Electrochemical Preparation of N‐Doped Cobalt Oxide Nanoparticles with High Electrocatalytic Activity for the Oxygen‐Reduction Reaction

Nitrogen‐doped CoO (N‐CoO) nanoparticles with high electrocatalytic activity for the oxygen‐reduction reaction (ORR) were fabricated by electrochemical reduction of CoCl₂ in acetonitrile solution at cathodic potentials. The initially generated, highly reactive nitrogen‐doped Co nanoparticles were readily oxidized to N‐CoO nanoparticles in air. In contrast to their N‐free counterparts (CoO or Co₃O₄), N‐CoO nanoparticles with a N content of about 4.6 % exhibit remarkable ORR electrocatalytic activity, stability, and immunity to methanol crossover in an alkaline medium. The Co?N_x active sites in the CoO nanoparticles are held responsible for the high ORR activity. This work opens a new path for the preparation of nitrogen‐doped transition metal oxide nanomaterials, which are promising electrocatalysts for fuel cells.     

Soft‐Chemical Exfoliation Route to Layered Cobalt Oxide Monolayers and Its Application for Film Deposition and Nanoparticle Synthesis

A colloidal suspension of exfoliated, layered cobalt oxide nanosheets has been synthesized through the intercalation of quaternary tetramethylammonium ions into protonated lithium cobalt oxide. According to atomic force microscopy, exfoliated nanosheets of layered cobalt oxide show a plateau‐like height profile with nanometer‐level height, underscoring the formation of unilamellar 2D nanosheets. The exfoliation of layered cobalt oxide was cross‐confirmed by X‐ray diffraction, UV/Vis spectroscopy, and transmission electron microscopy. The maintenance of the hexagonal in‐plane structure of the cobalt oxide lattice after the exfoliation process was evidenced by selected‐area electron diffraction and Co K‐edge X‐ray absorption near‐edge structure analysis. The zeta‐potential measurements clearly demonstrated the negative surface charge of cobalt oxide nanosheets. Adopting the nanosheets of layered cobalt oxide as a precursor, we were able to prepare the monodisperse CoO nanocrystals with a particle size of ≈10 nm as well as the heterolayered film composed of cobalt oxide monolayer and polycation.     

Cobalt‐Catalyzed E‐Selective Cross‐Dimerization of Terminal Alkynes: A Mechanism Involving Cobalt(0/II) Redox Cycles

A highly E‐selective cross‐dimerization of terminal alkynes with either terminal silylacetylenes, tert‐butylacetylene, or 1‐trimethylsilyloxy‐1,1‐diphenyl‐2‐propyne in the presence of a dichlorocobalt(II) complex bearing a sterically demanding 2,9‐bis(2,4,6‐triisopropylphenyl)‐1,10‐phenanthroline, activated with two equivalents of EtMgBr, gives a variety of (E)‐1,3‐enynes. A well‐characterized diolefin/cobalt(0) complex, with divinyltetramethyldisiloxane, acted as a catalytically active species without any activation, clearly indicating that a cobalt(0) species is involved in the catalytic cycle.     

Facile Synthesis of Graphene/Cobalt Oxide Nanohexagons for the Selective Detection of Dopamine

This work presents a simple green approach for the chemical synthesis of cobalt oxide nano hexagons (Co₃O₄ NHs) with an average size of 160±40 nm incorporated graphene nanosheets (GR). The techniques used to confirm the formation of GR−Co₃O₄ NHs are transmission electron microscopy (TEM), energy‐dispersive X‐ray spectroscopy (EDX), and X‐ray diffraction spectroscopy (XRD). The dopamine (DA) sensor was fabricated by drop casting GR−Co₃O₄ NHs on the pre‐cleaned glassy carbon electrode (GCE). GR−Co₃O₄ modified GCE displayed a sensitive and selective electrochemical determination of DA compared to only GR and Co₃O₄ NHs modified GCE. Our fabricated sensor showed a wide linear range from 0.2 to 3443 μM with low limit of detection (84 nM) towards the determination of DA. The sensitivity of our fabricated sensor was calculated to be 108 μA mM⁻¹ cm⁻². As well, a significant storage stability, repeatability and reproducibility were attained by GR−Co₃O₄ NHs modified GCE. Human urine samples were targeted for the demonstration of practicality of our sensor.     

Selective Isomerization of Epoxides to Allylic Alcohols Catalyzed by TiO2‐Supported Gold Nanoparticles

ReacTiO ₂ ns for rings : Gold nanoparticles supported on TiO₂ are used as a novel heterogeneous catalyst for the isomerization of epoxides to allylic alcohols by a concerted mechanism (see scheme). The reaction proceeds in high yields and the product selectivity is often remarkable.

     

Ordered PdCu‐Based Nanoparticles as Bifunctional Oxygen‐Reduction and Ethanol‐Oxidation Electrocatalysts

The development of superior non‐platinum electrocatalysts for enhancing the electrocatalytic activity and stability for the oxygen‐reduction reaction (ORR) and liquid fuel oxidation reaction is very important for the commercialization of fuel cells, but still a great challenge. Herein, we demonstrate a new colloidal chemistry technique for making structurally ordered PdCu‐based nanoparticles (NPs) with composition control from PdCu to PdCuNi and PtCuCo. Under the dual tuning on the composition and intermetallic phase, the ordered PdCuCo NPs exhibit better activity and much enhanced stability for ORR and ethanol‐oxidation reaction (EOR) than those of disordered PdCuM NPs, the commercial Pt/C and Pd/C catalysts. The density functional theory (DFT) calculations reveal that the improved ORR activity on the PdCuM NPs stems from the catalytically active hollow sites arising from the ligand effect and the compressive strain on the Pd surface owing to the smaller atomic size of Cu, Co, and Ni.     

Cobalt Single‐Atom Catalysts with High Stability for Selective Dehydrogenation of Formic Acid

Metal–organic framework (MOF)‐derived Co‐N‐C catalysts with isolated single cobalt atoms have been synthesized and compared with cobalt nanoparticles for formic acid dehydrogenation. The atomically dispersed Co‐N‐C catalyst achieves superior activity, better acid resistance, and improved long‐term stability compared with nanoparticles synthesized by a similar route. High‐angle annular dark‐field–scanning transmission electron microscopy, X‐ray photoelectron spectroscopy, electron paramagnetic resonance, and X‐ray absorption fine structure characterizations reveal the formation of Co^IIN_x centers as active sites. The optimal low‐cost catalyst is a promising candidate for liquid H₂ generation.     

The Inherent Electrochemistry of Nickel/Nickel‐Oxide Nanoparticles

The direct detection of nanoparticles is at the forefront of research owing to their environmental and toxicological applications. Herein, we studied the inherent electrochemistry of Ni and NiO nanoparticles and proposed a simple and direct electrochemical method for the determination of the concentrations of both nickel (Ni) and nickel oxide (NiO) nanoparticles in alkaline solution. A highly sensitive voltammetry technique was used to measure the oxidative signal of Ni(OH)₂ that formed spontaneously on the surface of Ni and NiO nanoparticles in alkaline media. Detection limits of 220 μg mL^?1 for Ni and 13 μg mL^?1 for NiO nanoparticles were obtained. Ni and NiO nanoparticles are used as electrode modifiers or as electrochemical signal labels in various biosensing applications. Therefore, methods to rapidly quantify the amount of Ni and NiO nanoparticles are of widespread potential use.     

Opto‐electrochemical In Situ Monitoring of the Cathodic Formation of Single Cobalt Nanoparticles

Single‐particle electrochemistry at a nanoelectrode is explored by dark‐field optical microscopy. The analysis of the scattered light allows in situ dynamic monitoring of the electrodeposition of single cobalt nanoparticles down to a radius of 65 nm. Larger sub‐micrometer particles are directly sized optically by super‐localization of the edges and the scattered light contains complementary information concerning the particle redox chemistry. This opto‐electrochemical approach is used to derive mechanistic insights about electrocatalysis that are not accessible from single‐particle electrochemistry.     

Electrocatalysis of Water Oxidation by H2O‐Capped Iridium‐Oxide Nanoparticles Electrodeposited on Spectroscopic Graphite

Electrocatalysis of water oxidation by 1.54 nm IrO_x nanoparticles (NPs) immobilized on spectroscopic graphite electrodes was demonstrated to proceed with a higher efficiency than on all other, hitherto reported, electrode supports. IrO_x NPs were electrodeposited on the graphite surface, and their electrocatalytic activity for water oxidation was correlated with the surface concentrations of different redox states of IrO_x as a function of the deposition time and potential. Under optimal conditions, the overpotential of the reaction was reduced to 0.21 V and the electrocatalytic current density was 43 mA cm^?2 at 1 V versus Ag/AgCl (3 M KCl) and pH 7. These results beneficially compete with previously reported electrocatalytic oxidations of water by IrO_x NPs electrodeposited onto glassy carbon and indium tin oxide electrodes and provide the basis for the further development of efficient IrO_x NP‐based electrocatalysts immobilized on high‐surface‐area carbon electrode materials.     

Bifunctional Cage‐Type Cubic Mesoporous Silica SBA‐1 Nanoparticles for Selective Adsorption of Dyes

Bifunctional SBA‐1 mesoporous silica nanoparticles (MSNs) with carboxylic acid and amino groups (denoted as CNS‐10‐10) have been successfully synthesized, characterized, and employed as adsorbents for dye removal. Adsorbent CNS‐10‐10 shows high affinity towards cationic and anionic dyes in a wide pH range, and exhibits selective dye removal of a two‐dye mixture system of cationic methylene blue and anionic eosin Y. By changing the pH of the medium, the selectivity of the adsorption behavior can be easily modulated. For comparison purposes, the counterparts, that is, pure silica SBA‐1 MSNs (CS‐0) and those with either carboxylic acid or amino functional groups (denoted as CS‐10 and NS‐10, respectively) were also prepared to evaluate their dye‐adsorption behaviors. As revealed by the zeta‐potential measurements, the electrostatic interaction between the adsorbent surface and the dye molecule plays an important role in the adsorption mechanism. Adsorbent CNS‐10‐10 can be easily regenerated and reused, and maintains its adsorption efficiency up to 80 % after four cycles.     

Enhanced Electrochemical Capacitive Properties of Nickel‐Cobalt Oxide Nano‐flakes Materials

Nickel‐cobalt oxide nano‐flakes materials are successfully synthesized by a facile chemical co‐precipitation method followed by a simple calcination process. The studies show that the as‐prepared nickel‐cobalt oxides with different Ni/Co ratio are composed of NiO and Co₃O₄ compounds. The Co_0.56Ni_0.44 oxide material, which exhibits a mesoporous structure with a narrow distribution of pore size from 2 to 7 nm, possesses markedly enhanced charge‐discharge properties at high current density compared with the pure NiO and pure Co₃O₄. The Co_0.56Ni_0.44 oxide electrode shows a specific capacitance value of 1227 F/g at 5 mA/cm², which is nearly three times greater than that of the pure NiO electrode at the same current density.     

Heterostructured Inter‐Doped Ruthenium–Cobalt Oxide Hollow Nanosheet Arrays for Highly Efficient Overall Water Splitting

The development of transition‐metal‐oxides (TMOs)‐based bifunctional catalysts toward efficient overall water splitting through delicate control of composition and structure is a challenging task. Herein, the rational design and controllable fabrication of unique heterostructured inter‐doped ruthenium–cobalt oxide [(Ru–Co)O_x] hollow nanosheet arrays on carbon cloth is reported. Benefiting from the desirable compositional and structural advantages of more exposed active sites, optimized electronic structure, and interfacial synergy effect, the (Ru–Co)O_x nanoarrays exhibited outstanding performance as a bifunctional catalyst. Particularly, the catalyst showed a remarkable hydrogen evolution reaction (HER) activity with an overpotential of 44.1 mV at 10 mA cm^?2 and a small Tafel slope of 23.5 mV dec^?1, as well as an excellent oxygen evolution reaction (OER) activity with an overpotential of 171.2 mV at 10 mA cm^?2. As a result, a very low cell voltage of 1.488 V was needed at 10 mA cm^?2 for alkaline overall water splitting.     

A Template‐Free Method for Preparation of Cobalt Nanoparticles Embedded in N‐Doped Carbon Nanofibers with a Hierarchical Pore Structure for Oxygen Reduction

Designing and preparing porous materials without using any templates is a challenge. Herein, single‐nozzle electrospinning technology coupled with post pyrolysis is applied to prepare cobalt nanoparticles embedded in N‐doped carbon nanofibers with a hierarchical pore structure (HP‐Co‐NCNFs). The resultant HP‐Co‐NCNFs have lengths up to several millimeters with an average diameter of 200 nm and possess abundant micro/meso/macropores on both the surface and within the fibers. Such a microstructure endows the surface area as high as 115 m² g^?1. When used as an electrocatalyst for the oxygen reduction reaction (ORR), the HP‐Co‐NCNFs exhibit outstanding electrochemical performance in terms of activity, methanol tolerance, and durability. The hierarchically porous structure and high surface area can effectively decrease the mass transport resistance and increase the exposed ORR active sites. The sufficient amount of exposed ORR active sites along with accessible transport channel and enhanced electrical conductivity may be responsible for the good electrocatalytic performance.     

Electrodeposition of Copper Oxide Nanoparticles on Precasted Carbon Nanoparticles Film for Electrochemical Investigation of anti‐HIV Drug Nevirapine

This work describes the development of a novel electrochemical sensor based on electrodeposition of copper oxide nanoparticles onto carbon nanoparticle (CNP) film modified electrode for the analysis of the anti‐HIV drug, nevirapine (NEV). The electrochemical experiments were performed using linear sweep and cyclic voltammetry. Atomic force microscopy was applied for surface characterization of the deposited modifier film (CuO‐CNP) on glassy carbon electrode (GCE). No oxidation peak was observed for NEV on the bare GCE, but both CNP‐GCE and CuO‐CNP‐GCE showed a distinctive anodic response towards NEV with considerable enhancement (276‐fold and 350‐fold, respectively) compared to CuO‐GCE. The mechanism of the electrocatalytic process on the modified electrode surface was investigated by cyclic and linear sweep voltammetry at various potential sweep rates and pHs of the buffer solutions. The modified electrode exhibited linear dynamic range in three concentration intervals (0.1–0.8, 1–10 and 10–100 µM) with a detection limit of 66 nM. The stability, reproducibility, and repetitive usability exhibited by the proposed modified electrode are good enough to make it a suitable sensor for the determination of NEV in real samples with complex matrices such as human blood serum.     

铟锡氧化物(ITO)纳米颗粒的制备及表征

以金属In和SnCl₄·5H₂O为主要原料，加入保护剂PVP，利用化学共沉淀法合成了球形的铟锡氧化物(ITO)纳米颗粒。分别对PVP的用量、溶液的pH值、热处理温度等因素对ITO纳米颗粒粒径的影响进行了分析。并且借助透射电镜(TEM)、X射线衍射(XRD)对所合成的ITO纳米颗粒进行了表征。XRD分析说明本文合成了金刚砂型结构的铟锡氧化物纳米颗粒，并且其晶型结构随着热处理温度的升高而转变为铁锰矿型。     

Zero‐Valent Amino‐Olefin Cobalt Complexes as Catalysts for Oxygen Atom Transfer Reactions from Nitrous Oxide

The synthesis and characterization of several zero‐valent cobalt complexes with a bis(olefin)‐amino ligand is presented. Some of these complexes proved to be efficient catalysts for the selective oxidation of secondary and allylic phosphanes, as well as diphosphanes, even with a direct P?P bond. With 5 mol % catalyst loadings the oxidations proceed under mild conditions (25–70 °C, 7–22 h, 2 bar N₂O) and afford good to excellent yields (65–98 %). In this process, the greenhouse gas N₂O is catalytically converted into benign N₂ and added‐value organophosphorus compounds, some of which are difficult to obtain otherwise.     

溶液中肼还原钴离子制备纳米金属钴的反应动力学

通过加入NaBH₄作为诱导剂, 可在室温下引发肼与Co^2＋在水-乙醇体系中的还原反应, 制得高纯度纳米金属钴粉. 机理研究表明, 该反应分二段进行: 第一段主要发生Co^2＋被N₂H₄还原的反应(2Co^2＋＋N₂H₄＋4OH^－＝2Co¯＋N₂­＋4H₂O), 第二段主要为金属Co催化的肼分解反应(N₂H₄＝N₂­＋2H₂­)和歧化反应(3N₂H₄＝N₂­＋4NH₃­). Co^2＋被N₂H₄还原是典型的自催化过程, 因此, 加入少量NaBH₄即可在288 K下启动反应. 通过测量气体产物的生成速率, 获得了Co^2＋还原的反应动力学方程, 发现Co^2＋, N₂H₄和产物Co的反应级数分别为1, 0和1, 反应活化能约为89 kJ/mol. 调节Co^2＋的浓度, 纳米金属钴的表面积可从11增加到25 m²/g.