Redox-active Transition Metal Research Articles

Deconvoluting Surface and Bulk Charge Storage Processes in Redox-Active Oxides by Integrating Electrochemical and Optical Insights.

Redox-active transition metal oxides (TMOs) play crucial roles in diverse energy storage and conversion technologies, such as batteries and pseudocapacitors. These materials show intricate electrochemical charge storage processes, encompassing both bulk ion-intercalation, typical of battery electrodes, and pseudocapacitive-like behavior localized near the surfaces. However, understanding the underlying mechanisms of charge storage in redox-active TMOs is challenging due to the coexistence of these behaviors. In this study, we propose an integrated approach that combines operando electrochemical and optical techniques to disentangle the contributions of bulk and surface phenomena. Using birnessite δ-MnO2-x as a model system, we account for surface pseudocapacitive-like layers and employ a refined model that incorporates both surface reactions and bulk chemical diffusion. This methodology allows us to extract essential kinetic parameters, establishing a fundamental framework for unraveling surface and bulk electrochemical processes. This advancement provides a valuable tool for the rational design of energy storage devices, enhancing our ability to tailor these materials for specific applications.

Elucidating the Interactions between Different Transition Metal Cations and Ti3C2Tx MXene through Intercalation Method for Electrochemical Applications

MXenes, are a family of two-dimensional (2D) transition metal carbides, nitrides and/ or carbonitrides.[1] The intercalation of different metal cations and organic molecules into MXene for tuning MXenes’ electronic and electrochemical properties have been widely reported.[2] [3] [4] However, transition metals (TMs) which have distinct electrochemical behaviors[5] [6] have not been explored in the literature of MXenes’ intercalation. Therefore, we herein compared the intercalation effects of different TM cations on Ti3C2Tx, for offering a general insight on the influences of multi-valent, redox-active TMs on MXenes. In particular, the changes on the physiochemical and electrochemical properties of MXenes were investigated using different in-situ and ex-situ methods, for a better understanding on the interfacial interactions of TM cations and MXenes in the confined environment of MXenes’ multilayer structures. This work serves as a foundation for the fine-tuning of MXenes’ properties by utilizing a variety of TM cations intercalation for different electrochemical systems.[1] B. Anasori, M. R. Lukatskaya, Y. Gogotsi, Nature Reviews Materials 2017, 2, 16098.[2] M. R. Lukatskaya, O. Mashtalir, E. Ren Chang, Y. Dall’Agnese, P. Rozier, L. Taberna Pierre, M. Naguib, P. Simon, M.W. Barsoum, Y. Gogotsi, Science 2013, 341, 1502-1505.[3] J. Li, H. Wang, X. Xiao, Energy & Environmental Materials 2020, 3, 306-322[4] M. Ghidiu, S. Kota, J. Halim, A. W. Sherwood, N. Nedfors, J. Rosen, V. N. Mochalin, M. W. Barsoum, Chemistry of Materials 2017, 29, 1099-1106.[5] D. Göhl, H. Rueß, M. Pander, A. R. Zeradjanin, K. J. J. Mayrhofer, J. M. Schneider, A. Erbe, M. Ledendecker, Journal of The Electrochemical Society 2020, 167, 021501.[6] M. Esmaeilirad, A. Baskin, A. Kondori, A. Sanz-Matias, J. Qian, B. Song, M. Tamadoni Saray, K. Kucuk, A. R. Belmonte, P. N. M. Delgado, J. Park, R. Azari, C. U. Segre, R. Shahbazian-Yassar, D. Prendergast, M. Asadi, Nature Communications 2021, 12, 5067.

A Novel Approach to Continuous and Scalable Synthesis of Cation-Disordered Rocksalt Cathodes

Cation disordered rocksalts (DRX) are an emerging class of high energy density LIB cathodes that can utilize earth-abundant and low-cost redox active transition metals. The DRX cathodes can be synthesized through a rich chemistry of transition metals, where commonly, metal-oxide precursors are combined with lithium source via ball-milling and calcined to achieve cation disordered phase. In this work, we present a new alternative synthesis method to the traditional solid-state synthesis, which provides scalable and continuous production of cathode precursors. A soft synthesis method in aqueous media was adopted to produce Mn-rich cathode precursors in large scale, through which homogenous mixing of the introduced transition metal cations was achieved. Here we report the electrochemical and structural properties of as-synthesized DRX cathodes with various Mn-compositions.

ROS-Responsive Methionine-Containing Amphiphilic Peptides Impart Enzyme-Triggered Phase Transition and Antioxidant Cell Protection.

Reactive oxygen species (ROS) are produced by cellular activities, such as metabolism and immune response, and play important roles in cell signaling and homeostasis. However, overproduced ROS causes irreversible damage to nucleic acids and membrane lipids, supporting genetic mutations and enhancing the effects of aging. Cells defend themselves against ROS using antioxidant systems based on redox-active sulfur and transition metals. Inspired by such biological redox-responsive systems, we developed methionine-containing self-assembling peptides. The Met-containing peptides formed hydrogels that underwent a gel-to-sol phase transition upon oxidation by H2O2, and the sensitivity of the peptides to the oxidant increased as the number of Met residues increased. The peptide containing three Met residues, the largest number of Met residues in our series of designed peptides, showed the highest sensitivity to oxidation and detoxification to protect cells from ROS damage. In addition, this peptide underwent a phase transition in response to H2O2 produced by an oxidizing enzyme. This study demonstrates the design of a supramolecular biomaterial that is responsive to enzymatically generated ROS and can protect cells against oxidative stress.

Tuning MXene Properties through Cu Intercalation: Coupled Guest/Host Redox and Pseudocapacitance.

MXenes are 2D transition metal carbides, nitrides, and/or carbonitrides that can be intercalated with cations through chemical or electrochemical pathways. While the insertion of alkali and alkaline earth cations into Ti3C2Tx MXenes is well studied, understanding of the intercalation of redox-active transition metal ions into MXenes and its impact on their electronic and electrochemical properties is lacking. In this work, we investigate the intercalation of Cu ions into Ti3C2Tx MXene and its effect on its electronic and electrochemical properties. Using X-ray absorption spectroscopy (XAS) and ab initio molecular dynamics (AIMD), we observe an unusual phenomenon whereby Cu2+ ions undergo partial reduction upon intercalation from the solution into the MXene. Furthermore, using in situ XAS, we reveal changes in the oxidation states of intercalated Cu ions and Ti atoms during charging. We show that the pseudocapacitive response of Cu-MXene originates from the redox of both the Cu intercalant and Ti3C2Tx host. Despite highly reducing potentials, Cu ions inside the MXene show an excellent stability against full reduction upon charging. Our findings demonstrate how electronic coupling between Cu ions and Ti3C2Tx modifies electrochemical and electronic properties of the latter, providing the framework for the rational design and utilization of transition metal intercalants for tuning the properties of MXenes for various electrochemical systems.

Metal Complexes of Redox Non-Innocent Ligand N,N'-Bis(3,5-di-tertbutyl-2-hydroxy-phenyl)-1,2-phenylenediamine.

Redox non-innocent ligands react with metal precursors to form complexes where the oxidation states of the ligand and thus the metal atom cannot be easily defined. A well-known example of such ligands is bis(o-aminophenol) N,N'-bis(3,5-di-tertbutyl-2-hydroxy-phenyl)-1,2-phenylenediamine, previously developed by the Wieghardt group, which has a potentially tetradentate coordination mode and four distinct protonation states, whereas its electrochemical behavior allows for five distinct oxidation states. This rich redox chemistry, as well as the ability to coordinate to various transition metals, has been utilized in the syntheses of metal complexes with M2L, ML and ML2 stoichiometries, sometimes supported with other ligands. Different oxidation states of the ligand can adopt different coordination modes. For example, in the fully oxidized form, two N donors are sp2-hybridized, which makes the ligand planar, whereas in the fully reduced form, the sp3-hybridized N donors allow the formation of more flexible chelate structures. In general, the metal can be reduced during complexation, but redox processes of the isolated complexes typically occur on the ligand. Combination of this non-innocent ligand with redox-active transition metals may lead to complexes with interesting magnetic, electrochemical, photonic and catalytic properties.

Computational Analysis of the Superoxide Dismutase Mimicry Exhibited by a Zinc(II) Complex with a Redox-Active Organic Ligand.

Previously, we found that a Zn(II) complex with the redox-active ligand N-(2,5-dihydroxybenzyl)-N,N',N'-tris(2-pyridinylmethyl)-1,2-ethanediamine (H2qp1) was able to act as a functional mimic of superoxide dismutase, despite its lack of a redox-active transition metal. As the complex catalyzes the dismutation of superoxide to form O2 and H2O2, the quinol in the ligand is believed to cycle between three oxidation states: quinol, quinoxyl radical, and para-quinone. Although the metal is not the redox partner, it nonetheless is essential to the reactivity since the free ligand by itself is inactive as a catalyst. In the present work, we primarily use calculations to probe the mechanism. The calculations support the inner-sphere decomposition of superoxide, suggest that the quinol/quinoxyl radical couple accounts for most of the catalysis, and elucidate the many roles that proton transfer between the zinc complexes and buffer has in the reactivity. Acid/base reactions involving the nonmetal-coordinating hydroxyl group on the quinol are predicted to be key to lowering the energy of the intermediates. We prepared a Zn(II) complex with N-(2-hydroxybenzyl)-N,N',N'-tris(2-pyridinylmethyl)-1,2-ethanediamine (Hpp1) that lacks this functional group and found that it could not catalyze the dismutation of superoxide; this confirms the importance of the second, distal hydroxyl group of the quinol.

Transition‐metal Substituted Polyoxometalates as Soluble RedOx Mediators in Electrocatalytic Biomass Conversion

AbstractPolyoxometalates (POMs) are known for their unique redox properties, making them interesting candidates as redox mediators in electro‐organic transformations. We investigated derivatives of H3[PMo12O40], a classical Keggin‐type POM, as a potential redox mediator in the indirect electrolysis of biobased glyceraldehyde (GLAD), focusing on the effects of double substitution of the Mo framework metal by redox active transition metals (Mo replaced by V, Ni, Co, Mn). By combining electrochemical techniques with HPLC, UV‐Vis spectroscopy, and 31P‐NMR spectroscopy, a comprehensive overview of the reaction pathways, as well as the electronic and structural changes of the POM during the reaction were revealed. This work not only contributes to the fundamental understanding of POMs as redox mediators, but also paves the way for innovative development of sustainable and environmentally friendly electro‐organic transformations.

Inhalation of particulate matter containing environmentally persistent free radicals induces endothelial dysfunction mediated via AhR activation at the air-blood interface.

Particulate matter (PM) containing environmentally persistent free radicals (EPFR) is formed by the incomplete combustion of organic wastes, resulting in the chemisorption of pollutants to the surface of PM containing redox-active transition metals. In prior studies in mice, EPFR inhalation impaired endothelium-dependent vasodilation. These findings were associated with aryl hydrocarbon receptor (AhR) activation in the alveolar type-II (AT-II) cells that form the air-blood interface in the lung. We thus hypothesized that AhR activation in AT-II cells promotes the systemic release of mediators that promote endothelium dysfunction peripheral to the lung. To test our hypothesis, we knocked down AhR in AT-II cells of male and female mice and exposed them to 280 µg/m3 EPFR lo (2.7e + 16 radicals/g) or EPFR (5.5e + 17 radicals/g) compared with filtered air for 4 h/day for 1 day or 5 days. AT-II-AhR activation-induced EPFR-mediated endothelial dysfunction, reducing endothelium-dependent vasorelaxation by 59%, and eNOS expression by 50%. It also increased endothelin-1 mRNA levels in the lungs and peptide levels in the plasma in a paracrine fashion, along with soluble vascular cell adhesion molecule-1 and iNOS mRNA expression, possibly via NF-kB activation. Finally, AhR-dependent increases in antioxidant response signaling, coupled to increased levels of 3-nitrotyrosine in the lungs of EPFR-exposed littermate control but not AT-II AhR KO mice suggested that ATII-specific AhR activation promotes oxidative and nitrative stress. Thus, AhR activation at the air-blood interface mediates endothelial dysfunction observed peripheral to the lung, potentially via release of systemic mediators.

Source differences in the components and cytotoxicity of PM2.5 from automobile exhaust, coal combustion, and biomass burning contributing to urban aerosol toxicity

Abstract. Although air quality guidelines generally use the atmospheric concentration of fine particulate matter (PM2.5) as a metric for air pollution evaluation and management, the fact cannot be ignored that different particle toxicities are unequal and significantly related to their sources and chemical compositions. Therefore, judging the most harmful source and identifying the toxic component would be helpful for optimizing air quality standards and prioritizing targeted PM2.5 control strategies to protect public health more effectively. Since the combustions of fuels, including oil, coal, and biomass, are the main anthropogenic sources of environmental PM2.5, their discrepant contributions to health risks of mixed ambient aerosol pollution dominated by the respective emission intensity and unequal toxicity of chemical components need to be identified. In order to quantify the differences between these combustion primary emissions, 10 types of PM2.5 from each typical source group, i.e., vehicle exhaust, coal combustion, and plant biomass (domestic biofuel) burning, were collected for comparative study with toxicological mechanisms. In total, 30 types of individual combustion samples were intercompared with representative urban ambient air PM2.5 samples, whose chemical characteristics and biological effects were investigated by component analysis (carbon, metals, soluble ions) and in vitro toxicity assays (cell viability, oxidative stress, inflammatory response) of human lung adenocarcinoma epithelial cells (A549). Carbonaceous fractions were plenteous in automobile exhaust and biomass burning, while heavy metals were more plentiful in PM2.5 from coal combustion and automobile exhaust. The overall ranking of mass-normalized cytotoxicity for source-specific PM2.5 was automobile exhaust > coal combustion > domestic plant biomass burning > ambient urban air, possibly with differential toxicity triggers, and showed that the carbonaceous fractions (organic carbon, OC; elemental carbon, EC) and redox-active transition metals (V, Ni, Cr) assisted by water-soluble ions (Ca2+, Mg2+, F−, Cl−) might play important roles in inducing cellular reactive organic species (ROS) production, causing oxidative stress and inflammation, resulting in cell injury and apoptosis, and thus damaging human health. Coupled with the source apportionment results of typical urban ambient air PM2.5 in eastern China, reducing toxic PM2.5 from these anthropogenic combustions will be greatly beneficial to public health. In addition to the air pollution control measures that have been implemented, like strengthening the vehicle emission standards, switching energy from coal to gas and electricity, and controlling the open incineration of agricultural straws, further methods could be considered, especially by preferentially reducing the diesel exhaust, lessening the coal combustion by replacement with low-ash clean coals, and depressing the rural crop straw biomass burning emissions.

Effects of copper on chemical kinetics and brown carbon formation in the aqueous ˙OH oxidation of phenolic compounds.

Many phenolic compounds (PhCs) in biomass burning and fossil fuel combustion emissions can partition into atmospheric aqueous phases (e.g., cloud/fog water and aqueous aerosols) and undergo reactions to form secondary organic aerosols (SOAs) and brown carbon (BrC). Redox-active transition metals, particularly Fe and Cu, are ubiquitous species in atmospheric aqueous phases known to participate in Fenton/Fenton-like chemistry as a source of aqueous ˙OH. However, even though the concentrations of water-soluble Cu are close to those of water-soluble Fe in atmospheric aqueous phases in some areas, unlike Fe, the effects that Cu have on SOA and BrC formation in atmospheric aqueous phases have scarcely been studied and remain poorly understood. We investigated the effects of Cu(II) on PhC reaction rates and BrC formation during the aqueous oxidation of four PhCs (guaiacol, catechol, syringol, and vanillin) by ˙OH generated from Fenton-like chemistry under different pH conditions. While the PhCs reacted when both H2O2 and Cu(II) were present in the absence (i.e., dark oxidation) and presence (i.e., photooxidation) of light, the reaction rates were at least one order of magnitude higher during photooxidation. Higher PhC reaction rates were measured at higher pH during both dark oxidation and photooxidation as a result of higher ˙OH concentrations produced by Fenton-like chemistry. Only water-soluble BrC was formed during dark oxidation and photooxidation when Cu(II) was present. Mass absorption coefficients (103 to 104 cm2 g-1) comparable to those of biomass burning BrC were measured during dark oxidation and photooxidation when Cu(II) was present. Light absorption was enhanced at higher pH during dark oxidation and photooxidation, which indicated that higher quantities and/or more absorbing BrC chromophores were formed at higher pH. The effects that Cu(II) had on the PhC reaction rates and the composition of SOAs and BrC formed depended on the PhC base structure (i.e., benzenediol vs. methoxyphenol). Overall, these results show how aqueous reactions involving Cu(II), H2O2, and PhCs can be an efficient source of daytime and nighttime water-soluble BrC and SOAs, which can have significant implications for how the atmospheric fates of PhCs are modeled for areas with substantial concentrations of water-soluble Cu in highly to moderately acidic cloud/fog water and aqueous aerosols.

Effect of Doping Process Route on LiNiO2 Cathode Active Material Properties

One way to obtain higher energy densities in lithium-ion batteries is to increase the nickel content in lithium nickel-cobalt-manganese oxide (NCM) cathode active materials (CAMs), ultimately approaching LiNiO2 (LNO). At the same time, a higher nickel content and specific capacity comes with more severe degradation of the CAM during battery cycling. Doping of the CAM with additional elements is a common approach to increase structural stability. For any CAM, comparisons of different dopants with each other and with undoped references are therefore commonly found in the literature.[1,2] In some cases, the effect of different dopants on the CAM particle morphology is also reported.[3,4] However, the influence of the process route of dopant introduction is rarely discussed. The most common ways are either the co-calcination of dopant source, lithium source and CAM precursor (pCAM), or the co-precipitation of dopant ions during pCAM precipitation. Impregnating the pCAM surface with a suspension of smaller dopant particles or a dopant solution, followed by solvent removal, can provide better dopant distribution in case of low dopant ion mobility or phase separation tendencies during calcination.Building on the previous finding that the primary particle morphology is the determining factor of LNO performance,[5,6] in this work, the primary particle morphology, but also dopant distribution in a series of 0.25 mol% Zr-doped LNO obtained from the three different process routes co-calcination, impregnation and co-precipitation, is investigated. This low dopant concentration is common in commercial CAM, as thus the content of redox-active transition metal content remains high to provide maximal energy density. Zr also tends to phase separate in the form of Li2ZrO3 at high concentrations, which is this way avoided as much as possible, since the chosen concentration is below the solubility limit of Zr in the LNO bulk. In this comparison, it is found that not the dopant itself, but the process route of its introduction affects the primary particle morphology of LNO, likely explained by the initial dopant localization early in the calcination.Differences in electrochemical performance, both in coin cells and long-term cycled pouch cells, as well as in specific capacitance and gas evolution are then also found to be due not to the dopant, as one would initially assume in comparisons of doped and undoped materials, but to the effect of the process route on LNO primary particle morphology.

(Invited) 2D Mxenes for Energy Storage Applications

MXenes are a family of two-dimensional (2D) transition metal carbides and nitrides, with a general structure of Mn+1XnT x , where M is the transition metal, X is carbon and/or nitrogen, and T represents the surface terminations (F, O, OH). MXenes have attracted attention in a multitude of energy storage applications due to their high electronic conductivity, tunable interlayer spacing, redox-active transition metals, and hydrophilic surface groups. In this talk, we discuss the use of MXene electrodes in supercapacitor applications, including aqueous, non-aqueous, and water-in-salt electrolytes. The variability of MXenes is demonstrated with each electrolyte system showing unique electrochemical responses, not limited to redox and/or intercalation pseudocapacitance, and hydrated cation intercalation. Furthermore, the versatility of the hydrophilic, 2D morphology of MXenes is demonstrated through its use in multiple form factors, not limited to flexible free-standing films, multilayer powder electrodes, interdigitated microsupercapacitors, knitted textiles, and more. New directions and perspectives for MXenes in energy storage are discussed, including MXenes’ use as passive components (separators, current collectors, binders, scaffolds, conductive additives) in energy storage systems. Figure 1 (A) Schematic illustration showing MXenes’ electrochemical properties for ion storage applications. (B) Cyclic voltammetry (CV) data collected at scan rates from 10 to 100,000 mV·s−1 for a 90-nm-thick Ti3C2T x film. (C) Influence of an electrolyte’s solvent on the lithium-ion storage capacity of Ti3C2T x ; CV curves of microporous Ti3C2T x electrode in 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in DMSO, acetonitrile (ACN), or propylene carbonate (PC) electrolytes. (D) A digital photograph showing the wafer scale fabrication of an array of 143 MXene microsupercapacitors. (E) Photograph of a knitted textile with an interdigitated pattern made using Ti3C2T x MXene-coated cotton yarn to produce electrodes for wearable textile supercapacitor.Reference[1] A. VahidMohammadi, J. Rosen, Y. Gogotsi, Science, 2021, 372, eabf1581. Figure 1

Simultaneous Boosting Nitrogen Reduction Activity and Suppressing Hydrogen Evolution Reaction Activity of Transition Metal Oxide Based Electrocatalyst

Ammonia (NH3) is widely served as fertilizer, safer chemical hydrogen storage, and energy conservation materials with an annual production around 200 million tons per year. Currently, NH3 is mainly synthesized via the Haber-Bosch process, which is an extremely energy- and capital-intensive (high temperature 400–500 °C and high pressure 100–350 atm) process, consuming over 1% of the global annual energy output, emitting massive amount of greenhouse gases (~420 Mt CO2 annually), and causing serious concerns with climate change. Electrochemical nitrogen reduction reaction (eNRR) allows NH3 production from nitrogen (N2) and water (H2O) under ambient conditions. Especially if driven by renewable energies, NRR represents a potentially clean and sustainable strategy for replacing the traditional Haber-Bosch process and alleviating climate change effect. One of the most critical fundamental challenges in production of ammonia via electrochemical nitrogen reduction reaction (eNNR) is developing catalysts which are capable to boost eNRR activity and concurrently suppress the overwhelming competitive hydrogen evolution reaction (HER). This work reports a new strategy to develop such catalysts to alleviate this challenge. This new strategy for the first time takes advantage of the outstanding capability of some redox active transition metal oxides (TMOs) in their super capability in electrochemically controlled proton interstitial doping and the associated remarkable structural changes to boost their NRR activity. Further, inspired by their unique hydrogen intercalation determined HER activity, this new strategy introduced cationic substitutional doping of the TMOs with nonmetal elements, such as phosphorus (P), to modulate their proton intercalation behavior, achieving HER suppression. In this work, tungsten oxide nanosheets (WO3) have been exploited as a typical example of such TMOs to demonstrate the feasibility of this innovative strategy. It is found that cationic P doping also accompanies introduction of large quantity of oxygen vacancies (OVs) in the matrix of the WO3 and structural changes of the WO3 lattice. The synergy of the substitutional doping and interstitial doping in tuning the electronic and the local geometric structures leads to significantly enhanced eNNR performance of WO3 nanosheets. An unprecedented high Faradaic efficiency (FE) of 64.1% with NH3 yield of 24.5 µg h-1 has been reached, representing the highest NRR performance for WO3 based catalysts. It is worth mentioning that the P-doped WO3 catalyst (200 nm square with a thickness of 20-40 nm) is much larger than most of the reported catalyst. The catalytic yield is even higher than that achieved with atomic thin two-dimensional (2D) WO3 nanosheets (OV-rich) catalysts (17 µg h-1 with a FE of 7.0%), which is known for their high catalytic efficiency due to the excellent accessibility of all the catalytic active sites. It is also worthwhile to mention that the FE of 64.1% is comparable to that of the natural nitrogenase can be reached (65%), which is unprecedented high compared to most of catalysts reported so far (<25%). In addition, inclusion of Li ions in the electrolyte further increased the NH3 yield to 60.1 µg h-1 with the high FE largely remained, reached the highest eNNR performance for all the TMO based catalysts. Density functional theory calculations further revealed the synergistic role of interstitial doping of H* and substitutional cationic doping of P, and the associated generation of OVs in increasing the electronic states crossing the Fermi level of the WO3 and thus reducing reaction energy barrier in N2 activation and hydrogenation. An interesting non-PCET (proton coupled electron transfer) mechanism is revealed in the first step and the rate determining step during eNNR, providing a new design principle for TMO-based catalysts. Figure 1

Iron and Copper Alter the Oxidative Potential of Secondary Organic Aerosol: Insights from Online Measurements and Model Development.

The oxidative potential (OP) of particulate matter has been widely suggested as a key metric for describing atmospheric particle toxicity. Secondary organic aerosol (SOA) and redox-active transition metals, such as iron and copper, are key drivers of particle OP. However, their relative contributions to OP, as well as the influence of metal-organic interactions and particulate chemistry on OP, remains uncertain. In this work, we simultaneously deploy two novel online instruments for the first time, providing robust quantification of particle OP. We utilize online AA (OPAA) and 2,7-dichlorofluoroscein (ROSDCFH) methods to investigate the influence of Fe(II) and Cu(II) on the OP of secondary organic aerosol (SOA). In addition, we quantify the OH production (OPOH) from these particle mixtures. We observe a range of synergistic and antagonistic interactions when Fe(II) and Cu(II) are mixed with representative biogenic (β-pinene) and anthropogenic (naphthalene) SOA. A newly developed kinetic model revealed key reactions among SOA components, transition metals, and ascorbate, influencing OPAA. Model predictions agree well with OPAA measurements, highlighting metal-ascorbate and -naphthoquinone-ascorbate reactions as important drivers of OPAA. The simultaneous application of multiple OP assays and a kinetic model provides new insights into the influence of metal and SOA interactions on particle OP.

Charge and Solvent Effects on the Redox Behavior of Vanadyl Salen-Crown Complexes.

The incorporation of charged groups proximal to a redox active transition metal center can impact the local electric field, altering redox behavior and enhancing catalysis. Vanadyl salen (salen = N,N'-ethylenebis(salicylideneaminato)) complexes functionalized with a crown ether containing a nonredox active metal cation (V-Na, V-K, V-Ba, V-La, V-Ce, and V-Nd) were synthesized. The electrochemical behavior of this series of complexes was investigated by cyclic voltammetry in solvents with varying polarity and dielectric constant (ε) (acetonitrile, ε = 37.5; N,N-dimethylformamide, ε = 36.7; and dichloromethane, ε = 8.93). The vanadium(V/IV) reduction potential shifted anodically with increasing cation charge compared to a complex lacking a proximal cation (ΔE1/2 > 900 mV in acetonitrile and >700 mV in dichloromethane). In contrast, the reduction potential for all vanadyl salen-crown complexes measured in N,N-dimethylformamide was insensitive to the magnitude of the cationic charge, regardless of the electrolyte or counteranion used. Titration studies of N,N-dimethylformamide into acetonitrile resulted in cathodic shifting of the vanadium(V/IV) reduction potential with increasing concentration of N,N-dimethylformamide. Binding constants of N,N-dimethylformamide (log(KDMF)) for the series of crown complexes show increased binding affinity in the order of V-La > V-Ba > V-K > (salen)V(O), indicating an enhancement of Lewis acid/base interaction with increasing cationic charge. The redox behavior of (salen)V(O) and (salen-OMe)V(O) (salen-OMe = N,N'-ethylenebis(3-methoxysalicylideneamine) was also investigated and compared to the crown-containing complexes. For (salen-OMe)V(O), a weak association of triflate salt at the vanadium(IV) oxidation state was observed through cyclic voltammetry titration experiments, and cation dissociation upon oxidation to vanadium(V) was identified. These studies demonstrate the noninnocent role of solvent coordination and cation/anion effects on redox behavior and, by extension, the local electric field.

Porous activated carbon and highly redox active transition metal sulfide by employing multi-synthesis approaches for battery-supercapacitor applications

Transition metal sulfide due to high theoretical capacity, large active sites, non-toxic and higher conductivity make them more favorable for energy storage applications. Therefore, we have synthesized Nickel sulfide by employing multiple approaches to study their electrochemical properties and utilized it for practical applications. Initially, the sample was confirmed by performing X-ray diffraction and scanning electron microscope. The hydrothermally synthesized electrode obtained specific capacity (Qs) of 434.16C/g at 1.6 A/g compared to its counterpart. Owing to maximum capacity, this electrode was assembled in two electrode configurations to explore their hybrid performance. The NiS//AC results in Qs of 261.6C g−1 at 1.5 A/g with great capacity retention of 86.7 % after testing for 10,000 GCD cycles. Furthermore, the device has revealed astonishing specific energy of 61.76 Wh/kg and power of 1275 W/kg. These experimental outcomes were investigated by using the Dunn's model to extract the capacitive part from the diffusive, demonstrating the nature of (NiS//AC) hybrid device. Moreover, Power's law was employed to validate the assembled device behavior by evaluating b values. In sum, it appears promising to utilize the suggested NiS//AC with elevated performance and great stability as anode material in hybrid supercapacitors.

150 Keynote: A New Aerosol Mass-Spectrometer for Simultaneous Detection of Health-Relevant Polycyclic Aromatic Hydrocarbons, Soot and Inorganic Components from Individual Airborne Particles

Abstract Air pollution by fine particles represents a severe environmental health-risk. The particle’s content of toxic compounds, such as polycyclic aromatic hydrocarbons (PAH), elemental carbon/soot or redox-active transition metals (e.g. Fe), is highly relevant for their toxicity. The particulate matter (PM) composition can be determined by chemical analysis of PM-loaded filter samples but no information on the mixing state of toxicants, i.e. the distribution of toxicants within the particle ensemble, is obtainable by this approach. The mixing state, however, is a crucial parameter to assess health effects as the toxicants may either be equally distributed over many particles (internally mixed) or could be highly concentrated within a small particle sub-population (externally mixed). In the latter case, the few particles with a very high concentration of toxicants can induce stronger cellular effects at the lung-deposition site. A new approach is based on single particle mass spectrometry (SPMS) but introduces a novel, tailored laser ionisation process. Aerosol particles are on-line sampled from the air and size-characterized by laser velocimetry. The organic coating of individual particles is desorbed by intense IR-laser pulses and subsequently the relevant toxicants (transition metals, PAH and soot) are ionized and MS-detected particle-by-particle, using a novel combined UV-laser ionization scheme (Schade et al. Anal., Chem. 2019; Passig et al. ACP 2022). The novel SPMS system offers the characterisation of the most relevant PM-toxicants (soot, metals, PAH) on a sized-resolved, single particle-basis and gives insight into their mixing state. First SPMS-ambient air monitoring results for PAH or metals show that, depending on conditions, the toxicants indeed either are concentrated on a very small fraction of the particle-ensemble or are rather uniformly distributed over all particles. Future application concepts of the new SPMS-technology in air monitoring and environmental health research are discussed.

Applications of Spent Lithium Battery Electrode Materials in Catalytic Decontamination: A Review

For a large amount of spent lithium battery electrode materials (SLBEMs), direct recycling by traditional hydrometallurgy or pyrometallurgy technologies suffers from high cost and low efficiency and even serious secondary pollution. Therefore, aiming to maximize the benefits of both environmental protection and e-waste resource recovery, the applications of SLBEM containing redox-active transition metals (e.g., Ni, Co, Mn, and Fe) for catalytic decontamination before disposal and recycling has attracted extensive attention. More importantly, the positive effects of innate structural advantages (defects, oxygen vacancies, and metal vacancies) in SLBEMs on catalytic decontamination have gradually been unveiled. This review summarizes the pretreatment and utilization methods to achieve excellent catalytic performance of SLBEMs, the key factors (pH, reaction temperature, coexisting anions, and catalyst dosage) affecting the catalytic activity of SLBEM, the potential application and the outstanding characteristics (detection, reinforcement approaches, and effects of innate structural advantages) of SLBEMs in pollution treatment, and possible reaction mechanisms. In addition, this review proposes the possible problems of SLBEMs in practical decontamination and the future outlook, which can help to provide a broader reference for researchers to better promote the implementation of “treating waste to waste” strategy.

Progress and challenges of Prussian blue analogs for potassium-ion batteries: a perspective on redox-active transition metals

This review comprehensively introduces recent researches on Prussian blue analogs (PBAs) for potassium-ion batteries (PIBs) in the perspective of redox-active transition metals. Some strategies are put forward for future development of PBAs.