Multivalence States Research Articles

Glucose oxidation on monoclinic Co2V2O7 nanorods: Intuitions on cell potential reduction in hybrid electrolyzer

The deleterious impact of burning fossil fuels has led to a strategic shift towards exploring the environmentally benign energy generation technologies and renewable green sources. From the prospect of energy-saving hydrogen generation approach, alkaline hybrid electrolyzer using an anodic glucose oxidation reaction in conjunction with cathodic hydrogen evolution reaction catalyzed by monoclinic Co2V2O7 nanorods (NRs) is investigated. The Co2V2O7 was prepared by facile thermal treatment (500 °C/1 h) and displayed a nanorod-like morphology. The results derived from X-ray photoelectron spectroscopy confirmed the presence of multivalence states for both V (+4 and + 5) and Co (+2 and + 3) species. The Co2V2O7 exhibits superior glucose oxidation performance with very low onset potential of 1.2 V (vs RHE) and very high current density of 400 mA cm−2 at an overpotential of 1.51 V (vs RHE) in 1 M KOH. Furthermore, the Co2V2O7 exhibits an onset potential of −0.054 V (vs RHE) and an overpotentials of −75 mV and −190 mV to achieve the current densities of 10 mA cm−2 and 100 mA cm−2 respectively in hydrogen evolution reactions (HER). The Co2V2O7-NRs perform well in both the HER and glucose oxidation reactions, with a smaller hybrid water splitting potential of ∼1.46 V, which is 260 mV less than the analogous value in the conventional electrolyzer. The proposed electrocatalyst Co2V2O7 opens new possibilities for the production enediol together with hydrogen generation at low energy consumption.

Metal-Organic-Framework Derived Co-Mo Multimetal Oxide Semiconductors: Selective Trace-Level Hydrogen Sulfide Detection.

The development of a highly selective and trace-level gas sensing platform for detecting hydrogen sulfide (H2S) remains a formidable challenge. To solve this problem, Co-Mo multimetal oxide semiconductors are rationally tailored by employing metal organic frameworks (MOFs) as self-sacrificial templates. The MOF-derived Co3O4/β-CoMoO4 based gas sensors displays high sensitivity (Rg/Ra = 22) to 10 ppm of H2S and ultralow limit of detection (10 ppb H2S). The formation of p-p heterojunction and multivalence states of Mo play a crucial role in electron transfer and oxygen adsorption. A sensor array constructed from four Co3O4/β-CoMoO4 materials with different Co/Mo ratios demonstrates a superior selective discrimination of H2S from other VOCs and malodorous gases by principal component analysis (PCA). Besides, a H2S gas sensing and alarming platform was designed for monitoring the environment contaminated with H2S. This finding provides a feasible approach for the discovery of highly efficient gas sensors to monitor environmental H2S concentration.

In-situ crystallization of CoCr2O4 in tellurite glass with enhanced optical nonlinear limiting, photoluminescence, and magnetic properties: Influence of Co content

This article reports the in-situ growth of spinel CoCr2O4 nanocrystals (NC) in tellurite glass through tailoring the Co content by melt-quenching method. The microstructure, optical, and magnetic properties of NC/ glass systems were systematically studied using various techniques. Well-defined 30 nm crystallization of CoCr2O4 (space group of Fd3m) homogeneously distributed in the glassy matrix and the concurrent formation of cubic BiCoO3 (space group of P4mm) when the Co content exceeds 3%. The coexistence of multivalence and coordination states of Co and Cr significantly modified the glass structure with conversion of TeO4→TeO3, BO4→BO3, and CoO4→CoO6 units. Exceptional performance of the glass containing 5% Co-tuned CoCr2O4 was obtained, showcasing the decrease of Eg (2.09 eV), strong ferro-magnetization of 7.04 emu/g, large α3 (4.88×10−10 m/W) and good optical limiting property (threshhold of 1.31×1012 W/m2). Furthermore, the same glass showed excellent red emission between 650 and 800 nm under the excitation of 460 nm, with an increased lifetime (2.648 ms) and good stability of 90.7% within 25–300 °C. The emission mechanism was discussed. EPR analysis confirmed the active role and spin-states of magnetic Cr and Co ions, contributing synergistically to the improved optical and magnetic properties of the glasses.

KBiFe2O5 triggered-phase transition of Bi2Fe4O9 and Fe3O4 in tellurite glass with huge nonlinear and magnetic properties

In the quest for glass materials with high nonlinearity and strong magnetism to meet the demands of advancing technology, magnetic nanocrystal (NC) doping emerges as a promising approach. The paper investigates the phase transition from KBiFe2O5 to Bi2Fe4O9 and Fe3O4 NCs within a TeO2–Bi2O3–B2O3 glass matrix. The novelty of this study lies in leveraging the coexistence of multiple phases to amplify both the polarization and magnetic moment of glass. Various techniques, including X-ray diffraction, transition transmission electron microscopy, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, and vibrational sample magnetometer were employed to analyze the impact of NCs content and heat treatment temperature on crystallization, structure modification, and properties. KBiFe2O5 NCs doping induces changes in crystal phases and modifies the glass network structure by forming multi-valence states and altering coordination numbers, such as FeO4→FeO6, TeO4→TeO3, and BO4→BO3. Concurrently, appropriate temperature conditions result in reduced NC size, preserving glass transparency and thermal stability. Spinel Fe3O4 NCs formation at higher temperatures enhances magnetic behavior. A glass sample containing 1 mol% KBiFe2O5 NCs, heat-treated at 410 °C, exhibits a narrow bandgap (Eg) of 1.82 eV, high nonlinear parameters (α3 = 3.98 × 10−10 m/W, χ(3) = 8.65 × 10−11 esu), and a low limiting threshold (1.01 × 1012 W/m2). Additionally, owing to the incorporation of high spin states and active magnetic exchange interactions, the same glass demonstrates robust ferromagnetic behavior (Ms = 2.3 emu/g and Hc = 850 G). The approach developed in this study has been demonstrated to be highly effective in producing transparent glass with promising nonlinearity and magnetic performance suitable for photonics applications.

Metal Valence State Modulation Strategy to Design Core@shell Hollow Carbon Microspheres@MoSe2/MoOx Multicomponent Composites for Anti-Corrosion and Microwave Absorption.

The exploitation of multicomponent composites (MCCs) has become the main pathway for obtaining advanced microwave absorption materials (MAMs). Herein, a metal valence state modulation strategy is proposed to tune the electromagnetic (EM) parameters and improve microwave absorption performances. Core@shell hollow carbon microspheres@MoSe2 and hollow carbon microspheres@MoSe2/MoOx MCCs with various mixed-valence states content are well-designed and produced by a simple hydrothermal reaction or/and heat treatment process. The results reveal that the thermal treatment of hollow carbon microspheres@MoSe2 in Ar and Ar/H2 leads to the in situ formation of MoOx and multivalence state, respectively, and the enhanced content of Mo4+ in the designed MCCs greatly boosts their impedance matching characteristics, polarization, and conduction loss capacities, which lead to their evidently improved EM wave absorption properties. Amongst, the as-prepared hollow carbon microspheres@MoSe2/MoOx MCCs achieve an effective absorption bandwidth of 5.80 GHz under a matching thickness of 1.97 mm and minimum reflection loss of -21.49 dB. Therefore, this work offers a simple and universal method to fabricate core@shell hollow carbon microspheres@MoSe2/MoOx MCCs, and a novel and feasible metal valence state modulation strategy is proposed to develop high-efficiency MAMs.

Efficient electrocatalytic nitrogen oxidation to nitrate by the self-assembly of supramolecular cucurbit[6]uril with a heteropolyacid

A supramolecular self-assembler of cucurbit[6]uril-phosphomolybdic acid with a multi-valence state is constructed to realize an efficient nitrogen oxidation reaction.

The Enigma of Titanium Electrodeposition on Various Substrates

Titanium is an oxiphilic reactive metal which readily forms passive oxide films onto substrates. The unique properties of the metal such as low density (d=4.5 g/cm3), high strength, and corrosion resistance in harsh environments offers practical advantages. The pure metal is used abundantly in aerospace, armors, submarines, missiles, biomedicals, golf clubs and special electronic applications. The electro-deposition of corrosion resistant coatings is imperative to protect base metals. A review of previous literature has indicated that methods such as roll-diffusion cladding, magnetron discharge sputtering, electron beam, vacuum evaporation, ion beam enhanced deposition (PVD), thermal spray, chemical conversion coatings etc. have been employed in special applications at a prohibitive cost. Plating of titanium films in molten salts at high temperature, and inert atmospheres is a challenge to follow stringent conditions. Electroplating in ionic liquids is extremely expensive and limited.It will be an important technological advancement if a feasible electrodeposition process for titanium is developed for light base metals and plastics in aqueous or semi-aqueous solutions. Titanium electrodeposition in aqueous systems is not a straight-forward process due to its far negative reduction potential than that of hydrogen. Its multivalence states, stability, limited potential range, gas evolution, and substrate passivation pose technical challenges. The present author has critically evaluated several recipes cited by Russian literature, and a few United States patents. Unfortunately, we could not substantiate their cited claims. We have developed an innovative and proprietary process for electro-deposition of Ti in aqueous and partially non-aqueous systems. Deposition of titanium and its alloy films is demonstrated on variety of substrates such as Steel, Pb, Zn, Al, and selected plastics. It is our hope that this endeavor will open new avenues in surface finishing applications.

Study of the synergistic role of multivalence states of 3d cations on the crystal lattice distortion and magnetic behavior of Sr2FeCoO6-δ: A spectroscopic study

In perovskite oxides, the multiple charge states of cations influence their local structure and correlated physical properties. In this report, we studied the role of multivalence cations on the local structure and magnetic behavior of the oxygen-deficient system Sr2FeCoO6-δ (SFCO), prepared by the solid-state synthesis technique. A detailed structural and geometrical analysis confirmed the coexistence of orthorhombic (Brownmillerite) and cubic crystal symmetries and a gesture of the Jahn-Teller (JT) distortion. The intense Raman modes are allowed to be indexed for BO-polyhedra and JT-distortion. Experimental and theoretical analysis of the X-ray photoelectron spectroscopy (XPS) spectra supported the mixed oxidation state of Fe (Fe3+/Fe4+) and Co (Co2+/Co3+), further confirmed by theoretically simulated X-ray absorption spectroscopy (XAS) spectra. The presence of the multivalence states leads to AFM/FM exchange interaction in the sample which further leads to glassy magnetic behavior.

Self-supported carbon cloth based-ammonium vanadate nanoribbons cathode for superior flexible aqueous zinc-ion batteries

Ammonium vanadate (NH4V4O10) is a prominent cathode material for zinc ion storage owing to the abundant active sites, tunable layered structure, and the multivalence state of vanadium ions. Despite the great potential of NH4V4O10, it is constrained by its weak fastness and homogeneity with substrates. A key issue with poor energy storage of flexible battery is extremely low active material load quality. Additionally, the severe self-aggregation phenomena and the brittle interlayer structures are the cause of the rapid capacity fading and the poor rate capacities. Herein, a novel flexible self-support carbon cloth (CC)-based NH4V4O10 (CC@NH4V4O10) cathode was rationally fabricated via a simple hydrothermal method. Apart from serving as a flexible interconnected conductive network, CC can provide uniform nucleation centers and induces ordered growth of NH4V4O10, which effectively reduces its agglomeration problem. The synthesized NH4V4O10 nanoribbons exhibit a unique micropore structure with enlarged interlayer spacing, which ensures rapid co-transfer of H+/Zn2+ ions with enhanced storage capacity. The CC@NH4V4O10 cathode delivers a stable specific capacity of 330 mAh g−1 at 0.25 A g−1 with almost no capacity fading (99% capacity retention) over 600 cycles at 5 A g−1. More impressively, the as-prepared package battery offers outstanding operation stability to power electronics under the low temperature, and it is able to maintain 76% energy retention after 100 cycles at 0 ℃ at a 0.5 A g−1 current density. This high-performance flexible battery may open a new prospect in wearable energy storage applications.

Facile-prepared Fe/Mn co-doped biochar is an efficient catalyst for mediating the degradation of aqueous ibuprofen via catalytic ozonation

The fabrication of efficient, stable, and low-cost catalysts is crucially important for the catalytic ozonation process for the removal of recalcitrant pollutants. In this study, we present a facile impregnation-pyrolysis method for the preparation of novel porous Fe/Mn co-doped biochar (Fe-Mn-C) with excellent catalytic activity and reusability for the catalytic ozonation of ibuprofen (IBP). The incorporation of Fe/Mn heteroatoms into the carbon skeleton of biochar not only produced more defective sites and promoted the charge transfer on the materials surface but also created active Fe/Mn species with multi-valence states for ozone activation. As a result, >95% of IBP (50 mg/L) and 80.5% of total organic carbon can be rapidly removed within 9 min in the Fe-Mn-C/O3 process at a pH of 7, ozone dosage of 4.93 mg/min, and Fe-Mn-C dosage of 0.5 g/L. The catalytic reaction rate in Fe-Mn-C/O3 was 6.58 times higher than that of sole ozonation and 2.3–4.1 times higher than that of catalytic ozonation with other catalysts (e.g., biochar, Fe-doped biochar, Mn-doped biochar, activated carbon, Fe3O4 and MnO2). Moreover, the obtained Fe-Mn-C can be reused for multiple cycles; the performance is not significantly reduced in subsequent cycles, and there is no significant metal leaching. Further studies suggested that the radical pathways (superoxide radicals and hydroxyl radicals) were mainly responsible for the degradation of IBP in the Fe-Mn-C/O3 system. Furthermore, the contributions of the surface functional groups, doped atoms, and delocalized π electrons of Fe-Mn-C to the decomposition of ozone and the formation of reactive species were identified by correlation analysis between the catalytic ozonation rate and the physiochemical properties of Fe-Mn-C to clarify the mechanism underlying the improved performance.

Structure, ferroelectric and magnetic behavior in Mn doped 0.75 BiFeO3-0.25BaTiO3 ceramics

Lead-free polycrystalline 0.75 BiFe 1-xMn xO3-0.25BaTiO3 (x = 0.00, 0.01, 0.02 and 0.03 hereby designated as BF-BT) ceramics were synthesized by high temperature solid state reaction technique. This study dwells on the role of Mn doping on the structure, ferroelectric and magnetic behavior of BF-BT ceramics. Structural phase analysis of the samples carried out by X-ray diffraction and Raman scattering measurements revealed single phase distorted perovskite structure with rhombohedral symmetry. No alteration in crystal structure was observed with increasing Mn concentration. The average crystallite size of the compounds increases (12.9–27.8 nm) with increasing Mn concentration. The saturated value of ferroelectric polarization (Pr) was found to decrease with increasing Mn-concentration and a maximum remnant polarization (Pr) of 0.6 μC/cm2 was recorded at an applied field of 25 kV/cm for x = 0.00 sample. Leakage current density was found to increase with increase in Mn concentration. Oxidation states of the cations probed by X-ray photoelectron spectroscopy (XPS) suggested that Fe/Mn were in mixed state (+3/+2), while Ti-ion demonstrated (+3/+4) state. Presence of multivalence states of Fe/Mn/Ti causing distortion in the lattice (attributed to Jahn Teller) with increasing Mn concentration significantly affects the magnetic behavior of the ceramics. A maximum value of saturation magnetization of Ms∼0.80emu/gm was recorded for x = 0.03 composition.

High polarizability enhanced EPR, optical linear & nonlinear and electric conductivity: Role of NiFe2O4 nanocrystals in transparent tellurite glass-ceramics

Glass containing magnetic nanocrystals is attractive to obtain high nonlinear and high polarizability. In this study, for the first time, 10 nm cubic NiFe2O4 (NFO) nanocrystals doped tellurite glass was studied in terms of the influence on glass structure, chemical bonds, EPR spectra, optical linear and nonlinearity, complex impedance, and dielectric constant. X-ray diffraction, FT-IR, and X-ray photoelectron spectroscopy revealed the single phase and chemical energy of NFO NCs and NFO- doped glasses. The introduction of NFO modified the glass structure through conversion of TeO4→TeO3, and PO4→PO3 units and producing non-bridging oxygen, which in turn enhanced the polarizability according. EPR analysis revealed the super-exchange interaction between multi-valence states of Ni and Fe ions, contributing to the deformation of NFO lattice and NBO defects in the glass network. The energy band gap of glass was red-shifted by NFO due to the multi-valence states of 3d ions. In addition, the linear and nonlinear refractive index, third-order absorption coefficient, and susceptibility were significantly enhanced because of the high polarizability. 3%NFO glass demonstrated huge third-order nonlinear susceptibility of 9.37 × 10−7 esu and giant DC electric conductivity of 8.84 × 10−4 S/cm at room temperature. The values obtained in the present study were much superior to values from the literature, and the obtained glasses are promising for high ultra-fast laser, supercontinuum generation, and holography applications.

Thermodynamic investigation of vanadium oxide in CaO–SiO2–VOx system at 1873 K

AbstractOwing to the complexity of the multivalence states of vanadium oxides in slag systems and experimental difficulties, thermodynamic properties of vanadium oxides have not been established yet. In the present study, the mixed‐valence states and activities of the vanadium oxides in CaO–SiO2–VOx slag were investigated experimentally at 1873 K and oxygen partial pressures of 3.2 × 10–9 and 3.1 × 10–7 atm. After the CaO–SiO2–VOx slag had equilibrated with a platinum strip, the mixed‐valence states of the vanadium oxides in the slag were estimated by performing X‐ray photoelectron spectroscopy, and the activities of the vanadium oxides in the slag were calculated using the activity of vanadium in the platinum strip at equilibrium using thermodynamic equations. At an oxygen partial pressure of 3.2 × 10–9 atm, V3+ was the dominant ion and V4+ was the second most abundant ion. With increasing VOx content or basicity (CaO/SiO2 ratio), the fraction of V3+ decreased, whereas that of V4+ increased. The activity of VO1.5 was greater than those of the other vanadium oxides. On the other hand, when the oxygen partial pressure increased to 3.1 × 10–7 atm, V4+ became the dominant ion. As the slag basicity increased, the fraction of V4+ increased further, whereas that of V3+ decreased to less than that of V5+. The activity of VO1.5 was greater than those of the other vanadium oxides, limiting the effect of the slag basicity. Consequently, the valence state of vanadium oxide was affected by the slag basicity at a low oxygen partial pressure by acting as a network modifier. In contrast, at a higher oxygen partial pressure, the activity of vanadium oxide increased further but was not affected by the slag basicity because of its contribution to the network structure formation. The present findings can be applied to optimize the slag composition in steel refining or vanadium pentoxide production processes to increase the yield rate of vanadium.

EPR, DFT, and Mott–Schottky study on visible light photocatalytic activity of Au and Co3O4 mediated Bi2WO6: role of SPR and multi-valence states

EPR, DFT, and Mott–Schottky study on visible light photocatalytic activity of Au and Co3O4 mediated Bi2WO6: role of SPR and multi-valence states

Al2O3 tailored La0.8Sr0.2FeO3 crystallization in heavy metal oxide glass: Synthesis, structure, and enhanced linear & nonlinear properties

Glass containing magnetic nanocrystals are attractive to provide high optical linear and nonlinearity properties. In this study, we reported the synthesis of perovskite La 0.8 Sr 0.2 FeO 3 nanocrystals in heavy metal oxide glass under the Al 2 O 3 tailoring. The influence of Al 2 O 3 amount to the formation of La 0.8 Sr 0.2 FeO 3 nanocrystals and the influence of nanocrystals to glass structure, optical linear& nonlinear properties were thoroughly investigated. The 10 nm-nanocrystals of orthogonal La 0.8 Sr 0.2 FeO 3 were synthesized by melting quenching followed with subsequent crystallization process at 400 °C for 30 min under the tuning of Al 2 O 3 . The formed La 0.8 Sr 0.2 FeO 3 were well distributed in matrix without aggregation. Structure and chemical valence study revealed the aluminum abnormality effect and the Sr 2+ induced multi-valence states of Fe ions and oxygen vacancies in La 0.8 Sr 0.2 FeO 3 lattice. Such modification clearly influenced the optical absorption, refractive index, polarizability, energy band gap shrinkage and nonlinearity. Physical parameters such as oxygen packing density, free volume etc. were calculated to confirm the influence of Al 2 O 3 tailored La 0.8 Sr 0.2 FeO 3 crystallization to glass. The glass with 10%Al 2 O 3 amount exhibited a large thermal stability (132 °C), low thermal expansion coefficient (10.2 ×10 -6 /K) and high BO 4 /AlO 4 units, providing suitable environment for La 0.8 Sr 0.2 FeO 3 crystallization. About 20 nm nanocrystals were formed and well distributed in glass which contributed to large nonlinearity absorption coefficient (5.19 ×10 −10 m/W) and FOM (13.6 ×10 3 esu cm) which much superior than from relative literatures. The obtained glass with extremely good optical linear and nonlinearity performances can be promising candidate for photonics device applications. • Synthesis and characterization of La 0.8 Sr 0.2 FeO 3 nanocrystals in PbO-Bi 2 O 3 -B 2 O 3 glass under Al 2 O 3 tailoring. • 10 nm-nanocrystals of orthogonal La 0.8 Sr 0.2 FeO 3 were synthesized at 400 °C for 30 min at 10% Al 2 O 3 . • Sr 2+ induced oxygen vacancy and multi-valence states of Fe ions in lattice increased polarizability. • La 0.8 Sr 0.2 FeO 3 crystallization red shifted optical absorption edge and decreased E g of glass. • Glass with large α 3 (5.19 ×10 −10 m/W) and FOM (13.6 ×10 3 esu) is promising for nonlinear devices.

Magnetic and magneto-optical properties of La0.8Sr0.2FeO3 crystals in alumina doped lead-bismuth-borate Faraday rotating glass matrix

In this study, we reported the synthesis of perovskite La0.8Sr0.2FeO3 nanocrystals in heavy metal oxide glass under the Al2O3 tailoring. 10 nm-nanocrystals of orthogonal La0.8Sr0.2FeO3 were synthesized and well distributed in glass by melting quenching followed with subsequent crystallization process at 400 °C for 30 min for 10% Al2O3 content. Aluminum abnormality effect and the Sr2+ induced multi-valence states of Fe ions and oxygen vacancies in La0.8Sr0.2FeO3 lattice, resulting in polarizability and oxygen packing density change. The glass with 10%Al2O3 amount exhibited a large thermal stability (132 °C) and significant enhancement in Verdet constant of 105 rad/T.m at 633 nm wavelength. The obtained Verdet constant values were compared with relative literatures and the values in this study are superior than values in literatures. The obtained glass with extremely good magnetic property and magneto optical performances can be promising candidate for photonics device applications.

Spinel ferrites NiFe2O4 NCs enhanced Mössbauer spectra, magnetization and Faraday rotation of diamagnetic tellurite glasses

Glass containing magnetic nanocrystals are attractive for obtaining high magnetic and magneto-optical properties. In this study, for the first time, 10 nm cubic NiFe2O4 (NFO) nanocrystals doped heavy metal oxide glasses were fabricated and the influence of NFO to glass structure, chemical bonds, Mössbauer spectra, magnetization and Faraday rotation was studied. X-ray diffraction, Raman and X-ray photoelectron spectra revealed the existence of multi-valence states of Fe/Ni ions, oxygen vacancies in cubic lattice and modifications on glass structure, which in turn adjusted the polarizability, oxygen packing density, Mössbauer spectra, magnetic property and magneto-optical behaviors. Through Mössbauer study, the increase of NFO amount enhanced the hyperfine field intensity of tetrahedral Fe3+ ions at the expense of octahedral ones. NFO doped glasses exhibited ferromagnetic behavior whose Ms and Hc increased with the NFO amount due to the NCs size effect. Verdet constant and Faraday rotation angle were studied as function of wavelength, magnetic field, polarizer angle and NFO amount. 3%NFO glass exhibited significant enhancement in magnetization and Verdet constant of 91 rad/T.m at 633 nm which is 5-fold of host glass and superior than literatures. In addition, due to the nanoscale NCs, the thermal stability of obtained NFO glasses remained higher than 100 °C which is promising for photonics devices fabrication.

N, S-co-doped carbon/Co1-xS nanocomposite with dual-enzyme activities for a smartphone-based colorimetric assay of total cholesterol in human serum

We fabricated a novel N,S-co-doped carbon/Co1-xS nanocomposite (NSC/Co1-xS) using a facile sol-gel approach, which featured a multiporous structure, abundant S vacancies and Co-S nanoparticles filling the carbon-layer pores. When the Co1-xS nanoparticles were anchored onto the surface of N,S-co-doped carbon, a synergistic catalysis action occurred. The NSC/Co1-xS nanocomposites possessed both peroxidase-like and oxidase-mimetic dual-enzyme activities, in which the oxidase-mimetic activity dominated. By scavenger capture tests, the nanozyme was demonstrated to catalyze H2O2 to produce h+, •OH and •O2−, among which the strongest and weakest signals were h+ and •OH, respectively. The multi-valence states of Co atoms in the NSC/Co1-xS structure facilitated electronic transfer that enhanced redox reactions, thereby improving the resultant color reaction. Based on the NSC/Co1-xS's enzyme-mimetic catalytic reaction, a visual colorimetric assay and Android “Thing Identify” application (app), installed on a smartphone, offered detection limits of 1.93 and 2.51 mg/dl, respectively, in human serum samples. The selectivity/interference experiments, using fortified macromolecules and metal ions, demonstrated that this sensor had high selectivity and low interference potential for cholesterol analysis. Compared to standard assay kits and previously reported visual detection, the Android smartphone-based assays provided higher accuracy (recoveries up to 93.6–104.1%), feasibility for trace-level detection, and more convenient on-site application for cholesterol assay due to the superior enzymatic activity of NSC/Co1-xS. These compelling performance metrics lead us to posit that the NSC/Co1-xS-based nanozymic sensor offers a promising methodology for several practical applications, such as point-of-care diagnosis and workplace health evaluations.

Ca-doped PrBa1-xCaxCoCuO5+δ (x = 0–0.2) as cathode materials for solid oxide fuel cells

Ca-doped perovskite oxides PrBa1-xCaxCoCuO5+δ (PBCCCO, x = 0–0.2) were prepared and investigated as SOFC cathode materials. PBCCCO samples are single perovskite structure with P4/mmm space group. Pr, Cu and Co ions in PBCCCO samples exist in the form of Pr3+/Pr4+, Cu2+/Cu+ and Co3+/Co4+ multi-valence states. The average TECs of PBCCCO samples were reduced from 17.4 × 10−6 K−1 (x = 0) to 16.7 × 10−6 (x = 0.1) and 16.1 × 10−6 K−1 (x = 0.2) whin RT-900°С. The electrical conductivity and electrochemical catalytic activity of PBCCCO perovskites was enhanced obviously by Ca doping. The ASR values decreased by 60.1% (@650 °C), 68.9% (@700 °C), 71.0% (@750 °C) and 72.8% (@800 °C) respectively when Ca doping content increased from x = 0 to 0.2. These results suggest PBCCCO sample with Ca doing content x = 0.2 can be a promising cathode for IT-SOFC.

Mini Review on Active Sites in Ce-Based Electrocatalysts for Alkaline Water Splitting

Hydrogen energy has become one of the most attractive candidates to replace traditional fossil fuels because of its lack of pollution and its high energy density. Electrocatalytic water splitting is a “green” and sustainable way to produce hydrogen but is still not sufficiently efficient at this stage. In recent years, Ce-based materials have become very popular as the electrocatalysts for water splitting primarily because of the multivalence state of Ce and easily formed oxygen vacancies readily formed in CeO2. However, until now, this interesting subject has seldom been reviewed, especially for electrocatalysts for alkaline water splitting. Herein, we outline and discuss recent progress on the active sites of Ce-based electrocatalysts for hydrogen evolution and oxygen evolution. Oxygen vacancies and interfaces between CeO2 and mixed metal components could provide optimized binding of hydrogen evolution reaction (HER) intermediates, thus promoting HER performance. For the oxygen evolution reaction (OER), Ce3+/Ce4+ redox, oxygen vacancies, and exogenous transition metals could optimize the binding of OER intermediates toward top catalytic activities. The aim of this review is to seek an overall understanding about the reaction sites in Ce-based electrocatalysts for water splitting, which may provide a guide for the future development of HER and OER Ce-based electrocatalysts toward industrial applications.