bluuebunny/crossref_metadata_2025 huggingface dataset:
Separation of Azeotropic Refrigerant Mixtures Using Ionic Liquids
Authors: Shiflett Mark , Baca Kalin
Published: November 2022

Refrigeration and air-conditioning systems are widespread throughout modern society, from the refrigerated cold chain that provides fresh foods and storage of medicines to the air conditioning of homes and buildings. Refrigeration is viewed as one of the most transformative engineering achievements of the 20th century and the demand for cooling will continue to increase as economic conditions improve and the climate continues to warm; however, refrigerants do come with an environmental cost.

In 1987, the Montreal Protocol phased out chlorofluorocarbon (CFC) refrigerants because of their high ozone depletion potential (ODP). The replacements, typically mixtures of hydrofluorocarbons (HFCs), are safe for the Earth's ozone layer, but most have high global warming potentials (GWPs). HFCs account for 7.8% of total global greenhouse gas emissions, with 63% of that from “indirect” emissions (i.e., energy for running the system). As a result, 197 countries signed the Kigali agreement in 2016 to phase out high-GWP HFCs, with the goal of reducing emissions by 80% in the next 20 years. Millions of metric tons (mts) of high-GWP refrigerants will need to be reclaimed, but there are no good methods for separating and recycling the individual components, given that many are azeotropic mixtures.

Currently, there is no means of separating azeotropic HFC mixtures, and the refrigerants will ultimately have to be incinerated. The commercial HFC mixture R-410A containing 50 wt.% HFC-32 (GWP = 675) and 50 wt.% HFC-125 (GWP = 3500) is a prime example. The HFC-32 can be reused when separated in new low-GWP products such as R-454B (69 wt% HFC-32 and 31 wt% HFO-1234yf) with a 75% lower GWP than R-410A.

Ionic liquids are being developed that can separate azeotropic HFC mixtures based on differences in solubility and used as entrainers in extractive distillation. This presentation will provide experimental data on the solubility of HFCs in ionic liquids that have been measured using gravimetric microbalances and modeling using the Peng-Robinson equation of state. ASPEN Plus simulations will show how a pilot process has been designed that can continuously separate azeotropic refrigerant mixtures such as R-410A.
(Invited, Digital Presentation) From Textile Waste to Cellulose Aerogel Beads Using Ionic Liquid
Authors: Negrier Marion , El Ahmar Elise , Sauceau Martial , Sescousse Romain , Bouet Guénaëlle , Eglin David , Budtova Tatiana
Published: November 2022

A huge amount of waste textile is produced every year, and the majority is either burned, or buried in landfills, or downcycled. We propose making high added-value materials, aerogels, from textile waste, using ionic liquids. Aerogels are light-weight and nanostructured porous materials with high specific surface area. Depending on the type of textile, we use ionic liquid either to completely dissolve it (case of rayon or viscose), or to selectively dissolve cellulose (case of polycotton). Cellulose aerogels were made in the form of beads by prilling via dissolution in ionic liquid, coagulation and drying with supercritical CO2. Reference cellulose aerogel beads were made from microcrystalline cellulose to compare with textile-based aerogels.

The rheological properties of cellulose-ionic liquid solutions were studied to select the processing conditions. Aerogel beads of the size from 0.5 to 1.5 mm with excellent circularity were obtained. Cellulose-based aerogel beads from textile and from microcrystalline cellulose have density around 0.1 g/cm3, porosity around 90% and high specific surface area, around 300 m²/g. Cytotoxicity tests showed that these aerogels may potentially be used for life science applications.

Acknowledgements

We are grateful to Institut Carnot MINES for the financial support of this work, Julien Jaxel (PERSEE) for the drying with supercritical CO2, Antoine Perron (GALA – RAPSODEE) for the prilling and Suzanne Jacomet (CEMEF) for the help in SEM pictures.
Incorporation of Functional Extraneous Cellulose in the Natural Fiber Welding Process
Authors: Larm Nathaniel E. , Stachurski Christopher D. , Johnson Peyton J. , Gulbrandson Anders J. , Chase Mary A. , Durkin David P. , Trulove Paul C.
Published: November 2022

The efficient and non-derivatizing dissolution of natural biopolymers by ionic liquids (ILs) is poised to redefine the application of these ubiquitous and structurally robust materials on a grand industrial scale. In concert with this idea is Natural Fiber Welding (NFW), a technique which exploits the solvating properties of ionic liquids to partially dissociate the outer biopolymer layers in strands of fibrous thread, followed by solvent removal to collapse the structures in a reconfigured and entangled hydrogen bonding network. For cotton, this welding produces a layered motif of mesoporous cellulose atop a core of unmodified crystalline cellulose, creating a hierarchical structure which retains a semblance of the native biomaterial. Aggressive welding conditions increase the thickness and surface area of the mesoporous layer, though excessive welding leads to full dissolution of the crystalline core creating a tradeoff between an increase in surface area with loss of product integrity. In the present work, we seek to subvert aggressive welding conditions by supplementing dissolved cellulose as an additive in the welding solution. We will demonstrate how this extraneous cellulose can coat and weld to the underlying cotton substrate to increase the size of the amorphous shell around the crystalline core and, ultimately, bolster the mesoporous network and enhance the overall surface area. In addition, we will discuss how Raman-sensitive functionalization can be used to identify inclusion depth of the extraneous material and as a way to probe the potential for layer-by-layer deposition of functional cellulose during the NFW process.
Ion Dynamics and Charge Transport in Imidazolium Chloroaluminate Ionic Liquids
Authors: Cosby Tyler , Durkin David P. , Mantz Robert A , Trulove Paul C.
Published: November 2022

Ion dynamics and charge transport in a homologous series of imidazolium chloroaluminate ionic liquids are investigated by broadband dielectric spectroscopy, rheology, viscometry, and differential scanning calorimetry. The interplay of anion speciation and alkyl chain length on local and mesoscale dynamics and the corresponding influence on the dc ionic conductivities, zero-shear viscosities, and static dielectric permittivities is investigated. These results are presented within a broader framework of current understanding of dynamics and transport properties of aprotic ionic liquids.
Kinetic and Thermodynamic Properties of Ytterbium Chloride and Fluoride Complexes in Chloride Melts
Authors: Kuznetsov Sergey A , Stulov Yuriy V. , Gaune-Escard Marcelle
Published: November 2022

An important problem concerning rare earth metals and molten salts is the reprocessing of nuclear fuel, since lanthanides are always present in spent nuclear fuel. According to the technology being developed for pyroelectrochemical processing of nuclear waste spent fuel is converted into molten salts by anodic dissolution, followed by electrochemical extraction of actinides from lanthanides.

Thus a knowledge of the electrochemistry and thermodynamics of lanthanide compounds in molten salt systems is very useful for the understanding the recycling of spent nuclear fuel.

The electroreduction of YbCl3 in alkali chloride melts (NaCl-KCl, KCl, CsCl) was studied in the temperature range 973-1173 K by different electrochemical methods. The diffusion coefficients (D) for Yb(III) and Yb(II) were determined by linear sweep voltammetry, chronopotentiometry and chronoamperometry methods. Decreasing values of D were obtained when the cation in the second coordination sphere changed from Na to Cs. It was shown that such changes are due to the decreasing of counter polarizing effect of cations with increasing cationic radius.

The standard rate constants of charge transfer (k
s) for the Yb(III)/Yb(II) redox couple were calculated on the basis of cyclic voltammetry data using Nicholson’s approach. The following row of the standard rate constants of charge transfer has been experimentally determined: k
s (KCl) < k
s (CsCl) < k
s (NaCl-KCl).

The formal redox potentials E*

Yb(III)/Yb(II were obtained in alkali chlorides melts from the linear sweep voltammetry data. From the values of the formal redox potentials were calculated the Gibbs energies and equilibrium constants for the reaction:

YbCl2(sol.) +1/2 Cl2(g.)
« YbCl3(sol.) (1)

It was determined the increasing of the formal entropy for the reaction (1) in transition from NaCl-KCl to CsCl melt that associated with a greater degree of ordering of the reaction products due to the complex formation.

Influence of fluoride ions (NaF) on the electrochemical behavior of the Yb(III)/Yb(II) redox couple in an equimolar NaCl-KCl melt was studied. It was determined а decrease of diffusion coefficients and standard rate constants, as well as a shift of the formal redox potentials to the negative region.
Compatibilization of Recycled Polypropylene with Polyethylene Blends Via Ionic Liquid to Enhance Mechanical Properties
Authors: Nulwala Hunaid , Diaz Carlos , Medlin Ken , Yan Zhijie
Published: November 2022

Polypropylene (PP) is the world's second-largest plastic resin based on production volume, after polyethylene (PE). In 2021, the global production volume of PP amounted to 80 million tons. Less than 2% of total produced PP is recycled annually. PP is sensitive to mixed polymers, and a minor amount of other polymeric contaminants reduces physical properties (Figure 1). To increase the recyclability of PP, there is a specific need to have additives that upcycle. PP represents the most significant opportunity in increasing recycling rates. Ionic liquids (ILs) are universal solvents and can promote compatibilization among different polymers. RoCo has developed several ILs that are non-toxic, and when mixed with polyolefins, they enhance the dispersion of fillers and improve mechanical properties thus opening doors to upcycling of recycled polymers. We have been evaluating the recycling of PP by using ionic liquids. We will be sharing our data on ILs compatibilizer results in retaining and enhancing the mechanical properties of PP even when mixed with 15% PE. Both the tensile and impact properties were improved resulting in upcycling of PP. We are in the process of investigating additional properties such as conductivity and surface properties.
(Physical and Analytical Electrochemistry Division Max Bredig Award In Molten Salt and Ionic Liquid Chemistry) Of Ionic Liquids and Hydrogen Bonds
Authors: Welton Tom
Published: November 2022

Whether it is the solubility of biopolymers, the rates of reactions, the physical properties of ionic liquids, or the formation of Deep Eutectic Solvents, the concept of the hydrogen bond often finds itself at the centre of explanations of ionic liquids’ behaviours. How strange it would seem to someone entering the field today that the idea that hydrogen bonds could form in ionic liquids was even recently controversial. So, how did this transformation come about?

In this presentation, you will meet some of the most well-known names in ionic liquids, both past and present. Key insights have only come from a variety of different techniques, both experimental and theoretical, being brought to bear on the question of whether hydrogen bonds exist or are of any use in ionic liquids and their solutions. You will also see that opposing views can turn out to both be correct and controversies are not always solved by one side ‘winning’ over the other.
Electrochemical Characterization of the Self-Assembled 4,4’-Bipyridine Layers at the Electrode | Ionic Liquid Interface
Authors: Siinor Liis , Ers Heigo , Pikma Piret , Lust Enn
Published: November 2022

Self-assembled monolayers (SAMs) have significant importance in many modern applications1-2. The properties of SAMs depend on many aspects, such as the characteristics of individual molecules, forming the monolayer; by the interactions between these molecules; and SAM interactions with the electrolyte; the crystalline surface of the substrate; etc3. Therefore, the fundamental studies of these systems are crucial in determining the function of SAMs in various applications4-5.

The aim of the current work was to study the adsorption characteristics of 4,4’- bipyridine from ionic liquid media at different electrodes6.

Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were conducted to characterize the electrochemical behavior of the self-assembled 4,4’-bipyridine (4,4’-BP) layers at the Sb(111) and Cd(0001) | 4,4’-BP+1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) interface. All the experiments were carried out in a three-electrode electrochemical cell in a glove-box, i.e., a nitrogen-controlled atmosphere.

CV method was used to examine the electrochemical characteristics of the system under investigation within the potential region −0.9 V < E < 0.0 V for Sb(111) and −2.1 V < E < -0.8 V for Cd(0001) vs. Ag|AgCl. The current values increase rapidly at the more negative end of the studied potential region, indicating that reduction processes started at the Sb(111) and Cd(0001) | 4,4’-BP+EMImBF4 interface. In contrast with the data measured in EMImBF4, where the system shows ideal polarisable behaviour in the whole potential range. Interfacial capacitance (C
s) values were calculated using the relation Cs=−(Z′′2𝜋f)−1

. Capacitance values calculated depend on the composition of the electrolyte (i.e., on the concentration of 4,4’-BP), electrode material as well as on applied potential. Cs
values are lower in the mixture than those measured in pure EMMImBF4 at a certain potential region in the case of both electrode materials. This effect is caused by the adsorption of 4,4’-BP molecules at the electrode surface. The shape of the phase angle vs. frequency (f) curves shows that mixed kinetic processes occur in the whole f range measured (i.e. diffusion and charge transfer steps in addition to adsorption).

Acknowledgments:

This work was supported by the Estonian Research Council grant PSG249, and by the EU through the European Regional Development Fund under project TK141 (2014-2020.4.01.15-0011).

References:

R. MacFarlane, et al.,
Energy Environ. Sci.
7, 232–250 (2014)

V. Plechkova et al., Chem. Soc. Rev.
37, 123–150 (2008)

Ulman, Chem. Rev.
96, 1533–1554 (1996)

Pikma et al., Electrochem. Commun., 61, 61-65 (2015)

Siinor et al., Electrochem. Commun., 78, 56-59 (2017)

H. Ers et al., DOI: 10.26434/chemrxiv-2022-5lcrq
(Digital Presentation) Silver Electrode Potentials in NaCl–KCl–Cscl Eutectic Melts
Authors: Volkovich Vladimir A. , Ivanov Alexander B. , Bessonova Dariya , Maltsev Dmitry S.
Published: November 2022

Molten salts have a number of potential applications including metals’ electrowinning and electrorefining, pyrochemical spent nuclear fuels’ reprocessing. Considerable efforts were devoted over decades to investigation of various electrochemical processes in molten salts, especially in fused chlorides. Silver chloride electrode is one of convenient types of reference electrodes often employed in potentiometry measurements. This electrode has several advantages (especially compactness) compare to the standard chlorine reference electrode, potential of which in chloride melts is taken as zero. Surprisingly little attention was paid so far to the systematic study (covering the effect of temperature and concentration) of silver electrode potentials in molten chlorides, with majority of the works dating back to 1950-s and 60-s. Molten LiCl–KCl eutectic was, on obvious reasons, the best studied, and several other melts (NaCl, NaCl–KCl, LiCl–KCl–CsCl, NaCl–CsCl) were also looked at.

The present study was directed at the systematic study of silver electrochemistry in fused alkali chlorides and determining silver electrode potentials. Here we present the results of the experiments performed in the melts based on the ternary NaCl–KCl–CsCl (30–24.5–45.5 mol. %) eutectic mixture at 823–1073 K. Electrode potentials of silver were determined using the electromotive force measurements method and the following galvanic cell:

Ag|(NaCl–KCl–CsCl)+AgCl||(NaCl–KC1–CsCl)|Cl2 (C)

Concentration of silver in the electrolyte varied from 0.1 to 5 wt. %.

Silver electrode quickly equilibrated with the electrolyte and the potential remained stable over long time, Figure. Experimentally obtained electrode potentials were then used to calculate silver formal standard electrode potentials.

Figure. An example of silver electrode potential evolution over time in (NaCl–KCl–CsCl)–AgCl (5 wt. %) melt at 823 K. 2Cl–/Cl2 reference electrode.

Figure 1
Secondary FeF2-Li Batteries in Ionic Liquid Electrolytes
Authors: Olbrich Lorenz Frank , Xiao Albert Wang , Sanghadasa Mohan , Pasta Mauro
Published: November 2022

Conventional intercalation Li-ion batteries are physico-chemically limited in their energy density and exhibit a restricted temperature operation range. To further increase energy density limit and enable reversible battery cycling at elevated temperatures, the exploitation of new cell chemistry is required. Conversion-type transition metal fluorides (TMFs) can store multiple Li-ions per metal center and thus increase the theoretical energy density by 200% to 300% compared to intercalation compounds. [1] Ionic liquids (ILs) are liquid salts (below 100°C) with improved thermal stability due to the ionic nature of its constituents, little to no flammability, and a low vapor pressure. Combining a TMF cathode with an IL electrolyte and a metallic lithium anode can provide an energy-dense, safe energy storage alternative with a broader operating temperature range and additional versatility for applications in the military, oil, and aerospace sector. [2]

In my talk, I will discuss our progress on the development and characterisation of a secondary FeF2-IL-Li-metal battery. We studied the impact of active material morphology and carbon-composite preparation techniques on the electronic conductivity and electrochemical performance in a bis(fluorosulfonyl)imide based IL electrolyte. In addition, we investigated different IL formulations for their applicability with TMFs and Li-metal. Both the cathode and anode electrolyte interphases were studied at different temperatures and their role in a full cell setup is elucidated.

[1] Olbrich, L. F., Xiao, A. W. & Pasta, M. Conversion-type fluoride cathodes: Current state of the art. Current Opinion in Electrochemistry 30, 100779 (2021).

[2] Lin, X., Salari, M., Arava, L. M. R., Ajayan, P. M. & Grinstaff, M. W. High temperature electrical energy storage: Advances, challenges, and frontiers. Chemical Society Reviews 45, 5848–5887 (2016).

Figure 1
A Multiphysics Understanding of Internal Short Circuit Mechanisms in Lithium-Ion Batteries upon Mechanical Stress Abuse
Authors: Duan Xudong , Wang Huacui , Jia Yikai , Wang Lubing , Liu Binghe , Xu Jun
Published: November 2022

Lithium-ion batteries (LIBs) have played an increasingly dominant role in the current mobile society. Due to the risky safety testing procedure, ultra-rigorous demands of the testing facility, and complicated multiphysics nature of the safety issues, lack of high-fidelity models to describe the safety behaviors of lithium-ion batteries upon abusive loading has significantly deferred the further application of LIBs. Herein, firstly, mechanical behaviors of the battery component materials are characterized by both in-situ and post-mortem experiments. Then, we reveal the formation process of various internal short circuit (ISC) modes inside batteries upon different abusive loadings with the aid of ex-situ observation using the X-ray Computed Tomography scanning technique and post-mortem characterization of the battery samples. To quantify the stress-driven ISC mode and failure behavior of the component material, numerical models for all component materials are established and applied in a cell model which can reveal the deformation-material failure-material contact-different ISC mode formation process. To further quantify the relationship between electrothermal response and mechanical response of battery, we develop a 2D detailed model with fully coupling of electrochemo-thermal-mechanics governing laws consisting of a 2D mechanical model, 2D ISC model, 2D heat model and Thermal Runaway model. The multiphysics model demonstrates a promising generalization in various SOC and loading situations. Results highlight the power of computational modeling to understand the underlying mechanism of safety issues in energy storage systems in a broader context.
(Invited) Pushing Lithium-Metal Batteries to the Limit: Fast Charging, Low Temperature, and Safety
Authors: Liu Ping
Published: November 2022

The performance of lithium metal batteries has advanced significantly, thanks to continuous improvement in the lithium metal anode. Many chemical and mechanical control strategies have been employed to combat its degradation mechanisms such as parasitic reactions, dendritic growth, and formation of isolated lithium. Electrolytes with high salt concentrations, including those with non-solvating diluents (known as localized high concentration electrolytes, or LHCE), electrolyte additives, artificial coatings, 3D plating hosts Li, and applying pressures in the 100s-1000s of kPa range have all been found to be effect in yielding dense, high efficiency Li metal deposits. Despite these advancements, reported lithium metal batteries tend to be charged at low rates, operated under ambient conditions, and lacking sufficient information on their safety characteristics. In this talk, we will review our recent progress in pushing the lithium metal batteries to extreme operating conditions in term of temperature, charging rates, and shorting behavior.

To enable fast charging, we have focused on developing a nucleation agent on the surface of current collector that can induce the formation of large, uniform nucleation sites. These nanoscopic sites enable dense lithium plating at 5 mA c-2 of current density, when a planar Cu electrode will fail catastrophically. This uniform nucleation method leads to a 45 um thick Li deposit that is nearly porosity free. A lithium metal cell with a metal oxide cathode is capable of 1C charging for extended cycles.

To enable low temperature operation, we have focused on the development of new electrolyte compositions that uses weakly solvating solvents. These electrolytes, represented by monodentate ethers and LHCEs made of ethers, promote the formation of contact ion pairs after solvation over solvent separated ion pairs. These electrolytes have enabled the formation of dense lithium metal deposits at as low as -60oC, while strongly solvating electrolytes will promote the formation of dendrites and cell shorting.

Finally, any practical implementation of lithium metal batteries operating under these extreme conditions have to feature safety designs that mitigate the impact of internal shorting. In this regard, we have focused on separator designs that can detect and intercept lithium dendrites.
(Invited) High Voltage, Energy, and Power Density Miniature Batteries Formed Using Stacked Electrodeposited Bifacial Electrodes
Authors: Braun Paul V.
Published: November 2022

Accessing high voltages (>9V) and high-power density in microbatteries with volumes below ~0.25 cm3 is challenging. At such scales energy density and voltage are highly constrained by packaging and serial integration of individual cells. Here, we demonstrate hermetically sealed, durable, compact (volume ≤ 0.165 cm3) lithium batteries (Li-LiCoO2 chemistry) with exceptionally low package volume (10.2%) in single- (~4 V), double- (~8 V) and triple-stacked (~12 V) configurations with energy densities reaching 990 Wh Kg-1 and 1929 Wh L-1 (triple-stacked battery discharged at C/10) and high power density for continuous and high-rate, high-frequency pulsed discharge (~124 mW cm-2 under continuous discharge for a triple stacked battery at C/2; ~75 mW cm-2 under pulsed discharge for double stacked battery at 2C). We achieve the high voltage-power-energy density landscape by using the current collectors as the package and stacked bifacial electrodes containing ~95% dense ultrahigh areal capacity (~50 mAh cm-2) electrodeposited LiCoO2 as cathode and lithium metal as anode. We demonstrate our microbatteries under ambient conditions powering wireless communication electronics, motors, and actuators, thus paving the way towards powering extremely small microdevices.
(Invited) The Behavior of High-Capacity Anodes at Low Temperature for Li-Ion Batteries
Authors: McDowell Matthew T
Published: November 2022

Lithium metal and alloy anodes offer the promise of improved capacity for Li-based batteries, and they could overcome low-temperature diffusion limitations associated with graphite. However, the electrochemical behavior of these materials at low temperatures has been seldom investigated, and most liquid electrolytes exhibit extremely low Coulombic efficiency (CE) for cycling of these high-capacity electrode materials at low temperatures. Here, we demonstrate an ether-based electrolyte system with carbonate additives that substantially improves the CE of lithium metal cycling down to -60 °C. Lithium metal deposited at low temperatures in this and other electrolytes shows a clear reduction in grain size with decreasing temperature, which is correlated with lower CE. Cryo-TEM and X-ray photoelectron spectroscopy investigation of the solid-electrolyte interphase (SEI) shows that this tailored electrolyte allows for greater inorganic content in the SEI at low temperatures, which enables a compact and conducting passivation layer. We further extend these studies to sodium metal anodes, which show improved CE at low temperatures compared to lithium. Finally, we investigate alloy anode materials and show that they can exhibit stable electrochemical cycling down to -40 °C, indicating the promise of these high-capacity materials for low-temperature batteries.
(Invited) Electrolyte Design for High Energy Batteries
Authors: Wang Chunsheng
Published: November 2022

Increasing adoption of Li-ion batteries for use in electric vehicles, aviation, and defense applications necessitates the development of chemistries capable of operating under extreme conditions. The current state-of-the-art electrolytes still do not enable high-energy batteries to operate under these extreme conditions. In this talk, we will discuss the electrolyte design principle for high energy batteries. The solid electrolyte interphase and catholyte electrolyte interphase requirements for high energy batteries will also be addressed.
Lab-Scale X-Ray Emission/Absorption Spectroscopy for Operando Measurement of Electronic Structure of Transition Metals in Battery Electrodes
Authors: Krishnan Abiram , Mitra Samantha , Lee Dong-Chan , Alamgir Faisal M.
Published: November 2022

Tracking the change in electronic structure of target elements is crucial to investigate the nature of redox reactions occurring in battery electrodes. X-ray emission spectroscopy (XES) and x-ray absorption fine structure (XAFS) perform this role well with high sensitivity and throughput, but the requisite of synchrotron facilities often limits those availability for material characterization.

Using a lab-scale x-ray emission/absorption spectrometer, we investigated the changes in the local structure and chemistry around the 3d transition metal elements of LiMO2 cathodes for Li-ion batteries as a function of the battery state of charge (SoC). Ex situ measurement was prepared from the electrode samples with discrete difference in SoC. Coupled with ex situ measurement, operando measurement was performed using pouch cells with LiMO2 cathode, which enabled a real-time monitoring of chemical shift in an element-specific manner resulted from changing electrode potential.

Through the XES mode of the bench-top spectrometer, fluorescence emissions from the LiMO2 cathode, or the cell containing it, was monochromatized by a spherically bent crystal analyzer (SBCA). The Kβ emissions of 3d transition metal elements such as cobalt display position/shape difference of spectrum with varying SoC. The trend of chemical shift and change in spectral features provided the information on the electronic structure variation, such as oxidation state change of 3d transition metals in LiMO2 during charge and discharge (i.e., delithiation and lithiation). Furthermore, valence-to-core (VtC) emission signals helped enable in-depth analysis such as spin structure characterization.

In addition to the XES analysis, we could measure K-edge XAFS for the same 3d transition metals in LiMO2 as well. In the XAFS mode of the spectrometer, SBCA monochromatized bremsstrahlung x-ray generated from a high-power x-ray tube is used to make an incident source energy-dispersive. While Kβ XES probed occupied levels, K-edge XAFS examined unoccupied levels providing comprehensive understanding on the change in electronic structure of 3d transition metals in LiMO2.

Figure 1
(Invited) Operando ‘Tender’ X-Ray AP-XPS Studies of Ir-Based PEM Electrolyzers
Authors: Hamlyn Rebecca , Crumlin Ethan J.
Published: November 2022

Synchrotron-based X-ray Photoelectron Spectroscopy (XPS) a is a versatile technique for surface chemical and elemental characterization of materials. Application of this technique to in situ studies was historically challenging in large part due to the attenuation of signal from interaction of photoelectrons with the surrounding environment. With the technological development of ambient pressure systems, we are now able to study catalysts in conditions that resemble their working environments. Further, the use of X-rays in the ‘tender’ regime (2-7 keV) allows for deeper probing than the conventional ‘soft’ x-ray (< 2000 eV) set up that is common at synchrotrons and lab-based sources. The photoelectrons generated from tender x-rays have enough energy to penetrate tens of nanometers through low density components such as a layer of liquid or polymeric electrolyte. This opens the door to access the chemistry at the interface of liquid electrolyte-electrocatalyst materials.

We have built a fully operational two-electrode system for the study of PEM electrolyzers in working conditions. Water flows through the cell and the chamber is held at 100% humidity (20 Torr at 300 K) to yield a fully hydrated environment for our electrocatalyst. We are then able to run operando electrochemical measurements while acquiring XP spectra to elucidate the important physical and chemical processes taking place at the interface. My talk will highlight recent results on iridium-based polymer electrolyte membranes for water splitting. With application of elevated potential, we can correlate the iridium valency and surface species with the appearance of product traces in a mass spectrum.

Figure 1
X-Ray Crystal Truncation Rod Studies of Electrochemical Double Layers
Authors: Kawaguchi Tomoya , Komanicky Vladimir , Rao Reshma , Shao-Horn Yang , Liu Yihua , You Hoydoo
Published: November 2022

Electrochemical double layers (EDL) is traditionally described as diffuse distributions of cations and anions, proposed in Gouy and Chapman (GC) model[1] and further developed extensively over decades largely based on voltammetry measurements. However, the GC model is suspected to break down at large potentials, because it predicts the unlimited rise in differential capacitance. Stern suggested long ago that there should be a layer with a finite ion density, known as ‘Stern layer’[2]. While it is generally accepted that Gouy-Chapman model or its modified versions describe well electrochemical interphase structures, recent studies of Pt(111) surface in CsF solution using a model-independent direct inversion method[3] have shown that Stern layer forms over the large double-layer potential range on Pt(111) surface.[4]

In this talk, we present synchrotron x-ray observation of Electrochemical Stern layers on the surfaces of RuO2 single crystals in 0.1 M CsF electrolyte. It is of fundamental importance to study if Stern layer forms on electrode surfaces other than Pt(111). In this case, we will examine RuO2 surfaces and compare the results to that of Pt(111) surface. RuO2 is chosen for several reasons. First, it is a well-studied system because of its oxygen evolution reactions and we are familiar with the structure because of our previous studies.[5,6] Second, it is an oxide with oxygen terminated while Pt is a pure metal. Third, the surfaces of RuO2 are squares or rectangles while that Pt(111) surface is triangles. The Stern layers formed at the interfaces of RuO2 (110) and (100) are compared to the previously reported Stern layer on Pt(111). [4] While the Cs+ density profiles at the potentials close to hydrogen evolution reactions are similar, the hydration layers intervening the surface and the Cs+ layer are significantly denser on RuO2 surfaces than that on Pt(111) surface, reflecting the oxygen termination of RuO2 surfaces. The overall similarities between Stern layers on ruthenium surfaces and platinum surface suggest the universal presence of Stern layers in all well-defined solid-electrolyte interfaces.

[1] Bard, A. J.; Faulkner, L. R., Electrochemical methods: fundamentals and applications. 2nd ed.; John Wiley: New York, 2001.

[2] Stern, O., The theory of the electrolytic double layer. Zeitschrift Für Elektrochemie 1924, 30, 508.

[3] Kawaguchi, T. et al., J. Appl. Cryst., 2018 51, 679.

[4] Liu, Y.; Kawaguchi, T.; Pierce, M.S.; Komanicky, V.; You, H., Layering and Ordering in Electrochemical Double Layers, J Phys Chem Lett, 2018, 9, 1265.

[5] Y.S. Chu, T.E. Lister, W.G. Cullen, H. You, Z. Nagy, Physical Review Letters 2001, 86, 3364.

[6] Rao, R.R. et al., Journal of Physical Chemistry C, 2018, 122, 17802
Mechanistic Insights into Proton Transport in Pure and Aqueous Phosphoric Acid
Authors: Zhu Zhenghao , Popov Ivan , Sokolov Alexei P. , Paddison Stephen J.
Published: November 2022

The transport of protons plays a key role in a variety of electrochemical processes and technologies. There are two major mechanisms underlying proton transport: the vehicular mechanism where a protonic defect moves with the aid of a molecular entity; and the ‘Grotthuss mechanism’ where a proton diffuses by being transferred between ‘chains’ of host molecules via elementary reactions within the hydrogen bond networks. The latter is regarded as the most efficient proton conductivity mechanism. Although Grotthuss proposed this concept more than 200 years ago, only indirect experimental evidence of the mechanism has thus far been reported. Recently, we observed the first direct experimental observation of proton transfer between the molecules in pure and 85% aqueous phosphoric acid by employing dielectric spectroscopy, and quasi-elastic neutron scattering (QENS). Complementary to these experiments, ab initio molecular dynamics (AIMD) simulations were performed to gain molecular insight into the underlying mechanisms of proton transport allowing for the breaking and forming of covalent bonds since it calculates the forces from electronic structure methods ‘on the fly’.

We calculated the self-intermediate scattering function of the protons, indicating three processes at high Q range consisting of two fast Q-independent processes and one slow Q-dependent process, which are in good agreement with QENS results. Also, the self-part of van Hove function of the protons for the fast characteristic time shows surprisingly short proton jumps of only ~0.5 - 0.7 Å confirmed by analysis of an individual proton trajectory. Furthermore, AIMD demonstrates that proton hopping plays an essential role in the long-range proton diffusion through the breaking and forming of hydrogen bonds. Our analysis confirmed the strong proton-proton correlations in these proton jumps. However, this correlated proton transport unexpectedly leads to a decrease of conductivity in these systems. Based on these results, we propose that the expected Grotthuss-like enhancement mechanism of conductivity cannot be realized in bulk liquids where ionic correlations always reduce conductivity, most likely because of the requirement for the momentum conservation. Our findings will propel the design of electrochemical materials with proton transfers involved in charge transport for achieving high proton conductivity in electrochemical applications including fuel cells.
Electrochemical Analysis in Charge-Transfer Science: Things Are Not Always What They Seem
Authors: O'Mari Omar , Clark John , Vullev Valentine I.
Published: November 2022

Charge transfer (CT) and charge transport (CTr) are essential for supporting life on Earth and for making our modern ways of living possible [Phys. Chem. Chem. Phys.
2020, 22, 21583-21629]. Electrochemical analysis, while relying on heterogeneous electron transfer (ET), is of key importance for characterizing CT systems and process [Curr. Opin. Electrochem.
2022, 31, 100862]. The huge difference between the timescales of electrochemical measurements and the picosecond CT reactions of interests places inherent demands for reliable interpretations of voltammetry analyses [J. Electrochem. Soc.
2019, 166, H3175-H3187]. Concurrently, the ubiquity of electric dipole warrants deep understanding of how they affect CT thermodynamics and kinetics [J. Am. Chem. Soc.
2014, 136, 12966-12973]. The localized dipole-generated fields affect the electrochemical potentials of donors and acceptors and, thus, the Franck-Condon contribution to the CT kinetics [Angew. Chem. Intnl. Ed.
2018, 57, 12365-12369]. In the context of our latest developments in electrochemical analysis, this presentation focuses on how molecular dipoles affect not only the potentials, but also the reorganization energy and the donor-acceptor coupling. Understanding the multifaceted nature of the effects of dipoles on charge transfer and charge transport drives the emergence of new paradigms for electronics, photonics and energy science and engineering.
Modeling and Experimental Analysis of pH Swing-Based Approaches to Electrochemical CO2 Capture
Authors: Kwabi David G.
Published: November 2022

The use of renewable electricity to drive large-scale electrochemical CO2 removal and concentration from point sources, air, and seawater is receiving considerable interest as one strategy for mitigating climate change.1 The low concentration of CO2 in air however makes rapid and energy-efficient CO2 capture challenging. Understanding and optimizing the energetic cost of CO2 separation at practically reasonable throughputs is a prerequisite for engineering devices that can be widely deployed.

I will review our past and current efforts at developing electrochemical pH-swing-based CO2 separation (EPCS) using a combination of modeling and experiments. In EPCS, CO2 is captured from a mixture of gases into an aqueous electrolyte in the form of (bi)carbonate ions when its pH is increased from acidic to strongly alkaline conditions, and then released as a pure gas when the pH is reversed. We have shown that CO2 separation is experimentally possible for less than 100 kJ/molCO2 using such a pH swing cycle that is driven by proton-coupled electron transfer (PCET).2 Thermodynamic modeling shows that the minimum work input for electrochemical CO2 separation is the sum of exergy losses incurred from differences in CO2 partial pressure between the CO2 source/exit streams and the electrolyte. This framework rationalizes minimum work inputs for pH-swing and redox-mediator-based CO2 separation cycles, and motivates the measurement or estimation of the aforementioned CO2 partial pressures in future experimental studies.

More recently, we have begun to consider a new design for EPCS in which PCET-active species are conformally attached to the internal surface area of a highly porous electrode, and effect a reversible pH swing in an adjacent layer of aqueous electrolyte upon redox cycling. We have formulated a continuum reaction-transport model that simulates reactive CO2 capture into and release from the electrolyte layer, as well as transport of (bi)carbonate species, and protons, in response to an applied current or voltage. Possible pathways toward achieving an energetic cost of direct air capture of CO2 less than 100 kJ/molCO2 will be discussed, as well as our efforts toward experimental demonstration of this concept.

References

Renfrew, S. E.; Starr, D. E.; Strasser, P., Electrochemical Approaches toward CO2 Capture and Concentration. ACS Catalysis
2020,
10 (21), 13058-13074.

Jin, S.; Wu, M.; Gordon, R. G.; Aziz, M. J.; Kwabi, D. G., pH swing cycle for CO2 capture electrochemically driven through proton-coupled electron transfer. Energy & Environmental Science
2020.
Tandem Electrokinetic/Electrocatalytic Remediation of Pfas in Soils
Authors: Lee Katherine , Skinn Brian , Snyder Stephen , Athmer Chris , Inman Maria
Published: November 2022

Per-/polyfluorinated species (PFAS) are a class of widely used, highly stable chemicals that do not readily break down in the environment or human body. As a result of their widespread use and persistence in the environment, PFAS can be found in soil, air, and water at numerous sites across the United States. Recent work has linked exposure to some types of PFAS found in the environment to adverse health effects in humans. The bio-accumulative nature of PFAS along with the potential adverse health effects has provided strong motivation for active remediation of these emerging contaminants at environmental sites. Development of energy- and cost-efficient technologies for the in-situ treatment of PFAS-contaminated soils would greatly facilitate efforts to remediate these contaminated sites and alleviate the public health threat they represent.

This talk will discuss recent efforts to develop a tandem electrokinetic/electrocatalytic technology for energy-efficient concentration and destruction of PFAS in contaminated soils. In this approach (Figure A), electrokinetic soil remediation technology is used to drive the PFAS contaminants to a localized area around the electrokinetic anode and electrocatalysis reactors situated near this electrokinetic anode degrade and destroy the concentrated PFAS species. Data will be presented describing the electrokinetic transport observed for various C4-C12 linear-chain PFAS in a Dayton, OH till soil on the bench scale (see Figure B). Experimental results to date suggest that larger PFAS species (above ~C6) experience sufficiently strong physicochemical attraction to the soil particles that electrokinetic transport is mostly or completely suppressed. Based on these results, current work is identifying ways to improve electrokinetic PFAS remediation by disrupting these PFAS-soil interactions in a fashion that is economically and environmentally favorable. Results demonstrating the ability to enhance electrocatalytic PFAS destruction through the use of pulsed-waveforms (relative to traditional direct current methods) will also be presented.

Figure Caption. (A) Mechanism of tandem electrokinetic/electrocatalytic PFAS destruction. (B) Bench-scale apparatus for soil electrokinetics tests.

Figure 1
Using Zirconium MOF Packed Microfluidic Electrochemical Cell As PFOA Screening Sensor in Water Source
Authors: Li Zhenglong , Schmid Julian , Kumar Abhishek , Rahman Maryom , Motkuri Radha Kishan , Basuray Sagnik
Published: November 2022

Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are human-made chemicals with high chemical resistance and thermal stability. The extremely stable fluoro-carbon (F-C) skeletons enable PFAS molecules can exist stably in nature especially in the water sources for a long time concerning thermal, chemical, and biodegradation. Perfluorooctanoic acid (PFOA) is one of the most dominant environmental contributors, and its half-life in water has been estimated to be longer than 92 years. Therefore, the monitoring of PFOA level in the water source is needed. It is reported that Zirconium (Zr) based metal-organic frameworks (MOFs) have shown considerable affinity to PFOA molecules. In addition, electrochemical impedance spectroscopy (EIS) as a rapid and sensitive detection method (based on measuring the impedance changes at the electrode/solution interface) is perhaps the most frequently used technique in the investigation of affinity-based transducers.

In the pursuit of building a highly efficient screening sensor to PFOA molecules. In this work, the application of Zr based MOF in NP-μFEC as a combined sensing platform to PFOA molecules is conducted. Here, the NP-μFEC is our group proposed new impedance sensing platform with enhanced, three-dimensional distributed electric field. To validate the feasibility of Zr based MOF packed NP-μFEC’s sensing performance. The work is conducted with a ranging concentration of PFOA (in 0.1X PBS) from 150 to 10 ng/L. We finally find that the proposed combination of Zr based MOF and NP-μFEC can show an excellent response to the PFOA molecules, which offers a detection limit lower than the established US Environmental Protection Agency (EPA)'s water contamination level (70 ng/L).
Electrochemical Analyses of Redox-Active Minerals: Insights and Persisting Challenges
Authors: Gorski Christopher A
Published: November 2022

Redox-active minerals often have complex electrochemical properties that are difficult to quantify and explain. Quantification is difficult because many redox-active minerals are poorly conductive, prone to dissolution, and capable of undergoing reversible and irreversible structural changes during redox cycling. Explaining a mineral's electrochemical properties is frequently challenging because minerals can undergo complex ion transport processes in their structures and undergo charge redistribution processes that occur within the crystal lattice on long time scales. In this talk, I will present the insights I have gained from studying environmentally relevant iron- and manganese-bearing minerals over the past 15 years. The presentation will include how electrochemical analyses can be used to quantify the thermodynamic properties of minerals and how these properties relate to their redox reactivities with environmentally relevant phases. The talk will also cover persisting challenges that exist in this field.