Co Sb Alloy Research Articles

Sb-modulated synthesis of novel CoSb alloy nanoparticles anchored on N-doped carbon as oxygen electrocatalysts

Rational modulation and optimization of structural properties plays a significant role in advancing the electrocatalytic performance of electrocatalysts. In this study, we report a novel Sb-modulated strategy to synthesize novel CoSb/NC catalysts comprised of CoSb alloy supported on nitrogen-doped carbon (denoted as CoSb/NC). Apart from alloying with Co to generate CoSb alloys, we demonstrated that the evaporation of Sb could modulate the particle size and pore structure of CoSb/NC. Such modulation has facilitated the formation of micro/meso-porous structure to accelerate the mass/charge transport and increase the accessibility of active sites, resulting in a highest kinetic current density of 22.6 mA cm−2 at 0.85 V vs. RHE as well as a low Tafel slope of 38 mV dec−1, which even outperforms the state-of-the-art Pt/C. Additionally, CoSb/NC is demonstrated to be electrocatalytic active toward OER with the overpotential to be 430 mV at 10 mA cm−2. Rechargeable Zn-air battery tests reveal that CoSb/NC possesses competitive performance in terms of charge-discharge ability and stability, suggesting its potential application in renewable energy conversion devices. This work provides a novel approach to modulate the structure of nitrogen-doped carbon based materials as efficient oxygen electrocatalysts.

Nanosized CoSb Alloy Confined in Honeycomb Carbon Framework Toward High‐Property Potassium‐Ion and Sodium‐Ion Batteries

Antimony‐based materials are promising anode candidates for Na‐/K‐ion batteries (SIBs/PIBs) but limited by the mediocre cycle performance due to the large volume change. Herein, a honeycomb‐like interconnected porous carbon framework embedded with CoSb nanoparticles is fabricated via a water‐soluble template‐assisted vacuum freeze‐drying technology followed by a heat‐treatment method. The CoSb nanocrystalline and 3D porous carbon matrix endow the CoSb@3DPCs composite electrode with a distinct structure, which buffers the volume expansion of Sb, shortens the diffusion distance of Na+/K+, and enhances the electronic conductivity. It exerts outstanding electrochemical properties in both SIBs and PIBs, such as remarkable cycling durability (the capacity is maintained at 211.2 mAh g−1 after 500 cycles for SIBs and 287.5 mAh g−1 for PIBs) and rate capability (144 mAh g−1 at 5 A g−1 for SIBs and 134 mAh g−1 at 5 A g−1 for PIBs). The kinetic analysis shows that up to 79% and 65% pseudocapacitance contributions for SIBs and PIBs are observed for CoSb@3DPCs at 4.0 mV s−1. Herein, an ingenious design route and simple preparation method toward exploring the high‐property electrode for PIBs and SIBs is provided, and broad application prospects in other electrochemical applications are opened up.

Thermodynamic and kinetic analysis for carbothermal reduction process of CoSb alloy powders used as anode for lithium ion batteries

Thermodynamic calculation and kinetic analysis were performed on the carbothermal reduction process of Co 3O 4–Sb 2O 3–C system to clarify the reaction mechanism and synthesize pure CoSb powder for the anode material of secondary lithium-ion batteries. The addition of carbon amount and thus the purity of CoSb powders were critical to the electrochemical property of CoSb anode. It was revealed that in an inert atmosphere, Co 3O 4 was preferentially reduced to CoO, followed by the reduction of Sb 2O 3 and CoO. CO 2 was the gas product for the reduction of Co 3O 4 and Sb 2O 3, while CO was the gas product for that of CoO. Based on the analysis result, pure CoSb powder without any oxides and residual carbon was synthesized, which showed a higher specific capacity and a lower initial irreversible capacity loss, compared to CoSb sample with residual carbon. This work can be a reference for other carbothermal reduction systems.

Preparation and electrochemical performance of CoSb alloy anode material for Li-ion batteries

Micro-sized CoSb alloy powders were synthesized by carbothermal reduction method from oxides of Co and Sb. The thermodynamic feasibility was calculated and the kinetic process was examined by DTA and XRD. Sb is firstly reduced from Sb 2O 3, followed by the reduction of Co from Co 3O 4 and the alloying of Sb with Co. The liquid feature of Sb at synthesis temperature renders the CoSb particles with a worm-like shape. Compared with nano-sized CoSb x composites, the synthesized CoSb anode with micro-sized particles exhibits lower initial irreversible capacities, mainly ascribed to the lower specific surface area and the higher chemical stability of so-obtained CoSb powders. CoSb electrode shows a high specific capacity (365 mAh/g or 2923 mAh/cm 3 after 35 cycles), good cycling stability and rate-capability, representing a promising anode material for Li-ion batteries.

Thermal chemistry and short-range order in Co-Sb melts

The enthalpies of mixing for the liquid Co-Sb alloys are measured by isoperibolic calorimetry at 1600 K over the whole concentration range relative to liquid Sb and undercooled liquid Co. The minimal integral enthalpy of mixing is −6.3 ± 0.6 kJ/ mole at xCo = 0.50. Activity of components, Gibbs energy, and the entropy of mixing are calculated using a short-range ordering model considering CoSb associates formed in molten Co-Sb alloys.

Dendrite growth during rapid solidification of Co-Sb alloys

Undercooling experiments were performed with Co-10%Sb and Co-60.5%Sb alloys in order to investigate the dendrite growth kinetics within the solutal and thermal diffusion-controlled growth regimes. These alloy compositions correspond to the two extremes of eutectic horizontal line and hence have the broadest equilibrium freezing temperature ranges. The maximum undercoolings obtained for these alloys are 274 K (0.16 T L) and 168 K (0.11 T L), which have either approached or exceeded their equilibrium freezing temperature ranges. The dendrite growth velocities were measured as a function of undercooling. The experimental results were analyzed within the current theories of dendritic growth. The results indicate that α-Co solid solution phase attains a growth velocity of 60 m s −1 at 274 K undercooling, whereas β-CoSb intermetallic compound grows more slowly with a maximum velocity of 12 m s −1. The investigations reveal a transition from solute diffusion-controlled growth to thermal diffusion-controlled growth by the onset of solute trapping at a critical undercooling. It is approximately 150 K in the case of Co-10%Sb alloy and 130 K for Co-60.5%Sb alloy. A ‘dendrite-equiaxed’ morphological transition is initiated once these alloys are undercooled by more than 100 K. This is interpreted within a recently developed model of dendrite fragmentation as a Rayleigh-like instability of rapidly growing dendrites.

Amorphous phase formation in ion implanted cobalt

Ion implantation has been used to investigate the tendency for Co to form an amorphous phase when implanted with Sb and Te. Films and foils of Co were implanted with 80 keV Sb + and Te+ ions, at room temperature, with doses up to 1017 ions cm−2. RBS and TEM were used to examine the compositional and structural state of the implanted specimens. At low doses the intercrystalline transition (hcp)Co to (fcc)Co was observed. At higher doses an amorphous phase, as indicated by the presence of diffuse scattering maxima in transmission electron diffraction, was observed in both Sb and Te implanted Co. An amorphous Co-Sb alloy was first observed at ≈ 6 at.% Sb and an amorphous Co-Te alloy at ≈ 2 at.%o Te. These values of Sb and Te place the lower composition at which an amorphous phase can be stabilized at the limit of the two phase region of the appropriate equilibrium phase diagram. It is suggested that ion beam techniques provide an efficient method for extending the composition range over which amorphous phases can be stabilized.