Number Of Electrons Research Articles

Passivation characteristics and corrosion behavior of S32202 duplex stainless steel in different temperatures polluted phosphoric acid

The passivation characteristics of S32202 duplex stainless steel in different temperatures polluted phosphoric acid were studied by electrochemical technology and X-ray photoelectron spectroscopy, and its corrosion behavior was studied through immersion corrosion and electrochemical corrosion. The results indicate that as the temperature increases, the open-circuit potential of the sample in polluted phosphoric acid moves forward, and the surface exhibits a rapid passivation process. The main phases of the passivation film are Fe2O3, Fe3O4, Cr2O3, Cr(OH)3, and corresponding phosphates and polyphosphates. The passivation film of the sample in polluted phosphoric acid exhibits n-p-n composite semiconductor properties. As the temperature increases, the electron density and number of defects in the passivation film increase, and the vulnerability of the passivation film increases. The increase in temperature promotes the formation of a porous thick film. The corrosion types of the sample in polluted phosphoric acid are total corrosion, phase boundary corrosion, and intergranular corrosion, accompanied by pitting corrosion in local areas. The corrosion current density and passivation current density of the sample gradually increase with increasing temperature, while the counter-passivation potential and passivation index decrease, the density and protective properties of the passivation film decrease. The doping of phosphate can alleviate the dissolution process of metals, but the increase in temperature increases the solution ionic activity and accelerates the rate of charge transfer at the interface. At the same time, FePO4, CrPO4 and other phosphates are poorly protected, and their large presence is not conducive to the stability of the passivation film structure, resulting in a decrease in the corrosion resistance of the material.

Texture measurements of archaeological objects at STRESS-SPEC neutron diffractometer

The main advantage of neutron diffraction over X-ray diffraction, arises from the fact that the interaction of neutrons with material is relatively weak and not related to the number of electrons, and consequently the penetration depth of neutrons is about 102-103 larger than that of laboratory X-ray diffraction. This is particular essential for the non-destructive texture analysis of archaeological objects as no additional surface treatments of the samples (e.g. polishing) are necessary. STRESS-SPEC at MLZ is designed as a state of the art multi-purpose diffractometer for strain and texture analysis. Besides the optimized high neutron flux the available large variability in gauge volume definition systems together with the robotic sample handling option offer high flexibility for bulk or gradient texture measurements. Since 2014, local and bulk textures of iron and gold artefacts collected by Bavarian State Archaeological Collection (Munich, Germany) have been thoroughly investigated at STRESS-SPEC. Results showed that heat treatment of iron artefacts at high temperatures can re-orientate the inner crystallites. In the gold foil artefacts, the texture represented by the measured pole figures shows a high symmetry – the so-called Cube component, which is commonly found in annealed fcc materials. For comparison, laboratory samples were produced by rolling, flat hammering, and pin / round hammering and also measured in order to elucidate possible manufacturing and processing routes. In turned out that both rolling and pin / round hammering followed by a high temperature annealing can produce similar pole figures to those of the gold artefacts foils.

CTAC Self-Assembled Alkylated β-Cyclodextrin Loaded onto Functionalized MWCNTs Electrochemical Sensor for NP Detection.

Nonylphenol (NP) is an important fine chemical raw material and intermediate that is widely utilized in industry and may be distributed in aquatic ecosystems. Following its entry into the food and water cycles, it can subsequently enter the human body and potentially harm the human reproductive system. For the purpose of monitoring NP in water, it is thus essential to build a straightforward, affordable, and robust electrochemical sensor. Based on a two-step chemical modification proceeding and an electrostatic self-assembly effect, a double-modified β-cyclodextrin functionalized multiwalled carbon nanotube sensor (HE-β-CD-CTAC/F-MWCNTs) has been successfully constructed. It incorporates the excellent host-guest interaction ability of β-cyclodextrin and the high chemical activity of cetyltrimethylammonium chloride (CTAC), and the carbon nanotubes have an enormous particular surface area and strong electrical conductivity. The electrochemical oxidation reaction of NP with the sensor is controlled by a surface adsorption process of equal numbers of protons and electrons. In accordance with the optimized experimental parameters, the limit of detection (LOD) for the sensor is 0.13 μM, and it responds linearly to NP in the concentration range of 1-200 μM. Meanwhile, the sensor has excellent repeatability, stability, and immunity to interference. For the detection of NP in real water samples, the sensor also showed an excellent recovery rate (92.8%-98.5%) and relative standard deviation (1.16%-3.26%).

Ultra-Nonlinear Subcycle Photoemission of Few-Electron States from Sharp Gold Nanotapers.

The generation of ultrashort electron wavepackets is crucial for the development of ultrafast electron microscopes. Recent studies on Coulomb-correlated few-electron number states, photoemitted from sharp metallic tapers, have shown emission nonlinearities in the multiphoton photoemission regime which scale with the electron number. Here, we study few-electron photoemission from gold nanotapers triggered by few-cycle near-infrared pulses, demonstrating extreme 20th-order nonlinearities for electron triplets. We report interferometric autocorrelation traces of the electron yield that are quenched to a single emission peak with subfemtosecond duration due to these high nonlinearities. The modulation of the emission yield by the carrier-envelope phase suggests that electron emission predominantly occurs during a single half cycle of the driving laser field. When applying a bias voltage to the tip, recollisions in the electron trajectories are suppressed and coherent subcycle electron beams are generated with promising prospects for ultrafast electron microscopy with subcycle time resolution.

Enhancing the radiation shielding performance of polyepoxide composites based on cement bypass dust

In this study, radiation shielding composite materials were created by combining epoxy with cement bypass dust (CBPD) at different weight percentages (0%, 10%, 20%, and 30%). The solution casting technique was employed to construct these materials. The FTIR spectra confirmed the formation of the composites and the production of complexes. The morphology and elemental content of the produced composite samples were illustrated using SEM pictures and EDX spectra. In addition, the research findings demonstrated that the composites exhibited improved resistance to changes in temperature as the loading of CBPD increased. The gamma-ray attenuation coefficients of composites consisting of Epoxy + x% CBPD exhibited an increase, along with an increase in the neutron removal cross-section. However, there was a gradual increase in both the mean free path (MFP) as well as the half value layer (HVL) with increasing energy. Additionally, the experimental and theoretical data for attenuation parameters were compared using the Phy-X/PSD software. The relationship between the effective atomic and electron numbers of the Epoxy + x% CBPD composites has been studied. The values of fast and thermal neutron attenuation were analyzed using the NGCal software. In general, these composites are appropriate for use in radiation shielding applications.

Charge Phenomena in the Elastic Backscattering of Electrons from Insulating Polymers.

Elastic peak electron spectroscopy (EPES) analyzes the line shape of the elastic peak. The reduction in energy of the elastic peak electrons is the result of energy transfer to the target atoms, a phenomenon known as recoil energy. EPES differs from other electron spectroscopies in its unique ability to identify hydrogen in polymers and hydrogenated carbon-based materials. This feature is particularly noteworthy as lighter elements exhibit stronger energy shifts. The energy difference between the positions of the elastic peak of carbon and the elastic peak of hydrogen tends to increase as the kinetic energy of the incident electrons increases. During electron irradiation of an insulating polymer, if the number of secondary electrons emitted from the surface is less than the number of electrons absorbed in the sample, the surface floats energetically until it stabilizes at a potential energy eVs. As a result, the interaction energy changes and modifies the energy difference between the elastic peaks of hydrogen and carbon. In this study, the charge effects are evaluated using the Monte Carlo method to simulate the EPES spectra of electrons interacting with polystyrene and polyethylene.

Quantitative Astrophotography: Interpreting Astrophysics from Star-Formation Regions

As undergraduates produce their own high-quality astrophotography images, STEM identity is shown to increase. Can more be obtained? Specifically, what student learning is possible about the physical processes occurring within these images? In this workshop, we focused on star-formation regions (stellar birth) as a model for quantification of astrophysical values. Narrowband, photometric observations from Skynet were processed in Afterglow Access, which included aligning, stacking, and coloring. Next, within the context of Strömgren sphere modelling, threshold boundaries were established for the electron number density. By securing an upper- and lower-bound on a common astrophysical quantity, undergraduates better understand how observation and theory work together for practicing scientists. In summary, this workshop reveals the capacity of astrophotography to deepen STEM identity and belonging within undergraduates by carrying out the same activities as scientists.

Machine learning-based simple and fast approach for the real-time characterization of laser-induced plasma

We report a simple approach to estimate the fast and real-time pulse-to-pulse prediction of plasma parameters, specifically electron temperature and electron number density, using an Artificial Neural network (ANN) in combination with Laser-induced breakdown spectroscopy (LIBS). In a variety of spectroscopic applications, it is essential to have real-time observation of plasma parameters. However, direct measurement of these parameters is challenging and requires complex and time-consuming calculations. Artificial Neural Network (ANN) can be used to model the relation between spectral features from recorded LIBS emission spectra and plasma parameters. The ANN is trained on a suitable preprocessed spectroscopic dataset with corresponding plasma parameters to predict electron temperature and electron number density. The accuracy of Artificial Neural Network (ANN) in predicting the plasma parameters is evaluated, and results are validated with existing conventional methods of calculating plasma parameters, namely the Boltzmann Plot Method for plasma temperature and the Stark Broadening Method for electron number density. The present results show that ANN is an effective method in accurately predicting the plasma parameters directly from the spectral features. The ability to fine-tune plasma in real time enhances control and accuracy in Pulsed Laser Deposition (PLD) process and other plasma coating techniques.

Constructing oxygen vacancies by selective anion doping in high entropy perovskite oxide for water splitting

High entropy perovskite oxide (HEPO) is a potential electrocatalyst for the oxygen evolution reaction (OER), but insufficient activity remains a problem. Oxygen vacancies can activate the lattice oxygen to induce the lattice oxygen-mediated mechanism (LOM), which can avoid the kinetic limitation present in adsorbate evolution mechanism (AEM), thereby improving the OER activity. Herein, we select the appropriate doping element (S) through analysis of ionic radius, electronegativity, and oxygen vacancy formation energy, and report an effective two-step oxygen vacancy strategy for introducing oxygen vacancies into HEPO through electrospinning and sulfurization treatment. This strategy optimizes the eg orbital filling electron number and significantly increases the active area, oxygen vacancy content and electroconductivity. Furthermore, the apparent pH dependence and the TMA+ inhibition phenomenon suggest the involvement of the LOM. Consequently, the resulting S/LMO-E has a lower overpotential (314 mV at 10 mA cm−2) and faster kinetics, and shows excellent stability. Meanwhile, the water splitting is achieved at 1.59 V to afford 10 mA cm−2 current density for S/LMO-E⎪⎢Pt/C, which is smaller than that of RuO2⎪⎢Pt/C (1.62 V). This work provides an attractive OER electrocatalyst for efficient water splitting to produce renewable hydrogen and opens a new way for the design of effective and stable high entropy material electrocatalysts.

Electronic Structure, Aromaticity, and Magnetism of Minimum-Sized Regular Dodecahedral Endohedral Metallofullerenes Encapsulating Rare Earth Atoms.

A series of minimally sized regular dodecahedron-embedded metallofullerene REC20 clusters (RE = Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd) as basic units of nanoassembled materials with tunable magnetism and UV sensitivity have been explored using density functional theory (DFT). The contribution of the 4f orbital of the rare earth atom at the center of the C20 cage to the frontier molecular orbital of REC20 gives the REC20 cluster additional stability. The AdNDP orbitals of the four REC20 superatoms that conform to the spherical jellium model indicate that through natural population analysis and spin density diagrams, we observe a monotonic increase in the magnetic moment from Ce to Gd. This is attributed to the increased number of unpaired electrons in the 4f orbitals of lanthanide rare earth atoms. The UV-visible spectrum of REC20 clusters shows strong absorption in the mid-UV and near-UV bands. REC20 clusters encapsulating lanthanide rare earth atoms stand out for their tunable magnetism, UV sensitivity, and stability, making them potential new self-assembly materials.

Electronic shells regulate the geometric structures, stabilities and electronic properties of AlnCum (n = 10–15, m = 1–3) clusters

The properties of AlnCum (n = 10–15, m = 1–3) clusters are explored using genetic algorithm combined with density functional theory (GA-DFT). The geometric structures of Al-Cu binary clusters are spherical when the numbers of the valence electrons are around the magic number 40 predicted by Jellium model. The stabilities decrease as the number of doping Cu atom increases. The stabilities also relate to the electronic configurations. In Al13Cu-a cluster, the 3d orbitals of the central Cu atom interact strongly with the superatomic 1D orbitals and formed five bonding orbitals and five antibonding orbitals. The bonding orbitals are dominated by 3d orbitals of Cu, and antibonding orbitals are composed mainly of the superatomic 1D orbitals. The “50 valence electrons” (including 3d10 of Cu) form closed 1S21P63d101D102S21F142P6 shells, and this electronic configuration can be taken as the combination of 40-electron rule. The 3d electrons of Cu atom don’t affect the Jellium model of the cluster.

Cooperative coupling of microscopic enhanced electric field and macroscopic efficient bubble traffic for industrial hydrogen evolution

The alkaline hydrogen evolution reaction (HER) for industrial hydrogen generation is a promising way to achieve intermittent energy storage. However, challenges, such as the insufficient supply of adsorbed hydrogen atoms (*H) and slow bubble dynamics, hinder the development of industrial HER. Here, we report a cooperative strategy by leveraging both microscopic enhanced electric field and macroscopic efficient bubble traffic for industrial hydrogen evolution, demonstrated through the NiCoP nanotips on NiP nanorods (NiCoP-tip@NiP). Specifically, during the HER process, the nanotips can accumulate a large number of electrons, enhancing the electric field of the Stern layer. This enhanced electric field accelerates the dissociation of water, resulting in favorable *H for HER. Simultaneously, the confined space between the nanotips hinders the growth of bubbles generated at the tips. Newly formed bubbles will push out the existing bubbles, thus accelerating gas release. As a result, NiCoP-tip@NiP exhibits a low overpotential of 300 mV at 1000 mA cm−2 and maintains stable operation over 90 h at approximately 300 mA cm−2 during HER processes. This cooperative strategy provides profound insights for industrial hydrogen generation.

Schottky-Barrier-Free Plasmonic Photocatalysts for Solar-Driven Ammonia Synthesis

Ammonia is not only an indispensable feedstock to produce essential industrial chemicals like fertilizers, but it is also a potential hydrogen energy carrier owing to its high energy density and hydrogen capacity. Currently, most ammonia required for humans comes from the Haber–Bosch process, which contributes more than 90% of the annual global ammonia output. However, the harsh reaction conditions of this process result in serious energy and environmental issues. According to the relevant statistics, the ammonia industry consumes about 2% of the total energy and generates about 1.6% of the total CO2 emission annually in the world.It is therefore crucial to develop a green and sustainable strategy for ammonia synthesis. Among various alternative technologies of the Haber–Bosch process, artificial photosynthesis has attracted wide research interests and has been regarded as a promising, environmentally friendly, and energy-saving process. Photocatalytic ammonia synthesis can utilize renewable solar energy to drive the reaction and operate under mild conditions, which possesses the benefits of the simple reaction system, low cost, and safety. Although numerous photocatalysts have been explored over the past several decades, their activity and efficiency have still been low and far from the practical application requirements. It is therefore a huge challenge to design efficient photocatalysts for ammonia synthesis.Localized surface plasmon resonance (LSPR) has recently drawn enormous attention. LSPR can not only endow plasmonic nanomaterials with large absorption cross-sections and intense local field enhancement but also generate energetic hot electrons and hot holes. Owing to the appealing features of LSPR, plasmonic photocatalysis has shown great potential in ammonia synthesis. Plasmonic photocatalysts are usually composed of noble metals and wide bandgap semiconductors. However, the Schottky barrier will form at the metal–semiconductor interface in such hybrid structures due to the mismatch of the band structures between plasmonic metals and semiconductors. Hence, a large portion of the hot electrons cannot cross the Schottky barrier and get lost in the metal through the recombination with the holes. To overcome the drawbacks caused by the Schottky barrier, it is strongly desirable to develop a new type of plasmonic semiconductor photocatalysts, i.e., Schottky-barrier-free plasmonic photocatalyst.The Schottky-barrier-free plasmonic photocatalysts are usually degenerately doped semiconductors containing lattice oxygen vacancies. They possess high free electron densities and strong plasmon resonance because of the high-level doping, which results in abundant hot charge carriers upon plasmon excitation. Moreover, they also have appropriate surface sites that can adsorb reactant molecules and activate them. The photogenerated plasmonic hot charge carriers can get trapped at the defect sites and thereafter drive redox reactions. Compared with traditional metal–semiconductor hybrid plasmonic photocatalysts, Schottky-barrier-free plasmonic photocatalysts enable hot charge carriers to be transported nearly freely in the material, resulting in high charge utilization and photocatalytic efficiency.We have demonstrated the synthesis of Schottky-barrier-free plasmonic MoO3−x nanospheres (NSs) with remarkably high oxygen vacancy (OV) contents by aerosol-spray. The MoO3−x NSs can achieve efficient ammonia photosynthesis through a “killing two birds with one stone” mechanism. On the one hand, the OVs can serve as chemisorption sites for N2 molecules and participate in their activation. On the other hand, the introduction of OVs generates a large number of free electrons near the conduction band, which induces a broad absorption band from the visible to the NIR region owing to the plasmon resonance. The Schottky-barrier-free nature of this plasmonic semiconductor allows free transportation of the plasmonic hot charge carriers, while the defect states introduced by the OVs can effectively trap the hot electrons to prevent rapid electron–hole recombination. As expected, the as-prepared material exhibits a superior ammonia production rate, with the highest apparent quantum efficiency (AQE) of 1.24% at 808 nm and an appreciable solar-to-ammonia conversion efficiency (SACE) of 0.057% for NH3 production. Besides MoO3−x , WO3−x is also an excellent candidate for Schottky-barrier-free plasmonic photocatalysts. We have synthesized square WO3−x nanoplates hydrothermally. The WO3-x nanoplates possess regular morphology, wide light absorption, and great ammonia production performance. Furthermore, by introducing doping elements (Mo, V, Fe, Bi) into WO3−x nanoplates, the N2 activation and dissociation can be improved by refining the defect states. The Mo-doped WO3−x nanoplates exhibit the highest ammonia production rate of 145.50 μmol g−1 h−1 with SACE of 0.011% since the Mo species can promote the chemisorption and polarization of N2 molecules and significantly reduce the reaction barrier. Notably, Mo-doped WO3−x nanoplates are a dual-function photocatalyst that can oxidize water to hydrogen peroxide in a stoichiometric ratio while synthesizing ammonia. Figure 1

High Energy Density Asymmetric Tetrathiafulvalene Derivative as a Catholyte for Non-Aqueous Redox Flow Batteries

The inherent intermittency challenge associated with renewable energy sources prompts the rapid development of cost-effective, grid-scale energy storage technologies. Redox flow batteries (RFBs) represent a promising solution to this problem owing to their remarkable potential for scalability and the tunability offered by a wide range of available solution-based chemistries. However, to-date, RFB commercialization has been challenged by a lack of long-lived, energy-dense, and earth abundant charge storage materials. Many of these challenges can be addressed with the development of non-aqueous organic redox flow batteries (NAORFBs). Such batteries leverage the wide potential window (> 5.5 V) offered by organic solvents with the synthetic tunability of organic redox cores to create highly energy dense battery systems with electrolytes based on earth abundant materials (i.e., carbon, nitrogen, sulfur, oxygen, etc.). The energy density of NAORFBs can be optimized with strategies such as increasing the solubility of redoxmers, increasing the number of electrons transferred by redoxmers, and increasing the magnitude of the potential of employed redox materials [1]. Of these, solubility can be enhanced through the grafting of polar side groups to a redoxmer, while redox potential can be increased through the attachment of either electron-withdrawing or donating substituents, in the case of catholyte and anolytes, respectively, near or in conjugation with the redox core [2]. Recently, our group has demonstrated tetrathiafulvalene (TTF) as a robust, two-electron active catholyte material in NAORFBs [3]. Namely, TTF exhibits reversible oxidation events at 0.03 and 0.43 V vs. Ag/Ag+ (Figure 1A). Underivatized TTF, which is highly insoluble in many polar organic solvents, can be made miscible in MeCN, carbonates, and ethereal solvents, with the attachment of four PEG3 chains to the TTF core ((PEG3)2-TTF) (Figure 1B). When paired with a low potential Li metal anode, an RFB incorporating 0.5 M (PEG3)2-TTF (1.0 M e- concentration) in 1.0 M LiPF6-EC/EMC supporting electrolyte exhibits overall operating cell potentials of 3.44 and 3.64 V vs. Ag/Ag+. Here we describe our most recent efforts to develop a further optimized, rationally designed asymmetric TTF derivative – (PEG3/PerF)-TTF – incorporating both a perfluorophenyl ring fused directly to the TTF core and two PEG3 side chains (Figure 1B). The electron-withdrawing perfluorophenyl group functions to substantially raise the potential of both redox events to 0.43 V and 0.65 V vs. Ag/Ag+, while the two PEG3 chains allow the material to retain miscibility in polar solvents. The performance of (PEG3/PerF)-TTF has been successfully demonstrated in a battery at an even higher concentration of 0.75 M (1.5 M e- concentration) (Figure 1C). When also paired with a Li metal anode in 1.0 M LiPF6-EC/EMC supporting electrolyte, the battery exhibits exceptional operational energy density of 96 Wh/L at 6 mA/cm2 current density and capacity retention of 83.1% over 16.8 d of continuous operation (99.0% per d). These results further demonstrate TTF as a highly versatile catholyte with remarkable potential for application in NAORFBs.

Exploring the Kinetics of Oxygen Reduction Reaction in Relation to Pitting Corrosion Resistance in Fe-Cr Alloys

Pitting corrosion, a major concern in materials science and engineering, threatens critical metallic structures and components. Its implications reach across daily life and industries such as energy, transportation, and infrastructure, potentially causing environmental harm, economic losses, and even loss of life. This complex process is influenced by factors including material composition, local environment, and mechanical stresses.1 Once initiated, pit propagation rates are largely dependent on the magnitude of the supporting cathodic current available from the oxygen reduction reaction (ORR) occurring on the external passive film.2 In Fe-Cr alloys, the ORR occurs on this film, undergoing a mixed diffusion and kinetic-controlled process. The number of electrons involved and the corrosion rate are determined by the thermodynamically stable state of the passive film.This research studies the ORR kinetics on FeCr alloys fabricated by arc-melting, using both computational and experimental methods. The rotating disc electrode technique was employed across various Fe:Cr alloys in alkaline and neutral electrolytes. The Koutecky-Levich analysis showed a dominant four-electron ORR pathway in all tested Fe-Cr alloys, with the ORR significantly inhibited by higher proportions of Cr2O3 in the film, suggesting a correlation with high chromium content. Experimental ORR overpotentials, when combined with theoretical potential-pH (Pourbaix) diagrams, helped discern the likely characteristics of the passive films on the alloys. It was deduced that the catalytic properties of potential passive films increased in the order Cr2O3 < Fe3O4 < Fe2O3 < FeCr2O4. These findings, excellently aligned with density functional theory (DFT) modelling, underscore the role of increased chromium levels in slowing pitting progression by suppressing the ORR.In summary, this research offers distinctive insights into the correlation between the kinetics of the ORR and the resistance to localized corrosion in Fe-Cr alloys, which enhances our understanding of the underlying mechanisms of pitting corrosion. Keywords FeCr alloy, pitting corrosion, ORR, rotating disc electrode, DFT Reference [1] B. Zhang, J. Wang, B. Wu, X. W. Guo, Y. J. Wang, D. Chen, Y. C. Zhang, K. Du, E. E. Oguzie, and X. L. Ma, Nat. Commun. (2018) 9, 2559.[2] G. T. Burstein, P. C. Pistorius, and S. P. Mattin, Corros. Sci. (1993) 35, 57.

Interrogation of Anodic Stripping Voltammetry Peaks of Metals for the Determination of Electrochemical Reaction Parameters

The aim of this study was to develop a method for the analysis of peaks obtained during anodic stripping voltammetry (ASV) at silver-based mercury film electrodes (SBMFE) in the presence of transition and rare earth metals. Such stripping peaks may originate from reversible or irreversible electrochemical processes, with a plethora of unknown parameters, such as number of electrons involved, electrochemical rate constant, formal potential, charge transfer coefficient, and metal concentration (in the film and/or solution). In particular, we were interested in the concentration of transition metals and rare earth elements deposited simultaneously in the mercury film during ASV in order to quantify the electrochemical amalgamation of each species and their rates of deposition.Herein, we studied the concurrent ASV of multiple metals using a mercury film electrode as part of the development of the OREATE (Oxide Reduction by Electrochemical Amalgamation and Thermal Extraction) process. Certain of these species generate electrochemically irreversible processes, while others produce reversible ones. In addition, the reduction of most rare earth metals into the mercury film occurs well below the onset of the hydrogen evolution reaction, preventing us from probing these reduction processes. For example, the reduction of cerium(III) (an electrochemically irreversible process) occurs at a formal potential of −1.64 V vs. Ag/AgCl (3 M KCl). Furthermore, the presence of multiple metals in solution can lead to overlapping stripping peaks and mask these oxidative processes. For instance, the irreversible oxidative stripping of cerium (−0.75 V vs. Ag/AgCl (3 M KCl)) from the mercury film can obscure the reversible stripping of zinc (−0.95 V vs. Ag/AgCl (3 M KCl)).In this talk, we describe the use of thin layer electrochemistry equations to extract electrochemical parameters from the ASV at a mercury film electrode. This electroanalytical method enables investigation of processes that are otherwise obscured by the hydrogen evolution reaction, as well as resolution of overlapping stripping processes. This permits the determination of the concentration of each metal deposited in the film during the electrochemical amalgamation. By summing the thin layer electrochemical equations for reversible and irreversible processes, we were able to extract the number of electrons involved, the electrochemical rate constants, and the charge transfer coefficients for simultaneous oxidative processes. Finally, we were able to obtain the concentrations of multiple species in the mercury film and their rates of deposition.In conclusion, we have established a protocol for the interrogation of electrochemical reaction parameters in anodic stripping voltammetry of mixed-metal systems. Moreover, we demonstrated an electrochemical method to quantitatively separate overlapping peaks for the determination of the species’ concentrations, all based on the principles of thin layer behavior.

Development of a 3-Electrode Setup for the Operando Detection of Parasitic Side Reactions: Exemplified at the Quantification of Released Oxygen

The most considerable push to higher energy density Li-ion batteries (LiBs) has been achieved by incremental improvements of the positive electrode cathode active materials (CAM).1 One approach has been to increase the nickel content of layered transition metal oxide CAMs like lithium nickel cobalt aluminum oxide (NCA; LiNixCoyAlzO2, with x+y+z=1) to above 80%, which has already been achieved on a commercial level. While this increase is accommodated by a higher achievable discharge capacity at a given upper cut-off potential, it also reduces the structural stability of the material at high degrees of delithiation (i.e. at high state-of-charge (SOC)).2,3 The structural instability of the CAM is associated with a release of lattice oxygen at high SOC, starting at approximately 80% SOC.2,3 The release of reactive oxygen species is reported to cause a cascade of degradation mechanisms resulting in capacity fade. During this process, the near-surface region of layered transition metal oxide particles is converted into an electrochemically inactive rock-salt phase, which results in the formation of a resistive surface layer.4 Furthermore, the released oxygen can stimulate the chemical oxidation of the typically employed electrolyte solvents, such as ethylene carbonate (EC), resulting in the formation of CO, CO2, and H2O, which in turn hydrolyzes the electrolyte salt.2,5 Consequently, the detection and quantification of released oxygen for different CAMs and cycling conditions is of high interest. Gas quantification methods such as differential electrochemical mass spectrometry (DEMS) and on-line electrochemical mass spectrometry (OEMS) are powerful tools for the qualitative and quantitative measurement of gaseous species such as O2 and CO2.2,6 However, such methods require an expensive mass spectrometer setup and a sophisticated interface between the LiB cell hardware and the mass spectrometer.Thus, in this study, we will present a simplified method that can detect and quantify released oxygen. The method is based on a setup consisting of a dual working electrode (WE) configuration, namely a primary WE with an NCA CAM (LiNi0.80Co0.15Al0.05O2, from BASF TODA Battery Materials LLC, Japan) and an auxiliary WE with only carbon (Vulcan-type carbon, XC-72, Tanaka, Japan), both being coated with a ; a lithium iron phosphate (LFP) electrode coated on aluminum serves as counter electrode (CE). The latter is delithiated to a degree of 90% and capacitively oversized, allowing the NCA working electrode to be cycled against a constant potential (with the LFP potential being at ~3.43 V vs. Li+/Li).8 While charging the NCA working electrode within the desired potential window, the carbon electrode is polarized to a constant potential of 1.21 V vs. the LFP counter electrode corresponding to ~2.20 V vs. Li+/Li. Since oxygen is reduced at that potential, a reductive current is detected once lattice oxygen is being evolved.9 By the precise knowledge of the number of electrons involved in the reduction of oxygen at the carbon electrode, we are able to convert the reductive current into an amount of released oxygen (e.g., in units of moles of oxygen per gram of cathode active material).We apply the developed cell setup to study the oxygen release characteristics of the NCA when being charged to 5.0 V vs. Li+/Li at 0.1 C and 25 °C, and compare these data to the gassing profile analyzed via OEMS. As will be shown, there is a good agreement between integrated and converted reductive current and the amount of detected O2 in the OEMS.

Rotating Disk Electrode Studies of Benzaldehyde Oxidation on Group Ib Metals

Water electrolysis is a green means of producing hydrogen gas to be used as a fuel or reactant in key industrial processes such as ammonia production. The conventional system of oxygen evolution (OER) and hydrogen evolution (HER) suffers from slow kinetics at the anode and a high cell voltage limited by thermodynamics. One solution is to replace OER with another reaction such as an organic oxidation reaction that has a lower equilibrium potential and produces a valuable organic byproduct at the anode. Recent work has demonstrated that biomass-derived aldehydes such as furfural and 5-hydroxymethylfurfural can be selectively oxidized to their corresponding carboxylates and H2 on Cu-based anodes at low potentials (~0.1 VRHE) in alkaline media. In alkaline media, a hydroxide ion adds to the carbonyl carbon of an aldehyde molecule forming a gem diolate in solution phase. It is argued that dehydrogenation becomes more facile due to the weaker C-H bond of the gem diolate compared to the aldehyde form of the molecule. This may enable oxidation without the need for coadsorbed-OH. Additionally, aldehyde oxidation is only active on Au, Ag, and Cu electrodes at higher pHs.The aim of this work is to identify the conditions under which low potential oxidation of aldehydes and high anodic Faradaic efficiency to H2 occurs, namely, electrode material and applied potential. To avoid polymerization side reactions of furans in alkaline media, we studied benzaldehyde as a model compound which has also been shown to exhibit low potential oxidation and anodic H2. The activity (rate of aldehyde consumption) and selectivity (to anodic H2 versus H2O) were compared for the group Ib metals (Au, Ag, Cu), each of which demonstrates a relatively early onset potential (<0.4 VRHE) and generates anodic H2 at certain potentials. Rotating disk electrode studies with Koutecky-Levich analysis were conducted to separate mass transfer effects from kinetic current to compare the intrinsic activity of each electrode. Additionally, the average number electrons transferred per aldehyde molecule consumed was estimated from Koutecky-Levich analysis; the one-electron pathway combines the aldehyde hydrogens to H2 while the two-electron pathway requires an additional electron per aldehyde molecule to oxidize the hydrogen from the surface to form H2O. Rotating ring disk electrode studies were used to further validate the anodic H2 generation as a Pt ring was still able to oxidize H2 despite the presence of benzaldehyde. This was used as an additional means of estimating the selectivity to H2 as a function of potential.CVs for benzaldehyde oxidation on each metal are shown in Figure a. Peak current followed the order of Au > Ag >> Cu. Au reached a mass transfer limiting current, and Ag also showed an RPM dependence but did not reach full mass transfer limitations. Cu was the least active and did not show any mass transfer dependence. On the other hand, Cu has the earliest onset potential followed by Ag then Au. The average number of electrons transferred per aldehyde molecule according to RRDE measurements is shown in Figure b, where one electron represents H2 and two electrons represents H-oxidation to H2O. Cu had 100% selectivity to H2 over its entire potential window of activity (up to 0.45 VRHE). Au and Ag have high selectivity to H2 at low potentials but decreases to near zero H2 production in the range of 0.6-0.8 VRHE; the decrease in selectivity to H2 on Ag occurs slightly earlier than Au (~0.1 V). H2 selectivity is related to the inability of each metal to oxidize H to H2O at low potentials. Figure 1

Quantum Chemistry Based Battery Electrochemistry: The Effect of Entropy and Anode Surface Structure

Lithium-sulfur (Li-S) battery is a promising battery technology, thanks to their high energy density and the use of inexpensive materials. A Li-S battery typically consists of a Li anode, a sulfur cathode or sulfur-based catholyte, and an organic solvent for lithium polysulfides (Li2S x ). Upon discharge, Li2S x chains accept Li and undergo successive chain shortening events, with the final discharge product being Li2S. Li2S is however insoluble in typical organic solvents and its irreversible precipitation leads to the impairment of Li-S batteries. The addition of phosphorus pentasulfide (P2S5) to a Li2S x catholyte has been experimentally and theoretically shown to form complexes with sulfur chains, which can accommodate Li2S, thus overcome the problem of Li2S precipitation and improving battery cyclability. [1]Quantum chemistry and specifically density functional theory (DFT) calculations have been used to predict molecular structures and electrochemical potentials for Li-S batteries, as well as other electrochemical systems. Here we present a series of DFT calculations (uB3LYP/6-31+G(2df,p)) using the P2S5-Li2S8 system as a case study to highlight considerations critical to reliable electrochemical predictions. Here, we focus on entropy, atomic structure of metal anode surface sites, and the level of DFT theory.The level of theory used throughout this study (uB3LYP/6-31+G(2df,p)) was chosen after careful comparison with other levels of theory, with varying methods and functionals (HF, B3LYP, M06, M11) and basis sets (3-21G, 6-31G(d), 6-31+G(2df,p), 6-311G(d), 6-311+G(2df,p), cc-pVTZ). The B3LYP functional with the 6-31+G(2df,p) or cc-pVTZ basis set performed best in predicting electrochemical potentials in agreement with the cyclic voltammetry experiments, as well as the nuclear magnetic resonance spectra. In addition, different solvents, all with similar dielectric constants, were considered and the resulting impact on E 0 was found to be negligible.The standard electrochemical potential for a full-cell reaction (E 0) is directly related to the Gibbs free energy of the reaction (ΔG 0): ΔG 0 = –nFE 0, where n is the number of electrons transferred and F is the Faraday constant. Gibbs free energy comprises an electronic energy (E elec), a temperature dependent sensible enthalpy (H sens) and a temperature dependent entropy term (–TS). Often, the sensible enthalpy and entropy terms are neglected and reaction Gibbs free energy is approximated as the difference of electronic energy between products and reactants. Our results for reactions involving lithium polysulfide chains and sulfur chains anchored on phosphorus groups indicate that, even at room temperature, the entropy term has a significant contribution to E 0 (of 0.2-0.3 V). Importantly, without considering this contribution, theoretically predicted electrochemical potentials do not match experimental results from cyclic voltammetry.Additionally, atomic structures of different surface sites impact the evaluation of E 0. Several surface sites, as shown in Fig. 1a, were simulated for the atom to be reacted (shown transparent in Fig. 1a), while keeping the rest of the atoms stationary. The Gibbs free energy of reaction was calculated for each site and its effect on E 0 was compared with that of the standard thermodynamic result for bulk Li(s), as shown in Fig. 1b. We found that as pexted, Li atoms in the ‘lone’ or ‘pair’ configuration react more readily. In the case of the ‘lone’ Li, E 0 increases by 0.35 V.In summary, DFT was used to identify the complexation and reaction mechanisms governing P2S5-Li2S8 catholyte batteries. In the calculation of electrochemical potentials for this system, we identified that special care should be taken to the temperature dependence of Gibbs free energy of reactions, the variation of local surface sites for the metal anode, and the level of DFT theory used. These considerations will aid the understanding of Li-S and other battery chemistry.[1] Wang, P., Kateris, N., Li, B., Zhang, Y., Luo, J., Wang, C., Zhang, Y., Jayaraman, A.S., Hu, X., Wang, H. and Li, W., 2023. High-Performance Lithium–Sulfur Batteries via Molecular Complexation. Journal of the American Chemical Society, 145 (2023) 18865–18876. Figure 1

Spatiotemporal measurement of electron number density in high density laser-induced plasmas using laser absorption

Laser absorption measurements were conducted on a high-density, laser-induced plasma produced in atmospheric-pressure air to investigate the spatiotemporal evolution of its electron number density. Measurements taken both along and perpendicular to the plasma’s symmetric axis showed that, upon formation, the plasma propagates in the direction opposite to the laser beam used for plasma generation, while expanding rapidly radially. The spatiotemporal evolution of the electron density was further analyzed from the measurements taken perpendicular to the plasma’s symmetric axis through tomographic reconstruction. Notably, the reconstruction was achieved using a genetic algorithm, as a probe laser beam used for absorption measurement is non-negligible in size compared to the plasma. Importantly, our measurements could reveal that the electron density reaches 4.99 × 1019 cm−3 immediately after the plasma formation at the center; moreover, there is a development of a pressure wave with high electron density, propagating outward radially due to the rapid expansion of the produced plasma.