bluuebunny/crossref_metadata_2025 huggingface dataset:
Bringing Components to Solar Fuels Prototypes: Material Discovery, Interface Engineering, and Integration
Authors: Sharp Ian D.
Published: February 2020

To achieve efficient and durable devices for spontaneous water splitting, it is necessary to overcome thermodynamic limitations on material stability, integrate catalysts with light absorbers, and engineer interfaces to reduce recombination loss. Central to this work is the discovery of new materials and methods, combined with the translational research required for their incorporation into prototypes. In our work, we use advanced x-ray and optical methods to understand the basic electronic structure, photocarrier dynamics, and chemical instabilities of existing semiconductor materials. This information allows for insights into the mechanisms of energy conversion and efficiency loss, as well as refinement of computational models for improved prediction of new semiconductors possessing desired band gaps, charge transport properties, and stabilities required for improved half-cell performance. Informed by these predictions, materials discovery efforts are aimed at synthesizing specific compositions for further investigation. These materials are typically compound thin film semiconductors, in which composition non-uniformities, structure, and morphology affect photoactivity. Probing these properties across different length scales, as well as their transformations in operational environments, allows for determination of chemical vulnerabilities and electronic deficiencies. Since these materials are typically characterized by poor intrinsic catalytic activity, it is generally necessary to integrate catalysts onto their surfaces. Process development and interface engineering are required to achieve desired catalyst composition and structure, while enabling efficient separation and transfer of photocarriers from semiconductor to catalyst.  Since the performance of integrated systems is often governed by defect properties that are difficult to predict, combinatorial studies of catalyst/semiconductor assemblies are used to aid in the discovery of efficient interfaces. Finally, advances made at the half-cell level must be incorporated into prototypes capable of spontaneous overall water splitting and product separation, which impose strict requirements on operational conditions, light transmission paths, and physical scale. Key examples of research spanning material and mechanism discovery, development, and integration into prototypes will be given.
Northeast Center for Chemical Energy Storage (NECCES)
Authors: Whittingham M. Stanley
Published: February 2020

NECCES Mission Statement

: To develop an understanding of how key electrode reactions occur, and how they can be controlled to improve electrochemical performance, from the atomistic level to the macroscopic level through the life-time of the operating battery.

The design of the next generation of rechargeable batteries requires both the development of new chemistries and the fundamental understanding of the physical and chemical processes that occur in these complex systems. Although some significant advances have been made to prepare and utilize new materials, efforts towards the understanding of mechanisms have waned. This will eventually choke efforts to efficiently develop new materials if this issue is not addressed now. Batteries are inherently complex and dynamic systems, their electrochemistry, phase transformations, and transport processes often varying throughout their lifetime. Although often viewed as simple to use by the customer, their successful operation relies heavily on a series of complex mechanisms, involving thermodynamic instability in many parts of the charge- discharge cycle and the formation of metastable phases. The requirements for long-term stability are extremely stringent and necessitate control of the chemistry at a wide variety of temporal and structural length scales. This in turn necessitates the development and use of new characterization tools to monitor these processes. The overall goal is to understand the transformations (and their rates) that occur in an electrode composite structure, from the atomistic level to the macroscopic level, throughout the lifetime of the functioning battery. The four-year scientific research goals are:

Close the gap between the theoretical and practical energy density for intercalation compounds.

Attain reversible multi-electron transfer in a cathode material using lithium.

Understand performance limiting transport in positive electrode structures from the local through the meso to the macroscale.

Enable new chemistries involving electrode systems that were previously considered intractable for use in batteries.
Nitrogen Doped Hydrothermal Carbon for Supercapacitors
Authors: Donne Scott W , Latham Kenneth
Published: February 2020

Although pure carbon materials have been readily adopted for energy storage applications, recent years have seen an increase in studies incorporating heteroatoms into the carbon matrix for energy storage applications. The doping of carbon materials with heteroatoms increases performance significantly in energy storage applications, specifically supercapacitors. This increase in performance is due to heteroatoms providing electrochemically active sites in which highly reversible redox reactions can occur (pseudocapacitance), boosting the overall performance of the electrode. This has led to the widespread development of doped carbon materials incorporating nitrogen, phosphorus, sulphur and various transition metals into almost every allotrope of carbon.

Currently, a number of technologies have been utilized to dope nitrogen into carbon structures, such as electric arc, pyrolysis, hydrothermal and pre/post treatments with nitrogen sources. Of these, hydrothermal carbonization (HTC) is one of the most promising techniques in carbon materials research. In comparison to other carbonization techniques, HTC offers an environmentally friendly approach to the formation of highly functionalized, doped carbon structures from renewable sources as carbonization occurs under water at substantially lower temperatures (180°-300°C). Furthermore, heteroatoms incorporation, chemical and structural morphology as well as surface functionality can be easily controlled through the manipulation of the treatment conditions, solution pH and addition of soluble additives (i.e., (NH4)2SO4.

In this study, we have investigated the chemical structure via NEXAFS, morphology and electrochemical performance of hydrothermal carbons produced from sucrose doped with different ammonium salts. This produced nitrogen doped carbons with a spherical morphology with a wide variety of oxygen and nitrogen functionalities spread across the surface. Electrochemically, these carbons displayed a wide range of psudocapacitive behaviour as well as electrical double layer capacitance, delivering up to 200 F/g in three electrode cells with 1 M KOH as the electrolyte.
A Time Resolved Study of Precoated AISI 441 for SOFC Interconnects Using STEM-EELS - Part II
Authors: Karlsson Lisa S , Lundberg Mats W , Berger Robert , Westlinder Jörgen
Published: February 2020

Precoated AISI441 for SOFC interconnectors were investigated by STEM-EELS looking at the diffusion processes in the initial stage of the oxidation. The PVD coating contained Ce and Co/Mn-alloy in two layers with at total thickness of 800nm. The samples were exposed up to 1000 hours at 800°C then characterized by TEM. Trivariate analysis of multiple linear least squares (MLLS) maps show that Cr2O3, (Co, Cr)-spinel, (Co, Cr, Mn).spinel and (Co,Mn)-spinel phases can be identified (Figure 1). Oxidation states are characterized from white line ratios of the present transition metals in these phases and can be correlated to changes in the O K-edge fine structure.

Figure 1
Abnormal Shrinkage upon Nickel Oxidation at Low Temperatures
Authors: Yashiro Keiji , Nakamura Takashi , Yamaji Katsuhiko , Hashimoto Shin-ichi , Amezawa Koji , Kawada Tatsuya
Published: February 2020

Chemical- and mechanical stability of Ni-YSZ cermet is an important factor for long-term operation of SOFCs, because the cermet is often used as not only an anode but a support of the cell.  It has been reported that microstructure of the cermet changes upon reduction and oxidation of nickel; and that nickel sintering takes place during long-term operation.  These phenomena lead to deterioration of cell performance. 

It is well known that oxidation of Ni causes increase in volume.  However we recently found that Ni-YSZ cermet was unexpectedly shrunk during the oxidation in the temperature range less than 500 °C.  To clarify this phenomenon, thermal expansion behavior of sintered nickel metal was measured in oxidizing atmosphere by a dilatometry.  Oxygen partial pressure and temperature varied from 10-3 to 0.2 bar and room temperature to 700 °C, respectively.  The extraordinary shrinkage behavior was observed in temperature range between 300-500 °C.  The amount of shrinkage depended on oxygen partial pressure and temperature ramp.  Maximum shrinkage of 1% was observed in 20%O2-N2at heating rate of 1 °C/min.  

Microstructure change of nickel was also observed by a scanning electron microscope before and after oxidation treatment at 400 °C in order to clarify the causes of volume increase.  Comparing the microstructure before and after oxidation, it seemed that nickel sintering was accelerated by oxidation of nickel.
Modeling Intermediate Temperature Protonic Ceramic Fuel Cells
Authors: Albrecht Kevin J , Duan Chuancheng , O'Hayre Ryan , Braun Robert J.
Published: February 2020

Protonic ceramics fuel cells (PCFC) have emerged as a promising candidate for distributed power generation and synthetic fuel production. The cells offer the potential for reduced temperature operation (~500°C) which enables faster startup times, longer life, and lower material cost components to be used compared to their oxygen ion conducting counterparts. The development of a protonic ceramic fuel cell computational modeling tool is imperative to the design and implementation of systems. A framework is presented for a predictive cell-level, interface charge transfer PCFC model capturing the mixed conducting nature of the protonic ceramic materials. The model employs a 1-D channel-level modeling strategy (Fig. 1) where fuel depletion and flow configuration effects are resolved and coupled to a semi-empirical electrochemical model. Modeling results calibrated against experimental data of a state-of-the-art PCFC composition are presented.

            The lower cell temperature and hydrogen removal from the anode channel present unique operational features which are considered in the present work. In particular, a thermodynamic analysis is presented for operating regimes where solid carbon formation is not thermodynamically favorable. Simulation results are presented for the operation of the cell over a variety of operational regimes. Model predicted distributions of gas phase species, temperature, and local current density are resolved. The model predicted cell performance when operating on a humidified methane fuel source with steam-to-carbon ratio (S/C) of 2.4 at 500oC and 80% utilization indicates a power density greater than 0.100 W/cm2 is attainable at an average current density of 0.15 A/cm2. Model-predicted cell performance is explored under various operating conditions (Temperature, utilization, S/C) and an evaluation of reactant flow configuration (co- vs. counter-flow) is also presented.

Figure 1
Analysis of Interfacial Processes at the SOFC Electrodes by I
n-Situ Raman Spectroscopy
Authors: Agarkov Dmitrii , Burmistrov Ilya , Tsybrov Fedor , Tartakovskii Ilya , Kharton Vladislav , Bredikhin Sergey , Kveder Vitaly
Published: February 2020

Kinetics of redox reactions and the variations of real charge-carrier concentrations across the SOFC electrode / electrolyte interfaces have critical importance for the fuel cell performance. The microscopic mechanisms of electrochemical processes in the vicinity of triple-phase boundary (TPB) can be assessed employing impedance spectroscopy, current-voltage measurements and various pulse techniques. Except for the micro-electrode approaches, however, these methods are cumulative. Moreover, unambiguous interpretation of the electrochemical measurement results requires, as a rule, to introduce complimentary experimental methods and/or to use simplified models. The present work is centered on the developments of a new combined technique for in-situ Raman spectroscopy studies of local chemical and electrochemical reactions, phase transitions, strains and morphological alterations in the SOFC electrodes under working conditions. The Raman spectroscopy was already successfully used to investigate both cathodic [1,2] and anodic [3] processes in SOFC, but the resultant information was mainly related to outer boundaries of the model electrochemical cells, primarily electrode surface, due to low penetration depth of the excitation radiation. The most important zones of the electrode systems, where the electrochemical reactions occur and ionic charge carriers are generated, cannot be achieved viewing the surface and edge areas. In the present work, this problem was solved by employing optically transparent, single-crystal membranes made of 10 mol.% Sc2O3 and 1% mol.% Y2O3 stabilized zirconia (10Sc1YSZ). In order to provide simultaneous Raman and electrochemical measurements of the cell placed under an oxygen chemical potential gradient, such as air/H2, a special controlled-atmosphere chamber was elaborated and tested. An appropriate selection of the electrodes geometry makes it possible to directly collect Raman spectra from the TPB zone, passing the beam through single-crystal solid electrolyte onto the interface, as a function of temperature, atmosphere, current density and/or overpotential. The results of case studies focused on redox kinetics of Ni-containing cermet anodes, are presented.

This work was supported by grant 14-29-04031 of Russian Foundation for Basic Research.

 References

S. Loridant, L. Abello, E. Siebert, G. Lucazeau, Solid State Ion. 78 (1995) 249-258

K. Blinn, H. Abernathy, M.Liu, Advances in Solid Oxide Fuel Cells V. (2010) 63-73

W. Bessler, M.Vogler, H. Stoermer, D. Gerthsen, A. Utz, A. Weber, E. Ivers-Tiffee, Phys. Chem. Chem. Phys., 12 (2010) 13888-13903
Intermediate Temperature - SOFCs: Nanoparticles Synthesis through Coprecipitation By Nitrate Route and By Oxide Route
Authors: Ribadeneira Paz Rafael Esteban , González Ocampo Javier
Published: February 2020

Solid Oxide Fuel Cells (SOFCs) are very promising devices to generate electrical energy for stationary applications as auxiliary power units for several purposes such as electrical grids, smart grids, cogeneration in different industrial processes, and also for transport, using mainly hydrogen and alternative fuels as syngas with high H2 - content. Additionally the SOFCs have the advantage of a high efficiency considering cogeneration (80-93%) and also this technology produces minimal pollutant emissions.

Despite of enormous progresses made to date, this technology has to reach all technical requirements in order to be competitive. In this sense, the SOFCs must operate at intermediate temperatures (450 – 650 °C) instead high temperatures (around 1000°C). To reach this objective the research of the chemical routes to synthesize the catalysts for anode and cathode, and also the electrolyte is a key step to achieve the best electrochemical behavior of SOFCs operating at intermediate temperatures.

The electrochemical and mechanical properties of anode, cathode and electrolyte oxides for SOFCs are primordially determined by the chemical synthesis route. In this work a comparison between two coprecipitation routes is presented using: i) nitrates and ii) oxides. These synthesis routes were tested for the anode (nickel oxide – NiO), the cathode (lanthanum strontium cobalt ferrite - LSCF) and the electrolyte (gadolinium and samarium doped ceria – GDC and SDC, respectively).

For these four compounds (NiO, LSCF, GDC and SDC) the physical characterization consisted in SEM – morphology analysis. Also the crystal structure and the nanoparticle size is determined by X-ray diffraction (XRD). The chemical characterization is carried out using energy-dispersive analysis (EDS). In addition to the physical and chemical characterization a symmetrical two-electrode electrochemical test cell is tested in the range of intermediate temperatures (450 – 650 °C).

These two routes of synthesis by coprecipitation are compared determining the most suitable and economical method to produce anodic, cathodic and electrolytic powders oriented to a better electrochemical behavior for intermediate-temperature solid oxide fuel cells (IT-SOFCs).
Low Temperature Methane Steam Reforming for SOFC
Authors: Sun Jie , Li Ji Gang , Zhu Yue Feng , Zhang Jing Jing , Zhou Tian , Li Li , Wang Yu Guang , Liu Shuai , Jiang Zhi Gang , Dong Zhong Chao , Sun Chun Wen , Li Hong , Chen Li Quan
Published: February 2020

The properties of flowerlike microspheres ceria based nickel catalyst for low temperature methane steam reforming were studied. The ceria microspheres were prepared by hydrothermal method. Catalyst of nano-sized nickel oxide particles based on flowerlike cerium oxide microspheres with high disperse were prepared to achieve simultaneous dehydrogenation of methane and water molecules on multi-active sites. The catalyst was characterized by means of Scanning Electronic Microscope (SEM), X-ray diffraction (XRD). Results showed that this special catalyst NiO/CeO2 had high activity and stability for methane steam reforming reaction below 600oC, improve the resistance of carbon deposition catalyst greatly. The stability of the catalyst was reached more than 1000 hours. The conversation of methane under 590oC was above 90%. The tests of the influence of different steam to carbon ratios on activity and selectivity of catalyst showed that 1.5~2.5 steam to carbon ratio was an ideal choice.

During the running of micro-tube methane steam reformer with this catalyst, the methane conversion of 555oC kept over 25mol.%, the selectivity of H2, CO, CH4 and CO2was 60 mol.%, 10 mol.%, 12 mol.% and 18 mol.%B

(This work was supported by National Key Basic Research Plan (973), No.2012CB215402 )

Figure 1
Carbon Tolerant Electrodes for SOFC and Reversible SOFC (RSOFC) Cells Operating on Carbon Containing Fuels
Authors: Niakolas Dimitrios K. , Neofytides Charalampos , Neophytides Stylianos G. , Tsiplakides Dimitrios , Papazisi Kalliopi-Maria , Balomenou Stella
Published: February 2020

Solid Oxide Fuel Cells (SOFC) and Electrolyzers (SOEC) hold great potential for the security of energy sector, providing solutions for efficient power generation and production of hydrogen and synthesis gas. A challenging barrier for the successful implementation of SOFC and SOEC technologies, remains the long term stability under realistic operating conditions by the effective control and minimization of degradation due to carbon built up. The problem arise from the fact that the commonly used anode cermets, e.g. Ni-YSZ and Ni-GDC, are prone to carbon deposition onto nickel, as a result of the Boudouard reaction (CH4cracking, disproportionation of CO), leading to low activity and fast degradation.

In this study, a class of Au-modified commercially available NiO/GDC and NiO/YSZ cermet powders has been developed and studied for their performance and tolerance to carbon deposition, operating as SOFC anodes for CH4 steam reforming, as well as bi-functional electrodes in a Regenerative SOFC operating on the CO2 cycle (SOEC mode: electrolysis of CO2, SOFC mode: electrochemical reaction of CO and oxygen for power generation). In- situ HT-XRD tests revealed that the presence of Au, in an optimum nominal loading of 3wt%, affects the Ni crystal phase and has a significant positive effect in inhibiting carbon deposition. The results from cell testing in the temperature range of 800-1000°C, showed promising, stable performance of electrodes under carbon forming conditions (e.g. H2O/CH4=0.25, CO or CO/CO2mixtures of 0.7/0.3).

The work is supported by the FCHJU project T-CELL (298300).
Effects of Current Collector Materials on Performances of Micro-Tubular Solid Oxide Electrolysers for Splitting CO2
Authors: Kleiminger Lisa , Kelsall Geoff H. , Li Tao , Li Kang
Published: February 2020

As renewable energy sources are inherently intermittent, their increasing contributions to electricity grids will necessitate large-scale energy storage to balance supply and demand. Storing electrical energy in chemical bonds by electrolysis of CO2 and / or H2O is one option to achieve this. We chose solid oxide reactors for this application, inter alia, because in principle they can be operated cyclically in electrolyser (SOE) and fuel cell (SOFC) modes.

Results will be presented of measurements of ohmic and electrode polarization resistances and global performances for CO2 splitting to CO and O2 in micro-tubular solid oxide electrolysers (SOEs), with different types of current collectors; electrolysis of steam and (CO2 + steam) exhibited similar behaviour.

Silver or nickel wire current collectors, with and without silver or nickel paste, were used to contact the 220 μm thick inner lumen Ni-YSZ electrode (SOE cathode) of micro-tubular solid oxide electrolysers [1] (SOEs: Ni-YSZ|YSZ|YSZ-LSM|LSM) incorporating 34 μm thick yttria-stabilized zirconia (YSZ) electrolyte, and 40 μm thick lanthanum strontium manganite (LSM, SOE anode), as described previously for CO2 reduction [2]. Silver wire and paste was used as the current collector for the LSM electrode.

As shown in Fig. 1, the best performance (ca. 1 A cm-2 at 1.5 V (thermo-neutral potential difference) at 800 °C) was achieved for reactors with nickel wire current collectors alone, implying metallic pastes had no net beneficial effects on area-specific ohmic resistances. Furthermore, applying silver paste had a detrimental effect on the Ni cathode polarization resistance, for reasons that will be presented. Fig. 2 shows polarization and ohmic resistance data at open circuit; similar behaviour was exhibited with potential differences applied to reactors. Ohmic resistances were expected to decrease by using silver wire, due to its higher electronic conductivity compared to nickel, but no stable cell performance was achieved.

References

[1]    L. Kleiminger, Ph.D. Thesis, Imperial College London, to be published (2015).

[2]    L. Kleiminger, T. Li, K. Li and G. H. Kelsall, RSC Adv., 4 (2014) 50003-50016.

Figure 1
Laser Modification of Micro Porous Layers Used in Polymer Electrolyte Membrane Fuel Cells
Authors: Schulze Mathias , Biswas Indro , Gazdzicki Pawel
Published: February 2020

In polymer membrane fuel cells (PEMFC) the performance as well as the degradation strongly depends on the water balance inside the fuel cell. The membrane must be humidified for a sufficient ion conductivity, but on the other side the excess product water needs to be removed from the fuel cell in order to avoid flooding of the pore system.

The gas diffusion layer (GDL), which also provides contact to the electrochemically active components, has to achieve the passive management of the water balance. The adjustment of the hydrophobicity of the GDL is crucial for stable operation, and non-uniform hydrophobicity has already been shown to be advantageous.

Typically, gas diffusion electrodes for polymer electrolyte fuel cells (PEFC) consist of conductive medium, either a carbon based powder in the microporous layer (MPL) or carbon felt/fibres/cloth in the macroporous backing, and a hydrophobicity impregnation agent like polytetrafluoroethylene (PTFE). The ratio of these components determines the hydrophobicity, which effects the performance. The MPL was modified by laser irradiation. The effect of the laser radiation on the MPL were characterized by x-ray photoemission spectroscopy, Raman and infrared absorption spectroscopy and correlated to the change in the hydrophobic properties.

In particular, non-uniform hydrophobicity was applied and also tested in PEMFC. The introduction of channels of reduced hydrophobicity leads to several benefits. The observed current density distributions became more homogeneous than that of MPL without additional modification. Thus, the area with extreme current densities decreases, resulting in a more homogeneous ageing and, consequently, in an improved lifetime. Moreover, this modification leads to distinct performance increase in certain combinations of CCM and GDL. As an additional finding, not every combination can be improved, or is even performing well.

Acknowledgements

The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) for Fuel Cell and Hydrogen Joint Technology Initiative under Grant No. 303446 (IMPALA).
Design of Electrochemical Cell for in-Situ X-Ray Microscopy Study for Energy Materials
Authors: Ge Mingyuan , Yan Hanfei , Huang Xiaojing , Chu Yong S
Published: February 2020

In-situ characterization of electrode material under electrochemical reaction provides the unique opportunity to understand the material structure evolution under operation condition, which gives fundamental understandings of the material property and its relation to battery performance. By taking advantages of the state-of-art synchrotron X-ray techniques, it is highly accessible to investigate the chemical information and structural information with high spatial resolution and sensitivity when a suitable electrochemical cell is designed. In this work, we proposed a cell design that is capable to do 3D tomography, X-ray absorption spectra (e.g. XANES and EXAFS), and powder or single crystal diffraction under electrochemical reaction. Specifically, we will take the advantages of using Hard X-Ray Nanoprobe (HXN) with a spatial resolution of 15 nm that is recently commissioned at National Synchrotron Light Source-II to investigate the phase transition of LiFePO4 and stress-strain analysis of other electrode materials through nanodiffraction.
Investigate of Cr Caused Degradation for SmxSr1-XMnO3 Cathode in the SOFC Atmosphere
Authors: Pu Jian , Xiong Chunyan
Published: February 2020

Solid Oxide Fuel Cell(SOFC) is a high efficiency, environmental friendly energy exchange equipment . Interconnect  is one of the necessary components in SOFC. However, the Cr evaporate from interconnect may react with cathode material and lead to severe degradation of SOFCs. This study demonstrate the significant effect of Cr- poisoning on the performance of SmxSr1-xMnO3(SSM) cathode. After 200h long-term aged with Cr at open circuit potential and short term test  under cathodic current , the SSM always shows very slow Cr caused degradation rate and low polarization resistance at 750℃. This results indicate that  the SSM is a promising candidate cathode material for SOFCs. The remarkable high anti-Cr poisoning effects may ascribe to the Sm in A site of ABO3  perovskite has smaller size which lead to  more robust bonding.
Performance Enhancement of a Direct Carbon Fuel Cell
Authors: Li Chengguo , Lee Donggeun
Published: February 2020

A new type of high-temperature fuel cell using solid carbon as fuel, which is called a direct carbon fuel cell (DCFC), has recently attracted scientific and industrial attention due to its excellent electrochemical efficiency, less production of CO2, and no need of CO2 separation. However, the state-of-the-art technology of the DCFC is still in an idea-developing stage, mainly because of fuel-related difficulties: discontinuous fuel supply and very limited formation of a triple-phase boundary. Hence, this study was devoted to developing a new way to maximize the formation of TPBs by using a porous Ni anode and realizing continuous fuel supply through various methods.
Study on Electrochemical Analysis of Supercapacitor Electrodes Containing Modified Reduced Graphene Oxide and Titanium Dioxide
Authors: Kim Seok , Jo Eun-saem , Kim Hoeseung , Jung Yongju
Published: February 2020

Graphene has attracted tremendous attention in spacious energy storage fields due to its high conductivity, excellent electrical and mechanical stability, and large specific surface area [1]. However, graphene shows lower electrochemical performance than theoretical reports because of restacking or agglomeration induced by strong van der Waals interactions between adjacent layers. To prevent this phenomenon and improve electric properties, transition metal oxides or hydroxides are generally introduced into the interlayer of graphene [2]. Among diverse transition metal oxides, TiO2 which has numerous advantages such as a high specific energy density, strong oxidizing power, low cost and environment friendly considered as a promising electrode material. In reported study, TiO2 / rGO composite was synthesized by two-step method [2]. Herein, we firstly designed a facile one-step method through the sol-gel approach to synthesize TiO2 / rGO composites, and they exhibited excellent electrochemical performances.

   Graphite oxide (GO) was synthesized by a modified Hummers method [3] and as reported before [4-5]. GO was dispersed in DI water and sonicated for 30 min. The mixture of titanium (IV) isopropoxide (TIP), ethanol and acetic acid added in the GO solution. Ammonium hydroxide was then added until pH 8~9 in dropwise under stirring for 1 hour at room temperature to form a brownish-black suspension. After this process, the obtained solution was sealed into a Teflon lined stainless steel autoclave at 160ºC for 3 hours. We can finally obtained TiO2 / rGO composite after filtering, washing and drying in air at 60ºC for 12 hours.

   We analyzed morphological properties of the synthesized composites using scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy (FT-IR). We confirmed TiO2 / rGO hybrid composites were well anchored on the interlayer of the graphene nanosheets. We also examined electrochemical performances of the composites with cyclic voltammetry (CV), electrical impedance spectroscopy (EIS) and galvanostatic charge-discharge curve. We studied a facile one-step sol-gel method for synthesis of titanium dioxide (TiO2) / reduced graphene oxide (rGO) composite. In conclusion, the as-prepared composite can be considered as promising electrode materials owing to high capacitance and long cycle life.

Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning, Korea (Grant No.: NRF-2011-0009007).

References

[1]  W. L. Zhang, H. J. Choi, Chem. Commun., 47 (2011) 12286.

[2]  A. Ramadoss, S. J. Kim, Carbon, 63 (2013) 434.

[3]  W. S. Hummers Jr., R. E. Offeman, J. Am. Chem. Soc., 80 (1958) 1339.

[4]  J. Kim, S. J. Park, S. Kim, Carbon Lett., 14 (2013) 51.

[5]  Y. Kim, S. Kim, Electrochimica Acta, 163 (2015) 252.
Ta-Mo Isomorphous Alloy Systems for Metal Gate Apllications
Authors: Yu Hung-Yi , Deng Yong-Jhong , Lai Yi-Sheng
Published: February 2020

Tantalum-molybdenum (Ta-Mo) thin films with various compositions are deposited on Si and HfO2/Si substrates by rf (radio frequency) magnetron sputtering. The isomorphous Ta-Mo thin film shows an amorphous structure with Mo/Ta rf power at 20/80 W. It is reported that an amorphous structure of gate electrodes can reduce threshold voltage variability among different devices, caused by different orientations of polycrystalline grains [1]. This amorphous layer may eliminate the effect for the fabrication of next generation CMOS devices.

Different thicknesses of HfO2 dielectrics (20, 40, 60, 80, and 100 Å) are obtained by metal-organic chemical vapor deposition. The Ta-Mo thin films are deposited on HfO2/Si by cosputtering Ta and Mo targets. The composition of Ta-Mo alloys are controlled by varying the rf power (0/100, 20/80, 40/60, 60/40, 80/20, 100/0 W) on Ta and Mo targets. After that, a TaN layer is deposited on Ta-Mo layers to form a TaN/Ta-Mo/HfO2/Si MOS capacitor. The capacitor is further annealed at 400oC in a N2-H2 mixture for 30 min to study the thermal stability of the gate structure. The crystal structure is identified by grazing incident angle X-ray diffraction. Chemical bonding of Ta-Mo films is characterized by X-ray photoelectron spectroscopy. The resistivity is measured by using a four-point probe. Electrical properties of the MOS capacitors are characterized by capacitance–voltage (C-V) measurements. The work function is extracted from the C-V curves with different thicknesses of HfO2.

The GIAXRD result suggests that the Ta and Mo phases appear for Ta-Mo films deposited with Mo/Ta rf power at 0/100 W and 100/0 W, respectively. Both of them are body-centered cubic (BCC) structures. For Ta-Mo thin films deposited with different Mo/Ta rf powers, the structures are also BCC structures, except for film deposited with Mo/Ta rf powers at 20/80 W. It exhibits an amorphous structure. In addition, the lattice constant decreases but the grain size increases as the rf power on Mo targets increases. The physical properties of Ta-Mo films and the effective work functions of the bilayer TaN/Ta-Mo gate electrodes will be addressed.

[1] M. E. Grubbs, X. Zhang, M. Deal, Y. Nishi, and B. M. Clemens, Appl. Phys. Lett. 97, 223505 (2010).

Figure 1
Dry and Wet Processed Interface Layer in Ge/High-K Devices Studied by Deep Level Transient Spectroscopy
Authors: Ding YI Ming , Misra Durga
Published: February 2020

In this work, dry and wet processed interface layer quality in Ge/High-K MOS structure (1) were studied by deep level transient spectroscopy (DLTS) (2). The MOS devices were pulsed from mid-bandgap to accumulation region, then return to mid-bandgap to obtain the majority carrier trap emission information. Figure 1(a-c) shows the DLTS data for three corresponding interface treatment. The Arrhenius plots are shown in Figure 1(d). Comparing the DLTS spectrum, it can be concluded that dry processes have discrete border traps at the interface (H3 and H5). No such traps at the interface of wet processed MOS devices were observed. For all three samples, however, interface like traps were detected (H1, H2, H4). The defects density was estimated by Eq. (1), where  is obtained from CV plot using measured . The results suggest that it is around 1013 cm-2/eV for all three samples. This further confirms that the origin of interface state density, Ditobserved for these samples (1) are mainly due to these traps. The time constants in the order of milliseconds were also previously observed. Table I summarizes the Energy levels and cross-sections of these traps.                                                  (1)

Acknowledgement:The authors would like to thank K. Tapily, R. D. Clark, S. Consiglio, C. S. Wajda, and G. J. Leusink of TEL Technology Center, Albany, NY, for supplying devices and helpful discussions.

Table I. Arrhenius plot fitting results

 
H1
H2
H3
H4
H5

ET-EV (eV)
0.16
0.1
0.18
0.04
0.45

 (cm2)a

6.3×10-17

1.3×10-19

3.6×10-19

5.8×10-21

8.6×10-13

a Cross section is calculated by assuming = 1020 cm-2 s-1K-2.

 

Figure 1. Deep level transient spectrum of (a) simple chemical oxidation (Chemox), (b) chemical oxide removal (COR) followed by 1 nm oxide by slot-plane-antenna (SPA) plasma (COR&SPAOx), (c) COR followed by vapor O3 treatment (COR&O3).  (d) shows the Arrhenius plots for all three samples.

References

1. Y. Ding, D. Misra, M. N. Bhuyiana, K. Tapily, R. D. Clarkb, S. Consigliob, C. S. Wajda and G. J. Leusink, ECS Transactions, 69, 313 (2015).

     2.    D. V. Lang, Journal Of Applied Physics, J. Appl. Phys., 45, 3203 (1974).

Figure 1
Ru Film Characterization Correlated to Advanced CMP Slurry Performance
Authors: Stender Matthias , Derecskei Bela , Schlueter James A
Published: February 2020

Ruthenium has been considered as a barrier liner film for copper in advanced back-end-of-the-line (BEOL) metallization schemes in particular for the 10 nm and beyond technology nodes [1]. Ru shows a lower resistivity than traditionally used barrier films such as Ta or TaN [2] as well as negligible solubility with Cu [3] and Ru films can be deposited with a variety of techniques like CVD or PVD [4], which makes it an attractive candidate. However, new advanced BEOL barrier CMP slurries will have to be developed for this application and Ru is considered a very hard material and chemically inert. Hence it is a big challenge to develop advanced node Ru CMP slurries.

Since Ru films can be deposited with various deposition techniques and onto different substrates the removal rate response of these different films to a given slurry can also be dramatically different. For example we found that the removal with a standard Cu-barrier slurry without any additional additives on Ru film type A was only 20 Å/min whereas it was 200 Å/min on the type B film even though both films had been deposited by PVD. Further investigation of the two films showed that the morphology and in particular the grain size was quite different as shown in the SEM images below.

Interestingly, these two images correlate very well with images in [5] of two films which have been deposited at different plasma pressures and the difference in removal rate can be explained by different residual stresses in the two films as a result of the different plasma pressures.

In this paper we will present the characterization of several different Ru films by XRF (film density), XRD (crystal structure), SEM (grain size and structure), AFM (surface roughness), XPS (atomic composition), contact angle (surface energy) and film hardness by micro/nano indentation. The analytical results will be correlated to CMP polishing performance and in particular on how the different films respond to rate boosting additives in the slurry. The goal is to be formulate a customized slurry by understanding the properties of individual Ru films.

References:

1) C.-C. Yang, S. Cohen, T. Shaw, P.-C. Wang, T. Nogami, and D. Edelstein, IEEE Electron Device Lett., 31, 722 (2010).

2) G.K. Schweitzer, L.L. Pesterfield, The Aqueous Chemistry of the Elements, Oxford, 2010.

3) O. Chyan, T.N. Arunagiri, T. Ponnuswamy, J. Electrochem. Soc., 150 C347 (2003).

4) H. Li, D.B. Farmer, R.G. Gordon, Y. Lin, J. Vlassak, J. Electrochem. Soc. 154 D642 (2007).

5) A. S. Alagoz, J.-D. Kamminga, S. Y. Grachev, T.-M. Lu, T. Karabacak, MRS Proceedings 2009

Figure 1
Bubble Tolerant Liquid Management
Authors: Young Alan
Published: February 2020

Initially CMP slurries were hand mixed in small quantities and drawn from buckets at the back of the tool using peristaltic pumps.  Batch to batch variations adversely affected yields as did pulsatile dispense.

Eventually, automated, batch verified, basement blending and loop distribution systems came into use.  These systems reduced batch to batch variation but, still relied upon peristaltic pumps for dispense volume control.

Particle generation from tubing and high chemical cost drove a need for a change at sub-micron (90 Nanometer) geometries.  Various flow control schemes were evaluated including paddle wheel, turbine and differential pressure based systems ultimately settling on ultrasonic based flow controllers as the preferred technology.

However, as feature sizes continue to shrink, the chemistries required to achieve smaller feature sizes becomes more and more exotic.  Mixtures including peroxides and hydroxides naturally out-gas which produce bubbles in the dispensed flow streams, and in some cases results in a two-phase flow regime.  At comparatively low volumetric void fractions bubble concentrations (less than 10%) can adversely affect measurement accuracy of DP, Paddle Wheel, Turbine or Ultrasonic flow measurement technologies to the extent that many of these flow measurement technologies cease to operate satisfactorily.

Malema has developed a mass based, flow controller for slurry and clear chemical dispense applications.  Based on Coriolis mass flow rate measurement, the Malema Coriolis Mass Flow Controller (CMFC) is essentially bubble tolerant. 

Flow meter / flow controller manufacturers used an assortment of software techniques to filter the effects of these entrained bubbles with limited results.  Since Coriolis measures mass directly, bubbles have very little effect on measured or dispensed volumes.  

A brief history of the Coriolis Effect, how it is applied to direct mass flow rate measurements will be presented and discussed including a description of Malema’s family of CMFCs and associated performance data.
Improvement of the Cycling Performance of Sulfur Cathode Active Materials By Dual-Conducting Polymer Coating
Authors: Lee Yoon-Sung , Jeong Tae-Gyung , Jung Hun-Gi , Chung Kyung-Yoon
Published: February 2020

Lithium-ion batteries (LIBs) as highly efficient energy storage devices have been utilized as large capacity power sources in various devices. The conventional LIBs rely on intercalation compounds as cathode materials, which have limited specific energy density of 150-200 Wh kg-1. However, the advent of electric vehicles and other high energy density applications require vast improvement in the energy density of current LIBs, which led to the search for cathode materials based on non-intercalation chemistries. Sulfur cathode is quite attractive for high energy density applications due to its advantages such as high specific theoretical capacity of 1675 mAh g-1, low cost, natural abundance, and environmental friendliness. Therefore, sulfur is considered as a promising high energy density cathode material for the next generation lithium-ion batteries. However, the poor cycle life of lithium-sulfur (Li-S) batteries due to the critical problems such as large volumetric expansion of sulfur upon lithiation, low ionic and electronic (5×10-30 S cm-1) conductivities and dissolution of lithium polysulfide into the electrolyte has been a significant hindrance for their commercialization. Recently, significant efforts have been paid to improve the cycling performance of Li-S batteries by suppressing the dissolution of polysulfide from sulfur active material and preventing the shuttling of lithium polysulfides to the anode side. Moreover, lithium polysulfide leads to serious lithium anode corrosion resulting in low coulombic efficiency. To solve these problems, extensive studies have been carried out by surface coating of cathode active materials with conductive polymers such as poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPY), and polyaniline (PANI). Surface modification of cathode active materials with conductive polymers is easy and effective way to enhance their electronic conductivity, thermal stability and electrochemical properties. Recently, we demonstrated that the cathode material coated with dual-conductive polymer can exert a significant influence on the cycling performances of lithium-ion batteries [1,2]. In the current work, we report the enhanced cycling performance and high rate performance of sulfur active cathode materials by surface modification with dual-conductive polymeric materials. The presence of protective conductive layer formed on the cathode suppresses the dissolution of lithium polysulfides on the cathode side resulting in more stable cycling characteristics when compared with those of pristine cathode material. Detailed synthesis procedure, characterization of the materials and electrochemical performance will be presented.

References

[1] S. H. Ju, I. –S. Kang, Y. –S. Lee, W. K. Shin, S. Kim, K. Shin, D. -W. Kim, ACS Appl. Mater. Interfaces., 6, 2546-2552 (2014).

[2] Y. -S. Lee, J W. K. Shin, A. G. Kannan, S. M. Koo, D. -W. Kim, ACS Appl. Mater. Interfaces., 7, 13944-13951 (2015).
(Invited) Three Dimensional Microstructure Measurements of SOFCs: Electrode Microstructural Evolution and Long-Term Durability
Authors: Barnett Scott A , Kennouche David , Wang Hongqian
Published: February 2020

Quantitative three-dimensional (3D) analysis of solid oxide fuel cell (SOFC) electrode microstructure has been shown to be a key means for connecting materials processing and electrochemical performance.  In addition, 3D imaging is being used to help observe and understand degradation mechanisms, important for developing degradation models that can predict long-term cell stability. This paper will describe 3D electrode tomography measurements, of various electrodes including Ni-Y-stabilized Zirconia (Ni-YSZ), (La,Sr)MnO3-YSZ, and (La,Sr)(Fe,Co)O3 (LSCF), made using focused ion beam scanning electron microscopy and transmission x-ray microscopy. Results on electrode structural evolution, and how the microstructure impacts electrochemical performance, will be described.  For the Ni-YSZ case, measured particle coarsening during high-temperature ageing is correlated with decreases in three-phase boundary density and increases in polarization resistance and a model developed to predict long-term degradation.  For LSCF, depending on ageing time and temperature, either particle coarsening or SrO surface segregation can impact electrode performance degradation.
Infiltrated CsH2PO4-Carbon Nanotube Composites for High Performance Solid Acid Fuel Cathodes with Low Pt Loading
Authors: Papandrew Alexander B. , Elgammal Ramez Ahmed , Tian Mengkun , Dyck Ondrej , Tennyson Wesley Daniel , Armstrong Beth L , Duscher Gerd , Veith Gabriel M , Zawodzinski Thomas A.
Published: February 2020

Fuel cells based on the inorganic proton conductor CsH2PO4 (CDP)1 have the potential to be efficient devices for intermediate-temperature (230-260 °C) distributed generation applications2. Realizing this potential is contingent on the development of next-generation electrodes with significantly higher activity and lower precious metal content than the state of the art.    

            Current SAFC electrodes are based on a porous framework of the CDP electrolyte functionalized with an interconnected film of platinum nanoparticles that serves as both the ORR catalyst and the electronic conductor3. The activity of these electrodes scales with the surface area of the electrolyte in the electrode2, but the requirement of a percolating Pt network also unfavorably scales the precious metal content of these high surface area electrodes.

            We have addressed this problem by developing a new electrode concept based on a multi-step, multiphase infiltration strategy.  The CDP electrolyte is first infiltrated in the liquid phase into chemically-treated multi-walled carbon nanotube (MWNT) bundles, followed by vapor-phase Pt deposition on the nanocomposite structure.  In addition to exerting a structural templating influence on the solid electrolyte, the role of electronic conduction is assumed by the MWNTs, allowing for much greater tri-phase boundary densities to be obtained at lower Pt content. 

            Cathodes formed from these nanocomposite materials can exceed the activity of the state-of-the-art cathode (2.8 mgPt/cm2) at a fraction of the Pt content (0.7 mgPt/cm2) (see Figure 1a).  Pt utilization is increased at lower Pt loadings, with Pt mass-specific activity greater than 1 A/mgPt at 0.5 V possible at 0.35 mgPt/cm2 (Figure 1b).  Cells based on this architecture are stable for greater than 150 hours at 0.6 V and 250 °C.

Acknowledgments

This work is supported by ARPA-E via cooperative agreement DE-AR0000499.

References

1 S.M. Haile, C.R.I. Chisholm, K. Sasaki, D.A. Boysen, and T. Uda, Faraday Discuss. 134, 17 (2007).

2 C. R. I. Chisholm, D. A. Boysen, A. B. Papandrew, S. K. Zecevic, S. Cha, K. A. Sasaki, Á. Varga, K. P. Giapis, and S.M. Haile, Electrochem. Soc. Interface 18, 53–59 (2009).

3 A. B. Papandrew, C. R.I. Chisholm, R. A. Elgammal, M. M. Özer, and S. K. Zecevic, Chem. Mater. 23, 1659–1667 (2011).

Figure 1