Oxidative Dissolution Research Articles

Modeling the Role in pH on Contaminant Sequestration by Zerovalent Metals: Chromate Reduction by Zerovalent Magnesium.

The role of pH in sequestration of Cr(VI) by zerovalent magnesium (ZVMg) was characterized by global fitting of a kinetic model to time-series data from unbuffered batch experiments with varying initial pH values. At initial pH values ranging from 2.0 to 6.8, ZVMg (0.5 g/L) completely reduced Cr(VI) (18.1 μM) within 24 h, during which time pH rapidly increased to a plateau value of ∼10. Time-series correlation analysis of the pH and aqueous Cr(VI), Cr(III), and Mg(II) concentration data suggested that these conditions are controlled by combinations of reactions (involving Mg0 oxidative dissolution and Cr(VI) sequestration) that evolve over the time course of each experiment. Since this is also likely to occur during any engineering applications of ZVMg for remediation, we developed a kinetic model for dynamic pH changes coupled with ZVMg corrosion processes. Using this model, the synchronous changes in Cr(VI) and Mg(II) concentrations were fully predicted based on the Langmuir-Hinshelwood kinetics and transition-state theory, respectively. The reactivity of ZVMg was different in two pH regimes that were pH-dependent at pH < 4 and pH-independent at the higher pH. This contrasting pH effect could be ascribed to the shift of the primary oxidant of ZVMg from H+ to H2O at the lower and higher pH regimes, respectively.

A proposed method for determining potentially environmentally available trace metals in paddy soil

ABSTRACT The validity of the Asami-Kumada method (sodium hydrosulfite + EDTA extraction, AK method) for determining the potentially environmentally available trace metals (Cr, Mn, Co, Ni, Cu, Zn, Cd, Pb) in paddy field soil was evaluated. This was accomplished by comparing it with the results of the dilute HNO3 extraction method (ISO method), nitrate acid – perchloric acid degradation method, and dilute hydrochloric acid extraction method on 250 paddy field soil samples. The coefficient of determination for the AK method in metals, excluding Cr, ranged from 0.92 (Ni of non-Andisols) to 0.99 (Mn, Cu, Zn and Cd of non-Andisols) compared to the ISO method. The slope of the linear regression of the AK method’s measured values against those of the ISO method for metals, excluding Cr, ranged from 0.99 (Cd of non-Andisols) to 1.52 (Cu of Andisols). However, the measurements of Fe using the AK method were significantly higher than those obtained using the ISO method. The slope was measured to be 3.6 (for non-Andisols) or 5.7 (for Andisols). The increase in trace metal measurements using the AK method was probably due to the dissolution of Fe oxides and hydroxides, which release trace metals after reduction by sodium hydrosulfite. Thus, although the measured values using the AK method of trace metals, excluding Cr, tended to be slightly higher than those obtained using the ISO method as Fe oxides and hydroxides dissolved, the measured values of those metals by both methods were closely correlated. The AK method is a viable alternative to the ISO method for measuring the potentially environmentally available trace metal contents, excluding Cr, in paddy field soils. Additionally, the AK method conveniently measures free Fe oxides simultaneously.

Electrochemical Behavior of the Oxidative Dissolution of Gold Catalyzed by Lead Ion in Thiourea Solution

ABSTRACT Thiourea is a low-toxicity gold lixiviant that has promise to substitute highly toxic cyanide for gold extraction. The electrochemical behavior of lead ion in the dissolution of gold in thiourea solution was investigated by electrochemical and analytical technique. Electrochemical results suggest that the addition of lead ion (10 mg/L and 20 mg/L) to thiourea solution increased the open circuit potential from 0.31 V to 0.32 V and 0.34 V, respectively, due to the significant increase of cathodic current density. The presence of lead ion could significantly improve the oxidative dissolution of gold and thus resulted in higher gold dissolution in thiourea solution, particularly at higher anodic potentials. The scanning electron microscope (SEM) equipped with energy dispersive spectroscope (EDS) and X-ray photoelectrode spectroscopy (XPS) analyses indicate the improvement of gold dissolution is attributed to the formation of gold-lead (AuPb2) layer on gold surface, which acts as a cathode to promote galvanic corrosion of gold. The possible mechanism is proposed that gold dissolution in thiourea solution with lead ion follows a two-step process: (1) the formation of AuPb2 layer on gold surface and (2) the dissolution of AuPb2 layer under the applied anodic potential.

Microbial-mediated oxidative dissolution of orpiment and realgar in circumneutral aquatic environments

Arsenic (As) is a toxic metalloid that causes severe environmental contamination worldwide. Upon exposure to aqueous phases, the As-bearing minerals, such as orpiment (As2S3) and realgar (As4S4), undergo oxidative dissolution, in which biotic and abiotic activities both contributed significant roles. Consequently, the dissolved As and S are rapidly discharged through water transportation to broader regions and contaminate surrounding areas, especially in aquatic environments. Despite both orpiment and realgar are frequently encountered in carbonate-hosted neutral environments, the microbial-mediated oxidative dissolution of these minerals, however, have been primarily investigated under acidic conditions. Therefore, the current study aimed to elucidate microbial-mediated oxidative dissolution under neutral aquatic conditions. The current study demonstrated that the dissolution of orpiment and realgar is synergistically regulated by abiotic (i.e., specific surface area (SSA) of the mineral) and biotic (i.e., microbial oxidation) factors. The initial dissolution of As(III) and S2− from minerals is abiotically impacted by SSA, while the microbial oxidation of As(III) and S2− accelerated the overall dissolution rates of orpiment and realgar. In As-contaminated environments, members of Thiobacillus and Rhizobium were identified as the major populations that mediated oxidative dissolution of orpiment and realgar by DNA-stable isotope probing. This study provides novel insights regarding the microbial-mediated oxidative dissolution process of orpiment and realgar under neutral conditions.

The role of plants in ironstone evolution: iron and aluminium cycling in the rhizosphere

The Carajás plateaus in Brazil host endemic epilithic vegetation (“campo rupestre”) on top of ironstone duricrusts, known as canga. This capping rock is primarily composed of iron(III) oxide minerals and forms a physically resistant horizon. Field observations reveal an intimate interaction between canga's surface and two native sedges (Rhynchospora barbata and Bulbostylis cangae). These observations suggest that certain plants contribute to the biogeochemical cycling of iron. Iron dissolution features at the root-rock interface were characterised using synchrotron-based techniques, Raman spectroscopy and scanning electron microscopy. These microscale characterisations indicate that iron is preferentially leached in the rhizosphere, enriching the comparatively insoluble aluminium around root channels. Oxalic acid and other exudates were detected in active root channels, signifying ligand-controlled iron oxide dissolution, likely driven by the plants' requirements for goethite-associated nutrients such as phosphorus. The excess iron not uptaken by the plant can reprecipitate in and around roots, line root channels and cement detrital fragments in the soil crust at the base of the plants. The reprecipitation of iron is significant as it provides a continuously forming cement, which makes canga horizons a ‘self-healing’ cover and contributes to them being the world's most stable continuously exposed land surfaces. Aluminium hydroxide precipitates (“gibbsite cutans”) were also detected, coating some of the root cavities, often in alternating layers with goethite. This alternating pattern may correspond with oscillating oxygen concentrations in the rhizosphere. Microbial lineages known to contain iron-reducing bacteria were identified in the sedge rhizospheric microbiome and likely contribute to the reductive dissolution of iron(III) oxides within canga. Drying or percolation of oxygenated water to these anaerobic niches have led to iron mineralisation of biofilms, detected in many root channels. This study sheds light on plants' direct and indirect involvement in canga evolution, with possible implications for revegetation and surface restoration of iron mine sites.

Risk assessment for the long-term stability of fly ash-based cementitious material containing arsenic: Dynamic and semidynamic leaching

Fly ash from municipal solid waste incineration (MSWIFA) contains leachable heavy metals (HMs), and the environmental risk of contained HMs is an important concern for its safe treatment and disposal. This paper presents a dynamic leaching test of fly ash-based cementitious materials containing arsenic (FCAC) in three particle sizes based on an innovative simulation of two acid rainfall conditions to investigate the long-term stability of FCAC under acid rain conditions. As well as semi-dynamic leaching test by simulating FCAC in three scenarios. Furthermore, the long-term stability risk of FCAC is evaluated using a sequential extraction procedure (SEP) and the potential risk assessment index. Results showed that the Al3+ in the FCAC dissolved and reacted with the OH− in solution to form Al(OH)3 colloids as the leaching time increased. Moreover, the oxidation of sulfide minerals in the slag produced oxidants, such as H2SO4 and Fe2(SO4)3, which further aggravated the oxidative dissolution of sulfides, thereby resulting in an overall decreasing pH value of the leachate. In addition, due to the varying particle sizes of the FCAC, surface area size, and adsorption site changes, the arsenic leaching process showed three stages of leaching characteristics, namely, initial, rapid, and slow release, with a maximum leaching concentration of 2.42 mg/L, the cumulative release of 133.78 mg/kg, and the cumulative release rate of 2.32%. The SEP test revealed that the reduced state of HMs in the raw slag was lowered substantially, and the acid extractable state and residual state of HMs were increased, which was conducive to lessening the risk of FCAC. Overall, the geological polymerization reaction of MSWIFA is a viable and promising solution to stabilize mining and industrial wastes and repurpose the wastes into construction materials.

Equilibrium, kinetics and thermodynamics of metal oxide dissolution based on CuO in a natural deep eutectic solvent

In the article, results of dissolution of metal oxides using a natural deep eutectic solvent (NDES or NADES) based on betaine, malic acid and ethylene glycol are presented. The obtained deep eutectic solvent was characterised by determining its physicochemical properties including density, viscosity as a function of temperature. The thermal stability of NADES was also determined. For CuO, equilibrium, kinetics, and thermodynamics of the oxide dissolution process in NADES and H2O were determined. Dissolution studies of selected metal oxides including ZnO, MgO, CaO, Fe2O3 in NADES and water were also carried out. It was found that the solubility of the metal oxides was 2 to 100 times higher in NADES compared to the solubility in water, despite the neutral pH of NADES. The study, using XRD and SEM methods, also shows changes in the morphology of particles subjected to dissolution in water and in NADES. The results indicate the possibility of extracting metal oxides by dissolution in NADES.

Impact of iron and sulfur cycling on the bioavailability of cadmium and arsenic in co-contaminated paddy soil

The biogeochemical cycling of iron (Fe) or sulfur (S) in paddy soil influences the cadmium (Cd) and arsenic (As) migration. However, the influence of coupled reduction effects and reaction precedence of Fe and S on the bioavailability of Cd and As is still not fully understood. This study aimed to reveal the influence of Fe and S reduction on soil Cd and As mobility under various pe + pH conditions and to elucidate the related mechanism in subtropical China. According to the findings, higher adsorption from Fe reduction caused high-crystalline goethite (pe + pH > 2.80) to become amorphous ferrihydrite, which in turn caused water-soluble Cd (62.0%) to first decrease. Cd was further decreased by 72.7% as a result of the transformation of SO42- to HS-/S2- via sulfate reduction and the formation of CdS and FeS. As release (an increase of 8.1 times) was consequently caused by the initial reduction and dissolution of iron oxide (pe + pH > 2.80). FeS had a lesser impact on the immobilization of As than sulfate-mediated As (V) reduction in the latter stages of the reduction process (pe + pH < 2.80). pe + pH values between 3 and 3.5 should be maintained to minimize the bioavailability of As and Cd in moderate to mildly polluted soil without adding iron oxides and sulfate amendments. The practical remediation of severely co-contaminated paddy soil can be effectively achieved by using Fe and S additions at different pe + pH conditions. This technique shows promise in reducing the bioavailability of Cd and As.

Enhanced electrochemical dissolution of iridium oxide in acidic electrolytes through presence of metal ions: shortened lifetime and hope for recovery

Cyclic deposition and stripping of metal ions (e.g. Cu2+) on Ir-oxides enhance electrochemical dissolution of Ir-oxides, likely due to weakening of the Ir–O–Ir bonds. The phenomenon is influential to IrOx catalyst stability and recovery perspective.

Co-doped RuO2 nanoparticles with enhanced catalytic activity and stability for the oxygen evolution reaction.

Efficient and durable electrocatalysts for the oxygen evolution reaction (OER) play an important role in the use of hydrogen energy. Rutile RuO2, despite being considered as an advanced electrocatalyst for the OER, performs poorly in stability due to its easy oxidative dissolution at very positive (oxidizing) potentials. Herein, we report a type of Co-doped RuO2 nanoparticle for boosting OER catalytic activity and stability in alkaline solutions. The replacement of Ru by Co atoms with a lower ionic valence and smaller electronegativity can promote the generation of O vacancies and increase the electron density around Ru, thus enhancing the adsorption of oxygen species and inhibiting the peroxidative dissolution of RuO2 during the OER process. It was found that Ru0.95Co0.05Oy exhibited excellent OER performance with overpotentials as low as 217 mV at 10 mA cm-2 and 290 mV at 100 mA cm-2 in 1 M KOH, as well as outstanding stability in continuous testing for 50 h at a current density of 100 mA cm-2, and nearly no significant degradation after the accelerated durability test of 2000 cycles.

The influence of bicarbonate concentration and ionic strength on peroxide speciation and overall reactivity towards UO2.

H2O2 produced from water radiolysis is expected to play a significant role in radiation induced oxidative dissolution of spent nuclear fuel under the anoxic conditions of a deep geological repository if the safety-barriers fail and ground water reaches the fuel. It was recently found that the coordination chemistry between U(vi), HCO32- and H2O2 can significantly suppress H2O2 induced dissolution of UO2 in 10 mM bicarbonate. This was attributed to the much lower reactivity of the U(vi)O22+-coordinated O22- as compared to free H2O2. We have extended the study to lower bicarbonate concentrations and explored the impact of ionic strength to elucidate the rationale for the low reactivity of complexed H2O2. The experimental results clearly show that dissolution of U(vi) becomes suppressed at [HCO3-] < 10 mM. Furthermore, we found that the reactivity of the peroxide in solutions containing U(vi) becomes increasingly more suppressed at lower carbonate concentration. The suppression is not influenced by the ionic strength, which implies that the low reactivity of O22- in ternary uranyl-peroxo-carbonato complexes is not caused by electrostatic repulsion between the negatively charged complex and the negatively charged UO2-surface as we previously hypothesized. Instead, the suppressed reactivity is suggested to be attributed to inherently higher stability of the peroxide functionality as a ligand to UO22+ compared to as free H2O2.

Can polymeric surface modification and sulfidation of nanoscale zerovalent iron (NZVI) improve arsenic-contaminated agricultural soil restoration via ex situ magnet-assisted soil washing?

Environmental context Arsenic (As) contamination in agricultural soil threatens safe agricultural production. Therefore, an ex situ magnet-assisted soil washing, using different types of nanoscale zerovalent iron was tested as a remediation option in soil restoration. Uncoated nanoparticles was the best tested option, with As removal at 45.5% and the nanoparticles were reusable up to four times. Rationale Arsenic (As) contamination in agricultural soil threatens safe food and medicinal herb production for millions of people. Methodology Therefore, ex situ magnet-assisted soil washing of metal-contaminated soil using bare nanoscale zerovalent iron (NZVI) is proposed as a novel remediation alternative. Conceptually, metal-contaminated soil is mixed with water and bare NZVI, and metals in the soil are transferred to the bare NZVI. The metal-sorbed NZVI is then retrieved from the soil slurry through magnetic separation, leaving behind treated soil. This study evaluated if advanced surface modification can improve ex situ soil restoration efficacy including polymeric coating and sulfidation of NZVI, proven beneficial in situ NZVI application. Sulfur and carboxymethylcellulose (CMC) at various S/Fe and CMC/NZVI ratios were used to modify NZVI via sulfidation and physisorption. Result Results revealed that sulfidised NZVI (S-NZVI) performed poorer (41.0%) than bare NZVI (45.5%) in As removal, even at the optimised S/Fe ratio of 0.31. This could be due to acid release via oxidative dissolution of FeS2 on the S-NZVI surface driven by O2. The incidental acid-dissolved NZVI sorption sites decreased As removal efficacy. Similarly, CMC-modified NZVI failed to improve As removal efficacy (11.0%) because it reduced NZVI reactivity and blocked As accessibility to NZVI sorptive sites. Discussion Nevertheless, S-NZVI and CMC-modified NZVI promoted non-phytoavailable As fractions in the treated soil. Overall, bare NZVI performed the best for As removal but moderately transformed As into more non-phytoavailable fractions. Bare NZVI can be reused for four cycles of soil washing. In every case, mobile As in treated soil was lower than the maximum contamination level.

Galvanic replacement-induced preparation of bloom-like Pt23Ni77 for methanol coupled efficient hydrogen production.

Galvanic replacement reaction (GRR) leverages the difference in metal reduction potentials to regulate the structure of nanomaterials. The crucial aspect of constructing highly active catalysts lies in the precise manipulation of both the oxidative dissolution of sacrificial template metals and reductive deposition of alternate metals. Herein, we investigated the morphological transformation of metal Ni as a sacrificial template in the presence of different amounts of H2PtCl6 solution and the Pt4+ substitution of Ni to achieve the redistribution of elements on the catalyst surface, which provides superior performance in both the methanol oxidation reaction (MOR) and hydrogen evolution reaction (HER). The uniform distribution of Pt on a three-dimensional transition metal Ni substrate allows for the complete exposure of the noble metal to the catalyst surface. This distribution increases the reaction area, facilitating easy access for reactants and promoting electron transfer. Meanwhile, Pt (1.39 Å) has a larger atomic radius compared to Ni (1.24 Å), and the substitution reaction in the transition metal phase induces strong compressive strain, which effectively regulates the electronic structure of Ni.

Corrosion properties of aluminum-based alloys used in building constructions for different purposes

The corrosion resistance of an aluminium alloy АD 31, that is used in building constructions, is investigated. The connection between change of samples weight and time of corrosion tests is established. It is shown, that the corrosion is accompanied by simultaneous course of two processes: by oxide film formation and dissolution of more active metal. The temperature dependences have shown, that with the temperature increase higher 80°С the corrosion resistance is reduced. The accounts of weight and deep parameters of corrosion are made.

Formation of lipid corona on Ag nanoparticles and its impact on Ag+ ion dissolution and aggregation of Ag nanoparticles against external stimuli

The application of lipid coated nanoparticles has been expanding in nanoscience over the past few years. Lipid corona formation is one of the novel ways for the lipid conjugation around the nanoparticles. Although several properties of nanoparticles and lipids are well reported in literature in last few years, the dependency of lipid corona formation on metallic core and surface ligands is poorly understood. The aggregation, surface oxidation and metal ions dissolution of nanoparticles limit their usefulness in various applications. Besides all the reported methods to overcome all of these limitations, lipid corona could be an alternative, feasible, and more efficient method. In the current manuscript, we investigate the interaction of aromatic amino acids (tyrosine and tryptophan) functionalized silver nanoparticles (Ag-Tyr and Ag-Trp NPs) with different surface charged and phase states lipid vesicles and compare them with the reported amino acid functionalized gold nanoparticles (Au-AA NPs). The effectiveness of different zwitterionic and positively charged lipid coated Ag-Tyr and Ag-Trp NPs to prevent the aggregation and Ag+ ion dissolution of Ag NPs against different external stimuli (acidic pH, high NaCl concentration, and freeze-thaw cycles) are investigated. Our results reveal that surface ligands around the NPs play crucial role for lipid corona formation irrespective of the metallic core of NPs. Although all the lipid coated Ag NPs exhibit greater stability against external stimuli than native Ag NPs, zwitterionic lipid coated Ag NPs is better choice than positively charged lipid coated Ag NPs. This study on lipid corona and its stability will help the nanoresearcher to choose the suitable lipid for lipid corona formation.

Cu ions release and the formation of CuO/Cu2O during PEO based on the work function

The Cu ions release was investigated by the work function by scanning kelvin probe (SKP), and the formation of CuO/Cu2O was also researched by recording plasma discharges during plasma electrolytic oxidation (PEO) of Ti-14Cu alloy with different morphologies Ti2Cu phase. It is found that L-Ti2Cu phases with lower work function enhances the escape of Cu valence electrons from the 4 s energy level more easily compared to the G-Ti2Cu and GL-Ti2Cu phases. Consequently, this leads to earlier Cu ions released from L-Ti2Cu phases as opposed to the G-Ti2Cu and GL-Ti2Cu phases. The earlier Cu+ released from L-Ti2Cu phases increases the formation of Cu2O and further oxidizes into CuO with increasing voltage, which lead to the enhanced the relative content of CuO. This enhancement contributes to improving antibacterial activity and tribocorrosion resistance due to stress response and lubrication effect by high relative content of CuO. This research provides a theoretical reference for the metal ions release of Ti-14Cu alloy in oxidation dissolution process of PEO and the formation of corresponding metal oxides.

Complex Speciation and Distribution of Iron, Sulfur, and Trace Metals in Coal Mine Soils Reflect Grain- and Sub-Grain-Scale Heterogeneity during Pyrite Oxidative Dissolution

Historical coal mining practices have caused various soil and water hazards, particularly through the dumping of mine waste. The primary environmental risk associated with this waste is the leaching of toxic metals from dumps of spoil or refuse into the subsurface soil or into nearby water resources. The extent of metal release is controlled via the oxidative dissolution of pyrite and potential re-sequestration through secondary Fe oxides. The characterization of the dominant Fe-bearing phase and the distribution of trace metals associated with these phases was determined via electron microscopy, synchrotron-based X-ray micro-fluorescence (μ-XRF) element and redox mapping from shallow mine soils from an impacted watershed in Appalachian Ohio. The dominant Fe-bearing phases were: (1) unweathered to partially weathered pyrite; (2) pseudomorphic replacement of pyrite with Fe(III) oxides; (3) fine-grained Fe oxide surface coatings; and (4) discrete Fe(III) oxide grains. Thicker secondary coatings and larger particles were sulfate rich, whereas smaller grains and thinner coatings were sulfate poor. The discrete Fe oxide grains exhibited the highest concentrations of Cr, Mn, Ni, and Cu, and sub-grain-scale concentration trends (Mn &gt; Cr &gt; Ni &gt; Cu) were consistent with bulk soil properties. Predicting future metal transport requires an understanding of metal speciation and distribution from the sub-grain scale to the pedon scale.

Numerical Simulations for in-Plane Distribution of Platinum Degradation in Dynamic Operating Conditions of Polymer Electrolyte Membrane Fuel Cells

Predicting degradation of polymer electrolyte membrane fuel cells (PEMFCs) is an important issue from the viewpoint of durability and cost. In fact, in technical roadmaps regarding fuel cell of each country, high targets of durability and performance are set for transport applications especially for heavy duty vehicles. One of important degradation process takes place in catalyst layer. PEMFC catalysts are typically platinum or platinum alloys and consist of nanoparticles to increase the electrochemically active surface area (ECSA). However, these particles are not stable in dynamic operating conditions of the transport applications. A typical degradation mechanism of the catalyst is the electrochemical Ostwald ripening mechanism, and it is known that the platinum particle size distribution shifts to larger particle diameter, resulting in lower ECSA and lower performance. Therefore, predicting platinum catalyst degradation is important to enhance durability of the products.Various numerical models for catalyst degradation of PEMFC have been proposed and used to explore degradation mechanisms. Many of these are zero or one-dimensional models, but factors that affect catalyst degradation, such as temperature, potential, and humidity, have non-uniform distributions in the active area of large-size (several hundred cm2) cells. Furthermore, these factors change unsteadily due to the dynamic operating conditions. In order to predict the degradation of cells, it is necessary to analyze the dynamic behavior of large-area cells, but there are few spatially resolved catalyst degradation predictions [1].In this analysis, transient analysis of a large-area cell for a dynamic operating conditions is performed to predict in-plane distribution of catalyst degradation. Furthermore, we will analyze changes in the power generation performance of the cells when these degradations progress. A three-dimensional numerical simulation model based on our original methodology [2] was used as the performance prediction model for the PEMFC. Catalyst degradation considers the mechanisms of platinum dissolution, oxidation, and platinum oxide dissolution [3]. The in-plane distribution of platinum degradation is predicted from the time-series results of in-plane distributions of temperature, potential, humidity, etc., obtained by the performance prediction model. The performance of the PEMFC at the time of progressive degradation is analyzed by reflecting the effect of ECSA decrease due to platinum degradation in the performance prediction model. Although this method considers only a part of the catalyst degradation process, a path is presented to analyze the distribution of catalyst degradation under dynamic operating conditions in large-area cells.

Oxidation of Alloy 690 in Simulated Pressurized Water Reactor Primary Coolant – Experiments and Modeling

During normal operation of the primary loop of a water cooled-water moderated energy reactor (WWER), the associated water chemistry evolves from an initially high-boron high-potassium (beginning-of-cycle, 1200 ppm B and 8 ppm K) to significantly lower concentrations (ca. 400 ppm B and 3.5 ppm K) at the end of the respective campaign. In addition to that, the concentration of Li produced by transmutation of B reaches ca. 0.7 – 0.9 ppm. To the best of our knowledge, the effect of such water chemistry changes on pressurized water reactor (PWR) internals such as Alloy 690 have not been studied yet. Such a study appears relevant also within the frames of a discussion for a possible transition from B-Li to B-K water chemistry in PWRs.In the present paper, the effect of evolution of primary water chemistry during operation on the corrosion rate and conduction mechanism of oxide films on Alloy 690 is studied by in-situ impedance spectroscopy at 280 °C / 8 MPa during 1-week exposures in an autoclave connected to a re-circulation loop. Impedance measurements were performed in three-electrode mode featuring a Pt sheet counter electrode and a Pd electrode negatively polarized with a current of -10 µA vs. another Pt to approximate the reversible hydrogen electrode (RHE). Spectra were recorded at the corrosion potential in a frequency range 10 kHz – 0.1 mHz using an ac amplitude of 50 mV (rms). At the end of exposure, the samples were polarized in the range of potentials -0.1 to 0.5 V vs. RHE to evaluate the stability of the passive oxide. Separate samples of Alloy 690 were simultaneously exposed in the autoclave and subsequently analyzed by Glow-Discharge Optical Emission Spectroscopy (GDOES) in order to estimate the thickness and the in-depth composition of the formed oxides.Impedance data were quantitatively interpreted using the Mixed-Conduction Model for Oxide Films (MCM) to estimate the rates of metal oxidation at the alloy/oxide interface, oxide dissolution and restructuring at the film/coolant interface and ion transport in the protective layer. The effect of water chemistry evolution on corrosion rate and conduction mechanism in the oxide on Alloy 690 in primary coolant is discussed on the basis of the obtained parameters.Acknowledgments: This study is funded by the European Union-NextGenerationEU, through the National Recovery and Resilience Plan of the Republic of Bulgaria, project № BG-RRP-2.004-0002 (BiOrgaMCT).

(Invited) Lithium Battery Interfacial Engineering with Thin Conformal Polymer Coatings

Coupled chemical and mechanical phenomena at electrode interfaces largely govern the reversibility and long term stability of lithium ion and lithium metal batteries. A well-known example in lithium ion batteries is the formation of the electrically insulating, ionically conductive, continuous solid electrolyte interface (SEI) on graphitic anodes, which passivates the electrode against further electrochemical reduction of the electrolyte. Unfortunately, this stable passivation does not occur in Si and Li metal anodes. High voltage cathodes are also prone to detrimental interfacial processes, resulting in electrolyte oxidation, gas formation, and transition metal dissolution. In response, a myriad of coating technologies has been developed to mitigate and control these interfacial phenomena and enable next-generation electrodes. These technologies must provide thin, conformal coatings over the entire electrochemically active surface area of the electrode; the coatings must also possess the requisite mechanical properties to accommodate volume dilation due to lithium insertion/extraction.This presentation will describe the development of conformal, compliant polymer thin film coatings for lithium battery electrodes. The polymer thin films are prepared by initiated chemical vapor deposition (iCVD), which provides exquisite control over film composition and morphology by facilitating heterogeneous free-radical polymerization of vinyl monomers with thickness precision on the order of 1 nm. Poly(1,3,5,7-tetravinyl-1,3,5,7-tetramethylcyclotetrasiloxane) (pV4D4) was deposited onto silicon thin film electrodes using iCVD. 25 nm-thick pV4D4 films on Si electrodes improved initial coulombic efficiency by 12.9% and capacity retention over 100 cycles by 64.9% relative to untreated electrodes. PV4D4 coatings also improved rate capabilities, enabling higher lithiation capacity at all current densities. Post-cycling FTIR and XPS showed that pV4D4 inhibited electrolyte reduction and altered the SEI composition, with enrichment in LiF. In another example, thin conformal coatings of perfluorinated polymer were deposited onto battery-grade Cu current collectors to function as an artificial solid electrolyte interface. The effect of the film thickness on Li cycling reversibility was characterized. By galvanostatically cycling Li in an asymmetric Li||Cu cell using 1M LiFSI in a 1:1 (v/v) mixture of dioxolane:dimethoxyethane at 30°C, it was shown that the average coulombic efficiency averaged over 50 cycles increased from 98.36% for bare, untreated Cu to 99.08% for Cu coated with 25 nm of the fluoropolymer. Moreover, the 25 nm coating suppressed interfacial impedance growth on the current collector; the resistance of the coated Cu was 40% lower than the untreated Cu after 100 cycles. The mechanism by which the polymer coating enhances coulombic efficiency and suppresses side reactions will be discussed, along with discussion of the performance in practical anode-free lithium metal batteries.