Cobalt Nanocluster Research Articles

The important role of diatomite on multifunctional modified separator of Li-S battery

The commercial applications of lithium-sulfur (Li-S) batteries are limited by decreased cycling performance caused by the shuttle effect of polysulfides, slower kinetic reaction rates, and lithium anode dendrites. This study demonstrates the important role of diatomite (DT) in regulating cycle performance of modified separator for Li-S batteries. A multifunctional separator (Co/NC/DT) with DT as a carrier assembled high loading cobalt nanocluster is prepared. The N-doped carbon is immobilized via Si-N bond between DT and N-doped carbon. The depth profiles of XPS indicate that the ratio of pyrrolic N to pyridinic N of Co/NC/DT reaches 5.31 at the etching of 100 nm versus 0.83 for Co/NC at surface, which suggesting that mainly N species is pyrrolic N after the addition of DT. Theoretical calculations confirm that cobalt nanoclusters grown on pyrrolic N-doped carbon have a lower adsorption energy for active materials compared to that on pyridinic N-doped carbon and can reduce the energy barrier, especially only 0.09 eV for reduction from Li2S6 to Li2S4. In-situ X-ray diffraction analysis confirms Co/NC/DT can effectively promote formation of Li2S. Lithium anode in-situ optical microscopy observation shows the modified separator could reduce lithium dendrites effectively. Li-S battery assembled with the modified separator can reach an initial capacity of 1331.3 mAh g−1 at 0.2 C and cycle 1500 cycles at 1.0 C with a decay of only 0.039% per cycle. Through regulation of DT, Co/NC/DT accelerates the conversion from long-chain sulfur to short-chain sulfur and Li+ transfer rate, resulting in improving cycling performance.

Self-Powered cobalt nanocluster decorated flexible graphene based Tribo-Sensors for respiratory diagnosis of critical asthma patient

Self-powered ultrafast sensors have received much attention for sustainable operation without any external power source in the Internet of Things (IoT) platform. This paper proposes faster responsive, highly sensitive triboelectric nanogenerator (TENG) sensors based on few layered nitrogen-doped graphene anchored with cobalt nanocluster (Co-N-Gr) to detect the relative concentration of target species, their proximity analysis, and monitor malfunction of human respiration in real-time. Herein, to understand the sensing mechanism, P-type behaviour of this active material is verified under the FET platform by reducing the leakage current density via the implementation of dual dielectric gate (NiO (200 nm)-SiO2 (10 nm)) oxides leading to better control over channel mobility. The device exhibits maximum sensitivity of around 4722 % at zero bias conditions with excellent response and recovery time of 1.16 s and 1.39 s, respectively which falls within the range of standard human breathing frequency. The triboelectric nature of the sensor device at 1 V bias under natural breathing exhibits a high sensitivity (39.56 %) towards relative humidity of 10–90 % with excellent stability over 13 h. In addition, our TENG sensor is highly sensitive towards NOx content upto ppb levelwhich can improve reliability towards asthma detection as NOx content is relatively higher in asthma patients. This approach provides an integrated platform not only towards selective detection of NOx content as well as to identify the individual breathing strength. Furthermore, as-fabricated self-powered device demonstrates its potential in differentiating various respiratory status and has the capability to detect acute exacerbation of chronic obstructive pulmonary disease (AECOPD) via a distinct pattern recognition. Therefore, the work paves the way to design a low-cost flexible device fabrication on Kapton substrate integrable with wearable appliances for commercialization.

Modulating the p-band center of carbon nanofibers derived from Co spin state as anode for high-power sodium storage

Carbon nanofibers (CNFs) have received extensive and in-depth studied as anodes for sodium-ion batteries (SIBs), and yet their initial Coulombic efficiency and rate capability remain enormous challenge at practical level. Herein, CNFs anchored with cobalt nanocluster (CNFs-Co) were prepared using chemical vapor deposition and thermal reduction methods. The as-prepared CNFs-Co shows a high initial Coulombic efficiency of 91% and a high specific discharge capacity of 246 mAh/g at 0.1 A/g after 200 cycles as anode for SIBs. Meanwhile, the CNFs-Co anode still delivers a high cycling stability with 108 mAh/g after 1000 cycles at 10 A/g. These excellent electrochemical properties could be attributed to the involved spin state Co, which endows CNFs with large interplanar spacing (0.39 nm) and abundant vacancy defects. Importantly, the spin state Co downshifts the p-band center of carbon and strengthens the Na+ adsorption energy from −2.33 eV to −2.64 eV based on density functional theory calculation. This novel strategy of modulating the carbon electronic structure by the spin state of magnetic metals provides a reference for the development of high-performance carbon-based anode materials.

The role of the Co reduction and Zn evaporation of ZnCo-MOF carbonization in peroxymonosulfate activation for levofloxacin purification from wastewater

Nowadays, emerging pollutants have been attracting many interests from the researchers. Many attentions are being paid to sulfate based advanced oxidation process for purification of emerging pollutants degradation, what depended on the activity in peroxymonosulfate (PMS) activation. In this work, the Zinc and Cobalt bimetallic zeolite imidazole framework (ZnCo-MOF) was conducted as precursor for preparing a novel magnetic ZnxCoy-CN-T through carbothermal reduction. The ZnxCoy-CN-T was further used to activate PMS for degrading levofloxacin (LEV) as a typical emerging pollutant. XRD, SEM, XPS and Raman spectra analysis were used to characterize the ZnxCoy-CN-T. Carbothermal reduction of ZnCo-MOF at 900 °C leads to the generation of zero-valent cobalt and the volatilization of Zn. Meanwhile, the volatilization of Zn not only brings about the adjacent diffusion of the Co atom but also constructs porous carbon (CN) for anchoring the well dispersed Co nanocluster. The Zn1Co5-CN-900 performed the high activity in PMS activation for LEV degradation with favorable efficiency and rate of 98.3% and 0.228 min−1 within 60 min, respectively. The Zn1Co5-CN-900 could be recycled five times with preferable stability and magnetism. The possible degradation pathways were proposed by identifying the intermediate products through liquid chromatography-mass spectrometry (LC-MS) analysis. In summary, a kind of zero-valent cobalt nanocluster anchored on CN was designed to construct a promising Zn1Co5-CN-900/PMS system for LEV degradation with favorable activity and reusability.

Structure Types and Magnetic Behavior of Cobalt Nanoclusters.

Caprylic hydrazide ligands are ideal ligands for the synthesis of novel polynuclear metal complexes, because they contain many N,O coordination atoms with a strong coordination ability, abundant hydrogen-bond donors, acceptors, and large conjugation systems. Here, we successfully obtained one dodecanuclear cobalt nanocluster [CoII8CoIII4(L1)4(Py)12(CH3OH)4(CH3COO)4]·(CH3OH)13 (1) and one octadecanuclear cobalt nanocluster [CoII18(L2)6(Py)48]·(DMF)5·(CH3OH)8 (2) by using H6L1 and H6L2 ligands, respectively (Py = pyridine; DMF = dimethylformamide). The cyclic cobalt nanocluster 1 can be regarded as two pentanuclear cobalt units (Co5(N-N)4) connected by two cobalt ions, and it is a mixed-valent Co nanocluster. Every H6L1 ligand contains 10 coordination atoms, each of which coordinates with the Co ions. And every two H6L1 ligands form a structure similar to a handshake. The abnormal cylindrical cobalt nanocluster 2 can be regarded six trinuclear cobalt units Co3(N-N)2 connected by one L26- ligand, and every L26- ligand splits the structure on both sides, with a twisted cyclohexane in the middle. AC magnetic susceptibilities show that nanocluster 1 exhibits no frequency-dependent behavior, but nanocluster 2 shows an obviously single-molecule magnetic behavior, and the relaxation process of the energy barrier is 20.4 K.

Layered double hydroxide supported cobalt nanocluster: size control and the effect in catalytic hydrogen generation

Synthesizing metal nanoclusters with diameters smaller than 5nm is challenging, but desirable because of the high ratio of surface area to interior atom. However, in this report it was achieved by utilizing magnesium-aluminium layered double hydroxide (Mg/Al-LDH) as a host for cobalt citrate anion precursor, which was later reduced into cobalt nanoclusters (Co-NC). Size of the Co-NC was controlled by changing the concentration of cobalt-citrate (Co-citrate) precursor during anion exchange. XRD and FTIR showed that Co-citrate precursor was successfully intercalated on the LDH while nitrogen adsorption/desorption isotherms confirmed that mesopores in the sample were formed after chemical reduction. Furthermore, TEM/STEM observations confirmed the formation of Co-NC. It was also verified that reducing the concentration of Co-citrate from 4mM to 0.5mM resulted in a reduction in the size of Co-NC from 4.4 to 1.3 nm. However, catalytic hydrogen generation from sodium borohydride (NaBH4) hydrolysis experiment indicated that catalytic activity decreased as the size of Co-NC decreases. This is mainly attributed to the limitation in mass transport within the interlamellar space of the smaller cluster LDH compared to the bigger one. Overall, Co-NC-LDH is a promising catalyst for NaBH4 hydrolysis. However, an optimum Co-NC size is critical for enhanced catalytic activity.

Metal-Organic Framework-Derived Nitrogen-Doped Cobalt Nanocluster Inlaid Porous Carbon as High-Efficiency Catalyst for Advanced Potassium-Sulfur Batteries.

Despite high theoretical capacity and earth-abundant resources, the potential industrialization of potassium-sulfur (K-S) batteries is severely plagued by poor electrochemical reaction kinetics and a parasitic shuttle effect. Herein, a facile low-temperature pyrolysis strategy is developed to synthesize N-doped Co nanocluster inlaid porous N-doped carbon derived from ZIF-67 as catalytic cathodes for K-S batteries. To maximize the utilization efficiency, the size of Co nanoparticles can be tuned from 7 nm to homogeneously distributed 3 nm clusters to create more active sites to regulate affinity for S/polysulfides, improving the conversion reaction kinetics between captured polysulfides and K2S3/S, fundamentally suppressing the shuttle effect. Cyclic voltammetry curves, Tafel plots, electrochemical impedance spectroscopy, and density functional theory calculations ascertain that 3 nm Co clusters in S-N-Cos-C cathodes exhibit superior catalytic activity to ensure low charge transfer resistance and energy barriers, enhanced exchange current density, and improved conversion reaction rate. The constructed S-N-Cos-C cathode delivers a superior reversible capacity of 453 mAh g-1 at 50 mA g-1 after 50 cycles, a dramatic rate capacity of 415 mAh g-1 at 400 mA g-1, and a long cycling stability. This work provides an avenue to make full use of high catalytic Co nanoclusters derived from metal-organic frameworks.

Light-Harvesting Property from Self-Assembly of Cobalt Nanocluster Aggregates for Efficient Hydrogen Evolution

Herein, we report the light-harvesting property (LHP) from a self-assembled cobalt nanoaggregate (S-CoNA) for an efficient hydrogen evolution. The syntheses of S-CoNAs were achieved using 3-mercaptopropylsulfonate (MPS) as the stabilizer, and the as-formed compound exhibits broad absorption at 407 and 496 nm which appears in the visible region that prompts us to investigate the photo-electrochemical studies. Interestingly, the as-prepared S-CoNAs achieved enhanced hydrogen energy production in the visible region. To know the mechanism of LHP from S-CoNAs and to examine the (M/L) ratios and varying the M/L contribution in detail, we further synthesized S-CoNAs in different metal to ligand ratios (M/L). Out of the five different ratios, the M/L (1:4) ratio resulted in a maximum response of 15 mA cm–2 at 0.3 V applied potential (vs Ag/AgCl). Further, we performed electrochemical studies by tuning the potentials (0, 0.3 V) followed by illumination in the presence and absence of visible light. Furthermore, Fourier-transform infrared spectroscopy analysis before and after photo-electrochemical reaction resulted in a notable peak at 998 and 2115 cm–1, respectively, which is attributed to a metal sulfur linkage via both the thiol (−SH) and sulfonate (−SO3H) terminals of MPS. The photo-electrochemical reaction which is observed after this effective stabilization for S-CoNAs via Co–S linkages was responsible for the hydrogen energy production.

Formation of a Highly Reactive Cobalt Nanocluster Crystal within a Highly Negatively Charged Porous Coordination Cage

AbstractEarth‐abundant first‐row transition‐metal nanoclusters (NCs) have been extensively investigated as catalysts. However, their catalytic activity is relatively low compared with noble metal NCs. Enhanced catalytic activity of cobalt NCs can be achieved by encapsulating Co NCs in soluble porous coordination cages (PCCs). Two cages, PCC‐2a and 2b, possess almost identical cavity in shape and size, while PCC‐2a has five times more net charges than PCC‐2b. Co2+ cations were accumulated in PCC‐2a and reduced to ultra‐small Co NCs in situ, while for PCC‐2b, only bulky Co particles were formed. As a result, Co NCs@PCC‐2a accomplished the highest catalytic activity in the hydrolysis of ammonium borane among all the first‐row transition‐metals NCs. Based on these results, it is envisioned that confining in the charged porous coordination cage could be a novel route for the synthesis of ultra‐small NCs with extraordinary properties.

Formation of a Highly Reactive Cobalt Nanocluster Crystal within a Highly Negatively Charged Porous Coordination Cage

Earth-abundant first-row transition-metal nanoclusters (NCs) have been extensively investigated as catalysts. However, their catalytic activity is relatively low compared with noble metal NCs. Enhanced catalytic activity of cobalt NCs can be achieved by encapsulating Co NCs in soluble porous coordination cages (PCCs). Two cages, PCC-2a and 2b, possess almost identical cavity in shape and size, while PCC-2a has five times more net charges than PCC-2b. Co2+ cations were accumulated in PCC-2a and reduced to ultra-small Co NCs in situ, while for PCC-2b, only bulky Co particles were formed. As a result, Co NCs@PCC-2a accomplished the highest catalytic activity in the hydrolysis of ammonium borane among all the first-row transition-metals NCs. Based on these results, it is envisioned that confining in the charged porous coordination cage could be a novel route for the synthesis of ultra-small NCs with extraordinary properties.

Detecting element specific electrons from a single cobalt nanocluster with synchrotron x-ray scanning tunneling microscopy

We use a nanofabricated scanning tunneling microscope tip as a detector to investigate local X-ray induced tunneling and electron emission from a single cobalt nanocluster on a Au(111) surface. The tip-detector is positioned a few angstroms above the nanocluster, and ramping the incident X-ray energy across the Co photoabsorption K-edge enables the detection of element specific electrons. Atomic-scale spatial dependent changes in the X-ray absorption cross section are directly measured by taking the X-ray induced current as a function of X-ray energy. From the measured sample and tip currents, element specific X-ray induced current components can be separated and thereby the corresponding yields for the X-ray induced processes of the single cobalt nanocluster can be determined. The detection of element specific synchrotron X-ray induced electrons of a single nanocluster opens an avenue for materials characterization on a one particle at-a-time basis.

Catalytic hydrolysis of ammonia borane for hydrogen generation using cobalt nanocluster catalyst supported on polydopamine functionalized multiwalled carbon nanotube

Hydrogen was generated from ammonia borane complex by hydrolysis using cobalt nanocluster catalyst supported on polydopamine functionalized MWCNTs (multi-walled carbon nanotubes). The impregnation-chemical reduction method was used for the preparation of the supported catalyst. The nanocluster catalyst support was formed by in-situ oxidative polymerization of dopamine on the MWCNTs in alkaline solution at room temperature. The structural and physical–chemical properties of the nanocluster catalyst were characterized by FT-IR (Fourier transform infrared spectroscopy), EDX (energy-dispersive X-ray spectroscopy), SEM (scanning electron microscope), XRD (X-ray diffraction) and TEM (transmission electron microscopy). The nanocluster catalyst showed good catalytic activity for the hydrogen generation from aqueous ammonia borane complex. A reusability test to determine the practical usage of the catalyst was also investigated. The result revealed that the catalyst maintained an appreciable catalytic performance and stability in terms of its reusability after three cycle of reuse for the hydrolysis reaction. Also, the activation energy for the hydrolysis of ammonia borane complex was estimated to be 50.41 kJmol−1, which is lower than the values of some of the reported catalyst. The catalyst can be considered as a promising candidate in developing highly efficient portable hydrogen generation systems such as PEMFC (proton exchange membrane fuel cells).

Exchange bias in reduced dimensions: Cobalt nanocluster arrays under the influence of nanometer thin MnPt capping layers

The magnetic behavior of cobalt nanocluster arrays arranged on a boron-nitride nanomesh and capped with MnPt layers of varying thickness θMnPt is investigated. The magnetic properties of the arrays are found to be strongly dependent on the cobalt nanocluster size: large 3-dimensional clusters of several nanometers size under the influence of only θMnPt∼5 nm exhibit prototypical exchange bias behavior, whereas small 2-dimensional clusters of about 1 nm in diameter show superparamagnetic behavior, however, with a strong quenching of the average cobalt magnetization. The latter effect is correlated with the formation of a stable antiferromagnetic phase at increasing θMnPt and is discussed in terms of the domain state exchange bias model. The quenching suggests either partial antiferromagnetic alignment of cobalt spins within a cluster or a random orientation of cobalt cluster macrospins with respect to each other.

Passivation of cobalt nanocluster assembled thin films with hydrogen

The effect of hydrogen passivation on bare and Pd capped cobalt nanocluster assembled thin films was studied with Rutherford backscattering spectrometry (RBS) and magnetic force microscopy (MFM) after exposure to ambient conditions. The nanoclusters are produced in a laser vaporization cluster source in which the helium carrier gas was mixed with hydrogen. RBS revealed that oxidation of the Co nanoclusters is considerably reduced by the presence of hydrogen during cluster formation. The capping did not modify the influence of the passivation. The hydrogen passivation method is especially effective in cases when capping of the films is not desirable, for example for magnetic studies. Clear differences in the magnetic domain structures between hydrogen passivated and non-passivated Co nanocluster films were demonstrated by MFM and are attributed to a difference in inter-cluster magnetic interaction, which is critically depending on the CoO content. The hydrogen passivation method may be used to tailor and stabilize properties of nanocluster assembled thin films.

Effect of stabilizer type on the activity and stability of water-dispersible cobalt(0) nanocluster catalysts in hydrogen generation from the hydrolysis of sodium borohydride

Hydrogen phosphate (HPO4 2−) or poly(acrylic acid) (PAA) stabilized cobalt(0) nanoclusters were in situ generated from the reduction of cobalt(II) chloride during the catalytic hydrolysis of sodium borohydride (NaBH4) in the presence of stabilizers, HPO4 2− or PAA. Cobalt(0) nanoclusters stabilized by HPO4 2− or PAA were characterized by using UV–Visible spectroscopy, TEM, XPS and FT-IR techniques. They were employed as catalysts in the hydrolysis of NaBH4 to examine the effect of stabilizer type on their catalytic activity and stability. Detailed reaction kinetics of the hydrolysis of NaBH4 in the presence of both catalysts was studied depending on catalyst concentration, substrate concentration and temperature. PAA stabilized cobalt(0) nanoclusters provided higher total turnover number (TTON = 6,600) than that of HPO4 2− stabilized cobalt(0) nanoclusters (1,285 turnovers). However, the HPO4 2− stabilized cobalt(0) nanoclusters provided a lower activation energy (E a = 53 ± 2 kJ mol−1) than the PAA stabilized cobalt(0) nanoclusters (E a = 58 ± 2 kJ mol−1) for the hydrolysis of NaBH4. The use of two types of stabilizers in the preparation of the same metal(0) nanoclusters following the same methodology enables us to compare the electrostatic and steric stabilization in terms of the catalytic activity and stability of metal(0) nanoclusters.

Preferential Nucleation of Metallic Clusters on a Nanotemplate: Co on Oxygen-Faceted Re(12 $$ \overline{3} $$ 1)

Preferential nucleation of cobalt nanoclusters at specific sites on oxidized faceted Re(12 $$ \overline{3} $$ 1) is investigated by means of Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and scanning tunneling microscopy (STM). An oxygen terminated nanofaceted Re surface containing ridges and valleys is used as the nanotemplate in this study. Deposition of cobalt onto this surface, followed by annealing to ~800 K, results in preferential cobalt nanocluster nucleation and growth within the valleys of the nanofaceted surface. Decreasing the nanofacet width, cobalt coverage, and annealing temperature lead to the same preferential cobalt nanocluster self assembly, an increase in nanocluster density, and a decrease in nanocluster volume. The preferential nucleation and growth observed for Co nanoclusters on faceted Re makes this a model system for future studies of different substrates and metallic overlayers more relevant to catalytic reactions.

Evolution of cobalt nanocluster and electronic structure deposited on stepped Cu(7 5 5) studied by angle-resolved ultraviolet photoelectron spectroscopy

Using Cu(7 5 5) stepped surface as a template, we prepared nanoclusters of Co and investigated their electronic structure by angle-resolved ultraviolet photoelectron spectroscopy using synchrotron radiation. From 0.28 to 1.6-ML Co coverage one broad peak is observed at 0.7 eV below the Fermi level. On the other hand, from 0.02 to 0.14-ML coverages non-dispersing two peaks are clearly resolved at 0.3 and 1.1 eV, respectively. The existence of the other peaks and the natures of these peaks are discussed based on the angular, step-orientation, and polarization dependences. The detailed assignments of each peak are done by the comparison with the literature. The spectral change dependent on the coverage was due to the shifts of these peaks. The peak shifts are explained by the enhanced exchange splitting at the low coverages due to both energetic and spatial localization which is consistent with the nanocluster model.

Structural and physical properties of cobalt nanocluster composite glasses

Composite systems with metallic nanoparticles embedded in dielectrics present peculiar physical properties which are attractive in several application fields. In the case of transition elements, the magnetic properties of the metal clusters embedded in a dielectric matrix mainly depend on the particle size and structure. In this work, silica films containing cobalt atoms were synthesized by RF magnetron co-sputtering deposition technique, with cobalt concentration of a few atomic percent. X-ray diffraction and transmission electron microscopy showed the presence of hcp cobalt nanoclusters in the as-deposited sample with the highest cobalt concentration. After deposition, thermal treatments were performed to promote cobalt compounds or nanoparticle formation. The thermal treatments were able to change the oxidation state of cobalt atoms, as well as the structure of metallic cobalt nanoclusters (from hcp to fcc), their final size depending on both the preparation parameters and the subsequent annealing atmospheres.

Magnetic force microscopy on cobalt nanocluster films

Magnetic force microscopy (MFM) has been employed to image the magnetic stray field from cobalt nanocluster films. The uniformly sized clusters with a diameter about 10nm were deposited at low energy with a gas aggregation source. Both isolated particles supported on silicon, and cluster-assembled films were analyzed. MFM measurements on individual clusters are complicated by interference from surface height variations, while for thicker layers a clear field pattern can be observed. The magnetic correlation length across such films is substantially larger than the size of a single cluster, indicating that the clusters are magnetically coupled to form stable domains. In ex situ magnetization experiments, a small increase or decrease in the MFM phase signal occurred depending on the direction of the applied field.

Arrays of Ferromagnetic Iron and Cobalt Nanocluster Wires

We report a fabrication of arrays of ferromagnetic iron and cobalt nanocluster wires (NCWs), ranging from 8 to 10 nm in diameter and up to a few millimeters in length. The iron and the cobalt nanoc...