Ionic Electronegativity Research Articles

Inductive effect of cationic equivalent substitution tuning europium valence in Na2Zr1-xHfxSiO5:Eu phosphors for WLEDs

The realization of Eu3+ reduction and its reduction mechanism have become focal points in the field of WLED phosphor research. In this study, the reduction of Eu3+ was successfully achieved through cationic substitution strategy by replacing Zr4+ with Hf4+ in Na2ZrSiO5:Eu3+. The effects of substituting Hf4+ for Zr4+ on the phase, crystal structure, and luminescence properties of Na2Zr1-xHfxSiO5:Eu0.03 (0 ≤ x ≤ 1) were thoroughly investigated based on Rietveld refinement, spectral data, DFT calculation and electronegativity of ions. Comprehensive consideration was given to the effect of site size change and site reducibility on Eu3+ reduction. The results demonstrate that the reduction of Eu3+ in Na2Zr1-xHfxSiO5:Eu0.03 is attributed to the alteration in inducible effect caused by cationic substitution and the enhancement in site reducibility rather than changes in site size. Therefore, the cationic substitution strategy based on induction effect presents a novel approach for achieving Eu3+ reduction and offers a new insight into developing and modifying Eu2+-activated phosphors.

Stabilizing Highly Active Ru Sites by Electron Reservoir in Acidic Oxygen Evolution.

Proton exchange membrane water electrolysis is hindered by the sluggish kinetics of the anodic oxygen evolution reaction. RuO2 is regarded as a promising alternative to IrO2 for the anode catalyst of proton exchange membrane water electrolyzers due to its superior activity and relatively lower cost compared to IrO2. However, the dissolution of Ru induced by its overoxidation under acidic oxygen evolution reaction (OER) conditions greatly hinders its durability. Herein, we developed a strategy for stabilizing RuO2 in acidic OER by the incorporation of high-valence metals with suitable ionic electronegativity. A molten salt method was employed to synthesize a series of high-valence metal-substituted RuO2 with large specific surface areas. The experimental results revealed that a high content of surface Ru4+ species promoted the OER intrinsic activity of high-valence doped RuO2. It was found that there was a linear relationship between the ratio of surface Ru4+/Ru3+ species and the ionic electronegativity of the dopant metals. By regulating the ratio of surface Ru4+/Ru3+ species, incorporating Re, with the highest ionic electronegativity, endowed Re0.1Ru0.9O2 with exceptional OER activity, exhibiting a low overpotential of 199 mV to reach 10 mA cm-2. More importantly, Re0.1Ru0.9O2 demonstrated outstanding stability at both 10 mA cm-2 (over 300 h) and 100 mA cm-2 (over 25 h). The characterization of post-stability Re0.1Ru0.9O2 revealed that Re promoted electron transfer to Ru, serving as an electron reservoir to mitigate excessive oxidation of Ru sites during the OER process and thus enhancing OER stability. We conclude that Re, with the highest ionic electronegativity, attracted a mass of electrons from Ru in the pre-catalyst and replenished electrons to Ru under the operating potential. This work spotlights an effective strategy for stabilizing cost-effective Ru-based catalysts for acidic OER.

Restricting the over-oxidation of active sites in high-entropy electrocatalysts towards ultra-stabilized oxygen evolution in alkaline water electrolysis

Based on ionic electronegativity, theoretical calculation guided the synthesis of np-MnFeCoNiCuOOH exhibiting ultra-stabilized oxygen evolution in alkaline water electrolysis.

Metal Doping and Ligand Engineering as Tools for Tailoring the Electronic Structure of Coordination Polymers and their Oxygen Evolution Electrocatalytic Activity

AbstractElectrocatalytic production of fuels [green hydrogen from water, C1‐high energy molecules from CO2, NAD(P)H from NAD(P)+], utilizing renewable energy sources, has in the oxygen evolution reaction (OER) its Achilles’ heel. Among the catalysts developed for facilitating OER, those based on coordination polymers (CPs) are attracting considerable interest due to their simplicity of preparation and modularity. In this review, after having recalled the key‐parameters that have to be considered when evaluating and benchmarking electrocatalysts, it is shown how the performance of CP‐based OER catalysts can be rationally improved by a) the suitable selection of the metal ion combination and b) engineering CPs with appropriate organic linkers. It is inferred that the catalytic effect of adding a different metal ion, than that of the CP structure (metal doping), occurs through an indirect alteration of the electronic features of the active metal center, which might be described by considering the energy of the d‐band with respect to that of the Fermi level (Ed), the eg occupancy or the metal ionic electronegativity (MIE). In rare cases, it is assumed that the added metal center can directly and synergistically participate at the catalytic process. The much less explored strategy b) to improve the performance of OER electrocatalysts, by properly engineering organic linkers, is related not only to an alteration of the electron density (acidity) of the metal center but also to a modification of the electron localization and conductivity of CPs.

Average metal ion electronegativity as a general descriptor for screening Ni-based double hydroxides with high electrocatalytic water oxidation activity

A descriptor based on the metal ion electronegativity is designed to screen the optimal Ni-based double hydroxides OER electrocatalyst. • The metal ion electronegativity (MIE) represents the intrinsic chemical property. • A volcano trend for MIE vs OER intrinsic activity of Ni-based DHs is described. • The best DHs in the peak of the volcano plot is Ni 0.8 Co 0.2 DHs (MIE = 1.39). • MIE differences affect the metallic electronic structure in OER activity. • A MIE descriptor is used to rapidly screen the DHs-based electrocatalyst. Due to the multiclass complex processes in the oxygen evolution reaction (OER) by Ni-based double hydroxides (DHs) electrocatalysts, it is necessary to seek a comprehensive assessment to uncover the electrochemical nature. Here, Ni 0.8 M 0.2 DHs and Ni 0.7 M 0.3 DHs nanowires (M = Zn, Co, Fe, Cu) were prepared by a hydrothermal method. As the intrinsic chemical property, metal ion electronegativity (MIE) as the descriptor, the structure–activity relationship between MIE and OER reaction intermediates' adsorption and desorption capacity was researched by the electrochemical impedance analysis. At the top of the volcano trend (MIE = 1.39, Ni 0.8 Co 0.2 DHs), it is screened and exhibits the lowest interfacial charge transfer resistance and the adsorption and desorption resistance of intermediates. This work provides a cost-effective method based on the theory of electronegativity equilibrium for the precise screening and design of high-active OER electrocatalysts.

Efficient near-infrared broadband garnet phosphor for pc-LED and its application to vascular visualization and night vision.

Ultra-broadband near-infrared (NIR) spectroscopy has unparalleled application prospects in intelligent detection and phosphor-converted light-emitting diodes (pc-LED), which are most likely to become the next generation of NIR light sources, has become a hot spot for research nowadays. To cope with the demand for more NIR spectroscopy applications, more efficient NIR phosphors need to be developed. Here, by screening the subject with a smaller band gap and by screening the suitable ion electronegativity of the lattice position where the Cr3+ is located, and then through the energy transfer, a series of Gd3Zn2GaGe2O12:xCr3+, yYb3+ (GZGG:Cr3+/Yb3+) NIR broadband garnet phosphors were found for the first time. By controlling the energy transfer process, the internal quantum yield (IQY) (54.9%), external quantum yield (EQY) (24.65%), bandwidth (260 nm), and thermal stability (60% at 150 °C) of NIR emission were substantially improved. The obtained phosphors are packaged with blue light chips into pc-LED, which can be applied in different fields such as vascular visualization and night vision.

Understanding of the bond covalency nature with ionic electronegativity in perovskite cuprates La2CuMO6-x (M = Ti, Mn, Ru)

A bond valence sums (BVS) modified ionic electronegativity (EN) scale was suggested for better accommodating the double perovskite La2CuMO6-x (M ​= ​Ti, Mn, Ru) with mixed bonding nature. Both the M ​− ​O bond covalency fraction (f) and the cooperative B-site sublattice distortion are highlighted to connect structure and physical properties. Particularly, the Ti-based compound hosts the largest M/O ionic EN difference and hence yields the smallest f value while the Ru-based analogue exhibits the opposite result. As the consequence, robust spin disordering accompany with poor dc conductivity is convinced in the Ti-based sample owing to its featuring B-site ionic arrangement and profound suppression of 3d(Ti)-2p(O) orbital hybridization. For the Ru-based sample, strong ferromagnetic spin frustration and low charge carrier hopping potential might be essentially ascribed to its large f value through enhancing orbital degeneracy between 4d(eg)-2p σ and 4d(t2g)-2p π bonding states. The Mn-based sample with the moderate f value exhibits the similar magnetic and electric behaviors as those of Ru-based sample. Both the d(M)-p(O) orbital hybridization and the M ​− ​O bond covalency could be tuned by rationally selecting the M cation with proper ionic EN value. This work provides a deep understanding of the bond covalency nature in perovskite cuprates and might help to develop novel electronic functional materials.

Correlation and Improvement of Bimetallic Electronegativity on Metal–Organic Frameworks for Electrocatalytic Water Oxidation

Oxygen evolution reaction (OER) plays a critical role in many renewable energy technologies including electrolyzers and rechargeable metal–air batteries. However, the sluggish kinetics of OER catalysts seriously impedes the efficiency of these aforementioned clean devices. Herein, a series of bimetallic metal–organic frameworks (MOFs) with tunable electronegativity (metal ionic electronegativity [MIE]) are prepared by precisely controlling the metal composition for efficient OER. Moreover, an experimental result‐derived volcano plot is first unveiled by presenting the correlation of the MIE and OER kinetic rate (Tafel slope) on the surface of the MOFs‐based electrocatalysts. Remarkably, a Ni0.9Fe0.1 MOF fabricated and based on the proposed electronegative equilibrium rationales, delivers a low overpotential of 206 mV at 10 mA cm−2 and 270 mV at 50 mA cm−2 along with a long‐term stability in 1 m KOH, superior than the previous reported catalysts. The excellent performance is ascribed to the MIE‐induced interface charge transfer resistance and intermediate adsorption resistance adjustment. The second metal introduction causes the formation of unsaturated metal sites during the electronegative equilibrium process, leading to adjustable OER kinetic rate. These findings pave the way to designing highly active MOF‐based OER catalysts.

Triple ionic-electronic conducting oxides for next-generation electrochemical devices.

Triple ionic-electronic conductors (TIECs) are materials that can simultaneously transport electronic species alongside two ionic species. The recent emergence of TIECs provides intriguing opportunities to maximize performance in a variety of electrochemical devices, including fuel cells, membrane reactors and electrolysis cells. However, the potential application of these nascent materials is limited by lack of fundamental knowledge of their transport properties and electrocatalytic activity. The goal of this Review is to summarize and analyse the current understanding of TIEC transport and electrochemistry in single-phase materials, including defect formation and conduction mechanisms. We particularly focus on the discovery criteria (for example, crystal structure and ion electronegativity), design principles (for example, cation and anion substitution chemistry) and operating conditions (for example, atmosphere) of materials that enable deliberate tuning of the conductivity of each charge carrier. Lastly, we identify important areas for further advances, including higher chemical stability, lower operating temperatures and discovery of n-type TIEC materials.

Screening highly active perovskites for hydrogen-evolving reaction via unifying ionic electronegativity descriptor

Facile and reliable screening of cost-effective, high-performance and scalable electrocatalysts is key for energy conversion technologies such as water splitting. ABO3-δ perovskites, with rich constitutions and structures, have never been designed via activity descriptors for critical hydrogen evolution reaction (HER). Here, we apply coordination rationales to introduce A-site ionic electronegativity (AIE) as an efficient unifying descriptor to predict the HER activities of 13 cobalt-based perovskites. Compared with A-site structural or thermodynamic parameter, AIE endows the HER activity with the best volcano trend. (Gd0.5La0.5)BaCo2O5.5+δ predicted from an AIE value of ~2.33 exceeds the state-of-the-art Pt/C catalyst in electrode activity and stability. X-ray absorption and computational studies reveal that the peak HER activities at a moderate AIE value of ~2.33 can be associated with the optimal electronic states of active B-sites via inductive effect in perovskite structure (~200 nm depth), including Co valence, Co-O bond covalency, band gap and O 2p-band position.

Paradigms and paradoxes: Hess’ law and the thermodynamic validity of Jolly’s method for estimating bond dissociation energies

This study evaluates Jolly’s method to estimate the difference in homolytic bond dissociation energy between two isoelectronic molecules by the use of atomic and ionic electronegativities. The use of intermediate species as an energetic “stepping stone” between the two diatomic species in question is discussed, particularly within the context of Hess’ law. We also show a sample calculation for a pair of diatomic species that is fully consistent with data from atomic physics.

Influence of Europium Doping on Various Electrical Properties of Low-Temperature Sintered 0.5Ba0.90Ca0.10TiO3-0.5BaTi0.88Zr0.12O3-0.1%CuO-xEu Lead-Free Ceramics

0.5Ba0.90Ca0.10TiO3-0.5BaTi0.88Zr0.12O3-0.1%CuO-xEu (BCT-BZT-Cu-xEu; x = 0–0.90%) lead-free ceramics were sintered at 1220°C with as-synthesized nanoparticles by a modified Pechini method. The structural characteristics and electrical properties of the ceramics that were influenced by varying europium-doping were investigated. All the ceramics featured high densification (relative density: ∼ 96%). X-ray powder diffraction results indicated the samples possessed pure orthorhombic phase. The maximum relative permittivity (e r, 10869) was found at x around 0.30%. Europium ions could dope on different substitution sites in the ABO3 lattice, which evidently influenced electrical properties with various volumes of oxygen vacancy. Moreover, the formation mechanisms of oxygen vacancy and defect electron complexes were stated. The piezoelectric properties were impacted by defect electron complexes, internal stress, ionic electronegativity, etc. The optimal electrical properties, i.e., d 33 = 384 pC/N, Q m = 92, and k p = 0.36, were detected at x = 0.45%.

Nucleation-dependant chemical bonding paradigm: the effect of rare earth ions on the nucleation of urea in aqueous solution.

Rare earth ions can be used to construct a variety of novel structures and are favorable to chemical bonding regulation and design. In this study, the chemical bonding paradigm between rare earth ions (Ln3+) and urea molecules in an aqueous solution can be tracked by the evolution of C[double bond, length as m-dash]O, NH2, and CN vibration bands during the urea nucleation stage. Rare earth ions such as La3+, Gd3+, and Lu3+ can manipulate the nucleation time of urea via regulating the nucleation-dependant N-C[double bond, length as m-dash]OH-N hydrogen-bonding between urea molecules. Two types of chemical bondings between Ln3+ and urea molecules have been confirmed, which are Ln3+O[double bond, length as m-dash]C-N and Ln3+NH2-C. Compared with Ln3+NH2-C, Ln3+ prefers to coordinate with the O[double bond, length as m-dash]C bond in urea. With a higher concentration of rare earth ions in the solution, some N-C[double bond, length as m-dash]OH-N hydrogen bonds are broken as a consequence of the incorporation of Ln3+ into the lattice, resulting in the decreased symmetry of local urea molecules in the crystalline nuclei and the consequent Ln3+ concentration-dependent nucleation time of urea. Moreover, using the ionic electronegativity scale of Ln3+, the different effects of La3+, Gd3+, and Lu3+ on urea nucleation can be further distinguished. The present study provides basic data for unrevealing the chemical bonding regulation role of rare earth ions in the formation of hydrogen bonded materials, which may give insight into the design and fabrication of novel materials utilizing rare earth ions to adjust the chemical bonding process.

Red emission enhancement by strong electronegativity in Na5Y4(SiO4)4F:Eu3+ phosphor for white light-emitting diodes

A red-emitting Eu3+ doped Na5Y4(SiO4)4F fluorosilicate phosphor with tetragonal structure was synthesized by conventional solid state reaction method. The crystal structure, photoluminescence properties and quenching concentration of Na5Y4(SiO4)4F:Eu3+ were investigated in detail. Excited by near-ultraviolet light at 397 nm, the dominant red emission in Na5Y4(SiO4)4F:Eu3+ phosphor is located at 615 nm, which is from the hypersensitive 5D0–7F2 transition of Eu3+ ion. The optimum doping concentration of Eu3+ ion into the host material is up to 50 %, based on which the critical transfer distance is calculated to be 7.72 A. The large transfer distance inhibits the emission quenching. Importantly, through the comparison with NaYSiO4:Eu3+, the intense red emission is attributed to the effect of the F− ion electronegativity on the distorted local crystal environment. All the results show that Na5Y4(SiO4)4F:Eu3+ could be a potential red phosphor for near-ultraviolet white light-emitting diodes.

Structure and properties of zinc aluminophosphate glasses and those doped with zirconium dioxide

Structure and properties of two glass systems, group A: 50P2O5–(50−x)ZnO–xAl2O3 (x=0, 5, 10, 15, 20mol%) and group B: 50P2O5–20Al2O3–(30−x)ZnO–xZrO2 (x=1, 2, 3, 4, 5mol%) were investigated. The density of the first series goes down with introducing more Al2O3, while the density increases as ZrO2 replaces ZnO in networks. Adding Al2O3 or doping more ZrO2 would raise Tg as well as Tc for both series of glasses. Adding Al2O3 does improve the chemical durability when comparing A1 with other members in the same group; further, doping ZrO2 into glasses based on A5 also makes some promotion in chemical properties. Structure analyses all coming from IR tests, it turns out that ion electronegativity does play an essential role in phosphate network when different kinds of ion exchange occur in glasses.

Study on the crystallization process of function inorganic crystal materials

Functional crystal materials used as the important conversion media of light, sound and electricity, have been widely applied to high-tech fields such as energy, information, aerospace and related hot topics at the forefront of materials science and engineering subject. Crystallization process is the core of the preparation of functional materials, crystal growth habit of materials directly affects the functional performances of optical, electrical, magnetic, and catalytic behaviors. During the crystallization process of inorganic materials, crystals are microscopically transformed from free-state ions into the crystalline solid-phase. We can use the ionic electronegativity and microscopic symmetry changes of constituent components, to study the crystallization process of aggregation formation and structure evolution. Using molecular vibration spectroscopy we can at the molecular scale, reveal the crystallization process of nonlinear optical crystal materials in aqueous solution crystallization process, to overcome the lack of traditional means of in situ observations determining those non-long-range order structures. Chemical bonding theory of single crystal growth can from both thermodynamic and kinetic aspects of the whole system, effectively guide the growth of large crystals, reasonably regulate the growth surface and interface thermodynamics and kinetics. The chemical bonding theory of single crystal growth is applied to the design and optimization of growth parameters of large-size crystal pulling growth system, we have built up a large-size crystal growth system, and successfully grown o 2 sapphire crystals, o 3 YAG crystals, and o 4 lithium niobate crystals.

Functionalized nanostructured silica by tetradentate-amine chelating ligand as efficient heavy metals adsorbent : Applications to industrial effluent treatment

Organofunctionalized nanostructured silica SBA-15 with tri(2-aminoethyl)amine tetradentate-amine ligand was synthesized and applied as adsorbent for the removal of Cu2+, Pb2+, and Cd2+ from both synthetic wastewater and real paper mill and electroplating industrial effluents. The prepared materials were characterized by XRD, N2 adsorption-desorption, TGA, and FT-IR analysis. The Tren-SBA-15 was found to be a fast adsorbent for heavy metal ions from single solution with affinity for Cu2+, Pb2+, than for Cd2+ due to the complicated impacts of metal ion electronegativity. The kinetic rate constant decreased with increasing metal ion concentration due to increasing of ion repulsion force. The equilibrium batch experimental data is well described by the Langmuir isotherm. The maximum adsorption capacity was 1.85 mmol g−1 for Cu2+, 1.34 mmol g−1 for Pb2+, and 1.08 mmol g−1 for Cd2+ at the optimized adsorption conditions (pH=4, T=323 K, t=2 h, C0=3 mmol L−1, and adsorbent dose=1 g L−1). All Gibbs energy was negative as expected for spontaneous interactions, and the positive entropic values from 103.7 to 138.7 J mol−1 K−1 also reinforced this favorable adsorption process in heterogeneous system. Experiment with real wastewaters showed that approximately a half fraction of the total amount of studied metal ions was removed within the first cycle of adsorption. Hence, desorption experiments were performed by 0.3M HCl eluent, and Tren-SBA-15 successfully reused for four adsorption/desorption cycles to complete removal of metal ions from real effluents. The regenerated Tren-SBA-15 displayed almost similar adsorption capacity of Cu2+, Pb2+, and Cd2+ even after four recycles. The results suggest that Tren-SBA-15 is a good candidate as an adsorbent in the removal of Cu2+, Pb2+, and Cd2+ from aqueous solutions.

Effect of Electrostatic and Size on Dopant Occupancy in Lithium Niobate Single Crystal

We proposed a simple and an effective method to predict the site occupancy and threshold concentration of metal ions in lithium niobate (LiNbO3, LN) single crystal. The ionic energy parameter E(i), defined by the ionic electronegativity and ionic radius, was proposed to describe the electrostatic and size effects of cations on the structural stability of LN. The dopant location can be easily identified by comparing the E(i) deviation of dopant from those of host cations Li(+) and Nb(5+), and the dopant prefers to occupy the lattice site with the smaller deviation of E(i). Our calculated occupancies agree well with those experimental results, which demonstrate the predictive power of our present method. We in this work predicted the preferred occupancies of 60 metal ions in LN single crystal. Further, the threshold concentrations of some frequently used dopants were calculated on the basis of the assumption that all doped LN crystals can endure the same variation of E(i).

SITE SELECTIVITY IN DOPED POLYANION CATHODE MATERIALS FORLi-ION BATTERIES

We propose a simple and effective method to determine the occupancy preference of cations doped in polyanion cathode materials for Li -ion batteries based on ionic electronegativity and ionic radius. The occupancy site can be predicted by comparing the combined deviation degree of electronegativity and radius between the dopant and the substituted ion, and dopants prefer to occupy the site where the deviation degree is less. Based on this method, we predicted the preferred occupancy sites of 38 frequently used ions doped in LiFePO4and Li3V2( PO4)3, which can be in accordance with the available experimental and other calculated results. This simple method established in current work can serve as an effective tool to well predict the preferred occupancy sites of cations doped in cathode materials, which can provide powerful guidance in designing cathode materials for high-performance Li -ion batteries.

Water-soluble inorganic salts with ultrahigh specific capacitance: crystallization transformation investigation of CuCl2 electrodes

Currently, one of the biggest challenges in the field of pseudocapacitors is their capacitance value. Current knowledge on improving specific capacitance values is mainly focused on the synthesis of electrode materials with different structures and sizes. However, no studies have addressed using soluble inorganic salts directly as electrode materials. For the first time, we have reported that water-soluble CuCl2 electrodes show a fast and reversible redox reaction of Cu2+ ↔ Cu+ and deliver a very high specific pseudocapacitance, ~5442 F g−1. We have identified that the cation Cu2+ is responsible for achieving this big number. The chemical and crystallization transformation of the CuCl2 electrode is presented. Commercial inorganic salts can be used directly as electrodes neglecting complex synthesis procedures, which is an easily scalable and highly economical method. This method can be extended to a large variety of commercial inorganic salt electrodes following the guideline of ionic electronegativity.