CoNi Alloy Nanoparticles Research Articles

Magnetic-field-induced rapid synthesis of defect-enriched Ni-Co nanowire membrane as highly efficient hydrogen evolution electrocatalyst

Metallic Ni-based materials are promising electrocatalysts for commercial alkaline water electrolysis towards hydrogen generation. It is therefore desirable to develop low-cost and controllable synthesis protocols for efficient Ni-based electrocatalysts. Here we report a rapid one-step method to fabricate self-supported membranes of highly-conductive Ni-Co nanowires, which are formed via self-assembly of reduced Ni/Co nanoparticles under a rotating magnetic field. The Ni-Co nanowires are composed of Co nanoparticles and NiCo alloy nanoparticles domains, with abundant inherent interface defects due to incomplete alloying and insufficient Ostwald ripening during the assembly. Nanowires with different Ni/Co ratios are tested as the HER electrodes in comparison to pure Ni mesh and Ni foam electrodes; And the Ni0.50Co0.50 nanowire electrode gives the most optimized performance. The HER activity shows little degradation for nearly 100 h. These nanowire electrodes are superior to the state-of-the-art metallic Ni-based ones. This facile technology may represent a critical step towards scalable production of highly active and durable metallic Ni-based electrocatalysts for industry applications.

NiCo Alloy Nanoparticles Decorated on N‐Doped Carbon Nanofibers as Highly Active and Durable Oxygen Electrocatalyst

AbstractThe exploring of catalysts with high‐efficiency and low‐cost for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is one of the key issues for many renewable energy systems including fuel cells, metal–air batteries, and water splitting. Despite several decades pursuing, bifunctional oxygen catalysts with high catalytic performance at low‐cost, especially the one that could be easily scaled up for mass production are still missing and highly desired. Herein, a hybrid catalyst with NiCo alloy nanoparticles decorated on N‐doped carbon nanofibers is synthesized by a facile electrospinning method and postcalcination treatment. The hybrid catalyst NiCo@N‐C 2 exhibits outstanding ORR and OER catalytic performances, which is even surprisingly superior to the commercial Pt/C and RuO2 catalysts, respectively. The synergetic effects between alloy nanoparticles and the N‐doped carbon fiber are considered as the main contributions for the excellent catalytic activities, which include decreasing the intrinsic and charge transfer resistances, increasing CC, graphitic‐N/pyridinic‐N contents in the hybrid catalyst. This work opens up a new way to fabricate high‐efficient, low‐cost oxygen catalysts with high production.

Metal-organic framework-derived CoNi-embedded carbon nanocages as efficient electrocatalysts for oxygen evolution reaction

The major challenge of electrocatalytic water splitting for hydrogen production is the sluggish kinetics of oxygen evolution reaction (OER). Herein, we report a facile synthesis of CoNi alloy embedded carbon nanocages (CoNi-C) through one-step annealing treatment of bimetallic organic frameworks as the precursors for application as efficient and economical electrocatalysts for OER. As a result, the optimized CoNi-C-200 sample with a Co/Ni atomic ratio of 9:1 exhibits a lower overpotential of 408 mV at a current density of 10 mA cm−2 and a smaller Tafel slope of 83 mV dec−1 compared to as-prepared CoNi-C-100 (410 mV, 93 mV dec−1), CoNi-C-400 (420 mV, 94 mV dec−1), and Co-C (447 mV, 97 mV dec−1). Moreover, it shows an excellent long-term stability during 5000 CV sweeps. Such improved performance can be attributed to the unique morphology and the synergistic effects of CoNi alloy nanoparticles and conductive carbon matrix in the composite.

Highly selective hydrogenation of phenol to cyclohexanol over MOF-derived non-noble Co-Ni@NC catalysts

The selective hydrogenation of phenol is an attractive routine to produce cyclohexanol that is an important basic chemical raw in chemical industry, but the design of cost-efficient and highly selective catalysts remains a great challenge. Herein, we report the first example of non-noble bimetallic nanocatalysts for the selective hydrogenation of phenol with cyclohexanol as the sole product. These catalysts consisting of bimetallic Ni-Co alloy nanoparticles (NPs) encapsulated in N-doped carbon matrix were simply synthesized by using our previously developed MOF-templated strategy (Long et al., 2016). The sum of characterization results revealed that the Co and Ni elements were successfully alloyed in every individual NPs that were confined by N-doped carbon layers. Detailed catalytic test results suggested that both the pyrolysis temperature and the composition of these alloy NPs played the key roles in guiding their catalytic performance in the selective hydrogenation of phenol. It has been shown that Co-Ni@NC system was much more effective for hydrogenation of phenol than Cu@NC, Co-Cu@NC and Ni-Cu@NC systems. The optimal 1Co-1Ni@NC could completely catalyze the hydrogenation of phenol to >99.9% cyclohexanol with a TOF of 0.21h−1, which was approximately 2.8- and 4.3-fold higher than that of the Co@NC and Ni@NC respectively, underscoring a strong positive synergistic effect between Ni and Co for this reaction. The mechanism study revealed the cyclohexanol was formed directly by the one-step hydrogenation of phenol in our catalyst system. This one-step pathway could avoid the formation of other hydrogenated intermediate product thereby leading to >99.9% selectivity of cyclohexanol. Furthermore, this catalyst also showed good recyclability, magnetically reusability and general applicability for a wide range of phenol substrates, which together with the superior activity and selectivity make it a good potential for the industrial applications.

Well-organized Co-Ni@NC material derived from hetero-dinuclear MOFs as efficient electrocatalysts for oxygen reduction

We reported a novel Co-Ni@NC nanocatalysts derived from a new N-containing hetero-dinuclear Co-Ni-ZIF [CoNi(MIM)2]. The Co-Ni@NC alloy nanocatalysts showed well-defined frameworks and interconnected porous structure. Characterization results manifested that all elements were uniform distributed in catalysts. The Co-Ni alloy nanoparticles were wrapped by a highly ordered graphitic structure, leading to a high dispersion of metal active centres. When used as ORR catalysts, the optimal Co-Ni(1:1)@NC-900 showed the best catalytic activity, the activity of which were much higher than that of monometallic catalysts and almost equal to that of Pt/C catalysts. Moreover, it also showed an excellent stability and durability.

Two-dimensional CoNi nanoparticles@S,N-doped carbon composites derived from S,N-containing Co/Ni MOFs for high performance supercapacitors

CoNi alloy nanoparticles incorporated into S,N-doped carbon structure was obtained by pyrolysis treatment of 2D S,N-containing Co/Ni MOFs nanosheets, as electrode material exhibiting high supercapacitor performance.

Non-noble bimetallic alloy encased in nitrogen-doped nanotubes as a highly active and durable electrocatalyst for oxygen reduction reaction

Exploring highly active, cost-effective and durable oxygen reduction reaction (ORR) electrocatalysts as substitutes for the rare platinum-based catalysts is of great significance in energy conversion and storage devices, such as alkaline fuel cells, metal-air batteries, etc. Herein, we fabricated a new type ORR electrocatalyst of NiCo nanocrystal alloy encapsulated in N-doped carbon nanotubes (NCNTs) through a facile, scalable route utilizing nickel acetate and cobalt chloride as metallic Ni and Co precursors, thiourea as a nitrogen and carbon source, respectively, under a Ni/Co atomic ratio of 3:7 at 700 °C. The obtained nanocomposite catalyst NiCo@NCNT-700 exhibited an outstanding ORR activity close to that of the state-of-the-art Pt/C catalyst and superior operational durability under alkaline conditions, which could be attributed to the co-contributions among the uniformly distributed NiCo alloy nanoparticles, graphitic NCNTs and the formation of CoN species. This work provides a new insight for the rational design and development of efficient non-noble metal electrocatalysts by integrating electrochemically active units into the nanocomposite for challenging electrochemical energy-related technologies.

Strategic Preparation of Efficient and Durable NiCo Alloy Supported N‐Doped Porous Graphene as an Oxygen Evolution Electrocatalyst: A Theoretical and Experimental Investigation

Development of an efficient and durable water splitting electrocatalyst holds a great commitment for the future energy devices. The real application of oxygen evolution reaction (OER) catalysts mainly suffers from sluggish kinetics and high overpotential except for the Ir and Ru‐based systems. However, the high cost and vulnerability of the Ir and Ru metals are the main hostiles to use them for marketization. Herein, a high‐performance OER electrocatalyst consisting of NiCo alloy nanoparticles supported on high surface area N‐doped porous graphene (NiCo/pNGr(75:25)) is reported. The importance of the doped‐N for achieving the uniform dispersion‐cum‐effective interaction of the size controlled NiCo alloy nanoparticles has been explicitly investigated by transmission electron microscopy, X‐ray diffraction, X‐ray photo­electron spectroscopy, Raman, density functional theory (DFT) calculations, etc. The electrochemical analysis of NiCo/pNGr(75:25) shows an overpotential of ≈260 mV at 10 mA cm−2 with a smaller Tafel slope of ≈87 mV dec−1 and long catalytic durability. DFT calculations are done to check the interaction between the NiCo alloy nanoparticles and the defective sites of pNGr and also with the doped‐N, which could be attained for maintaining long catalytic durability. Furthermore, NiCo/pNGr(75:25) is used as an OER catalyst to fabricate an electrolyzer, which works at very low potential of 1.5 V in 1 m KOH.

Microwave absorption properties of CoNi nanoparticles anchored on the reduced grapheme oxide

In this work, CoNi alloy nanoparticles anchored on the reduced grapheme oxide (rGO) composites were prepared by a facile hydrothermal method. The rGO/CoNi composites were analyzed by the scanning electron microscopy, X-ray diffraction, fourier transform infrared spectrometer and Raman spectroscopy. The results show that the CoNi alloy nanoparticles were uniformly wrapped by the wrinkled rGO sheet. The electromagnetic wave absorption properties of rGO wrapped CoNi composites were investigated by the vector network analyzer. The minimal reflection loss of composites is −23.3 dB at 17.5 GHz. The results show that CoNi nanoparticles anchored on the reduced grapheme oxide composite may be a promising microwave absorber with the characteristics of the low density, strong-absorption, wide-band and thin-thickness.

Ni-Co alloy catalyst from LaNi1−xCoxO3 perovskite supported on zirconia for steam reforming of ethanol

The critical problem facing catalysts for the steam reforming of ethanol (SRE) is deactivation due to carbon deposition and/or sintering of the active components. To overcome this problem, a new scheme for designing and preparing Ni-Co alloy catalysts for SRE has been developed in this study using a perovskite-type oxide of LaNi1−xCoxO3 as the precursor. According to the scheme, a series of zirconia-supported LaNi1−xCoxO3 catalysts were prepared by impregnating ZrO2 with a mixed solution composed of ions consisting of nickel, cobalt, lanthanum and citric acid. After reduction, the Ni-Co alloy nanoparticles were highly dispersed on ZrO2 and modified with La2O3. The bimetallic catalyst exhibited very good catalytic performance for SRE, including high activity, high selectivity to hydrogen and very good stability due to the synergistic catalysis of cobalt and nickel. The synergy between cobalt and nickel led to a higher anti-coking ability compared to the corresponding monometal catalysts, and the bimetallic catalyst exhibited very good anti-sintering ability. This preparation scheme could be extended to the preparation of many other supported bimetallic catalysts because many transitional metal ions can act as the ions of a perovskite-type oxide.

NiCo alloy nanoparticles anchored on polypyrrole/reduced graphene oxide nanocomposites for nonenzymatic glucose sensing

The combination of PPy and graphene oxide was used as an effective supporting substrate for the loading of alloys.

Controllable synthesis and electromagnetic interference shielding properties of magnetic CoNi alloy nanoparticles coated on biocarbon nanofibers

CoNi alloy nanoparticles with different molar ratios of Co:Ni were uniformly coated on the surface of biocarbon nanofibers (BCF) by electroless plating. Transmission electron microscopy, X-ray diffraction and vibration sample magnetometry were employed to characterize the morphologies, phase structures and magnetic properties of the coated BCF. The permittivity behavior of coated BCF-paraffin wax matrix composites was studied in the frequency range of 8.2–12.4 GHz by vector network analysis. Magnetic measurements showed that the saturation magnetizations increased linearly with increasing Co content in CoNi deposits and that the coercivity is insensitive towards the Co content. Of the four synthesized BCF with various Co:Ni molar ratios, the BCF with Co:Ni molar ratio of 1:2 displayed higher electromagnetic interference shielding efficiencies of 30.7 dB (99.91 % attenuation) due to its higher permittivity.

Template-free synthesis of magnetic CoNi nanoparticles via a solvothermal method

CoNi alloy nanoparticles were prepared via a solvothermal method, and ethanol and water mixed solution was used as solvent. No surfactant or template was employed during the entirely synthetic procedure. The dependences of product size and shape on the temperature and volume ratio of ethanol to water were investigated in details. As the volume ratio of ethanol to water decreased, the shape of CoNi alloy changes from particle to platelets. The obtained samples were characterized by XRD, SEM, and VSM techniques. Magnetic measurement at room temperature showed that the CoNi nanoparticles possessed ferromagnetic behavior, and these CoNi nanoparticles could be used in magnetic media, sensors, and other devices.

3D distribution of magnetic CoNi alloy nanoparticles electrodeposited on vertically aligned MWCNT showing exceptional coercive field

A novel, fast and simple method to achieve a 3D distribution of CoNi nanoparticles (NPs) by electrochemical deposition on vertically aligned multiwall carbon nanotubes is described. Alignment is maintained during the electrodeposition. This method allows to easily obtain magnetic anchored, no aggregation, nanoparticles spatially distributed almost homogenously in a thick 3D structure (10µm). Potential and charge of deposition condition size, composition and crystalline structure of the CoNi NPs and then the magnetic properties of the NPs/CNTs structures. The structures with hcp CoNi NPs of around 70nm obtained at low deposition potentials present an exceptional high coercive magnetic field (higher than 1kOe), never previously found for CoNi NPs. Structures with hcp+fcc CoNi NPs present lower coercivity, which corresponds to the lower magnetic anisotropy of the fcc crystalline phase.

A study on the synthesis of Ni50Co50 alloy nanostructures with tuned morphology through metal-organic chemical routes.

NiCo bimetallic nanostructures with various morphologies have been synthesized using a broad range of solvents, surfactants and precursors that are available in the metal-organic chemical toolbox. Polygonal particles, nanowires and isotropic nanospheres have been obtained, among others. We describe the chemical pathways to achieve anisotropic growth either by an 'in situ' seed-mediated approach or by simply selecting suitable reaction media and growth modifiers. We describe the role of a variety of synthetic factors that influence the final shape of such an alloy material at the nanoscale. The alloying between cobalt and nickel is evidenced by XRD and HRTEM techniques. Room-temperature ferromagnetic behavior is observed for NiCo nanoparticles and high values for saturation magnetization and coercivity are recorded by SQuID magnetometry. The saturation magnetization value for the NiCo nanostructures is typically set between the corresponding "bulk" ones of cobalt and nickel metals. It is always comparable to the suggested value of the Ni50Co50 bulk alloy. The synthetic protocols derived from our extensive study are quantitative and versatile, allowing high reaction yields. Although macroscopic characterization techniques evidence the presence of a stoichiometric NiCo alloy, we show that in certain cases nanoscale characterization analyses are also needed for a more accurate evaluation of the alloy composition at the atomic level.

Microwave-absorbing properties of CoNi nanoparticles

The CoNi alloy nanoparticles with different molar ratios of Co:Ni were prepared by the liquid-phase reduction, and the morphology, chemical composition and structure of the particles were investigated by field-emission scanning electron microscopy and X-ray powder diffraction. The complex permittivity and permeability of the nanoparticles were investigated by network analyzer in the frequency range of 1–18 GHz. The reflection loss was calculated based on the determined complex permittivity and permeability. The field-emission scanning electron microscopy results showed that all samples with different Co:Ni molar ratios were spherical and evenly distributed with the diameter ranging from 60 to 200 nm. Compared with other samples with different Co:Ni molar ratios, the sample with Co:Ni molar ratio of 1:2 displayed higher microwave-absorbing properties due to the higher imaginary parts of the complex permittivity and permeability.

Enhanced microwave absorbing performance of CoNi alloy nanoparticles anchored on a spherical carbon monolith

CoNi alloy nanoparticles anchored on a spherical carbon monolith (CoNi-C) were prepared by a solvothermal route and subsequent heat treatment without any templates. Their permittivity and permeability behaviors were studied in the frequency range of 2-18 GHz. The CoNi-C composites showed the best microwave absorbing performances compared to those of Co-C and Ni-C. The maximum reflection loss of the CoNi-C nanocomposites can reach -50.2 dB at 7.7 GHz with samples of 4 mm in thickness, better than that of the Ni-C composites, while the Co-C composites showed almost no absorption at all. The absorption mechanism of the three absorbents was also discussed.

Synthesis and Magnetic Properties of Nanocrystalline Co-Ni Alloys: A Review

This review article deals with the synthesis, characterization and magnetic properties of Co-Ni nanoalloys. The various physical and chemical methods for the synthesis of Co-Ni alloy nanoparticles are discussed. Co-Ni alloy nanoparticles with different size and shape such as spherical, rods, wires chain-like assembly are found to depend on the synthesis method and experimental condition. The structure of Co-Ni alloys is eitherfcc,hcpor mixedfccandhcpphase and found to depends on size, shape and concentration of Co in the Co-Ni alloys. Sodium hydroxide (NaOH) concentration and Co to Ni ratio influence the shape of bimetallic Co-Ni nanoparticles. Pt nucleating agents produced smaller size of Co-Ni alloy particles compared to Ru and Ag. Higher Co concentration in the Co-Ni alloys also influences the size alloy particles. The magnetic properties of Co-Ni nanoalloys depend on the size, shape and composition of the binary alloys. Surface oxidation of Co-Ni alloy nanoparticles decrease the saturation magnetization and increases with Co concentration in the alloys. The shape of Co-Ni alloy nanoparticles has an influence on coercivity. The microwave absorption properties of the Co-Ni alloys found to depend on the shape, size and composition of the binary alloys. The absorbance peaks shifts to higher frequency with decrease in size of the alloy particles. Potential applications of Co-Ni alloys in various fields are highlighted.

Synthesis and magnetic properties of size-controlled CoNi alloy nanoparticles

CoNi alloy nanoparticles were obtained using liquid phase reduction method. The size of particles was selected as the research index, and the impacts of experimental conditions on the particle size were investigated. These experimental conditions included reaction temperature, solvent, initial concentration, and the amount of reducing agent and surface active agent. Through the orthogonal test, the optimized process parameters of preparing CoNi alloy nanoparticles by liquid-phase reduction were determined. The size of the particles prepared on the basis of the optimum technology was 60nm. The particle size would impact the magnetic properties of CoNi nanoparticles measured by the test of hysteresis loops. The test result showed that the Hc of the CoNi alloy nanoparticles decreased and the Ms increased, with the increase of the particle size.

Solvent-Adoptable Polymer Ni/NiCo Alloy Nanochains: Highly Active and Versatile Catalysts for Various Organic Reactions in both Aqueous and Nonaqueous Media

The synthesis of solvent-adoptable monometallic Ni and NiCo alloy nanochains by a one-pot solution phase reduction method in the presence of poly(4-vinylphenol) (PVPh) is demonstrated. The elemental compositions of the as-prepared alloys are determined by inductively coupled plasma optical emission spectroscopy (ICP-OES) and energy-dispersive X-ray spectroscopy (EDS), which are matching well with the target compositions. The morphology analysis by TEM and FESEM confirms that the nanochains are made up of organized spherical monometallic Ni or bimetallic NiCo alloy nanoparticles (NPs). However, there is no nanochain formation when the alloy is prepared without the polymer PVPh. A possible mechanism for the formation of such NiCo alloy nanochains is discussed. The X-ray diffraction and selected area electron diffraction patterns reveal that the Ni/NiCo alloys are polycrystalline with fcc structure. The obtained Ni or NiCo alloy nanostructures are ferromagnetic with very high coercivity. The polymer Ni/NiCo alloy nanochains are dispersible in both water and organic media that makes them versatile enough to use as catalysts in the reactions carried out in both types of media. The catalytic activities of these Ni/NiCo alloy nanochains are extremely high in the borohydride reduction of p-nitrophenol in water. In organic solvents, these nanochains can act as efficient catalysts, under ligand-free condition, for the C-S cross-coupling reactions of various aryl iodides and aryl thiols for obtaining the corresponding cross-coupled products in good to excellent yield up to 96%. The NiCo nanochain also successfully catalyzes the C-O cross-coupling reaction in organic medium. A possible mechanism for NiCo alloy nanochain-catalyzed cross-coupling reaction is proposed.