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.

Mn(x)O(y)/NC and Co(x)O(y)/NC nanoparticles embedded in a nitrogen-doped carbon matrix for high-performance bifunctional oxygen electrodes.

Abstract: Reversible interconversion of water into H2 and O2, and the recombination of H2 and O2 to H2O thereby harnessing the energy of the reaction provides a completely green cycle for sustainable energy conversion and storage. The realization of this goal is however hampered by the lack of efficient catalysts for water splitting and oxygen reduction. We report exceptionally active bifunctional catalysts for oxygen electrodes comprising Mn3O4 and Co3O4 nanoparticles embedded in nitrogen-doped carbon, obtained by selective pyrolysis and subsequent mild calcination of manganese and cobalt N4 macrocyclic complexes. Intimate interaction was observed between the metals and nitrogen suggesting residual M-N(x) coordination in the catalysts. The catalysts afford remarkably lower reversible overpotentials in KOH (0.1 M) than those for RuO2, IrO2, Pt, NiO, Mn3O4, and Co3O4, thus placing them among the best non-precious-metal catalysts for reversible oxygen electrodes reported to date.

Metal (Ni, Co)‐Metal Oxides/Graphene Nanocomposites as Multifunctional Electrocatalysts

Abstract: Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) along with hydrogen evolution reaction (HER) have been considered critical processes for electrochemical energy conversion and storage through metal-air battery, fuel cell, and water electrolyzer technologies. Here, a new class of multifunctional electrocatalysts consisting of dominant metallic Ni or Co with small fraction of their oxides anchored onto nitrogen-doped reduced graphene oxide (rGO) including Co-CoO/N-rGO and Ni-NiO/N-rGO are prepared via a pyrolysis of graphene oxide and cobalt or nickel salts. Ni-NiO/N-rGO shows the higher electrocatalytic activity for the OER in 0.1 m KOH with a low overpotential of 0.24 V at a current density of 10 mA cm−2, which is superior to that of the commercial IrO2. In addition, it exhibits remarkable activity for the HER, demonstrating a low overpotential of 0.16 V at a current density of 20 mA cm−2 in 1.0 m KOH. Apart from similar HER activity to the Ni-based catalyst, Co-CoO/N-rGO displays the higher activity for the ORR, comparable to Pt/C in zinc-air batteries. This work provides a new avenue for the development of multifunctional electrocatalysts with optimal catalytic activity by varying transition metals (Ni or Co) for these highly demanded electrochemical energy technologies.

One-Pot Synthesis of Zeolitic Imidazolate Framework 67-Derived Hollow Co3S4@MoS2 Heterostructures as Efficient Bifunctional Catalysts

Abstract: Herein, we present a facile metal–organic framework-engaged strategy to synthesize hollow Co3S4@MoS2 heterostructures as efficient bifunctional catalysts for both H2 and O2 generation. The well-known cobalt-based metal–organic zeolitic imidazolate frameworks (ZIF-67) are used not only as the morphological template but also as the cobalt precursor. During the two-step temperature-raising hydrothermal process, ZIF-67 polyhedrons are first transformed to hollow cobalt sulfide polyhedrons by sulfidation, and then molybdenum disulfide nanosheets further grow and deposit on the surface of hollow cobalt sulfide polyhedrons at the increased temperature. The crystalline hollow Co3S4@MoS2 heterostructures are finally obtained after subsequent thermal annealing under a N2 atmosphere. Due to the synergistic effects between the hydrogen evolution reaction active catalyst of MoS2 and the oxygen evolution reaction active catalyst of Co3S4, the obtained hollow Co3S4@MoS2 heterostructures exhibit outstanding bifunctional ...

Relation between metal electronic structure and morphology of metal compounds inside carbon nanotubes

Abstract: SEVERAL attempts have been made to fill carbon nanotubes1 with metals or metallic compounds to obtain nanocomposite materials with potentially interesting properties. Capillary action, predicted2 to be a filling mechanism, has been used3'4 to encapsulate lead and bismuth in open tubes. Compounds of yttrium5, manganese6 and gadolinium7 have also been encapsulated by formation of the nano-tubes in an arc discharge with the metals present in situ. Very recently, Tsang et al.8 showed that oxides of nickel, cobalt, iron and uranium can be encapsulated by opening the tubes and deposit-ing the filling material using wet chemical techniques. Here we report a search for general principles relating to the nature and structure of the filling material, using the arc-discharge method to fill tubes with fifteen metals and/or their compounds: Ti, Cr, Fe, Co, Ni, Cu, Zn, Mo, Pd, Sn, Ta, W, Gd, Dy and Yb. We find that the propensity for forming continuous 'nanowires' throughout the length of the tubes seems to be strongly correlated with the existence of an incomplete electronic shell in the most stable ionic state of the metal. We also find that the interplay between growth of the nanotube and growth of the filling results, in one case, in the formation of an unusual helical filling morphology.