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.

Electrochemical, spectroscopic and theoretical studies of a simple bifunctional cobalt corrole catalyst for oxygen evolution and hydrogen production

Abstract: Six cobalt and manganese corrole complexes were synthesized and examined as single-site catalysts for water splitting. The simple cobalt corrole [Co(tpfc)(py)2] (1, tpfc = 5,10,15-tris(pentafluorophenyl)corrole, py = pyridine) catalyzed both water oxidation and proton reduction efficiently. By coating complex 1 onto indium tin oxide (ITO) electrodes, the turnover frequency for electrocatalytic water oxidation was 0.20 s−1 at 1.4 V (vs. Ag/AgCl, pH = 7), and it was 1010 s−1 for proton reduction at −1.0 V (vs. Ag/AgCl, pH = 0.5). The stability of 1 for catalytic oxygen evolution and hydrogen production was evaluated by electrochemical, UV-vis and mass measurements, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDX), which confirmed that 1 was the real molecular catalyst. Titration and UV-vis experiments showed that the pyridine group on Co dissociated at the beginning of catalysis, which was critical to subsequent activation of water. A proton-coupled electron transfer process was involved based on the pH dependence of the water oxidation reaction catalyzed by 1. As for manganese corroles 2–6, although their oxidizing powers were comparable to that of 1, they were not as stable as 1 and underwent decomposition at the electrode. Density functional theory (DFT) calculations indicated that water oxidation by 1 was feasible through a proposed catalytic cycle. The formation of an O–O bond was suggested to be the rate-determining step, and the calculated activation barrier of 18.1 kcal mol−1 was in good agreement with that obtained from experiments.

Bread-making synthesis of hierarchically Co@C nanoarchitecture in heteroatom doped porous carbons for oxidative degradation of emerging contaminants

Abstract: Employing low-cost and abundant wheat flour, sodium bicarbonate, cysteine and cobalt nitrate as precursors, we for the first time present a facile one-pot pyrolysis strategy for homogeneous assembly of core-shell Co@C nanoparticles with nitrogen and sulfur into hierarchically porous carbons (Co-N-S-PCs). The samples are highly efficient for oxidative decomposition of p-hydroxybenzoic acid (HBA) and phenol. It was found that Co@C nanoparticles are crucial for the generation of singlet oxygen in advanced oxidation processes (AOPs), which works together with hydroxyl and sulfate radicals in efficient decomposition of HBA. Density functional theory (DFT) calculations disclose that electron transfer from metal Co to C shells greatly improves the Fermi level and chemical activity of the C atoms. The combination of Co-C interaction with N, S codoping further bring in catalytic active sites in the graphitic shells where the charge states of C atoms are increased. This template-free strategy is scalable to prepare highly efficient catalysts, including functional carbon materials modified with non-precious metal species or pure and well-dispersed porous core-shell nanoparticles for environmental or energy applications.

Perfectly Alternating Copolymerization of CO2 and Epichlorohydrin Using Cobalt(III)-Based Catalyst Systems

Abstract: Selective transformations of carbon dioxide and epoxides into biodegradable polycarbonates by the alternating copolymerization of the two monomers represent some of the most well-studied and innovative technologies for potential large-scale utilization of carbon dioxide in chemical synthesis. For the most part, previous studies of these processes have focused on the use of aliphatic terminal epoxides or cyclohexene oxide derivatives, with only rare reports concerning the synthesis of CO2 copolymers from epoxides containing electron-withdrawing groups such as styrene oxide. Herein we report the production of the CO2 copolymer with more than 99% carbonate linkages from the coupling of CO2 with epichlorohydrin, employing binary and bifunctional (salen)cobalt(III)-based catalyst systems. Comparative kinetic studies were performed via in situ infrared measurements as a function of temperature to assess the activation barriers for the production of cyclic carbonate versus copolymer involving two electronically ...