Effect Of Cobalt Substitution Research Articles

Effect of cobalt substitution for nickel on microstructural evolution and hydrogen storage properties of La0.66Mg0.34Ni3.5–xCox alloys

Superlattice hydrogen storage alloys offer a compelling advantage with rapid hydriding rate and high storage capacity. However, its practical applications face challenges including complex structure, low dehydriding capacity, and cyclic instability. In this work, we successfully prepared La0.66Mg0.34Ni3.5–xCox superlattice hydrogen storage alloys with enhanced dehydriding capacity and stability by partially substituting Co for Ni. X-ray diffraction (XRD) refinements analysis reveals the presence of (La,Mg)3Ni9, (La,Mg)5Ni19, and LaNi5 phases within the alloy. Following Co substitution in the La0.66Mg0.34Ni3.4Co0.1 alloy, there is a significant increase in content of the (La, Mg)3Ni9 phase and a reduction in the hysteresis factor, resulting in an improved reversible hydrogen storage capacity from 1.45 wt% to 1.60 wt%. The dehydriding kinetics of the alloy is controlled by diffusion model with an activation energy of 8.40 kJ/mol. Furthermore, the dehydriding enthalpy value of the Co-substituted alloy decreases from 30.84 to 29.85 kJ/mol. Impressively, the cycling performance of the alloy after Co substitution exhibits excellent stability, with a capacity retention rate of 92.3% after 100 cycles. These findings provide valuable insights for the development of cost-effective hydrogen storage materials.

Dielectric performance of nanostructured magnesium oxide and effect of cobalt substitution

Here, we examined effect of Co substitution on dielectric characteristics of MgO nanostructures at various doping concentrations with the view to finding its use as a capacitor. The grain and grain boundary have significant impact on the dielectric characteristics' temperature and frequency dependency. Pure and Co doped MgO nanostructures showed dramatic drop in their dielectric constant and dielectric loss with increasing frequency. Reverse micelle micro emulsions of water-cyclohexane-CTAB ternary oil-surfactant-water systems were used to synthesize both pure and Co doped MgO nanostructures. Energy-dispersive X-ray spectroscopy (EDX), powder X-ray diffraction (PXRD), dynamic light scattering based particle size analysis (DLS-PSA), photoluminescence (PL), and Raman spectroscopy were used to analyze the synthesized materials. Different frequency and temperature range were studied for the complex permittivity of dielectric characteristics (ε * = ε'-jε") and the loss tangent (tanδ) and based on the experimental data, ε', ε", tanδ decreases as frequency and temperature increase.

Enhanced Photocatalytic Water Splitting of SrTiO3 Perovskite through Cobalt Doping: Experimental and Theoretical DFT Understanding.

Throughout extensive research endeavors, SrTiO3 has emerged as a promising photocatalytic material for utilizing solar energy and facilitating hydrogen production via water splitting. Yet, the pursuit of enhanced efficiency and amplified hydrogen generation has prompted researchers to delve into the realm of advanced doping strategies. In this work, using experimental characteristics and DFT calculations, we studied the effect of cobalt substitution on the structural, electronic, optical, and magnetic properties as well as the photocatalytic activity of SrTi1-xCoxO3-δ (x = 0, 0.125, 0.25, 0.375, and 0.5) perovskites. The samples were successfully prepared by using the solid-state reaction method. Based on X-ray diffraction and the Rietveld refinement method, the elaborated samples were shown to preserve the absorption range up to the visible region. Moreover, the position of band edge levels after cobalt doping becomes more appropriate for water splitting. Our findings report that all cobalt-doped compounds exhibit good photocatalytic activities and could be used as suitable photocatalyst materials for hydrogen production.

Effect of cobalt substitution on the structural, ferroelectric, and magnetic properties of bismuth ferrite thin films

Epitaxial films of multiferroic BiFe1−xCoxO3 (BFCO) with 0≤x≤0.35 are grown on (001)-oriented SrTiO3 and SrRuO3 buffered SrTiO3 substrates using the pulsed laser deposition technique. The effect of structural transformation from rhombohedral to tetragonal phase with increasing cobalt substitution on the magnetic, electrical, and piezo-/ferroelectric properties is investigated. Piezoresponse force microscopy is used to quantify the coercive voltage from the phase hysteresis loops for different thickness films to investigate the semi-empirical Kay–Dunn scaling law with varying cobalt concentrations. For the rhombohedral structure, a reduction of the coercive voltage is observed with increasing substitution of Fe by Co. The coercive voltage of a 10 nm BFCO (x=0.35) film is found to be 0.63 V, which is 67% lower than that of a pure BiFeO3 (BFO) (1.9 V) film of the same thickness. Cobalt substitution also leads to changes in the magnetic and electrical properties due to modification of spin ordering and reduction of the bandgap, respectively. Further, to validate the experimental results, we have performed theoretical calculations using density functional theory. The theoretical results indicate a reduction in unit cell volume and enhancement in net magnetization can be achieved with cobalt substitution, in agreement with experimental results. Partial Co substitution can, thus, provide a pathway to realize BFO-based nonvolatile magnetoelectric devices with reduced operating voltage.

Insights into the effect of cobalt substitution into copper-manganese oxides on enhanced benzene oxidation activity

Co-substituted Cu-Mn spinel oxides were synthesized, characterized, and catalytic performance for benzene oxidation was evaluated. Spinel phases, and the substitution of Mn sites by Co were confirmed for the ternary oxides. Co0.2Cu0.8MnOy showed the highest activities with the lowest apparent activation energy among the ternary oxides. The improved catalytic properties due to Co substitution are attributed to more activated lattice oxygen, stronger adsorption of benzene, and a larger specific surface area. Density functional theory simulations also revealed that the Co substitution enhanced the reactivity of the lattice oxygen. Adsorbed and activated benzene reacted with lattice oxygen to form abundant oxygen defects, which promoted O2 adsorption and dissociation, contributing to enhanced catalytic activity. The effect of water vapor on the catalytic benzene oxidation was also clarified.

Effect of Cobalt Substitution on the Structural and Magnetic Properties of Bismuth Ferrite Powders

BiFeO3 (BFO) is a multiferroic material with excellent ferroelectric properties but with poor magnetic behavior. Therefore, we focused principally on the enhancement of the magnetic order of BFO. These multiferroic properties make BFO an excellent candidate for magnetoelectric devices at room temperature. Pure and Co-BiFeO3 powders were successfully synthesized via the sol–gel method at 700 °C. The effect of Co substitution on the corresponding structural and magnetic properties of BFO was studied. X-ray diffraction and Fourier Transform Infrared Spectroscopy measurements confirmed the rhombohedral perovskite structure in all samples. A secondary phase of CoFe2O4 (CFO) was detected for 9, 10, and 15% of Co doping. The scanning electron microscopy images of the Co-BFO particles showed a reduction in the particle size compared to the pure BFO powders. Vibrating sample magnetometry measurements evidenced the ferromagnetic hysteresis loop for the Co-BFO powders with values of saturation magnetization of 4.1 emu/g and a coercivity of 1083 Oe for 15% of Co doping. In this work, we report impurity free samples with notable magnetic properties at the same time, which is a difficult challenge in bismuth ferrite synthesis. This is the first step for later applications in future technology.

Effect of cobalt substitution in Zn1-xCoxFeCrO4 ferri-chromate: emerging light absorber for degradation of model textile dye

The concentration (x = 0.0 to 1.0) of cobalt doped magnetically separable Zn1-xCoxFeCrO4 ferrite was produced by sol-gel auto combustion utilizing glycine as a fuel. We can deduce that a single-phase cubic spinel system is synthesized based on powder XRD measurements and Rietveld refinement of the Zn1-xCoxFeCrO4 ferrite system. With the increase in cobalt content in the Zn1-xCoxFeCrO4 ferrite system, morphological examination revealed irregularly formed nanostructures ranging in size from 10 nm to 40 nm. When this ferrite system was exposed to TEM examination, similar morphological results were found. The coercivity of the Zn1-xCoxFeCrO4 ferrite system increased as the density and crystallite size were reduced. The remanence ratio rises in proportion to the increase in cobalt content. The visible region's optical characteristics were studied, and a blue shift in the band gap was observed with the increase in concentration of cobalt. The photo catalytic activity of as-synthesized Zn1-xCoxFeCrO4 ferrites on methylene blue (MB) dye degradation was evaluated because the band gap of the catalysts lies in the visible region. Within 85 minutes, the targeted photocatalyst degraded 96.7% of methylene blue, equating to a high degradation reaction rate constant k value up to 0.0089 min−1. As a result, the catalyst has a bright future in terms of environmental remediation. Increased photo catalytic activity is attributed to inhibition of load carrier separation due to crystallinity, proper band energy structure, and morphology of Co2+ doped Zn1-xCoxFeCrO4 ferrite. In addition, our targeted photo catalyst Zn0.25Co0.75FeCrO4 showed good stability and radical scavenger tests suggesting that holes/ hydroxyl radicals were the primary components for increased activity.

Cobalt Demand for Automotive Electrification in China: Scenario Analysis Based on the Bass Model

With accelerating automotive electrification process, quantitative analysis of cobalt demand becomes a critical issue in China. How much cobalt is expected to be needed from 2021 to 2030 to support a smooth automotive electrification in China? This study aims to answer this question comprehensively by examining the responses of annual cobalt demand to variations in electric vehicle sales, battery capacity factors, and cobalt substitution effects, which has not been fully explored in previous literature. Scenario analysis based on the Bass model is adopted and historical data from 2012 to 2020 are used for this study. The results show that 1) the peak annual cobalt demand will reach 35.58–126.97 kt/year during 2021–2030; 2) cobalt demand is expected to decline by 14.29% if the market share of ternary lithium-ion battery decreases by 10%; 3) while cobalt substitution can reduce the demand substantially, it cannot offset the growth of cobalt demand driven by the increasing EV sales and battery capacity. These results provide a knowledge base for policy suggestions to manage the cobalt demand—supply balance in China better.

The effect of cobalt substitution on the structural and elastic properties of MnFe2O4 nanoparticles

The effect of cobalt substitution on the structural and elastic properties of MnFe2O4 nanoparticles

Outstanding thermoelectric performance of [formula omitted]-type half-Heusler V(Fe[formula omitted]Co[formula omitted])Sb compounds at room-temperature

The effects of cobalt substitution at the Fe-site on the crystal structure, electronic structure and thermoelectric (TE) properties of half-Heusler (HH) V(Fe1−xCox)Sb compounds are investigated. Crystal structural analysis using powder X-ray diffraction clarified that all compounds have deficient HH structures (Huang et al., Chem. Mater., 32, 5173-5181, 2020). With Co-substitution at the Fe 4c sites, defects are observed in the V 4a and Fe 4c sites, and a small amount of Fe atoms enter into 4d sites, which is normally vacant in an ideal HH structure. The deficient HH structures of the V(Fe1−xCox)Sb compounds are supported by electronic structural analysis using the Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA). All compounds exhibit n-type behaviour in both calculations and experiments with deficient HH structures. The absolute value of the Seebeck coefficient |S|, decreases with an increase in the cobalt content x. The tendency of the experimental |S| value to decrease corresponds well with the |S| determined by KKR-CPA calculations. Cobalt substitution acts as an electron dopant that effectively tunes the carrier concentration. The optimised carrier concentration of 2.1×1020 cm−3 leads to the highest power factor of 5.7×10−3 W/K2m at room temperature for the V(Fe0.99Co0.01)Sb compound. The V(Fe1−xCox)Sb compounds are thus potential candidates as n-type TE materials for power generation near room temperature.

Cobalt substitution effects on critical current, inter-grain full penetration field, and critical temperature study for Tl2Ba2Ca2Cu3-xCoxOy bulk superconductor, where x is from 0.005 to 0.050

Thallium-based cuprates are known to exhibit high critical temperatures and currents. Usually, partial substitution of copper by transition elements leads to the suppression of superconducting properties. This contribution reports on the studies of Tl2Ba2Ca2Cu3-xCoxOy. All specimens were found to be superconductors with critical temperatures of 102.4 K, 112.9 K, 112.2 K, 113.5 K, 112.8 K, and 94.8 K for x = 0.005, 0.010, 0.020, 0.030, 0.040, and 0.050, respectively. The samples were characterised by scanning electron microscopy, X-ray diffraction, AC susceptibility, resistance, and vibrating sample magnetometry.

Outstanding Thermoelectric Performance Of N-Type Half-Heusler V(Fe <sub>1-X</sub> Co <sub>x</sub>)Sb Compounds at Room-Temperature

The effects of cobalt substitution at the Fe-site on the crystal structure, electronic structure and thermoelectric (TE) properties of half-Heusler (HH) V(Fe1-X Cox)Sb compounds are investigated. Crystal structural analysis using powder X-ray diffraction clarified that all compounds have deficient HH structures (Huang et al., Chem. Mater., 32, 5173-5181, 2020). With Co-substitution at the Fe 4c sites, defects are observed in the V 4a and Fe 4c sites, and a small amount of Fe atoms enter into 4d sites, which is normally vacant in an ideal HH structure. The deficient HH structures of the V(Fe1-X Cox)Sb compounds are supported by electronic structural analysis using the Korringa-Kohn-Rostoker method with the coherent potential approximation (KKR-CPA). All compounds exhibit n-type behavior in both calculations and experiments with deficient HH structures. The absolute value of the Seebeck coefficient |S|, decreases with an increase in the cobalt content x . The tendency of the experimental |S| value to decrease corresponds well with the |S| determined by KKR-CPA calculations. Cobalt substitution acts as an electron dopant that effectively tunes the carrier concentration. The optimized carrier concentration of 2.1×1020 cm-3 leads to the highest power factor of 5.7×10-3 W/K2 m at room temperature for the V(Fe 0.99Co0.01)Sb compound. The V(Fe1-X Cox)Sb compounds are thus potential candidates as n-type TE materials for power generation near room temperature.

Carbon Material and Cobalt-Substitution Effects in the Electrochemical Behavior of LaMnO3 for ORR and OER.

LaMn1−xCoxO3 perovskites were synthesized by a modified sol-gel method which incorporates EDTA. These materials’ electrochemical activity towards both oxygen reduction (ORR) and oxygen evolution reactions (OER) was studied. The cobalt substitution level determines some physicochemical properties and, particularly, the surface concentration of Co and Mn’s different oxidation states. As a result, the electroactivity of perovskite materials can be tuned using their composition. The presence of cobalt at low concentration influences the catalytic activity positively, and better bifunctionality is attained. As in other perovskites, their low electrical conductivity limits their applicability in electrochemical devices. It was found that the electrochemical performance improved significantly by physically mixing with a mortar the active materials with two different carbon black materials. The existence of a synergistic effect between the electroactive component and the carbon material was interpreted in light of the strong carbon–oxygen–metal interaction. Some mixed samples are promising electrocatalysts towards both ORR and OER.

Insight into the Effect of Cobalt Substitution on the Catalytic Performance of LaMnO3 Perovskites for Total Oxidation of Propane

Cobalt-substituted LaMnO3 perovskite catalysts synthesized by the citric acid sol–gel method have been investigated for the total oxidation of propane, as a model for emission control of hydrocarbo...

Enhanced magnetic properties of cobalt-doped bismuth ferrite nanofibers

This study demonstrates the effect of Cobalt substitution on the structure, ferroelectric, and magnetic properties of BiFeO3 (BFO) nanofibers. The BiFe1−xCoxO3 (x = 0, 0.05, 0.1) nanofibers were successfully synthesized by a sol-gel based electrospinning method followed by thermal treatment. The BiFe1−xCoxO3 nanofibers prepared under optimized conditions are a polycrystalline fiber that presents a rhombohedral distorted perovskite structure with a little amount impurity phase. Room temperature polarization and magnetization results indicated the multiferroic behavior of the nanofibers. Especially, the remnant magnetization is increased from 0.18 emu g−1 to 1.72 emu g−1 on increasing amount of Co substitution. The improvement of magnetism can be attributed to the Cobalt doping and size-effect.

Substitution of Co with Ni in Co/Al2O3 Catalysts for Fischer–Tropsch Synthesis

The effect of cobalt substitution with nickel was investigated for the Fischer–Tropsch synthesis reaction. Catalysts having different Ni/Co ratios were prepared by aqueous incipient wetness co-impregnation, characterized, and tested using a continuously stirred tank reactor (CSTR) for more than 200 h. The addition of nickel did not significantly modify the morphological properties measured. XRD, STEM, and TPR-XANES results showed intimate contact between nickel and cobalt, strongly suggesting the formation of a Co-Ni solid oxide solution in each case. Moreover, TPR-XANES indicated that nickel addition improves the cobalt reducibility. This may be due to H2 dissociation and spillover, but is more likely the results of a chemical effect of intimate contact between Co and Ni resulting in Co-Ni alloying after activation. FTS testing revealed a lower initial activity when nickel was added. However, CO conversion continuously increased with time on-stream until a steady-state value (34%–37% depending on Ni/Co ratio) was achieved, which was very close to the value observed for undoped Co/Al2O3. This trend suggests nickel can stabilize cobalt nanoparticles even at a lower weight percentage of Co. Currently, the cobalt price is 2.13 times the price of nickel. Thus, comparing the activity/price, the catalyst with a Ni/Co ratio of 25/75 has better performance than the unpromoted catalyst. Finally, nickel-promoted catalysts exhibited slightly higher initial selectivity for light hydrocarbons, but this difference typically diminished with time on-stream; once leveling off in conversion was achieved, the C5+ selectivities were similar (≈ 80%) for Ni/Co ratios up to 10/90, and only slightly lower (≈ 77%) at Ni/Co of 25/75.

Structural, Optical, Magnetic, and Electrical Properties of Ni0.5Co0.5Al2O4 System

In this present work, we have focused on the effect of cobalt substitution in the nickel aluminate system. The aluminate samples were synthesized by the chemical precipitation method. The structural and optical properties of the NiAl2O4, CoAl2O4, and Ni0.5Co0.5Al2O4 samples were studied through X-ray diffraction and UV-DRS absorbance spectral analysis. The XRD pattern confirms the cubic phase with the space group of Fd-3 m through its analysis of the diffraction peaks. The UV absorption peaks around at 360, 480, 551, 580, and 621 nm extend the formation of NiAl2O4, CoAl2O4, and Ni0.5Co0.5Al2O4 system. The surface morphological images of the samples were scanned by using the scanning electron microscope. The room temperature magnetic nature of the aluminate samples was carried out using VSM, and the observed result reveals a weak ferromagnetic and super-paramagnetic nature for NiAl2O4 and Ni0.5Co0.5Al2O4, respectively. The temperature dependence impedance spectra and AC conductivity were measured using an impedance analyzer at selected temperatures, and that reveals the bulk resistance of the grain and the grain boundary region of the sample. The observed results were analyzed and discussed.

Single Site Cobalt Substitution in 2D Molybdenum Carbide (MXene) Enhances Catalytic Activity in the Hydrogen Evolution Reaction.

Two-dimensional (2D) carbides, nitrides, and carbonitrides known as MXenes are emerging materials with a wealth of useful applications. However, the range of metals capable of forming stable MXenes is limited mostly to early transition metals of groups 3-6, making the exploration of properties inherent to mid or late transition metal MXenes very challenging. To circumvent the inaccessibility of MXene phases derived from mid-to-late transition metals, we have developed a synthetic strategy that allows the incorporation of such transition metal sites into a host MXene matrix. Here, we report the structural characterization of a Mo2CTx:Co phase (where Tx are O, OH, and F surface terminations) that is obtained from a cobalt-substituted bulk molybdenum carbide (β-Mo2C:Co) through a two-step synthesis: first an intercalation of gallium yielding Mo2Ga2C:Co followed by removal of Ga viaHF treatment. Extended X-ray absorption fine structure (EXAFS) analysis confirms that Co atoms occupy Mo positions in the Mo2CTx lattice, providing isolated Co centers without any detectable formation of other cobalt-containing phases. The beneficial effect of cobalt substitution on the redox properties of Mo2CTx:Co is manifested in a substantially improved hydrogen evolution reaction (HER) activity, as compared to the unsubstituted Mo2CTx catalyst. Density functional theory (DFT) calculations attribute the enhanced HER kinetics of Mo2CTx:Co to the favorable binding of hydrogen on the oxygen terminated MXene surface that is strongly influenced by the substitution of Mo by Co in the Mo2CTx lattice. In addition to the remarkable HER activity, Mo2CTx:Co features excellent operational and structural stability, on par with the best performing non-noble metal-based HER catalysts. Overall, our work expands the compositional space of the MXene family by introducing a material with site-isolated cobalt centers embedded in the stable matrix of Mo2CTx. The synthetic approach presented here illustrates that tailoring the properties of MXenes for a specific application can be achieved via substitution of the host metal sites by mid or late transition metals.

Effect of Cobalt Substitution on Magnetic, Resistivity and Dielectric Properties of Nickel–Zinc Ferrite (CoxNix–0.5Zn0.5Fe2O4)

Effect of Cobalt Substitution on Magnetic, Resistivity and Dielectric Properties of Nickel–Zinc Ferrite (Co<i>_x</i>Ni<i>_x</i>_–_0.5Zn_0.5Fe₂O₄)

Effect of cobalt substitution on structure and magnetic properties of Nd0.4Zr0.6Fe10–xCoxSi2 (x = 0–3) alloys and their ribbons

This study reports the stabilization of the RFe12-type based compounds where part of R and Fe are substituted with Zr and Co and Si, respectively, in order to examine whether these rare-earth-lean materials are suitable for applications as permanent magnets. Structural and magnetic characterization of the family of alloys with the general formula Nd0.4Zr0.6Fe10–xCoxSi2 (x = 0–3) and their melt-spun ribbons were carried out using X-ray diffraction and Mössbauer spectroscopy. The ThMn12-type structure is obtained for all samples as the majority phase with a minority α-Fe(CoSi) phase (less than 5 wt%) as it was estimated by XRD for x = 1 and 2. The Curie temperature increases linearly with Co substitution from 561 K for x = 0 to 712 K for x = 3. The saturation magnetization decreases slightly from 130.5 (x = 1) to 129.1 A·m2/kg (x = 3), while the anisotropy field is following the same trend.