bluuebunny/crossref_metadata_2025 huggingface dataset:
Electrochemical Behavior of the SmF3 in Alkali Chloride Melts
Authors: Stuliov Yuriy V. , Kuznetsov Sergey A.
Published: December 2020

Today, existing methods of recycling spent nuclear fuel do not solve the problem of separation of transuranium elements and lanthanides. Electrolysis of molten salts is promising for separation of lanthanides and actinides. To solve this problem, it is necessary to have experimental data on the electrochemical behavior of various lanthanides in molten salts.

The aim of this study is the electrochemical investigation by cyclic voltammetry of the Sm(III)/Sm(II) redox couple in NaCl-KCl, KCl and CsCl melts containing SmF3.

Electrochemical studies were carried out in a temperature range of 973-1173 K by cyclic voltammetry using an AUTOLAB PGSTAT 20 potentiostat with a package of application programs GPES (version 4.4.). The sweep rate (v) varied between 0.1 up to 3.0 V s-1. The melt container was a glassy carbon crucible of SU-2000 brand, which also served as an auxiliary electrode. Tungsten wire was used as a working electrode and platinum wire was utilized as a quasi-reference electrode.

It was found in NaCl-KCl-SmF3, KCl-SmF3 and CsCl-SmF3 melts that the recharge process was reversible up to the scan rate 1.0 V s-1. In this range of sweep rate the diffusion coefficients (D) of Sm(III) were calculated using the Randles–Shevchik equation. The diffusion coefficients decrease with a change of the composition of the second coordination sphere from sodium to cesium. Similar dependencies for D values are well known. It is associated with a decrease of the counter-polarizing effect during the transition from Na to Cs, which in turn causes a decrease of the metal – ligand bond length and increase the strength of samarium complexes.

A transition from reversible to quasi-reversible process was found at v > 1.0 V s-1 in NaCl-KCl-SmF3, KCl-SmF3 and CsCl-SmF3 melts.

The standard rate constants of charge transfer (k
s) of the redox couple Sm(III)/Sm(II) were determined by cyclic voltammetry in all studied melts by using the Nicholson’s equation, which is valid for quasi-reversible processes.

The following series of the standard charge transfer constants was found k
s(CsCl)<k
s(KCl)<k
s(NaCl–KCl). According to the theory of elementary charge transfer, the smaller and stronger bond complexes require a higher rearrangement energy, and in consequence, the charge transfer proceeds at a slower rate. Therefore, a decrease of the standard rate constants for the redox reaction would have been expected, which is in an agreement with obtained experimental results.
Molten Salts Based Electrochemical Approach to Regenerative Fuels
Authors: Chen George Zheng
Published: December 2020

Electrochemical energy storage (EES) technologies, such as rechargeable batteries, supercapacitors and supercapatteries, are featured by their capability of direct storage of electricity, fast charging-discharging, and modular flexibility and convenience for scaling [1,2]. However, they also suffer from several obvious shortcomings, for example, high manufacturing cost, low specific energy (or energy density), and short storage time in comparison with technologies based on combustion of fossil fuels. In fact, the specific energy values resulting from either thermochemical or electrochemical oxidation are very much comparable, considering the thermodynamics of the following common reactions that convert chemical energy in the fuels to work, i.e. Gibbs energy change. Therefore, the key to increase the specific energy of EES technologies depends largely on how to achieve the conversion.

Reaction number

Energy conversion reactions

Maximum work (Gibbs energy change)

(1)

H2 + O2 = H2O(g)

9.9 (88.8) kJ/g

(2)

C + O2 = CO2

9.0 (33.3) kJ/g

(3)

CH4 + 2O2 = CO2 + 2H2O(g)

10.0 (50.0) kJ/g

(4)

4Li + O2 = 2Li2O

14.3 (30.8) kJ/g

(5)

Al + O2 = Al2O3

12.5 (23.5) kJ/g

(6)

Si +O2 = SiO2

11.4 (24.3) kJ/g

The values given in brackets are calculated without considering the mass of oxygen gas.

In these oxidation reactions, the reactants are the fuels that can all be reproduced or regenerated from the oxide products via appropriate electrochemical reduction driven by renewable energy (light, heat and electricity) [3]. Therefore, these fuels can all be called regenerative fuels [4]. In this presentation, the author will analyze and discuss the feasibility of, and some preliminary findings from using molten salt electrochemistry to enable the regenerative fuels technology in the context of affordable, durable and portable high density energy storage.

References:

(1) Chen GZ, Supercapacitor and supercapattery as emerging electrochemical energy stores,
Int. Mater. Rev.
, 62 (2017) 173–202.

(2) Xia L, Yu LP, Hu D, Chen GZ, Electrolytes for electrochemical energy storage, Mater. Chem. Front.
, 1 (2017) 584–618.

(3) Ijije HV, Lawrence RC, Siambun NJ, Jeong SM, Jewell DA, Hu D, Chen GZ, Electro-deposition and re-oxidation of carbon in carbonate containing molten salts,
Faraday Discuss.
, 172 (2014) 105–116.

(4) Xia L, Chen GZ, High density electrochemical energy storage via regenerative fuels,
Chin. J. Catal.
40 (s1) (2019) 111-119.

Acknowledgement: The author thanks the financial supports from the EPSRC (EP/J000582/1 EP/F026412/1), Royal Society (Braine Mercer Feasibility Award, 2006), and Ningbo Municipal People’s Governments (3315 Plan and 2014A35001-1).

Figure 1
Effects of Ionic Liquids on the Polymerization of 3-D Print Resins
Authors: Reichert W. Matthew Matthew , Duranty Edward R. , Poole Greg
Published: December 2020

The application of additive manufacturing in various areas of chemistry has increased dramatically in recent years including in the field of ionic liquids (ILs). It has been shown that ILs can be incorporated into the resins used in stereolithography (SLA) 3-D printing either as part of the polymer backbone or as an additive. Results have shown a change in the properties of the resulting printed polymer based on the structure of the ILs. The incorporation of the ILs into 3-D printed polymers provides the ability to customize the chemical and physical properties of a printed part. In particular, ionic liquids have been shown to act as plasticizers when incorporated into 3-D printed PMMA.

In this presentation, we will explore the effects that selected ILs have on the polymerization of the various resins used in SLA printing including the IL’s effects on the resin’s heat of polymerization. These experiments have incorporated a new technique to measure the temperature change during the polymerization process using a “TinyLev” acoustic levitator. This device provided a contact-free, container-less sample holder for a 10 µL droplet of the resin/IL mixture suspended on a standing acoustic wave. A FLIR camera was used to record the temperature change as the polymerization reaction progressed. Since the polymerization of SLA resins is typically initiated by UV light, these experiments used a 405 nm laser to initiate the polymerization reaction. A variety of ILs with different cation and anion functionalities were examined with the collected data compared to pure resin. Thermal decomposition data for these samples collected using DSC and TGA was corroborated with GPC data in order to determine the effect of the ILs on the molecular weight. This data, combined with the FLIR thermography results, provides an understanding of the role ILs have in the polymerization reaction of the resin—either as additives or as a co-polymer.

Figure 1
Solubility of Rare Earth Oxides in Fused Alkali and Alkaline Earth Halides
Authors: Volkovich Vladimir A. , Ivanov Alexander B. , Shchetinskiy Andrey V. , Mukhamadeev Andrey S. , Ryzhov Alexander A. , Afonin Yurii D. , Polovov Ilya B. , Petrov Anton I.
Published: December 2020

Melts based on mixtures of alkali and/or alkaline earth halides are considered as prospective media for electrowinning rare earth metals as well as for pyrochemical reprocessing spent nuclear fuels. Fluoride or mixed fluoride-chloride baths can be operated at high temperatures yielding molten rare earth metals (REMs) thus simplifying separation of the metal and salt. One of the problems in using fluoride melts is possible formation of fluorine at the anode. This can be avoided by adding a rare earth oxide to the melt both as the source of REM and oxide ions. The latter will be oxidized to oxygen producing carbon mono- or dioxide at the anode. The limiting factor for feeding the electrolysis bath with REM oxides is their solubility in the halide melt.

The aim of the present study was determining the effect of temperature and melt composition on solubility of REM oxides in fused halides. The experiments were performed in CaCl2–CaF2 mixtures containing 20 or 75 mol. % CaF2; BaCl2–BaF2 mixtures containing 15 or 73 mol. % BaF2; equimolar CaF2–BaF2 mixture and NaCl–NaF eutectic mixture (34 mol. % NaF). Solubility of REM oxides was determined by the method of isothermal saturation. Time required for reaching the equilibrium between solid REM oxides and fused salts was determined in a preliminary set of experiments. To compare the behavior of 4f- and 5f-elements, solubility of uranium dioxide was also measured.

The measurements were performed at the temperatures up to 1400 oC under argon atmosphere. The lower limit of the temperature range varied from 700 to 1100 oC depending on the melting temperatures of the salt mixtures used. Oxides of yttrium, lanthanum, cerium, praseodymium, neodymium and samarium were selected for the study. To assess a possible mutual influence of rare earth elements on solubility of their oxides in fused salts the solubility of a mixture of REM oxides was determined in a separate series of experiments and concentrations of individual REMs in the melt was determined.

Solubility of REM oxides increased with increasing temperature and an example of effect of temperature on solubility of neodymium oxide in various melts is shown in Fig.

Fig. Concentration of neodymium in alkali and alkaline halide based melts saturated with Nd2O3. Melt: CaCl2–CaF2 20 mol. % (1); CaCl2–CaF2 75 mol. % (2); BaCl2–BaF2 73 mol. % (3); BaCl2–BaF2 15 mol. % (4); CaF2–BaF2 50 mol. % (5; and NaCl–NaF 34 mol. % (6).

Figure 1
Additive Effects of La, Sr, Cs and Ca in a Molten Carbonate Fuel Cell
Authors: Lee ChoongGon , Ebenezer Arthur , Koomson Samuel
Published: December 2020

Current research has shown that Li2CO3-Na2CO3 electrolyte has better ionic conductivity, a lower rate of cathode dissolution and a lower electrolyte loss than Li/K carbonate. Lower oxygen gas solubility has been one of the disadvantages of the Li/Na electrolyte. Modification of the electrolyte such as the addition of alkali metals and alkaline earth metals have led to an improvement in the oxygen reduction reaction (ORR). In this experiment, the effects of lanthanum, strontium, cesium, and calcium were analyzed using several electrochemical half-cells and 7 cm2 coin-type MCFCs operated at 973 K. A eutectic mixture of Li2CO3 and Na2CO3 (52:48) was used as the electrolyte. For the half-cell, the reference electrode compartment was supplied with a 33% Air/67% CO2 gas mixture while the electrolyte compartment was supplied with different CO2/Air gas compositions. The anode of the coin cells was supplied with a mixture of H2, CO2 and H2O in the ratio 72:14:14 mol% and the cathode was supplied with air and CO2 in the ratio 70:30 mol%. 0.5 mol% La2O3, 3 mol% Cs2CO3, 3 mol% CaCO3, and 3 mol% SrCO3 were added separately and also as a combination of two (i.e. La2O3/SrCO3, CaCO3/La2O3, and Cs2CO3/La2O3) to the Li/Na electrolyte. The effects of these additives were observed and analyzed using Electrochemical analysis techniques such as electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used for the half-cell analysis. Steady-state polarization (SSP), internal resistance (IR) using the Nyquist plot, and step chronopotentiometry were employed in the analyses of the coin cell. The mass transfer parameter (C√D) values obtained from the cyclic voltammetry measurements increased as the oxygen partial pressure increases in all electrolytes. From the results obtained, the combined addition of Ca/La proved to have the most significant effect on the overall performance of the cell.
Electrochemical Methods for Analysis of Hydroxide and Oxide Impurities in Li, Mg/Na, and Ca Based Molten Chloride Salts
Authors: Gonzalez Mario Alberto , Faulkner Emma , Zhang Chao , Choi Suhee , Simpson Michael Forrest
Published: December 2020

With applications that include thermal energy storage in Gen3 concentrated solar power (CSP), molten salt batteries in grid scale energy storage, fuel and coolant in molten salt reactors (MSR), and oxide reduction/electrorefining of spent nuclear fuel; molten salts are potentially the most important all around medium for advanced energy systems. In particular, molten halide salts are known to be extremely hygroscopic, typically resisting complete thermal dehydration. Incomplete removal of water leads to hydrolysis; promoting formation of volatile HCl and insoluble oxide/hydroxide impurities in the molten salt. Depending on the application, this can accelerate corrosion, lower product yield through formation of insoluble oxides and oxychlorides, and/or reduce cell efficiency in electrolytic processes. Consequently, the generation, speciation, and electrochemical response of oxide and hydroxide impurities in various molten chloride salts have been widely studied. In this presentation, previously published work with LiCl-Li2O, MgCl2-KCl-NaCl, CaCl2, and CaCl2-CaO-CeCl3 molten chloride salts will be reviewed and discussed to reveal underlying commonality and lessons learned. In LiCl-Li2O and MgCl2-KCl-NaCl, LiOH and NaOH, respectively, were found in the salt after melting water-contaminated starting material. Electrode response signals were ascribed to both LiOH and NaOH contamination, and a nondestructive, in-situ method for determining their concentrations using cyclic voltammetry (CV) was developed. In CaCl2, Ca(OH)2 was found to be unstable, reverting to CaO at operating temperatures. Electrode signals were ascribed to the CaO, and an in situ measurement technique using CV to measure the CaO concentration was developed. The effect of CaO contamination on an electrorefining process was further studied in CaCl2-CaO-CeCl3, where CaO presence was shown to promote the formation of both insoluble Ce2O3 and CeClO. Electrochemical methods in all cases were further substantiated through support analyses including titration, thermogravimetric analysis, quadrupole mass spectrometry, and inductively coupled plasma mass spectrometry. These quantitative electroanalytical methods are shown to be both effective and versatile, showing promise as the development of real-time, in-line sensors for many molten salt processes continues to be of great consequence. Moreover, their versatility in different molten chloride salt systems is encouraging, as they can become an integral step in the evaluation of new use-cases for other molten halide salts and/or their suitability for new applications.
Decrystallization Kinetics of Cotton Yarns in Ionic Liquids – Raman Spectral Mapping
Authors: Cosby Tyler , Aiello Ashlee , Durkin David P. , Trulove Paul C.
Published: December 2020

Ionic liquids (ILs) are promising solvents for the treatment and processing of cellulosic biopolymer materials. Despite the discovery of numerous ILs capable of dissolving varying amounts of cellulose, a detailed understanding of the dissolution process in ILs is still lacking. In this study, a new approach, Raman spectral mapping, is employed to investigate the kinetics of cellulose decrystallization and dissolution in a prototypical solvent IL, 1-ethyl-3-methylimidazolium acetate. The cellulose utilized is in the form of mercerized cotton yarns. By monitoring Raman bands characteristic of the crystalline domains, we investigate the degree and spatial extent of crystallinity in IL treated yarns. To elucidate the interplay of kinetic (viscosity) and thermodynamic (solvation) factors in the decrystallization process, the treatment time and temperature were systematically varied. A detailed analysis of the experimental results reveals three distinct temperature-dependent decrystallization regimes including (i) homogeneous decrystallization and cotton yarn collapse, (ii) fast-heterogeneous decrystallization of the collapsed yarn, and (iii) slow heterogeneous decrystallization. These results are discussed within the framework of the current understanding of cellulose and polymer dissolution.
Optimization of Lithium Content and Sintering Additives in Tape Cast Lithium Garnet Electrolyte Sheets
Authors: Jonson Robert , Shen Fengyu , Tucker Mike
Published: December 2020

The lithium garnet (LLZO) remains one of the most promising electrolyte materials for producing solid state batteries. Tape casting is one method for producing the thin ceramic electrolyte layer required for a high-performance solid state battery. Processing of LLZO is complicated by several factors including lithium volatilization, abnormal grain growth and phase instability. Many of these issues are exacerbated in tape cast sheets by the sheets’ higher surface area to volume ratio, when compared to pellet processing methods. We report on an environmentally friendly aqueous tape casting process for LLZO using methylcellulose as a binder and compare final sheet properties to other, solvent-based, options. Solids loading, binder content, dispersant composition, and wetting agent type are varied to improve ease of casting and enhance properties of the as-cast tape. Lithium content in sintered LLZO sheets is controlled by the inclusion of excess Li2CO3 as lithium source in the ceramic tape itself and by a novel method of producing a lithium-saturated furnace atmosphere. Sintering time and temperature are optimized, and rapid thermal processing is investigated as a method of reducing lithium loss. Al2O3 and MgO are examined for use as sintering additives. Characterization of LLZO sheets is performed with XRD, EIS and SEM. Li2CO3 and sintering additive levels are optimized for ionic conductivity and density. The optimization effort improved the conductivity and density of 100µm thick sintered sheets to greater than 3x10-4 S/cm conductivity and 90% density.

Figure 1
(Invited) Structure, Chemistry, and Charge Transfer Resistance of the Interface between Garnet Solid Electrolyte and Oxide Cathodes
Authors: Yildiz Bilge , Kim Younggyu
Published: December 2020

All-solid-state batteries promise significant safety and energy density advantages over liquid-electrolyte batteries. The interface between the cathode and the solid electrolyte is an important contributor to charge transfer resistance. Strong bonding of solid oxide electrolytes and cathodes requires sintering at elevated temperatures. Knowledge of the temperature dependence of the composition and charge transfer properties of this interface is important for determining the ideal sintering conditions. To understand the interfacial decomposition processes and their onset temperatures, model cathode systems of LiCoO2 (LCO) and LiNi0.6Mn0.2Co0.2O2 (NMC622) thin films deposited on cubic Al-doped Li7La3Zr2O12 (LLZO) pellets were studied as a function of temperature, gas composition and electrochemical conditions. The methods combine interface-sensitive techniques, including X-ray photoelectron spectroscopy (XPS), synchrotron X-ray absorption spectroscopy, hard X-ray photoemission (HAXPES), and synchrotron X-ray diffraction. In this talk, we will present the found precipitation products at the interface as a function of synthesis and electrochemical conditions, their role in altering the interface resistance to Li transfer, and compare the LCO and NMC related cathodes in terms of their instability onset conditions. Results in particular indicate the importance of the selected temperature and gas conditions in giving rise to more stable interfaces, with fast Li transfer between the garnet electrolyte and the oxide cathodes.
Study on Mechanical Strength Measurement and Strength Improvement of Sulfide-Based Electrodes
Authors: Kim Kiyoul , Park Taeryong , Ahn Tae-Young , Cho Jang-Hyun
Published: December 2020

The thermal battery is a primary battery that is used in special fields such as defense due to its high power and high reliability characteristics. In the thermal battery, a lithium or lithium compound negative electrode and a metal sulfide-based positive electrode system are used. There is always a demand for reducing the weight of the system and a need for increasing the area of the electrode. Therefore, it is essential to study the mechanical strength of the electrode and improve its strength. In this research, the strength of the compaction of the positive electrode material was quantitatively measured, and research was conducted to improve the strength for weight reduction and large area. Two methods of measurement were proposed for quantifying the mechanical strength of the electrode of the disk-shaped green compact electrode. The fracture strength of the green compact was measured by the "Monotonic equi-biaxial flexural strength test" method proposed by ASTM C1499-09, and the fracture toughness was measured by the double cantilever beam (DCB) test. In order to improve the mechanical strength, the strength according to the powder particle size and the compression pressure was measured. Higher fracture strength and fracture toughness more than double that of green compacts with reference powder grain size and differentiation smaller than 45μm were measured. The effect of powder particle size and compression pressure on strength was analyzed through powder characterizations and microstructure observations. In addition, actual electrodes were fabricated and the possibility of battery utilization was verified through discharge tests.

Figure 1
Combination Technology for Safer Design of Lithium-Ion Batteries
Authors: Senoh Hiroshi , Mukai Takashi , Ikeuchi Yuuta , Yamashita Naoto , Sakamoto Taichi , Tanaka Hideaki
Published: December 2020

For further penetration of lithium-ion battery, safer battery design with high energy density is required. In the case of the thermal runaway of conventional lithium-ion batteries, the reaction of electrolyte on the surface of graphite anode at higher temperature causes the gas generation with the temperature rise. Subsequently, the short circuit due to the separator meltdown leads to the oxygen release by the pyrolysis of cathode and the thermite reaction above the melting of aluminum utilized for the current collector and the cell package. The construction of novel safer battery systems with high energy density is possible through a judicious choice of each component: cathode material, electrolyte, separator, anode material, current collector and package.

We develop safer battery configurations through the analysis of practical batteries using various techniques such as calorimetry and overcharge / internal short-circuit tests. In this study, we assemble 1 Ah class pouch-type full cell with lithium iron phosphate cathode and silicon oxide anode [1]. The full cell shows good charge-discharge properties even at high-rate and 100˚C (Figure 1). On the estimation, however, the electrochemical energy of both electrode active materials is only about 3% of the total thermal energy of full cell. Thus, we replace aluminum with stainless steel utilized for the current collector and package. In addition, we select a separator of heat-stable nonwoven fabric instead of polyethylene/polypropylene. The total thermal energy of full cell by the alternative separator, current collector and package is found to be reduced to 14% of the initial value. In short-circuit testing, the full cell did not show fire though heat and smoke were generated since the maximum temperature of the cell is only 52˚C.

In this way, it is possible to design batteries with highly safe by considering the non-flammability of each component such as the current collector and the package as well as the separator.

References

[1] M. Yanagida, T. Mukai, Y. Ikeuchi, N. Yamashita, T. Sakamoto, H. Senoh and H. Tanaka, Abstract of the 60th Battery Symposium in Japan, 2B23 (2019).

Figure 1
Gas Generation Evaluation of Lib in Case of Thermal Runaway Reaction
Authors: Okada Ken , Shibata Tsuyoshi , Saito Yoshiyasu
Published: December 2020

In recent years, lithium-ion batteries (LIB) have advanced in performance and capacity, and their applications to electric vehicles, next-generation mobility, mobile devices, etc. are expanding. However, LIB may be ignited or exploded due to external stimuli such as short circuit, impact, heating, etc., and the number of accidents of ignition or explosion is increasing with the expansion of these applications and the increase of energy density.

In this study, we investigate the case where the external environmental temperature of LIB rises, and the reaction runaway occurs. As an item of safety evaluation, the purpose is to establish a method for measuring the temperature rise and pressure rise of a battery and evaluating the amount of reaction product gas and the gas composition. If the amount of gas generated is known in advance, it can be used for studying protective measures and designing closed containers for safety tests.

In the experiment, the 20L closed chamber used for the explosive experiment was modified and used for LIB experiment. A LIB with electric heater were introduced into the explosion chamber and the behavior of runaway reaction was observed, monitoring the terminal voltage, internal pressure, and temperature. Further, after the test, the gas was sampled, and the amount of gas was estimated and the gas composition was analyzed. We also compared the results of two LIBs with SOC (State of Charge) of 0% and 95%.

As a result, the following findings were obtained. (1) An experimental system was developed to evaluate the amount of the gas without leakage causing the thermal runaway while monitoring the LIB temperature, voltage, and pressure inside the container. (2) It was found that the LIB temperature reached ~ 1200 ° C (SOC 95%) and ~ 600 ° C (SOC 0%) during the runaway reaction. (3) The amount of gas during the runaway reaction is 141 to 152L (SOC 95%), 72L (SOC 0%), and special attention should be paid to the gas generation when the LIB is charged completely. (4) The gas after the runaway reaction contains about 30% carbon monoxide, 15% hydrogen, 26% hydrocarbon (SOC 0%), 50% (SOC 0%). We should pay attention to the CO poisoning, backdraft, and flash.

Figure 1
Analysis of Lithium-Ion Cell Deterioration through Parameter Measurement
Authors: Kim Youngmin , Jeong Kyeong-Min
Published: December 2020

Deterioration analysis of aged lithium-ion cells is becoming increasingly important as demand for longer life of cells increases for electric vehicles and energy storage systems. In this work, we propose a non-destructive analysis of the degree of deterioration of aged cells by measuring the physicochemical parameters. Low-rate charge-discharge, galvanostatic intermittent titration technique, and electrochemical impedance spectroscopy were used to measure the quasi-equilibrium potential, diffusion coefficient, and exchange current density of the active material in graphite / NCM cell after cycling aging. Loss of active material, loss of lithium inventory, and the internal resistance changes of aged cell were analyzed from differential voltage analysis and capacity variations after aging. Then the measured kinetics and mass transfer related parameters were compared with those of fresh active materials and analyzed as functions of aging conditions. The changes of quasi-equilibrium potential is attributed to the loss of active materials, and decreased kinetic parameters and increased resistances show the formation of inactive phases or byproducts that cause pore structure changes of electrodes.
(Invited) Low-Cost and High Rate Na-FeCl2 Batteries for Large Scale Energy Storage Applications
Authors: Zhan Xiaowen , Reed David , Sprenkle Vincent , Li Guosheng
Published: December 2020

Developing battery systems that are inexpensive, enduring, and safe is essential for integrating renewable energy sources such as solar and wind power into the electricity grid and providing valuable grid services such as frequency regulation, peak shaving, and arbitrage. In this regard, Na-based batteries are promising candidates because they use naturally abundant sodium (Na) as the charge carrier, which can potentially reduce the materials cost and support multiple energy storage applications. Among various Na-based batteries developed to date, thorough investigations have been done on high-temperature (~300°C) Na-metal halide (Na-MH) batteries, which offer long cycle life and superior safety. In particular, the tubular sodium-nickel chloride (Na-NiCl2 or Zebra) battery has been commercialized and found wide application in the telecom and oil/gas industries. However, the high operating temperature and cost of the Zebra battery has hindered its further market penetration. Considering constraints of the Ni-based cell chemistry, it is highly desirable to develop an alternate cathode for Na-MH batteries towards next-generation energy storage applications. This pursuit, unsurprisingly, led us to the Fe/NaCl cathode. In this study, we present an advanced Na-FeCl2 battery with unprecedented high-rate performance and low cost for stationary energy storage applications. Operated at an extremely high current density of 33.3 mA/cm2 at 190°C, the cell can output 74% of its total capacity—a capacity retention double that of IT Na-NiCl2 cells. The origin of the high rate capability of Na-FeCl2 batteries was elucidated by means of comprehensive phase/structure analysis and electrochemical/electroanalytical characterizations. Moreover, Fe particle pulverization originating from liquid-phase reactions was determined to be the major source of capacity fading during long-term cycling. Accordingly, we designed a unique cathode with Ni additive, which delivered a high discharge specific energy density of over 295 Wh/kg for 200 cycles at C/5 with almost no capacity fading.
(Invited) Stress Evolution on the Solid Electrolyte in Lower Temperature Operating Planar Sodium Nickel Chloride Batteries
Authors: Yang Choongmo , Park Yoon-Cheol , Moon Jiwoong , Kwon Ohmin , Park Inchul , Kim Yeongwoo , Kim Hwa-Jung , Choi Hanul , Lee Younki , Jung Keeyoung
Published: December 2020

Sodium nickel chloride (Na-NiCl2) battery is one of the most promising candidates as a large scale electrochemical energy storage device since it offers high safety, long lifetime, and high energy density. The battery comprises molten metallic Na and NiCl2 as negative and positive electrodes, respectively, separating them by a β”-Al2O3–family solid electrolyte (BASE). In order to facilitate fast sodium-ion transport in the cathode compartment, the battery typically operates at 300oC accompanying with molten NaAlCl4 (catholyte), which is infiltrated into the cathode materials powder. A drawback of the efficient battery hampering broader market penetration is high manufacturing cost as it adopts expensive heterogeneous sealing technologies, such as thermal compression bonding, glass sealing, and laser beam welding, which are inevitable to withstand its high operating temperature. However, when lowering the operating temperature down to below 200oC, inexpensive polymer can be introduced replacing all the expensive sealing technologies, through which cell manufacturing process can be substantially simplified at the same time.

In developing the lower temperature operating planar Na-NiCl2 battery, one of the major cell failure modes is mechanical failure in solid electrolytes either by thermal stress accumulation upon freeze-thaw cycles or by stresses developed by pressure difference between cathode and anode compartments during charge-discharge cycles. The presentation will start with defining failure modes of this new class of Na beta-alumina battery with special emphasis on electrolyte failure. In order to understand the stress accumulation in the vicinity of the solid electrolyte, a set of finite element analyses (FEA) has been conducted for various simulated conditions. It turns out that (1) sealing temperature, and (2) inner volumes of cathode and anode compartments need to be carefully designed to avoid the mechanical failure. The results of the calculation and cell design strategy for this novel battery will be discussed.

Figure 1
(Invited) Van Der Waals Crystal for Battery Applications
Authors: Shim Wooyoung
Published: December 2020

Wetting liquid metal on the solid electrolyte of a liquid-metal battery determines the battery’s operating temperature and performance. Liquid sodium electrodes are particularly attractive because of their low cost, natural abundance, and geological distribution, but wet poorly on a solid electrolyte near its metaling temperature, limiting their widespread suitability for low-temperature batteries used for large-scale energy storage systems. We present (1) an isolated metal island and (2) sparked two-dimensional (2D) material strategy that can improve sodium wetting in sodium-beta alumina batteries that allows operation at lower temperatures. Our results suggest that in situ heat treatment of a solid electrolyte followed by metal deposition effectively eliminates oxygen and moisture from the surface of the solid electrolyte, preventing the formation of an oxide layer on liquid sodium, leading to enhanced wetting. We also show that employing isolated metal islands and 2D material significantly improves cell performance, retaining 94% charge after the initial cycle, an improvement over cells without such materials. These results suggest that coating isolated metal islands and 2D material is a promising but simple strategy for the development of low-temperature sodium-beta alumina batteries.
Visible Light Photocatalyst Prepared from Active Organic Photovoltaic Cell
Authors: Nagai Keiji , Kuwabara Takayuki , Ahmad Mohd Fairus , Nakano Masahiro , Karakawa Makoto , Taima Tetsuya , Takahashi Koushin , Abe Toshiyuki
Published: December 2020

The organic photovoltaic devices (OPVs) have potential in low-cost, large-area printing routes with high efficiency owing to the variety of organic materials. The active layer has a role to absorb photon and convert to electrostatic energy of separated electron and hole pair. If the separated charge in its active layer can be utilized to chemical reaction directly without collecting by electrodes, it would be a simple device for photoenergy conversion and has a great merit to use the photon energy. Here we introduce an large negative threshold potential of −0.35 V vs. Ag/AgCl by the use of ZnPc/PCBM:P3HT/ZnO electrode, which was prepared by removing PEDOT:PSS/Au electrode of an inverted OPV device [1] and coating with ZnPc. A co-photocatalysis property of ZnPc was observed in the photoelectrochemistry and scanning Kelvin probe microscopy.

From the mother OPV, the gold electrode was removed mechanically and ZnPc was coated by vapor deposition. The detailed experimental conditions and characterizations of the electrode are shown in Ref [2].

Fig. shows voltammograms in a thiol solution for the BHJ electrode (a) and the ZnPc coated BHJ electrode (b). The photoanodic current (red) for the electrode with ZnPc (b) was much larger than that without ZnPc (a). For the ZnPc coated BHJ electrode with ZnO, the threshold potential of the photoanodic current was around −0.35 V vs. Ag/AgCl. On the other hand, for the ZnPc coated BHJ electrode without ZnO, the threshold potential of the photoanodic current was around −0.0 V vs. Ag/AgCl as shown in our previous paper [3]. The present larger gain than that without ZnO would be due to the effect of ZnO as a hole blocking layer. The threshold value of −0.35 V vs. Ag/AgCl was almost equal to the conduction band edge potential of ZnO, that is, the photogenerated electrons in the BHJ active layer can preferentially transfer to ZnO when the anodic polarization of ITO was deeper than the ZnO edge. Note that the ZnPc electrode exhibited an anodic current in the dark with the threshold potential of +0.25 V vs. Ag/AgCl, that is, the ZnPc can function as a catalyst of 2-mercaptoethanol oxidation. The large anodic photocurrent may be caused by such a catalytic function of ZnPc.

References

T. Kuwabara, et al., Sol. Energy Mater. Sol. Cells, 2008, 92, 1476.

K. Nagai, et al., Chem. Commun. 2019, 55, 12491.

T. Abe, et al. Chem. Phys. Lett., 2012, 549, 77.

M.-F. Ahmad, et al. NPG Asia Mater., 2018, 10, 630.

Figure 1
Room Temperature Synthesis of Ordered Intermetallic Electrocatalysts
Authors: Hall Shoji
Published: December 2020

The conversion of O2 to H2O is an important fuel cell reaction for the recovery of renewable electricity from chemical fuels. Alloys of Pt-group metals (PGMs) with transition metals have emerged as catalysts with enhanced activity and durability for the oxygen reduction reaction (ORR). To date, most studies focus exclusively on alloys that adopt a Face-centered cubic (FCC) or Face-centered tetragonal (FCT) crystal lattice. Under ORR operating conditions, these materials evolve from alloys to Pt core-alloy shell materials, in this case both the alloy core and Pt shell retains the FCC or FCT type crystal structure; indicating that materials can dynamically change during catalysis.

Here we present the synthesis of Pd-Bi based ordered intermetallics by partial dealloying of a Bi rich alloy. We found that under ORR operation conditions, β-PdBi2 (I4/mmm space group) which adopts a tetragonal lattice, transforms to α-Pd3Bi (Pmma space group) which adopts an orthorhombic crystal structure; this transformation is mediated by oxidative Bi corrosion under potential cycling, and reconstruction of the atoms in the bulk. To the best of our knowledge, this is the first report of a material that exhibits an electrochemically driven, non-congruent phase transition among materials with different crystal structures. The resulting phase-converted Pd3Bi is stable and exhibits high performance for ORR. Phase-converted Pd3Bi outperform Pt and Pd metal, reaching mass activities of 2.6 A/mgPd, which is nearly 10X higher than Pt/C (~0.3 A/mgPt) and Pd/C (~0.2 A/mg) at 0.9 V vs the Real Hydrogen Electrode (RHE). The mass activity of Pd3Bi decreases by ~38% after 10,000 cycles, indicating that it is stable. Activation energy (Ea) determined by temperature dependent electro-kinetic measurements indicates that the activity enhancement on phase-converted Pd3Bi originates from anion-poisoning resistant behavior. These results establish that PGMs-based ordered intermetallics with low-symmetry crystal structures can be highly active and durable electrocatalysts.
(Invited) Mechanism of a Sensitized Thermal Cell
Authors: Matsushita Sachiko
Published: December 2020

Efficient and low-cost thermal energy-harvesting systems are crucial to solve the global energy problem. A new energy conversion system for the generation of electric power directly from heat energy is described herein. The device is a sensitized thermal cell (STC) based on a dye-sensitized solar cell. In the established system, thermally-excited electrons in a semiconductor were utilized instead of photon-excited electrons in a dye. Consequently, the STC generated electricity by “placing” or “burying” the cell in the heat source.

To prove the concept, first, we examined the redox ability of thermally excited electrons (Mater. Horiz., 2017, 4, 649–656.). Next, we demonstrated that the semiconductor-sensitized solar cell can generate electric power by thermally excitation (ACS Applied Energy Materials, 2019, 2, 13–18.; J. Phys. Chem. C, 123, 2019, 12135-12141.). Lastly, we performed the long-time power generation at 80 degree using STC and observed the end; and surprisingly found that the battery characteristics were restored after discharging by placing or burying the battery in a heat source ( J. Mater. Chem. A, 2019, 7, 18249-18256.). Additinally, we show that the open circuit voltage of STC has the Fermi level dependnce of the semiconductor electrode (Chem. Lett. in press). In the presentation, these recent results were summarized and the difference between photo excitation and thermally excitation will be discussed..
(Invited) Si-Based Water Splitting Photoanodes Conjugated with Earth-Abundant Transition Metal-Based Catalysts
Authors: Jang Ho Won
Published: December 2020

The development of a carbon-free hydrogen production method by photoelectrochemical (PEC) water splitting is a promising pathway to deal with the increased energy demands and deleterious environmental issues derived from the usage of fossil fuels. Silicon, which is the second most earth-abundant element and a small band-gap material, is an applicable candidate for an efficient solar water splitting photoelectrode. However, the stability of Si-based photoelectrodes hampers efficient water splitting because of its thermodynamic instability and etching of silicon surface. Until now, much research has been conducted to deal with the challenges of using Si to fabricate efficient and stable photoelectrodes. Over the decades, earth-abundant transition metal-based electrocatalysts (metals, sulfides, and hydroxides, phosphies) have been investigated intensively. We briefly introduce the photoelectrochemistry and important parameters for evaluating the performance of the Si photoelectrodes. We present our strategies to overcome the challenges of silicon by combining the advantages of transition metal-based electrocatalysts, which are cost-effective, stable, and highly active for both oxygen evolution and hydrogen evolution reactions. To realize spontaneous water splitting, we introduce Si-based PEC-photovoltaic cells using transition metal-based materials.
HOMO-LUMO Energy Levels and the Bandgaps to Understand Porpc Photocatalytic Activity
Authors: De Lile Jeffrey , Son Young-A , Lee Seung Geol
Published: December 2020

A dye-sensitized solar cell (DSSC) assembly can be used not only to harvest solar energy but also to purify water using suitable dye-sensitizers. Here, we theoretically investigated four dye-sensitizers, namely, PORPC-1, PORPC-2, PORPC-3, and PORPC-4 for photocatalytic water purification using PBE, B3LYP, PBE0 functionals, and ∆SCF, TD-DFT and GW methods to characterize their activity trends. The energy levels of highest occupied molecular orbitals (HOMO) and the lowest unoccupied molecular orbitals (LUMO) were elucidated using gas-phase and aqueous phase calculations to understand charge injection ability and the dye-regeneration process. However, PBE, B3LYP, PBE0, and TD-DFT methods fail to predict the best sensitizers. The ∆SCF coupled with the implicit solvation method and the GW method HOMO-LUMO energies corrected for aqueous environment effect predicted PORPC-2 and PORPC-4 as the best sensitizers. Thus, it emphasized the importance of aqueous environment effect in simulation. However, none of these methods accurately predicted the photocatalytic performance trend of all the four dye-sensitizers. Hence, we have used the dye-molecular aggregation assembly pattern in an aqueous environment to further probe into activity trends and found that the PORPC-3 and the PORPC-4 prefer J-aggregate assembly, whereas the PROPC-1 and the PORPC-2 adopt H-aggregate assembly pattern. Therefore, the synergistic effect of the HOMO-LUMO energy levels and the aggregate assembly pattern determine the photocatalytic performance of the dye-molecules, and the activity trend is PORPC-4>PORPC-2>PORPC-3>PORPC-1, agreed well with the experimental findings.

Acknowledgements

This study was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and Future Planning (Nos. NRF-2017R1E1A1A01074266, NRF-2015M1A2A2057129, and NRF-2016M1A2A2937151).
Effect of the Fe/Co Ratio on Electrocatalytic OER Activity of Cofe-LDH
Authors: Hemmi Shota , Takashima Toshihiro , Irie Hiroshi
Published: December 2020

Solar hydrogen production through photocatalytic or photoelectrochemical water splitting has been considered as a promising route for overcoming the current global reliance on fossil fuels. Within these processes, oxygen evolution reaction requires a large overpotential due to its slow reaction kinetics. Therefore, achievement of efficient OER catalysis using abundant elements has been highly demanding challenge and understanding of the reaction mechanism of OER is important for a rational design of active catalysts. Recently, we identified that Fe4+ acts as an intermediate species of OER on α-Fe2O3, and its efficient formation was found to be necessary to lower the overpotential [1]. Meanwhile, Fe ions incorporated into Ni and Co hydroxides have been reported to be oxidized to Fe4+ during electrochemical anodization [2],[3], and efficient OER has been demonstrated using NiFe and CoFe layered double hydroxides (LDHs) [4]. In this study, we studied the effect of Fe addition on electrical property and OER activity of CoFe-LDH.

CoFe-LDH with different ratio of Co and Fe was synthesized on FTO substrate using hydrothermal method, and its formation was confirmed by XRD measurements. Figure shows chrono amperograms of CoFe-LDH measured at alkaline conditions. As the ratio of Fe was increased up to 36%, a gradual improvement in current density and a negative shift in the onset potential were observed although further increase in Fe content was detrimental for OER activity. Notably, all the CoFe-LDH showed higher OER activity compared with both monometallic Co and Fe oxyhydroxide, indicating that coexistence of Co and Fe is beneficial for the catalyst performance. Details will be discussed in the conference.

Reference

[1] T. Takashima, K. Ishikawa, H. Irie, J. Phys. Chem, 2016, 120, 24827

[2] Hans Christian Bruun Hamen, Christian Bender Koch, Inorg. Chem, 1994, 33, 5363-5365

[3] G. Rajeshkhanna, Thangjam Ibomcha Singh, Nam Hoon Kim, Joong Hee Lee, ACS Appl. Mater. Interfaces, 2018, 10, 42453-42468

Figure 1