Co-B Alloy Research Articles

Synthesis of graphene-based Co-B catalyst via simultaneous chemical reduction for hydrolysis of sodium borohydride

Co-B nanoparticles are deposited on graphene sheets by simultaneous chemical reduction of Co+2 and graphite oxides using NaBH4 as the reducing agent. The reduced Co−B/graphene nanocomposites were characterized by X-ray diffraction, Fourier transform infrared spectra, X-ray photoelectron spectroscopy, and thermogravimetric analysis. The results show that after reduction, not only considerable amount of functional groups has been removed but also exhibited formation of Co-B alloy on the graphene sheets. The catalytic activity of nanocomposites was investigated by the hydrolysis of NaBH4 in aqueous solution. Graphene support material greatly enhances the hydrolysis of NaBH4 with respect to graphite and active carbon supports, and chemical reduced graphene sheets can readily form stable aqueous colloids through electrostatic stabilization. The present method is promising for the synthesis of effective supported catalysts for hydrolysis of NaBH4.

High capacity cobalt boride prepared via vacuum freeze-drying method and used as anode material for alkaline secondary battery

In recent years, some metal borides, especially cobalt boride, have been regarded as anode candidates of high energy alkaline secondary batteries for their potential of carrying out multi-electron reactions. So far, there are some reports on the synthesis of metal borides, such as ball milling method, arc melting method, high-temperature solid-phase method, and so on. Herein, a vacuum freeze-drying method is adopted to synthesize cobalt boride with small size, uniform particle size distribution, high specific surface area, as well as excellent electrochemical activity. The crystal structures, particle size, and specific surface area of the as-prepared Co–B alloys were characterized and analyzed via X-ray diffraction, scanning electron microscopy, and nitrogen adsorption–desorption test. The electrochemical activities of the Co–B samples were examined by cyclic voltammetry (CV) and charge–discharge test. It is found that the Co-B alloy synthesized via the vacuum freeze-drying method exhibits good reversibility and cycle stability, and achieves a maximum discharge capacity of 437 mAh/g at the current density of 300 mA/g, which is much superior to that of the sample prepared via traditional chemical reduction method.

Discharging characteristics of CoB nano powders

CoB nano powders, which are considered as prospective anode material for the secondary nickel batteries, were synthesized by the chemical reduction method and their charge/discharge cyclic characteristics were investigated. The effect of heat-treatment on the structure and the discharging behavior of CoB alloy was also investigated. It was observed that the amorphous/nano-crystalline CoB had very limited hydrogen storage capacity and the crystallized CoB had no hydrogen adsorption ability at all. The big portion of boron present in CoB alloy dissolved selectively into 6 M KOH solution in the first discharge process. After selective dissolution of boron even the amorphous/nano-crystalline CoB alloy lost its hydrogen adsorption ability. The initial discharge capacity of CoB alloy increased as the boron content of CoB alloy increased since the oxidation of boron contributed to (created complication in) the initial discharge process of CoB alloy. After initial charge/discharge process all the subsequent charge/discharge processes were controlled totally by the perfectly reversible Co oxidation/reduction reactions which took place more efficiently in the crystallized structures. So this study makes important contribution to the resolution of the disagreement in the literature that CoB cannot be considered as the hydrogen storage alloy.

A New Preparation Method for Amorphous Co-B Alloys Nanoparticles

The Co–B alloy can be prepared facilely by a solid-solid reaction of CoCl2•6H2O and KBH4 powders at room temperature. Various characterizations, such as the chemical analysis, inductively coupled plasma-atomic emission spectroscopy (ICP), powder X-ray diffraction, electron diffraction and TEM have been performed. The results indicate that the Co-B alloy obtained by the solid-solid reaction is amorphous nanoparticles. The composition of the alloy is Co1.36B. The average diameter of the Co–B alloy nanoparticles is 30nm–50nm. The room temperature solid-solid reaction is mainly a surface reaction. The direct solid solid reaction between the borohydride and some metal-salts is thermodynamically possible. This simple preparation method may also be used for the large-scale production of the amorphous nanoparticles of some metal-boron alloys.

Investigation of amorphous CoB alloy as the anode catalyst for a direct borohydride fuel cell

Co-B amorphous alloy powders have been synthesized by chemical reduction of cobalt chloride with potassium borohydride in an aqueous solution. We find that this alloy can be used as an anode catalyst for a direct borohydride fuel cell (DBFC). This catalyst exhibits excellent electrocatalytic activity. An essential power output of 220 mW cm −2 has been achieved at 15 °C, and a life test last for 160 h with no attenuation has been observed. The amorphous structure of the CoB alloy is still stable after the life test.

Amorphous tunable-size Co–B magnetic nanoparticles from the cobalt-catalyzed NaBH4 hydrolysis

The cobalt-catalyzed hydrolysis of sodium borohydride (NaBH(4)) has become an attractive process in view of the possibilities of using the hydride for hydrogen storage material and also for the production of amorphous and tunable-size magnetic nanoparticles. This process in which the metallic catalyst transforms into a Co- and B-based magnetic by-product when in contact with NaBH(4) has been modified in order to control the mechanism of formation, tune the final size and study the particular magnetic behavior of the Co-B alloy nanoparticles provided.

Electrochemical effect of AB 3 alloy on CoB alloy in CoB- x wt.% AB 3 mixture electrodes

CoB alloy prepared by arc melting possesses excellent cyclic stability but low discharge capacity, while AB 3 hydrogen storage alloy prepared by inductive melting exhibits high discharge capacity but poor cyclic stability as negative electrode materials of alkaline rechargeable nickel-based batteries. A series of CoB- x wt.% AB 3 mixtures were synthesized by simple mixing of CoB alloy powders and AB 3 alloy powders. Electrochemical measurements revealed that the reversible discharge capacity and cycle stability of the mixture electrodes were largely improved, compared with CoB alloy electrode and AB 3 alloy electrode. The CoB- x wt.% AB 3 ( x = 20) electrode displays the highest discharge capacity of the 40th cycle and the CoB- x wt.% AB 3 ( x = 10) electrode displays the highest discharge capacity of the 100th cycle among all the mixture electrodes. The electrochemical effect of AB 3 alloy on CoB alloy in mixture electrodes was also systematically investigated.

Cobalt, a reactive metal in releasing hydrogen from sodium borohydride by hydrolysis: A short review and a research perspective

Cobalt is commonly admitted as being a promising catalyst in accelerating NaBH4 hydrolysis, being as reactive as noble metals and much more cost-effective. This is the topic of the present paper. Herein, we survey (i) the NaBH4-devoted literature while especially focusing on the Co catalysts and (ii) our work on the same topic. Finally, we report (iii) reactivity results of newly developed Co-based catalysts. From both surveys, it mainly stands out that Co has been investigated as catalysts in various forms: namely, as chlorides, reduced nanoparticles (metal Co, Co boride, Co-B alloy), supported over supports and shaped. In doing so the reactivity can be easily varied achieving H2 generation rates from few to >1000 L(H2)/min·g (metal). Nevertheless, our work can be distinguished from the NaBH4 literature. Indeed, we are working on strategies that focus on making alternative Co-based catalysts. One of these strategies is illustrated here as we report new reactivity data of Co-based bimetallic supported catalysts. For example, we show that 20 wt% Co90Y10/γAl2O3-20 wt% Co95Hf5/γAl2O3 > 20 wt% Co99Zr1/γAl2O3 > 20 wt% Co/γAl2O3, the best catalysts showing HGRs of about 245 mL(H2)/min or 123 L(H2)/min·g (metals).

Facile preparation and good electrochemical hydrogen storage properties of chain-like and rod-like Co-B nanomaterials

Chain-like and rod-like Co-B nanomaterials are prepared by chemical reduction method in cetyltrimethylammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) aqueous solution, respectively. XRD patterns demonstrate that the two materials both have amorphous structures. SEM and TEM images show that the chain-like Co-B constructs of one-by-one tactic ball-like particles with nanoflakes on the surface, whereas the rod-like Co-B alloy possesses a porous nanostructure. The results of electrochemical measurements indicate that, as negative electrode materials of Ni-MH batteries, their electrochemical properties are both better than those of regular Co-B alloy. At the discharge current density 25 mA g −1, the discharge capacities of the chain-like and the rod-like Co-B alloys are 314 mAh g −1 and 292 mAh g −1 after 50 cycles, respectively, which are both higher than that of regular Co-B alloy. XRD patterns of the electrodes on different charge–discharge states illustrate that the discharge capacity is attributed to hydrogenation of Co-B alloy.

PREPARATION AND ELECTROCHEMICAL BEHAVIORS OF Co-B ALLOY POWDERS

Alkaline rechargeable batteries,such as Ni/Cd batteries and Ni/MH batteries have been widely used as power sources,however,their further applications are limited due to contamination of Cd in Ni/Cd batteries and lower discharge capacities of Ni/MH batteries.Some metal borides, such as Co-B,Ni-B,Fe-B,V-B and Ti-B,have been known to own very high discharge capacity in alkaline aqueous solution,in which Co-B alloy exhibits the highest reversible discharge capacity and the best cyclic stability.However,the reversible capacity of Co-B alloy prepared by arc melting process is usually less than 250 mA·h/g,which is only one fourth of the theoretical capacity of the alloy electrode(908 mA·h/g).In the present study,chemical reduction method was used to prepare Co-B alloy to further enhance the electrochemical capacity of the alloy.A series of ultrafine powders of amorphous Co-B alloys,Co_(0.68)B_(0.32),Co_(0.55)B_(0.45) and Co_(0.50)B_(0.50),were prepared by reducing CoSO_4 with solution of NaBH_4.Electrochemical measurements indicate that the prepared alloys exhibit excellent electrochemical properties.At a high current density of 300 mA/g,the initial discharge capacities of these alloys are 510.6,666.4 and 667.2 mA·h/g,respectively,their discharge capacities still keep 331.6,379.5 and 390.5 mA·h/g after 60 cyc,respectively.Even at a discharge current density as high as 1200 mA/g,the three alloys still deliver reversible capacities of 336.2,373.4 and 390.1 mA·h/g,respectively.In the Co-B alloy electrodes,the boron atoms have two functions.First, boron can be oxidized to BO_3~(3-),thereby partly contributes to the discharge capacity.Second,most importantly,the gradual dissolution of boron into the electrolyte(in the form of BO_3~(3-)) during the charging/discharging creates a new surface in the electrodes,which can effectively increase the surface area of the active material in contact with the electrolyte.The alloy with higher boron content thereby can produce a larger reaction surface area by boron dissolution than the alloy prepared with lower B content.So the higher B content in the Co-B alloys can be helpful for improving their electrochemical properties.

Drastically enhanced cycle life of Co-B alloy electrode by 8-hydroxyquinoline at elevated temperature

The effect 8-hydroxyquinoline (8-HQ) additive in electrolyte on the cyclic stability of Co-B alloy electrode was investigated at elevated temperature (55 °C). Charge–discharge measurements show that 8-HQ can drastically enhance the cycle life of Co-B alloy electrode. Specifically, in the electrolyte containing 0.028 M 8-HQ additive, the discharge capacity of Co-B alloy electrode after 100 cycles are still up to 385.8 mAh/g at 55 °C. However, for the electrode in 8-HQ-free electrolyte, its discharge capacity is sharply decreased to only 138.5 mAh/g after 100 cycles. ICP-OES, XRD and ATR/FT-IR measurements were used to clarify the reason of the improvement in the cyclic stability. These results show that beneficial effect of 8-HQ on cycle life of Co-B alloy electrode can be attributed to the formation of insoluble complex (8-HQ)2Co(II)·2H2O protective layer that can suppress the dissolution of Co(OH)2 into electrolyte at elevated temperature.

Electrochemical hydrogen storage performance of AB5-CoB composites synthesized by a simple mixing method

AB5 (MlNi4.0Al0.3Cu0.5Zn0.2) alloy and CoB alloy were prepared by arc melting. AB5-CoB composites were synthesized by simple mixing of AB5 alloy powders and CoB alloy powders, and their electrochemical hydrogen storage properties were studied as negative electrodes in KOH aqueous solution. The maximum discharge capacity of the AB5-CoB(50%) composite (the content of CoB in the composite is 50 wt.%) reached 365.3 mAh·g−1. After 100 charge-discharge cycles, the discharge capacity of the AB5-CoB(50%) composite was still much higher than that of the AB5 alloy. The high rate discharge capability (HRD) and potentiodynamic polarization were also tested.

Thin-film CoB catalyst templates for the hydrolysis of NaBH4 solution for hydrogen generation

Thin-film CoB alloy catalysts were prepared on Ni-foam substrates using electroless as well as electroplating techniques. Electroless plating was carried out using cobalt (II) sulfate as the source of Co2+, sodium succinate as the complexing agent, and dimethyamine borane as the source of boron as well as the reducing agent. Electroplating was carried out using cobalt (II) sulfate and cobalt (II) chloride as the sources of cobalt, and boric acid as the source of boron. The thin-film CoB/Ni-foam templates were characterized using ICP, XRD and SEM techniques. The normalized B content was in the range of 1.0–1.30 and 0.20–0.60wt.% for electroless and electroplated templates, respectively. The B content is less than that required for stoichiometric alloy formation, which indicates the simultaneous deposition of the Co metal along with CoB alloy. An optimum condition of 0.100ML−1 each of cobalt (II) sulfate heptahydrate Co(SO4)·7H2O, sodium succinate (Na2C4H4O4) and dimethylamine borane (CH3)2NHBH3, at 60°C with the pH value of 4–5 and a plating time of 1h was identified for the preparation of the catalyst templates by electroless plating. Where as, 0.125ML−1 each of cobalt (II) chloride hexahydrate (CoCl2·6H2O), Co(SO4)·7H2O, 0.125ML−1 of boric acid at the current density range of 160–320mAcm−2 and a temperature of 60°C was identified as the optimum condition for the electroplating method. Maximum H2 generation rates of 1.64 and 0.30Lmin−1g−1 of catalyst were obtained with electroless and electroplated thin-film CoB/Ni-foam templates, respectively. The suitability of the electroless plated CoB/Ni-foam catalyst template for extended duration of hydrogen generation from NaBH4 was studied up to 60h. Activation energies of 44.47 and 54.89kJmol−1 were calculated for electroless and electroplated CoB/Ni-foam catalyst templates, respectively.

Structure and electrochemical behaviors of a series of Co–B alloys

A series of Co x B ( x = 1, 2, 3) alloys were prepared by arc melting, the phase structure of the alloys were characterized by X-ray diffraction (XRD). The electrochemical experimental results demonstrated that the Co x B ( x = 1, 2, 3) series alloys showed excellent cycling stability, the capacity retention was 94.2%, 93.6% and 93.8% in the 100th cycle, respectively, as the cobalt content decreased. The CoB alloy electrode showed very good electrochemical reversibility in cyclic voltammetry (CV) curves, the oxidation and reduction peaks resembled the pure cobalt element powder electrode. The electrode mechanism was discussed by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), using pure CoB alloy cast electrode. From the SEM, after first and second cycle, the surface became porous and pulverous; also, the oxidation state of Co changed through XPS, after second cycle, the Co of 0 oxidation state could not be found on the surface. Based on the experiment, a proper mechanism was proposed: on this condition, the discharge capacity may due to the Co(OH) 2/Co reaction, which happened on the porous surface as the boron dissolved when the cycle increased.

The modification effect of Fe on amorphous CoB alloy catalyst for chemoselective hydrogenation of crotonaldehyde

Binary CoB and ternary CoFeB amorphous alloy catalysts with different Fe contents were prepared by the chemical reduction method. In liquid-phase hydrogenation of crotonaldehyde, incorporation of Fe into the CoB catalyst reduced the overall activity while effectively improving the selectivity and yield to crotyl alcohol. On the optimum CoFeB-3 catalyst with a nominal Fe/(Co + Fe) molar ratio of 0.6, the initial selectivity amounted to 71%, and the yield of crotyl alcohol reached 63%. It is found that the selectivity enhancement was due to the lower decrement in the intrinsic formation rate of crotyl alcohol compared with that of butanal, not to the increment in the activation of the C O bond. Based on the characterizations, including X-ray photoelectron spectroscopy and X-ray absorption spectroscopy, and previous findings, the enhanced selectivity from Fe modification was tentatively attributed to an ensemble size effect.

Effects of amorphous CoB on the structural and electrochemical characteristics of MgNi alloy

Amorphous CoB was prepared by chemical reduction method. The influence of CoB on the electrochemical properties of MgNi alloy was investigated. MgNi–CoB composite was prepared by mechanical alloying (MA). The cycle life of the electrodes was improved by CoB. The morphology of the material was modified by CoB. The MgNi–CoB (weight ratio 100:15) composite which was MA 15 h exhibited the best electrochemical performance. The hydrogen diffusion coefficient in MgNi was increased by CoB ( D H = 1.195 × 10 - 10 cm 3 g - 1 ) . The exchange current density I 0 increased with the increasing of CoB (from 67.60 mA g - 1 to 189.35 mA g - 1 ). It was indicated that CoB improved the kinetics of the hydrogenation/dehydrogenation of MgNi-type alloy. The High rate discharge capability (HRD) of the MgNi–CoB composite was higher than that of MgNi. Potentiodynamic polarization results showed that the larger corrosion resistance of MgNi alloys in an alkaline solution which benefited from the introduction of amorphous CoB. The electrochemical impedance test results showed that the values of solution resistance ( R s ) and charge transfer resistance ( R 1 ) of the MgNi–CoB alloy were reduced by CoB comparing with MgNi. In conclusion, CoB improved the electrochemical performance of the MgNi alloy significantly.

Preparation and characterization of amorphous Co-B catalysts with mesoporous structure

Amorphous Co-B alloy catalyst with mesoporous structure was firstly prepared via reduction of cobalt acetate by potassium borohydride in the presence of an organic template hexadecyl–trimethyl–ammonium bromide. The as-prepared mesoporous Co-B was characterized by Fourier transform infrared (FTIR), X-ray powder diffraction (XRD), scanning electron micrograph (SEM), inductively coupled plasma (ICP), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) measurement, N 2 adsorption–desorption, CO temperature-programmed desorption (TPD), and magnetic performance test. Investigations demonstrated that such mesoporous structure has a pronounced influence on the magnetic properties of Co-B alloy and the enhanced magnetic performance enables the as-prepared mesoporous Co-B to be recycled by magnetic method in the liquid-phase cinnamaldehyde (CMA) hydrogenation. During the hydrogenation, the as-prepared mesoporous Co-B exhibited higher cinnamaldehyde conversion and cinnamyl alcohol (CMO) selectivity than the regular Co-B obtained without using organic template, which is attributed to the larger specific surface area and the stronger affinity to C O. After 11 cycles, the conversion of cinnamaldehyde over the mesoporous Co-B was 85.2%, which is higher than that of the fresh regular Co-B. The good cycle performance is attributed to its preserved mesoporous structure in spite of the collapse of some mesopores during cycling. In addition, the increase of selectivity for cinnamyl alcohol after several cycles is attributed to the growth of particle size.

Evidence of B- and Si-type magnetic relaxations in Co-based amorphous alloys

The kinetics of the structural magnetic relaxations (MRs) in the Co-based amorphous alloys has been investigated by magnetic after-effect spectroscopy. The experimental evidence and characterization of two types of MRs in the amorphous ${\mathrm{Co}}_{75}{\mathrm{B}}_{25}$ and ${\mathrm{Co}}_{75}{\mathrm{Si}}_{15}{\mathrm{B}}_{10}$ alloys are rendered in this work. The binary CoB alloy shows only the B-type MR with the most probable energy of the activation energy spectrum $Q*=1.35\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and the preexponential factor ${\ensuremath{\tau}}_{0}=2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}17}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$. In the ternary CoSiB amorphous alloy, the additional Si-type MR with $Q*=1.96\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and ${\ensuremath{\tau}}_{0}=6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$ occurs. Low-temperature annealing shifts either of the relaxation parameters of both alloys to higher values. Roles of the free volumes, the dimension, and affinity of the B and Si atoms for Co in the MR are discussed.

Exceptional Electrochemical Activities of Amorphous Fe-B and Co-B Alloy Particles Used as High Capacity Anode Materials

Exceptional Electrochemical Activities of Amorphous Fe-B and Co-B Alloy Particles Used as High Capacity Anode Materials

Production of Co-B Alloy Powders by Chemical Reduction

Co-B powders were prepared by chemical reduction. The powders had a spherical shape with an average diameter of about 0.1μm. X-ray diffraction and differential scanning calorimetry studies confirmed that the powders were amorphous. The amorphous powders showed lower saturation magnetization than the crystalline counterparts. Heat treatment of the powders above the crystallization temperature resulted in the formation of fcc Co, hcp Co, Co2B, and Co3B phases. The saturation magnetization of the annealed powders monotonically increased as the annealing temperature increased. On the other hand, the coercivity of the annealed powders rapidly increased with increasing annealing temperature. The powders annealed at 500°C had a saturation magnetization of 92 emu/g with a high coercivity of 1670 Oe.