bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis by the Dissipation Theorem of Turbulent Flow in a Pipe
Authors: Newman John
Published: February 2020

More than a year ago, I proposed analyzing turbulent flow and predicting friction and mass transfer by relating one statistical quantity for the flow to other statistical quantities on a local basis. This is what we do with laminar flow, where the stress is related to the viscosity and the velocity gradient. Excellent data could be found on turbulent mass transfer in the system where one cylinder rotates within a larger stationary cylinder. Excellent data on fluid friction and pressure drop are found for turbulent pipe flow. The dissipation theorem has been applied to this system. In the course of doing this, several aspects of the earlier work have been refined. Furthermore, one can make predictions of the eddy viscosity and the dissipation that accord with old measurements. Of course, some empiricism is required, but one strives to keep this on a local level where the volumetric dissipation is related to the eddy viscosity. The behavior of the system is surprising, and the literature data are quite different from what one might have expected.
(Invited) Speciation during Wet Etching of III-V Semiconductors
Authors: Hinckley Adam , Foster Elijah , Corley Tim , Muscat Anthony J.
Published: February 2020

III-V materials could be a substitute for Si and Ge in semiconductor device development because they possess higher carrier mobilities. Wet chemical cleaning and patterning of III-Vs produces soluble species that can remain in the liquid phase, precipitate as solids and remain on the surface, or evaporate as gases. Because etching products contain elements such as In, As, and Sb, they can pose health risks during industrial wafer processing. To better understand the products generated from III-V etching, vapor-phase arsenic levels were measured above wet etching solutions commonly used to clean or etch GaAs. A differentially pumped mass spectrometer system was used to sample the vapor above the etching solution at atmospheric pressure. The mass fragments detected as a function of time were used to determine the arsenic species present and estimate concentrations.

Mass fragments corresponding to AsO+, AsH2
+ and AsH3
+ were detected above GaAs immersed in aqueous HF at room temperature. The partial pressure of the etching products was on the order of 0.1 mTorr. Using N2as a reference, the total gas-phase arsenic concentration above 0.6 M and 28.9 M aqueous HF was approximately 1 ppm and 2 ppm, respectively. These concentrations are about 400 times the Permissible Exposure Limit (PEL) set by the Occupational and Safety Health Administration (OSHA) for inorganic arsenic species. Gallium was not detected in the vapor phase. Inductively-coupled plasma mass spectrometry (ICP-MS) was used to measure etching species in solution. The Ga concentration was higher than that of As by a factor of 100. Combining these techniques, a mass balance was closed between liquid and vapor phase arsenic species within approximately 1 nmol.

Etching GaAs in aqueous SC-2 (HCl and H2O2 in DI water) solutions produced AsO+, AsH2
+ and AsH3
+ in the vapor phase. The total gas-phase arsenic concentration above SC-2 was 5 nmol (about 4 mg/m3) regardless of the reactant concentration. The concentration of AsO+ increased by a factor of 2 when vapor was collected for 30 min prior to measurement. One interpretation is that etching produces AsCl3 which hydrolyzes readily in the liquid or gas phase. To test this hypothesis, arsenic species were examined as a function of time above a GaAs coupon in partially aqueous SC-2 (HCl:H2O2:H2O:CH3OH, 4:3:12:250 v/v). Figure 1 shows mass spectra after pulses of product gases were sampled above the solution. The total gas-phase arsenic concentration increased by a factor of 3.3 when GaAs was etched in partially aqueous SC-2. The primary arsenic fragment was As+, and Cl+ increased by a factor of 5 with respect to GaAs etched in aqueous SC-2. The comparison of As and Cl fragments detected to known cracking patterns supports the hypothesis that AsCl3is produced during etching of GaAs and is hydrolyzed. Speciation of etching products will be compared to OSHA PEL standards for inorganic arsenic species to identify potential hazards present in III-V manufacturing.

Figure 1
Thermally Activated Gas-Phase Chemical Reactions in a Single-Wafer Wet Clean Process
Authors: Kawaguchi Mark N , Zhu Ji , Fischer Christian , Man Xia , Bandarapu Bhaskar , Kon Stanley
Published: February 2020

A conventional high-dose ion-implanted photoresist strip and clean process flow consists of using a dry remote plasma ashing tool to remove the crust layer and underlying photoresist formed during the implant, followed by sulfuric-peroxide mixture (SPM) and ammonium hydroxide-hydrogen peroxide (SC1) chemistries applied on a wet clean tool to remove the remaining bulk photoresist and implant residues. However, film loss control and residue removal are increasingly difficult to maintain for sub-10 nm devices with conventional approaches. We investigate an alternative sequence that replaces the remote plasma strip with a thermally activated, atmospheric gas-phase oxidation process and replaces the SPM chemistry with a de-ionized water/ozone (DIO3) wet clean. The alternative sequence is entirely processed in a modified single-wafer wet clean chamber. For the oxidation process, a dry O3/O2 gas mixture decomposes and reacts directly with the ion-implanted photoresist wafer that is heated above 300°C from the backside. 9,000 Å/min strip rates are measured on 193 nm photoresist, and 650 Å/min are measured for the implanted crust removal. Based on both X-ray photoelectron spectroscopy (XPS) analysis of the reacted surface as well as the composition of the gas phase products by residual gas analysis (RGA), the crust layer and bulk photoresist are removed by oxidation mechanisms similar to remote oxygen plasma strip processes. Above 350°C, it is found that O2 gas itself reacts with the photoresist but to a lesser extent than the O3/O2 mixture. Reactivity to silicon is lower than a typical remote oxygen plasma based on ~1 Å silicon loss measured on blanket films. This in-situ thermally activated oxidation reaction allows for subsequent wet processing without any queue time delay. The integrated process completely removes 5E15-1E16 at/cm2 high-dose implanted 193 nm photoresist with no residue on patterned substrates.

Fig 1: In-situ thermally activated oxidation reaction in a single-wafer wet clean chamber process sequence consisting of (a) a dry ozone-oxygen gas environment, (b) ozone-oxygen decomposition and reaction on a heated wafer surface, (c) ozonated de-ionized water rinse in an N2 environment, (d) ammonium hydroxide-hydrogen peroxide clean in an N2 environment, and (e) a de-ionized water rinse and spin dry.

Figure 1
(Invited) Materials Selectivity in Atomic Layer Etching of SiO2, Si, and Si3N4 Using Plasma Process Sequences
Authors: Oehrlein Gottlieb S.
Published: February 2020

Using steady-state Ar plasma in conjunction with periodic injection of a defined number of C4F8 molecules and synchronized plasma-based Ar+ ion bombardment enables controlled removal of SiO2 layers with a thickness in the Angstrom-range.1 The physical sputter rate of SiO2 vanishes for Ar+ ion bombardment with a maximum ion energy of 20 eV and lower, whereas for a fluoroccarbon-coated SiO2 surface, chemical modifications of the SiO2 surface are induced by low energy ion bombardment and SiO2 etching is initiated. In this work we examined SiO2:Si and SiO2:Si3N4 etching selectivity and the roles of maximum ion energy, etching step length (ESL), FC surface coverage, and fluorocarbon precursor selection in controlling these. By optimization of ALE process parameters, e.g. low ion energies, ESL, and FC film deposition per cycle, highly selective SiO2 to Si3N4 etching can be achieved for conditions where FC selectively accumulates on Si3N4 surfaces.2 Surface oxidation of Si takes place during the Ar+ ion bombardment step, and makes it more difficult to achieve abrupt and highly selective removal of thin SiO2 layers from Si. Mechanism of the observed ALE behaviors will be discussed using real-time and post-plasma surface analysis data.

1 D. Metzler, R. Bruce, S. Engelmann, E. A. Joseph, and G. S. Oehrlein, J. Vac. Sci. Technol. A 32, 020603 (2014).

2 C. Li, D. Metzler, C. S. Lai, E. A. Hudson, and G. S. Oehrlein, J. Vac. Sci. Technol. A 34, 041307 (2016).

* I gratefully acknowledge the essential contributions and collaboration of Kang-Yi Lin, C. Li, D. Metzler, S. Engelmann, R. Bruce, E. Joseph , C. S. Lai, and E. A. Hudson on which this talk is based. Additionally, funding from Semiconductor Research Corporation (No. 2017-NM-2726), National Science Foundation (CBET-1134273), and US Department of Energy (DE-SC0001939) is thankfully acknowledged.
(Invited) Selective Atomic Layer Deposition of Cobalt for Back End of Line
Authors: Elko-Hansen Tyler D.-M. , Ekerdt John Gilbert
Published: February 2020

This talk explores the area-selective atomic layer deposition (A-SALD) of cobalt on copper versus silicon dioxide and a porous low-k dielectric. Cobalt reduces copper electromigration as a capping layer on the copper metal line in back end of line applications. As device dimensions scale there is an increasing urgency to develop area-selective deposition methods that are selective for cobalt deposition on copper to eliminate the need for metal etching steps in metallization process schemes. The half reactions of bis(N-tert-butyl-N’-ethylpropionamidinato) cobalt(II) (CoAMD) and H2 are evaluated on Cu, SiO2, and a porous low-k (~2.6) dielectric. The first and second ALD half reactions of CoAMD on the respective substrates are evaluated by adsorbing the precursor on the substrates under ALD cycling conditions at 265 °C with and without H2 coreactant exposure. The adsorption studies indicate that CoAMD preferentially deposits most on Cu and least on the low-k surface. Further, CoAMD, like other amidinate precursors, readily dissociates on the Cu transition metal surface but the ultimate per-cycle coverage is self-limited by the slow desorption of amidinate ligands and fragments from the Cu surface. Co films deposited by ALD from CoAMD on Cu at 265 °C indicate that Co burrows into the lower energy Cu surface as the film grows in order to reduce the free surface energy. The Cu remains as a surfactant-like layer on the topmost Co surface up to film thicknesses of at least 16 nm. Moreover, considerable intermixing at the Co/Cu interface and Cu concentration several nm into the Co films is observed indicating high surface mobility of the two materials and Cu diffusion at polycrystalline Co grain boundaries. Finally, employing low-temperature ALD and selectively passivating the dielectric surfaces with OH targeting passivants, such as trimethylchorolosilane, leads to enhanced selectivity of CoAMD for deposition on Cu versus SiO2 and porous low-k surfaces. Depositing Co from CoAMD on Cu and the porous low-k surface at 165 °C after exposure to trimethylchlorosilane at 50 °C leads to a 30:1 preference for Co accumulation on Cu, a twelve times improvement compared to deposition on clean Cu or the low-k dielectric at 265 °C.
Exploring Electrochemical Energy Storage of SnO2, Sn3N4, and SnOxNy through Ald
Authors: Stewart David Murdock , Pearse Alex , Gregorczyk Keith , Rubloff Gary W
Published: February 2020

As conversion electrodes in lithium ion batteries, Sn and SnO2 have been well studied in the literature, while the properties of Sn3N4 and SnOxNy have yet to be been explored in any detail. To study the differences in the electrochemical performance of SnO2, Sn3N4, and SnOxNy, an ALD process was developed which allows for a controlled N/O ratio. This process uses tetrakis(dimethylamido)tin (TDMAS) as a precursor with remote nitrogen plasma and H2O. As with many nitride ALD processes, obtaining Sn3N4 films with low O and C contamination is challenging due to the greater reactivity of Sn with O, and incorporation of precursor ligands. Optimized process parameters for the pulse times and substrate temperature were obtained for the nitride process, which were incorporated into the oxynitride process. SnOxNy films were grown by periodically pulsing water into the reactor after several cycles of the nitride process. By varying the number of nitride cycles between water pulses, the relative concentration of O and N in the film can be controlled between 0% N and 95% N.

The Li2O matrix formed on conversion of SnO2 is expected to be more chemically stable than the Li3N matrix formed from Sn3N4, but at the cost of lower ionic conductivity. Solid-state half cells were constructed using SnO2, Sn3N4, and SnOxNy thin films versus thermally evaporated Li with ALD LiPON as the electrolyte. The electrochemical properties of the anodes were tested by cyclic voltammetry and galvanostatic cycling. Only a single narrow conversion reaction was observed, regardless of film composition, but the voltage at which the reaction occurred shifted as a function of the N/O ratio. At voltages below 0.4 V vs Li/Li+ the half cells shorted, possibly due to mechanical breakdown of the LiPON layer from significant volume expansion of the anodes during the alloying reaction with Li. However, the stability of the cells was improved by varying the composition and thickness of the anodes. Galvanostatic intermittent titration and impedance spectroscopy were used to analyze the ionic conductivity of the anodes before and after the initial conversion reaction and as the N/O ratio was varied. The high energy storage capacity of SnOxNy electrodes, which can be deposited conformally by ALD, makes them attractive materials for applications in thin film, solid state devices, where the particle aggregation and delamination effects are limited by the physical constraints of the device.
Atomic Layer Deposition of NbC-Al2O3 Composite Films for Efficient Solar Selective Coatings
Authors: Avila Jason R , Peters Aaron , Mane Anil U. , Libera Joseph A. , Yanguas-Gil Angel , Farha Omar , Hupp Joseph T. , Elam Jeffrey W
Published: February 2020

Solar selective films hold great promise for improving the efficiency of concentrated solar power (CSP) facilities. In this study, we used atomic layer deposition (ALD) to prepare solar selective films composed of metal-dielectric nanocomposites with tunable optical and electronic properties. We used niobium carbide (NbC) as the metallic component and Al2O3 as the dielectric component of the nanocomposite films, and these components were blended at the atomic scale by alternating between the NbC and Al2O3 ALD processes. In-situ quadrupole mass spectrometry and quartz crystal microbalance (QCM) measurements were performed to examine the growth of the NbC-AlO composite films as well as to establish the NbC ALD growth mechanism. These measurements revealed that the NbC inhibited the Al2O3 ALD, while the Al2O3 enhanced the NbC ALD. Next, NbC-AlO nanocomposite films wereprepared over the full range of 0-100% NbC in Al2O3 and the physical, optical and electrical properties were measured. We discovered that the band gap and electrical resistivity could be precisely tuned by controlling the composition, and that higher NbC contents yielded a lower band gap and a smaller resistivity. Based on the absorption spectra of the NbC-AlO composite films, we established that 10-20% NbC yield the highest selective absorption efficiencies due their high visible light absorption and low infrared absorption. However, the selective absorption properties of the NbC-AlO composite films were lost upon annealing to 400°C in air as a result of oxidation of the NbC. Our study demonstrates the efficacy for ALD preparing metal-dielectric nanocomposite films with tunable properties to achieve a high selective absorber efficiency. By applying this technique to more thermally robust metallic materials we hope to produce solar selective coatings suitable for deployment in CSP facilities.
Interface Studies of III-V Semiconductors and Oxides with an I
n-Situ Spectroscopic Ultra-High Vacuum (UHV) System Capable of Atomic Layer Deposition (ALD) and Atomic Layer Etch (ALEt)
Authors: Larrabee Thomas James , Prokes S. M.
Published: February 2020

Preparation of gate dielectrics and high-quality interfaces by atomic layer deposition onto III-V and other sensitive substrates, which typically have multicomponent native oxides after air exposure, is a challenging problem that cannot be completely understood by ex-situ surface analysis techniques. Surface oxides can be detrimental or, in specific cases, even beneficial to device performance depending on how the interface affects the Fermi-level of the semiconductor.1,2 One such system is GaSb, which is a case study here for a high mobility p-type material. In this work, surfaces of GaSb <001> have been examined, with methods of oxide removal including H-atoms, Ar+ ions, and both, simultaneously tested as a function of temperature for determining the threshold of surface damage. The re-oxidation of the interface is examined after oxygen and water exposure, and after oxide films growth.

Description of the unique system designed and built at NRL for these type of studies will be presented.3 It combines a surface science UHV chamber; with X-ray photoelectron and Auger electron spectroscopies (XPS & AES), transmission or reflection-absorption thin-film FTIR spectroscopy, low-energy electron diffraction (LEED), reflection electron energy loss spectroscopy (REELS), and surface preparation, with a chamber-within-a-chamber design for performing ALD and ALEt at pressures from mTorr to Torr. Without exposure to ambient, the ALD system is pumped out and opened to the UHV environment for spectroscopy. A quantified, micro-dosing gas reagent delivery system is also implemented, so quantitative ALD reactant exposure may be correlated with actual surface reactions.4 Spectroscopic results and surface reconstruction patterns for GaSb interfaces acquired in above system will be presented.

1L.B. Ruppalt et al., Appl. Phys. Lett.
101, 231601 (2012).

2V.M. Bermudez, J. Appl. Phys.
114, 024903 (2013).

3V.M. Bermudez, Rev. Sci. Instrum.
85, 114101 (2014).

4T.J. Larrabee, T.E. Mallouk, D.L. Allara, Rev. Sci. Instrum.
84, 014102 (2013).
(Invited) Thermal and Thermoelectric Transport in Semiconductor Nanowires
Authors: Chen Renkun
Published: February 2020

During the last two decades we have witnessed tremendous advancement in the characterization and understanding of thermal transport in nanostructures, particularly in the ‘phonon boundary scattering’ regime where the characteristic size of nanostructures ranges from tens to hundreds nanometers and is comparable to phonon mean free path. This understanding is one of the key underlying reasons for improved performance observed in nanostructured thermoelectric materials. However, the boundary scattering mechanism may reach its limit and new mechanisms for improving thermoelectric performance need to be explored. One of the opportunities may arise from the study of thermal transport beyond the boundary scattering regime, where the characteristic size of nanostructures is below 10-20 nanometers and is comparable to phonon wavelength. However, there is little experimental work on thermal transport in nanostructures in this regime. In this talk, we will discuss our recent work on using rationally designed nanostructures to study nanoscale thermal and thermoelectric transport phenomena in this regime. We will describe the instrumentation we developed that enables the characterization of thermal and thermoelectric properties of these nanostructures and discuss and interpret the measurement results.
An Economical Half-Cell and Modified Rotating Disk Electrode for Electrochemical Characterizations of Fuel Cell Catalyst-Coated Membranes and Gas Diffusion Electrodes
Authors: Bonakdarpour Arman , Kwan Jason , Pinaud Blaise A , Daniel Lius , Afonso Greg , Wilkinson David P
Published: February 2020

Common methods of fuel cell electrocatalyst characterization, in particular the oxygen reduction reaction (ORR) catalysts, include thin-film RDE and PEMFC measurements using fuel cell test stations. The former is generally available in many electroanalytical labs, however, ink deposition on RDE tips and limited solubility of oxygen in the electrolyte lead to testing environments which are quite different from those of fuel cell hardwares. The latter option requires fuel cell hardware and an appropriate test station which are expensive and not widely accessible by many labs. We present two approaches in order to bridge the gap between these methods: 1) a modified RDE tip which accepts catalyst-coated membranes (CCMs), thus eliminating the potential issues of catalyst ink deposition and the associated variabilities, and 2) a low-cost half-cell setup which allows fuel cell-like current densities (~ 1 A cm-2) to be obtained using gaseous oxygen feed. The novel RDE tip has been tested with Pt foil and commercial CCMs in 0.1 M HClO4 at room temperature (20°C) and good agreements with polycrystalline Pt and H2/O2 fuel measurements have been obtained, respectively. In addition, CCM degradation tests, using an accelerated degradation test protocol (ADT) with potential cycling, have been performed and the loss of Pt and Pt surface area have been quantified. With the half-cell setup, constant current polarizations with IR drop measurement at each step were found to provide a simple, reproducible method of measuring catalyst performance using an optimal electrolyte concentration of 1.0 M HClO4. Accurate ORR activity of commercial GDEs/CCMs and good agreement with measurements made in fuel cell hardware have been obtained with the half-cell setup. Both of these approaches are low cost (< $1000 USD) and can be implemented in a typical electroanalytical lab. Cells designs and results of ORR experiments with both approaches will be presented.

Figure 1
Octahedral Pt-Ni Nanoparticles for Electrocatalytic ORR – New Insights Using in-Situ Scattering, Spectroscopy and Microscopy
Authors: Beermann Vera , Holtz Megan E , Gocyla Martin , Kühl Stefanie , Padgett Elliot , Erini Nina , Heggen Marc , Dunin-Borkowski Rafal E. , Muller David A. , Strasser Peter
Published: February 2020

Shape-controlled octahedral Pt-Ni core shell nanoparticles have attracted much attention in recent years due to their promising oxygen reduction reaction (ORR) activities, presumably owing to their particular geometry and facet exposure. Yet much about their growth and degradation has remained insufficiently understood.

Here, we present some recent work where we learned more about the relations between particle synthesis, morphology, bulk structure, surface composition and their catalytic ORR activity and stability using, among others, in situ high-temperature TEM and in situ electrochemical TEM. We follow the particle morphology in real time during annealing protocols, and, using real time imaging, we track and observe changes in the catalyst structure and particle shape during different electrochemical treatments

Our study provides some interesting new insights in the real time behavior and degradation of shaped PtNi electrocatalysts, and may aid in out understanding of some of the parameters that will optimize the lifetime of the catalyst.
Insights into Platinum-Cobalt Electrochemical Dissolution from Platinum-Cobalt Alloy Polymer Electrolyte Fuel Cell Fuel Cell Cathode Catalysts Using Online ICP-MS
Authors: Kariuki Nancy , Papadias Dionissios D. , Myers Deborah J , Ahluwalia Rajesh
Published: February 2020

The catalysts of choice in polymer electrolyte fuel cells (PEFCs) remain Pt-based nanoparticles on high-surface-area carbon support. One critical challenge facing commercialization of this fuel cell is the gradual decline in performance during operation, mainly caused by the loss of electrochemical surface area (ECA) of the Pt or Pt alloy nanoparticles at the cathode. In this respect, the understanding of the dominant mechanisms of the loss of ECA and loss of oxygen reduction activity, such as the electrochemical dissolution of Pt or the transition metal alloy component, is of vital importance. Several mechanisms for dissolution of platinum have been proposed including direct Pt dissolution and electrochemical oxidation of the Pt surface atoms followed by chemical dissolution of the resulting Pt surface oxide.

This presentation will outline the dissolution of PtCo under various operating conditions. Studies are performed to quantify the amount of dissolved Co and Pt during potentiodynamic conditions in an electrochemical flow cell system connected to an inductively-coupled plasma-mass spectrometer (ICP-MS) capable of detecting trace concentrations (<ppb) of dissolved elements in solution. The electrochemical data combined with the ICP-MS data are used to evaluate the influence of various factors such as potential, potentiodynamic profile parameters (e.g., scan rate, upper and lower potential limits), particle size, and support type on the dissolution processes in acidic electrolytes at room temperature.

Preliminary measurements showed that Pt dissolution occurs during both the positive-going and negative-going potential sweeps. When the potential was cycled from 0 to 1.0 VRHE, two distinct dissolution peaks were detected by the ICP-MS online analysis. The ratio of the amount of Pt dissolved during the two sweeps was found to be dependent on the sweep rate, potential hold times, and potential profile. Fundamental models will be developed to explain the mechanisms of degradation process under various potential conditions.

This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Fuel Cell Performance and Durability Consortium (FC-PAD). Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, also under contract DE-AC-02-06CH11357.
Unsupported Platinum-Metal Two-Dimensional Nanoframe Oxygen Reduction Electrocatalysts: Effect of Transition Metal Composition on Activity and Stability
Authors: Ying Yuanfang , Godinez-Salomon Fernando , Archer Randall , Rhodes Christopher
Published: February 2020

Currently, oxygen reduction reaction (ORR) electrocatalysts used within proton-exchange membrane fuel cells (PEMFCs) are primarily platinum (Pt) and Pt-based alloys that are supported on high surface area carbon. At elevated voltages encountered during start-up/shut-down, the corrosion of the carbon support is accelerated which can significantly degrade the long-term stability of the catalyst. Recent work by our group has shown that unsupported (carbon-free) Pt-Ni two-dimensional (2D) nanoframes enable ORR electrocatalysts with significantly improved activity and stability compared with carbon-supported Pt and bimetallic Pt-metal alloy catalysts.1 The unique nanoframe structure consists of a hierarchical 2D framework composed of a highly catalytically active Pt-metal alloy phase with an interconnected solid and pore network that results in three-dimensional molecular accessibility. The effect of altering the transition metal was investigated as a route to further improve the ORR activity through control of the surface atomic and electronic structure of Pt. Unsupported Pt-metal (metal=Ni, Co) two-dimensional (2D) nanoframes were synthesized through controlled thermal treatments of Pt-decorated metal hydroxide/oxide nanosheets. The structure of the 2D nanoframes were determined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Analysis of XRD and SEM data supports that Co and Ni can be incorporated into Pt-metal 2D nanoframes. Electrochemical characterizing using a rotating disk electrode configuration shows that the Pt-M 2D nanoframes exhibit significantly higher activities compared with Pt/C. The ability to create metallic 2D structures with 3D molecular accessibility opens up new opportunities for the design of high activity and stability carbon-free catalyst nanoarchitectures for numerous electrocatalytic and catalytic applications.

References

Godínez-Salomón, F.; Mendoza-Cruz, R; Arellano-Jimenez, M. Jose-Yacaman, M.; Rhodes, C.P; (manuscript submitted).
Oxygen Reduction Reaction Activity of Platinum Thin Films with Different Densities
Authors: Ergul Busra , Begum Mahbuba , Kariuki Nancy , Myers Deborah J , Karabacak Tansel
Published: February 2020

Polymer electrolyte membrane fuel cells (PEMFCs) have gained significant attention as alternative power sources, especially for automotive applications due to their high energy conversion efficiency, low operating temperature and being environmentally friendly compared to the other types of fuel cells. However, sluggish kinetics of oxygen reduction reaction (ORR) on the cathode requires a high loading of platinum (Pt), which increases the cost of the fuel cell. In addition, dissolution and agglomeration of Pt nanoparticles and oxidation of the carbon support are among the major factors that cause electrode degradation and performance loss. Therefore, extensive efforts are focused on developing high performance, durable, and low-cost electrocatalysts. Extended surfaces such as nanostructured thin films are good candidate for non-conventional catalysts due to their high surface area and having no need for a support material.

In this work, a new density-modulated platinum thin film (Pt-TF) design was fabricated by high pressure sputtering deposition (HIPS) and was investigated as potential electrocatalysts for the ORR in PEMFCs using cyclic voltammetry and rotating disk electrode techniques in aqueous perchloric acid electrolyte. Scanning electron microscopy and X-ray diffraction methods were used to study morphological and crystallographic properties of the density-modulated Pt-TF electrocatalysts. The Pt-TF catalyst was produced by changing working gas pressure from low to high values during film growth, which results in denser film bottoms and more porous tops. Low-density film top provides effective transportation of oxygen, which could enhance catalyst utilization and result in reduced Pt-loading and enhanced activity. Porous yet interconnected network of Pt atoms in the low-density Pt-TF surface can also eliminate the agglomeration and dissolution problems. In addition, high-density film bottom provides a strong adhesion to the substrate leading to enhanced physical and electrochemical stability of the Pt-TF. Stronger bonds along with self-protection against the acidic environment due to the dense-packing of Pt atoms at the interface with the substrate can hinder leaching of Pt and avoid the detachment of large regions of Pt-TF from the substrate as a whole. In addition, high-density layer can reduce contact resistance and enhance the electronic conductivity. This presentation will focus on electrochemically active surface area, area specific activity, and mass activity of density-modulated Pt-TFs during accelerated stability tests and compare them to conventional high-density Pt-TF and Pt/C electrocatalysts.
(Carl Wagner Memorial Award of the Electrochemical Society Address) Mixed Protonic-Electronic Membrane Reactors; Converting Hydrocarbon Resources and CO2 to Fuels
Authors: Wachsman Eric D.
Published: February 2020

Membrane reactor technology holds the promise to circumvent thermodynamic equilibrium limitations by in-situ removal of product species, resulting in improved chemical yields. Recent advances in mixed-conducting oxide-membrane technology present the possibility for a dramatic reduction in the cost of converting petroleum, coal and biomass derived feed stocks to hydrogen and other “value added” hydrocarbons. We have developed novel membrane reactor technology, based on high temperature proton conductors, that can convert a wide range of hydrocarbons to pure H2, and syngas for synthesis of liquid fuels and chemical feed stocks. By simultaneous H2 permeation and catalysis, we have demonstrated the ability to increase water gas shift yields >70% over thermodynamic limitations. Similarly we have demonstrated increases in steam reforming yields, and the ability to reform CH4 with CO2. The later creates the opportunity for a revolutionary method for carbon sequestration. Moreover, we have now developed single-step gas to liquid reactors that convert natural gas to C2+ products with high yields.
Correlation of Structure and Surface Exchange Kinetics on Bismuth-Based Oxides
Authors: Huang Yi-Lin , Pellegrinelli Christopher , Abdul Jabbar Mohammed Hussain , Robinson Ian , Wachsman Eric D.
Published: February 2020

High temperature cubic phase bismuth oxide has the highest ionic conductivity because of the highly defective fluorite structure, with near unity ionic transference number. However, bismuth oxide has multiple crystallographic polymorphs at different temperature domains and the conductivity of bismuth oxide can vary by orders of magnitude depending on the phase. Although cubic phase bismuth oxide can be stabilized by doping, doped bismuth oxides, such as erbium stabilized bismuth oxide (ESB), undergo an anion ordering transition near 600 °C, leading to a decrease in ionic conductivity. The phase transition and anion ordering in stabilized bismuth oxides provides a unique opportunity to directly correlate crystal structure, conductivity and surface exchange properties on ionically conducting oxides. Here, gas phase isotopic oxygen exchange was performed on Bi2O3 and ESB as a function of exchange time at different temperatures, to determine the structure effect on surface exchange kinetics. Our results suggest that bismuth-based oxides have intrinsic catalytic activity toward oxygen exchange and the doping of erbium affects the surface exchange rate. The relationship between diffusion coefficient (D) and surface exchange coefficient (k) on bismuth-based oxides is explored and possible rate-limiting steps are proposed.
Accelerated Computational Design of Mixed Protonic and Electronic Conduction for H2 Separation through Tailoring Polaron
Authors: Bai Qiang , Zhu Yizhou , He Xingfeng , Mo Yifei
Published: February 2020

The technology of H2 separation is essential for the utilization of hydrogen fuel, which is strongly motivated by the grand challenge of climate change. Electrochemical membrane based on cerate, titanate and zirconate ceramics is a promising technology of H2 separation. In particular, SrCeO3 perovskites with mixed protonic and electronic conductivities are promising materials for H2 separation due to negligible oxygen permeability. However, low electronic conductivity of SrCeO3 often limits the overall H2 flux. The increase of electronic conductivity via B-site doping has been largely based on trial-and-error experiments. This lack of understanding limits further design and development of hydrogen membrane materials. In this presentation, we will share our computation studies of revealing distinctive behaviors of different dopants in enhancing electronic conductivity via novel polaron mechanism, using first principles hybrid functional calculations. Our study shows SrCeO3 can trap excess charge as electron or hole polarons on Ce4+ or certain dopants. The enhancement of different dopants to electronic conductivity can be determined by the ability of polaron formation and migration. Based on the insight of the polaron enhancement mechanism, new promising dopants are predicted to increase electronic conductivity, and the computation predictions are verified by preliminary experiments. Thus, our study demonstrates first principles techniques in accelerating deign of mixed conductors through tailoring polaron, and provides new avenues for the future design of the materials with different polaronic behavior to achieve improved conductivity and other properties.
Exploring the Effects of Doping on the Electrochemical Performances of LiCoO2 at High Cut-Off voltage
Authors: Zhang Jienan , Zhao Enyue , Wang Yi , Wang Junyang , Wang Fangwei , Yu Xiqian , Li Hong
Published: February 2020

Increasing the energy density of cathode materials for lithium-ion batteries requires raising up the working voltage of cathode materials or/and extracting more lithium ions from their crystal lattice. Therefore, the cathode materials are inevitably exposed to extreme working environment, which may cause the instability of both global crystal structure and/or surface/interfacial structure. Introducing doping elements to electrode is currently the expedient method to improve the performance, however, whether the alien element is doped in the host crystal or not usually lacks of solid experimental proofs, and whether the positive effects is caused by doping is still unknown. The situation becomes even more complex when several elements are doped at the same time. In this report, with a case study focusing on LiCoO2, evaluation of the interaction between different alien elements including Ti, Mg and Al is conducted with orthogonal experiments. The effects of doping and coating are compared in detail to find out a better way to improve the electrochemical performances of LiCoO2 at high cut-off voltage of 4.6V vs. Li+/Li. The question regarding whether the alien elements are doped in the host crystal or presented as a secondary phase that is aggregated on surface or grain boundaries is also discussed with both first-principle calculations and experimental investigations, such as XRD, X-ray imaging, XPS, thermal analysis by TG and electrochemical tests. By summarizing the results, the major factors affecting the performance of high voltage LiCoO2 are clearly demonstrated, which we hope it will also be valuable information for the development of other cathode materials for high energy density lithium-ion batteries.
(Invited) Post Lithium-Ion Technologies: Novel and Sustainable Materials for Energy Storage
Authors: Hintennach Andreas
Published: February 2020

Ever since the development of lithium-ion batteries the spirit of invention has mainly lead to an evolution of existing materials. With the focus on olivine and Nickel- and cobalt based materials the energy densities, power densities and ageing mechanisms could be investigated over the years and support the understanding of the underlying mechanisms of electrochemical energy storage and conversion.

With increasing numbers of cells being used in the world the need of a Post-Lithium-Ion technology emerges due to a limited availability of highly pristine nickel and cobalt and increasing need for recycling, environmental protection and overall energy efficiency. Nevertheless the is still an ongoing and very promising approach for e. g. novel stoichiometries of NMC materials, Lithium cobalt phosphate and nickel-rich materials with can significantly increase the energy density. Due to the very high reactivity and potential (i. e. 4.5 V) these materials require highly stable electrolytes.

Finally, lithium-sulphur can lead to a highly recyclable, environmentally friendly system. Having a silicon-based anode (> 85 % Si) included both volumetric and gravimetric energy density can mean an interesting alternative to metal-oxide based materials.

With the increased energy density, safety becomes a more and more important aspect in thermodynamic and kinetic investigations of these materials. This aspect can lead to the development of non-flammable electrolytes or solid state cells.

Solid state cells are a very different but highly promising approach. Having a solid-solid interphase between electroactive materials and electrolyte the chemicals mechanisms significantly change to solid state chemistry rather than solid-organic interphases chemistry.

All types of novel chemistries exhibit very different chemical mechanisms which require specific synthetically work for electrolytes, additives, binders, carbon materials, and even the surfaces of the electro-active materials itself.
Enhanced Electrochemical Performance of the Cathode for a Lithium Ion Secondary Battery Using Lithium Ion Conductive Glass-Ceramics
Authors: Katoh Takashi , Satoh Ryouhei , Nakajima Kousuke , Hoffman Brion
Published: February 2020

Ceramics powder such as SiO2 and Al2O3 are incorporated in to the polymer electrolyte to form the composite film for the sake of improving ionic conductivity, mechanical and thermal properties. Though these filler enhanced ionic conductivity of gel electrolyte due to the disruption of polymer matrix and increasing micro pores, these are not ionic conductive material. We found that the gel electrolyte film (Pvdf based polymer) was enhanced ionic conductivity by adding LICGCTM.

We have developed lithium ion conducting glass-ceramics LICGCTM with a NASICON type structure for solid lithium ion electrolyte.1-
3) The ionic conductivity of the glass ceramics with a Li1+x+yAlxTi2-yGeyPO4 composition shows over 1×10-4 Scm-1 at room temperature. Such ceramics have a very stable in ionic conduction. In addition, the ionic conductivity does not decrease, even if it was soaked in an aqueous of Li salt solution4-5), and does not lose the weight in boiling distilled-water for 1 h. The glass-ceramics with the crystalline form of Li1+x+yAlxTi2–xSiyP3–yO12 with a NASICON-type structure by heat-treated glass with a specific composition1-2). This glass-ceramics has a high lithium-ion conductivity that is equal to or more than 10–3 Scm–1at room temperature. Furthermore, because it is very stable in the atmosphere and even to exposure to moist air, it is possible to use this material to apply a solid-electrolyte for a lithium ion secondary battery using organic liquid electrolyte.

In this work, the effect of LICGCTM as additive for a lithium ion secondary battery was investigated. We synthesized LiCoO2 cathode with 5wt.% LICGCTM filler and evaluated it the charge and discharge property using a half cell. We confirm the rate performance at room temperature is enhanced at 0.2-3.0C comparing pristine LiCoO2 cathode. The rate performance was indicated 20 percent increasing at 2.0C rate as compared to pristine LiCoO2 cathode. The charging performance was also enhanced at higher rate at room temperature.
Implementation of Tin Dioxide/Graphene/Graphene Oxide for High Capacity and Long Cycle Life Supercapacitors and As Anode Material for Lithium Ion Batteries
Authors: Dorvilien Valerio , LopezdeVictoria Monica , Rivera Kevin , Suleiman Amal , Tripathi Balram , Mendoza Frank , Cabrera Carlos , Morell Gerardo , Weiner Brad R.
Published: February 2020

Energy storage and conversion mechanism are different for on lithium ion batteries (LIB) and supercapacitors (Electrical Double Layer Capacitors- EDLCs), materials that can be used for both could lead in the future the energy storage and conversion technologies. We explored a non-conventional process to synthesize SnO2/G/GO composite powder which is conformal structure was characterized under different techniques. Comprehensive analysis of the structural and chemical properties reveals that the material consists of highly dispersed SnO2 nanoparticles in G/GO matrix.

The dispersed SnO2/G/GO suspension was coated an aluminum foil for the supercapacitors electrodes. We examine the electrical conductivity of the electrodes by atomic force microscope (AFM), scanning electron microscope (SEM) and transmission electron microscope (TEM). We assembled the Al coated SnO2/G/GO composite as a supercapacitor inserting one solid-state electrolyte between two electrodes, assembled into a sandwich structure. The specific capacitance and cycle-life stability of the supercapacitor was investigated by cyclic voltammetry analysis. For LIB applications, the SnO2-G/GO composite exhibited high capacity and excellent electrochemical performance as anode material. For both applications, the quantitative/qualitative results show that G/GO is providing contact areas which results in more energy density at the interface electrode/electrolyte and that the SnO2 provides additional ions to the EDL and the electrochemical process. The Overscreening phenomena observed, which is a function of ionic size, surface charge density of the electrodes, can also be a function of concentration of the electrolyte, porosity of the electrodes (G/GO) and the ions provided to the electrode/electrolyte interface by the electrode.
Energetics of Dendrite Propagation in Garnet Solid Electrolytes Using First-Principles Simulations
Authors: Dawson James Alexander , Canepa Pieremanuele , Statham Joel , Parker Stephen C. , Islam M. Saiful
Published: February 2020

Developing new battery technologies to satisfy the ever-growing demand of energy storage constitutes one of the great scientific challenges of society. Lithium-ion batteries are at the centre of this energy revolution as they power millions of portable electronics. Super-ionic conductivity of Li+ in solids, greater than 1 mS/cm, has stimulated renewed interest in solid-state Li-ion batteries, which would have substantial advantages in terms of safety and lifetime. While significant attention has been paid to the optimisation of the bulk ionic conductivity of Li, the electrochemical stability of solid electrolytes against the electrodes have been largely neglected. Although the garnet Li7La3Zr4O12 is a fast-ionic conductor and is believed to be stable against the Li-metal anode, recent reports show that Li dendrites propagate through the grain boundaries, compromising the safety and performance of the device. In this presentation, using first-principles modelling, we will present a detailed assessment of the competitive energetics of two distinct scenarios, i) the interaction of Li-metal and Li7La3Zr4O12 grains and ii) the interaction of Li7La3Zr4O12 grains.
Enhancement of Cycle Performance of Si/TiFeSi2 Nanocomposite As Lithium Storage Material By Mechanical Deformation
Authors: Park Hyeong-Il , Sohn Myungbeom , Choi Jeong-Hee , Park Cheolho , Kim Jae-Hun , Kim Hansu
Published: February 2020

Although silicon has higher reversible capacity than graphite as a lithium storage material, its large volume change during lithium insertion and extraction causes poor capacity retention. To address this technical issue, melt-spun Si based alloy materials have been suggested as promising materials for lithium ion batteries because of their high capacity and relatively low production cost. However, their long-term cycle performance should be further improved for the commercial success. In this study, it is demonstrated that mechanical deformation can improve the electrochemical performances of melt-spun Si alloy material. By applying the high-energy mechanical milling to melt-spun Si/TiFeSi2, Si/TiFeSi2 nanocomposite is successfully modified with a size of few nanometer, and that is clearly observed by X-ray diffraction (XRD) and transmission electron microscope (TEM). As s result, the microstructurally tuned Si/TiFeSi2 showed a reversible capacity of more than 1000 mAh g-1 with stable capacity retention up to 100 cycles. More detailed studies on the reasons for better cycle performance of milled Si/TiFeSi2 will be discussed in this presentation.