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.

Fischer–Tropsch synthesis: study of the promotion of Re on the reduction property of Co/Al2O3 catalysts by in situ EXAFS/XANES of Co K and Re LIII edges and XPS

Abstract: A direct relationship between the Fischer–Tropsch synthesis (FTS) rate and the number of surface cobalt atoms available for reaction is usually obtained. For Co/Al2O3 catalysts in particular, the site density depends on two primary factors: (1) the average size of the cobalt clusters on the support; and (2) the fraction of cobalt reduced to the metallic state. The addition of small amounts of noble metal promoters, such as Pt and Ru to cobalt alumina, may catalyze the reduction of cobalt oxide shifting the temperature of reduction of both steps (Co3O4→CoO and CoO→Co0) to lower temperatures. However, Re affects only the second step. Re is reduced at a higher temperature than Pt or Ru, and at approximately the same temperature as the first step of cobalt reduction (Co3O4→CoO). Thus, Re metal is present to catalyze only the second step. In situ extended X-ray absorption fine structure (EXAFS) at the LIII edge of Re has been used to show that there is direct contact of Re with cobalt atoms, while evidence for ReRe bonds is not observed. Even though direct atom-to-atom contact is found, temperature-programmed reduction (TPR) suggests that hydrogen spillover from the promoter to cobalt oxide clusters is important for the catalysis of cobalt oxide reduction. In situ EXAFS at the K edge of Co shows that the average cobalt cluster size decreases with increasing Re loading. Re promotes reduction of smaller species which interact with the support, and therefore, for a given reduction temperature, the average cobalt metal cluster size decreases as a function of increasing Re content. After reduction at a temperature slightly above the first peak in the TPR (Co3O4→CoO), the species remaining on the surface displayed XANES spectra identical to that of CoO. After reduction at a temperature above the second broad TPR peak, XPS showed that a residual oxide species was present, with a binding energy equivalent to cobalt aluminate.

Accelerated Hydrogen Evolution Reaction in CoS2 by Transition-Metal Doping

Abstract: Cobalt pyrite (CoS2) is one of the promising candidate catalysts for electrocatalytic hydrogen evolution because of its efficient catalytic activity sites and inherent metallicity. Herein, we report the greatly improved electrocatalytic activity of CoS2 resulting from Mn doping. First, we give the theoretical prediction that Mn is the most excellent dopant to activate the electrocatalytic activity of CoS2 with the smallest Gibbs free energy (|ΔGH*|) while remaining metallic. Second, to provide experimental evidence, Mn-doped CoS2 nanowires are prepared by a hydrothermal and postsulfuration method. The optimized sample shows a low overpotential of 43 mV at 10 mA/cm2, a Tafel slope of only 34 mV/dec, and long-time stability for the hydrogen evolution reaction. This work reveals a new way to stimulate the electrocatalytic activity of other pristine candidate catalysts.

In Situ Formation of Cobalt Nitrides/Graphitic Carbon Composites as Efficient Bifunctional Electrocatalysts for Overall Water Splitting.

Abstract: Developing cost-effective and highly efficient bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is of great interest for overall water splitting but still remains a challenging issue. Herein, a self-template route is employed to fabricate a unique hybrid composite constructed by encapsulating cobalt nitride (Co5.47N) nanoparticles within three-dimensional (3D) N-doped porous carbon (Co5.47N NP@N-PC) polyhedra, which can be served as a highly active bifunctional electrocatalyst. To afford a current density of 10 mA cm-2, the as-fabricated Co5.47N NP@N-PC only requires overpotentials as low as 149 and 248 mV for HER and OER, respectively. Moreover, an electrolyzer with Co5.47N NP@N-PC electrodes as both the cathode and anode catalyst in alkaline solutions can drive a current density of 10 mA cm-2 at a cell voltage of only 1.62 V, superior to that of the Pt/IrO2 couple. The excellent electrocatalytic activity of Co5.47N NP@N-PC can be mainly ascribed to the high inherent conductivity and rich nitrogen vacancies of the Co5.47N lattice, the electronic modulation of the N-doped carbon toward Co5.47N, and the hierarchically porous structure design.

A Zinc Cobalt Sulfide Nanosheet Array Derived from a 2D Bimetallic Metal-Organic Frameworks for High-Performance Supercapacitors.

Abstract: Porous ternary metal sulfide integrated electrode materials with abundant electroactive sites and redox reactions are very promising for supercapacitors. Herein, a porous zinc cobalt sulfide nanosheet array on Ni foam (Zn-Co-S/NF) was constructed by facile growth of 2D bimetallic zinc/cobalt-based metal-organic framework (Zn/Co-MOF) nanosheets with leaf-like morphology on NF, followed by additional sulfurization. The Zn-Co-S/NF nanosheet array acted directly as a supercapacitor electrode showing much better electrochemical performance (2354.3 F g-1 and 88.6 % retention over 1000 cycles) when compared with zinc cobalt sulfide powder (355.3 F g-1 and 75.8 % retention over 1000 cycles), which originates from good electrical conductivity and mechanical stability, abundant electroactive sites, and facilitated transportation of electrons and electrolyte ions due to the unique nanosheet array structure. An asymmetric supercapacitor (ASC) device assembled from Zn-Co-S/NF and activated carbon electrodes can deliver a highest energy density of 31.9 Wh kg-1 and a maximum power density of 8.5 kW kg-1 . Most importantly, this ASC also shows good cycling stability (71.0 % retention over 10000 cycles). Furthermore, a red LED can be powered by two connected ASCs, and thus as-synthesized Zn-Co-S/NF has great potential for practical applications.