Cobalt

About: Cobalt is a research topic. Over the lifetime, 69899 publications have been published within this topic receiving 1242058 citations. The topic is also known as: Co & Element 27.

CoP as an Acid-Stable Active Electrocatalyst for the Hydrogen-Evolution Reaction: Electrochemical Synthesis, Interfacial Characterization and Performance Evaluation

Abstract: Films of CoP have been electrochemically synthesized, characterized, and evaluated for performance as a catalyst for the hydrogen-evolution reaction (HER) The film was synthesized by cathodic deposition from a boric acid solution of Co2+ and H2PO2– on copper substrates followed by operando remediation of exogenous contaminants The films were characterized structurally and compositionally by scanning-electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Raman spectrophotometry The catalytic activity was evaluated by cyclic voltammetry and chronopotentiometry Surface characterization prior to electrocatalysis indicated that the film consisted of micrometer-sized spherical clusters located randomly and loosely on a slightly roughened surface The composition of both the clusters and surface consisted of cobalt in the metallic, phosphide, and amorphous-oxide forms (CoO·Co2O3) and of phosphorus as phosphide and orthophosphate The orthophosphate species, produced

Water-soluble mononuclear cobalt complexes with organic ligands acting as precatalysts for efficient photocatalytic water oxidation

Abstract: The photocatalytic water oxidation to evolve O2 was performed by photoirradiation (λ > 420 nm) of an aqueous solution containing [Ru(bpy)3]2+ (bpy = 2,2′-bipyridine), Na2S2O8 and water-soluble cobalt complexes with various organic ligands as precatalysts in the pH range of 6.0–10. The turnover numbers (TONs) based on the amount of Co for the photocatalytic O2 evolution with [CoII(Me6tren)(OH2)]2+ (1) and [CoIII(Cp*)(bpy)(OH2)]2+ (2) [Me6tren = tris(N,N′-dimethylaminoethyl)amine, Cp* = η5-pentamethylcyclopentadienyl] at pH 9.0 reached 420 and 320, respectively. The evolved O2 yield increased in proportion to concentrations of precatalysts 1 and 2 up to 0.10 mM. However, the O2 yield dramatically decreased when the concentration of precatalysts 1 and 2 exceeded 0.10 mM. When the concentration of Na2S2O8 was increased from 10 mM to 50 mM, CO2 evolution was observed during the photocatalytic water oxidation. These results indicate that a part of the organic ligands of 1 and 2 were oxidized to evolve CO2 during the photocatalytic reaction. The degradation of complex 2 under photocatalytic conditions and the oxidation of Me6tren ligand of 1 by [Ru(bpy)3]3+ were confirmed by 1H NMR measurements. Dynamic light scattering (DLS) experiments indicate the formation of particles with diameters of around 20 ± 10 nm and 200 ± 100 nm during the photocatalytic water oxidation with 1 and 2, respectively. The particle sizes determined by DLS agreed with those of the secondary particles observed by TEM. The XPS measurements of the formed particles suggest that the surface of the particles is covered with cobalt hydroxides, which could be converted to active species containing high-valent cobalt ions during the photocatalytic water oxidation. The recovered nanoparticles produced from 1 act as a robust catalyst for the photocatalytic water oxidation.

Cobalt- and nitrogen-codoped porous carbon catalyst made from core–shell type hybrid metal–organic framework (ZIF-L@ZIF-67) and its efficient oxygen reduction reaction (ORR) activity

Abstract: The development of carbon-based oxygen reduction reaction (ORR) catalysts to substitute the expensive and unstable platinum-based ORR catalysts is of great importance for their optimal utilization in energy conversion and storage. Herein, we report the production of highly active carbon-based ORR catalyst from well-designed core–shell type hybrid metal–organic framework (MOF). Cobalt- and nitrogen-codoped porous carbon leaves (Co,N-PCLs) are prepared via a simple one-step pyrolysis of well-designed leaf-shaped core-shell type hybrid MOFs (ZIF-L@ZIF-67, ZIF (zeolitic imidazolate framework) is a subclass of MOF), which contain two different metal ions (Zn2+ in core and Co2+ in shell) and sufficient nitrogen source with a thin flat morphology. The structural and compositional features of resulting Co,N-PCLs are characterized using scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and N2 sorption isotherms, and the analyses reveal that they possess the ideal structural and compositional features for ORR, such as numerous carbon nanotubes (CNTs), substantial Co- and N-doping, large surface area, and high pore volume while maintaining the advantageous thin leaf-shape. Owing to such unique structural and compositional features, Co,N-PCLs display much better ORR activity than their counterparts prepared from the parent materials (ZIF-L or ZIF-67). In addition, Co,N-PCL even shows a better electrochemical stability and a better methanol tolerance compared to commercial Pt/C material.