bluuebunny/crossref_metadata_2025 huggingface dataset:
Surface Modification of Li Metal Anodes Using Ag Nanoparticles and PVDF: An EC-AFM Investigation
Authors: To-a-ran Weerawat , Kim Young-Jun
Published: February 2024

Lithium metal has captured interest as an attractive anode material for next-generation batteries due to its extremely large theoretical specific capacity (approximately 3800 mAh/g) and low reduction potential. However, challenges related to uncontrolled lithium plating and stripping, unwanted side reactions, and uneven lithium growth on the surface (top growth) contribute to safety concerns and poor cycling performance, hindering the widespread application of lithium metal batteries [1]. In this study, we conducted electrochemical atomic force microscopy (EC-AFM) to investigate the lithium deposition behavior of silver nanoparticles (Ag NPs) on lithium metal substrate surfaces. Kelvin probe force microscopy (KPFM) revealed that Ag NPs possess a lower surface potential than the lithium substrate surface, providing reaction sites for lithium deposition during the plating process. This leads to the formation of a lithium-silver (LiAg) solid solution instead of pure lithium metal, effectively mitigating the issues associated with uncontrolled Li plating. The LiAg alloy phase exhibited improved reversibility compared to bare lithium metal, resulting in improved cycling performance [2]. Additionally, we found that coating the lithium metal surface with a layer of polyvinylidene fluoride (PVDF) promotes bottom-up lithium deposition while physically suppressing dendrite formation. As an ionically conductive but electronically resistant polymer, PVDF allows Li+ transport while suppressing lithium deposition on the top surface [3], reducing safety issues associated with dendrite formation during lithium deposition. Our EC-AFM results reveal the morphological evolution of Ag NPs and PVDF on lithium metal during the plating and stripping process, offering preliminary insights into the underlying mechanisms. Based on our investigations, we propose that the combination of Ag NPs and PVDF could potentially be an effective choice for modifying lithium metal surfaces. This approach aims to enable controlled lithium plating and stripping, as well as bottom-up lithium deposition, with the goal of improving safety and cycling performance for anodes in the next generation of high-energy-density lithium metal batteries, focusing on improving safety and achieving long life cycle.

[1] H. Park et al, Adv. Energy Mater. 2021, 11, 2003039.

[2] S. Jin et al, J. Am. Chem. Soc. 2020, 19, 8818.

[3] J. Yun et al, ACS Energy Lett. 2020, 5, 3108.
Fitting Kinetics of Arbitrarily-Shaped Finite Reactive Features Using Their Scanning Electrochemical Microscopy Images
Authors: Leslie Nathaniel , Mauzeroll Janine
Published: February 2024

Computer modelling of scanning electrochemical microscopy (SECM) images allows for the kinetics of chemical reactions at surfaces to be fit. Until recently, methods for fitting kinetics from SECM images of reactive features required models with custom geometries that approximated the feature shape.[1,2]

The kinetics of arbitrarily-shaped features can be fit by discretizing the surface into pixels and modelling the surface rate constant of a reaction as a discrete function. The shapes of the underlying reactive feature responsible for hot spots in an SECM image were determined by deconvolution,[3] edge detection,[4] or microscopy and were used to control the surface reaction boundary condition in finite element method simulations. The use of deconvolution or edge detection to obtain an estimate for the shape of the underlying features seen in SECM images was of particular interest since they did not require any characterization of the surface beyond SECM.

Simulated SECM images of reactive features on flat surfaces were controlled using three parameters: the tip to substrate distance of the scanning electrode, the rate constant for the reaction at the surface feature and the erosion and dilation of the initial estimate of the shape of the reactive feature. The parameters of these SECM images were optimized such that the simulated images fit experimental SECM images to obtain shape and kinetic information of reactive sites.

The ability to accurately fit arbitrarily shaped features dramatically broadens the scope of reactive features that can be treated to include features of interest such as grain boundaries, scratches and irregularly shaped inclusions.

[1] Filice, F. P.; Li, M. S. M.; Ding, Z. Simulation Assisted Nanoscale Imaging of Single Live Cells with Scanning Electrochemical Microscopy. Adv. Theory Simul. 2018, 2, 1800124

[2] Leslie, N.; Mena-Morcillo, E.; Morel, A.; Mauzeroll, J. Fitting Kinetics from Scanning Electrochemical Microscopy Images of Finite Circular Features. Anal. Chem. 2022, 94, 44, 15315–15323

[3] Stephens, L. I.; Payne, N. A.; Mauzeroll, J. Super-resolution Scanning Electrochemical Microscopy. Anal. Chem. 2020, 92, 3958– 3963

[4] Stephens, L. I.; Payne, N. A.; Skaanvik, S. A.; Polcari, D.; Geissler, M.; Mauzeroll, J. Evaluating the Use of Edge Detection in Extracting Feature Size from Scanning Electrochemical Microscopy Images. Anal. Chem. 2019, 91, 3944– 3950
Thermodynamic Analysis of Coal Derived Graphite for Battery Anodes Using the Multi-Species, Multi-Reaction Model
Authors: Paul Abigail , Magee Regan , Wilczewski Warren , Wolfe Kody D , Wichert Nathan , Mollah Rafid , Jones Matthew , Trembly Jason , Staser John A. , Garrick Taylor R.
Published: February 2024

Automotive manufacturers are working to improve individual cell and overall pack design by increasing their performance, durability, and range, while reducing cost. As the time from initial design to manufacture of electric vehicles is decrease, design work that used to rely solely on testing needs to be supplemented or replaced by virtual methods. As electrochemical engineers drive battery and system design using model-based methods, models that have a basis in physics, rather than purely empirical representations, are necessary to allow engineers to drive design through a linkage to manufacturing methods. In this study, we apply the Multi-Species, Multi-Reaction model as popularized by Verbrugge and Baker to an electrochemical system comprised of a counter electrode and a working electrode synthesized from graphite derived from coal.

To do this, the open circuit voltage of the coal derived graphite and a standard commercially available graphite was quantified. Linear sweep voltammetry provided insight into the shift in electrochemical reactions based on the structure and composition of the coal derived graphite. This then allows the MSMR model to capture the thermodynamic performance of the coal derived graphite, and sheds further insight into the performance compared to the standard commercially available system. Commentary on the thermodynamic differences between the systems will be provided and additional analytical techniques may be used to rationalize differences in performance.
Activity and Selectivity Modulation of CO2 Electroreductions at Au-Water Interfaces Via Tuning Localcation Concentrations
Authors: Qin Xueping , Vegge Tejs , Hansen Heine Anton
Published: February 2024

Electrochemical CO2 reduction reaction (CO2RR) is a promising technique for converting the greenhouse gas CO2 into valuable fuels and chemicals in a clean energy society. To understand the underlying electrocatalytic reaction mechanism from the atomic level, researchers are investigating the role of electrolyte ions, particularly alkali metal cations, in various electrocatalytic reactions including CO2RR. Despite this attention, the impact of alkali metal cations is still a topic of debate, and it remains unclear how cations affect the CO2RR and the competing hydrogen evolution reaction (HER).

In this study, explicit cations and water solvents were added to Au-water interfacial models to simulate the pathways of CO2RR and HER. Two cations (K+, Li+, and/or H+) were used in the model system to create similarly charged Au surfaces, and the local concentration of alkali metal cations (AM+) was adjusted by replacing AM+ (K+ and Li+) with H+. The first electron transfer step was considered critical in electrocatalytic reductions, so CO2 activation and water dissociation were evaluated for CO2RR and HER, respectively. Ab initio molecular dynamics (AIMD) simulations with the slow-growth sampling approach (SG-AIMD) were used to simulate the corresponding reaction mechanisms, and kinetic barriers were obtained through thermodynamic integrations. With these Au-water-cations interfacial models, a systematic study was conducted to investigate the mechanism of CO2 activation at Au-water-2AM+, Au-water-1AM+, and Au-water-0AM+ interfaces. These results show that a high concentration of metal cations with 2AM+ promotes CO2 activation through short-range electrostatic interactions between cations and key intermediates.

Besides CO2 activation, this study also investigated water dissociation during the competing HER. Contrary to the promotion effect observed in CO2RR, local alkali metal cations were found to suppress water dissociation with a high reaction barrier (Figure 1). This can be attributed to the broken connectivity of the hydrogen bond network at Au-water-2AM+ interfaces. The reaction kinetics can be improved by reducing the metal cation concentration. Notably, K+ was found to have a more pronounced promotion effect than Li+ on CO2 activation, while the opposite suppression effect was observed on HER. By tuning the local alkali metal cation concentration, it is anticipated that the overall performance of CO2RR, including both activity and selectivity, can be engineered.

Figure 1
The Chemistry of Interfacial Ions: In Situ XPS and XAS
Authors: Nagra Hassan , Deka Nipon , Favaro Marco , Knop-Gericke Axel , Mom Rik
Published: February 2024

The choice of electrolyte ions has significant impact on the performance of electrochemical systems, affecting properties such as the electrocatalytic activity and capacitance. To understand how ions influence electrochemical processes, a key step is to determine the chemical behavior of ions at the electrode-electrolyte interface. Here, I will show how X-ray photoelectron spectroscopy (XPS) and soft X-ray absorption spectroscopy (XAS) allow one to obtain such information. Traditionally, these techniques are vacuum-based, only providing a detailed chemical analysis before or after electrochemistry. However, advanced spectro-electrochemical cell design now makes it possible to interface the vacuum needed for XPS and soft XAS with wet electrochemical environments, enabling us to study the electrode-electrolyte interface during electrocatalytic reactions.

Using recent case studies from my group, I will show how operando XPS and soft XAS are able to detect the interfacial ion concentration, the hydration shell structure of the ions, and the electrostatic potential in the double layer. These insights allowed us, for example, to follow the intercalation of Na+ ions into NiFeOx and IrOx in alkaline electrolytes, and to obtain a measure of the double layer layer thickness at a RuOx electrode in 0.1 M H2SO4. Finally, I will give a perspective on how to bring operando XPS from the synchrotron to the laboratory, which will be an important step towards widespread implementation of the technology.

Figure 1
Role of Chemisorbing Species in Growth at Liquid Metal-Electrolyte Interfaces Revealed by in Situ X-Ray Scattering
Authors: Sartori Andrea , Magnussen Olaf M , Murphy Bridget
Published: February 2024

Liquid-liquid interfaces offer intriguing possibilities for nanomaterials growth. Especially, growth at liquid metal surfaces has recently received renewed interest. Here, fundamental interface-related mechanisms that control the growth behavior in these systems are studied for the case of Pb halide compound formation at the interface between liquid mercury electrode and aqueous salt solutions, using in situ X-ray reflectivity and grazing incidence X-ray diffraction, supplemented by electrochemical measurements and optical microscopy. The nucleation and growth of these compounds at potentials in the regime of Pb de-amalgamation was investigated in NaX + PbX2 (X = F, Cl, Br) to systematically explore the role of the halide species. X-ray reflectivity studies reveal the rapid formation of well-defined ultrathin precursor adlayers in Cl- and Br-containing solution. This adlayer formation is followed by subsequent quasi-epitaxial growth of Pb(OH)X bulk crystals, that are oriented with the c-axis along the surface normal. In contrast, growth in F-containing solution proceeds by slow formation of a more disordered deposit, resulting in random bulk crystal orientations on the Hg surface. A detailed structural analysis of the Pb(OH)Br and Pb(OH)Cl precursor adlayers reveals that they determine the orientation of the subsequently formed bulk crystals, with the arrangement in the adlayer providing a template. Together with our previous results on the pseudo-epitaxial growth of PbFBr on Hg (A. Elsen, et al., Proc.Nat.Acad.Sci., 2013, 110, 6663), these data reveal the decisive role of the interface chemistry, especially the strong chemisorption of the anions bromide and chloride, in steering the formation of these textured deposits at the liquid metal surface.
In Situ Electrochemical Raman Spectroscopy of MXenes in Confined Electrolytes
Authors: Shevchuk Kateryna , Matthews Kyle , Wang Ruocun (John) , Gogotsi Yury
Published: February 2024

MXenes, a large family of two-dimensional materials, have attracted interest due to their large chemistry space and diverse chemical, electrical, mechanical, and optical properties. MXenes follow the general formula Mn+1XnT
x
(n = 1-4) with M representing an early transition metal, X—carbon and/or nitrogen, and T—surface terminations (=O, –OH, and –F). In particular, MXenes’ metallic conductivities and redox-active surfaces make them attractive for electrochemical energy storage. Like with many other 2D materials, Raman spectroscopy has proven to be a crucial tool for MXene characterization. More recently, in situ Raman was used to elucidate structural changes in MXene electrodes during electrochemical cycling with a subset of aqueous electrolytes. Confined electrolytes (water-in-salt, PEG, etc.) have shown promise in various electrochemical systems, with recent results pointing to new charge storage mechanisms in MXenes. Further exploration is needed to understand the effect of the cations, anions, and concentrations of confined electrolytes on charge storage mechanisms. This work focuses on using in situ electrochemical Raman spectroscopy to analyze different confined electrolyte systems in MXene cells. The findings demonstrate the potential of using MXenes in aqueous electrochemical devices.
(Invited) In Situ Atomic Force Microscopy and X-Ray Spectroscopy of Electrocatalysts
Authors: Akbashev Andrew
Published: February 2024

In situ characterization offers an effective way to study and quantify chemical, structural and morphological changes of electrocatalysts as well as to capture the kinetics of transformations and dissolution. For fundamental understanding of electrochemically induced transformations, such in situ experiments require well-defined materials (ideally single crystalline) as they can provide precise potential-dependent quantities that can be used to accurately assess theoretical models and predictions. In this regard, the study of materials under water oxidizing conditions represents a particular challenge due to multiple pathways for the degradation of the surface and bulk and complexity of high-quality material preparation.

In this talk, I will discuss how a combination of in situ microscopy techniques can provide insight into the surface and bulk behavior of electrocatalysts during electrocatalytic water oxidation (OER). Specifically, I will show how operando electrochemical atomic force microscopy (EC-AFM) can be used to record nanoscale changes in the surface morphology during anodic corrosion of a perovskite surface. I will also discuss how operando EC-AFM can be combined with operando transmission X-ray microscopy and scanning electrochemical cell technique to probe the evolution and reactivity of single particles of Co(OH)2. In the end, I will cover key bulk and surface processes that occur in oxides under oxidative conditions as well as possible future development of in situ techniques that can help us probe such transformations.
Operando XAS Investigation of Bimetallic Iron−Molybdenum Sulfide Electrocatalysts for the Hydrogen Evolution Reaction
Authors: Khan Anastassiya , Morozan Adina , Artero Vincent , Zitolo Andrea
Published: February 2024

Nowadays green hydrogen production has been seen as a key element for the future development and large-scale implementation of fuel cell technology, while electrolyzer technologies represent the most advanced methods for producing pure hydrogen from water. The preparation of efficient, cost-effective, and stable noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) at the cathode of proton exchange membrane electrolyzers (PEMEL) remains one of the main issues that need to be solved to allow the widespread use of hydrogen as an energy carrier.

Molybdenum sulfide (MoSx) is a well-known material showing promising HER catalytic activity, especially in its amorphous state and when doped with other transition metals1. The successful implementation of a bimetallic iron-molybdenum sulfide electrocatalyst for HER into a PEM electrolyzer has been recently reported2. However, the structure of their active sites requires a more elaborate investigation. In this study, we employed operando X-ray absorption spectroscopy to identify potential-induced structural and electronic changes in FeMoSmw bimetallic iron−molybdenum sulfides and MoSmw obtained by a microwave irradiation synthetic approach 2. Extended X-ray absorption fine structure (EXAFS) spectra at Mo and Fe K-edges under operando conditions provided us with accurate structural characterization of the catalytic active sites: while an amorphous MoS3 phase is detected and retained in both MoSmw and FeMoSmw at low potential, a FeS phase is observed at the Fe K-edge, likely explaining the better performance of the bimetallic iron-molybdenum sulfides electrocatalysts compared to iron-free molybdenum sulfides.

References:

Ren, X.; Wang, W.; Ge, R.; Hao, S.; Qu, F.; Du, G.; Asiri, A. M.,Wei, Q.; Chen, L.; Sun, X. An amorphous FeMoS4 nanorod array toward efficient hydrogen evolution electrocatalysis under neutral conditions. Chem. Commun. 2017, 53, 9000−9003.

Morozan, A.; Johnson, H.; Roiron, C.;Genay, G.; Aldakov,D.; Ghedjatti, A.; Nguyen, C.;Tran P.; Kinge, S.; Artero, V. (2020). Nonprecious Bimetallic Iron–Molybdenum Sulfide Electrocatalysts for the Hydrogen Evolution Reaction in Proton Exchange Membrane Electrolyzers. ACS Catalysis. 10. 10.1021/acscatal.0c03692.
(Digital Presentation) In-Situ Spectroelectrochemistry to Unveil the Mechanism of Green Ammonia Production on the Ti2n Nitride Mxene
Authors: Johnson Denis , Yoo Ray , Djire Abdoulaye
Published: February 2024

Electrochemical nitrogen reduction reaction (NRR) is used to convert nitrogen (N2) to ammonia (NH3) at ambient temperature and pressure. In general, acidic electrolytes are used to provide protons (H+) for the reduction process. However, this leads to a low NH3 selectivity because of H2 by-product formation via the hydrogen evolution reaction (HER). Recently, we showed that a Ti2N MXene is active and selective for NRR, and provided preliminary evidence that this catalyst works through a Mars-van Krevelen (MvK) mechanism rather than conventional associative/dissociative mechanisms. To improve the selectivity of the NRR process, the electrolyte was shifted from acidic to neutral pH values. From this, it was seen that NRR in 0.1M Na2SO4 was able to achieve a selectivity significantly greater than that of 0.1M HCl. We also observed that at more cathodic potentials, the material begins to irreversibly decompose into TiO2 as evidenced by cyclic voltammetry analysis before and after chronoamperometry experiments. To further understand the performance of this material, we use in-situ/operando techniques, including X-ray absorption spectroscopy (XAS) and Fourier-transform infrared (FTIR) spectroscopy, to deconvolute the mechanism of NH3 production. We use XAS to track the Ti oxidation state shift and degree of shift as a function of reaction time and applied potential. We also use XAS to track the change in the atomic bond lengths at the local coordination environment of the Ti atoms throughout time and voltage. Furthermore, we use FTIR to elucidate in real-time the adsorption of NRR reactive species and intermediates on the MXene surface. All findings are further corroborated with density functional theory (DFT) calculations to track the reaction energy pathway over each intermediate. We plan to expand these findings to other materials and systems, and use the knowledge obtained from these studies to design optimal electrolytic conditions to produce NH3 through NRR.
In Situ Transmission Electron Microscopy and Soft X-Ray Spectro-Microscopy to Understand Electrochemical Processes
Authors: Higgins Drew Higgins , Abdellah Ahmed , Zhang Chunyang , Abousalem Kholoud , Black Robert , Eraky Haytham , Hitchcock Adam
Published: February 2024

Electrochemical CO2 conversion offers a route to use renewable sources of electricity to convert CO2 into valuable carbon-based fuels and chemicals, including carbon monoxide, ethanol and ethylene. For electrochemical CO2 conversion technologies to become a viable component of future sustainable energy infrastructures, improved performance materials (catalysts, electrodes, membrane electrode assemblies) are needed to achieve high conversion rates, selectivity and single-pass utilization of CO2. This talk will focus on the development of techniques to characterize the properties of electrochemical CO2 conversion materials under reaction conditions. These in-situ methods are producing results which will guide the design of next generation materials and reactors. The talk will focus primarily on in situ transmission electron microscopy (TEM) and related spectroscopic techniques (energy dispersive X-ray analysis and selected area electron diffraction), along with synchrotron-based methods including in-situ soft X-ray scanning transmission X-ray microscopy (STXM).
Investigating the Electrochemical CO2 Reduction Mechanism on Oxide-Derived Copper Using in Situ FTIR Spectroscopy
Authors: Delmo Ernest Pahuyo , Song Yihua , Wang Yian , Shao Minhua
Published: February 2024

Oxide-derived copper (OD-Cu) electrocatalysts have been extensively used for CO2 reduction reaction (CO2RR) applications in recent years due to their capability to selectively produce valuable C2 compounds. The mechanism of CO2 reduction on these surfaces, however, is still not clearly understood. Using in situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), we show how the copper pre-oxidation process can significantly influence the adsorption of various CO2RR intermediates. Upon mildly anodizing a Cu thin film, we observed a redshift on the *CO2
– band, indicating that the initial CO2 adsorption and activation step is promoted on the oxide-derived surface. Additionally, we observed a faster growth of the *COatop band for the anodized copper film at low overpotentials, which demonstrates how a high *CO coverage can be achieved on OD-Cu. Finally, for the first time, we observed the simultaneous formation of two bands at 1327 cm–1 and 1425 cm–1 on the anodized Cu thin film. Using DFT calculations, we show that these bands match the theoretical vibrational frequencies of the *COCHO dimer, a key intermediate of the C2 pathway. Furthermore, our calculations show that the thermodynamics of *CO and *CHO coupling can be improved in the presence of the subsurface oxygen sites in OD-Cu. Our findings reveal the different aspects through which the CO2 reduction mechanism can be improved on OD-Cu electrocatalysts as compared to metallic copper.

This work was financially supported by the Research Grants Council (16310419, 16309418, and 16304821) and the Innovation and Technology Commission (grant no. ITC-CNERC14EG03).
Exploring the Influence of Malachite Forming on Oxide-Derived Copper Electrodes on C2+ Product Selectivity
Authors: Tafazoli Saeede , Yusufoğlu Muhammed , Balkan Timuçin , Kaya Sarp
Published: February 2024

Electrocatalytic activity and C2 product selectivity of two distinguished oxide-derived Cu in electrochemical carbon dioxide reduction reaction (CO2RR) were investigated. Cu oxide layers electrodeposited at different deposition rates exhibited different morphologies, the electrode with a more compact structure was found selective to C2 products with two times higher faradaic efficiencies (40%). Both Cu+ and Cu2+ species have been identified on the surface of oxide-derived Cu electrodes by X-ray photoelectron spectroscopy (XPS). Also, oxide-derived electrodes were investigated by X-ray diffraction (XRD). Results confirmed the presence of Cu oxide phases for primary electrodes, which were then fully reduced to the metallic Cu after CO2RR. Moreover, SEM investigations helped us distinguish the morphology of the two electrodes and monitor morphological differences before and after CO2RR. To shed light on the adsorbed species, intermediate (metastable) phases, and reaction mechanisms during CO2RR, electrochemical surface-enhanced Raman spectroscopy (SERS) was utilized. This method helped us vividly observe the formation of a metastable phase (malachite) on the electrode surface, which showed lower FEs for C2 products. Moreover, the analysis of SERS indicated a strong tie between the presence of the malachite phase and strongly adsorbed CO on electrode surfaces, preventing dimerization and further reduction. This malachite phase terminating the surface can hinder the charge transport and interfere with further reductions in C2 products.

Figure 1
Real Time Analysis of the CO2 Reduction Reaction Products in a Cu-Gde Setup
Authors: Sajevic Urban , Parada Villarroel Walter Agustin Agustin , Nikolaienko Pavlo , Mayrhofer Karl J. J.
Published: February 2024

The electrochemical reduction of CO2 (CO2RR) on copper is widely regarded as one of the most promising topics in green-energy research, due to it´s potential to produce a wide array of building block chemicals while consuming CO2 and utilizing renewable energy sources. Contrary to traditional electrolysers that utilize dissolved CO2, a gas diffusion electrode (GDE) approach is capable of circumventing the CO2 diffusion dependency and hence reach economically relevant currents of >300 mA/cm². Although GDE brings eventual industrial application closer, such systems suffer from short-lived stability, mostly on account of catalyst layer deactivation and GDE flooding. As a consequence, most GDE based electrolysers are incapable of reaching a true steady-state, rendering batch-based analyses such as gas chromatography less useful when it comes to studying sensitive properties such as on-set potentials, catalyst deactivation and product selectivity shifts.

In this work we present a novel set-up capable of exploring GDE-based systems and presenting both qualitative and quantitative response in real time. We base our system of a custom cell-design that is coupled to a proton transfer reaction mass spectrometer (PTR-MS) that analyses the liquid products and quadrupole mass spectrometer (QMS) for gaseous products analysis. As a proof of concept, we evaluate the CO2RR performance of copper based GDE´s in various electrolytes, showing how electrolyte´s pH influences properties such as product selectivity and on-set potentials. All experiments were conducted at industry-relevant currents of 200-600 mA/cm².
Tracking Mn and Zn in Rechargeable Aqueous Zn-MnO2 Batteries By Operando X-Ray Absorption
Authors: Liu Cheng , Wang Wenhai , Black Serra Ashley , Martin Diaconescu Vlad , Stievano Lorenzo , Simonelli Laura , Tonti Dino
Published: February 2024

Zn-MnO2 batteries with mildly acidic electrolytes are a promising chemistry for large scale storage thanks to their remarkable energy density, low cost, and high safety. This is mainly obtained thanks to the high capacity of the Zn metal anode, and the nonflammable character of the aqueous electrolyte. MnO2 is one of the most common cathode of choice, not only for being Earth-abundant, but also because it can undergo a two-electron mechanism, which is however complex and still not fully understood. There is currently agreement in considering for discharge a MnO2 dissolution, leading to soluble Mn2+ and simultaneous precipitation of Zinc Hydroxide Sulfate (ZHS, ZnSO4[Zn(OH2)]3·xH2O). When charging the process is not simply reverted. In fact, a distinct electrochemical profile is observed, with at least two distinct plateaus and a third, apparently pseudocapacitive stage (Figure 1a). A similar multistage profile is observed during the second discharge. Although such profile is characteristic and observed with different MnO2 phases and architectures, the underlying mechanism remains elusive, as it seems to involve mainly poorly crystallized phases.

We studied the mechanism by operando X-ray absorption (XAS) at the Mn and Zn K-edges to follow speciation simultaneously and quantitatively in the cathode and in the electrolyte via principal component analysis. Beam intensity needed appropriate regulation to avoid interference with the experiment.

Simultaneous X-ray diffraction allowed precise correlation with the MnO2 dissolution and ZHS formation. We found evidence of Mn(III) intermediate occurring during local bond reorganization, which is inferred by the significant evolution of the absorption fine structure region (EXAFS) of the Mn K-edge (Figure 1b). In contrast, minor Zn spectral changes reflect primarily processes of precipitation and dissolution, suggesting that no Zn-Mn mixed phases form during cycling.

Figure 1
Understanding Aluminium Electrochemistry in Aqueous and Aqueous-Ionic Liquid Mixtures for Aluminium-Ion Batteries
Authors: Lahiri Abhishek , Chutia Arunabhiram
Published: February 2024

Among various batteries, Aluminium ion batteries are potential low-cost alternatives to Li-ion batteries, which possess highest theoretical volumetric capacity of 8056 mAh cm-3 and a modest gravimetric capacity of 2981 mAh g-1. 1 However, due to passive layer formation of Aluminium and lack of suitable cathode materials, there are major challenges to overcome in order to accomplish a suitable Al-ion battery.

Here, we have studied the Al electrochemistry on electrodeposited MnO2 cathode and Zn anode in aqueous and aqueous-ionic liquid mixtures. Both from experiment and DFT calculations, we show that the presence of ionic liquid (1-ethyl-3-methylimidazolium trifluoromethanesulfonate) changes the Al solvation chemistry, which leads to a change in Al electrochemistry both on Zn and MnO2 (figure below). A strain-induced intercalation/deintercalation process was identified in MnO2 cathode leading to crack formation and capacity fading during Zn/Al-MnO2 battery cycling. By developing a MnO2-polymer matrix, a relatively stable average capacity of 150 mAh g-1 could be achieved over 50 cycles at a current density of 0.1 A g-1.

Acknowledgement:

The financial support by Royal Society grant (RGS\R2\212184) is gratefully acknowledged.

References

Faegh et al, Nat. Energy, 2021, 6, 21-29

Figure 1
Electrodeposition of Reactive Aluminum-Nickel Coatings in an AlCl3:[Emim]Cl Ionic Liquid Containing Nickel Nanoparticles
Authors: Mejia Chueca María del Carmen , Baumer Christoph , Stich Michael , Ispas Adriana , Bund Andreas
Published: February 2024

The electrodeposition of reactive aluminum-nickel dispersion coatings was performed by pulsed direct current (PDC) onto copper substrates in the ionic liquid 1.5:1 AlCl3:[EMIm]Cl (1-Ethyl-3-methylimidazolium chloride). A cathodic current density of 15 mA/cm2 was used with two different frequency (f)/duty cycle (r
c) combinations, i.e., f= 0.33 Hz/ r
c= 0.33 (t
on= 1 s, t
off= 2 s) and f= 0.05 Hz/ r
c= 0.5 (t
on= 10 s, t
off= 10 s). Several electrochemical techniques like Cyclic Voltammetry, Electrochemical Impedance Spectroscopy and Open Circuit Potential measurements were used besides X-Ray Diffraction, Confocal Microscopy, Scanning Electron Microscopy, Atomic Absorption Spectroscopy and 27Al/1H Nuclear Magnetic Resonance in order to shed more light on the mechanism of Ni particle incorporation into the Al metal matrix. We could show that particle incorporation at the beginning of the deposition mainly takes place via particle adsorption at the substrate. As the thickness of the coating increases, it seems that the main mechanism for particle incorporation is via the reduction of Al2Cl7
- ions adsorbed at the particles surface. Three different Ni NPs concentration were tested in this work: 5, 10 and 20 g/L. Although a considerable high incorporation of Ni NPs has been achieved from the IL electrolyte containing the highest concentration of Ni NPs (i.e. ~ 33 wt.% from a 20 g/L of Ni NPs bath), a high concentration of NPs in the ionic liquid resulted having a negative effect in terms of quality of the coatings, due to local cathodic passivation, or solidification of the electrolyte in a poorly conductive compound. This phenomenon has been related to the increase in viscosity originating from the decrease in rotational mobility of the [EMIm]+ cation, as detected by 1H NMR. Despite this fact, almost equivalent amounts of Ni and Al (Ni ~ 45 wt.% and Al ~ 44 wt.%) have been detected by energy-dispersive X-ray spectroscopy mapping in some areas of the coatings prepared with longer pulse off-time (f = 0.05 Hz, t
off= 10 s). Such a layer composition would be convenient for the targeted application. Nevertheless, more studies related to the homogeneity of the deposits, as well as ignition tests, must be performed to evaluate the suitability of the coatings to trigger a self-propagating reaction.
Synthesis and Characterization of Neoteric Boronium Ionic Liquids
Authors: Trulove Paul C. , Stachurski Christopher D. , Davis James H. , Cosby Tyler , Larm Nathaniel E. , Durkin David P.
Published: February 2024

Ionic liquids (ILs) are highly tailorable materials with unique physical and chemical properties that set them apart from conventional organic solvents. As the library of readily accessible ILs continues to grow, so too does their relevance in applications ranging from material processing to electrochemical energy storage as solvents capable of accessing new chemistries disallowed by traditional chemicals. While a great deal of interest has been directed towards imidazolium and quaternary ammonium based ionic liquids, there are other understudied classes of cations which have potentially favorable properties for energy related applications. One such class is that with boronium cations. These cations have a unique structure with a formally negative boron flanked by positive nitrogens. This inherently zwitterionic structure presents interesting possibilities for electrochemical applications. To date only a handful of boronium cation-based ionic liquids have been thoroughly characterized despite exhibiting impressive electrochemical stabilities (> 5.0 V). In the present study we synthesized a series of ILs with novel boronium cations coupled with the bis(trifluoro-methanesulfonyl)imide anion. We then characterized the electrochemical and physical properties of these boronium ionic liquids by techniques such as cyclic voltammetry, broadband dielectric spectroscopy, oscillatory shear rheology, and thermogravimetric analysis. We will discuss how systematic variations in boronium cation structure impacted electrochemical and physical properties.
Electrochemical Approach for Studying Local Dynamic Heterogeneity of Ionic Liquids Applied to Neoteric Boroniums
Authors: Durkin David P. , Stachurski Christopher D. , Cosby Tyler , Larm Nathaniel E. , Davis James H. , Trulove Paul C.
Published: February 2024

Ionic liquids (ILs) are liquid salts (below ca. 100 °C) whose ions can be designed to impart unique physicochemical properties. An emergent class of ILs based on the boronium cation (BILs) can have unique zwitterionic structure within the cation that presents potential for electrochemical applications. In the present study we first show how broadband dielectric spectroscopy (BDS) can be used to evaluate local dynamic heterogeneity in imidazolium-based ionic liquid systems. We then apply this approach to a series of BILs (coupled with the bis(trifluoro-methanesulfonyl)imide ([Tf2N]–) anion), whose cationic structures show similar features, suggesting may have potential to promote more favorable ion transport for application in supercapacitors. Preliminary cyclic voltammetry and electrochemical impedance spectroscopy data will also be shown that evaluates the chemical stability of each BILs when combined with common electrode materials.
Solid-State NMR Revealing the Impact of Polymer Additives on Li-Ion Motions in Plastic-Crystalline Succinonitrile Electrolytes
Authors: Möller Julia
Published: February 2024

To enhance the safety of lithium-ion batteries (LIBs), alternatives to liquid electrolytes are widely studied. One of them is the plastic-crystal succinonitrile (SN) which can solvate various Li salts.[1] This system can be further extended by inserting polymers, bringing additional advantages such as higher melting points and the possibility of adjusting thermo-mechanical and electrochemical properties.[2]

The plastic-crystalline electrolyte consisting of the Li salt lithium bis(trifluoro-methanesulfonyl)imide (LiTFSI) dissolved in SN was extended by adding various thermoplastic polymers, namely, polyacrylonitrile (PAN), poly(ethylene oxide) (PEO), polyethylene carbonate (PEC), and polyvinylpyrrolidone (PVP). Even small amounts (10 wt %) of added polymer to the SN-base were found to impact the Li-ion mobility. Variable temperature investigations on structure and ion dynamics were performed using static and magic angle spinning (MAS) solid-state NMR and various relaxometry measurements. Influence of the Li-concentration and the polymers’ functional groups on the structure of SN and the resulting Li-ion mobility was elaborated. Activation energies and jump rates of the Li-ions were determined.

As a result, the PAN containing system stands out to be a promising candidate for application in future LIBs as it shows high ion mobility, low activation energy, and a high potential for further modifications. Solid-state NMR turned out to be a reliable method and a good alternative to impedance spectroscopy measurements for investigating ion mobility behaviour providing even more information.[3]

Literature:

[1] S. Long, D. R. MacFarlane, M. Forsyth, Solid State Ionics
2004, 175, 733.

[2] N. Voigt, L. van Wüllen, Solid State Ionics
2014, 260, 65.

[3] J. Möller, V. van Laack, K. Koschek, P. Bottke, M. Wark, J. Phys. Chem. C
2023, 127, 1464.
Solvation Structure and Dynamics in Ionic Liquid Electrolytes with Hydrofluoroether for Li-Ion Batteries
Authors: Gurkan Burcu , Penley Drace , Gerber Hazel , Garaga Mounesha N , Greenbaum Steve G , Maginn Edward
Published: February 2024

The addition of hydrofluoroethers (HFEs) to Li-ion battery electrolytes reduces flammability and enhances the cycling behavior at a wider temperature range. In the case of ionic liquid electrolytes, where the ion concentration is high and Li+ solvation by anions govern the transport properties, HFEs facilitate the separation of ion aggregates. In this study, the addition of HFE to n-methyl-n-butylpyrrolidinium bis(trifluoromethanesulfonyl)imide [PYR14][TFSI] with Li-salts of lithium (nonafluorobutane)(trifluoromethanesulfonyl)imide [Li][IM14] and [Li][TFSI] (0 ≤ x
Li ≤ 0.3), were studied to understand the compositional changes in phase, the liquid structure and the transport properties. A suppression in the melting point with the addition of HFE was accompanied with improved conductivities at lower temperatures. Li+ was found to primarily solvated by [TFSI] with some contribution by [IM14], as determined from Raman spectroscopy and molecular dynamics (MD) simulations. Further, HFE encouraged florous domain formations as determined by HOESY NMR and even short contacts between HFE and Li+ as a result of tighter anion-solvated Li+ without aggregation. Li+ diffusivity of 1.2610-12 m2/s at 0 °C and x
Li = 0.2 was achieved with a high Li+ transference of 0.16, relative to ionic liquid electrolytes at 0 °C. The developed electrolytes demonstrated cyclable Si-Li half cells. This study demonstrates the tunability of ionic liquid electrolytes by asymmetric fluorinated anions and HFE co-solvents for low temperature Li-ion battery applications.
Use of Ionic Liquid as Crystallization Inhibitor in Water-Lithium Bromide Absorption Chiller
Authors: Brahim Sean , Walczuk Joseph , Maat Stefan , Richter Lutz , Tillmann Christine , Safarik Mathias
Published: February 2024

Chillers are used in commercial buildings and industrial plants to provide air conditioning, refrigeration, and process fluid cooling. There are two basic types of chiller cycles: vapor compression and sorption. Sorption chillers are available as either absorption or adsorption designs, depending on the state of the sorbent. Absorption chillers use fluid refrigerants and absorbents (liquid or dissolved), while adsorption chillers employ a solid sorbent (typically silica gel) in combination with a fluid refrigerant. Among the former category, the use of highly hygroscopic LiBr salt as absorbent in combination with H2O as refrigerant comprises LiBr-H2O absorption chillers. Such chillers possess cooling capacities ranging from a few kilowatts (kW) to megawatts (MW) which match with small residential to large scale commercial or even industrial cooling needs. One of the major debilitating factors associated with LiBr-H2O absorption chillers is crystallization. A crystallization event causes a loss of cooling and requires de-crystallization by applying external heat, which results in extensive down-time and requires redundancy designed into a chiller plant. We investigated the use of the imidazolium-based ionic liquid, 1-butyl-3-methylimidazolium bromide ([BMIm]-Br), as crystallization inhibitor additive to LiBr-H2O in the ratio 1:19 [BMIm]-Br:LiBr. It was found that under the operating boundary conditions of 27°C/9°C (cooling water inlet temperature/chilled water outlet temperature), the LiBr-H2O absorption chiller can be operated without modifications and with around 10 K higher heating water inlet temperatures when adding [BMIM]-Br before crystallization occurs compared to pure LiBr-H2O solution. When using the [BMIM]-Br ionic liquid, the refrigeration capacity of the absorption chiller under the above operating conditions and at 85°C heating water inlet temperature exhibited 10% increase after optimizing the solution flow, that lead to higher outputs, such as lower cooling water temperatures. By adding the [BMIM]-Br to the aqueous lithium bromide solution the operating range of the absorption refrigeration system could also be extended to resorption mode, which allows refrigeration below 0 °C. Thus, there is an excellent potential for a significant extension of the application range of LiBr-H2O chillers, e.g. in the field of food cooling and refrigeration processes.

Figure 1
(Invited) Electrolyte Design for Li-Ion and Li Metal Batteries
Authors: Wang Chunsheng
Published: February 2024

The energy density, safety, and cycle life of batteries are critical for electric vehicles (EV), electric aviation, and renewable energy storage. However, current Li-ion batteries still cannot simultaneously meet all the requirements for these applications. We developed non-flammable fluorinated organic electrolytes, aqueous electrolytes, and solid-state electrolytes to form nano-scaled solid electrolyte interphase, which enhanced the energy density, safety, and cycle life of Li batteries. The electrolyte design principle for high-capacity anodes and high-voltage cathodes will be discussed.
Exploring the Role of Molecular Intercalants in Electrochemical Production of Graphene-Based 2D Materials
Authors: Xia Zhenyuan , Zhang Daheng , Sasidharan Sankar , Sasikala Devi Assa Aravindh , Shi Jiahao , Su Jian-Hua , Huang Jinhai
Published: February 2024

Since the discovery of graphene, two-dimensional (2D) materials have gained extensive attention due to the unique material properties from their reduced dimensionality. Numerous techniques have been thoroughly investigated for the fabrication of graphene-based 2D materials. Among them, electrochemical synthesis is one of the most promising approaches for the large-scale production of 2D materials with tunable properties [1-3]. Especially, intercalation of various ions/molecules electrochemically driven in between the graphene sheets plays the key role in the synthesis of single or few-layer 2D materials. However, the influence of molecular intercalants is still poorly understood.

In this work, we studied different types of intercalants (i.e., ClO4
-, PF6
-, BF4-, HSO4
-) and explored the inserting process of molecular anions in-between the weekly-bonded layered materials driven by electrochemistry. Combining the cyclic voltammetry, XRD, Raman and density functional theory computation modeling, we can monitor the intercalation behavior of different anions and evaluate the contribution of intercalants in the high-yield production of graphene by electrochemical exfoliation. By optimizing the use of certain molecular intercalants, high exfoliation yield (>80 %) of graphene nanosheets with moderate oxidation damage and good electrochemical stability was achieved assisted by electrochemical exfoliation. Our study provides new insights into the electrochemical production of graphene-based 2D materials and suggests that the introduction of molecular intercalants is a promising tool for the controlled synthesis of layered 2D materials.

Reference:

(1) Xia, Z. Y.; Pezzini, S.; Treossi, E.; Giambastiani, G.; Corticelli, F.; Morandi, V.; Zanelli, A.; Bellani, V.; Palermo, V. The Exfoliation of Graphene in Liquids by Electrochemical, Chemical, and Sonication-Assisted Techniques: A Nanoscale Study. Advanced Functional Materials
2013, 23 (37), 4684-4693. DOI: 10.1002/adfm.201203686.

(2) Xia, Z. Y.; Maccaferri, G.; Zanardi, C.; Christian, M.; Ortolani, L.; Morandi, V.; Bellani, V.; Kovtun, A.; Dell'Elce, S.; Candini, A.; et al. Dispersion Stability and Surface Morphology Study of Electrochemically Exfoliated Bilayer Graphene Oxide. Journal of Physical Chemistry C
2019, 123 (24), 15122-15130. DOI: 10.1021/acs.jpcc.9b03395.

(3) Cao, J. Y.; He, P.; Mohammed, M. A.; Zhao, X.; Young, R. J.; Derby, B.; Kinloch, I. A.; Dryfe, R. A. W. Two-Step Electrochemical Intercalation and Oxidation of Graphite for the Mass Production of Graphene Oxide. Journal of the American Chemical Society
2017, 139 (48), 17446-17456. DOI: 10.1021/jacs.7b08515.