Cobalt Doping Research Articles

Impact of Co-doping on the microstructural and electrochemical features of mesoporous 3D oval–shaped Ni3-xCoxV2O8 electrodes for high-performance hybrid supercapacitors

Transition metal vanadates have sparked much attention as positive electrode materials for supercapacitors; nevertheless, their poor electronic conductivity, low electroactive sites, and sluggish charge transfer kinetics continue to be problematic. Herein, we incorporate Co dopants in nickel vanadates (NCV) and successfully tailor porous 3D oval-shaped particles using hydrothermal synthesis at 210 °C for 12 h. The interconnected particles, as well as the porous nature of each oval-shaped particle, provide high accessibility to active species and improve charge transfer kinetics. Additionally, the incorporation of cobalt dopants improves electronic conductivity and enriches redox chemistry. As a consequence, NCV delivered a specific capacitance of 391/376 F/g at 0.5/1 A/g current density, with capacitance retention of 98.6 % after 8000 cycles, indicating outstanding cycling stability. Moreover, the micro-spherical layered-structured BiOBr electrode was chosen for the negative electrode and demonstrated a specific capacitance of 132 F/g at a current density of 1 A g−1, in the potential window of −1 to +0 V. Furthermore, the solid-state Ni3-xCoxV2O8//BiOBr hybrid supercapacitor device demonstrated 118 F/g specific capacitance, 25.5 Wh kg−1 energy density, and exceptional cycle stability (85.9 % capacitance preserved after 10,000 cycles).

Modulating Electronic Structure to Improve the Solar to Hydrogen Efficiency of Cobalt Nitride with Lattice Doping

Development of state-of-the-art catalytic systems for highly efficient solar to hydrogen energy conversion is desirable but remains a challenge. In this work, transition metal (M = V, Mo, and W) doped cobalt nitride has been synthesized for solar to hydrogen energy conversion. Neutron diffraction results suggest that the composition of our as-prepared cobalt nitride is Co3.75N0.14, which contains many lattice defects. Neutron pair distribution function (PDF) analysis confirms the structural defects and lattice distortion in M-Co3.75N0.14. The M-doping is demonstrated to tune the electronic structure and properties of Co3.75N0.14 due to the formation of M–N bonds, which significantly improves charge carrier separation efficiency and the reaction kinetics. Density functional theory (DFT) calculations suggest that the d-band center of the doped cobalt nitrides exhibit downshifts compared to pure cobalt nitride. This is beneficial for the desorption of hydrogen atoms, promoting hydrogen evolution activity. The hydrogen evolution rate of the optimal V–Co3.75N0.14-Eosin-Y system reaches 21.21 μmol·mg–1·h–1, with quantum efficiency around 38% at 405 nm excitation wavelength. This remarkable value surpasses those reported for other hybrid photocatalysts.

Preparation and investigation of physiochemical, magnetic, and anti-microbial properties of cobalt-doped Bi2S3 nanostructure

The current study proposes the synthesis of cobalt-doped Bi2S3 nanostructures by the unique reverse micelle method at room temperature. Analysis using Energy dispersive analysis of X-rays (EDAX) demonstrated the correct stoichiometry, powder X-ray diffraction (PXRD) data were Rietveld refined using GSAS-II software confirming the formation of orthorhombic Bi2S3 with some residuals for cubic CoS2 phase. As the weight% of cobalt increases, the unit cell volume of orthorhombic Bi2S3 increases from 503.17 (16) (A0)3 to 507.34 (4) (A0)3. The Raman measurement shows the vibrational mode of both orthorhombic Bi2S3 and cubic CoS2 phases. The weak peak centered at 255 cm−1 is due to the symmetric vibration of the Bi–S bond which disappears in cobalt-doped samples and was replaced by new peaks related to Co–S bond vibration. This indicates the deformation in host orthorhombic Bi2S3 crystal due to cobalt doping and is consistent with Rietveld refinement results of PXRD. This work also gives the value of isobaric Gruneisen parameter for CoxBi2-xS3 (x = 0.0,1.0,1.5 & 2.0 wt%) were 5.1, −7.3, −4.8, and −5.2 respectively obtained from the low-temperature Raman measurement. The optical study shows the increment in band-gap with doping and proves to have visible light active band-gap. The pristine Bi2S3 nanostructures showed broad emission from the violet region (400 nm) to the yellow region (590 nm) with maximum emission at 440 nm in the blue region. The PL intensity decreases as cobalt weight% increases because of electron-hole recombination. The morphological study through high-resolution transmission electron microscopy (HR-TEM) revealed the single crystalline nature and showed the change in morphology from nanocylinders and nanorods with nanoparticles. The room temperature ferromagnetic behavior increases as cobalt weight% increases and reaches the maximum for 1.5 wt% cobalt. This study showed that the prepared nanostructures have potential application as an antimicrobial agent against both Gram + ve and Gram-ve microorganisms.

Photocatalytic degradation of sulfamethoxazole with Co-CuS@TiO2 heterostructures under solar light irradiation

This work describes a successful approach to dope copper sulfide with different amounts of Co2+ ions and combine it with TiO2 through a simple one-step hydrothermal process. Compared with the bare CuS, the synthesized Co-CuS@TiO2 heterostructures promote charge transport and restrict the recombination of photoexcited electrons and holes. The intrinsic properties of Co-CuS@TiO2 samples are systematically examined through experimental characterizations and density functional theory (DFT) theoretical calculations. Photocatalytic degradation tests under simulated solar light irradiation were performed using sulfamethoxazole degradation as a model emerging persistent antibiotic. The photocatalytic performance was enhanced after cobalt doping, and the heterostructure doped with 3% of Co exhibited the best degradation with an apparent rate constant of 0.0216 min−1. This sample also showed a much faster settling than bare TiO2, which indicates a much easier separation of the reaction media after being used. The enhancement of degradation is attributed to the increased light absorption and the more efficient charge transfer and separation. The plausible photocatalytic degradation mechanism of sulfamethoxazole was also proposed. This study presents a novel strategy to prepare potential photocatalysts for the elimination of emerging pollutants.

Expediting Toluene Combustion by Harmonizing the Ce-O Strength over Co-Doped CeZr Oxide Catalysts.

Low-temperature catalytic degradation of volatile organic compounds (VOCs) by enhancing the activity of non-precious metal catalysts has always been the focus of attention. The mineralization of aromatic VOCs requires the participation of a large number of oxygen atoms, so the activation of oxygen species is crucial in the degradation reaction. Herein, we originally adjust the Ce-O bond strength in CeZr oxide catalysts by cobalt doping to promote the activation of oxygen species, thus improving the toluene degradation performance while maintaining high stability. Subsequent characterizations and theoretical calculations demonstrate that the weakening of the Ce-O bond strength increases the oxygen vacancy content, promotes the activation of oxygen species, and enhances the redox ability of the catalysts. This strategy also promotes the activation of toluene and accelerates the depletion of intermediate species. This study will contribute a strategy to enhance the activation ability of oxygen species in non-noble metal oxide catalysts, thereby enhancing the degradation performance of VOCs.

Cobalt ions induced morphology control of metal-organic framework-derived indium oxide nanostructures for high performance hydrogen sulfide gas sensors

Real-time gas sensors with high response and selectivity are highly desirable for hydrogen sulfide (H2S) monitoring concentration changes in the environment, especially at the ultra-trace level. Herein, cobalt-doped indium oxide (In2O3) with shorter-length nanorings was synthesized by foreign metal cobalt ions. By controlling the morphology of the material and calcinating the indium-based metal-organic frameworks (In-MOFs), the nanostructures of the obtained materials have a larger specific surface area, which further improves the sensing performance. The sensor prepared with a suitable amount of cobalt doping materials can exhibit the best gas-sensing performance. The Co-doped In2O3 sensor shows a high response to 2 ppm H2S (∼12.6) at 225 °C, low detection limits (100 ppb), and excellent selectivity, which is 5.34 times higher than pure In2O3 at 300 °C. Moreover, the potential growth mechanism speculates that the presence of Cobalt ions leads to a change in material morphology from nanorods to nanorings. This work provides an implementable method for controlling the morphology of the materials, which could facilitate the development of high-performance gas sensors.

Solvothermal synthesis of magnetically separable Co–ZnO nanowires for visible light driven photocatalytic applications

Magnetically retrievable Cobalt doped ZnO nanowires were synthesised by simple solvothermal method. The prepared Co–ZnO nanowires were analysed with several characterization instruments such as FESEM, XRD, FTIR, VSM, UV–vis spectroscopy, XPS and PL spectroscopy. No other phase has been identified besides wurtzite phase, according to the structural analysis of pure ZnO and Co–ZnO nanowires. As the concentration of Co doping increased, ZnO nanowires' band gap energy dropped. Moreover, ZnO's absorption peak has a minor wavelength shift toward longer wavelengths. Green light emission was detected by PL analysis of ZnO nanowires and also the PL intensity of ZnO nanowires was decreased after cobalt doping. Co–ZnO nanowires exhibited ferromagnetic property. The coercivity and retentivity of Co–ZnO nanowires were increased with increase of Cobalt concentration. Improved visible light photocatalytic activity for the breakdown of methyl orange dye was achieved by Co–ZnO nanowires.

Controllable synthesis of nickel–cobalt-doped Prussian blue analogs for capacitive desalination

The unique framework structure of Prussian blue imparts excellent sodium storage capacity and cycling stability, thus making it an ideal capacitive deionization (CDI) electrode. Herein, Prussian blue analogs were prepared by the controlled doping of nickel–cobalt bimetallic ions to improve their desalination capacity and stability. Process parameters such as cell potential, current, inlet flow rate, and solution concentration were investigated to determine the optimal conditions for Prussian blue desalination, and a high-performance Prussian blue analog (CNF-4) was successfully synthesized by accurately controlling the nickel–cobalt doping ratio. The desalination capacity and rate of CNF-4 (Ni:Co=1:2) reached 65.31 mg g−1 and 4.38 mg g−1 min−1, respectively, and 98% of the capacity retention rate was maintained after 50 cycles of desalination. The excellent capacity and performance of the CNF-4 material indicate its superiority to conventional PBA CDI electrodes and its prospective applications in seawater desalination.

Effect of cobalt doping on antimicrobial, antioxidant and photocatalytic activities of CuO nanoparticles

Copper oxide nanoparticles doped with 3 %, 5 %, and 7 % cobalt have been prepared via the green method using Annona muricata leaf extract to find their antimicrobial, antioxidant and photocatalytic activities. The synthesized nanoparticles was analysed by XRD, FTIR, XPS, EDX, SAED, HRTEM, SEM and UV–Visible techniques. XRD pattern indicate all nanoparticles had single-phase monoclinic structure. Functional groups present in the samples were confirmed by FTIR analysis. The incorporation of Co2+ ions into CuO lattice were identified by XPS analysis. Morphological changes of nanoparticles were confirmed by SEM and HRTEM micrograph. Chemical composition of elements were confirmed by EDX spectra. Antimicrobial efficiency of pure and cobalt doped CuO nanoparticles was identified by their zone of inhibition of bacterial and antifungal strains. Moreover, the green synthesized CuO nanoparticles have considerable antioxidant action. Further, the photocatalytic performance of pure and cobalt doped CuO nanoparticles was done by the degradation of methylene blue.

Cobalt incorporation and MoS2–NiS2 heterostructure synergistic for improving full water electrolysis efficiency

Cobalt doping MoS2/NiS2 is first obtained using a chemical vapor vulcanization method. Cobalt doping further modified the electronic structure of MoS2/NiS2 and modulated the electron density of catalytic sites, beneficial for HER and OER.

Effect of ‘Co’ modification in multiferroic BiFeO3 perovskite on structural and dielectric properties

Multiferroics are the materials comprising of at least two ferroic orders like ferromagnetism, ferroelectricity, or ferroelasticity all in a single phase. Extensive research is underway in the field of material science on multiferroism as it is rarely observed in materials. It has widespread applications especially in spintronics. In this view, bismuth ferrite (BiFeO3) is one of the best multiferroic materials among the number of available multiferroic materials. It is capable of showing ferroelectricity as well as antiferromagnetic nature simultaneously at room temperature. In the present work, efforts have been made to synthesize the BiFeO3 in pure phase as well as with the doping of Cobalt in the ratio of 2 %, 4 %, and 8 % via solid state reaction route and were denoted by BFC0, BFC2, BFC4 and BFC8 respectively. We have optimized our samples on specific calcination as well as sintering temperature. Structural and dielectric analysis has been done and the enhancement has been concluded in the end results. The structural analysis confirms the distorted rhombohedral structure along with some impurities. Impurities reduce on doping BiFeO3 with “Co”. The BFC2 has the maximum dielectric constant (∼155.4 at 1 kHz and ∼ 106.1 at 10 kHz), dielectric loss (∼0.34 at 1 kHz and ∼ 0.27 at 10 kHz) in comparison to other compositions.

A crosslinked network polypyrrole coated cobalt doped Fe2O3@carbon cloth flexible anode material for quasi-solid asymmetric supercapacitors.

Iron(III) oxide (Fe2O3) exhibits a substantial theoretical specific capacitance and a broad operational voltage window, making it a prospective anode material. The crystal structure of Fe2O3 was altered through cobalt doping, and its electronic conductivity was improved by supporting it with carbon cloth (Co-Fe2O3@CC). Subsequently, a crosslinked network of polypyrrole (PPy) was synthesized onto Co-Fe2O3@CC via an ice-water bath, resulting in the formation of PPy/Co-Fe2O3@CC. This PPy nano-crosslinked network not only established three-dimensional electron transport pathways on the Fe2O3 surface but also amplified the composite material's specific surface area to 45.229 m2 g-1, thereby promoting its electrochemical performance. At a current density of 2 mA cm-2, PPy/Co-Fe2O3@CC displayed an area specific capacitance of 704 mF cm-2, a value 2.2 times higher than that of Co-Fe2O3@CC. The assembled PPy/Co-Fe2O3@CC//Ni-MnO2@CC asymmetric supercapacitor demonstrated an energy density of 1.41 mW h cm-3 at a power density of 54 mW cm-3, making the synthesized electrode material a promising candidate for flexible supercapacitors.

Impact of Tin and Cobalt Doping on the Hyperthermia Efficacy of Magnetite Nanoparticles

Impact of Tin and Cobalt Doping on the Hyperthermia Efficacy of Magnetite Nanoparticles

Effect of electronic structure modulation and layer spacing change of NiAl layered double hydroxide nanoflowers caused by cobalt doping on supercapacitor performance

Layered double hydroxides (LDHs) with high theoretical capacity have broad prospectsin energy storage applications. However, their slow charge transfer kinetics and easy agglomerate hinder their applications in high-performance supercapacitors. Herein, Co2+-doped nickel aluminum layered double hydroxides (NiAl-LDH-Co2+-x, x=0, 0.3, 0.6, 0.9, 1.2, 1.5) have been designed and prepared by a convenient hydrothermal process. The multicomponent layer structure formed by cobalt doping facilitates sufficient penetration of the electrolyte and accelerates the charge transfer kinetics. Furthermore, the more open layer spacing and electronic interactions induced by Co2+ doping are conducive to accelerating ion de-intercalation, thereby further improving the kinetic behavior of charge storage. Benefiting from the unique microstructure and Co2+ doping effect, the prepared NiAl-LDH-Co2+-0.9 provides a superior specific capacity of 985 C g-1 at 1 A g-1. In addition, the assembled hybrid supercapacitor with the NiAl-LDH-Co2+-0.9 as the positive electrode provides a remarkable energy density of 22.51 Wh kg-1 at a power density of 800Wkg-1 and exhibits an excellent cycle life with 80% capacity retention after 20,000 cycles. This study demonstrates the great potential of efficient microstructure design and doping strategy in enhancing the charge storage of electrode materials.

Enhanced electrocatalytic oxygen redox reactions of iron oxide nanorod films by combining oxygen vacancy formation and cobalt doping.

A synergistic effect of Co-doping and vacuum-annealing on electrochemical redox reactions of iron oxide films is demonstrated in the present work. In this research, a series of defect-rich iron oxy/hydroxide nanorod arrays: α-FeOOH, Fe2O3, and FeOx nanorod thin film catalysts were synthesized via a hydrothermal approach followed by thermal and vacuum treatments. Besides, a cobalt doping process was employed to prepare the thin film of Co-doped FeOx nanorods. The morphology, crystallinity, and electrochemical activities of Co-doped oxygen-deficient FeOx (Co-FeOx/FTO) show strong correlations with metal concentration and thermal treatments. The electrochemical measurements demonstrated that the as-deposited Co-doped FeOx NR catalyst could achieve a maximum OER current of 30 mA cm-2, which was six times greater than that recorded by as-deposited Co-doped FeOOH NR catalysts (5.7 mA cm-2) at 1.65 V vs. RHE, confirming the superior electrocatalytic OER activity at the as-deposited Co-doped FeOx NR catalyst after cobalt doping. It is believed that these results are attributed to two factors: the synergistic effect of Co doping and the defect-rich nature of FeOx nanorod catalysts that are used in sustainable energy systems.

Post cobalt doping and defect engineering of NbSSe for efficient hydrogen evolution reaction

Post cobalt doped NbSSe was synthesized by combining chemical vapor transport and the hydrothermal method, which exhibited excellent HER performance due to the synergistic effect of cobalt doping and S/Se vacancies.

Electrocatalytic Lignin Valorization into Aromatic Products via Oxidative Cleavage of Cα-Cβ Bonds.

Lignin is the most promising candidate for producing aromatic compounds from biomass. However, the challenge lies in the cleavage of C-C bonds between lignin monomers under mild conditions, as these bonds have high dissociation energy. Electrochemical oxidation, which allows for mild cleavage of C-C bonds, is considered an attractive solution. To achieve low-energy consumption in the valorization of lignin, the use of highly efficient electrocatalysts is essential. In this study, a meticulously designed catalyst consisting of cobalt-doped nickel (oxy)hydroxide on molybdenum disulfide heterojunction was developed. The presence of molybdenum in a high valence state promoted the adsorption of tert-butyl hydroperoxide, leading to the formation of critical radical intermediates. In addition, the incorporation of cobalt doping regulated the electronic structure of nickel, resulting in a lower energy barrier. As a result, the heterojunction catalyst demonstrated a selectivity of 85.36% for cleaving the Cα-Cβ bond in lignin model compound, achieving a substrate conversion of 93.69% under ambient conditions. In addition, the electrocatalyst depolymerized 49.82 wt% of soluble fractions from organosolv lignin (OL), resulting in a yield of up to 13 wt% of aromatic monomers. Significantly, the effectiveness of the prepared electrocatalyst was also demonstrated using industrial Kraft lignin (KL). Therefore, this research offers a practical approach for implementing electrocatalytic oxidation in lignin refining.

Unveiling the role of cobalt doping in optimizing ammonia electrosynthesis on iron–cobalt oxyhydroxide hollow nanocages

A series of FeCoOOH HNCs were constructed via controlled Co doping; the right amount of Co doping can lower the energy barrier of *N2 → *NNH → *NNHH, induced by the preferential proton adsorption on Co sites to drive NH3 electrosynthesis.

Doped metal clusters as bimetallic AuCo nanocatalysts: insights into structural dynamics and correlation with catalytic activity by in situ spectroscopy.

Co-doped Au25 nanoclusters with different numbers of doping atoms were synthesized and supported on CeO2. The catalytic properties were studied in the CO oxidation reaction. In all cases, an enhancement in catalytic activity was observed compared to the pure Au25 nanocluster catalyst. Interestingly, a different catalytic performance was obtained depending on the number of Co atoms within the cluster. This was related to the mobility of atoms within the cluster's structure under pretreatment and reaction conditions, resulting in active CoAu nanoalloy sites. The evolution of the doped Au clusters into nanoalloys with well-distributed Co atoms within the Au cluster structure was revealed by combined XAFS, DRIFTS, and XPS studies. Overall, these studies contribute to a better understanding of the dynamics of doped nanoclusters on supports upon pretreatment and reaction, which is key information for the future development and application of bimetallic nanocluster (nanoalloy) catalysts.

COMPARATIVE CATALYTIC STUDY OF PURE COBALT OXIDE SPINEL AND NON-NOBLE METAL DOPED COBALT OXIDE SPINEL FOR SELECTIVE OXIDATION OF ALCOHOL TO ALDEHYDE: A REVIEW

The selective oxidation of alcohol by heterogeneous catalysts, such as noble and non-noble metal oxide spinels and doped metal oxide spinels, is one of the challenging and interesting routes in catalysis. In this review, the selective oxidation mechanism of non-noble cobalt oxide spinel and various metal-doped cobalt oxide spinel-based catalyst systems are examined. Selective oxidation of alcohol to aldehyde by using cobalt oxide spinel (Co<sub>3</sub>O<sub>4</sub>) and various metal-doped cobalt oxide spinels (Fe, Mn, Ni, Al, Cu, Sr) has been reviewed carefully. The selective oxidation by pure cobalt oxide spinel showed higher activity. However, a large number of studies have also been devoted to selective oxidation by various metal-doped cobalt oxide spinels. The metal-doped Co<sub>3</sub>O<sub>4</sub> showed higher selective oxidation activity compared to the pure spinel Co<sub>3</sub>O<sub>4</sub>. The mechanistic aspects and the role of cobalt and doping metal in the selective oxidation of alcohol have been studied thoroughly.