Cobalt oxides as Co2B catalyst precursors for the hydrolysis of sodium borohydride solutions to generate hydrogen for PEM fuel cells

Cobalt boride (Co₂B) is an inexpensive catalyst for the hydrolysis of sodium borohydride (NaBH₄) to generate hydrogen (H₂) for PEM fuel cells. Preparation of Co₂B in situ in the H₂ generation vessel as well as in an external reactor was studied using cobalt (III) oxide (Co₃O₄) and lithium cobalt oxide (LiCoO₂) as precursors. The oxide precursors were characterized by XRD and the Co₂B catalysts by XRD and ICP. Co₂B formation from the oxide precursors depends on the crystallinity of the oxides as well as the concentration of NaBH₄ in the solution. During reduction of the oxides to CoB₂, Co(s) metal, Co(BO₂)₂ may also form from competing side reactions, however crystalline oxides react faster leading to higher Co₂B yield and better H₂ generation efficiency. Crystallinity of Co₃O₄ was improved by preparing it at a higher temperature. Co₃O₄ prepared at 600 °C reacts faster leading to enhanced Co₂B formation than Co₃O₄ prepared at lower temperatures (200 °C and 400 °C). The activation energy for the hydrolysis of NaBH₄ by Co₂B formed in situ from Co₃O₄ produced at 600 °C was calculated to be 77.90 kJ mol⁻¹. This activation energy value is found to be slightly higher than that of Pt, Ru-based catalysts.     

Cover Picture: Colloidal Synthesis of Hollow Cobalt Sulfide Nanocrystals (Adv. Funct. Mater. 11/2006)

Hollow nanocrystals have been synthesized through a mechanism analogous to the Kirkendall Effect. When a cobalt nanocrystal reacts with sulfur in solution, the outward diffusion of cobalt atoms is faster than the inward diffusion of sulfur atoms through the sulfide shell. The dominating outward diffusion of cobalt cations produces vacancies that can condense into a single void in the center of the nanocrystal at high temperatures. This process provides a general route to the synthesis of hollow nanostructures of a large number of compounds and is described in the Full Paper by A. P. Alivisatos and co‐workers on p. 1389. Formation of cobalt sulfide hollow nanocrystals through a mechanism similar to the Kirkendall Effect has been investigated in detail. It is found that performing the reaction at > 120 °C leads to fast formation of a single void inside each shell, whereas at room temperature multiple voids are formed within each shell, which can be attributed to strongly temperature‐dependent diffusivities for vacancies. The void formation process is dominated by outward diffusion of cobalt cations; still, the occurrence of significant inward transport of sulfur anions can be inferred as the final voids are smaller in diameter than the original cobalt nanocrystals. Comparison of volume distributions for initial and final nanostructures indicates excess apparent volume in shells, implying significant porosity and/or a defective structure. Indirect evidence for fracture of shells during growth at lower temperatures was observed in shell‐size statistics and transmission electron microscopy images of as‐grown shells. An idealized model of the diffusional process imposes two minimal requirements on material parameters for shell growth to be obtainable within a specific synthetic system.     

Fabrication and characterization of Co-Pt nanodot arrays by nanoimprint lithography and electrodeposition

Co-Pt nanodot arrays of 50 nm in diameter and 100 nm pitch were fabricated by nanoimprint lithography and electrodeposition process. A polymer mold used was replicated from a Si master mold with nanopatterns which were fabricated by EBL and ICP-RIE, where hydrophobic surface of these was achieved by FOTS coating. UV-NIL was successfully performed under pressures of 5 MPa for 5 min with an UV exposure time of 30 s, where the substrate was Ru (30 nm)/NiFe (10 nm)/Ta (5 nm)/Si (1 0 0). The size of patterns was measured at 53 nm in diameter, 25 nm in height, 100 nm in pitch. Finally, Co-Pt nanodot arrays were galvanostatically electrodeposited and characterized. The size and the composition of these arrays were measured to be 50 nm in diameter and 100 nm in pitch and Co-23.6 at.% Pt, respectively. According to MFM analysis, these arrays for the remnant states represent a single domain structure of perpendicular direction with a magnetic field, where a field of 15 kOe was applied perpendicular to the sample plane. These results show that for the Co-Pt dot arrays of 50 nm diameter perpendicular magnetic signal can be recorded and switched.     

Catalytic activity of cobalt on nanotextured polymer films for hydrogen production

We describe the mechanism of cobalt and ligand binding on nanotextured poly(chloro-p-xylylene) (PPX) films as supports for catalytic release of H₂ from alkaline aqueous solutions of sodium borohydride. Cobalt catalysts are prepared on nanotextured PPX substrates via electroless plating using a Sn-free Pd(II) colloid with adsorbed pyridine ligand as an adhesion promoter. Gas physisorption studies on PPX, using N₂ and CO₂ as probe gases, indicate the presence of micropores (∼1 to 2 nm width) responsible for the adsorption and non-covalent stabilization of pyridine molecules on the nanotextured surface. The strongly adsorbed pyridine molecules promote Co adhesion onto the PPX surface during subsequent electroless deposition, thereby retaining the metal's catalytic activity for H₂ evolution even after multiple reaction cycles. In contrast, conventionally deposited PPX is devoid of any nanotexture and contains fewer micropores capable of stabilizing pyridine adsorption, resulting in poor metallization and catalytic activity for H₂ evolution. We also demonstrate the effect of patterning the PPX substrate as a means to further improve the activity of the Co catalyst to achieve H₂ evolution rates comparable to those obtained using precious metal catalysts.     

Synthesis and Lithium Storage Properties of Co3O4 Nanosheet‐Assembled Multishelled Hollow Spheres

Single‐, double‐, and triple‐shelled hollow spheres assembled by Co₃O₄ nanosheets are successfully synthesized through a novel method. The possible formation mechanism of these novel structures was investigated using powder X‐ray diffraction, scanning and transmission electron microscopies, Fourier transform IR, X‐ray photoelectron spectroscopy, and thermogravimetric analysis. Both poly(vinylpyrrolidone) (PVP) soft templates and the formation of cobalt glycolate play key roles in the formation of these novel multishelled hollow structures. When tested as the anode material in lithium‐ion batteries (LIBs), these multishelled microspheres exhibit excellent cycling performance, good rate capacity, and enhanced lithium storage capacity. This superior cyclic stability and capacity result from the synergetic effect of small diffusion lengths in the nanosheet building blocks and sufficient void space to buffer the volume expansion. This facile strategy may be extended to synthesize other transition metal oxide materials with hollow multishelled micro‐/nanostrucutures, which may find application in sensors and catalysts due to their unique structural features.     

1,3-Butadiene polymerization using binary,ternary and quaternary cobalt catalysts for high 1,4-transpolybutadiene

Binary, ternary, and quaternary cobalt catalysts for 1,4-transpolybutadiene were prepared, and their reactivity and microstructure were studied. A novel binary catalytic system composed of cobalt adduct (2-PhC₆H₄O)₃Al·Co(OAc)₂/AlR₃, a ternary system of Co(2-ethylhexanoate)₂/AlEt(OPh)₂/AlEt₃, where OPh is p-dodecyl phenolate, and a quaternary system of cobalt carboxylate·(dialkyl phosphite)/AlR₃/(HOPh, p-dodecyl phenol), for high 1,4-transpolybutadiene were compared in polymerization. The binary molecular catalyst, (2-PhC₆H₄O)₃Al·Co(OAc)₂/AlR₃, was designed as cobalt and aluminum bimetallic form of an intermediate structure in the active site of 1,3-butadiene polymerization for high trans configuration. The bulky ligand, 2-PhC₆H₄O-, promotes the syn conformation in the active site in favor of trans configuration in polybutadiene. The catalytic activity was reached to 215 kg/(Co mol h) in the quaternary catalytic system. The microstructure consisted of ca. 91% trans, 2% cis and 7% vinyl. Molecular weight was able to be controlled to ca. 700,000 with MWD ca. 2.0. Catalytic reactivity in 1,3-butadiene polymerization was in the order of quaternary > binary > ternary. Diethyl phosphite and triethyl phosphate remarkably reduce molecular weight with high reactivity. The transpolybutadiene prepared by the quaternary catalyst had the glass transition temperature of ca. −80 °C, the melting point of ca. 30 °C, and possessed a low level of crystallinity at room temperature. In the carbon black composite, transpolybutadiene showed superior abrasion resistance, tear strength and chipping resistance to natural rubber, but exhibited high compound Mooney viscosity and low moduli.     

Co-Cu-Zn-Pb-Ni-Cl-H2O体系的热力学分析

根据配位化学热力学平衡原理,通过热力学平衡计算绘制出了298.15 K时钴电解液体系中5种金属离子(Co2+、Cu2+、Zn2+、Pb2+、Ni2+)及其配离子的c-lg c[Cl]T图和c-pH图。热力学计算显示,pH为2.5时钴电解液中铅、锌主要以配合阴离子形式存在,钴、铜、镍主要以阳离子形式存在,可以采用阴离子树脂交换法将微量铅、锌与钴、铜、镍有效分离。对所绘的热力学平衡图分析表明,高浓度氯离子有利于与金属形成配合离子,提高铅锌的配合阴离子含量,有利于阴离子树脂交换除铅、锌。     

Hydrothermal synthesis of β-cobalt hydroxide with various morphologies in water/ethanol solutions

Various morphologies of cobalt hydroxides have been successfully prepared from cobalt nitrate with the assistance of dimethylglyoxime in water/ethanol solutions by hydrothermal processing at 220 °C. The crystalline products are hexagonal phase of β-cobalt hydroxide, and the crystallinity increases as the volume ratio of water to ethanol rises. Hexagonal plate-like, broom-like or straw bundle-like, and grass-like cobalt hydroxides are obtained with water to ethanol ratios of 1:0, 2:1 and 1:2, respectively. The novel bundle-like assemblies are further constructed from lots of nanobelts, which mainly grow along [100] direction and evolve from less-crystalline disc-like structures and semi-crystalline flower-like assemblies as the hydrothermal time extended.     

Synthesis of cobalt boride nanoparticles using RF thermal plasma

Nanosize cobalt boride particles were synthesized from the vapor phase using a 30 kW–4 MHz radio frequency (RF) thermal plasma. Cobalt and boron powder mixtures used as precursors in different composition and feed rate were evaporated immediately in the high temperature plasma and cobalt boride nanoparticles were produced through the quenching process. The X-ray diffractometry (XRD) patterns of cobalt boride nanoparticles prepared from the feed powder ratio of 1:2 and 1:3 for Co:B showed peaks that are associated with the Co₂B and CoB crystal phases of cobalt boride. The XRD analysis revealed that increasing the powder feed rate results in a higher mass fraction and a larger crystalline diameter of cobalt boride nanoparticles. The images obtained by field emission scanning electron microscopy (FE-SEM) revealed that cobalt boride nanoparticles have a spherical morphology. The crystallite size of the particles estimated with XRD was found to be 18–22 nm.     

还原熔炼失效锂离子电池的研究

根据从失效锂离子电池中再生有价金属的现状,提出用还原熔炼的方法回收锂离子电池中的钴和铜,并从热力学原理分析其可行性,进行实验验证,证明了用碳作还原剂此工艺是可行的。电池中的铝也能作为还原剂来还原钴氧化物。用电弧炉还原熔炼后,钴回收率78.63%,铜回收率81.54%。