bluuebunny/crossref_metadata_2025 huggingface dataset:
Strain Engineering and Two-Dimensional Electron Gas in Polar ε-Ga2O3
Authors: Cho Sung Beom , Mishra Rohan
Published: February 2020

As a wide gap semiconductor, Ga2O3 is rapidly emerging as a promising candidate for power electronics applications. While most of the studies have focused on its stable β-phase, there are a handful of reports on its metastable polar ε-phase having a spontaneous polarization. Numerous experimental groups have recently attempted to stabilize ε-Ga2O3 using epitaxial strain using substrates such as Al2O3(0001)1, GaN(0001)1, AlN(0001)1, MgO(111)2 and SiC(0001)3. However, due to the lack of an understanding of the stability of various Ga2O3 phases under epitaxial strain, these trial-and-error based attempts have been of limited success. All the films are observed to be of inherently poor quality. There are also diverging reports on the structure and properties of the deposited thin films. A recent experimental report of ε-Ga2O3 grown on Al2O3 substrate has even suggested the film to be ferroelectric, where the direction of the spontaneous polarization could be switched with an external electric field. It implies that the stabilization of ε-Ga2O3 will open new avenue of polarization engineering in Ga2O3 power electronics4.

We have used first-principles density-functional theory (DFT) calculations in combination with coincidence site lattice theory to develop a phase-diagram of Ga2O3 under epitaxial strain. We show that all the previously used substrates impose an epitaxial strain over 3% on ε-Ga2O3, which explains the poor structural quality of the deposited thin films. In this presentation, we will discuss promising commercially available substrates that can stabilize ε-Ga2O3 with epitaxial strain < 1 %. We will discuss the electronic structure of ε-Ga2O3 under epitaxial strain, including properties such as the band gap, polarization constants and its ferroelectric nature. We will theoretically demonstrate a way to achieve two-dimensional electron gas (2DEG) in ε-Ga2O3 heterostructure simply by using polarization engineering. The formation of 2DEG is due to the polar catastrophe, and the formation and sheet charge density 2DEG can be controlled by thickness of ε-Ga2O3 and its polarization direction. Our study highlights the potential of the polar behavior of ε-Ga2O3 and suggest pathway to realize its stabilize epitaxial growth.

Y. Oshima, E.G. Víllora, Y. Matsushita, S. Yamamoto and K. Shimamura: Journal of Applied Physics
118, 085301 (2015).

2. H. Nishinaka, D. Tahara and M. Yoshimoto: Japanese Journal of Applied Physics
55, 1202BC (2016).

X. Xia, Y. Chen, Q. Feng, H. Liang, P. Tao, M. Xu and G. Du: Applied Physics Letters
108, 202103 (2016).

F. Mezzadri, G. Calestani, F. Boschi, D. Delmonte, M. Bosi and R. Fornari: Inorganic Chemistry
55, 12079 (2016).
Solid-State Diffusional Behaviors of Functional Metal Oxides at Atomic Scale
Authors: Chen Jui-Yuan , Huang Chun-Wei , Wu Wen-Wei
Published: February 2020

Metal/ metal oxides have attracted extensive research interesting due to their combination of functional properties and compatibility with industry process. The diffusion and thermal reliability become essential issues that requiring detailed study for developing the atomic scaled functional devices. In this work, the diffusional reaction behaviors are investigated that transformed piezoelectric ZnO into magnetic Fe­3O4 at atomic scale. The growth kinetics of metal oxide have systematically studied through macro to micro analysis. The growth rates are evaluated from morphology change, which can realize that the growth behavior is either a diffusion- or reaction- controlled process. Besides, the atom attachment on kink step are observed at atomic scale, which has important implications for thermodynamics in functional metal oxides. The faster growth planes simultaneously become smaller, which results in remaining of low surface energy planes. These results exhibit directly observing the atomic formation process of metal oxide via solid state diffusion. In addition, the nanofabricated method provides a novel approach to investigate metal oxide evolution, and sheds light on the diffusion reaction behavior. More importantly, the results and phenomena of this study provide significant inspiration on materials stability and reliability for the metal/oxide-based devices.

Figure 1
Effect of Phosphor Layer Size on the Optical and Thermal Properties of Chip Scale Packaged Light-Emitting Diodes
Authors: Bak Gyu Hyeong , Oh Sun Woo , Sung Hyun Ho , Kim Won Jung , Yoon Sukbum , Jeong Hwanhee , Song June-O , Seong Tae-Yeon
Published: February 2020

Light-emitting diodes (LEDs) have been widely applied for backlight unit for displays, general lighting, and automotive illumination because they have a high light efficiency and long life time, and are environmentally friendly. These diverse applications require smaller and slim LED chip scale packages (CSPs). CSP LEDs have been developed to produce white LED chips by forming a thin phosphor film on blue LED chips. In this study, we investigated the effect of phosphor layer thickness and area on the optical and thermal properties of the CSP LEDs. The phosphor-conversion of chips is maximized by varying the thickness and area of the phosphor layer. Eight different types of phosphor-converted white CSPs with normal performance (CRI > 70, CCT ~ 5700 K) were prepared by using mixed multicolor phosphor materials. In other words, for five samples whose CSP area was fixed at 1.8 x 1.8 mm2, flip-chip area was 1.4 x 1.4 mm2, and flip-chip thickness was 250 μm, the thickness of the phosphor layers was varied from 100 to 500 μm at intervals of 100 μm. For other three samples where the phosphor layer thickness was fixed at 300 μm, the flip-chip area was 1.4 x 1.4 mm2, and flip-chip thickness was 250 μm, the CSPs had three different areas of 1.6 x 1.6, 1.8 x 1.8, and 2.0 x 2.0 mm2. First, the relative luminous flux and LED beam distribution were characterized using integrating sphere and a goniometer. It was shown that as the thickness of the phosphor layer increased, the luminous flux and the directivity angle increased. On the other hand, as the CSP area increased, the luminous flux and the directivity angle decreased. This could be attributed to the fact that CSP does not have a reflector (namely, a housing material) and so the blue light of the chip does not excite the whole area of the phosphor. This may be confirmed by the images showing light distribution and luminescence characteristics, which is currently under investigation. Furthermore, a junction temperature measurement system was used to characterize the junction temperatures of the five different samples whose phosphor layer thicknesses were varied from 100 to 500 μm. It was found that when the thickness of the phosphor layer exceeded the thickness of the chips (250 μm), the junction temperature of the samples dramatically increased. Further details regarding the phosphor layer thickness of the junction temperature characteristics will be investigated and described.
Transport in Low Pt-Loading Cathodes: The Impact of Electrode and Catalyst Support Morphology
Authors: Litster Shawn
Published: February 2020

This tutorial will focus on recent learning by the polymer electrolyte fuel cell (PEFC) research community on the impact of electrode and catalyst support structure on the transport processes and voltage losses in low Pt-loading cathodes. This includes the porous electrode structure, but also the catalyst support morphology and how carbon supports of varying surface area impact the catalyst utilization and local transport losses. The tutorial will cover the distinct differences between medium surface area supports (e.g., Vulcan carbon black) where the Pt primarily resides on the exterior of the carbon versus high surface area supports (e.g., Ketjen black) that feature a high proportion of internal Pt. The discussion on morphology will include the current understanding of ionomer distributions within the electrode and over the catalyst and support surfaces. The tutorial will also cover the current understanding of oxygen and proton transport mechanisms at the catalyst and support length-scales, with particular attention paid to the transport of reactants through non-electroneutral water domains to the internal catalyst surfaces embedded within the porous carbon support. Maintaining the active surface area and catalytic activity of the catalyst is paramount to achieving good high current density durability, thus the tutorial will also cover aspects of Pt migration and alloying element dissolution that relate to low Pt-loading and catalyst support selection.

Figure 1
Toward Ionomers for Low Pt Performance
Authors: Novitski David , Holdcroft Steven
Published: February 2020

The role of the ionomer in catalyst layers is critical to the performance of PEM fuel cells. Attention needs to be paid not only to the inherent properties of the ionomer but also to the choice of dispersing solvent and the catalyst support, as these also control the porosity and proton conductivity of the catalyst layer in conjunction with the ionomer. The ionomer also influences electrochemical FC kinetics through its influence on surface adsorption and gas permeability. Mass transport of oxygen in cathode catalyst layers (CCLs) is of particular importance in achieving high current densities in proton exchange membrane fuel cells. The technical push toward low platinum loading in CCLs has resulted in a disproportionate transport resistance attributed to oxygen transiting through thin ionomer films to reach active platinum sites. The replacement of PFSA ionomer in the catalyst layer with hydrocarbon ionomers is thus particularly challenging as this often decreases electrochemical fuel cell kinetics and mass transport. For these reasons, permeability phenomena of oxygen at the ionomer/platinum interface has gained renewed interest. Electrochemical techniques, such as potential step chronoamperometry at microelectrodes, will be shown to be a useful to probe oxygen diffusion and oxygen solubility at catalyst/membrane interface. Data obtained under different conditions and with different ionomers is useful for understanding oxygen transport resistance through ionomer films in the context of low platinum loaded cathode catalyst layers
The Influence of the Platinum Loading and the Ionomer to Carbon Ratio on the Durability of the PEMFC
Authors: Andrea Vinicius , Santiago Elisabete I. , Fonseca Fabio C. , Linardi Marcelo
Published: February 2020

Cost and durability are the major barriers to the success of the Proton Exchange Membrane Fuel Cells (PEMFCs), and reducing the platinum loading of the catalyst layer could reduce the cost of the device. Thus, in this work, long-term durability tests in constant-current mode were performed using single-cells of 25 cm2 with Membrane Electrode Assemblies (MEAs) prepared with 20% Pt/C (BASF) catalyst and electrodes with platinum loadings of 0.4 and 0.1 mgPt.cm-2. Different ionomer to carbon ratios were also studied with the electrodes containing 0.1 mgPt.cm-2 of catalyst loading. To characterize the electrochemical and structural properties of the MEAs, cyclic voltammograms, electrochemical impedance spectroscopy and field-emission scanning electron microscopy were utilized before and after the long-term durability tests. Concerning the platinum loading, the electrodes prepared with 0.1 mg Pt cm-2 have lost proportionally more electrochemical surface area than the ones prepared with 0.4 mg Pt cm-2 but at the same time, the electrodes with the lowest platinum loading presented lower irreversible performance loss rate when using higher ionomer to carbon ratio. The analyses made by several electrochemical techniques have indicated that the raise of the ohmic and mass transport resistances are the factors that most contribute to the irreversible performance loss, meanwhile the charge transport resistance due to the electrodes flooding is the main responsible for the reversible performance loss. The proportion of ionomer in the catalytic layer was studied and it was possible to infer that the highest ionomer proportion studied has contributed to mitigate the MEA degradation, although it facilitates the occurrence of flooding in the electrodes. Finally, it was observed that the quality of the contact formed between the electrodes and the membrane has remarkable influence on the PEMFCs durability.
(Invited) Electrochemical Generation of Fuels: Matching Research and Application for Advanced Water Splitting and Other Technologies
Authors: Ayers Katherine E , Gellett Wayne L. , Capuano Christopher B
Published: February 2020

Electrochemistry is becoming increasingly important in transitioning from primarily fossil fuel based energy sources to more renewable options. This challenge will require a combination of solutions, depending on geography, the mix of renewables, and other factors. The intermittent nature of wind, solar, and other forms of renewable energy, as well as demand fluctuations which do not match the generation capacity, drives the need for modular, distributed energy storage solutions, where electrochemistry can be ideal. However, for very long storage times, conversion of energy to a chemical fuel is often the most practical solution. Electrochemical generation of fuels such as hydrogen, ammonia, and CO2-derived hydrocarbons are all related and have similar R&D challenges. In addition, all of these chemicals have different advantages and disadvantages, and have benefits in different scenarios. This talk will focus on some of the considerations in developing a new electrochemical device, and research challenges applicable to low temperature electrochemical fuel generation.

While fundamental research in understanding electrocatalytic reactions at the molecular level is valuable from a basic science perspective, understanding the application requirements for each market, and pricing structure vs. scale, can guide application of this research to the next logical stage. There is a large application space for fuels and industrial chemicals with widely varying price points based on scale and requirements. For example, different ground vehicle classes (consumer vehicles, heavy duty trucks, fork trucks, industrial equipment etc.,) may each be best served by different fuels depending on power and range requirements as well as customer preferences. Ships and airborne vehicles may have different optimal solutions. Smaller scale or emerging markets such as unmanned vehicles may also serve as easier market entry points.

At the materials discovery stage, all of the above reactions require catalyst design and fundamental understanding in order to achieve high activity and efficiency. Specifically for ammonia and carbon-based fuels, selectivity is a key issue, and structural approaches to control the active site and competition for binding sites are being pursued. Beyond the catalyst, the electrode structure and integration also need to be designed for optimal performance, including effective fluid flow and catalyst access. While the individual catalyst composition and structures will be different, all of these pathways involve hydrogen or oxygen evolution reactions and ion exchange membranes, and can both leverage and inform electrolysis research. Proton’s work in these areas will be discussed, as well as key needs for additional research and collaborations between applied and fundamental science.
Power to Chemicals with High Temperature Solid Oxide Cells: Concepts, Challenges & Prospects
Authors: Costa Rémi , Han Feng , Lang Michael , Sata Noriko , Schiller Guenter
Published: February 2020

In the context of growing CO2 emissions, the need of more efficient low carbon technologies for energy storage and energy efficiency is pressing. Owing to their unique characteristics, ceramic based solid oxide cells present the valuable feature to be able of operating in fuel cell and electrolyzer mode. If the latter allows primarily efficient conversion of steam into hydrogen, it has the huge benefit of allowing co-electrolysis of CO2 and H2O into a valuable synthetic gas consisting in a mixture of CO and H2 that can be processed downstream into chemicals, for instance via the Fischer-Tropsch process. As practical operation requires a stable function of the electrochemical cells, it is of crucial importance to understand their behavior and the underlying degradation mechanisms in order to be able to identify countermeasures for improving durability.

In this context, the electrochemical behavior of solid oxide cells is being investigated at DLR, from cell to stack level, in different configurations ranging from steam electrolysis to co-electrolysis and reversible operation. In this respect fuel electrode supported cells and electrolyte supported cells have been operated in electrolysis and co-electrolysis mode in different short-term and long-term runs of more than 1000 hours of operation with various gas conditions, operating temperatures and current densities. The electrochemical behavior was investigated by electrochemical impedance spectroscopy while the degradation was monitored by chronopotentiometry. Post-test microstructural analysis of functional ceramic layers was systematically performed with scanning electron microscopy in order to correlate possible microstructural changes with degradation phenomena.

Among others, it is found that the standard Nickel / Yttria-Stabilized-Zirconia cermet in fuel electrode supported cells suffers irreversible degradation through Nickel agglomeration and Nickel depletion, a phenomenon which was found to be correlated with temperature and current density. In electrolysis operation, cracking within the electrolyte along the air electrode is often observed. The main degradation features will be presented and discussed on the basis of the key identified drivers. Advanced materials solutions to mitigate the degradation issues will be presented and prospective applications will be introduced.
Modeling and Test-Bed Development of Vapor Feed Electrochemical CO2 Reduction Devices
Authors: Xiang Chengxiang("CX")
Published: February 2020

Electrochemical CO2 reduction in vapor feed configurations has some unique opportunities and challenges in relative to aqueous electrolyte based devices. In particular, the vapor feed devices could achieve significantly higher operational current densities and could operate at high pH ranges that were un-favorable for aqueous electrolyte based devices due to the depletion of dissolved CO2 at the electrode surface.

In this talk, I will show some recent results on modeling and test-bed development of two vapor-feed device configurations. A multi-physics agglomerate model that describes the operational details for a gas diffusion electrode (GDE) based device, including the local CO2 concentration profiles, pH gradients, polarization losses, CO2 utilization challenges and impact on Faradaic efficiency due to hydrogen evolution reaction, will be discussed in detail. The modeling results were then compared to the performance of Cu nanoparticle based GDEs. As predicted by the model, Cu-GDEs operating at alkaline conditions for CO2 reduction and CO reduction exhibited significantly higher partial current density for C2 products generation than the planar analogy. The transformation of the Cu catalyst in GDE under various electrochemical potentials for CO2 reduction was also investigated by in situ X-ray absorption spectroscopy. In addition, a proof-of-concept, full vapor feed device for CO2 reduction to formic acid using a reverse-configured bipolar membrane to achieve advantageous product separation will be discussed.
The Role of Central Metal Atom and Ligand in Transition Metal Based Metal Organic Frameworks for Selective Electrochemical Reduction of CO2 to Value-Added Chemicals
Authors: Kolla Praveen , Kendrick Ian , Miller Todd , Mukerjee Sanjeev
Published: February 2020

Considering the rapid decline of the cost of renewable electrons (wind and solar), electrochemical conversion of carbon dioxide (CO2) to energy-dense or value-added chemicals with high selectivity (Faradaic efficiency >80%) is an increasing economic imperative. Despite the recent optimization efforts on noble, alkali, alkaline-earth and transition metal (TM) based electrocatalysts for efficient CO2 reduction, the rising cost of these metals (esp. noble metals) hinders large-scale commercialization. Recently, research into the electrocatalytic reduction of CO2 has focused on efficient and cost-effective catalysts such as metal-free, organometallic, hetero-atom doped or conducting polymers (1). Alternatively, electrocatalysts containing pyridinium derivatives have been proposed to avoid the overpotentials required for activating of carbon dioxide (via a high energy intermediate radical of CO2
-) and to promote CO2 reduction through successive proton-hydrate transfers (PT-HT) (2-4). To this end, Metal-Organic Framework (MOF) catalysts with central (TM based) heteroatom and surrounding pyridinic or pyrrolic ligands have been prepared and electrochemically characterized for selective CO2 reduction to methanol or carboxylic acids. In this study, the effect of electrolyte pH on reaction selectivity and reaction kinetics via Tafel analysis of the electrocatalysts were determined. Additional variables such as reactant’s partial pressure and phase, and electrolyzer temperature for optimum electrochemical reduction of CO2 will be also be discussed. This presentation will showcase our efforts to tailor electrocatalyst for value added chemicals such as methanol and formic acid. We will present electrochemical data such as Tafel kinetics and Faradaic efficiency in close concert with spectroscopy such as in situ Raman and Synchrotron X-ray Absorption.

Acknowledgements:

The authors gratefully acknowledge the financial support from arpa.e under the auspices of the REFUELS initiative. This grant lead by Sustainable Innovation (grant # DE-AR0000810) involves the participation of Northeastern University Center for Renewable Energy Technology as a catalyst partner. The authors also acknowledge instrumental support from Thermo Fisher Corp., and access to synchrotron based facility for x-ray absorption spectroscopy at National Synchrotron Light Source-II (NSLS-II) situated in Brookhaven National Laboratory (BNL), Upton, NY, under grant # DE-SC0012704.

References:

X. Mao and T. A. Hatton, Industrial & Engineering Chemistry Research, 54, 4033 (2015).

P. K. Giesbrecht and D. E. Herbert, ACS Energy Letters, 2, 549 (2017).

A. J. Morris, R. T. McGibbon and A. B. Bocarsly, ChemSusChem, 4, 191 (2011).

Y. Yan, E. L. Zeitler, J. Gu, Y. Hu and A. B. Bocarsly, Journal of the American Chemical Society, 135, 14020 (2013).
Local Atomic Modulation of Metal Sites Drives Efficient Electrochemical Reduction of CO2
Authors: Zheng Xueli , Sargent Edward H. , Cui Yi
Published: February 2020

Electrochemical reduction of carbon dioxide (CO2RR) has attracted intense research attention since it provides an avenue to the renewable-electricity-powered synthesis of value-added carbon-based fuels and feedstocks. Unfortunately, high selectivity in formate electrosynthesis has thus far only been achieved at the expense of low current density and high over-potential. Herein, we report a strategy to create high active sites in tin catalysts by incorporating copper and non-metal sulfur in an intimately integrated fashion. We hypothesized that the presence of copper and sulfur atoms in the catalyst surface could promote under-coordinated metal sites, and thereby improve the electrochemical reduction of CO2 to formate. We explored, using density functional theory, how the incorporation of copper and sulfur atoms into tin favours formate generation. The resultant under-coordinated tin sites accelerate CO2RR at record geometric current densities with a Faradaic efficiency of 93% and exhibit prolonged stability. Furthermore, the partial current density for formate on under-coordinated tin sites – normalized by electrochemically active surface area – is also three times higher than that of unmodified tin catalysts. X-ray absorption studies and density functional theory reveal the synergistic role of copper, sulfur and tin in producing local coordination and a consequent electronic structure that enhances electron capturing ability.
Beyond Flatland: Exploring 3D Cu Catalysts for CO2 Reduction
Authors: Vedharathinam Vedasri , Qi Zhen , Stadermann Michael , Biener Juergen , Biener Monika M.
Published: February 2020

The electrochemical CO2 reduction reaction (CO2RR) has become a promising path forward to a carbon neutral energy cycle by combining carbon capture with hydrocarbon production, especially if excess power from regenerative resources such as wind and solar is available and used. The key obstacle for deployment of the one-step electrochemical CO2RR technology is the development of low-cost electrocatalysts that facilitate energy-efficient production of hydrocarbons from CO2 with high selectivity and long-term stability. Here, copper has emerged as the most promising catalyst for the formation of hydrocarbons at ambient pressures and temperatures.

We have developed a unique expertise in the synthesis of nanoporous metal catalysts including nanoporous Cu (npCu) made from CuMn and CuZn alloys, Cu nanocube surface functionalizations and Cu-oxide/Cu nanowire forests (Fig. 1). Preliminary CO2RR tests of these materials have confirmed that oxidized npCu electrodes have a significantly increased transient reactivity towards the electrochemical reduction of CO2. We will discuss results using a novel electrochemical cell geometry that is designed to take full advantage of the high surface area of the catalyst.

Fig. 1: (a) NpCu prepared by dealloying CuZn alloys; (b) Cu nanocube surface functionalization of npCu; (c) Cu-oxide nanowires grown on Cu foam formed by annealing in air (1h @ 500C).

This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

Figure 1
Electrochemical Reduction of CO2 to Formate on Sn@Cu By Electrodeposition with Hydrogen Bubble Template
Authors: Hou Xiaofan , Liu Junyu , Zhang Qi , Zhou Yue , Qiao Jinli
Published: February 2020

In recent years, the emissions of carbon dioxide (CO2) into atmosphere caused by industrial production has been considered to be one of the main causes of global warming, which has recently attracted much attention1. Electrochemical reduction of CO2 could provide an attractive solution to this climate issue with CO2 converted into useful fuels such as formic acid, methane, methanol, ethylene, etc., which represents a value-added path that can simultaneously produce alternative fuels and remedy the carbon emissions generated by conventional fuels2. Metal catalysts have been demonstrated effectively and widely used materials to obtain formate by reducing CO2. Among these metals, tin or copper-tin alloys are excellent candidates regarding to CO2 electroreduction to produce formate fuel. However, the fabrication production of catalysts is complicated for practical application, as the synthetic process need high-temperature calefaction or the addition of expensive additives3.

Electrodeposition with hydrogen bubble template in aqueous solution is a facile, low-energy method, which can easily create a 3D structure so that can provide large specific surface area on the substrate. Meanwhile, the porous foam attributed to concurrent hydrogen bubbles with different deposition time has a distinct impact on the catalytic activity and selectivity during CO2 electrochemical reduction. By applying electrodeposition methods, we have successfully synthesized the Sn@Cu catalysts, which was controlled by simply adjusting the electrodeposition time. As demonstrated by both CV and LSV results, highly selective HCOO- production (Faradaic efficiency = 86.7%) can be realized at a potential of -1.6 V vs. SCE with really high current density greater than 10 mA cm-2.

References

[1]. J.L. Qiao; M.Y. Fan; Y.S. Fu; Z. Bai; C. Ma; Y. Liu; X.D. Zhou, Electrochim. Acta, 153, 559 (2015)

[2]. Y. Wang; J. Zhou; W. Lv; H. Fang; W. Wang, Appl. Surf. Sci., 362, 394 (2016)

[3]. X. Zhang; T. Lei; Y.Y. Liu; J.L. Qiao, Appl. Catal., B,
218, 46(2017)
Enhanced CO2 Electrochemical Conversion at Bi-Modified Pb Foams
Authors: Guay Daniel , Fan Mengyang , Garbarino Sebastien , Botton Gianluigi A. , Tavares Ana C
Published: February 2020

CO2 conversion methods to remediate anthropogenic emissions appear promising, as they offer the potential to produce liquid and gaseous fuels for use either in the aeronautics industry, or as a chemical storage method for intermittent energy produced by windmills and photovoltaic panels. Fuel synthesis may be achieved via either the production of a syngas mixture (H2 and CO) through the water gas shift reaction and subsequent conversion into hydrocarbon fuel, or by direct electrochemical reduction of CO2. Direct electrochemical conversion of CO2 into value-added products is a low-temperature process, with the advantage of requiring relatively simple equipment.

Formic acid, or formate salts, are used in a variety of chemical processes such as electrowinning, leather tanning, and aircraft de-icing. Alternatively, formic acid and formate salts may be considered as a hydrogen storage medium. On top of that, direct formic acid, and more recently direct formate, fuel cells, have been investigated as they demonstrate significant benefits over methanol fuel cells, including higher open circuit voltage and lower crossover.

Pb and Bi are promising catalysts with good selectivity for formate. In the case of lead, it can be prepared in the form of dendrites with nanometre-sized tips. Local high electric fields can exist at the tip of these dendrites that can induce a concentration of electrolytes which in turn leads to improve electroreduction of CO2 [[1]]. Bismuth is non-toxic and has negligible environmental impact. It has few commercial applications, and its price has been low and relatively stable in recent years.

In this work, we studied the activity and stability for CO2 electroreduction onto high surface area metallic Pb films. The latter Pb films were further functionalized by Bi overlayers to enhance CO2 reduction properties. For both materials, the material films were prepared through a potentiostatic method. Both types of films were extensively characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HR-TEM) and x-ray diffraction (XRD), while electrochemical activities were characterized by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and potentiostatic measurements.

[1] M. Fang, S. Garbarino, G.A. Botton, A.C. Tavares and D. Guay, J. Mater. Chem A 5 (2017) 20747-20756
Engineered Electrolyte-Electrocatalyst Nanocomposites for Enhanced CO2 Electroreduction
Authors: Elgammal Ramez A. , Zawodzinski Thomas A
Published: February 2020

The development of a viable approach to capture, store, and convert carbon dioxide into fuels and chemicals may offer a means to mitigate climate change while also creating value added commodity chemicals. Critical bottlenecks in existing technologies that have impeded commercialization of CO2 electrosynthesis include catalysts with high overpotentials and limited selectivities. Furthermore, current approaches often employ PEM-based electrolyzers that suffer from low CO2 solubility in acidic aqueous solutions, limiting mass transport and reaction rates, or AEM-based systems which have much higher CO2 solubilites in alkaline electrolytes, but have the added problem of membrane poisoning by bicarbonate and carbonate.

We have recently developed an electrochemical reactor that overcomes many of the shortcomings that have limited the above technologies. Our preliminary results suggest that onset potentials for CO2 reduction are more than 200 mV lower than with current densities in excess of 150 mA/cm2 at -1 V vs RHE. We have examined several cathode electrocatalysts and some of the most promising include a series of nanostructured mixed and/or doped transition metal and main group metal oxides that also suppress the hydrogen evolution reaction. We will present detailed electrochemical and structural studies and will comment on possible reaction mechanisms as well as the key features of the reactor that enable the enhanced kinetics.
Electrochemical Reduction of CO2 Facilitated By Vitamin-Based Catalysts
Authors: Budanović Maja , Webster Richard David , Urbancok Dejan , Er Yan Hui Jasmine
Published: February 2020

The electrochemical conversion of carbon dioxide to valuable fuels is in the focus of academic and industrial research due to increasing demand for greener alternatives. Thus far, pyridine has been shown as the most promising homogenous electrocatalyst in the electrochemical reduction of CO2 to methanol due to the low overpotential required to achieve faradaic yields of ca. 20%. Family of water-soluble vitamins B3 and B2 represent environmentally friendly class of electrocatalysts. Therefore, this study investigated the activity of nicotinic acid, nicotinamide and riboflavin to convert carbon dioxide to methanol (Figure). The optimization experiments revealed improvements in efficiency for methanol formation by varying the working electrode, electrocatalyst concentration, electrolysis duration and temperature. Vitamins B3 exhibit chemically reversible one electron reduction at ca. -0.5 to -0.6 V vs. Ag/AgCl with a Pt working electrode. The respective electrochemical systems are energy efficient with having overpotential less than 100 mV, however the evolution of hydrogen appears to be main competitive reaction on Pt. Riboflavin demonstrated chemically reversible reduction peak at ca. -0.65 V and -0.55 V vs. Ag/AgCl with Pt and GC electrode, respectively. Glassy carbon electrodes are known to have higher capacitance, resistance and relatively large overpotentials to hydrogen. Consequently, most methanol was generated on GC with 20 mM riboflavin and within the first 10 minutes of electrolysis, giving a yield of 19%. The result findings revealed that vitamins can served as the alternative electrocatalysts to a more expensive, toxic and less environmentally friendly pyridine. Recent developments and challenges in mechanism for future efficient and selective CO2 reduction to methanol will be discussed in the frame of attractive and sustainable energy sources.

Figure 1
Employing Mg Powder As a Scavenger to Improve Mg Electrolytes for Mg Rechargeable Batteries
Authors: Luo Jian , Bi Yujing , Liu T. Leo
Published: February 2020

Electrochemical performance of Mg electrolytes is highly sensitive to water and other impurities. The water sensitivity of a MgCl2/AlCl3 electrolyte in DME was demonstrated, showing increased overpotential and poor Coulombic efficiency for Mg deposition. Mg powder treatment was found to be very effective and convenient to remove deleterious impurities present in MgCl2/AlCl3 electrolytes to yield unprecedented electrochemical performance for reversible Mg deposition including 100% Coulombic efficiency, low overpotential (< 200 mV), and high anodic stability (up to 3.8 V). It is also found the Mg powder scavenger is also effective for other Mg electrolytes, highlighting the generality of the Mg powder treatment approach. The working mechanism of the Mg powder scavenger will be discussed. In addition, we will show that ternary Mg/MgCl2/AlCl3 (MMAC) electrolytes are reliable for Mg battery applications.

References:

(1) Luo, J; .He, S.; Liu, T. L.* ACS Energy Letters 2017, 2, 1197-1202.

(2) He, S.; Luo, J. Liu, T. L.*, J. Mater. Chem. A 2017, 12718-12722.

(3) He, S.; Neilson, K. V.; Luo, J..; Liu, T. L.*, Energy Storage Mater 2017, 8, 184-188.
Tuning the Surface Properties of Li Metal Anode in Li-S Batteries Via Metal Fluoride-Based Artificial Solid Electrolyte Interphase
Authors: Ren Yuxun , Xiong Cheng , Jiang Haoran , Zeng Lin , Xu Jianbo , Zhao Tianshou
Published: February 2020

Abstract

Lithium-sulfur (Li-S) batteries promise the next-generation energy storage. However, one of the issues facing Li-S batteries is the high reactivity of the Li metal, leading to serious interfacial side reactions; the other is the dendritic Li growth that can usually breach the solid electrolyte interphase (SEI) applied for mitigating side reactions. To address these issues, we propose the indium fluoride-based artificial solid electrolyte interphase with tunable surface properties. Over the initial charging, InF3 nanoparticles coated on the Li anode surface can be lithiated to form a layer of nanoporous lithium/indium alloy (LixIn) encapsulating lithium fluoride (LiF) nanoparticles (3Li++3e-+InF3→3LiF+In) as shown in Figs. 1(a, b). The tightly anchored LixIn layer well attaches LiF on the anode surface during Li stripping/plating, while LiF with a higher Young’s modulus physically suppresses dendritic Li growth. Both LixIn and LiF provide facile adsorption towards Li atoms as well as high Li+ conductivity, inducing uniform Li plating [1-4]. In addition, both materials are stable with corrosive electrolyte containing polysulfides and shield Li anode from side reactions. Tuning the SEI surface properties via adding other metal fluorides such as BiF3 and AlF3, we further show the possibility to further enhance the Young’s modulus and flexibility for the SEI. Applying the rationally designed artificial SEI, substantial enhancement in terms of Li stripping/plating stability (Fig. 1c) and Li-S battery cyclability is achieved even using LiNO3-free electrolyte and the gas evolution arising from interfacial electrolyte decomposition is suppressed [5]. With enhanced mechanical strength and chemical stability, the metal fluoride-based artificial SEI paves a new way in developing durable and safer Li-S batteries.

Key words: Li metal; artificial solid electrolyte interphase; dendrite; side reaction; metal fluoride.

Acknowledgement

The work described in this paper was fully supported by a grant from the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. T23-601/17-R)

Reference

[1] Y. Ren, T. Zhao, M. Liu, Y. Zeng, H. Jiang, Journal of Power Sources, 361 (2017) 203-210.

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Figure 1
In Situ Polysulfide Detection in Lithium Sulfur Batteries
Authors: Jones John-Paul , Jones Simon C. , Krause Frederick C. , Pasalic Jasmina , Bugga Ratnakumar V
Published: February 2020

Lithium-sulfur (Li/S) batteries promise significant specific energy improvements over traditional lithium-ion technology resulting from the high theoretical capacity of both the sulfur cathode and the lithium anode. However they are constrained by low voltage, safety issues due to the lithium anode, charge retention, and cycle life to name a few issues. A variety of these drawbacks are frequently attributed to the so-called “polysulfide shuttle” where partial discharge products from the cathode (polysulfide species such as Li2S6, Li2S4, etc.) dissolve in the electrolyte and migrate to the anode where they wreak havoc.1–4 Many approaches have been developed to mitigate this issue, however few attempts have been made to measure the amount of polysulfide in the electrolyte, particularly during cycling in a representative cell. Here we describe an electrochemical in situ method for detecting and quantifying polysulfide species in the electrolyte of experimental Li/S cells during operation. This method has been applied to experimental Li/S and lithium sulfur-molybdenum disulfide (Li/S-MoS2) cells developed previously in our laboratory.5 High concentration electrolytes and ceramic coated separators were also investigated using this method as they have also been shown to influence the performance (cycle life in particular) of Li/S cells.6 The method utilizes an auxiliary electrode inserted into the electrolyte for a quantitative determination of the redox behavior of the polysulfides. Several interesting trends were observed using this method, including that Li/S-MoS2 cathodes, ceramic coated separators and concentrated electrolytes all display lower concentration of polysulfide compared to the baseline Li/S cells. The quantity of polysulfide species changes during discharge, increasing dramatically during the second discharge plateau. This technique can thus be used to determine the efficacy of new modifications (for example to the cathode or separator) designed to improve sulfur sequestration within or near the cathode

Acknowledgement:

This work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The authors acknowledge the funding support of Army (CERDEC).

© 2017 California Institute of Technology. Government sponsorship acknowledged.

References:

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R. V. Bugga, S. C. Jones, J. Pasalic, C. S. Seu, J.-P. Jones, and L. Torres, J. Electrochem. Soc., 164, A265–A276 (2017).

R. Bugga, J. Jones, S. C. Jones, F. C. Krause, J. Pasalic, D. S. Ganapathi, M. Hendrickson, and E. J. Plichta, 165, 6021–6028 (2018).
Enhanced Long-Term Cycling Performance of Single Crystalline LiCo0.95Ni0.05O2 cathode Material at High Cut-Off Voltage in Li-Ion Cell
Authors: Yoon Moonsu , Cho Jaephil
Published: February 2020

A significant interest in developing high volumetric energy density and high power energy storage systems (ESSs) has facilitated development of ideal cathode material in Lithium-ion batteries. Among various cathode materials, LiCoO2 (LCO) is one of the promising candidates because of single crystalline morphology with relatively high electrode density (>3.9g cm-3) and superior electrochemical performance. However, Increased cut-off voltage, higher than the conventional operating voltage of LCO (~4.3 V vs. Li/Li+), to maximize energy storage capacity gives rise to severe electrochemical degradation at the electrode-electrolyte interface and irreversible structural deformation at highly delithiated states of cathode material, which result in a rapid decrease of capacity and nominal voltage in a continuous cycle.

Herein, for an enhanced cycle life of LCO particularly in high cut-off voltage, we proposed LiCo0.95Ni0.05O2 (LCNO) which not only enabled to demonstrate remarkable cycling performance and but also to be synthesized as a single crystalline with layered structure(R-3m) by the solid-state method in air condition. For comparison, the electrochemical behaviors of active materials, LCO and LCNO, charged up to 4.45V, were investigated. Even though LCO showed an initial reversible capacity of ∼182 mAh/g, higher than that of LCNO (∼176 mAh/g), LCNO exhibited much better capacity retention of 93.6% than that of LCO (74.3%) under continuous 100 cycles. We identified the less formation of irreversible byproducts on the surface of LCNO, compared to that of LCO, indicating the reactivity of interface between LCNO-electrolyte was highly stabilized with the assistance of Ni-ions. Furthermore, the evolution of interfacial change between LCNO-electrolyte after electrochemical cycling has been also investigated by high-resolution scanning transmission electron microscopy (HR-TEM). Based on electron energy-loss spectroscopy measurements (EELS), we confirmed that Ni-ions in LCNO may have a potential ability to initiate the oxidation state of Co ions around the surface to be partially reduced to Co2+/Co3+ mixed-valence state during cycles with a change of surface structure from layered structure to spinel-like phase, thus reducing surface side reaction simultaneously.
Process Development for Thin Film Solid State Battery on Four Inch Wafer Using Glove Box Attached Custom Built Single Chamber PVD System
Authors: K H Thulasi Raman , Ramaprabhu Sundara , Gowravaram Mohan rao
Published: February 2020

A process for fabricating thin film solid state battery on four-inch silicon wafer has been developed in a custom built hybrid PVD configuration in a single chamber attached to a glove box. In this work, we have performed six layer deposition, which includes Lithium evaporation in the same chamber. As the cathode current collector, Aluminum of 2-5 microns thick, was deposited using specially designed compact thermal evaporation sources, after aluminium deposition thin layer metallic nickel or cobalt was used as the barrier for Lithium cobalt oxide cathode. The total thickness of the thin film solid state battery is 15-18 micron, with a specific capacity between 50-80 µAh-Cm2. The capacity of the batteries reduced to 20-30 percent from the initial capacity after 100 cycles. Some batteries were cycled up to 15,000 cycles and the capacity fading is about 50-60 percent. Based on different studies, we have established the protocol to make reliable thin film battery processing using custom built PVD system in the laboratory scale. The investigations have shown degradation due to the intrinsic material limitations rather than process induced degradation.
Scalable Preparation of Porous Silicon Anode Material By Nontoxic Wet Etching for High-Performance Lithium-Ion Batteries
Authors: Lee Dong Geun , Sohn Myungbeom , Park Hyeong-Il , Kim Dae Sik , Kim Hyun Jong , Kim Hansu
Published: February 2020

Lithium-ion batteries (LIBs) have led to the success of portable electronics and gained a great deal of attention as energy storage systems for emerging applications such as wearable devices, electric vehicles and robots. However, current LIBs technology reaches its technological limits for increasing their energy densities. To solve this issue, much research effort has been devoted to finding high capacity electrode materials to replace currently used materials such as graphite anode in LIBs. Silicon-based materials are regarded as one of the most promising candidates for anodes because of their high capacities. However, huge volume expansion/contraction of Si during cycling leads to drastic capacity degradation. Recently, porous silicon materials have been revealed to reduce the volume change of Si due to their porous structure, thus showing outstanding electrochemical performances. However, their use in LIBs suffers from the complicated and limited routes for their synthesis. In this presentation, we represent porous Si materials prepared by scalable and nontoxic wet etching process. This materials synthesis concept presented herein represents a means of improving the electrochemical properties of porous Si anode materials for use in commercial LIBs.