling of charge carriers (electrons and electron holes) between the metal and the redox reaction center and theory shows that this barrier has a profound effect upon the tunneling probability and hence upon the values of the exchange current density and the Tafel constant. In this presentation, the role of quantum-mechanical tunneling of charge carriers through the barrier oxide layer on a passive metal, in determining the electrochemical kinetic parameters is explored theoretically. The exchange current density for a redox reaction occurring on the passive metal surface is assumed to be the product of the exchange current density on the bare metal surface and the quantum mechanical tunneling probability (QMTP) of charge carriers through the barrier layer, which is inversely proportional to the exponential of the barrier thickness and the tunneling constant that in turn is proportional to the square root of the product of barrier height and the effective electron mass. The QMTP is used to redefine the exchange current density for the cathodic reaction (e.g., reduction of oxygen), as measured on the passive surface, to that on the (hypothetical) bare metal alone. Thus, knowing the voltage, the barrier layer thickness can be calculated from the Point Defect Model (PDM), which in turn can be used to estimate the QMTP for that particular set of conditions. Then, the exchange current density for the redox reaction on the passive metal surface is calculated and used, if the barrier height and the effective electron mass are constants, in the generalized Butler-Volmer equation to describe the current/voltage characteristics of the redox reaction. In doing so, it becomes evident that the kinetics of a redox reaction are fully determined by specifying a (hypothetical) exchange current density and transfer coefficient of the reaction on the bare metal (“hypothetical” because the bare metal condition may not be realizable experimentally), the QMTP, the electric field strength within the barrier layer, the polarizability of the barrier layer/solution interface, and the potential of zero thickness of the barrier layer. The application of this theory is illustrated with respect to the hydrogen electrode reaction (HER) on passive carbon steel and on aluminum and in predicting the corrosion potentials of stainless steels and nickel alloys in the primary coolant circuits of water-cooled nuclear reactors.
Novel Ni Based Duplex Coatings for Anticorrosion Applications
Authors: Yusuf Moinuddin M , Bahgat Ahmed , Shakoor R A , Kahraman Ramazan , Montemor M. F
Published: February 2020

Ni-B/Ni-P-CeO2 duplex coatings containing inner Ni-B layer were synthesized through the electrodeposition process. A mild steel sheet was used as substrate material to deposit the coatings. The structural, surface and electrochemical properties of the duplex coatings in their as synthesized condition were compared with Ni-P, Ni-B and binary Ni-B/Ni-P duplex coatings to demonstrate the improved performance of Ni-B/Ni-P-CeO2 duplex coatings. The structural analysis (XRD) indicates that the developed coatings exhibit amorphous behavior. The SEM and AFM studies indicate that Ni-B/Ni-P-CeO2 duplex coatings have less surface defects and more defined nodular structure compared to Ni-P, Ni-B and Ni-B/Ni-P duplex coatings. However, these coatings show an increase in surface roughness which may be attributed to the incorporation of CeO2 ceramic particles used as reinforcement. The Ni-B/Ni-P-CeO2 duplex coatings present superior anticorrosion properties compared to Ni-B and duplex Ni-B/Ni-P coatings. The improved electrochemical performance of novel Ni-B/Ni-P-CeO2 duplex coatings can be regarded as the effect of less defective structure produced due to blocking of pores and reduction in the active area of the Ni-B/Ni-P matrix by the presence of CeO2 ceramic particles. Owing to tempting properties, Ni-B/Ni-P-CeO2 duplex coatings may be considered as potential candidate for oil and gas industry.
Multifunctional Inhibition Based on Layered Double Hydroxides to Comprehensively Control Corrosion of Steel Rebar in Concrete
Authors: Cao Yanhui , Dong Shi-Gang , Lin Changjian
Published: February 2020

Concrete is the most widely used construction material in the world due to its versatility and relatively low cost. However, the early deterioration of reinforced concrete constructions due to corrosion of the steel reinforcement has become a major problem in the society, not only resulting in a huge economic loss, but also inducing serious safety disasters frequently. In this work, A novel multifunctional inhibitor of MgAl-layered double hydroxides (LDHs) loaded with nitrite anions was synthesized via a calcination-rehydration in ambient atmosphere. It was demonstrated that such LDHs loaded with inhibitor was able to comprehensively control the corrosion of carbon steel in simulated concrete pore solution (SCPS) as well as in mortar. Based on the systematic measurements, a conceptual model was proposed for the first time to further understand the mechanism of multifunctional corrosion protection of MgAl-LDHs-NO2
- in steel reinforced concrete, involving the increase of pH and decrease of free chloride ions in concrete, release of inhibitor ions, and impeding the transport process of the aggressive ions in the concrete. Such unique multifunctional composite is markedly helpful to comprehensively control corrosion of steel in concrete.
Broadband Dielectric Spectroscopic Characterization of Thermal Stability of Low-k Dielectric Thin Films for Micro- and Nanoelectronic Applications
Authors: Sunday Christopher E , Montgomery Karl R. , Amoah Papa K. , Iwuoha Emmanuel I , Obeng Yaw S.
Published: February 2020

In this paper, we discuss the use of broadband microwaves (MW) (up to 20 GHz) to characterize the thermal stability of dielectric thin films for emerging nanoelectronic applications. We will illustrate the talk with examples from our on-going work on the thermal stability of organic and hybrid silicon-organic thin films meant for insulation applications in micro- and nanoelectronic devices. We will illustrate our use of MW propagation characteristics to extract changes in electrical and mechanical properties, and their links to the changes in chemistry of prototypical materials. These studies shine light on the chemical changes that occur within the dielectric films that could impact the performance and reliability, as well as provide basis for rational selection of organic dielectrics for integrated devices.
Analysis of Amorphous Indium-Gallium-Zinc-Oxide Thin-Film Transistors with Bi-Layer Gate Dielectric Stacks Using Maxwell-Wagner Instability Model
Authors: Kiani Ahmed , Bayer Bernhard C. , Hasko David G. , Milne William I , Flewitt Andrew J.
Published: February 2020

Aluminium oxide (Al2O3) and hafnium oxide (HfO2) have been grown, using atomic layer deposition (ALD), as single and bi-layer gate dielectric films. Electrical and structural characterisation indicates that the material properties depend on layer thickness and growth order, when deposited as bi-layers. Charge trapping at the interface between the bi-layer stacks results from the Maxwell-Wagner (MW) instability, which states a difference of conductivities at the dielectric-dielectric interface with respect to the bulk dielectric films. Hence a build-up of this interface charge compensates for the condition that the current densities of individual dielectric films match that of the overall stack. This causes electrical instabilities in stack behaviour. Bottom-gate amorphous indium-gallium-zinc-oxide thin-film transistors are fabricated with these gate oxides, single and bi-layer stacks, with low VTH
and gate leakage current to understand this instability. By empirically adopting ideal MOSFET equations and single gate dielectric film behaviour as a reference, this MW instability in bi-layer gate dielectric stacks has been accounted for in amorphous indium-gallium-zinc-oxide thin-film transistor transfer characteristics with a good fit in both above threshold and sub-threshold regimes.
Kelvin Force Probe Microscopy of Ferroelectric Si:HfO2
Authors: Marinskiy Dmitriy , Polakowski Patrick , Lagowski Jacek , Wilson Marshall , Edelman Piotr , Müller Johannes
Published: February 2020

Since the demonstration of the ferroelectric properties in hafnium based oxides in 2011 there is large interest to such films for ferroelectric FET, memory, and other applications. Engineering of ferroelectricity in HfO2 relies on doping and annealing. For Si-doped HfO2films, a top metal electrode capping layer is deposited prior to annealing which is shown to cause ferroelectric behavior.

In this paper we present results of non-contact corona-Kelvin characterization of poling phenomena for ferroelectric Si:HfO2 thin films. Measurements were performed on free dielectric surfaces. The method uses corona charging and Kelvin force probe measurements. Corona charging pulses are analogous to voltage biasing, except that no top electrode is needed. Corona charging enables biasing the Si:HfO2to a near coercive field where onset of poling occurs. Mapping of the surface voltage with a small diameter Kelvin force probe allows to quantify poling phenomena, its uniformity and degradation during repetitive switching (Fig. 1).

These results are of importance for fundamental understanding of switching mechanisms of ferroelectric Si:HfO2 films.

Figure 1
(Invited) Improvement of Perovskite Films and the Perovskite/TiO2 Interface
Authors: Zhang Peng , Wang Yafei , Liu Detao , Li Shibin , Chen Zhi David
Published: February 2020

Perovskite solar cells (PSCs) based on organometallic halide have received wide attention and been developed rapidly in recent years. However, the grain boundaries in perovskite film and defects in the interface in perovskite films dramatically degrade PSCs performance.

Solvent annealing is an efficient method to fabricate high quality perovskite film with less grain boundaries. While most works carried out focused on the solvent annealing of perovskite films, we annealed PbI2 films in DMF, DMSO, acetone, and isopropanol (IPA) atmospheres and studied the effect of different atmospheres. We found that dense PbI2 was formed by annealing in DMF, acetone, and IPA atmospheres, which impeded the full reaction between PbI2 and CH3NH3I. Meanwhile, DMSO solvent annealing process led to porous PbI2 films, which facilitated the complete conversion of PbI2 to perovskite with larger grain sizes. As a result, Solar cells based on DMSO solvent annealing process exhibited the best efficiency of 18.5%, with a fill factor of 76.5%.

We also annealed PbI2 in DMSO and CH3NH3PbI3 in ethanol for fabrication of pinhole-free CH3NH3PbI3 films on ZnO nanorods. Due to the suppression of carrier recombination by large grains, ZnO nanorods based PSCs with best efficiency of 17.3% was obtained.

To suppress the interface defect, Li-doping compact TiO2 was also used as electron transport layer (ETL). Li doping reduced electron trap density and increased the conductivity of the ETL. As a result, the Li-doped compact TiO2 based planar heterojunction PSCs exhibit negligible hysteretic J-V behavior. Comparing with the undoped compact TiO2 based PSCs, the PCE of the Li-doped compact TiO2 film based PSCs is improved from 14.2% to 17.1%.

Figure 1
(Invited) Structures and Electronic Characteristics of Lattice Defects at Interfaces in the Perovskite Solar Cell. a First-Principles Study
Authors: Sugimoto Manabu
Published: February 2020

We will discuss about our recent first-principles calculations on lattice defects at interfaces in perovskite solar cells (PSCs). In this presentation, we will show computational results on some kind of defect systems including point defects and impurities. The main focus in the discussion will be on defects near the surface of the metal halide perovskite layer. The calculation shows that, when the surface with underlying lattice defects is fabricated with appropriate molecules, defect levels are modulated and become inactive for carrier trapping. Some factors pertinet to the level modulation are clarified through detailed analyses on the computational results. The present computational analysis suggests importance of surface modification to enhance the energy conversion efficiency of the PSCs.
(Invited) Enabling New Domains of Energy Storage through Atomic Layer Deposition
Authors: Rubloff Gary W
Published: February 2020

The portfolio of materials accessible by atomic layer deposition (ALD) processes has encompassed all key components of electrochemical energy storage (EES) – cathodes, anodes, solid electrolytes, and interphases. This provides a rich environment in which to advance the science of EES, particularly due to the exceptional thickness and conformality control inherent in underlying ALD mechanisms. Here we highlight three regimes where ALD is most promising to impact battery technology. (1) ALD-based electrode protection layers seem to offer the shortest term technology impact, providing ion permeability while serving as passivation against the varied modes chemical, electrochemical, and mechanical degradation regularly found in batteries, improving cycle life and suppressing dendrite formation. (2) ALD-based solid state batteries offer benefits in structural simplicity and control well beyond that available in commercial devices employing sputtered films. ALD solid electrolytes play a critical role in both protection layers and solid state batteries. (3) 3D solid state batteries exploit high surface areas and thin conformal layers over high aspect ratio topography to achieve higher power-energy performance than planar counterparts. Examples illustrating these opportunities include ALD LiPON protection of metal anodes and conversion electrodes, new pathways to solid electrolyte synthesis, and planar and 3D solid state batteries employing ALD for most or all components.

Supported as part of the Energy Frontier Research Center (EFRC) Nanostructures for Electrical Energy Storage (NEES), funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under award number DESC0001160.
(Invited) Functional Oxides for Energy Efficient Information Technology
Authors: Dubourdieu Catherine
Published: February 2020

Complex oxides exhibit a wide range of electrical, magnetic, optical, mechanical properties, which may even be coupled. In the past fifteen years, tremendous progresses have been achieved in the growth of complex oxides on oxide substrates, resulting in unit-cell scale control (~0.4 nm for a perovskite). Concurrently, breakthroughs in characterization techniques and modeling have resulted in a better understanding of the effects of composition, size, strain and boundaries conditions on their properties. If complex oxides could be integrated as an add-on to semiconductor technologies in a seamless process, their extraordinary wealth of physical properties could offer new functionalities in devices in order to address societal needs related to health, energy or information & communication technologies.

In this presentation, I will review some aspects on the synthesis, characterization and integration of oxide heterostructures on semiconductors. The scientific and technological challenges for achieving monolithic integration will be presented. Molecular beam epitaxy provides unique advantages to precisely construct, almost atom by atom, the oxide/semiconductor interface to achieve epitaxy. With the case of the ferroelectric BaTiO3 perovskite on Si and SiGe, we will exemplify the various strategies developed to engineer the interface with the semiconductor and to control the oxide crystalline structure and properties.

Regarding SiGe substrates, we will show that a direct growth of BaTiO3 can be achieved on strained Si0.8Ge0.2/Si. The passivation of the starting surface will be discussed. From the X-ray diffraction analysis, the films are found to be oriented with <112> directions perpendicular to the substrate's surface and show two distinct in-plane orientations. An orthorhombic epitaxial silicate is formed at the interface with Si0.8Ge0.2 which gives rise to the 112 epitaxial growth of BaTiO3.The cationic and oxygen compositions of the film and interface will be discussed.

Regarding the growth on Si substrates, we will emphasize the role of size effect and of electrical /mechanical/chemical boundary conditions on the resulting ferroelectric properties. Ferroelectricity down to 4 monolayers of BaTiO3 (1.6 nm) is evidenced with two distinct switchable polarization states.

Finally, we will present current and potential realizations towards complex oxide nanoelectronics with reduced power consumption and towards integrated photonics. The integration of amorphous/nanocrystallites BaTiO3 is a promising approach to reach ferroelectricity in a metal-oxide-semiconductor device. Such composite material exhibits the advantageous properties of an amorphous dielectric of medium relative permittivity with a low leakage current density (˜ 10-7 A/cm2at -1V) while being ferroelectric at room temperature. It is particularly suitable for negative capacitance field-effect devices as well as for memristive devices.
Rate Dependent Multi-Mechanism Discharge of Ag0.50VOPO4·1.8H2o: Insights from in-Situ Energy Dispersive X-Ray Diffraction
Authors: Huie Matthew M. , Bock David C , Bruck Andrea , Yin Jiefu , Takeuchi Kenneth J , Takeuchi Esther S , Marschilok Amy C
Published: February 2020

Ag0.
50VOPO4·1.8H2O (silver vanadium phosphate, SVOP) demonstrates a counterintuitive higher initial loaded voltage under higher discharge current. Energy dispersive X-ray diffraction (EDXRD) from synchrotron radiation was used to create tomographic profiles of thick cathodes at various depths of discharge for two discharge rates. SVOP displays two reduction mechanisms, reduction of a vanadium center accompanied by lithiation of the structure, or reduction-displacement of a silver cation to form silver metal. In-situ EDXRD provides the opportunity to observe spatially resolved changes to the parent SVOP crystal and formation of Ag0 during reduction. Discharge rate can influence the preferred initial reaction either V5+ reduction or reduction of Ag+ with formation of conductive Ag0. Discharge rate also affects the spatial location of reduction products. This study highlights the importance of mesoscopic analysis and illuminates the roles of electronic and ionic conductivity limitations within a cathode and how they impact the course of reduction processes and loaded voltage.
Interactions of Nanostructured TiO2 with Nonaqueous Electrolytes for Na-Ion Batteries
Authors: Smith Kassiopeia , Parrish Riley , Barnes Pete , Savva Andreas , Karsann Devan , Deng Changjian , Dufek Eric J. , Xiong Hui (Claire)
Published: February 2020

Current shifts towards renewable energy technologies have increased the drive for high performance and cost effective battery systems. Sodium ion batteries present a promising alternative to the commonly used lithium-ion batteries and offer several benefits such as low cost and high availability. While lithium-ion battery systems have been studied intensively, it has become apparent that the interfacial chemistry differs significantly for sodium ion batteries, even when using the same solvents.

In previous work, we have shown that amorphous TiO2 nanotube electrodes are a suitable anode materials for Na-ion batteries. The optimization of electrolytes is important to develop a system with good solubility, high transport properties, electrochemical and interfacial stability. In this work, we have investigated the electrochemical properties of TiO2 nanotube electrodes - as a model system - in various electrolytes containing different solvent mixtures (cyclic and acyclic carbonates) with NaClO4 and NaPF6 salt. In addition, we have conducted fundamental studies of chemical, thermal, and electrochemical stability of the chosen sodium-based electrolytes with a phosphazene-based additive FM2 as well as the commonly used FEC additive.
(Invited) The Effects of Zinc-Tin-Oxide Nanosphere Monolayer on Improvement of Light Extraction in Light-Emitting Diodes
Authors: Kim Taek Gon , Shin Dong Su , Kim Do Hyun , Park Jinsub
Published: February 2020

Over the last two decades, III-nitride-based light-emitting diodes (LEDs) have been widely used for our daily life, such as illumination, various backlight units for full-color displays, and automotive headlamps. In spite of the versatile advantages of GaN-LEDs, relatively low external quantum efficiency is still a problem to expand their application fields. For the viable solution to unravel pending issues in solid state light-emitting research fields, many efforts have been conducted. In this study, we report on the applications of zinc-tin-oxide (ZTO) nanoparticles and monolayer as a light extraction layer for GaN-based LEDs. The ZTO layers formed on top of an LED epi-structure with a variable Sn-ratio, which was deposited by the spin coating method. The transmission spectra of the ZTO layers with Zn to Sn ratios of 1:1 (ZTO-I) and 1:5 (ZTO-II) exhibited optical transmittances of 98% and 88% in the visible region, respectively. The electroluminescence (EL) and light power-current-voltage (L-I-V) measurements show that double ZTO layers consisting of various Zn to Sn ratios led to enhanced light extraction from blue LEDs. Finally, we will discuss the effects of ZTO monolayer transferred onto the p-GaN surface on the external quantum efficiency of LEDs. The ZTO monolayers were prepared by using the ZTO nanospheres synthesized by precipitation solution method. The transferred ZTO nanosphere monolayers on top surface of LED are very effective way to improve the light extraction efficiency.
(Invited) Molecularly Tunable Quantum Emitters
Authors: Wang YuHuang
Published: February 2020

New properties arise as the size of a crystal reaches the Bohr radius of excitons. This phenomenon, known as quantum confinement, has enabled powerful synthetic strategies to control the optical and electronic properties of a material through size engineering. In this talk, we will discuss a fundamentally new approach that allows systematic tailoring of nanostructure excitons through covalently bonded surface functional groups that are themselves non-emitting. Specifically, we show that by varying the surface functional groups, a semiconducting carbon nanotube can be chemically converted to create a large series of distinct near-infrared quantum emitters that are molecularly specific, systematically tunable, and significantly brighter than the parent semiconductor. In contrast with quantum confinement, where size matters, this new property-tailoring capability arises from the creation of fluorescent quantum defects that can be chemically controlled at the molecular level. This new family of quantum emitters opens up exciting new opportunities for potential applications ranging from bioimaging and sensing to quantum information processing.
Auspicious Metal-Doped-Cu2O/Cu Dendrite (M=Ni, Co, Fe) Catalysts for Direct Alkaline Fuel Cells: Effect of Dopants
Authors: El-Nagar Gumaa A. , Derr Igor , Kottakkat Tintula , Roth Christina
Published: February 2020

Herein, honeycomb nickel-, cobalt- and iron-doped Cu2O/Cu foams with dendrite-like structures are in-situ formed atop of a copper foil substrate using the facile and low-cost dynamic hydrogen bubbles template technique (DHBT), wherein the copper nanoparticles are electrodeposited and grow in the interstitial spaces between the hydrogen bubbles. The incorporation of nickel, cobalt and iron impurities (less than 4%) in the Cu2O/Cu structures improved the performance of Cu2O/Cu significantly for various electrochemical reactions (i.e., water splitting, glucose and glycerol electrooxidation). Besides, only minor additions of these transition metals are dramatically changed the average particle size and morphology of the deposited copper nanoparticles. For instance, the un-doped Cu2O/Cu foam showed an artichoke flower-like structure (particle size ~150 nm) which is converted into a grape cluster-like structure (~92 nm), corncob-like structure (~58 nm) and grass-like structure (~78 nm) with nickel, iron and cobalt particles doping. The iron-doped Cu2O/Cu dendrites exhibited 7 and 4 times higher electrocatalytic activity along with 230 mV and 190 mV negative shift of the glucose and glycerol electro-oxidation peak compared to the un-doped Cu2O/Cu structures. This outstanding enhancement is attributed to the catalysts dendritic structures providing an accessible high active surface area. In addition, the doped metals are believed to increase the electrochemically active surface area and to facilitate the electron transfer in the studied reactions. Besides, the existence of these dopants improved the adsorption of glucose and glycerol molecules on the copper surface active sites together with increasing of the Cu2O inherent conductivity.

Figure 1
Pt-Ru/C Catalyst Performance during Direct Methanol Fuel Cell Operation
Authors: Pereira Drew Joseph , Wilkins Cody H , Shimpalee Sirivatch , Weidner John W.
Published: February 2020

A methodology for the electroless deposition (ED) of ruthenium (Ru) on a commercial, carbon-supported Platinum (Pt) catalyst has been developed for electrochemical and fuel cell applications [1, 2]. Several different bimetallic catalysts composed of Pt and Ru have been produced using this methodology with promise of having better catalytic activity. Figure 1 shows how the SEA/ED method produces a finer, more evenly dispersed bimetallic distribution with less monometallic clustering [1]. These bimetallic catalysts have shown higher activities compared to both commercially-available Pt-Ru/C catalysts and monometallic Pt or Ru catalysts [3, 4]. This method’s bimetallic catalyst is proven to show better resistance to CO poisoning as well [3, 5, 6]. In application, this Pt-Ru/C catalyst has promise to be an optimal catalyst for use in a Direct Methanol Fuel Cell (DMFC).

The objective for this study is to test the performance of the new Pt-Ru/C catalyst within a DMFC and compare the results to the commercially-available catalyst. This includes synthesis of the SEA/ED, Pt-Ru/C catalyst, characterization of the commercially-available and newly-synthesized catalyst with analysis, and finally, testing of each catalyst within a DMFC testing station and analyzing performance results. The DMFC testing and comparison is important to help show the catalysts’ real-world performance as well as effects of possible CO-poisoning during operation. The newly-synthesized catalyst has an increased electrochemical area as well as a better bi-metallic dispersion, to allow ruthenium to better prevent any platinum from being poisoned, causing the catalyst to perform better and last longer.

1. Diao, W., et al., Preparation and Characterization of Pt–Ru Bimetallic Catalysts Synthesized by Electroless Deposition Methods. ACS Catalysis, 2015. 5(9): p. 5123-5134.

2. Cho, H.-R. and J.R. Regalbuto, The rational synthesis of Pt-Pd bimetallic catalysts by electrostatic adsorption. Catalysis Today, 2015. 246: p. 143-153.

3. Garrick, T.R., et al., The Effect of Bimetallic Surface Composition for Methanol Oxidation. Student Posters (General) - 223rd Ecs Meeting, 2013. 53(29): p. 79-84.

4. Garrick, T.R., et al., The Effect of the Surface Composition of Ru-Pt Bimetallic Catalysts for Methanol Oxidation. Electrochimica Acta, 2016. 195: p. 106-111.

5. Galhenage, R.P., et al., Platinum–ruthenium bimetallic clusters on graphite: a comparison of vapor deposition and electroless deposition methods. Physical Chemistry Chemical Physics, 2015. 17(42): p. 28354-28363.

6. Kabbabi, A., et al., In situ FTIRS study of the electrocatalytic oxidation of carbon monoxide and methanol at platinum–ruthenium bulk alloy electrodes. Journal of Electroanalytical Chemistry, 1998. 444(1): p. 41-53.

Figure 1
Electrochemical Conversion of Carbon Dioxide into Formic Acid Using Porous Tin Catalyst
Authors: Kim Hyenki , Lee Hyunju , Ahn Sang Hyun
Published: February 2020

As the atmospheric carbon dioxide concentration increases by huge use of fossil fuels, the global warming is recognized as much serious problem in recent. To solve the problem, various researches on carbon capture utilization storage (CCUS) have been conducted by many researching groups. Among them, carbon utilization via electrochemical conversion of carbon dioxide is considered as one of the essential technologies because it can remove the carbon dioxide as well as convert it into the useful products such as CH4, CH3OH, CO and HCOOH. However, the electrochemical conversion usually suffers from huge energy losses due to the high overpotential originated from chemical stability of carbon dioxide. Therefore, the highly active catalyst should be required to realize the electrochemical conversion of carbon dioxide. Currently, various transition metals were mainly used as catalysts for the electrochemical carbon dioxide conversion to produce formic acid. Among them, the tin has been considered as a promising catalyst because it has high conversion efficiency and low prices. In this work, porous tin catalyst was fabricated by electrodeposition and following annealing process. In order to obtain the large electrochemical surface area, the roughness was controlled by varying the deposition current density. The field emission scanning electron microscope analysis confirmed the formation of porous tin catalyst deposited at highly negative current density. The roughness factor of the catalysts was measured by performing the cyclic voltammetry in 0.1 M NaHCO­3 with changing the scan rate. The deposited porous tin catalyst was used as cathode for electrochemical carbon dioxide conversion in H-type cell which was separated by proton conducting membrane. To characterize the reaction products both of liquid and gas chromatography were used. The obtained results indicated that the Faradaic efficiency to produce formic acid had significant relationship with the catalyst roughness.