Metal Electrode Surface Research Articles

Diphenylphosphoryl Azide as a Multifunctional Flame Retardant Electrolyte Additive for Lithium-Ion Batteries

Graphite anode materials and carbonate electrolyte have been the top choices for commercial lithium-ion batteries (LIBS) for a long time. However, the uneven deposition and stripping of lithium cause irreversible damage to the graphite structure, and the low flash point and high flammability of the carbonate electrolyte pose a significant fire safety risk. Here, we proposed a multifunctional electrolyte additive diphenylphosphoryl azide (DPPA), which can construct a solid electrolyte interphase (SEI) with high ionic conductivity lithium nitride (Li3N) to ensure efficient transport of Li+. This not only protects the artificial graphite (AG) electrode but also inhibits lithium dendrites to achieve excellent electrochemical performance. Meanwhile, the LIBS with DPPA offers satisfactory flame retardancy performance. The AG//Li half cells with DPPA-0.5M can still maintain a specific capacity of about 350 mAh/g after 200 cycles at 0.2 C. Its cycle performance and rate performance were better than commercial electrolyte (EC/DMC). After cycling, the microstructure surface of the AG electrode was complete and flat, and the surface of the lithium metal electrode had fewer lithium dendrites. Importantly, we found that the pouch cell with DPPA-0.5M had low peak heat release rate. When exposed to external conditions of continuous heating, DPPA significantly improved the fire safety of the LIBS. The research of DPPA in lithium electrolyte is a step towards the development of safe and efficient lithium batteries.

Formation of field-induced breakdown precursors on metallic electrode surfaces

Understanding the underlying factors responsible for higher-than-anticipated local field enhancements required to trigger vacuum breakdown on pristine metal surfaces is crucial for the development of devices capable of withstanding intense operational fields. In this study, we investigate the behavior of nominally flat copper electrode surfaces exposed to electric fields of hundreds of MV/m. Our novel approach considers curvature-driven diffusion processes to elucidate the formation of sharp breakdown precursors. To do so, we develop a mesoscale finite element model that accounts for driving forces arising from both electrostatic and surface-tension-induced contributions to the free energy. Our findings reveal a dual influence: surface tension tends to mitigate local curvature, while the electric field drives mass transport toward regions of high local field density. This phenomenon can trigger the growth of sharper protrusions, ultimately leading to a rapid enhancement of local fields and, consequently, to a runaway growth instability. We delineate supercritical and subcritical regimes across a range of initial surface roughness. Our numerical results are in qualitative agreement with experimentally reported data, indicating the potential practical relevance of field-driven diffusion in the formation of breakdown precursors.

Engineering a lithium silicate-based artificial solid electrolyte interphase for enhanced rechargeable lithium metal batteries

The main motivation for replacing lithium-ion batteries with lithium metal batteries is to achieve a higher energy density by using the metallic lithium anode. One of the major challenges with rechargeable lithium metal batteries is the formation of lithium dendrites and dead lithium during repeated cycling. Another challenge is the formation of the unstable solid electrolyte interphase (SEI) on the surface of the lithium metal electrode, which can reduce battery efficiency and cycle life. In the present work, two different lithium silicates (Li2Si2O5 and Li2SiO3) are successfully synthesized and implemented as an artificial SEI layer via a simple dry coating method. The lithium silicate coating acts as a protective barrier that prevents direct contact between the lithium metal and the electrolyte, which can cause undesirable side reactions and reduce the efficiency and lifetime of the battery. The lithium silicate artificial SEI layer improves the stability of lithium metal batteries by reducing unwanted surface reactions, optimizing ion transport kinetics, and protecting the lithium metal anode from mechanical deformation and unstable SEI formation during extended cycling. This laminated lithium anode structure can be an effective design for the future development of rechargeable lithium metal batteries.

Lithium Silicates as an Artificial SEI for Rechargeable Lithium Metal Batteries

The major motivation of replacing lithium-ion batteries with lithium metal batteries is to obtain higher energy density by adopting the metallic lithium anode (3860 mAh g-1, theoretically), which means they can store more energy in the same volume or weight. One of the main challenges of rechargeable lithium metal batteries is the formation of lithium dendrites during the charging process.1 Lithium dendrites are tiny needle-like structures that can grow from the surface of the lithium metal electrode and penetrate the separator, causing battery short-circuiting. This can lead to safety issues, including the potential for fire or explosion. Another challenge is the formation of solid-electrolyte interface (SEI) on the surface of the lithium metal electrode, which can reduce the battery's efficiency and cycle life.2 The SEI layer can also lead to the formation of inactive lithium and increase the risk of dendrite growth.In the present work, various lithium silicates have been synthesized to be implemented as the artificial SEI layer via a facile dry coating method.3,4 The lithium silicate coating acts as a protective barrier that prevents direct contact between the lithium metal and the electrolyte, which may cause undesirable side reactions and reduce the efficiency and lifespan of the battery.4 The lithium silicate-based artificial SEI layer improves the stability and efficiency of lithium metal batteries by reducing unwanted surface reactions, improving ion transport kinetics, and protecting the lithium metal anode from mechanical deformation and unstable SEI formation during extended cycling. This laminated lithium anode structure could be an effective design for the future development of long-cycle-life lithium metal batteries. F. Wu et al., Energy Storage Materials, 15, 148–170 (2018).X.-B. Cheng et al., Adv. Sci., 3, 1500213 (2016).A. Bhat, P. Sireesha, Y. Chen, and Y. Su, ChemElectroChem, 9 (2022) https://onlinelibrary.wiley.com/doi/10.1002/celc.202200772.Y.-S. Su, K.-C. Hsiao, P. Sireesha, and J.-Y. Huang, Batteries, 8, 2 (2022). Figure 1

The Effects of AC Electric Field on Ice Nucleation in the Super‐Cooling of a Distilled Water

The effects of an AC electric field on ice nucleation temperature and nucleation rate were investigated by freezing distilled water while exposing it to varied AC electric field strengths and frequencies. To eliminate the influence of ion injections and electric field concentrations at a metal electrode surface on ice nucleation, distilled water filled in resin cuvettes are used as samples. The samples are exposed to AC electric field induced by parallel plate electrodes placed outside of the cuvettes. The cuvettes and parallel plate electrodes placed in a freezer with an inside temperature fixed at −15°C. The electric field strength in the sample is 2 or 7.5 kV/m and frequency varies from 50 Hz to 10 kHz. The ice nucleation temperature and the nucleation rate of distilled water increase with increasing the electric field strength and the frequency. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Gold-Nanolayer-Derived Zincophilicity Suppressing Metallic Zinc Dendrites and Its Efficacy in Improving Electrochemical Stability of Aqueous Zinc-Ion Batteries.

Herein, an Au-coating layer adjusted on the surface of a Zn metal electrode that effectively suppresses the dendrite growth as well as the mechanisms underlying the dendrite suppression as a result of the zincophilic character of Au is introduced. For the Au-coated Zn metal symmetric cell, uniform deposition of Zn-derived compoundswas revealed by operando synchrotron tomography. Microscopic studies demonstrate that the Au-coating layer is induced to form a new Zn-Au alloy during the initial Zn deposition, resulting in stabilized long-term stripping/plating of Zn via the 'embracing effect' that intimately accommodates Zn deposition for further cycles. This property supports the successful operation of symmetrical cells up to 50 mA cm-2 . According to Zn electrodeposition simulation, it is verified that the suppression of dendrite growth is responsible for the electro-conducting Au nanolayer that uniformly distributes the electric field and protects the Zn electrode from corrosion, ultimately promoting uniform Zn growth. The compatibility of the Au-coating layer for full cell configuration is verified using NaV3 O8 as a cathode material over 1000 cycles. This finding provides a new pathway for the enhancement of the electrochemical performance of ZIBs by suppressing the dendritic growth of Zn by means of a zincophilic Au nanolayer.

SEI growth on Lithium metal anodes in solid-state batteries quantified with coulometric titration time analysis

Lithium-metal batteries with a solid electrolyte separator are promising for advanced battery applications, however, most electrolytes show parasitic side reactions at the low potential of lithium metal. Therefore, it is essential to understand how much (and how fast) charge is consumed in these parasitic reactions. In this study, a new electrochemical method is presented for the characterization of electrolyte side reactions occurring on active metal electrode surfaces. The viability of this new method is demonstrated in a so-called anode-free stainless steel ∣ Li6PS5Cl ∣ Li cell. The method also holds promise for investigating dendritic lithium growth (and dead lithium formation), as well as for analyzing various electrolytes and current collectors. The experimental setup allows easy electrode removal for post-mortem analysis, and the SEI’s heterogeneous/layered microstructure is revealed through complementary analytical techniques. We expect this method to become a valuable tool in the future for solid-state lithium metal batteries and potentially other cell chemistries.

Plasma Electrochemistry for Carbon-Carbon Bond Formation Via Pinacol Coupling Reaction

Low-temperature, atmospheric-pressure plasmas in contact with liquids have attracted interest for various chemical applications including the degradation of organic pollutants,1 conversion of abundant feedstocks,2,3 and more recently, organic chemistry.4 Compared to other chemical approaches, plasma-liquid chemistry does not require a catalyst material, is electrified, and produces unique reactive species such as solvated electrons, one of the strongest chemical reducing species.5 Here, we present an application of plasma-liquid chemistry to the formation of carbon-carbon bonds via the well-known pinacol coupling reaction. Pinacol coupling is conventionally carried out by using an electron donating reagent such as magnesium to initially reduce a carbonyl group forming a ketyl radical anion species. A pair of these ketyl groups then react to form a vicinal diol, which in the presence of a proton donor such as water, leads to the final diol product. We show that the pinacol coupling reaction can instead be driven at a plasma-liquid interface without any catalyst. Our study was performed using a direct-current (DC) powered plasma formed between a metal electrode and liquid water surface similar to previous reports.2 Parametric studies were focused on methyl-4-formylbenzoate (MFB) as the substrate. We find that the faradaic efficiency of the pinacol product depends on the initial concentration, increasing from 20% to 80% as the concentration increased from 0.06 M to 0.18 M. For an initial concentration of 0.12 M and a constant operating current of 3 mA, a yield of 46% can be reached after 12 h. The experimental results were supported by a reaction-diffusion model, and a rate constant of 10^10 L-1 mol-1 s-1 was extracted from kinetic studies. In addition to the pinacol product, nuclear magnetic resonance (NMR) spectroscopy also indicated methyl 4-(dimethoxymethyl)benzoate, methyl 4-(hydroxymethyl)benzoate, and 4-(methoxycarbonyl)benzoic acid as side products. By carrying out scavenger control experiments, we show that the vicinal diol is produced by solvated electron reduction while these other side products are formed by reactions with other radicals or the solvent. The generality of the approach is demonstrated by extending to several other aromatic aldehydes and ketones.

Natural sources of intense ultra-high-frequency radiation in high-voltage atmospheric discharges.

We study the sources of intense ultra-high-frequency (UHF) radiation (in the frequency range 1-6GHz) arising during the development of high-voltage atmospheric discharges. The discharges were initiated in a long discharge gap by applying an approximately 1-MV pulse with positive or negative polarity. By employing a radio registration system based on ultrawideband antennas, we managed to localize the UHF radiation sources in the discharge with centimeter accuracy and investigate their temporal and spatial correlation with the discharge structures. The vast majority of the localized sources turned out to be concentrated in the near-electrode regions. It is found that the generation mechanism of intense UHF radiation in a laboratory discharge cannot be unambiguously associated with such basic processes as the head-on collision of opposite-polarity streamers or the interaction of single streamers with the near-electrode plasma at the surface of metal electrodes. We discovered that the observed UHF emission appears basically as a precursor of the intense plasma development in a certain discharge region, whereinto a bright counterstreamer comes a bit later. The findings were confirmed by the statistical observations and results of imaging the dynamics of the discharge structures with a nanosecond temporal resolution.

Polyethylene Glycol-Mediated Directional Conjugation of Biological Molecules for Enhanced Immunoassays at the Point-of-Care.

Rapid and reliable point-of-care (POC) diagnostic tests can have a significant impact on global health. One of the most common approaches for developing POC systems is the use of target-specific biomolecules. However, the conjugation of biomolecules can result in decreased activity, which may compromise the analytical performance and accuracy of the developed systems. To overcome this challenge, we present a polymer-based cross-linking protocol for controlled and directed conjugation of biological molecules. Our protocol utilizes a bifunctional thiol-polyethylene glycol (PEG)-hydrazide polymer to enable site-directed conjugation of IgG antibodies to the surface of screen-printed metal electrodes. The metal surface of the electrodes is first modified with thiolated PEG molecules, leaving the hydrazide groups available to react with the aldehyde group in the Fc fragments of the oxidized IgG antibodies. Using anti-Klebsiella pneumoniae carbapenemase-2 (KPC-2) antibody as a model antibody used for antimicrobial resistance (AMR) testing, our results demonstrate a ~10-fold increase in antibody coupling compared with the standard N-hydroxysuccinimide (NHS)-based conjugation chemistry and effective capture (>94%) of the target KPC-2 enzyme antigen on the surface of modified electrodes. This straightforward and easy-to-perform strategy of site-directed antibody conjugation can be engineered for coupling other protein- and non-protein-based biological molecules commonly used in POC testing and development, thus enhancing the potential for improved diagnostic accuracy and performance.

Oriented Zn plating guided by aligned ZnO hexagonal columns realizing dendrite-free Zn metal electrodes

Aqueous zinc-ion batteries (AZIBs), featuring low cost and high safety, have become a research hotspot in recent years. However, the low Zn stripping/plating reversibility, caused by dendritic growth, harmful side reactions, and Zn metal corrosion, severely influences the applicability of AZIBs. Zincophilic materials have shown great potential to form protective layers at the surface of Zn metal electrodes, whereas those protective layers are usually thick, lack fixed crystalline orientation, and require binders. Herein, a facile, scalable, and cost-effective solution method is used to grow vertically aligned ZnO hexagonal columns with (002) top surface and low thickness of 1.3 µm onto Zn foil. Such oriented protective layer can promote homogenous and nearly horizontal Zn plating not only on the top but also at the side of ZnO columns due to the low lattice mismatch between Zn (002) and ZnO (002) facets and between Zn (110) and ZnO (110) facets. Accordingly, the modified Zn electrode exhibits dendrite-free behavior with considerably suppressed corrosion issue, inert byproduct growth, and hydrogen evolution. Thanks to that, the Zn stripping/plating reversibility is significantly improved in Zn//Zn cell, Zn//Ti cell, and Zn//MnO2 battery. This work provides a promising avenue for guiding metal plating process via oriented protective layer.

Insulation Reinforcement for Cable Connector of CRH2 Electric Multiple Unit Under Standard Lightning Impulse Voltage

In order to improve the insulation capacity of cable connector (Cc) in the high voltage equipment box (Hveb), this article proposes an optimization scheme that does not change the size of the Hveb and the structure of Cc fittings. In this article, the change in the impulse voltage withstand value of Cc after installing insulating sheath was verified by the lightning impulse flashover test. Based on the finite-element software and the structure of Cc fittings, a special shaped shielding ring (Sr) was designed to adjust the partial area where the electric field intensity are concentrated. Besides, the optimal parameters of the Sr under different working conditions were determined by the orthogonal design. Finally, utilizing ultraviolet (UV) imaging technology and image processing method, the discharge intensity of Cc fittings were characterized. The results demonstrate that with the combination of insulation measures, the impulse voltage withstand value of Cc can be increased from 155 to 235 kV. The maximum electric field strength on the surface of bolts and metal electrode can be reduced by 57.8% and 72%; UV discharge facular area had an exponential relationship with the applied voltage, the initial discharge voltage of Cc can increase by 243% after installing the Sr.

Experimental Demonstration of Light-Trapping Transparent Electrode Geometries

The intrinsic trade-off between conductivity and transparency has long impeded the development of truly transparent electrodes. Recently, a transparent electrode design was introduced that promised remarkably high electrical conductivity while allowing near-complete transmission of incident light into the underlying optical device. The approach is based on the use of metallic wires with inclined surfaces, embedded in a transparent dielectric film. Light reflected by metallic regions of the sample can be recovered by total internal reflection, resulting in efficient trapping of light incident on conductive regions. Prototype electrode geometries were fabricated by multiphoton lithography and selective chemical deposition. Light trapping is observed by optical microscopy and laser scanning experiments for surface tilt angles exceeding 25°. Approximately 60% of light reflected by the metallic electrode surface was recovered through total internal reflection. The presented approach could lead to optoelectronic devices with significantly improved performance across a wide spectral bandwidth.

Nanoimprint lithography-based replication techniques for fabrication of metal and polymer biomimetic nanostructures for biosensor surface functionalization

Nanostructuring is a promising and successful approach to tailor functional layers and to improve the characteristics of biosensors such as signal transmission and tighter cell-surface coupling. One of the major objectives in biosensing and tissue engineering is the development of interfaces that mimic the natural environment of biosystems composed of extracellular matrix biomolecules. Nevertheless, effective techniques to reconstruct the random distribution of these biomolecules are still not well established. For this reason, the presented work demonstrates different methods based on nanoimprint lithography to replicate randomly distributed natural nanostructures with complex geometries into different polymers and metals. The fidelity of the replicated nanostructures has been evaluated by atomic force microscopy and the attributes of the fabrication processes have been discussed. Finally, different replication techniques have been combined for the biomimetic nanostructuring of the dielectric passivation layer as well the metal electrode surface to develop novel whole-surface-nanostructured microelectrode arrays.

Understanding molecular and electrochemical charge transfer: theory and computations.

Electron, proton, and proton-coupled electron transfer (PCET) are crucial elementary processes in chemistry, electrochemistry, and biology. We provide here a gentle overview of retrospective and currently developing theoretical formalisms of chemical, electrochemical and biological molecular charge transfer processes, with examples of how to bridge electron, proton, and PCET theory with experimental data. We offer first a theoretical minimum of molecular electron, proton, and PCET processes in homogeneous solution and at electrochemical interfaces. We illustrate next the use of the theory both for simple electron transfer processes, and for processes that involve molecular reorganization beyond the simplest harmonic approximation, with dissociative electron transfer and inclusion of all charge transfer parameters. A core example is the electrochemical reduction of the S2O82- anion. This is followed by discussion of core elements of proton and PCET processes and the electrochemical dihydrogen evolution reaction on different metal, semiconductor, and semimetal (say graphene) electrode surfaces. Other further focus is on stochastic chemical rate theory, and how this concept can rationalize highly non-traditional behaviour of charge transfer processes in mixed solvents. As a second major area we address ("long-range") chemical and electrochemical electron transfer through molecular frameworks using notions of superexchange and hopping. Single-molecule and single-entity electrochemistry are based on electrochemical scanning probe microscopies. (In operando) scanning tunnelling microscopy (STM) and atomic force microscopy (AFM) are particularly emphasized, with theoretical notions and new molecular electrochemical phenomena in the confined tunnelling gap. Single-molecule surface structure and electron transfer dynamics are illustrated by self-assembled thiol molecular monolayers and by more complex redox target molecules. This discussion also extends single-molecule electrochemistry to bioelectrochemistry of complex redox metalloproteins and metalloenzymes. Our third major area involves computational overviews of molecular and electronic structure of the electrochemical interface, with new computational challenges. These relate to solvent dynamics in bulk and confined space (say carbon nanostructures), electrocatalysis, metallic and semiconductor nanoparticles, d-band metals, carbon nanostructures, spin catalysis and "spintronics", and "hot" electrons. Further perspectives relate to metal-organic frameworks, chiral surfaces, and spintronics.

Rational Design of a Robust Flexible Triblock Polyurea Copolymer Protective Layer for High-Performance Lithium Metal Batteries.

Dendrite growth and volume expansion in lithium metal are the most important obstacles affecting the actual applications of lithium metal batteries. Herein, we design a robust flexible artificial solid electrolyte interphase layer based on a triblock copolymer polyurea film, which promotes uniform lithium deposition on the surface of the lithium metal electrode and has a high lithium-ion transference number. The high elasticity and close contact of polyurea compounds effectively suppress lithium dendrite growth and volume expansion in the Li anode, which are effectively confirmed by electrochemical characterization and optical microscopy observation. The symmetrical batteries with the PU-Li metal anode can achieve stable and reversible Li plating/stripping over 500 h at a current density of 5 mA cm-2. Matched with the high-mass-loaded S cathode and the commercial NCM523 cathode, this film significantly improves the cycle life of lithium metal batteries.

Advanced Two-Dimensional Materials for Green Hydrogen Generation: Strategies toward Corrosion Resistance Seawater Electrolysis─Review and Future Perspectives

Excessive usage of nonrenewable resources to meet global energy requirements has become a serious concern from the energy and environmental perspective. The continuous emission of CO2 in the environment from fossil fuels has become a major cause of global warming. Green hydrogen generation through seawater electrolysis has been an emergent technology that can play a prominent role in replacing conventional energy sources. Electrolysis of seawater using renewable sources such as solar, wind, and geothermal generates green hydrogen which has almost negligible harmful byproducts. Different ions present in seawater such as chlorides and sulfates impose serious corrosion problems during the electrolysis process as chloride ions penetrate the metal electrode surface and oxidize it and also liberate chlorine gas at the anode. For the electrolysis processes, catalysis plays a challenging task to reduce the kinetic barrier for the conversion of water molecules to hydrogen and oxygen products. Photoelectrocatalysts are another kind of semiconductor-based catalyst in which band gap, exchange charge carrier, and surface area play key roles in the water-splitting process. Two-dimensional nanomaterials offer many advantages like high specific surface area for electron transfer, high tunable functionalities, and flexible structural properties that make them suitable for different applications. Layered double hydroxide (LDH) as a highly efficient catalyst has the potential to perform the hydrogen production process as per the industrial application. LDH has many advantages in an effective water-splitting mechanism that includes easy synthesis methods, flexible morphology, long-term stability, and adaptability to different applications. Another major advantage is the corrosion inhibition property of LDH by different mechanisms like adsorption of corrosion-responsible ions, self-healing technique, and protective film formation which are discussed briefly in this review. This review provides a state-of-the-art analysis about the various important strategies to be adopted for effective seawater electrolysis. Finally, we examine the new challenges and the novel approaches to suppress corrosion processes during seawater electrolysis.

The SEI on Lithium Metal Anodes: From Understanding to Enhancement

Lithium metal batteries (LMB) have risen back into focus of battery research in resent years, due to the high theoretical specific capacity of the lithium metal anodes (3860 mAh g-1).[1] However, the utilization of lithium metal as an anode material requires an in depth understanding of the solid electrolyte interphase (SEI) on lithium metal electrodes, since its formation, composition and electrochemical characteristics significantly impact important LMB lifetime parameters, e.g. lithium stripping/plating behaviour, dendrite growth and in operando electrolyte consumption.[2] Lithium metal electrode performance is influenced by a variety of different, however often overlooked factors, e.g. the native passivation layer, inevitably present on each lithium metal electrode surface, which has only recently gathered more attention as an influencing factor in respect to SEI characteristics.[3] The presented research utilizes the preformation of an uncontaminated SEI on the lithium metal electrode surface to circumvent the influence of native lithium metal passivation. A systematic study of different preformed SEIs resulted in a better understanding of the influence by different electrolyte components on relevant SEI characteristics, namely, selected conducting salts (LiFSI, LiPF6) and functional additives (VC, FEC). Analyses of the SEIs electrochemical properties, composition, morphology and dynamics were conducted via stripping/plating experiments as well as in operando EIS, SEM (incl. cryogenic cross section and post mortem) and XPS (post mortem) measurements. Finally, careful tailoring of the preformed SEI was shown to have an enhancing effect on NMC811||Li cells, increasing the LMB lifetime by up to 25%. Furthermore, the application of a tailored preformed SEI has also shown a positive impact on the performance of solid state LMBs.The presented results highlight the importance of an in depth understanding regarding the cause and effect of varying electrolyte components on the SEIs characteristics. This understanding will ultimately have a significant impact on the research towards enhanced and reliable LMB performance and future applicability.

A Few Questions about Single-Atom Catalysts: When Modeling Helps

ConspectusSingle-atom catalysis (SAC) is a fascinating and rapidly growing field in heterogeneous catalysis. In less than 20 years, this has become one of the most widely investigated subjects by the catalytic community for various good reasons: the ability to synthesize active catalysts using a minimum amount of precious metals, the expected higher selectivity of SACs compared to assemblies of nanoparticles of variable sizes, and the fact that SACs represent a bridge between homogeneous and heterogeneous catalysis. The relative simplicity of SAC structures compared to classical heterogeneous catalysts based on supported metal nanoparticles has stimulated an intense simulation activity aimed at predicting new potential catalysts from first principles, often based on machine learning algorithms. This is a very ambitious objective and ultimately represents the final goal of every modeling activity: the possibility to provide realistic predictions of new material properties and catalytic reactivity. However, one of the main reasons that theory is useful is and remains the interpretation and analysis of experimental results, with the no less crucial goal of understanding the basic principles that determine a certain functionality or reactivity. The combination of advanced characterization techniques and theoretical calculations can provide a general conceptual framework to better understand structure–function relationships. In this Account, we will address this aspect in trying to provide answers to some fundamental questions related to the structure, stability, and activity of SACs. We will start by addressing a question that arises every time a new SAC is synthesized: where are the metal atoms? What is their coordination mode with the support? Once we have shown how to address this point, we will move on to the next fundamental question: do the single atoms stay put? How does the chemical environment of a SAC depend on the preparation or reaction conditions? Next, we will analyze the importance of a full characterization of the reaction mechanism to predict reactivity. SACs, due to their analogy to coordination compounds, can form intermediates that do not exist on the surface of metal electrodes. The formation of these intermediates can influence the kinetics of the process and must be considered in the simulation. Finally, we will briefly address a more general question: how does the catalytic activity of SACs compare with that of the corresponding supported metal nanoparticles on the one hand or homogeneous molecular complexes on the other? The final message is that to answer these questions and to take full advantage of quantum chemical modeling, the results of the calculations should be continuously verified with experimental data in a cross-fertilization that is beneficial for both sides.

Gas-Discharge Point Source of UV Radiation Based on a Gas-Vapor Mixture of Argon and Copper

The characteristics of a pulse periodic source of a long-range UV radiation with overvoltage pumping by a bipolar discharge of nanosecond duration between copper electrodes in argon at atmospheric pressure are investigated. Copper vapors were introduced into the discharge due to the ectonic mechanism, in which a sufficient amount of the electrode material vapors is introduced into the discharge gap due to microexplosions of inhomogeneities of the surface of metal electrodes in a strong electric field of an overvoltage high-current nanosecond discharge. The characteristics of an overvoltage nanosecond discharge at a distance between the electrodes of 2 mm are studied. The emission spectra of the discharge were analysed, and the intensity of the UV radiation of a point emitter was optimized depending on the supply voltage of the high-voltage modulator and the repeti-tion rate of discharge pulses. The identification of the emission spectra of plasma made it possible to establish the main excited plasma products that form the spectrum of the UV radiation of the plas-ma. The study of the spectral characteristics of plasma based on gas-vapor mixtures "copper – ar-gon" showed that the most intense were the spectral resonance spectral lines of the copper atom and ion. It was found that a space-uniform overvoltage nanosecond discharge was ignited between copper electrodes at an inter-electrode distance of 2 mm. It was found that the maximum value of the average UV power at p(Ar) = 101 kPa was observed for the UV-A range.