bluuebunny/crossref_metadata_2025 huggingface dataset:
In Situ Investigation of CO2 Separation in Macrocyclic and Porous Ionic Liquids
Authors: Mahurin Shannon , Thapaliya Bishnu Prasad , do-Thanh Chi-Linh , Dai Sheng
Published: December 2020

With the continued rise in atmospheric CO2 levels and the potential impact on climate, carbon capture and storage has gained prominence as a potential technological solution to reduce CO2 emissions, resulting in increased interest in advanced materials to facilitate the removal of CO2 from energy-related emissions. While a number of approaches have been explored to separate CO2 from mixed streams, ionic liquids are promising materials due to their negligible vapor pressure, high thermal stability, and the ability to tune physicochemical properties such as CO2 solubility. The incorporation of free volume into ionic liquids through appropriate development of bulky cation/anion pairs or through the creation of porous ionic liquids can impact both gas transport and solubility. Macrocyclic ionic liquids where the bulky cation consists of a nitrogen heterocycle connected by ether linkages can selectively remove CO2 from mixed gas streams and offer a potential avenue for CO2 capture. Porous ionic liquids are emerging materials that combine the attributes of porous materials within a nonvolatile liquid matrix. Permanent porosity is incorporated into the ionic liquid by adding a framework material (zeolitic imidazolate framework) where the cations and anions are too large to diffuse into the host. We investigated the selective absorption of CO2 in both macrocyclic and porous ionic liquids and examined the effect of porosity on CO2 sorption capacity and gas transport. Relevant physical and chemical properties of these unique materials such as solubility, density, viscosity and structure were measured. In addition, analysis of the vibrational modes of both the ionic liquid and the CO2 through in situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) measurements was used to better understand the mechanisms of CO2 interaction with the ionic liquids and the impact on solubility and transport. Moreover, we find that certain of these ionic liquids exhibit a unique binding and release of CO2 which could open new avenues for CO2 capture and storage.
Synthesis of Refractory Metal Carbides on Carbon Fibers in Molten Salts and Their Electrochemical and Electrocatalytic Properties
Authors: Miklashov Dmitriy , Luneva Svetlana , Dolmatov Vladimir , Kuznetsov Sergey
Published: December 2020

Method of currentless transfer in molten salts was used for synthesis of tantalum and niobium carbides coatings and crystals of molybdenum carbide on carbon fibers. Temperature of process was varied from 800 up to 900 °C, and time of process from 0.5 up to 24 hours.

Figure 1. Micrographs of carbon fiber with TaC and NbC coatings and Mo2C crystals (from left to right), obtained in molten salts melts by currentless transfer.

The splicing of fibers with each other was not observed; coatings were uniform in a cross section as well as along the fiber. Thickness of TaC and NbC coatings on carbon fiber was 50 – 250 nm. Size of crystals of Mo2C was approximately several micrometers.

Investigation of refractory metal (Ta, Nb, Mo) carbides on carbon fiber of the Carbopon-B-22 brand was carried out by impedance spectroscopy method. The values of the standard rate constants of charge transfer and capacities of the double electric layer were determined for synthesized materials in water solution with hydrogen peroxide.

Coatings and crystals of refractory metal carbides on carbon fibers can be used as catalysts and electrocatalysts. The kinetics of the electrocatalytic decomposition of hydrogen peroxide on the surface of TaC/C, NbC/C and Mo2C/C composite materials was studied. This reaction was investigated on measuring the volume of released oxygen. The initial carbon fiber of the Carbopon-B-22 brand was used as the cathode. The composite materials made of carbon fiber coated with tantalum carbide TaC (NbC) or modified by molybdenum carbide Mo2C served as the anode. The reaction order was established, the rate constants and activation energies of the hydrogen peroxide decomposition were calculated. The composition with the highest electrocatalytic activity was determined.

Figure 1
Electrochemical Reduction of ZrO2 in Molten Electrolytes
Authors: Omel'chuk Anatolii A , Gritsai Larisa V. , Bosenko Olga V , Skryptun Igor N
Published: December 2020

The results of the electrochemical reduction of zirconium dioxide in molten electrolytes based on calcium or magnesium chloride on a liquid gallium cathode, bypassing the stage of granulation and sintering with carbohydrates, are presented. The liquid gallium cathode provides not only reliable contact with zirconium dioxide, but also favourable conditions for its reduction. The contact area of the gallium cathode with fine oxide powder is much larger than the contact area of the granulated and sintered zirconium dioxide with a solid conductor. This ensures a more uniform cathode polarization. Due to the lower specific mass, zirconium dioxide is located on the surface of gallium cathode, the convective movement of which provides more intense mass transfer at the interface of the phases and removal of recovery products from the zone of electrode reaction. Products of electrolysis under such conditions do not block neither the surface of zirconium dioxide nor the surface of the cathode. Zirconium, which is formed during the renewal, due to a larger specific mass, precipitates to the bottom of the electrolyser, and the layer of gallium protects it from interaction with the components of the molten electrolyte. In addition, due to the formation of alloys, the reduction of metal cations on liquid cathodes proceeds at more positive potentials than on solid indifferent cathodes, which reduces the specific energy consumption by electrolysis. The results of voltammetric studies confirm this conclusion.

The reduction product is fine-grained zirconium powder with an average particle size of 1—3 microns, and purity of 99.9 %. As the density of the current increases, the value of the specific surface of the powder, the specific volume of the micropore and their average radius decrease. The degree of extraction depends on the composition of the electrolyte mixture and naturally decreases when replacing cations in the melts both on the basis of calcium chloride and on the basis of magnesium chloride in the following sequence Na+ > K+ > Li+. The melt based on compounds of calcium and sodium chloride provides the best performance. The removal degree of zirconium from such melt reaches 77 %.
Factors Affecting Li+ Transport Properties of Molten Li Salt Solvate Electrolytes
Authors: Shigenobu Keisuke , Dokko Kaoru , Watanabe Masayoshi , Ueno Kazuhide
Published: December 2020

Among Li+ transport properties of electrolytes, ionic conductivity and Li+ transference number (t
Li) are key factors contributing to enhancement of the battery performance. High t
Li enables rapid charging even if the ionic conductivity is lower than that of conventional organic electrolytes and would also suppress the lithium dendrite formation despite the relatively low mechanical properties of the electrolytes [1], [2]. Our group focuses on molten Li salt solvate electrolytes including glyme (G4)-based solvate ionic liquids (SILs) owing to their attractive thermal and electrochemical properties. Recently, we have reported that high t
Li (= 0.77) resulting from unique Li ion hoppling/exchange conduction mechanism in sulfolane (SL)-based electrolytes allows for the improved charge-discharge rate performance of Li-ion and Li-S batteries [3], [4]. Few studies, however, have clarified the relationship between t
Li, which is affected by the correlations of ionic motions and molecular structure for highly concentrated electrolyte systems like molten Li salt solvates. In this study, we attempted to understand the cross-correlations of ionic motions and clarify their effects on the transport properties in molten Li salt solvate electrolytes with different solvent and anion structures.

Table 1 Two transference numbers of the electrolytes.

Sample

t
Li NMR

t
Li PP

[Li(G4)][TFSA]

0.52

0.03

[Li(SL)3][TFSA]

0.57

0.69

Table 1 illustrates two different t
Li values of the electrolytes; one is estimated from self-diffusion coefficients measured by pulse field gradient (PFG)-NMR (t
Li NMR
) and the other is estimated from the electrochemical method (t
Li PP
) [5], [6]. In the case of [Li(G4)][TFSA], t
Li PP
is extremely low compared with t
Li NMR
, which implies the concentration polarisation in this electrolyte is more pronounced under the electric field. By contrast, for [Li(SL)3][TFSA], t
Li PP
is higher than t
Li NMR
. This suggests that the interionic correlations can enhance t
Li PP
in [Li(SL)3][TFSA]. We further discuss the interionic cross-correlations and their relationship with Li ion transport properties of other electrolytes in detail.

References

[1] K. M. Diederichsen; E. J. McShane; B. D. McCloskey, ACS Energy Lett., 2017, 2, 2563-2575.

[2] P. Barai; K. Higa; V. Srinivasan, J. Electrochem. Soc., 2018, 165, 11, A2654-A2666.

[3] K. Dokko; D. Watanabe et al., J. Phys. Chem. B, 2018, 122, 10736-10745.

[4] A. Nakanishi; K. Ueno et al., J. Phys. Chem. C, 2019, 123, 14229-14238.

[5] P. G. Bruce; J. Evans; C. A. Vincent, Solid State Ionics, 1988, 28-30, 918-922.

[6] M. Watanabe; S. Nagano et al., Solid State Ionics, 1988, 28-30, 911-917.
Ionic Liquid Membraneless Redox Flow Battery
Authors: Chaabene Nesrine , Ngo Kieu , Turmine Mireille , Vivier Vincent
Published: December 2020

Today, ionic liquids are more and more present in many fields and more particularly in electrochemistry. Indeed, their physical and chemical properties are appealing and attractive. They are conductive solvents in which organic and inorganic salts can be dissolved depending on the nature of the anion and cation that make up the ionic liquid. However, only very few studies have reported their use in membraneless redox flow batteries (RFBs) for the storage of renewable energy 1, 2. The concept of membraneless redox-flow batteries was first reported by Ferrigno et al.3 in 2002, with the development of a millimeter-scale redox fuel cell based on the vanadium aqueous electrolyte solutions.

In this work, we have developed an ionic liquid membraneless RFB by using 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (C2mimTFSI) as supporting electrolyte and Quinone (Q) and iron chloride (FeCl2) as electroactive species in a microfluidic system. Polarization curve and cyclic voltammetry were used to characterize the electrochemical properties as well as the performance of the microbattery. The proof-of-concept of the system has been shown with an open circuit potential of 0.6 V, obtained with both polarization curve and cyclic voltammetry, and with a current density ranging from 0.3 to 0.65 mA cm-2 for total flow rates of 10 to 20 µL min-1. As shown on fig. 1(b), a maximum of power of 40 µW cm-2 has been obtained. Such a technology is promising and performances can be enhanced by using 3D electrodes and optimizing the choice of the redox mediators (concentration, potential, etc.)

Navalpotro, P.; Palma, J.; Anderson, M.; Marcilla, R., A Membrane-Free Redox Flow Battery with Two Immiscible Redox Electrolytes. Angew. Chem. Int. Ed. Engl.
2017,
56 (41), 12460-12465.

Chen, R.; Bresser, D.; Saraf, M.; Gerlach, P.; Balducci, A.; Kunz, S.; Schroder, D.; Passerini, S.; Chen, J., A Comparative Review of Electrolytes for Organic-Material-Based Energy-Storage Devices Employing Solid Electrodes and Redox Fluids. ChemSusChem
2020,
13 (9), 2205-2219.

Ferrigno, R.; Stroock, A. D.; Clark, T. D.; Mayer, M.; Whitesides, G. M., Membraneless vanadium redox fuel cell using laminar flow. Journal of the American Chemical Society
2002,
124 (44), 12930-12931.

Figure 1
Quantum-Chemical Study of the Electron Transfer in CaTiF6+12CaCl2 Model System
Authors: Stuliov Yuriy V. , Kremenetsky Vyacheslav G. , Kuznetsov Sergey A.
Published: December 2020

Today, quantum-chemical studies of the mechanism of electron transfer in molten salts based on a direct calculation of the transition state are faced with practically insurmountable computational difficulties. As our experience shows, model systems assigned to investigate the mechanism of charge transfer should include, in addition to the electroactive complex, two more of its coordination spheres. For electrolytes based on alkaline earth metal halides, this can be, for example, MTiF6+12MX2 type systems (M – Mg, Ca, Sr, Ba; X – F, Cl). The search for a transition state by standard methods will require enormous computer time and is almost unrealistic. In this paper, we proposed another approach, which is based on the analysis of frontier molecular orbitals (FMO) under various deformations of the initial structure.

The aim of this work was the using of the method of frontier molecular orbitals to study the mechanism of the electron transfer in the CaTiF6+12CaCl2 model system.

The geometry optimization of structures was performed with the Firefly program package, partially based on the source code of the GAMESS(US) program, by the density functional theory DFT/UHF method with the use of the B3LYP hybrid functional. For the F and Cl atoms quasi-relativistic basis set Stuttgart RLC ECP was used; for Ti and Ca – Stuttgart RSC 1997 ECP basis set.

In this work, we were interested in the state of the complex TiF6
2- near the cathode surface. For this reason, on one side of the model system, a flat boundary layer consisting of 12-15 chlorine and calcium ions was formed. The titanium complex is in contact with one of the calcium cations belonging to the boundary layer, because our previous studies indicate the bridge nature of electron transfer to the TiF6
2- complex. Note that adding of carbon cluster to the main system CaTiF6+12CaCl2 would require a drastic increase of the computation time. However, for qualitative conclusions, it is enough to analyze the CaTiF6+12CaCl2 system.

Based on the experimental data and the quantum-chemical analysis of FMO in the CaTiF6 + 12CaCl2 system, a mechanism for the charge transfer was proposed. The geometric structure of the transition state was shown to be not intermediate between the initial and final states of the system. As a result, it was found that the structure of this state is much less ordered than the initial structures of the boundary layer. The high efficiency of FMO method allows recommending this method as the instrument for testing hypotheses on the mechanism of electron transfer in molten salts.
Electrodeposition of Tungsten from Molten KF–KCl–WO3 and CsF–CsCl–WO3
Authors: Nohira Toshiyuki , Meng Xianduo , Ide Tatsuya , Norikawa Yutaro , Yasuda Kouji
Published: December 2020

Introduction

Tungsten metal is known for its robustness, especially high melting and boiling points and hardness. However, its hardness and brittleness make it difficult to work. Thus, electrodeposition of flat and dense tungsten films is worth investigating. There are a number of reports on the electrodepositon of tungsten from high temperature molten salts such as fluorides [1], chlorides [2], oxides [3], etc. It is known that dense and coherent tungsten deposits are more easily obtained from molten fluorides compared to molten chlorides. One drawback of typical fluoride melts like LiF–NaF–KF is difficulty in removing the adhered molten salts by water washing because LiF and NaF have limited solubility to water [4]. Although good tungsten deposits can be electrodeposited from molten oxides [3], the operation temperature tends to be very high, typically over 1123 K.

From this background, we proposed new electrolyte baths, molten KF–KCl [5,6] and CsF–CsCl. Since all the components salts of KF, KCl, CsF and CsCl have large solubility to water [4], solidified salts on deposited films can be easily removed by water washing.

Results & Discussion

First, electrodeposition of tungsten was investigated in eutectic KF–KCl melt to which WO3 was added at 923 K. Cyclic voltammograms at copper and gold electrodes indicated the deposition of tungsten metal at more negative potential than 1.55 V vs. K+/K. The effects of electrolysis conditions on the morphology of deposits were studied by changing the cathodic current density from 12.5 to100 mA cm−2. As shown in Fig.1(a), a dense tungsten film with a thickness of approximately 20 µm was obtained on a copper substrate electrode at 12.5 mA cm−2 for 120 min. From the Raman spectra of molten KF–KCl and molten KF–KCl–WO3 at 923 K, the coordination structure of W(VI) complex ion was indicated to be fac-[WO3F3]3−.

Secondly, eutectic CsF–CsCl melt was used to lower the operation temperature. After adding 2.0 mol% of WO3, the electrodeposition was investigated using copper and gold electrodes at 823–923K. As shown in Fig.1(b), a flat and dense tungsten film was obtained by galvanostatic electrolysis at 12.5 mA cm−2 for 120 min at 873 K.

Acknowledgement

This study is supported by Sumitomo Electric Industries, Ltd. The present address of Kouji Yasuda is Graduate School of Engineering, Kyoto University.

References

[1] S. Senderoff, G. Mellors, Science, 153, 1475 (1966).

[2] M. Masuda, H. Takenishi, A. Katagiri, J. Electrochem. Soc., 148, C59 (2001).

[3] K. Koyama, M. Morishita, T. Umezu, Electrochemistry, 67, 667 (1999).

[4] D. R. Lide (Ed.), CRC Handbook of Chemistry and Physics, 88th Edition, Chap.4, p.43-101, CRC Press, Boca Raton (2007).

[5] K. Maeda, K. Yasuda, T. Nohira, R. Hagiwara, T. Homma, J. Electrochem. Soc., 162, D444 (2015).

[6] T. Nohira, Molten Salts, 62, 3 (2019).

Figure 1
Electrochemical Reduction of Tungsten Oxide in Molten Chlorides
Authors: Skryptun Igor N , Bosenko Olga V
Published: December 2020

The direct electrochemical reduction of titanium oxide to titanium metal in molten CaCl2 salt has been proven by the FFC Cambridge process. [1] Subsequently, the process has been applied to a number of refractory metals. However, there are limitations to the FFC Cambridge process. For example, the current efficiency of the process is quite low, 10-40%, to achieve sufficiently low oxygen content, 0.3%, in the final titanium product. [2] This could be due to a number of reasons, such as the increasing concentration of O2- ions in the melt as the reduction process proceeds. The metal oxide electrode has an inherent pore structure and sponge-type substrate electrodes can be used with a range of pore sizes, which has the advantage of high surface area and access of the melt to the oxide. However, when the metal oxide is reduced, oxide ions accumulation in the pores can significantly change the potential needed for the reduction, as shown in the Littlewood [3] predominance diagram. It can also result in the formation of other unwanted metal phases, such as those that include the salt’s metal, as it reacts with the oxide ions. Oxide ion build up close to the electrode surface can ultimately bring the reduction process to a halt, leaving the inner parts of the metal oxide unreduced.

1. Chen, G.Z., D.J. Fray, and T.W. Farthing, Direct

electrochemical reduction of titanium dioxide to

titanium in molten calcium chloride. Nature,

2000. 407(6802): p. 361-364.

2. Schwandt, C., D.T.L. Alexander, and D.J. Fray,

The electro-deoxidation of porous titanium

dioxide precursors in molten calcium chloride

under cathodic potential control. Electrochimica

Acta, 2009. 54(14): p. 3819-3829.

3. Littlewood, R., Diagrammatic Representation of

the Thermodynamics of Metal‐Fused Chloride

Systems. Journal of the Electrochemical Society,

1962. 109(6): p. 525.
Limited Ionicity in Protic Ionic Liquids: Organic Acid/Trialkylamine Mixtures
Authors: Klapatiuk Devin Oscar , Johnson Keith Edward , East Allan L. L.
Published: December 2020

Mixtures of amines with carboxylic acids give not only limited ionicity, but also fascinating profiles of conductivity vs mixing ratio. These acids, when mixed with pyridine or tertiary amines, produce conductivity maxima at 5:1 (not 1:1) mole:mole mixing ratios. Other historical cases of amine/acid mixtures have produced double maxima vs mixing ratio. A good theory to quantitatively explain these is, after over 100 years, still lacking. Here we report on our recent efforts to extend our 2018 pyridine/acetic acid theory to apply to trialkylamine/acid cases. Unlike the pyridine case, where the maxima in volume contraction, viscosity, ion concentration, and conductivity are all at the 5:1 ratio, the trialkylamine cases show more structural complexity; for instance, triethylamine with propionic acid produces these four maxima at four unique ratios (2:1, 3:1, 4:1, and 5:1 respectively). Our extension incorporates some excellent advances put forward by Huyskens in 1980 for these trialkylamine cases.
Understanding Metal Deposition in Solid Electrolytes Due to Mixed Ionic-Electronic Conduction
Authors: Tu Qingsong , Shi Tan , Ceder Gerbrand
Published: December 2020

The effect of ionic and electronic conductivity in the solid electrolytes (SE) on metal (such as Li, Na) deposition and dendrite propagation in the SE are investigated. A new framework for metal formation inside defects (such as voids, grain boundaries) in the SE due to the electronic conductivity of the SE is established. We find that for typical SE material (with ionic conductivity ~0.1mS/cm and electronic conductivity ~10^-5 mS/cm) isolated voids in the SE that are close enough to the anode side (~0.1 um) may be filled in with metal within several minutes under typical galvanostatic charging condition (with current density 0.1~1mA/cm^2). Continuous deposited metal in the voids may lead to fracture of the SE, which triggers mode II dendrite growth (isolated dendrites growth in the SE). We will propose two strategies to prevent metal deposition in the SE.
Redesigned Solid Polymer Electrolytes By Atomistic Predictions and Supramolecular Chemistry
Authors: Choudhury Snehashis , Bao Zhenan
Published: December 2020

Advancement in energy dense, yet safe batteries is essential for several applications including portable electronics and transportation. However, a major challenge in energy storage systems is the instability of electrolyte materials due to their limited chemical and electrochemical stability, as well as their flammability. We believe, solid-state polymer electrolytes can address the inherent problems of their liquid counterparts and simultaneously provide new avenues for battery development with unprecedented mechanical design. In this regard, polyethylene oxide (PEO) have been the most widely studied solid electrolyte because of their ability of solvating metal salts for ion transport. However, conductivity of PEO is highly temperature dependent because of their crystallinity and they have limited electrochemical stability due to the ease of electron extraction at high voltages (>3.8V vs Li/Li+). In this talk, I will discuss our recent work of redesigning monomer chemistry of ion conducting polymers by ab-initio calculations. Based on the theoretical predictions, we synthesized a new class of polymer electrolytes and evaluated their ion transport and rheological properties. We further utilized nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR) coupled with molecular dynamics (MD) simulations to understand the solvation structure and ionic aggregations. Finally, we demonstrate the application of these rationally designed polymer electrolytes in a high-voltage lithium metal battery, under specific conditions where conventional PEO electrolytes fail to operate.
In Situ Neutron Scattering to Elucidate the Mechanism of Rapid Lithium Ion-Conducting Garnet Synthesis Using Nanoparticles
Authors: Sacci Robert , Malkowski Thomas , Chen Xi Chelsea , Kirkham Melanie J. , McAuliffe Rebecca D , Armstrong Beth L , Veith Gabriel M. , Daemen Luke L
Published: December 2020

Consumer safety is a market force that is impeding high energy-dense lithium metal batteries from entering the marketplace. As such, research and development into solid electrolytes (SE) have yielded several promising candidates for solid-state batteries. However, each class of SEs comes with particular problems that either increase processing cost, or decrease performance relative to current liquid electrolytes, or both. For example, Lipon and other similar lithium silicates and phosphates are stable against high voltage cathodes (>4.5 V) and lithium metal; however, their conductivity is poor, leading to low power density. Lithium phosphorus sulfides (LPS) have the opposite problem, high conductivity, and instability. Ceramic phases such as Li7La3Zr2O12 (LLZO) have attractive advantages to both classes of materials, inherently high Li conductivity and chemical robustness. However, these advantages come with a cost: complicated processing in terms of high-temperature synthesis and interface control. Concerning the first perceived processing problem, temperatures used for the solid-state synthesis of LLZO are 1000 °C or greater. These temperatures not only adds to the manufacturing costs, but it also promotes lithium evaporation, which then requires the addition of 5-20% excess lithium precursor; costs increase further. Because Li loss leads to a Li concentration gradient resulting in a mixed-phase product, single-phase cubic LLZO synthesis requires manual separation or multiple grinds and calcines. Therefore, we need a new method for LLZO synthesis, and to do that, we need to understand the reaction pathway.

This work demonstrates a method to improve the reaction kinetics and purity of LLZO through the use of nanoparticles of a known intermediate to improve the reaction kinetics and purity of LLZO. We will show in situ neutron scattering results that suggest the formation of La2Zr2O7 during typical LLZO occurs right before LLZO. This fact led to a strategy for reducing both synthesis time and temperature. We describe an efficient synthesis pathway for Al-doped LLZO using La3Zr2O
x
nanoparticles with nitrate precursors. The reaction is completed within one hour and produces a porous network of LLZO.

This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Materials Science and Engineering. This research used resources at the Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory.
Identifying Descriptors to Predict the Sintering Temperature of Doped Llzo from First-Principles Simulations
Authors: Wan Liwen , Dive Aniruddha Mukund , Kang ShinYoung , Wood Brandon C.
Published: December 2020

The charge-discharge performance of a solid-state ceramic lithium battery is strongly affected by the interfacial contact between the electrodes and the solid-electrolyte. Post-annealing has shown promises to improve the physical contact between solid-electrolyte and Li metal anode, however this approach is far less effective at the interface with the cathode because very high ceramic processing temperatures are required to produce full densification at the interface. For example, typical sintering temperature of garnet LLZO is around 1100ºC, yet most cathode materials cannot survive a temperature above 900ºC. Lowering the LLZO sintering temperature to below 900ºC would enable new processing of more robust ceramic solid-state batteries. In this work, we use first-principles based simulation technique to explore how chemical modification of LLZO would affect its sintering behavior. We will determine a group of descriptors that can accurately and efficiently predict the sintering temperatures of doped LLZO compounds. We will further discuss the implication of doping towards Li-ion mobility in these doped LLZO compounds.
Engineering of Fermi Level by Construction of Hybrid Systems
Authors: Bienkowski Krzysztof , Solarska Renata Anna
Published: December 2020

Hybrid heterostrures provide a versatile and largely enhanced systems in comparison to their single components. However, construction of effective visible-light responding and stable hybrid heterojunction based photoelectrodes remains a challenge due to stricte requirements regarding band alignment in such constructions. Therefore implementation of a conductive mid-layer of reduced graphene oxide (RGO) might be a crucial factor in band structure engineering. Herein we demonstrate the formation of an outperforming hybrid heterojunction photocatalyst containing diversified synthetic approaches RGO and thus allowing to engineer the Fermi level position within the working architecture.

Shifting the position of the Fermi level makes possible to increase the size of the depletion layer and PEC efficiency of the entire system increases.
Fluorescent pH-Nanosensors for the in-Operando Visualization of Fast Dynamics, Interfacial pH in Electrochemical Reactions
Authors: Elsutohy Mohamed M. , Fuladpanjeh-Hojaghan Behzad , Roberts E.P.L. , Trifkovic Milana
Published: December 2020

The in-operando visualization of interfacial pH distribution, at electrode-electrolyte interface, provides crucial insights into the mechanism and performance of many electrochemical processes. However, due to the fast dynamics and wide pH range, the spatiotemporal visualization of such interfacial pH changes requires the development of appropriate probes capable of capturing evolution of pH changes in the harsh chemical environments that normally occur in electrochemical processes. In this study, ratiometric, fluorescent, pH-sensitive nanosensors were fabricated with a wide pH measurement range (pH 3.5 to 11), for the in-operando visualisation of fast-dynamic, interfacial pH changes during an electrocoagulation process. The developed nanosensors were synthesised from the crosslinked polyacrylamide matrix, covalently linked to three pH-sensitive dyes and a reference fluorophore, to provide ratiometric nanosensors with protective but proton permeable matrix and comparable sensitivity and responsiveness to the free dyes. Using the developed nanosensors and an electrochemically coupled laser confocal fluorescence microscope, the in-operando visualization of the dynamic interfacial pH distribution during electrocoagulation of synthetic and real oil-sands produced water was achieved for the first time. The results (Figure 1) revealed the differences between the real and synthetic produced water and reflected the crucial roles of factors such as the rate of water electrolysis and chemical composition of the system on the evolution of the pH boundary layer and the interfacial pH. Overall, this study provides powerful probes (nanosensors) that can be utilized to study interfacial pH changes in a wide range of electrochemical reactions such as batteries and electrolyzers.

Figure 1: Selected time series, processed images shows the differences in the interfacial pH boundary layers evolved during the electrocoagulation treatment of synthetic and real produced water. In-operando imaging was conducted using the developed nanosensors and an electrochemically coupled laser scanning confocal microscopy.

Figure 1
Correlating Oxidation State and Surface Area to Activity from Operando Studies of Copper CO Electroreduction Catalysts in a Gas-Fed Device
Authors: Sullivan Ian , Lee Soo Hong , Larson David M , Liu Guiji , Toma Francesca M. , Xiang Chengxiang("CX") , Drisdell Walter
Published: December 2020

The rational design of high-performance electrocatalysts requires a detailed understanding of dynamic changes in catalyst properties, including oxidation states, surface area, and morphology under realistic working conditions. Oxide-derived Cu catalysts exhibit a remarkable selectivity towards multi-carbon products for the electrochemical CO reduction reaction (CORR), but the exact role of oxide remains elusive for explaining the performance enhancements. Here, we used operando X-ray absorption spectroscopy (XAS) coupled with simultaneous measurements of catalyst activity and selectivity by gas chromatography (GC) to study the relationship between oxidation states of Cu-based catalysts and activity for ethylene (C2H4) production in a CO gas-fed cell. By utilizing a custom-built XAS cell, oxidation states of Cu catalysts can be probed in device-relevant settings and under high current densities (>80 mA/cm-2) for CORR. By employing an electrochemical oxidation process, we found that the Cu oxidation states and specific ion species do not correlate with C2H4 production. The difference in CORR activity is also investigated in relation to the electrochemical surface area (ECSA) changes. While hydrogen evolution reaction (HER) activity is positively correlated to the ECSA changes, the increased C2H4 activity is not proportional to ECSA. Ex-situ characterization from microscopic techniques suggests that the changes in C2H4 activity and selectivity may arise from a morphological transformation that evolves into a more active structure. These comprehensive results give rise to the development of a cell regeneration method that can restore the performance of Cu catalyst without cell disassembly. Our study establishes a basis for the rational design of highly active electrocatalysts for broad-range reactions in a gas-fed device.
Enabling Real-Time Detection of Electrochemical Desorptionphenomena with Sub-Monolayer Sensitivity
Authors: Cavalca Filippo , Trimarco Daniel
Published: December 2020

Across many scientific and industrial fields, it is a challenge to analyze chemical reaction products with high sensitivity and fast time-response. This is especially true in systems related to electrochemical energy conversion and storage, such as batteries and fuel cells, where accurate monitoring of fast and transient reaction phenomena often reveals key insights.

Here, we present a unique analysis instrument using a microchip-based inlet system to couple a mass spectrometer directly to any liquid test environment, aqueous or non-aqueous, and exhibits a sensitivity 3-4 orders of magnitude than conventional differential electrochemical mass spectrometry (DEMS).1–3 The instrument allows to measure the evolution of volatile products and consumption of reactants at electrode surfaces. Due to its extraordinary sensitivity, the system can measure all the individual volatile molecules desorbing from an electrode surface during a single electrochemical turnover. Product formation can be measured from total Faradaic currents of 1 mA all the way down to 1 nA, corresponding to approximately 10 ppm of a monolayer desorbing from the electrode surface in 1s. These features enable time-resolved, fully quantitative measurements of transient phenomena during electrochemistry, providing fundamental insight in the electrochemical reaction mechanisms. Furthermore, an accurately calibrated on-chip gas system allows rapid gas switching between different gases, both inert and reactive. Due to the near-instantaneous equilibration between gas and electrolyte, the transient response of electrodes to rapid gas exposure changes can be measured.

The capabilities of this analysis system are showcased by various examples, including electrochemical water-splitting at low overpotential and low-surface area CO-stripping. In situ quantification of hydrogen and oxygen evolution is shown at Faradaic currents on the order of 1 nA. In comparison, conventional techniques can only detect down to about 10 μA of continuous product formation. Finally, the electrochemical stripping of < 1 % of a CO monolayer at standard potential scan-rates of 50 mV/s is shown (Fig. 1).

Figure 1. H2 evolution and CO stripping experiments using a polycrystalline Pt electrode in 1M HClO4.

Trimarco, D. B. et al. Enabling real-time detection of electrochemical desorption phenomena with sub-monolayer sensitivity. Electrochim. Acta
268, 520–530 (2018).

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Figure 1
Revealing Solvent Effects on Ion Insertion within Battery Primary Particles Using Operando Scanning Transmission X-Ray Microscopy
Authors: Chung Jinkyu , Koo Bonho , Kim Juwon , Seo Sungjae , Lee Danwon , Han Jeongwoo , Jo Sugeun , Kim Namdong , Shin Hyunjoon , Yu Young-Sang , Shapiro David , Lim Jongwoo
Published: December 2020

LiFePO4 (LFP), the attractive commercial cathode materials, exhibits the phase separation between lithium-poor and lithium-rich phase within individual particles due to the wide miscibility gap. The boundaries between such phases develop large stress, lead to cracks within individual particles, and decay the cycle life. There have been lots of interest in investigating the origin of lithium heterogeneity and manipulating the phase boundaries within the particles during cycling. Previously, we revealed that insertion kinetics is dependent on the local lithium composition from which the hysteresis of lithium spatiodynamics originate. [ref.1] In addition, uniformity of ion insertion kinetics at electrolyte-electrode interface governs lithium heterogeneity and spatiodynamics in ether-based organic electrolyte. [ref.1] However, it remains still unclear how the chemical interaction of lithium ions, electrolyte molecules, and solid electrode controls nanoscale ion insertion kinetics. By developing operando scanning transmission x-ray microscopy (STXM) platform which maps lithium composition within individual LFP particles at 50 nm resolution during cycling, we investigated the interfacial lithium transport in various electrolytes: water, carbonates, and ethers. We synthesized LFP particles with platelet morphology and [010] crystallographic axis, which is fast ion diffusion direction, lied parallel to the monochromatic X-ray allowing to visualize lithium transport in the particles. Herein, we discover that aqueous electrolyte greatly accelerates lithium insertion kinetics, completely redirecting lithium heterogenesity and spatiodynamics compared with organic-based electrolyte. Aqueous environment kinetics show higher exchange current density (~700 mAm-2) than organic EC/DMC (~200 mAm-2) and also higher surface diffusion rate which account for the higher degree of intraparticle phase separation within the particles. By extracting kinetics parameters from our result, we experimentally demonstrate that heterogeneity and spatiodynamics in the single particle kinetics is determined by the strong interaction between the electrolyte molecules and the surface of electrode particles.

Ref. 1 J. Lim et al. Science (2016) 353 p566

Figure 1
Copper Sulfide Derived Nanoparticles Supported on Carbon for the Electrochemical Reduction of Carbon Dioxide
Authors: Tapia Rosales Marisol , van Oversteeg Christina H.M. , Helfferich Kristiaan H. , Ghiasi Kabiri Mahnaz , Ngene Peter , de Mello Donegá Celso , de Jongh Petra E.
Published: December 2020

The electrocatalytic reduction of CO2 (CO2RR) and H+ (or H2O) into chemicals and fuels is attracting attention as a way to address current energy and environmental issues. One of the main focus in this field is the development and understanding of electrocatalysts that can promote the electrochemical CO2 reduction efficiently, and with high selectivity for the desired product. Copper electrodes are extensively studied and stand out because of their unique ability to produce a range of different products including hydrocarbons and oxygenates, which is ascribed to their intermediate binding strength for the CO intermediate. The use of oxide-derived Cu electrodes has arisen, because it promotes CO and COOH formation at low overpotentials, even though the electrodes are operating at potentials where the CuO should be reduced to metallic copper. Inspired by this, some recent studies have also shown that the use of sulfur-containing Cu or sulfide-derived Cu increases the selectivity towards formates, ethanol, propanol, or ethylene at intermediate overpotentials. The origin of these effects is still under debate, but it is often attributed to a change in the binding energy of the intermediates such as *OCHO, *COOH, and CO due to the formation of specific Cu surface structures or the presence of sub-surface sulfur or oxygen in the Cu or mixed phases.

In this work, we investigated the phase stability and catalytic performance of carbon-supported sulfide (CuS and Cu2S) derived Cu nanoparticles in the electrochemical reduction of CO2 in aqueous media. The CuS@C and Cu2S@C nanoparticles were prepared via a novel, liquid phase sulfidation method, in which carbon-supported CuO (CuO@C) nanoparticles were converted to either CuS@C (25±13 nm) or Cu2S@C (17±1 nm) as shown in Figure 1a. The stability of the supported nanoparticles was investigated using cyclic voltammetry, where reduction peaks were observed in the first cathodic scans of both CuS@C and Cu2S@C (figure 1c). The reduction was monitored operando under CO2 reduction conditions using in-situ X-ray absorption spectroscopy (XAS). The in-situ XAS spectra showed that at a potential of -0.9V vs. the reversible hydrogen electrode (RHE), both CuS@C and Cu2S@C are reduced to metallic Cu@C. Finally, the products formed by the CuS@C and Cu2S@C-derived catalysts were compared to those of CuO@C-derived catalyst. At current densities of -1.5mA/cm2, the CuS@C- and Cu2S@C-derived catalysts show increased production of formate (figure 1d), while CO production is suppressed, in comparison to the CuO@C catalyst. Cu-sulfide derived catalyst showed differences in formate production, indicating the initial Cu-sulfide phase influences the product selectivity.

Figure 1
(Invited) First-Principles CO2 Reduction Catalyst Design at Electrified Solid-Liquid Interfaces
Authors: Ringe Stefan
Published: December 2020

Electrocatalysis at electrified solid-liquid interfaces is the key to sustainable storage and conversion of energy. In the search for more active electrocatalysts, first-principles calculations based on Density Functional Theory have become a state-of-the-art means, which, however generally, ignore the presence of the interface. In this talk, we revisit the implications of this approximation at the example of electrocatalytic CO2 reduction. In contrast to previous believes, we find the interfacial electric field to be significant and even determine the product selectivity and conversion rate on Gold and Copper catalysts. From experimental and theoretical studies, we then derive novel interface-aware design principles and apply them for material and electrical engineering towards highly optimized energy conversion systems. We also use the concepts to initiate a descriptor-based screening of catalyst materials for CO2 reduction and highlight critical differences to previous studies. Finally, we extend the approach by including also mass transport effects which enables the design of electrode materials on all relevant time and size scales.
Octahedral SnO2 Single Crystals for Selective CO2 Electroreduction
Authors: Liu Hai , Kuang Siyu , Ma Xinbin , Zhang Sheng
Published: December 2020

CO2 electrochemical reduction is one of the effective ways to close the global anthropogenic carbon cycle. However, CO2 reduction is a sluggish process involving multi-electrons and multi-protons transfer and needs to compete with hydrogen evolution reaction (HER)1. According to the pioneering studies by Hori et al., metal catalysts can be classified into four categories in terms of main products, where formic acid/formate as an ideal hydrogen storage carrier is an attractive product. Indeed, a recent technoeconomic analysis shows that the 2e- products (formate and CO) are more desirable. The p-block transition metals (such as In, Sn, Pb, Tl, Bi) have been found to be able to selectively convert CO2 to formate. In particular, tin-based catalysts have been intensively investigated owing to its inexpensive price and low toxicity.

Our previous work has explored the size effect of SnO2 nanoparticles and carbon support effect on the catalytic activity for CO2 electroreduction2. Kanan’s group has also investigated bulk tin oxide layer for the CO2 electroreduction3. Unfortunately, all the aforementioned tin catalysts display volcano-type formate selectivity against potential plots, since too positive or too negative potentials favor competitive hydrogen evolution reaction, which limits their applications in practical CO2 electrolyzers.

Herein, we have synthesized octahedral SnO2 single crystals exposed with facets denoted (332) and (111). Interestingly, those high-energy facets exhibit remarkably high CO2 catalytic activity and high formate selectivity of over 80% within a ~500 mV potential window. Density function theory (DFT) calculations and In situ Raman spectroscopic studies demonstrate that the strong adsorption energies for *OCHO species and weak binding strength to HCOOH* favor formate production in a broad potential range. We believe this work will advance the development of practical CO2 electrolyzers.

Reference

1 Zhang, S.; Fan, Q.; Xia, R.; Meyer, T. J. Acc. Chem. Res. 2020, 53 (1), 255-264.

2 Zhang, S.; Kang, P.; Meyer, T. J. J. Am. Chem. Soc. 2014, 136 (5), 1734-1737.

3 Chen, Y.; Kanan, M. W. J. Am. Chem. Soc. 2012, 134 (4), 1986-1989.
First-Principles Study of Oxygen Evolution Reaction Mechanisms in RuO2 and IrO2
Authors: Alexandrov Vitaly
Published: December 2020

Electrocatalytic water splitting has received a great deal of attention as an attractive way of storing energy in the form of pure hydrogen. RuO2 and IrO2 catalysts are archetypical materials used for the anodic oxygen evolution reaction (OER) in acidic media, but even for these oxides atomistic understanding of activity-stability relationships remains incomplete. For example, unlike other metal-oxide catalysts, it is still disputed whether lattice oxygen can be involved in OER in RuO2 and IrO2. In this work employing the density functional theory calculations we demonstrate that the lattice oxygen mechanism (LOM) can indeed outperform the conventional adsorbate evolving mechanism (AEM) at the active sites involving structural defects. These defects include metal vacancies that are known to be formed during electrocatalytic dissolution and metal dopants in the parent structure such as nickel and cobalt. According to calculations IrO2 should be less prone to LOM than RuO2 that is consistent with its greater stability under OER conditions. The obtained theoretical results will be discussed in the context of interplay between different OER mechanisms across OER electrocatalysts, as well as available experimental data.