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"Cobalt"
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Dual-Engineering Tailored Cosub.3Osub.4 Hollow Microspheres Assembled by Nanosheets for Boosting Oxygen Evolution Reaction
The development of efficient, low-cost electrocatalysts for the oxygen evolution reaction (OER) is crucial for advancing sustainable hydrogen production through water splitting. This study presents a dual-engineering strategy to enhance the OER performance of Co[sub.3]O[sub.4] by synthesizing hollow microspheres assembled from nanosheets (HMNs) with abundant oxygen vacancies and highly active crystal facet exposure. Through a modified one-step hydrothermal process, Co[sub.3]O[sub.4] HMNs with exposed (111) and (100) crystal facets were successfully fabricated, demonstrating superior OER activity compared to Co[sub.3]O[sub.4] nanocubes (NCs) with only (100) facet exposure. The optimized Co[sub.3]O[sub.4]-5% HMNs exhibited a low overpotential of 330 mV at 10 mA cm[sup.−2] and a Tafel slope of 69 mV dec[sup.−1]. The enhanced performance was attributed to the synergistic effects of crystal facet engineering and defect engineering, which optimized the Co-O bond energy, increased the number of active sites, and improved conductivity. The unique hollow structure further facilitated mass transport and prevented nanosheet stacking, exposing more edge sites for catalytic reactions. This work highlights the potential of geometric and electronic structure modulation in designing high-performance OER catalysts for sustainable energy applications.
Journal Article
Cobalt red : how the blood of the Congo powers our lives
\"An unflinching investigation reveals the human rights abuses behind the Congo's cobalt mining operation-and the moral implications that affect us all. Cobalt Red is the searing, first-ever exposé of the immense toll taken on the people and environment of the Democratic Republic of the Congo by cobalt mining, as told through the testimonies of the Congolese people themselves. Activist and researcher Siddharth Kara has traveled deep into cobalt territory to document the testimonies of the people living, working, and dying for cobalt. To uncover the truth about brutal mining practices, Kara investigated militia-controlled mining areas, traced the supply chain of child-mined cobalt from toxic pit to consumer-facing tech giants, and gathered shocking testimonies of people who endure immense suffering and even die mining cobalt. Cobalt is an essential component to every lithium-ion rechargeable battery made today, the batteries that power our smartphones, tablets, laptops, and electric vehicles. More than 70 percent of the world's supply of cobalt is mined in the Congo, often by peasants and children in sub-human conditions. Billions of people in the world cannot conduct their daily lives without participating in a human rights and environmental catastrophe in the Congo. In this stark and crucial book, Kara argues that we must all care about what is happening in the Congo-because we are all implicated\"-- Provided by publisher.
Book
Cobalt oxides : from crystal chemistry to physics
Unparalleled in the breadth and depth of its coverage of all important aspects, this book systematically treats the electronic and magnetic properties of stoichiometric and non-stoichiometric cobaltites in both ordered and disordered phases.
eBook
The High-Temperature Performance of Pt/Ba/Co.sub.xMg.sub.1-xAl.sub.2O.sub.4 Catalysts for Lean-Burn NO.sub.x Removal
A series of catalysts Pt/Ba/Co.sub.xMg.sub.1-xAl.sub.2O.sub.4 supported by cobalt doped hydrotalcite materials were prepared by coprecipitation-impregnation method for NO.sub.x removal at 250-500 °C. The techniques of XRD, TEM, XPS, BET, H.sub.2-TPR, NO.sub.x-TPD, and FT-IR were employed to study the structure and properties of the catalysts. After Co doping, the specific surface area of the catalyst is significantly increased, while the number of surface reactive oxygen species is increased, making NO more easily oxidized to NO.sub.2, which is conducive to NO.sub.x storage. Meanwhile, XRD and TEM results show that Co doping also promotes the dispersion of BaCO.sub.3, which is the NO.sub.x storage site. In addition, the results of TEM and XPS before and after high temperature reaction showed that the active center Pt maintained good dispersion, no obvious sintering occurred, and the valence state of Co remained unchanged. The above characterization results show that the addition of Co significantly improves the storage capacity and thermal stability of the storage intermediates in the catalyst, that is, enhances the elimination performance of lean burn NO.sub.x at high temperatures. Co-doped catalysts Pt/Ba/Co.sub.xMg.sub.1-xAl.sub.2O.sub.4 (x = 0.1, 0.3 and 0.5) showed better high-temperature activity than Pt/Ba/MgAl.sub.2O.sub.4. Pt/Ba/Co.sub.0.3Mg.sub.0.7Al.sub.2O.sub.4 showed the highest De-NO.sub.x efficiency of 93.2% at 400 ºC and 88.7% at 450 ºC, respectively.
Journal Article
Oxygen doping of cobalt-single-atom coordination enhances peroxymonosulfate activation and high-valent cobalt–oxo species formation
The high-valent cobalt–oxo species (Co(IV)=O) is being increasingly investigated for water purification because of its high redox potential, long half-life, and antiinterference properties. However, generation of Co(IV)=O is inefficient and unsustainable. Here, a cobalt-single-atom catalyst with N/O dual coordination was synthesized by O-doping engineering. The O-doped catalyst (Co-OCN) greatly activated peroxymonosulfate (PMS) and achieved a pollutant degradation kinetic constant of 73.12 min−1 g−2, which was 4.9 times higher than that of Co-CN (catalyst without O-doping) and higher than those of most reported single-atom catalytic PMS systems. Co-OCN/PMS realized Co(IV)=O dominant oxidation of pollutants by increasing the steady-state concentration of Co(IV)=O (1.03 × 10−10 M) by 5.9 times compared with Co-CN/PMS. A competitive kinetics calculation showed that the oxidation contribution of Co(IV)=O to micropollutant degradation was 97.5% during the Co-OCN/PMS process. Density functional theory calculations showed that O-doping influenced the charge density (increased the Bader charge transfer from 0.68 to 0.85 e), optimized the electron distribution of the Co center (increased the d-band center from −1.14 to −1.06 eV), enhanced the PMS adsorption energy from −2.46 to −3.03 eV, and lowered the energy barrier for generation of the key reaction intermediate (*O*H₂O) during Co(IV)=O formation from 1.12 to 0.98 eV. The Co-OCN catalyst was fabricated on carbon felt for a flow-through device, which achieved continuous and efficient removal of micropollutants (degradation efficiency of >85% after 36 h operation). This study provides a new protocol for PMS activation and pollutant elimination through single-atom catalyst heteroatom-doping and high-valent metal–oxo formation during water purification.
Journal Article
Effects of folic acid and cobalt sulphate supplementation on growth performance, nutrient digestion, rumen fermentation and blood metabolites in Holstein calves
To investigate the influences of cobalt (Co) and folic acid (FA) on growth performance and rumen fermentation, Holstein male calves (n 40) were randomly assigned to four groups according to their body weights. Cobalt sulphate at 0 or 0·11 mg Co/kg DM and FA at 0 or 7·2 mg/kg DM were used in a 2 × 2 factorial design. Average daily gain was elevated with FA or Co supplementation, but the elevation was greater for supplementing Co in diets without FA than with FA. Supplementing FA or Co increased DM intake and total-tract nutrient digestibility. Rumen pH was unaltered with FA but reduced with Co supplementation. Concentration of rumen total volatile fatty acids was elevated with FA or Co inclusion. Acetate percentage and acetate to propionate ratio were elevated with FA inclusion. Supplementing Co decreased acetate percentage and increased propionate percentage. Activities of xylanase and α-amylase and populations of total bacteria, fungi, protozoa, Ruminococcus albus, Fibrobacter succinogenes and Prevotella ruminicola increased with FA or Co inclusion. Activities of carboxymethyl-cellulase and pectinase increased with FA inclusion and population of methanogens decreased with Co addition. Blood folates increased and homocysteine decreased with FA inclusion. Blood glucose and vitamin B12 increased with Co addition. The data suggested that supplementing 0·11 mg Co/kg DM in diets containing 0·09 mg Co/kg DM increased growth performance and nutrient digestibility but had no improvement on the effects of FA addition in calves.
Journal Article
Heterogenized cobalt oxide catalysts for nitroarene reduction by pyrolysis of molecularly defined complexes
Molecularly well-defined homogeneous catalysts are known for a wide variety of chemical transformations. The effect of small changes in molecular structure can be studied in detail and used to optimize many processes. However, many industrial processes require heterogeneous catalysts because of their stability, ease of separation and recyclability, but these are more difficult to control on a molecular level. Here, we describe the conversion of homogeneous cobalt complexes into heterogeneous cobalt oxide catalysts via immobilization and pyrolysis on activated carbon. The catalysts thus produced are useful for the industrially important reduction of nitroarenes to anilines. The ligand indirectly controls the selectivity and activity of the recyclable catalyst and catalyst optimization can be performed at the level of the solution-phase precursor before conversion into the active heterogeneous catalyst.
Pyrolysis of defined nitrogen-ligated cobalt acetate complexes onto a commercial carbon support transforms the complexes into heterogeneous Co
3
O
4
materials. These reusable non-noble-metal catalysts are highly selective for the industrially important hydrogenation of structurally diverse and functionalized nitroarenes to anilines.
Journal Article
Study of supercapacitor applications of supported and unsupported cobalt ferrite and Zn-doped cobalt ferrite nanocomposites
In this study, novel nanocomposites of CoFe
2
O
4
, CoFe
2
O
4
/MWCNTs, Co
0.5
Zn
0.5
Fe
2
O
4
, and Co
0.5
Zn
0.5
Fe
2
O
4
/MWCNTs were synthesized using the sol–gel and one-pot wet-impregnation method and further applied in the form of electrode material for their supercapacitor applications. The structural and optical properties of the as-synthesized electrode materials were investigated via X-ray diffraction, Fourier transform infrared, and Diffuse reflectance spectroscopic techniques. These materials exhibited crystallinity evident from X-ray diffraction analysis. No additional peak was envisioned upon addition of Zn to the crystal structure of CoFe
2
O
4
, which confirmed doping of Zn into CoFe
2
O
4
. Morphological analysis inferred the incorporation of synthesized ferrites into MWCNTs. The scanning electron micrographs further demonstrated a highly porous framework that provided enhanced ion transportability as well as high surface area for substantial charge storage. The electrochemical performance was evaluated using cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy for supercapacitors applications. All of these synthesized materials demonstrated good electrochemical potential, but MWCNTs-supported ferrite nanocomposites attained higher specific capacitance (CV; 175 F g
−1
& 590 F g
−1
, 418 F g
−1
& 1123 F g
−1
at 15 mV s
−1
, GCD; 19 F g
−1
& 217 F g
−1
, 95 F g
−1
& 832 F g
−1
at current density of 0.1 A g
−1
) for CoFe
2
O
4
, CoFe
2
O
4
/MWCNTs, and Co
0.5
Zn
0.5
Fe
2
O
4
, Co
0.5
Zn
0.5
Fe
2
O
4
/MWCNTs with capacitance retention of 92% and 95% after 2000 stability cycles, respectively. This inferred that CoFe
2
O
4
/MWCNTs and Co
0.5
Zn
0.5
Fe
2
O
4
/MWCNTs have the potential to be used for capacitive storage as well as in optical electronics due to their structural and good electrochemical properties.
Graphical Abstract
Journal Article