Cathode Region Research Articles

Corrosion mechanism of eutectic high-entropy alloy induced by micro-galvanic corrosion in sulfuric acid solution

The corrosion behavior of AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) in aerated 0.5 M H2SO4 solution was investigated. The initial and long-term corrosion of EHEA were respectively controlled by the micro-galvanic corrosion cells established between Cr-rich FCC (cathode) and Al-rich/Cr-depleted BCC (anode) phases and between the lamellar (anode) and irregular (cathode) regions. Correspondingly, the main corrosion type of EHEA transformed from the preferential dissolution of BCC phase to the predominant localized corrosion of the whole lamellar region. EHEA exhibited electrochemical passivation property comparable to 304 L stainless steel and superior corrosion resistance relative to most Al-containing dual-phase HEAs.

Characterization of Corrosion Behavior of TA2 Titanium Alloy Welded Joints in Seawater Environment.

Titanium alloy has been widely used in Marine pipeline system because of its excellent corrosion resistance. However, there are differences in microstructure and electrochemical properties because of the heterogeneous structure of the welded joint, the corrosion behavior is often different. In this paper, the corrosion behavior of TA2 titanium alloy welded joint in seawater at different temperatures was studied by traditional macro electrochemical test analysis combined with microelectrode array test and surface morphology analysis. Conventional macroscopic electrochemical analysis results show that the corrosion resistance of heat-affected zone is always the best, followed by the base metal and the weld. And the higher the temperature, the easier the formation of passivation film. The results of microelectrode array test show that the heat-affected zone is always the cathode region of the whole welded joint, and part of the cathode near the base metal region has the largest current density, which acts as the main cathode to slow down corrosion. At slightly higher temperatures, the polarity deflection will occur in the base metal zone and weld zone due to the different formation speeds of passivation film in early corrosion stage. With the prolongation of corrosion time, the base metal eventually becomes the cathode zone and the weld zone eventually becomes the anode zone.

Flexible battery-less wireless glucose monitoring system

In this work, a low power microcontroller-based near field communication (NFC) interfaced with a flexible abiotic glucose hybrid fuel cell is designed to function as a battery-less glucose sensor. The abiotic glucose fuel cell is fabricated by depositing colloidal platinum (co–Pt) on the anodic region and silver oxide nanoparticles-multiwalled carbon nanotubes (Ag2O-MWCNTs) composite on the cathodic region. The electrochemical behavior is characterized using cyclic voltammetry and chronoamperometry. This glucose hybrid fuel cell generated an open circuit voltage of 0.46 V, short circuit current density of 0.444 mA/cm2, and maximum power density of 0.062 mW/cm2 at 0.26 V in the presence of 7 mM physiologic glucose. Upon device integration of the abiotic glucose hybrid fuel cell with the NFC module, the data from the glucose monitoring system is successfully transmitted to an android application for visualization at the user interface. The cell voltage correlated (r2 = 0.989) with glucose concentration (up to 19 mM) with a sensitivity of 13.9 mV/mM•cm2.

Strategies for Approaching One Hundred Percent Dense Lithium-Ion Battery Cathodes

Creating thick electrodes with low porosity can dramatically increase the available energy in a single cell and decrease the number of electrode stacks needed in a full battery, which results in higher energy, lower cost, and easier to manufacture batteries. However, existing electrode architectures cannot simultaneously achieve thick electrodes with high active material volume fractions and good power. These particle-based architectures rely on electrolyte transport within the pores of the cathode to fully lithiate active material particles during discharge. As cathode solid volume fractions approach 100%, batteries experience electrolyte depletion which leads to inaccessible cathode reaction sites (see Fig. 1A). The additional theoretical capacity that comes from increased cathode density, therefore, is impractical if that energy cannot be fully extracted.We combine experiments and simulations of high density and high thickness cathodes to understand the transport and performance trade-offs of LIBs as the cathode solid volume fraction approaches 100%, which we use to reveal the cathode properties needed to achieve high performance at high relative density and thickness. We use one- and two-dimensional simulations to compare the discharge performance of two cathode architectures, a traditional particle-based architecture and a continuous cathode architecture created via electrodeposition. In addition, a model with spaced diffusion-barriers explores the design space between these two architectures and elucidates the influence of increasing solid-diffusion length on discharge performance. We show that there is a large opportunity space for improved energy density at high relative densities by using new electrode manufacturing techniques to create continuous diffusion pathways and high diffusivities. Increasing the solid diffusion length from 4.78 µm to 55 µm in cathodes with high diffusivity leads to an increase in areal capacity (from 1.6 mAh/cm2 to 4.8 mAh/cm2) for a 110 µm thick, 95% dense LCO cathode discharged at a 1C rate.We also apply concepts and designs from these models to simulate the discharge performance of thick, high-density lithium-ion batteries with solid electrolytes to motivate even higher energy battery architectures. When discharged at a 1C rate, solid-state batteries with traditional particle-based composite cathodes (110 µm thick) cannot extract any energy at volume fractions above 94%, while batteries with high-diffusivity continuous cathodes and no solid electrolyte in the cathode region can achieve 3.8 mAh/cm2 at 95% solid volume fraction. These new cathode architectures which contain no electrolyte in the cathode region can significantly improve the gravimetric energy density of solid-state lithium-ion batteries.This work uses a comparative analysis of cathode architectures to explore the interdependent impact of solid volume fraction, solid-diffusivity, cathode thickness, and discharge rate on lithium-ion battery areal capacity. We should how a combination of high diffusivity and continuous solid-state diffusion pathways provides an exciting path for realizing ultra-dense and thick cathodes with high energy density. Figure 1

(Digital Presentation) A Mathematical Model for Localized Corrosion of Copper Under a Droplet

The Nuclear Waste Management Organization (NWMO) is responsible for the implementation of Adaptive Phased Management (APM), the federally-approved plan for the safe long-term management of Canada’s used nuclear fuel.1 Under APM, used nuclear fuel will ultimately be placed within a deep geological repository (DGR) in a suitable host rock formation. Part of evaluating the long-term performance and safety of the repository system is understanding the behavior of the copper coated container with respect to localized corrosion. Even though localized corrosion is not expected in the DGR design system, there is still a need to develop a mathematical model for localized corrosion of copper.The presentation will describe the development of a 2-D axisymmetric time-dependent model for the localized corrosion of copper under a drop of electrolyte using the concept of an Evans droplet.2 The model accounts for two reversible electrochemical reactions on the metal surface (copper dissolution/plating and hydrogen (H2) evolution/reduction) and two irreversible electrochemical reactions (cupric ion (Cu2+) reduction and oxygen (O2) reduction). Dissolved cuprous ion (Cu+) reacts in a second chemical step to form the cuprous chloride (CuCl) salt film treated as a diffusion barrier, or it reacts to form the cuprous oxide (Cu2O) film that partially blocks the active area on the metal surface. The model also accounts for a series of homogeneous reactions involving copper chloride complex, copper hydroxide complex, copper carbonate complex, and superoxide species. The associated equilibrium constants were obtained from PHREEQC thermodynamic software.3 The model includes a total of 23 dependent spatial-temporal variables.The mathematical model is developed using the finite-element method (COMSOL Multiphysics). The model includes coupled nonlinear conservation equations for ionic species, which include the contribution of diffusion, migration, local electroneutrality, and homogeneous reactions. The anodic and cathodic regions are not predefined but are rather determined by values of local concentration and potential from the simulation results. The surface coverage of film was calculated implicitly and expressed in terms of the thickness in units of monolayers. The model also accounted for the effect of porous CuCl film thickness on the surface oxygen concentration and potential applied on electrochemical reactions.In this preliminary study, two extreme conditions were chosen such that the droplet boundary could either have an infinite supply of oxygen or it could have no external supply of oxygen for an initially air-saturated droplet. The results show a 3-year time-dependent radial distribution of anodic and cathodic current density, surface coverage of CuCl film and Cu2O film, and localized corrosion rates and depths. The results include a distribution of pH, potential, and concentrations of dissolved gaseous and ionic species through the entire droplet. The potential change as the system transitions from aerobic to anaerobic conditions matches the expected equilibrium potential difference.4 The model could be used to explore the influence of different parameters on the localized corrosion rate and depth, film thickness and growth, and each individual current profiles. The parameters may be adjusted to conform to the DGR environment.References NWMO, “Choosing a Way Forward. The Future Management of Canada’s Used Nuclear Fuel. Final Study,” Nuclear Waste Management Organization, Toronto, Ontario, 2005.R. Evans, The Corrosion of Metals, E. Arnold & Company, London, 1926.PHREEQC Version 3, United States Geological Survey, 202, https://www.usgs.gov/software/phreeqc-version-3Cleveland, M. E. Orazem, and S. Moghaddam, “Response to “Comment on “Nanometer-scale corrosion of copper in de-aerated deionized water” [J. Electrochem. Soc., 161, C107 (2014)],” Journal of the Electrochemical Society, 163 (2016), Y5-Y11. AcknowledgementThis work was supported by the Nuclear Waste Management Organization, Canada, under project 2000904.

The synergistic adsorption-electrocatalysis research of Mn2P interlayer for durable large-capacity and high-energy-efficiency Li-S batteries

The commercialization of Li-S batteries (LSBs) as next-generation high-energy–density energy storage devices is hindered by the remarkable shuttle effect of soluble lithium polysulfides (LiPSs). In this study, Mn2P-based materials (Mn2P@C) were investigated as an interlayer between S-contained cathode and separator to confine S species in the cathode region. Specifically, the porous structure of amorphous carbon layer has a physical adsorption effect on LiPSs, while Mn2P not only exhibits a strong chemical bonding force with LiPSs but also helps enhance the solid–liquid phase conversion and Li2S nucleation growth kinetics. Benefiting from the desirable modulation of Mn2P@C, the LSBs have good cycling stability (0.04% capacity decay per cycle), favorable rate capability (659.7 mAh g−1 at 5C), and high energy efficiency (81.4% at 5C). The LSBs still show a specific capacity of 490 mAh g−1 even with a high S loading (8.6 mg cm−2) and lean electrolyte (E/S = 6.2 μL mg−1). Furthermore, the LSBs with Mn2P@C exhibited high resistance to self-discharge. This study shows Mn2P@C’s great potential in the field of LSBs with high energy density and efficiency and provides some insights into commercial design and other relevant fields.

Electrowinning of gold from a dilute solution using hydrocyclone-type cell

ABSTRACT The redox reaction mechanism of gold−cyanide [Au(CN)2 −] during hydrocyclone electrowinning was investigated in this work by conducting Hull cell test, potentiodynamic polarization, and computational fluid dynamics (CFD) simulations. A leaching solution of waste printed circuit boards (WPCBs) was prepared as an electrolyte, and the effects of flow rate and applied voltage on the recovery of gold and destruction of cyanide through hydrocyclone electrowinning were investigated. A numerical simulation of the flow field in the cell was performed, and the results were visualized by conducting a finite element analysis in FLUENT. The CFD simulations and Hull cell test showed that the cylindrical cathode region had a flow velocity of ~11.05 m·s−1, which was higher than that at the center of the cylindrical part (<6.45 m·s−1). The optimum conditions for electrowinning were found to be as: an electrode distance of 4.9 mm and a current density of 73.78 mA·cm−2. The anodic polarization results showed that an Ir-based mixed metal oxide (MMO) anode could more efficiently oxidize the free cyanide because of its high current density than other types of anodes (Ir-based MMO: 299.3 mA·cm−2 > SS304: 3.5 mA·cm−2 > Pt-coated Ti: 1.3 mA·cm−2). Through the demonstrated hydrocyclone electrowinning test, the gold concentration could be decreased from 100 to 0.24 mg·L−1 within 12 h while destroying almost total amount of free cyanide in a day.

A novel fire safety separator decorated by Co2P/Co/C multifunctional layer for Li-S batteries

Lithium-Sulfur (Li-S) battery is a potential alternative energy storage system owing to its high theoretical capacity, low cost, and eco-friendly features. However, the commercialization of Li-S battery has been hindered by the notorious “shuttle effect”. To overcome the above-mentioned long-standing problem, herein, an advanced separator modified by N and P heteroatoms co-doped carbon frameworks with confined Co2P nanoparticles (named Co2P/Co/C) has been successfully prepared. The introduction of functional coating can obviously enhance the thermal stability of separator. To be specific, it showed higher initial decomposition temperature (475 ℃) and lower maximum mass loss rate (1.755%℃−1) values than the Celgard separator (400 ℃ and 2.915%℃−1, respectively). Notably, when kindled separators directly, the modified separator can quench by itself with many residual remains. In addition, the engineered functional layer possesses the capability of capturing lithium polysulfides (LiPSs), and then confines them within the cathode region so that the “shuttle effect” can be restrained effectively. After assembling the modified separator in the Li-S cell, compared with the cell with Celgard separator of low initial specific discharge capacity (730 mAh g−1), the cell with Co2P/Co/C separator delivered a superior initial discharge capacity of 1310 mAh g−1 at 0.5 C. Also, the modified cell can perform remarkably enhanced rate performances. In addition, As a consequence of these merits, the modified separator with improved thermal stability, preferable fire safety, and satisfied electrochemical performances shows significant guiding value for advancing the practical application of Li-S batteries.

Proton-Coupled Electron Transfer in a Ruthenium(II) Bipyrimidine Complex in Its Ground and Excited Electronic States.

Proton-coupled electron transfer (PCET) was studied for the ground and excited electronic states of a [Ru(terpy)(bpm)(OH2)(PF6)2] complex, Ru-bpm. Cyclic voltammetry measurements show that the Ru(II)-aqua moiety undergoes PCET to form a Ru(IV)-oxo moiety in the anodic region, while the bpm ligand undergoes PCET to form bpmH2 in the cathodic region. The photophysical behavior of Ru-bpm was studied using steady-state and femtosecond transient UV-vis absorption spectroscopy, coupled with density functional theory (DFT) calculations. The lowest-lying excited state of Ru-bpm is described as a (Ru → bpm) metal-to-ligand charge-transfer (MLCT) state, while the metal-centered (MC) excited state was found computationally to be close in energy to the lowest-energy bright MLCT state (MC state was 0.16 eV above the MLCT state). The excited-state kinetics of Ru-bpm were found via transient absorption spectroscopy to be short-lived and were fit well to a biexponential function with lifetimes τ1 = 4 ps and τ2 = 65 ps in aqueous solution. Kinetic isotope effects of 1.75 (τ1) and 1.61 (τ2) were observed for both decay components, indicating that the solvent plays an important role in the excited-state dynamics of Ru-bpm. Based on the pH-dependent studies and the results from prior studies of similar Ru-complexes, we hypothesize that the 3MLCT state forms an excited-state hydrogen-bond adduct with the solvent molecules and that this process occurs with a 4 ps lifetime. The formation of such a hydrogen-bond complex is consistent with the electronic density accumulation at the peripheral N atoms of the bpm moiety in the 3MLCT state. The hydrogen-bonded state 3MLCT decays to the ground state with a 65 ps lifetime. Such a short lifetime is likely associated with the efficient vibrational energy transfer from the 3MLCT state to the solvent.

Ambipolar, multichromic metallopolymers of poly(3,4-ethylenedioxythiophene)

In this study, two novel bipyridine-based Ru(II) complexes (E1-Ru and E2-Ru) which contain different number of 3,4-ethylenedioxythiophene (EDOT) groups were synthesized and subjected to electrochemical polymerization both in absence and presence comonomer (EDOT). The resultant metallopolymers were examined in terms of their electrochemical and electrochromic properties. Cyclic voltammetry and spectroelectrochemistry studies revealed the ambipolar and multichromic nature of all the polymers where the reversible redox activity in the cathodic region was found to be mainly due to ligand centered reduction of the complex (Ru2+/1+ and Ru1+/0) and metal centered oxidation (Ru2+/3+) was found to be available along with redox activity of the conjugated backbone of the polymers in the anodic region. Contrary to pristine PEDOT all polymers displayed vibrantly multichromic behavior thanks to superimposed but independently functioning electrochromic/redox nature of the conjugated polymer backbone and the Ru complex. In general, increasing the number of polymerizable units in the monomer structure increased the quality of the films and brought color diversity to these metallopolymers. Copolymerization, on the other hand, not only contributed positively to the band gap and switching time but also widened the color pallet of these polymers which became even more remarkable upon changing the comonomer feed ratio.

Co-localizing Kelvin Probe Force Microscopy with Other Microscopies and Spectroscopies: Selected Applications in Corrosion Characterization of Alloys.

Kelvin probe force microscopy (KPFM), sometimes referred to as surface potential microscopy, is the nanoscale version of the venerable scanning Kelvin probe, both of which measure the Volta potential difference (VPD) between an oscillating probe tip and a sample surface by applying a nulling voltage equal in magnitude but opposite in sign to the tip-sample potential difference. By scanning a conductive KPFM probe over a sample surface, nanoscale variations in surface topography and potential can be mapped, identifying likely anodic and cathodic regions, as well as quantifying the inherent material driving force for galvanic corrosion. Subsequent co-localization of KPFM Volta potential maps with advanced scanning electron microscopy (SEM) techniques, including back scattered electron (BSE) images, energy dispersive spectroscopy (EDS) elemental composition maps, and electron backscattered diffraction (EBSD) inverse pole figures can provide further insight into structure-property-performance relationships. Here, the results of several studies co-localizing KPFM with SEM on a wide variety of alloys of technological interest are presented, demonstrating the utility of combining these techniques at the nanoscale to elucidate corrosion initiation and propagation. Important points to consider and potential pitfalls to avoid in such investigations are also highlighted: in particular, probe calibration and the potential confounding effects on the measured VPDs of the testing environment and sample surface, including ambient humidity (i.e., adsorbed water), surface reactions/oxidation, and polishing debris or other contaminants. Additionally, an example is provided of co-localizing a third technique, scanning confocal Raman microscopy, to demonstrate the general applicability and utility of the co-localization method to provide further structural insight beyond that afforded by electron microscopy-based techniques.

The Tribocorrosion Behaviour of Ti-6Al-4 V Alloy: The Role of Both Normal Force and Electrochemical Potential

The tribocorrosion behaviour of Ti-6Al-4 V exposed to phosphate buffered saline was investigated under a range of normal forces in both cathodic and anodic regions to provide a basis for properly deriving the tribological constants of this alloy. To achieve this, a new customised tribotester was designed and manufactured to rub the Ti-6Al-4 V disks against zirconia balls. The tests were conducted at a sliding frequency of 1 Hz and a sliding distance of 4.8 mm under various normal forces and potentials as 17.5, 10.8, 6, 3.5 N, and − 1.2, − 0.6, 0, 0.4, 0.8 V/VAg/AgCl, respectively. The damaged surfaces were characterised by scanning electron microscopy and energy-dispersive X-ray spectroscopy, profilometer, and micro-hardness tester. The post analyses confirmed the appearance of some minor cracks together with third-body wear particles. No significant changes in the hardness were detected after the tribocorrosion tests. The results of profilometry and electrochemical current indicated that in the anodic region the chemical losses accounted for a significant proportion (up to 36%) of the total loss. The proportional chemical loss increased with the potential; however, neither direct nor reverse relationship was found with the normal force. Overall, in the anodic domain, the material loss increased with the potential level due to the formation of oxide layer which may induce more shear cutting. In the cathodic domain, hydrogen embrittlement changed the properties of the interface and thus, the amount of material loss. Both the mechanical and chemical wear were described by an existing tribocorrosion theory; thereby, the theory was equipped with its tribocorrosive constants for future analyses on the tribocorrosion of this alloy extensively used in various applications including biomedical implants.

Fabrication of superhydrophobic stainless-steel mesh for oil-water separation by jet electrodeposition

A method for fabricating superhydrophobic stainless-steel meshes based on magnetic field-assisted jet electrodeposition is proposed. Ferromagnetic nickel particles (Nip) were added to the electroplating solution to prepare Ni/Nip coatings with mountain-like rough structure on stainless-steel meshes, followed by application of a parallel magnetic field in the cathode region. Magnetic fields play an indispensable role in the preparation of coatings. Exposure to air for 6 days resulted in a spontaneous switch of the coating from superhydrophilicity to superhydrophobicity and exhibited superoleophilicity. X-ray photoelectron spectroscopy revealed that this transition in wettability was related to spontaneous adsorption of hydrocarbons in the air induced by the coating. Based on the superhydrophobicity and superoleophilicity of the as-prepared Ni/Nip-coated meshes, high-efficiency, high-throughput, and high-purity separation of oil-water mixtures was achieved with a 300-mesh mesh. Furthermore, the as-prepared meshes continue to exhibit a separation efficiency greater than 97.0% and stable reusability even after 50 repeated separations.

Cyclic voltammogram analysis of the 3,3´- (1,4-phenylene) perchlorates

As a consequence of a three-stage synthesis from terephthalic aldehyde, a series of 3,3 '- (1,4-phenylene) perchlorates including methyl, hydrogen, acetyl, bromio, methoxy and nitro groups (R = Br, H, Me). The matching formazans were reacted with formalin in dioxane in the presence of perchloric acid to produce tetrazin ium salts. Formazans were synthesized by reacting terephthalic aldehyde phenylhydrazone with ar ene diazonium tosylates in a DMF/pyridine combination. The use of ar ene diazonium tosylates greatly simplified the separation and purification of formazans. The p henylhydrazone was produced in aqueous dioxane using the usual approach from terephthalic aldehyde and phenylhydrazine/hydrochloric acid. Individual f ormazans and tetrazinium perchlorates were isolated and characterized by elemental analysis, IR, NMR, UV spectroscopy. The electrochemical reduction of tetrazinium perchlorates was investigated using cyclic voltammetry (CV). Thus, all salts in the cathode region have two one-electron reduction peaks, which are connected to the sequential production of a radical cation and a biradical. It was discovered that donor substituents (R: OMe, Me) in the aromatic ring at position 1 accelerate tetrazinium cation reduction, whereas acceptor substituents (R: NO2, COMe,) inhibit this process. On this premise, it was proposed that in the presence of donor substituents in the aromatic ring at position 1, the matching bis-verdazyl radicals should be easily generated. As a result, 3,3'- (1,4-phenylene) perchlorates are possible antecedents of symmetric biradical systems based on verdazyl radicals.

Effect of dispersion particles and precipitates on the corrosion properties of ODS-Cu, Cu-Cr-Zr and Cu-Cr alloys in Na2SO4 solutions

• Corrosion resistance of Cu alloys in a 0.1 M Na 2 SO 4 solution was evaluated. • In ODS-Cu, oxide particles degraded protective performance of the passivation film. • Precipitation hardened Cu alloys showed good corrosion resistance. • Cu-Cr-Zr alloy showed corrosion due to the coarse columnar Cr precipitates. Precipitation-hardened Cu-Cr-Zr alloy is proposed as a heat sink material for various components of the ITER (blanket first wall, divertor, electrical straps and others) owing to its high strength, high conductivity and superior resistance against neutron irradiation. ODS-Cu (Oxide Dispersion Strengthened Copper) is also selected as a candidate material. Corrosion properties of alumina-dispersed copper alloys (GlidCop® CuAl15, CuAl25), aevaluated by electrochemical methods in 0.1 M and 0.01 M sodium sulfate (Na 2 SO 4 ) solutions. In open circuit potential (OCP) measurement in 0.1 M Na 2 SO 4 solution, the potential of all alloys decreased immediately after immersion and then gradually decreased. CuAl15 showed good corrosion resistance in the OCP measurement with little potential drop. In the polarization curve measurements, a difference was observed for each material in the cathode region. The corrosion current densities tended to be higher for CuAl25 and Cu-Cr-Zr, and the corrosion potential was also low in both solutions. In these alloys, the surface observation after the polarization curve measurements showed variations in the thickness of the Cu 2 O passivation film, and there were large areas where the film was thought to be thin. In Cu-Cr-Zr, coarse columnar Cr precipitates and segregation of Zr at the precipitate/matrix interface are thought to deteriorate corrosion resistance. In the case of CuAl25, it is suggested that dissolution of the passivation film is enhanced due to large volume fraction of alumina particles.

Excavating Anomalous Capacity Increase of Li-S Pouch Cells by Electrochemical Oscillation Formation.

The insufficient activation of a S/C cathode makes insufficient utilization of S in Li-S pouch cells, while the deep activation of a S/C cathode in a formation process is time-consuming and produces lithium polysulfides, which corrode a Li anode. Both situations lead to a low actual capacity of the Li-S pouch cells with a high S loading but are ignored for coin cells. In this work, electrochemical oscillation (EOS) formation employing hundreds of shallow discharge/charge cycles with high frequency was used to replace the resting and/or one deep discharge/charge cycle of traditional (TD) formation protocols. By controlling the discharge/charge capacity separately, symmetric oscillation (SOS) and asymmetric oscillation (ASOS) protocols were performed to facilitate the infiltration of electrolyte into the S cathode and restrict the formed lithium polysulfide in the cathode region. For SOS formation, the batteries were discharged/charged above 2.4 V with the same (symmetric) capacity with 2.78 × 10-3 Hz of oscillation frequency (∼1.4 mAh/g for SOS-500), in which the polysulfide dissolution was suppressed effectively. For ASOS formation, 100% discharge capacity (also ∼1.4 mAh/g for ASOS-500) and 92% charge capacity are set in each oscillation period, which leads to better activation effect but more shuttling polysulfides than SOS. Compared with SOS protocol, for ASOS protocol, more oxidative S (instead of polysulfides) inside original nonactivated cathode will be preferentially reduced in the next discharging process, but all the accumulated polysulfides during discharge of activation are oxidized into elemental S in the final charging process. These efficient formation protocols increase the practical capacity by up to 160% after 50 cycles without any change in pouch cell assembly.

Dynamic and localized microelectrochemical approaches to evaluate the corrosion resistance of newly developed lean duplex stainless steel alloys

AbstractA combination of scanning microelectrochemical techniques along with the conventional electrochemical approaches is explored to attain insight information on the localized corrosion on the newly developed lean duplex stainless steel (LDSS) alloys. The obtained results from dynamic electrochemical impedance spectroscopic (DEIS) tests explained the beneficial role of different alloying elements on the passive and transpassive regions of the investigated LDSS alloys in a 3.5% NaCl solution. The scanning vibrating electrode technique (SVET) was effective in examining the anodic and cathodic regions on the corroding LDSS, whereas the scanning electrochemical microscopy (SECM) technique was employed to explore the localized corrosion sites on LDSS in NaCl solution. The acquired SVET results revealed a reduction in the susceptibility of the newly developed alloys to localized corrosion concerning their composition, accounting for the enhanced corrosion resistance. The obtained result from conventional and scanning microelectrochemical techniques obviously revealed the LDSS alloy with the composition of Fe–16Cr–2Ni–2Mn–1Mo exhibited higher localized corrosion resistance in NaCl solution.

New copper(II) μ-alkoxo-μ-carboxylato double-bridged complexes as models for the active site of catechol oxidase: synthesis, spectral characterization and DFT calculations

A series of four copper(II) μ-Alkoxo-μ-carboxylato double bridged complexes, [{Cu2(L)}2][(μ–O2C–CO2] 1, [{Cu2(L)}2(μ–O2C–(CH2)CO2] 2, [{Cu2(L)}2(μ–O2C–CH2–CO2] 3 and [{Cu2(L)}2(μ–O2C–C6H4–CO2] 4 (H3L = 4-bromo-2-((E)-((3-(((E)-5-chloro-2-hydroxybenzylidene) amino)-2-hydroxypropyl) imino) methyl)-6-methoxyphenol and μ-dicarboxylate ions = oxalate, malonate, succinate and terephthalate) have been synthesized and characterized using several physicochemical techniques. The tridentate nature of H3L is interpreted from IR spectra. The Epr spectra of these complexes are characteristic of the quintet state (S = 2) in central features and the triplet state (S = 1) of these tetranuclear complexes. The electrochemical potential of these complexes was investigated using CV (cyclic voltammetry) and DPV (differential pulse voltammetry). All complexes showed quasi reversible reduction peaks in the cathodic region. To explore the stability of these complexes, quantum chemical parameters like electronegativity, ionization potential, electron affinity, global hardness and softness, and electrophilicity were estimated and discussed. The synthesized complexes have been designed as structural and functional models of the catechol oxidase enzymes to investigate the catecholase activity. Additionally, superoxide dismutase activity data of all complexes have also been evaluated and compared with known SOD mimics.

In-situ electrochemical reconstruction of tungsten carbide using Na2CO3-containing molten salt

This paper reports a novel method for rapid atomic-level reconstruction of tungsten carbide (WC) using Na2CO3-containing molten salt. Herein, WC was used as consumable anode and Na2CO3 was active species on WC anode and carbon donor. Thermodynamic calculations were used to verify the feasibility of this electrolytic method for reconstructing WC. Experimental results showed that the addition of Na2CO3 significantly enhanced dissolution efficiency of WC. Therefore, more tungsten (W) source was supplied. Electrochemical analysis demonstrated that Na2CO3 also supplied carbon by two-step reduction process, which led to the formation of WC. These experiments confirmed that cathode product was converted from W to WC by the introduction of Na2CO3 additive into molten salt. WC phase started to form at cell voltages above 2.2 V. In initial stage of reaction, carbonate was preferentially reduced in cathode region to form amorphous C. As the reaction proceeded, W ions migrated from anode and began to participate in reduction process, forming W. Finally, W was transformed to WC by carbonization process.

In situ quantification of NO synthesis in a warm air glow discharge by WMS-based Mid-IR QCL absorption spectroscopy

Nitric oxide (NO) is one of the most crucial products in the plasma-based nitrogen fixation process. In this work, in situ measurements were performed for quantifying the NO synthesis spatially in a warm air glow discharge, through the method of Mid-infrared quantum cascade laser absorption spectroscopy (QCL-AS). Two ro-vibrational transitions at 1900.076 cm−1 and 1900.517 cm−1 of the ground-state NO(X) were probed sensitively by the help of the wavelength modulation spectroscopy (WMS) approach to increase the signal/noise (S/N) level. The results show a decline trend of NO synthesis rate along the discharge channel from the cathode to the anode. However, from the point of energy efficiency, the cathode region is of significantly low energy efficiency of NO production. Severe disproportionality was found for the high energy consumption but low NO production in the region of cathode area, compared to that in the positive column zone. Further analysis demonstrates the high energy cost of NO production in the cathode region, is ascribed to the extremely high reduced electric field therein not selectively preferable for the processes of vibrational excitation or dissociation of N2 and O2 molecules. This drags down the overall energy efficiency of NO synthesis by this typical warm air glow discharge, particularly for the ones with short electrode gaps. Limitations of further improving the energy cost of NO synthesis by variations of the discharge operation conditions, such as discharge current or airflow rate, imply other effective manners able to tune the energy delivery selectively to the NO formation process, are sorely needed.