bluuebunny/crossref_metadata_2025 huggingface dataset:
Photovoltaic Effect in ITO/Rgo/BFO/Au Heterostructures
Authors: Agarwal Radhe , Sharma Yogesh , Mendoza Frank , Morell Gerardo , Katiyar Ram S.
Published: February 2020

In recent years, BiFeO3 (BFO) thin films showed promising potential towards photovoltaic applications due to its superior ferroelectric properties and optical bandgap lies in the visible region. Among other wide bandgap ferroelectric photovoltaic (Fe-PV) materials (i.e. BaTiO3, LiNbO3 and Pb(Zr,Ti)O3), BFO exhibits large open circuit voltage (VOC), tunable output, and switchable photovoltaic effect. It has been reported that insertion of semiconductor layer to a conventional metal/ferroelectric/metal structure can result into novel heterostructures based photovoltaic cells. However, integration of novel carbon materials in ferroelectric photovoltaic devices has not been very popular. We have studied photovoltaic effect in In2O3-Sn2O3 (ITO)/reduced graphene oxide (rGO)/BiFeO3/Au (metal/semiconductor/ferroelectric/metal heterostructure). We have synthesized graphene oxide using modified hummers method. We spin coated GO solution on ITO substrate and dried overnight at 50oC to achieve thin films. Resultant GO thin films were annealed in NH3:H2 (3:1) atmosphere at 600oC. Electrical measurements confirmed n-type doping in thermally reduced GO (rGO) films. Whereas, BFO act as p-type semiconductor due to charge defects mainly, Oxygen vacancies. BFO films were grown using pulsed laser deposition technique. ITO/rGO/BFO/Au heterostructures shows a reasonable photovoltaic response. Such heterostructure shows short-cicuit current density of 86 µA/cm2. We believe that two built-in fields generated at Au/BFO and BFO/rGO interface are responsible for separation and transport of photo-excited electron-hole pairs. Our work may provide a new way to integrate carbon materials to ferroelectrics to produce heterojunction based solar cells.
Synthesis and Characterization of Fullerene Derivatives with Alkyl Spacers and Alkyl Chains in Organic Photovoltaic Devices
Authors: Moriyama Hiroshi , Igawa Mizuki , Kuda Yuki
Published: February 2020

Bulk heterojunction-type organic photovoltaic (OPV) cells have attracted attention because of their light weight, flexibility and solution-process construction. In our ongoing work in preparing a series of the PCBM analogues, we prepared Methyl-C61-phenyl carboxylic acid methyl ester (MPCM) as well as its C70derivatives and fabricated OPV devices with poly(3-hexylthiophene) (P3HT) as the donor. The performance of devices with [60]MPCM and [70]MPCM was compared, [70]MPCM showing a higher PCE than [60]MPCM.

However, because of the high aggregated property of MPCM, the OPV device performance using MPCM and P3HT gave often morphology problem; thus we also prepared new fullerene derivatives with an alkyl spacer as the modification of MPCM and fabricated OPV devices with P3HT as the donor.

The performance of OPV devices of these fullerene derivatives with an alkyl spacer was investigated, some of them showing higher PCE than that of PCBM.

Furthermore, we synthesized novel fullerene derivatives with different carboxylic acid esters, e.g., hexyl ester; methyl-C61-phenyl carboxylic acid hexyl ester (MPCH). These derivatives have the merit of higher solubility because of the long alkyl chain. Organic photovoltaic devices were fabricated using these fullerene derivatives as an electron acceptor and P3HT as an electron donor. MPCH showed PCE that is higher than that of PCBM.

Figure 1
Arrays of Single-Domain Nanomagnets As Memory- Logic-Hybrid Device - a Nonvolatile Magnetic Memory That Can Perform Logical Operations
Authors: Wanzenboeck Heinz , Bertagnolli Emmerich
Published: February 2020

With nonvolatile NAND flash memory becoming the dominant memory type the former champion for mass data storage – magnetic memory – has now become a niche player. This is – at least to some extent – unjustified, as magnetic data storage has still its advantages such as radiation-hardness, and long data storage time. In this work we celebrate a renaissance of magnetic data storage with a new concept that allows not only storing of information but also data processing with nanomagnets. We use focused electron beam induced deposition of single domain nanomagnets to fabricate arrays of magnetic nanowires and magnetic nanopillars. If the single nanomagnets are in close vicinity, then the stray fields allow to influence neighboring nanomagnets.

With a majority gate such a nanomagnet assembly can even perform logical calculations. In this work we will present the fabrication process for such nanomagnetic devices, characterize their magnetic properties by magnetic force microscop, and design and fabricate nanomagnet arrays.

With this dual functionality as memory and as logic unit these directly-written nanomagnet devices promise a promising future potential. Further applications of advanced device structures based on single domain nanomagnetswill be discussed.

We will report on the optimization of the device fabrication process and chemical and structural analysis of nanomagnets. The functional characteristics of these hybrid devices will be described and future system applications will be discussed.

Figure 1
Compliance-Free Picosecond Smart Pulse Programming for Rram
Authors: Nminibapiel David Malien , Shrestha Pragya , Kim J. H. , Campbell J P , Baumgart Helmut , Cheung K. P.
Published: February 2020

RRAM is generally considered as the next generation of nonvolatile memory due to its simple structure, low power consumption, high-speed, high density and its compatibility with conventional CMOS processing. Another attractive feature of RRAM is its tunable resistance with applied voltage, making it a promising candidate for multi-level cell (MLC) storage and for neuromorphic computing. However, reliability and variability issues limit the potential of RRAM. Particular for MLC and neuromorphic application, poor uniformity poses as a severe hindrance. This variability is related to the stochastic nature of, filament formation, resistance switching and poor control of switching energies. While material engineering and structural optimization techniques are employed to reduce the intrinsic randomness in RRAM, these strategies are ineffective when programming energy is not under control. In this work, we propose a Compliance-free Ultra-Short Smart Pulse Programming (CUSPP) technique which offers improved control of FORMING/SET/RESET energies. This technique can potentially lead to tighter distribution of critical RRAM parameters, such as RON and ROFF, resulting in well-defined resistance window during extended cycling.

CUSPP is a custom-built fast pulse-train programming and measurement system with real-time resistance sensing and automatic cycling between SET and RESET when specific resistance is reached. An ultra-short (~100 ps) pulse generator with controllable repetition rate and pulse height (up to 6V) is our source. The custom-built circuit continuously monitors the device resistance using a low DC sensing voltage to determine if the SET/RESET resistance is achieved, and to automatically change the pulse train’s height and/or polarity to enable rapidly cycling up to 2.5 million cycles per second. Unique to CUSPP measurement setup is the absence of a current limiting element such as a series resistor or transistor. The ultra-short pulse width limits the duration of current flow through the device and provide a tight control of switching energies. In the current version of the CUSPP, resistance programming is solely achieved by repetitive pulsing the device with constant pulse amplitude and pulse width. This is in contrast to many reported programming protocols where pulse amplitude and/or width are incrementally increased to reach the target resistance state. In targeting RON/ROFF, higher precision can be achieved by lowering the pulse amplitude and a concomitant higher number of pulses. Thus, high precision comes at a cost of programming speed. With the pulse repetition rate up to a few MHz this cost is entirely acceptable for mechanism studies. CUSPP is a versatile tool that can perform all essential programming of the RRAM with precision and speed while allowing the experimenter to look at the filament kinetics in details.
Silicon Oxide-Based Memory and Three-Dimensional Nanoporous System for Ultrahigh Density Storage
Authors: Wang Gunuk
Published: February 2020

Two-terminal oxide-based resistive random access memories (RRAM) are garnering enormous interest for the development of next generation nonvolatile memory beyond current Si-based memory technology. We have previously demonstrated a unipolar nonvolatile memory with silicon oxide (SiOx) for the first time . SiOx is among the most common and low-cost material in the semiconductor industry, which can be formed by various ways. These SiOx memory elements have shown desirable performance metrics such as excellent switching behavior by conducting nanofilaments forming at a sub-5-nm scale. We fabricated highly transparent memory and 1-kilobit one diode-one resistor crossbar devices using SiOx material, which show low energy consumption (~10^-3 J/Gbit), multi-bits ability, and high ON-OFF ratio (up to 10^7) without a compliance current. Furthermore, we recently developed an industry-applicable fabrication approach to new resistive random access memory platform employing a nanoporous SiOx material. This exhibits reversible memory states, which outperform the switching ability of any other unipolar memory. As the major topic, I will focus on the switching properties and the mechanism of SiOx memory and its nanoporous device platform, and present the recent approach for ultra-high density of memory array.
Electrodeposition of Magnetic SmCo Films from Deep Eutectic Solvents
Authors: Panzeri Gabriele , Magagnin Luca
Published: February 2020

SmCo alloys have attracted attention for their high Curie temperature, magnetic anisotropy and relatively high saturation magnetization[1]. Because of the very negative reduction potential of Sm (<-2.3V) in aqueous solution its electrodeposition is problematic due to strong hydrogen evolution at the cathode surface[2,3]. Ionic liquids represents a useful alternative to the aqueous solution because of limited quantity of water present and thus wider potential window[4]. Deep eutectic solvent solution of 1 choline chloride: 2 ethylene glycol at T=70°C is studied for the electrodeposition of SmCo deposit. The interest relies in the preparation of homogeneous film and nanowires having magnetic properties. Electrochemical characterization of the solution is performed for different bath composition. Deposits with variable Sm% content are obtained depending on the experimental conditions e.g. current density; both potentiostatic and galvanostatic deposition are performed. XRD analysis is carried out to evaluate the phase deposited. Magnetic properties of the film are analysed. SmCo nanowires are obtained using alumina template; magnetic performances are compared to the film deposit.

[1] YQ Guo, W Li, J Luo, WC Feng, JK Liang. Structure and magnetic characteristics of novel SmCo-based hard magnetic alloys, J Magn Magn Mater. 303 (2006) e367.

[2] J Zhang, P Evans, G Zangari. Electrodeposition of Sm–Co nanoparticles from aqueous solutions, J Magn Magn Mater. 283 (2004) 89-94.

[3] X Long, G Guo, X Li, Q Xia, J Zhang. Electrodeposition of Sm–Co film with high Sm content from aqueous solution, Thin Solid Films. 548 (2013) 259-262.

[4] AP Abbott, KJ McKenzie. Application of ionic liquids to the electrodeposition of metals, Physical Chemistry Chemical Physics. 8 (2006) 4265-4279.
Electrochemical Synthesis and Characterization of Fe-Ni-Pt Alloy Films
Authors: Ge Siyuan , Wodarz Siggi , Hashimoto Shougo , Saitou Manabu , Homma Takayuki , Zangari Giovanni
Published: February 2020

Fe-Pt alloy films and nanopatterns have been intensively investigated for magnetic recording applications, but their practical use may be limited by the maximum magnetic field available from the write head. Heat Assisted Magnetic Recording (HAMR)1 overcomes this limitation by locally heating the magnetic medium close at or above the Curie temperature to decrease its anisotropy, thus overcoming the limitations brought by the write field. The possibility to modulate magnetic anisotropy by tailoring composition on the other hand could provide close control over coercivity, which could then be matched to the available write field.

Partial substitution of Ni for Fe, leading to Fe50-xNixPt50 alloys, could modulate the magnetic anisotropy in a wide range, varying ideally from the full Fe-Pt value (6.6 MJ/m3) down to zero. Fe-Ni-Pt films were grown using an electrolyte modified from a slightly alkaline citrate-glycinate electrolyte previously used for Fe-Pt synthesis2, with the addition of NiSO4. Electrodeposition was performed at 75°C onto Ru films sputtered on Si wafers; the thickness of Fe-Ni-Pt was kept between 10 and 80 nm. In order to achieve a wide range of Ni fractions in the alloy while maintaining a sufficiently fast deposition rate, it was necessary to use different Ni++ concentrations in the electrolyte (2- 20 mM). For a given [Ni++], the Ni fraction in the alloy generally decreased with increasing overvoltage. On the other hand, the Ni fraction at a given potential did not increase monotonously with [Ni++], suggesting the occurrence of an anomalous deposition process3.

Annealing in forming gas (5% H2, 95% Ar) at 650°-700°C was necessary to observe the (100) reflection of the L10 phase, evidencing the phase transformation. The resulting films were unoriented and showed an approximately isotropic magnetic behavior. Film coercivity after annealing increased with Fe fraction, from about 2 to 10 kOe, demonstrating the possibility to tailor coercivity via composition. Finally, temperature-dependent magnetic measurements between 100-300 K showed a monotonous increase both in magnetization and coercivity, as expected.

References

[1] M.H. Kryder, E.C. Gage, T.W. McDaniel, W.A. Challener, et al. Proc. IEEE 96, 1810 (2008)

[2] D. Liang, J.J. Mallett, G. Zangari, J. electrochem. Soc. 158, D149 (2011)

[3] M. Matlosz, J. electrochem. Soc. 140, 2272 (1993)
Optimized Cofeb Alloy Films for Electroformed Resonators
Authors: Pillars Jamin Ryan , Langlois Eric Donald , Arrington Christian L. , Monson Todd , Staruch Margo , Finkel Peter
Published: February 2020

Magnetostrictive CoFe films were investigated for use as magnetoelastic tags or sensors. The ability to electrodeposit these films enables batch fabrication processes to pattern a variety of geometries while controlling the film stoichiometry and crystallography. Previous research developed a chemistry and plating parameters to maximize magnetostriction with a stoichiometry range of Co0.7-0.75Fe0.3-0.25 and 20-30nm grain size. A bimorph test structure with electrodeposited CoFe was used in a DC magnetic field to measure the magnetostriction. Resonators were then electroformed into photo definable molds and testing showed no signal in an AC magnetic field. The impedance of the films was analyzed and to minimize attenuation, the resistivity of the films was increased by introducing boron into the films. Dimethylamine borane was added incrementally to the electrochemistry bath and ternary alloy films were produced with boron concentrations of 1-10 atomic %. The stoichiometry of the alloy films were confirmed using inductively coupled plasma mass spectrometry (ICP-MS) and X-ray photoelectron spectroscopy (XPS). The resistivity of the films and the crystal structure were analyzed as a function of the boron concentration. The magnetic properties of the films and the strength of the resonant signal were also correlated with the film composition.

 

Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.
(Invited) Beyond Lithium Ion Batteries
Authors: Amine Khalil , Chen Zonghai , Lu Jun
Published: February 2020

In other to enable 40 miles PHEVs and long electric drive range EVs, there is a need of developing advanced battery systems that offer at least 250 to 300 wh/kg energy density. The challenge is to develop batteries that are able to perform the requirements imposed by a PHEV system and yet meet market expectations in terms of cost and life. In this case, the PHEV battery will experience both deep discharge, like an electric vehicle, and shallow cycling necessary to maintain the battery for power assist in charge sustaining HEV mode.

Conventional lithium-ion batteries based on metal oxides and graphite have made significant progress in recent years for HEV applications, however, durability with the PHEV duty cycle and the ultimate cost and safety of the technology remain key challenges. To achieve a very high all electric drive range, a new battery system is needed. In this talk, we will disclose new systems based on beyond lithium ion chemistry. Li/S batteries have attracted lots of attention because of their low cost and high energy-density. However, the dissolution of lithium polysulfides in non-aqueous electrolytes causes the accelerated capacity fade and low round turn energy efficiency of Li/S batteries during normal charge/discharge cycling. Alternatively, Li/Se has been newly explored to take advantage of extremely low solubility of Li2Se in non-aqueous electrolyte. In situ X-ray absorption spectroscopy at K edge of Se (~12.66 KeV) during the normal charge/discharge cycling of a Li/Se cell clearly shows that Se can be reversibly reduced to Li2Se upon lithium insertion reaction, and can be fully recovered upon the subsequently lithium removal reaction. More progress on Li/Se and Li/SeSx chemistry will be discussed in this talk. We will also disclose new lithium air based on Lithium superoxide and new close system based on lithium oxide/lithium superoxide that offers significantly high energy density.
Investigation on Electrochemical Properties and Degradation Mechanism of Silicon Oxide-Containing Negative Electrode for Li-Ion Rechargeable Battery
Authors: Kobayashi Hironori , Kuratani Kentaro , Shikano Masahiro , Okumura Toyoki , Saito Yoshiyasu
Published: February 2020

Recently Li-ion rechargeable battery (LIB) has been widely used as power source for not only portable device but also electric vehicle (EV). For EVs, a high-performance LIB with a high energy density is strongly required to increase the mileage. Si-containing materials are promising negative electrode materials for LIB because of large theoretical capacity compared with that of conventional carbon materials. Therefore, a great deal of effort has been made to put Si-containing materials into practical use. However, there are still some problems to be solved.

In this paper, we investigated electrochemical properties of the Si or SiO-containing negative electrodes. We selected the ketjen black as a conductive enhancer and the polyimide-based binder as a binder material, and then tried to fabricate the negative electrode with an excellent cycle property and long life. However, the electrodes where only Si or SiO-containing material was used as the active material showed a rapid decrease in capacity with cycles. Therefore, we fabricated the composite electrode where SiO was composed with graphite in weight ratio of 1:2, 1:1 and 2:1, and checked electrochemical properties using various electrolytes. For the electrode where the weight ratio of SiO and graphite was 1:2, the initial discharge capacities of ca. 596 and 614 mAh/g were observed using 1M LiPF6 in EC:DMC (= 1:2) with and without 5wt% FEC, respectively, for the voltage range of 0.02 and 1.0 V. On the other hands, the reversible discharge capacities of ca. 542 and 244 mAh/g were observed using 1M LiPF6 in EC:DMC (= 1:2) with and without 5wt% FEC, respectively, after 200 cycles. Therefore, it is important to clarify the degradation mechanism due to the difference of the electrolyte for improving cycle proeprty and life.

In the presentation, we will clarify the degradation mechanism of SiO-containing negative electrode by the combination of Li MAS NMR and XPS measurements.

Acknowledgement

This work was partly supported by the New Energy and Industrial Technology Development Organization (NEDO).
Lithium Detection in the Electron Microscope
Authors: Gauvin Raynald , Brodusch Nicolas , Demers Hendrix , Demopoulos George P. , Zaghib Karim
Published: February 2020

This paper will present the results for the determination of concentration of Li in silicates cathode materials using x-ray microanalysis with windowless SDD EDS technology and with Electron Energy Loss Spectroscopy (EELS) with state of the art field emission scanning electron microscopes at high spatial resolution. Advantages and disadvantages of both techniques will be covered. The aim of this work is to characterize Li concentration variation at the nm scale in batteries materials. The issue of electron beam damage will be covered and the advantage to work at electron beam energies below 30 keV will be demonstrated.
Towards the I
n-Operando Observation of Lithium Dendrite Growth Via X-Ray Computed Tomography
Authors: Frisco Sarah , Liu Danny X. , Mandal Pratiti , Choi Paul , Kedlaya Vinayak , Litster Shawn , Whitacre Jay , Love Corey T , Swider-Lyons Karen
Published: February 2020

The formation of lithium dendrites causes significant safety concerns in current lithium ion cells and prevents the implementation of commercial lithium metal batteries. To better understand this phenomenon, we are using nanoresolution x-ray computed tomography (nano-CT) to observe the in-operando nucleation and growth of dendrites during lithium deposition. Preliminary results of lithium films deposited ex-situ reveal that different deposition conditions affect not only the surface morphology but also subsurface features. Figure 1 displays the results of cycling the lithium film at high rates: the higher rate sample shows a dramatic increase in thickness and porosity within the film.

The observational cell can also be used to observe other degradation processes occurring within lithium-ion batteries such as the deposition of copper dendrites during an overdischarge event. We will show preliminary results on the effect of deposition conditions (rate, temperature, etc.) on the surface and subsurface morphology of the lithium. From this, we are able to investigate how suppression methods such as electrolyte composition affect these features and develop more targeted strategies at dendrite prevention.

Figure 1
Ssnmr Studies of Li3V2(PO4)3/C Cathode Reactions: Structural Evolution, Dynamics and LVP-Carbon Interface
Authors: Huo Hua , Shao Jinyu , Zhong Guiming , Wu Di , Peng Luming , Yang Yong , Dai Changsong , Xiong Yueping
Published: February 2020

Monoclinic lithium vanadium phosphate Li3V2 (PO4)3(LVP) is a highly promising cathode material for lithium-ion batteries. In the past decades, extensive efforts have been made to improve the electrochemical performance of LVP by carbon coating and cation doping[1]. In-depth understanding of the local structures and charge-discharge mechanism of LVP can provide valuable information for the design of cation doping or surface modification. SSNMR has been demonstrated a powerful tool of local structure analysis and dynamics. However, due to sever line broadening and signal coalescence caused by the heating effect of carbon in the cathode composite, SSNMR study of LVP material was only limited to samples prepared by chemical delithiation[2], which cannot fully represent the real electrochemical process.

We hereby present the first SSNMR study of LVP/C cathode reaction. The electrodes have been prepared in a binder free and carbon additive free fashion, in order to reduce the heating effect to a minimum during NMR spectra acquisition. A variety of SSNMR techniques have been combined to obtain structural information from different aspects. The structural changes of the polyhedron framework upon delithiation-lithiation were traced by 7Li and 31P NMR. The dynamic processes involving Li exchange and migration were monitored by variable temperature 7Li NMR and EIS technique. 13C-7Li REDOR NMR and HRTEM were performed to investigate Li-O-C connectivity and the short range structure at the LVP-carbon interface. The NMR results have elucidated the driving force of the asymmetric phase formation during charge-discharge within the voltage window of 4.3-4.8 volts and provided experimental evidence of direct chemical bonding between LVP and carbon coating.

Our study helps the battery community to understand the (de)lithiation mechanism of LVP cathode, and more important, the role of carbon coating.

[1]. Rui X, Yan Q, Skyllas-Kazacos M, et al. Li3V2(PO4)3 cathode materials for lithium-ion batteries: A review[J].
J. Power Sources
, 2014, 258(21):19-38.

[2]. Yin S C, Grondey H, Strobel P, et al. Charge ordering in lithium vanadium phosphates: electrode materials for lithium-ion batteries.[J].
J. Am. Chem. Soc.
, 2003, 125(2):326-7.
Superconformal Film Growth: Challenges and Opportunities
Authors: Moffat Thomas P. , Liu Guokun , Zou Shouzhong , Ou Yang Liang Yueh , Lee Chang Hwa , Josell Daniel
Published: February 2020

State of the art manufacturing of semiconductor devices involves electrodeposition of copper for device wiring and more recently for through-silicon-vias (TSVs). The process depends on the use of electrolyte additives that affect the local deposition rate thereby resulting in superconformal, or bottom–up “superfilling” of trenches and vias. In the case of Damascene processing of submicron features the deposition process is explained by the recently developed curvature enhanced accelerator coverage (CEAC) mechanism. The model stipulates that 1.) the growth velocity is proportional to the local accelerator, or catalyst, surface coverage and 2.) the catalyst remains segregated at the metal/electrolyte interface during copper deposition. For growth on non-planar geometries this leads to enrichment of the catalyst on advancing concave surfaces and dilution on advancing convex sections; thereby giving rise to bottom-up superfilling of recessed surface features such as trenches and vias. In the case of larger features other avenues for feature filling become available that will be outlined in some detail. Despite the success of these superconformal growth processes much remains to be known concerning the detailed molecular nature of the competitive co-adsorption processes involved in both the suppression and acceleration of the metal deposition reaction. The application of in situ surface science tools such as in situ STM and SEIRAS towards a better understanding of the additive interaction will also be detailed. Finally, the talk will conclude with an overview of the current understanding of additive adsorption, consumption and/or deactivation dynamics relevant to superfilling and microstructural evolution in both Damascene and TSV Cu processing.
Self-Terminated Electrodeposition Reactions for Electrocatalysis
Authors: Moffat Thomas P. , Liu Yihua , Ahn Sang Hyun , Wang Rongyue , Ritzert Nicole L. , Gokcen Dincer , Hangarter Carlos , Bertocci Ugo
Published: February 2020

Development of a sustainable hydrogen economy based on water electrolysis and fuel cells is constrained by the performance, longevity and high cost of Pt group electrocatalysts. Important strategies for improving catalytic reactivity include alloying, forming bimetallic or alloyed surfaces, and engineering substrate–catalyst interactions. At the same time, significant effort is underway to minimize the loading of Pt group metals by examining new synthesis methods and electrode geometries. Of particular interest is atomic layer deposition (ALD) for growing ultrathin films that maximize utilization of rare, expensive metals and facilitate the exploration of bimetallic effects in electrocatalysis.

Recently, an inexpensive “wet form” of ALD based on self-terminated electrodeposition reactions was uncovered that enables controlled formation of ultrathin films of Pt, Ir and Fe-group metals and alloys thereof. The mechanism of self-terminated deposition reactions will be discussed and the utility of these films as bimetallic electrocatalysts will be demonstrated. For example, monolayer equivalent Pt and Ir films were found to match or exceed the best known specific HER/HOR activity for bulk polycrystalline Pt or Ir electrodes and thereby offer the promise of increasing the scalability of these important precious metals in energy conversion devices.
First Principles Studies of the Structural and Electrocatalytic Properties of Ultrathin (OXY)Hydroxide FILMS on Precious Metal Substrates
Authors: Zeng Zhenhua , Kubal Joseph J. , Chun Hee-Joon , Greeley Jeff
Published: February 2020

Advances in the theoretical understanding of interfacial electrochemistry have, over the past decade, permitted the extension of periodic Density Functional Theory studies, which have traditionally been applied to probe chemistry at gas/solid interfaces, to electrochemical systems where potential-dependent structural and chemical phase transformations occur at liquid/solid interfaces. Indeed, such techniques have been employed to study a surprisingly wide class of electrochemical processes, ranging from electrocatalysis to corrosion. In this talk, we will discuss how these strategies can be applied to predict the detailed, atomic-scale properties of monolayer (oxy)hydroxide base metal films on precious metal and precious metal alloy substrates as a function of applied potential in alkaline solutions. We will describe the analysis of Moire patterns, variable oxidation states, and three-phase boundaries of these films, and we will demonstrate how these results may be used to predict the shape and oxidation states of supported two-dimensional nanoislands as a function of electrochemical conditions. We will close with some perspectives on the possibilities for alkaline electrocatalyst design offered by these systems.
High Mass Activity and Stability of Core-Shell Pd-Ni Nanoparticles Electrodeposited on Diamond Electrodes for Direct Alcohol Fuel Cell Applications
Authors: Mavrokefalos Christos K. , Hasan Maksudul , Rohan James F. , Foord John S.
Published: February 2020

Sustainable ‘green’ energy applications have received increasing research efforts in the last few years to deal with issues such as climate change, energy shortage and environmental pollution. A subcategory of fuel cells, the direct alcohol fuel cells (DAFCs) have been established in that field due to their ability to convert the chemical energy stored in the fuel into electricity and can be utilised in portable devices and transportation applications. Electrocatalysis is an important aspect in the development of such sustainable technologies. Hybrid materials consisting of graphitic nanostructures and various metal or metal oxide complexes have been widely studied as functional components in catalysis for fuel cell applications. The development core-shell nanostructures and replacing or reducing noble metal content by the incorporation of non-noble metals promises to increase the overall mass activity and improve stability due to electronic interactions with the interfacial layer in the inner shell.

Herein, the electrodeposition of Ni and Pd nanoparticles supported on oxygen terminated boron-doped diamond (OBDD) electrodes is described. The electrochemical modification involves two-steps; first electrodeposition of Ni as nanoparticles on OBDD followed by Pd onto the freshly deposited Ni nanoparticles. SEM imgage of the sequential deposition of Pd-Ni produced nanoparticles in the size range of 10-13 nm is shown in Fig. 1 (a). XPS and electrochemical characterization showed that Ni nanoparticles act as reactive centres on OBDD for the subsequent deposition of Pd to form core-shell nanostructures. The Pd-Ni/OBDD electrocatalysts were evaluated in an alkaline aqueous solution containing ethanol and compared to Pd/OBDD itself. The formation of core-shell nanostructures led to high current responses for ethanol oxidation. The phenomenon is attributed to the improved dispersion of Ni onto the BDD and the electronic interaction between the interfaces of the two metals. Of note is the fact the core-shell catalysts exhibited enhanced mass activity and operational stability. After chronopotentiometric measurements, there was only 12% current drop of the Pd-Ni/OBDD in comparison to 35% current drop of the Pd/OBDD catalyst itself. The Pd-Ni electrocatalysts even with 4 times less palladium loading showed higher amperometric response than the pure Pd/OBDD (Fig. 1(b)). The higher mass activity is likely due to an increased tolerance to carbon based reaction by-products poisoning effects at the bimetallic interface with the transition metal in the inner shell.

Figure
1 (a) SEM image of Pd-Ni modified OBDD electrode (b) Cyclic voltammograms of Pd and Pd-Ni modified OBDD in 0.5 M KOH and 1 M EtOH at a potential scan rate of 100 mV s-1.

Figure 1
Electrodeposited and Oxidized Mn/Co-Fe As Bi-Functional Electrocatalysts for Rechargeable Zinc-Air Batteries
Authors: Xiong Ming , Ivey Douglas G
Published: February 2020

Electrochemically rechargeable zinc-air batteries are one of the best candidates to store very large amounts of electrical energy[1]. However, due to the sluggish ORR (oxygen reduction reaction) and OER (oxygen evolution reaction) at the air electrode, the efficiency of zinc-air batteries is comparatively low, leading to energy losses. In addition, the stability of the catalysts is poor because they can peel off or pulverize during battery cycling. The air electrode contains a gas diffusion layer (GDL) as the substrate and a catalyst layer. The key to increasing efficiency and stability is to properly combine catalysts with the GDL to facilitate the ORR and OER. Manganese oxides have been shown to be excellent ORR catalysts, while oxidized Co-Fe performs well in catalyzing OER[2,3]. The proper amalgamation of the two materials may be able to generate a highly efficient bi-functional catalyst that can catalyze both ORR and OER.

In this study, Mn and Co-Fe were sequentially electrodeposited onto the GDL and then annealed in air to produce transition metal oxide catalysts. The fabricated material was then assembled into a zinc-air battery as the air electrode component to run battery cycling tests. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) results show that a porous Mn-layer was firstly formed on the GDL and then covered by another layer of Co-Fe nanoparticles (Fig. 1). The nanocomposite structure provides a high surface area for electrochemical reactions. The electrocatalytic properties of the bi-functional catalysts were studied by cyclic voltammetry (CV) in 6M KOH solution. The CV results demonstrate that the oxidized Mn/Co-Fe nanocomposite exhibits activities for both ORR and OER. Preliminary cell test results show that the discharge-recharge efficiency is increased from 50% to 58% at 10 mA/cm2 current density when the catalysts are used in the battery. The efficiency can be further improved with optimized catalysts design and fabrication. In addition, the deposited catalyst layer shows strong adhesion to the GDL and excellent stability after 40 hours of battery testing. The influence of electrodeposition conditions on the electrochemical performance is also discussed.

References

1. Y. Li and H. Dai, Chemical Society Reviews, 2014, 43, 5257-5275.

2. K. Zhang, X. Han, Z. Hu, X. Zhang, Z. Tao and J. Chen, Chemical Society Reviews, 2015, 44, 699-728.

3. J. Ahmed, B. Kumar, A. M. Mugweru, P. Trinh, K. V. Ramanujachary, S. E. Lofland and A. K. Ganguli, The Journal of Physical Chemistry C, 2010, 114, 18779-18784.

Fig. 1 SEM image of Co-Fe nanoparticles.

Figure 1
Cascading Alignment of Multilayered SnO2/WO3/BiVO4 Inverse Opal Skeletons in Photoelectrochemical Water Splitting
Authors: Yun Gun , Kang Soon Hyung
Published: February 2020

Tin dioxide (SnO2) inverse opals (IOs) having a pore size of approximately 260 nm in the 370 nm sized polystyrene bead (PS) templates were developed by a spin-coating-assisted sol−gel process. Upon this template, the SnO2/WO3 core-shell IOs were developed by the facile electrodeposition under a constant potential (−0.47 V vs. sat. Ag/AgCl), where the thickness of WO3 layer depended on the applied charge amount for WO3 electrodeposition (200−800 mC/cm2). As a control sample, a pure WO3 IO film with the same thickness of ∼3.1 μm and a band gap (Eg
) of 2.6 eV was also prepared in the same method. The pore diameter of the SnO2 IO structure declined noticeably as the charge amount of the deposited WO3 layer increased from 200 to 800 mC/cm2, leading to eventual coverage of the SnO2 IO structure in the WO3 (800 mC/cm2) layer. The optimum photoelectrochemical (PEC) response was achieved with the SnO2/WO3 (600 mC/cm2) IO electrode, which exhibited the highest photocurrent density (Jsc) of 2.8 mA/cm2 (0.5 VAg/AgCl) under full-sun conditions and 0.91 mA/cm2 (0.5 VAg/AgCl) under visible light, indicating that the enhancement of the Jsc under visible light contributed significantly to the improvement of the total Jsc, compared with the values for the pure SnO2, SnO2/WO3 (200, 400, and 800 mC/cm2), and WO3 IO electrodes. Furthermore, considering that the favorable cascading band alignment can boost the fast charge separation and transport through the conductive SnO2 IO skeleton, we try to develop the multilayered SnO2/WO3/BiVO4 IOs structure showing the well-matched band alignment. And then, the dual doped (W and Mo) BiVO4 layer was adapted in the surface layer due to the more narrowing Eg
of ~ 2.4 eV. Herein, the PEC performance and other results would be presented.

Figure 1
Ni/SiC Composite Coating on Graphite– Geometry Effect on the Coatings
Authors: Harinipriya S , Usmani Belal
Published: February 2020

Ni/SiC nanocomposite coatings were electrodeposited on different shape geometry of graphite under galvanostatic condition. The effect of geometry of graphite on the surface morphology, composition and structure of the composite coatings were studied by scanning electron microscope (SEM), energy dispersive system (EDS) and X-ray diffraction. The major content in the composite coatings were silicon carbide (Si5C3, CSi), nickel silicon (Ni0.92Si0.08) and graphite (C). Porous and fine grain structure was formed with cracks. Uniform distributions of silicon carbide nanoparticle were observed. Circular graphite possessed higher adhesion and thickness of the coatings in comparison with rod and square shaped graphite substrate.
Gas Anodes for Electrowinning of Aluminium
Authors: Mokkelbost Tommy , Khalaghi Babak , Osen Karen Sende , Bai Wei , Kjos Ole Sigmund , Haarberg Geir Martin
Published: February 2020

Aluminum is today commercial produced by the Hall-Haroult process using consumable carbon anodes. Consumable anodes have several drawbacks such as CO2 emission, continuous anode-cathode distance adjustments and replacements of anodes. Replacing the consumable anodes with inert anodes has been a topic for many decades without commercial success. Using porous inert gas anodes where natural gas or hydrogen take place in the anode reaction has been shown in laboratory tests to reduce the anode potential and reduce the CO2emission. However, formation of water results in evolution hydrogen fluorides which must be solved. Different type of anodes have been prepared and evaluated as possible gas anodes for this concept. Three different graphite materials with different pore sizes and porosity, commercially available, have been used to fabricate gas anodes. Porous SnO2 based materials have been prepared using either foam preforms or coarse SnO2 based particles sintered together with fine SnO2 based powders. These fabrication routes results in significant different materials. The materials are evaluated as possible porous anodes for this concept.

Laboratory experiments using porous depolarized SnO2-based with CH4 and H2-gases have been performed with off-gas analysis and with special attention to hydrogen fluoride evolution. An theoretical mass balance with focus on HF emission has been performed and two different scenarios are presented 1) gas anode process and 2) conventional Hall Heroult cell. In addition we present simulation of the gas transport of a possible industrial gas anode. The challenging side effects of HF emission might be utilized in the process and is discussed.
(Keynote) The Electrochemical Behavior of an Inhibitor Containing Ce3+ for a Low-Alloy Steel in a 3.5% NaCl Solution
Authors: Yong Xingyue , Du Ranran , Fu Yong , Wnag Ying , Chen Zhenglin , Xiao Ning
Published: February 2020

The effects of Ce3+ ions on the electrochemical behavior of a low-alloy steel in a 3.5% NaCl solution were investigated by polarization curves in conjunction with EIS spectra. The results show that Ce3+ ions were beneficial to promoting the anodic passivation and improving the performance of the inhibitory film. The inhibitor containing Ce3+ was an anodic inhibitor with the inhibitory efficiency of 94.0%. The net-shaped film formed on the surface of low-alloy steel in a 3.5% NaCl solution with the inhibitor containing Ce3+ was observed. The EIS spectra of the low-alloy steel in a 3.5% NaCl solution with the inhibitors were composed of a capacitive loop at high frequency region and an inductive impedance loop at low frequency region and there were two time constants. The charge-transfer resistance (Rt) increased with immersed time. And that the charge-transfer resistance (Rt) of the inhibitor containing Ce3+ was higher than that of the inhibitor containing no Ce3+. Therefore, the inhibitor containing Ce3+ had a higher inhibitory efficiency than the inhibitor containing no Ce3+. Simultaneously, based on the EIS spectra, the equivalent circuit was developed. Finally, The EIS spectra were fitted by Simplex method with the equivalent circuit. It was found that all electrochemical parameters of the equivalent circuit increased with immersed time, indicating that the inhibition efficiency of the inhibitor increased with immersion time. As regards the equivalent circuit, if the equivalent resistance (R0) and the inductive impedance (L) would increase enough with the immersion time, EIS spectra would have a capacitive loop with one time constant. In this case, the inhibitory film on the electrode surface become more and more uniform and integrated.
Magnesium Alloy Corrosion Under Thin Electrolyte Layer Using Electrochemical Impedance Spectroscopy and Polarization Curve
Authors: Cao Fahe , Zhu Zejie , Liu Xiaoyan , Zhang Jianqing
Published: February 2020

Here, we reported some simulated atmospheric corrosion studies of magnesium alloy (including AZ91D and AM60) based on electrochemical impedance spectroscopy and polarization technology, and the effect of rare earth element Ce or La on corrosion behavior of magnesium alloy. In the case of AZ91D magnesium alloy, the electrochemical results reveal that the corrosion rate of AZ91D under thin electrolyte layers (TELs) is slower than that in bulk solution and decreases with the TEL thickness thinning. Bothe the anodic and cathodic reactions are restrained under TELs, especially in thickness thinning to around 200 μm and lower. For AM60 magnesium alloy and pure magnesium, the corrosion processes are also inhibited by decreasing thickness of TEL. All those corrosion rates and behavior of magnesium and its alloy are different from that of aluminum, copper and zinc alloy, which are due to the special cathodic reaction for magnesium alloy. Rare earth elements Ce or La have a strong effect on the dissolution of AM60 magnesium alloy under TEL. Typical impedance diagrams consist of two capacitive arcs at high and intermediate frequencies in all cases. At low frequencies, an arc or tail in the Nyquist plots appears sometimes disappears due to the complex corrosion reaction. Comparing to AM60, AM60 with rare earth element addition presents the 3rd capacitive loop sometimes instead of an inductive tail under the TEL thicknesses of 200 and 300 μm, which is associated with reaction taking place on the cathodic intermetallic compounds formed with rare earth elements. The EIS and polarization measurements indicate the rare earth element alloying can reduce corrosion rate of AM60 and AZ91D both under TEL and in bulk electrolyte.
(Invited) Synergy of Nyquist and Bode Electrochemical Impedance Spectroscopy Studies to Stoba in Lithium Ion Battery
Authors: Wang Fu-Ming , Yang Lyu-Ye
Published: February 2020

Self Terminated Oligomer Branched Architecture (STOBA) was developed to enhance the safety performance in lithium ion battery. Previous studies [1-3] were shown that the STOBA is able to prevent a short circuit problem when battery suffers nail penetration. However, recent inverstigations indicated that the STOBA is constructed by four reaction mechanisms and only one reaction mechanism is used to increase battery performances including safety and cycle life.

In this study, a new STOBA is initialized owing to the reaction mechanism is purified. According to the Electrochemical Impedeance Spectroscopy (EIS) results, the new STOBA battery system shows the lowest charge transfer resistance at the first and ten cycle. Fig. 1a indicates that the new STOBA with single reaction mechanism provides high ionic diffusivity, which enhances the electrochemcial reaction on interface. In addition, Fig. 1b demonstrates that a passivation layer was formed and is clearly defined in both cases. The impedance of passivation layer in pure lithium-rich layered nickle maganease oxide (LLNMO) reveals 270 ohm and the STOBA inside LLNMO shows only 200 ohm. Figs. 1c and 1d show the Bode polts of both batteries. This result demonstrates the highest Qeff coeffcicent (at 30 Hz) is taking place at STOBA battery system compare with the pure LLNMO battery system, indicating 3D distribution arises from surface heterogeneity. After ten cycles, Fig. 1d shows that STOBA battery system still provides the highest Qeff coeffcicent (at 7 Hz); nevertheless, a sensitive shoulder (at the range of 1.3~0.09 Hz) is discovered at pure LLNMO system, indicating an phase exchange irreversible reaction of bulk material is enclosed. This result indicates the new STOBA inhibits the phase exchange irreversible reaction and provides good performance for further application.

Reference

1. Fu-Ming Wang, Shen-Chuan Lo, Chin-Shu Cheng, Jung-Hsuan Chen, Bing-Joe Hwang, Hung-Chun Wu, J. Membrane Sci 368 (2011) 165

2. Yu-Han, Meng-Lun Lee, Fu-Ming Wang, Chang-Rung Yang, Peter P. J. Chu, Jing-Pin Pan, Electrochim. Acta 85 (2012) 72

3. Yu-Han, Meng-Lun Lee, Fu-Ming Wang, Chang-Rung Yang, Peter P. J. Chu, Jing-Pin Pan, Appl. Sur. Sci. 261 (2012) 306

Figure 1