Transition Metal Ions Research Articles

Revealing the degradation pathways of layered Li-rich oxide cathodes.

Layered lithium-rich transition metal oxides are promising cathode candidates for high-energy-density lithium batteries due to the redox contributions from transition metal cations and oxygen anions. However, their practical application is hindered by gradual capacity fading and voltage decay. Although oxygen loss and phase transformation are recognized as primary factors, the structural deterioration, chemical rearrangement, kinetic and thermodynamic effects remain unclear. Here we integrate analysis of morphological, structural and oxidation state evolution from individual atoms to secondary particles. By performing nanoscale to microscale characterizations, distinct structural change pathways associated with intraparticle heterogeneous reactions are identified. The high level of oxygen defects formed throughout the particle by slow electrochemical activation triggers progressive phase transformation and the formation of nanovoids. Ultrafast lithium (de)intercalation leads to oxygen-distortion-dominated lattice displacement, transition metal ion dissolution and lithium site variation. These inhomogeneous and irreversible structural changes are responsible for the low initial Coulombic efficiency, and ongoing particle cracking and expansion in the subsequent cycles.

Synthesis and Characterization New 1, 2, 4-Triazole Derivative and Its Complexes with Some Transition Metal Ions

An innovative class of ligand compounds using The ions of transition metals (Cr(III), Fe(III), and Ni(II)).The ligand N,N'-(4H-1,2,4-triazole-3,5-diyl)bis(4-methoxybenzamide) was produced by reacting 2,5-di amino-1,2,4-triazole with two moles of methyl 4-methoxybenzoate in the presence of ethanol and a few drops of glacial acetic acid. The recently produced chemicals were studied using a battery of analytical tools, analysis of elements (C, H, and N), nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, mass spectrometry, and atomic absorption are some of the techniques that are included. The aforementioned diagnostic procedures led to the formation of ligand-containing octahedral complexes with (Fe and Cr) ions and a square planer complex with nickel.

The effect of complex formation on the static and frequency-dependent nonlinear optical properties: A combined experimental and theoretical investigation

A novel mixed ligand Mn(II) complex of 6-Bromopyridine-2-carboxylic acid (6Brpca) and 4,4′-dimethyl-2,2′-dipyridyl has been prepared and structurally characterized using single-crystal X-ray diffraction. The spectroscopic properties were also analyzed by using FT-IR and UV–Vis spectral techniques. The coordination complexes having transition metal ions are known to have promising optical nonlinearity behavior. Therefore, B3LYP level density functional theory was used to investigate first- and second-order hyperpolarizabilities (β and γ) and provide a deep understanding of the relation between the structure and NLO properties. The calculations of frequency-dependent α, β, and γ at frequencies of ω = 0.0856252 and 0.0428126 au. for 6Brpca and Dmdpy ligands as well as Mn(II) complex have been also carried out using B3LYP/LanL2DZ level. Especially second harmonic generation (SHG) first and second hyperpolarizabilities (β(−2ω;ω,ω) and γ (−2ω;ω,ω,0)) parameters for Mn(II) complex have been calculated as 11448 × 10−30 and 680035 × 10−36 esu, respectively. It has been determined that there is a tremendous increase in β and γ parameters when 6Brpca and Dmdpy ligands coordinate to the high spin multiplicity Mn(II) ion. Theoretical calculations revealed that the large first- and second-order hyperpolarizabilities are caused by strong intramolecular charge transfer between the transition metal and the coordinated ligands. These results indicate that the the organometallic complex under investigation is valuable candidate for optoelectronic and photonic applications.

MnFe Prussian Blue Analogue Open Cages for Sodium-Ion Batteries: Simultaneous Evolution of Structure, Morphology, and Energy Storage Properties.

Prussian blue analogues (PBAs) exhibiting hollow morphologies have garnered considerable attention owing to their remarkable electrochemical properties. In this study, a one-pot strategy is proposed for the synthesis of MnFe PBA open cages. The materials are subsequently employed as cathode electrode in sodium-ion batteries (SIBs). The simultaneous evolution of structure, morphology, and performance during the synthesis process is investigated. The findings reveal substantial structural modifications as the reaction time is prolonged. The manganese content in the samples diminishes considerably, while the potassium content experiences an increase. This compositional variation is accompanied by a significant change in the spin state of the transition metal ions. These structural transformations trigger the occurrence of the Kirkendall effect and Oswald ripening, culminating in a profound alteration of the morphology of MnFe PBA. Moreover, the shifts in spin states give rise to distinct changes in their charge-discharge profiles and redox potentials. Furthermore, an exploration of the formation conditions of the samples and their variations before and after cycling is conducted. This study offers valuable insights into the intricate relationship between the structure, morphology, and electrochemical performance of MnFe PBA, paving the way for further optimizations in this promising class of materials for energy storage applications.

A Review on Synthesis and Biological Activities of 2‐Aminophenol‐Based Schiff Bases and Their Transition Metal Complexes

ABSTRACT2‐Aminophenol‐based Schiff bases and their metal complexes have drawn a lot of interest because of their wide range of biological activity and their uses in several fields. These Schiff bases are synthesized through the condensation of 2‐aminophenol and various carbonyl compounds, and metal complexes formed easily by coordinating Schiff bases with transition metal ions possess a wide range of intriguing properties that have rendered them promising candidates in biomedical research. These compounds have a diverse array of captivating biological properties including antibacterial, antifungal, anticancer, and antioxidant actions. Their versatile nature and potential for tailored modifications hold the promise for innovative biomedical applications. Compared to standard antibiotics and other studied compounds, C2, C8–C11, and C116 complexes, along with L16 and L17 ligands, exhibit the highest antibacterial activity, while C3 and C115 complexes demonstrate the highest antifungal activity. The metal chelate formation of the ligands enhanced the antimicrobial activity by increasing their lipophilic nature. C66, C76, and C112 complexes and L39 ligand showed higher anticancer activity than standard anticancer drugs. The metal complexes have higher anticancer activity than the ligand due to improved permeability and cellular uptake. The anticancer activity of the complexes is related to the substituents of the Schiff base ligands. In compounds containing an electron‐withdrawing group (e.g., Cl or Br or NO2), the activity is obviously better than others. Ligands L1–L3 and L5, L6, and L32 demonstrated the most potent antioxidant activity, surpassing both metal complexes and standard conventional antioxidants. The ligands showed greater antioxidant activity than the metal complexes due to their capability of donating free protons to scavenge free radicals. More study is needed to fully explore the potential of 2‐aminophenol‐based Schiff bases and their transition metal complexes for the development of new drugs. This review summarizes different synthetic methods, biological activities, and the structure–activity relationship. This study aims to conduct further research on 2‐aminophenol‐based Schiff bases and their metal complexes.

Effect of doping of metal salts on polymers and their applications in various fields

Abstract Transition metal compounds (TMCs) provide the benefits of vast reserves, affordability, non-toxicity, and environmental friendliness, making them highly sought-after in recent times. Integrating transition metal salts into polymers may result in substantial enhancements in optical and electrical characteristics, making them appealing for many applications. Transition metal ions may display a range of electronic transitions, which enables the adjustment of absorption and emission spectra. This characteristic has significant value in applications such as light-emitting devices (LEDs) and sensors. The photoluminescence of polymers may be improved by the addition of transition metal salts, which results in light emission that is both more brilliant and more efficient. On the other hand, this is advantageous for screens and optoelectronic devices. The presence of transition metal salts in polymers may help to improve their optical stability, hence lowering the probability that the polymers will degrade or change color over time. When it comes to the performance of optical devices over the long run, this is quite essential. Elevating the electrical conductivity of polymers is possible via the use of transition metal salts. This is very helpful in the process of developing conductive polymers for use in applications such as electronic fabrics, organic solar cells, and flexible electronic devices. Transition metal salts can affect the electrical band structure of polymers, which enables the band gap of the material to be tuned. This is very necessary in order to maximize the amount of light that is absorbed by photovoltaic devices. Through having all these benefits, we conducted a review to find out the effects on polymeric materials.

Synthesis of metal-doped covalent triazine frameworks: Incorporation into 6FDA-Durene polyimide for CO2 separation through mixed matrix membranes

The development of advanced mixed matrix membranes (MMMs) is expanding through the design of functionalized materials and efficient hybrid mass transfer mechanisms to meet the growing needs for practical and cost-effective gas separation technologies. Here, a novel series of transition metal-doped covalent triazine frameworks (M2+CTFs) was synthesized and incorporated into a 6FDA-Durene polyimide (PI) matrix in the range of 0–0.5 wt% to prepare cost-effective facilitated transport MMMs with high CO2 separation performance. Qualitative and quantitative analyses including FTIR, XPS, CHN, XRF, BET, XRD, TGA, DLS, FESEM, EDX, and TEM were carried out. The presence of nucleophilic N sites and electron-rich heterocycles in highly porous CTFs (through the π–π-stacking interactions with CO2 molecules), together with transition metal ions (Fe2+, Cu2+, and Zn2+) as the fixed site active carriers (with strong CO2 facilitated transport through the π complexation/decomplexation reaction), improves the affinity for CO2 molecules, facilitates their transport, and subsequently increases the CO2/non-polar gas selectivity of MMMs. The resultant M2+CTF/PI MMMs successfully surpass the 2008 upper bound at filler loading of 0.4 wt% for CO2/CH4 and CO2/N2 separations. Embedding M2+CTFs into the PI matrix improves the mechanical properties of the membranes. The Zn2+CTF/PI MMM represents the best separation performance with a CO2 permeability of 1408 Barrer, a CO2/N2 selectivity of 37, and a CO2/CH4 selectivity of 39, which represents a 120 %, 111 %, and 110 % increase compared to the neat PI membrane at a feed pressure of 2 bar. The excellent results of the present study indicate the high potential of cost-efficient synthesized M2+CTF particles and related facilitated transport MMMs for possible application in industrial processes.

Electronic and magnetic phase diagram of Sr2FeO4 at high pressure: A synchrotron Mössbauer study

Transition metal (TM) oxides with high oxidation state TM ions exhibit a variety of unconventional electronic and magnetic states owing to electron correlations effects combined with highly covalent TM–O bonding. Here, we have studied the pressure dependence of electronic state and magnetism of the K2NiF4-type iron(IV) oxide Sr2FeO4 up to 89 GPa by temperature and magnetic field dependent energy-domain synchrotron Mössbauer spectroscopy and derived a (P,T) magnetic phase diagram. Considering also previous resistance studies [Rozenberg , ] several magnetic and electronic regimes with increasing pressure can be identified. Near 7 GPa, the insulating cycloidal antiferromagnetic low-P state is transformed into a semiconducting ferromagnetic state and the magnetic ordering temperature Tm increases from 55 K at ambient pressure to about 100 K at 13 GPa. Between 18 and about 50 GPa the system is ferromagnetic and metallic (FMM) with a strong rise of Tm to above room temperature (RT). Contrary to a recent theoretical study [Kazemi-Moridani , ], the FMM state is attributed to a high-spin t2g3eg1 electronic state with itinerant eg coupled to more localized t2g electrons. Between 50 and 89 GPa a doublet with large quadrupole splitting in the RT Mössbauer spectra indicates a partial high-spin to low-spin (t2g4) transition leading to a decrease in Tm again. The general features of the (P,T) phase diagram of Sr2FeO4 are comparable to those of other simple and A-site ordered iron(IV) perovskite-related oxides with the peculiarity that Sr2FeO4 adopts an insulating state without charge disproportionation of Fe4+ in the low-P region. The high-pressure behavior of Sr2FeO4 and other iron(IV) oxides may be relevant for exploring the role of Hund's physics in multiorbital systems and contributing to the understanding of the electronic situation in unconventional superconductors such as La3Ni2O7 and Sr2RuO4. Published by the American Physical Society 2024

Tailoring structural and optical properties of Ti1-xMxO2 (M = Fe, Co, Ni, Cu, and Zn) nanoparticles for enhanced antimicrobial activity: a sol-gel synthesis study

Titanium dioxide (TiO2) nanoparticles possess intriguing properties and have been extensively utilized in medical applications due to their exceptional antimicrobial characteristics. The antimicrobial efficacy can be heightened by altering the structural morphology, size, and optical properties through the introduction of transition metal ions (M: Fe, Co, Ni, Cu, and Zn) with a concentration of x = 0.02 into TiO2, thereby producing Ti1 -xMxO2 powder via the sol-gel method at a sintering temperature ranging from 500 °C to 600 °C. The morphological characteristics of Ti1 - xMxO2 were analyzed using FT-IR, UV-DRS, XRD, TGA, BET, and SEM-EDAX techniques. Substituting M-doped TiO2 at a sintering temperature of 500 °C results in all doping ions yielding the Ti1 -xMxO2 anatase phase. Conversely, at 600 °C, the doping ions M: Cu, Co, Zn exhibit a tendency to substitute the TiO2 structure, destabilizing the anatase phase and leading to the formation of an anatase-rutile dual phase with larger crystal size. At elevated temperatures, ions with larger radii than Ti (0.61), namely Cu (0.73), Co (0.75), and Zn (0.74), tend to be substituted, thereby altering the structure of TiO2. The antimicrobial efficacy, evaluated based on the inhibition zone, demonstrates that Ti1 -xMxO2 effectively inhibits the cellular activity of Salmonella typhimurium (Gram -) and Staphylococcus aureus (Gram +) bacteria compared to TiO2.

Incorporating Transition Metal Ions into Uranium Oxide Hydrates: The Role of Zn(II) and the Effect of the Addition of Cs(I) Ions.

The synthesis of two zinc-bearing uranium oxide hydrate (UOH) materials has been achieved, and their crystal structures, obtained via single-crystal X-ray diffraction using synchrotron radiation, and additional structural and spectroscopic properties are reported herein. Although both structures incorporate Zn2+ cations, the two differ significantly. The compound Zn2(OH)2(H2O)5[(UO2)10UO14(H2O)3] (UOHF-Zn), forming a framework-type structure in the P1̅ space group, was composed of β-U3O8 layers pillared by uranyl polyhedra, with the Zn2+ cations incorporated within the framework channels. In contrast, the compound Cs2Zn(H2O)4[(UO2)4O3(OH)4]2·3H2O (UOH-Zn) crystallized in the Cmc21 space group with a schoepite-like uranyl oxide hydroxide layered topology and both Zn2+ and Cs+ cations making up the interlayer species. The apparent driving force for the differences in the structures was the change from KOH to CsOH during synthesis, with the smaller K+ ions excluded in lieu of a higher proportion of Zn2+ (U/Zn ratio of 5.5:1) in UOHF-Zn, whereas in UOH-Zn, the larger Cs+ ions were preferentially incorporated at the expense of fewer Zn2+ cations (U/Cs/Zn ratio of 8:2:1). Highlighted in this work is the effect of the chemical species and, in particular, their ionic radius on UOH formation, further improving the understanding of UO2 alteration in the setting of deep geological repositories.

Effect of additives on the photocatalytic degradation of malachite green using NiS:Tb3+ nanoparticle and their photoluminescence properties

The contamination of wastewater with synthetic dyes presents a critical challenge, highlighting the need for advanced technologies and approaches to effectively manage, treat, and remediate polluted wastewater and mitigate its adverse environmental and health impacts. This study focuses on the photocatalytic degradation of malachite green dye, a widely used synthetic dye, using nickel sulfide nanoparticles doped with Tb3+ ions. The objective is to explore the potential of this approach in breaking down the dye into harmless components, thereby reducing its toxicological impacts on the environment and human health. The catalyst was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photoluminescence spectroscopy (PL), X-ray photoelectron spectroscopy (XPS), and ultraviolet-visible spectroscopy (UV). The effects of pH levels and various additives, including transition metals, inorganic oxidants, and inorganic anions, on the degradation process were systematically examined. The results demonstrate a high degradation efficiency of 94 % within 90 min, highlighting the efficacy of the photocatalytic process. Notably, adding transition-metal ions and inorganic oxidants enhanced the degradation rate, whereas inorganic anions had an inhibitory effect. Furthermore, an artificial neural network (ANN) model was developed to predict the degradation rate, demonstrating a strong correlation between experimental data and predicted values. This study provides valuable insights into optimizing photocatalytic degradation processes. It showcases the potential of ANN modelling in predicting the photocatalytic activity of nickel sulfide nanoparticles doped Tb3+ in the presence of various additives.

Metal Ion Modulated Electron Transfer in Metalloviologen Compounds: Photochromism and Differentiable Amine Detection.

Different types of electron transfers (ETs) underlie the versatile use of various solid viologen-derived compounds, which is still insufficiently understood and difficult to control. Here, we demonstrate an effective strategy for modulating the key ET process in crystalline metalloviologen compounds (MVCs). By adjusting the coordinated transition metal ions bearing different electronic structures (e.g., d5, d7, d10), three MVCs (i.e., Mn-1, Co-2, and Cd-3) with highly consistent coordination environments have been synthesized successfully. Surprisingly, whether the photochromism (energy-induced ET mechanism) or the specific analyte recognition (molecule-induced ET mechanism), compound Cd-3 exhibits obvious photochromic behavior and differential dimethylamine detection. Combined detailed structural analysis with theoretical calculations, such unique ion-dependent properties, were correlated to the fine modulation of the electron density of the bipyridinium cores by metal ions. Additionally, thanks to the delicate recognition of dimethylamine vapor, a convenient test strip Cd-3-PAN was prepared as a sensitive biogenic amine sensor for evaluating the real-time freshness of seafood.

Polyoxometalate-Ionic Liquids for Mitigating the Effects of Iron Gall Ink Corrosion on Cellulosic Supports.

Iron gall ink (IGI), renowned for its indelibility, was the most important writing ink in the Western world from the 15th to the late 19th century. However, it is now known that IGIs induce acid-catalyzed hydrolysis and iron-catalyzed oxidation of the cellulose in historical paper documents. These mechanisms of deterioration cause significant damage to the writing support materials, including color alteration and burn-through appearance, and in the worst scenarios, physical disintegration of the supports. Minimally invasive, long-term effective conservation treatments that tackle the underlying mechanisms of IGI degradation and their corrosion effects are yet to be developed. This study introduces the deployment of hydrophobic and anticorrosive polyoxometalate-ionic liquids (POM-ILs) as colorless coatings to counteract IGI-corrosion of cellulosic supports. Model IGI-containing papers (mockups) were prepared, coated with POM-ILs, and artificially aged to assess the compatibility of POM-ILs with IGI-containing documents. Comprehensive monitoring using colorimetric and scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM/EDS) analyses showed minimal interference with the aesthetic properties and morphology of the IGI mockups. In addition, polyoxometalates (POMs) with vacant metal atom sites in the cluster shell can be used to coordinate free transition metal ions. The ability of a monolacunary Keggin-type polyoxotungstate to coordinate free Fe(II) from IGI solution was demonstrated using UV-vis analysis. This led to the formation of a dimeric species, [(SiW11O39Fe)2O]K12·28H2O, which was characterized by single-crystal X-ray diffraction. Altogether, this study points to POM-ILs as promising protective coatings for effectively preserving historical IGI-written heritage.

Modulating the isomerization of bpp-modified azoheteroarene by transition metal ions coordination

A new photoswitchable azoheteroarene L was design and synthesized by replacing one of the phenyl rings of azobenzene moiety with a 2,6-di[pyrazol-1-yl]pyridine(bpp) unit. The assembly of L with transition metal ions results in the formation of three metal complexes, namely, M(L)2(OTf)2 (M=ZnII, FeII and CoII). These complexes are fully characterized by ESI-TOF-MS, UV–vis spectrum, 1H NMR spectrum and single-crystal X-ray diffraction. Upon irradiation with 380 nm light, L exhibits excellent E to Z photoisomerization in solution, achieving up to 82 % Z-configuration with a thermotropic isomerization half-life time of 301 days. After coordination with ZnII, FeII and CoII, the photoisomerization properties of L were significantly varied. Coordinating with the ZnII ion, the conversion of Z-L slightly decreased from 82 % to 77 %. However, this coordination significantly extends thermal isomerization half-life time to 564 days, resulting in a 1.9-fold enhancement compared to free Z-L. In contrast, the coordination with open-shell transition metal ions FeII and CoII noticeably inhibits the formation of Z-L and only yields E-L isomers. Moreover, the spin-crossover behavior of Fe(E-L)2(OTf)2 was also investigated. The analysis of variable temperature NMR indicates that Fe(E-L)2(OTf)2 shows a spin transition temperature of 265 K in solution. This work provides valuable insights into tunning conformational transitions of azoheteroarene molecules.

Molecular Origins of Near-Infrared Luminescence in Molybdenum and Tungsten Oxyhalide Perovskites.

Materials with near-infrared (near-IR) luminescence are desirable for applications in communications and sensing, as well as biomedical diagnostics and imaging. The most used inorganic near-IR emitters rely on precise doping of host crystal structures with select rare-earth or transition metal ions. Recently, another class of materials with intrinsic near-IR emission has been reported. The compositions of these materials were initially described as vacancy-ordered halide double perovskites Cs2MoCl6 and Cs2WCl6, but further investigation by some of us on the compound reported as Cs2WCl6 revealed an oxyhalide instead, with a composition Cs2WO x Cl6-x , where 1 < x < 2. Here we demonstrate that the Mo compounds similarly possess the composition Cs2MoO x Cl6-x or Cs2MoO x Br6-x where 1 < x < 2. Preparing the pure halide appears harder for Mo than for W, and we have not succeeded in doing so. The distinctly different composition requires the coordination environment and oxidation state for the Mo and W centers to be reconsidered from what was assumed for the pure halides. In this work, we examine the mechanism for near-IR emission in these materials given their true structures and compositions. We demonstrate that the luminescence is due to the specific d-orbital splitting caused by the presence of oxygen in the distorted [MOX5]2- octahedra (X is Cl or Br). The fine structure in the emission spectra at low temperatures has been resolved and is attributed to vibronic coupling to the Mo-O and W-O bond stretches. Understanding the true structure and composition of these interesting materials, besides explaining the near-IR luminescence, suggests how this desirable emission can be realized and manipulated.

Upconversion nanoparticles-CuMnO2 nanoassemblies for NIR-excited imaging of reactive oxygen species in vivo

Here, we designed a ratiometric luminescent nanoprobe based on lanthanide-doped upconversion nanoparticles-CuMnO2 nanoassemblies for rapid and sensitive detection of reactive oxygen species (ROS) levels in living cells and mouse. CuMnO2 nanosheets exhibit a wide absorption range of 300–700 nm, overlapping with the visible-light emission of upconversion nanoparticles (UCNPs), resulting in a significant upconversion luminescence quenching. In an acidic environment, H2O2 can promote the redox reaction of CuMnO2, leading to its dissociation from the surface of UCNPs and the restoration of upconversion luminescence. The variation in luminescence intensity ratio (UCL475/UCL450) were monitored to detect ROS levels. The H2O2 nanoprobe exhibited a linear response in the range of 0.314–10 μM with a detection limit of 11.3 nM. The biological tests proved the excellent biocompatibility and low toxicity of obtained UCNPs-CuMnO2 nanoassemblies. This ratiometric luminescent nanoprobe was successfully applied for the detection of exogenous and endogenous ROS in live cells as well as in vivo ROS quantitation. The dual transition metal ions endow this probe efficient catalytic decomposition capabilities, and this sensing strategy broadens the application of UCNPs-based nanomaterials in the field of biological analysis and diagnosis.

Simple generic self-assembly fabrication of transition metal borates on polyaminophenylboric acid modified foam nickel for highly-efficient overall water splitting

Water electrocatalysis for hydrogen production as a prospect strategy to store renewable energy and reduce carbon emissions has attracted great attention, and exploring water electrolysis catalysts has become a research hotspot for widespread industrial water electrolysis application. Very recently, transition metal borates have been demonstrated great potential for electrocatalytic hydrogen or oxygen evolution in alkaline media. However, a generic method for fabricating transition metal borates as bifunctional oxygen catalysts are still challenging. Herein, through a two-step process including poly-aminophenylboronic acid electrodeposition and subsequent electrostatic self-assembly of transitional metal ions, for the first time, to our best knowledge, a simple and generic approach to fabricate polyaminophenylborate transition metal salt modified nickel foam electrodes (PAB-M/NF, M represents transition metal element) was developed for highly efficient water splitting. As a proof of concept, the obtained PAB-Ru/NF exhibited remarkable bifunctional HER and OER catalytic activities and stability in alkaline medium. To drive the HER and OER with a current density of 10 mA cm−2 in 1 M KOH electrolyte, PAB-Ru/NF only required an overpotential of 14 mV and 301 mV, respectively. Moreover, even at a great current density of 250 mA cm−2, PAB-Ru/NF can exhibit very favorable long-term stability for over 35 h. When assembled into an electrolyzer with PAB-Ru/NF as both the anode and cathode, a current density of 10 mA cm−2 can be achieved at a very low cell voltage of 1.50 V. In addition, the other PAB-M/NF catalysts (M including but not limited to Fe, Co and Ni) prepared by the same way also show excellent bifunctional HER and OER catalytic activities and durability. This study provides a prospective and economically feasible generic approach for developing practical bifunctional catalysts for industrial water electrolysis.

Disentangling the Ligand and Electronic Structure in KVPO4F1-XOx Positive Electrode Materials by Valence-to-Core X-Ray Emission Spectroscopy

Among all positive electrode materials for K-ion batteries (KIBs), KVPO4F offers a high theoretical capacity of 131 mAh·g-1 and an average working potential reaching above 4.3 V vs K+/K, resulting in a theoretical energy density of up to 520 Wh·kg-1. [1] The anionic substitution of fluorine by oxygen in KVPO4F1-xOx (x = 0, 0.25, 0.5, 0.75, 1) induces an increasing working potential by activating the V3+/4+ and V4+/5+ redox couples and replacing the VO4F2 “ionic” entity by {V=O}O5 unit with a highly “covalent” vanadyl-type bond. [2] The accurate prediction of the electrode potential as well as the understanding of the mechanisms involved upon cycling requires the determination of how the coordination environment of the transition metal ion influences the ionicity/covalency of the metal-ligand bonds and thus the electronic structure. Nevertheless, discriminating these ligands remains a challenge due to the limited sensitivity to light elements of common characterization techniques such as X-ray diffraction and extended X-ray absorption fine structure. Despite the valuable information from these techniques, fundamental concerns still need to be addressed which include: i) the implication of the covalent V=O vanadyl bond in the electronic structure; ii) the difference of Vcis and Vtrans, the two different sites for V, in the electronic configuration of the material; and finally, (iii) the impact of F/O ligands on the electrochemical mechanism upon battery cycling.To address this issue, we employed valence-to-core Kβ X-ray emission spectroscopy (VtC XES) combined with ab initio modelling and conducted a systematic investigation of KVPO4F1-xOx: two distinct regions were identified in the spectra, Kβ" and Kβ2,5, which are critical to probe the electronic structure close to the Fermi level and to discriminate different ligands coordinated with the vanadium atoms. [3] Our approach allows distinguishing in KVPO4F1-xOx the contributions of V-F, V-O, and V=O bonds, with intensities at the Kβ" region highly correlated to the F- and O2- anionic composition. Additionally, the evolution of the features at the Kβ2,5 region is highly associated to the presence of short V=O bonds, strongly influencing the electrode potential of the material.Overall, we present a detailed and reliable approach for understanding the occupied electronic states of the electrode material, proving valuable for a thorough comprehension of the structural and redox mechanisms involved in batteries.AcknowledgementThis work was supported by the DESTINY Marie Skłodowska-Curie Actions COFUND PhD Programme (Grant Agreement #945357) co-funded by the European Union's Horizon2020 research and innovation program and the Synchrotron SOLEIL. ANR is also acknowledged for funding the RS2E network through the STORE-EX Labex Project ANR-10-LABX-76-01, and the ANR TROPIC project ANR-CE05-0026. Alistore-ERI network is also acknowledged.

Proton Activity and Pathway in Aqueous Organic Redox Flow Battery Electrolyte

Aqueous soluble organic (ASO) redox-active materials have recently shown great promise as alternatives to transition metal ions employed as energy-bearing active materials in redox flow batteries for large-scale energy storage because of their structural tunability, cost-effectiveness, availability, and safety features. However, development so far has been limited to a small palette of organics that are aqueous soluble. This presentation will use fluorenone as an example to showcase how a natively redox-inactive molecule can be tuned to possess two-electron redox reversibility through hydrogenation and dehydrogenation. The modified fluorenone molecules demonstrated high energy density and recorded stable cycling. Furthermore, research has shown the unique chemical-electrochemical coupled redox reactions mechanism; thus, the system rate capabilities can be improved by incorporating suitable hydrogen acceptors that regulate the proton pathway for faster kinetics.Reference:Feng et al., Science 372, 836–840, 2021Feng et al., Joule 7, 1–14, 2023

(Invited) Highly Water-Soluble Fullerene Derivatives for Durable Polymer Electrolyte Membrane Fuel Cells

Recently, the focus of proton-exchange membrane fuel cell (PEMFC) applications has shifted from fuel cell vehicles (FCVs) to heavy-duty vehicles (HDVs), necessitating enhanced fuel cell durability. The degradation of carbon-supported metal nanoparticle catalysts and electrolyte membranes are the primary factors responsible for fuel cell durability. Particularly in the context of HDVs, augmenting the chemical stability of electrolyte membranes, such as Nafion, stands as a crucial factor in improving fuel cell lifetime. The degradation mechanism of Nafion is believed to involve the cleavage of polymer chains by OH∙ radicals, formed by crossover hydrogen and crossover oxygen in the presence of trace transition metal ions. A common strategy to mitigate Nafion's chemical degradation involves adding radical quenchers like cerium ion (Ce+) to Nafion. However, Ce+ may migrate out of Nafion during fuel cell operation, leading to a decline in its highly efficient radical quenching ability over extended operational periods.In this study, we demonstrate that a fullerene-derived radical quencher with multiple hydroxy groups significantly contributes to enhancing the durability of Nafion. Our approach involves synthesizing fullerene derivatives with various kind of hydroxy and functional groups for remarkable water solubility to realize their homogeneous dispersion within the Nafion membrane. The abundant functional groups also aid in improving proton conductivity. Moreover, the chelating effect of the spherically distributed functional groups immobilizes themselves, preventing any observed leakage from the Nafion membrane. These fullerene-derivative radical quenchers effectively enhance fuel cell durability and hold promise for future applications in HDVs.This study was supported by the New Energy and Industrial Technology Development Organization (NEDO), Japan (JPNP20003).