Ultrafine Co3 O4 Nanoparticles within Nitrogen-Doped Carbon Matrix Derived from Metal-Organic Complex for Boosting Lithium Storage and Oxygen Evolution Reaction

Iron atomic cluster supported on Co/NC having superior water oxidation activity over iron single atom

Carbon-supported iron-cobalt bimetallic electrocatalysts usually exhibit robust catalytic activity toward the oxygen evolution reaction (OER). However, the spatial isolation of Fe species at atomic level on cobalt-carbon solid remains a great challenge for practical catalytic applications in the OER. Here, we report the fabrication of CoFe bimetal porous carbon electrocatalysts by pyrolysis of molecularly defined iron complexes such as FePc (Pc = phthalocyanine) and Fe(acac)₃ pre-encapsulated in the cavities of zeolitic imidazolate framework (ZIF)-67. With this unique strategy, high-loading atomic Fe nanoclusters (Fe-ACs) and Fe single atoms (Fe-SAs) were supported on Co/NC hybrids relying on the size of the molecular Fe precursors. The former exhibited superior OER performance to the single Fe atom-decorated Co/NC, as well as other ZIF-67-derived electrocatalysts. Theoretical modulation suggests Co as the OER active site for Fe-ACs@Co/NC at the in situ-formed FeOOH-ACs/Co₃O₄ interface, while Fe was proposed as the active site for Fe-SAs@Co/NC.

Highly Stable and Efficient Oxygen Evolution Electrocatalyst Based on Co Oxides Decorated with Ultrafine Ru Nanoclusters

Exploring highly active and durable electrocatalysts for oxygen evolution reaction (OER) is significant to achieve efficient anion exchange membrane (AEM) water electrolysis. Herein, hollow Co-based N-doped porous carbon spheres decorated with ultrafine Ru nanoclusters (HS-RuCo/NC) are reported as efficient OER electrocatalysts via the pyrolysis of carboxylate-terminated polystyrene-templated bimetallic zeolite imidazolate frameworks accommodating Ru (III) ions. The unique hollow structure with hierarchically porous characteristics contributes to the electrolyte penetration for fast mass transport and the exposure of more metal sites. Theoretical and experimental studies reveal the synergistic effect between the in situ formed RuO₂ and Co₃ O₄ as another critical factor for the high OER performance, where the coupling of RuO₂ with Co₃ O₄ can optimize the electronic configuration of RuO₂ /Co₃ O₄ heterostructure and decrease the energy barrier during OER. Meanwhile, the presence of Co₃ O₄ can efficiently suppress the over-oxidation of RuO₂ , endowing the catalysts with high stability. As expected, when the resultant HS-RuCo/NC was integrated into an AEM water electrolyzer, the obtained electrolyzer exhibits a cell voltage of 2.07 V to launch the current density of 1 A cm^-2 and excellent long-term stability at 500 mA cm^-2 under room temperature in alkaline solution, outperforming the commercial RuO₂ -based AEM water electrolyzer (2.19 V).

Porous biscuit-like nanoplate FeNb11O29-x@C for lithium-ion storage and oxygen evolution

The development of efficient and stable electrode materials for lithium-ion batteries (LIBs) and the oxygen evolution reaction (OER) is critical for clean and sustainable energy storage and conversion. In this work, porous biscuit-like nanoplate FeNb₁₁O_29-x@C is reasonably prepared by morphology control and microstructure modification, and presents many advantages in LIBs and the OER. In particular, FeNb₁₁O_29-x@C displays a large specific surface area, abundant active sites and a significant edge effect, thus improving the Li⁺ reactivity and OER kinetics. Meanwhile, the oxygen vacancies and lattice defects in FeNb₁₁O_29-x@C enhance the Li⁺ transport rate and reduce the OER barrier. In addition, the carbon layer structure not only inhibits the irreversible reaction between the electrolyte and metal ions, but promotes the stability, cycling ability and conductivity of LIBs and the OER. Generally, FeNb₁₁O_29-x@C demonstrates good electrochemical performance in LIBs (providing 240.8 mA h g^-1 reversible capacity at a current density of 0.25C and just 0.98% capacity attenuation after 500 cycles at a current density of 10C). Again, it also shows high catalytic performance in the OER (a low overpotential (290 mV@10 mA cm^-2), a small Tafel slope (44.4 mV dec^-1) and desirable catalytic stability).

Engineering oxygen vacancies in CoO@Co3O4/C nanocomposites for enhanced electrochemical performances

Efficient electrocatalyst materials for several applications, including energy storage and conversion, have become vital for achieving technological progress. In this work, a CoO@Co₃O₄/C composite with abundant oxygen vacancies was successfully synthesized. The concentration of the oxygen vacancies was well controlled by changing the degree of vacuum during the heat treatment and was characterized by XPS and EPR. The existence of the porous structure arising from the cobalt oxide particles embedded in the carbon matrix provided an efficient charge and gas transmission path, significantly improving the performance of electrocatalytic oxygen evolution. Sufficient reactive sites were provided from both the oxygen vacancies and the heterogeneous interface. The mechanism of enhanced OER originating from the built-in electric field derived from oxygen vacancies was investigated. Consequently, the CoO@Co₃O₄/C composites offered an OER overpotential of 287 mV at a current density of 10 mA cm^-2 with good stability in 1 mol L^-1 KOH. In addition, combined with surface photovoltage (SPV), transient photovoltage (TPV), DFT, and in situ Raman spectroscopy, the effect of oxygen defects on the electron migration ability and transformation of the intermediate products were investigated to further understand the nature of catalytic activity in OER.

Inspirations of Cobalt Oxide Nanoparticle Based Anticancer Therapeutics

Cobalt is essential to the metabolism of all animals due to its key role in cobalamin, also known as vitamin B12, the primary biological reservoir of cobalt as an ultra-trace element. Current cancer treatment strategies, including chemotherapy and radiotherapy, have been seriously restricted by their side effects and low efficiency for a long time, which urges us to develop new technologies for more effective and much safer anticancer therapies. Novel nanotechnologies, based on different kinds of functional nanomaterials, have been proved to act as effective and promising strategies for anticancer treatment. Based on the important biological roles of cobalt, cobalt oxide nanoparticles (NPs) have been widely developed for their attractive biomedical applications, especially their potential for anticancer treatments due to their selective inhibition of cancer cells. Thus, more and more attention has been attracted to the preparation, characterization and anticancer investigation of cobalt oxide nanoparticles in recent years, which is expected to introduce novel anticancer treatment strategies. In this review, we summarize the synthesis methods of cobalt oxide nanoparticles to discuss the advantages and restrictions for their preparation. Moreover, we emphatically discuss the anticancer functions of cobalt oxide nanoparticles as well as their underlying mechanisms to promote the development of cobalt oxide nanoparticles for anticancer treatments, which might finally benefit the current anticancer therapeutics based on functional cobalt oxide nanoparticles.

CuCo2O4 Hollow Microspheres with Graphene Composite Targeting Superior Lithium-Ion Storage

CuCo₂O₄, a type of promising lithium-ion storage material, exhibits high electrochemical properties in lithium-ion batteries and enormous economic benefits. However, its practical application is limited by problems such as structural collapse and electrochemical stability during the charging and discharging process. In this work, the reduced graphene oxide (rGO)-coated CuCo₂O₄ (CuCo₂O₄/rGO) hollow microspheres were successfully prepared by electrostatic self-assembly. The CuCo₂O₄/rGO electrode shows an outstanding capability for lithium-ion storage and a remarkable rate capacity, e.g., 445 mA h g^-1 at 5 A g^-1. After 150 cycles at 0.1 A g^-1, the reversible capacity of the CuCo₂O₄/rGO electrode is as high as 1080 mA h g^-1, and it can still retain about 530 mA h g^-1 in the 400th cycle at 1 A g^-1. The hollow microspheres with mesoporous shells can cause electrolyte penetration into the spherical shell to effectively shorten the transfer distance of lithium ions, and the encapsulation of graphene improves the conductivity and stability of CuCo₂O₄, which endows CuCo₂O₄/rGO with a wonderful Li⁺ storage performance. It is proved that this is an efficient method to improve the electrochemical performance of metal compounds for better applications in energy storage.

Nanocomposite of ultra-small MoO2 embedded in nitrogen-doped carbon: In situ derivation from an organic molybdenum complex and its superior Li-Ion storage performance

MoO₂ is a promising anode material for lithium-ion batteries, however, the lithiation of bulk MoO₂ is usually limited to addition-type reaction at room temperature, and the conversion reaction is hindered because of the sluggish kinetics. Herein, a nanocomposite of MoO₂ embedded in nitrogen-doped carbon (MoO₂/NC) is synthesized through the in situ thermolysis of an organic molybdenum complex MoO₂(acac)(phen) (acac = acetylacetone, phen = 1,10-Phenanthroline). Owing to the fact that [MoO₂]²⁺ can be strongly chelated by phen, the molybdenum source in the MoO₂(acac)(phen) precursor is highly dispersed, leading to the formation of ultra-small MoO₂ nanoparticles in the nanocomposite, which can facilitate the conversion reaction. Moreover, the NC matrix can guarantee a high electrical conductivity and effectively accommodate the volume changes triggered by the conversion reaction. Consequently, the MoO₂/NC nanocomposite exhibits outstanding electrochemical properties, including large reversible capacity of 950 mA h g^-1 at 0.1 A g^-1, high-rate capability of 605 mA h g^-1 at 2 A g^-1, and excellent cycling stability over 500 cycles as an anode material for lithium-ion batteries.

Morphologically controlled cobalt oxide nanoparticles for efficient oxygen evolution reaction

Electrochemical water oxidation is one of the thrust areas of research today in solving energy and environmental issues. The morphological control in the synthesis of nanomaterials plays a crucial role in designing efficient electrocatalyst. In general, various synthetic parameters can direct the morphology of nanomaterials and often this is the main driving force for the electrocatalyst in tuning the rate of the oxygen evolution reaction (OER) for the electrochemical water-splitting. Here, a facile and cost-effective synthesis of spinel cobalt oxides (Co₃O₄) via a one-pot hydrothermal pathway with tunable morphology has been demonstrated. Different kinds of morphologies have been obtained by systematically varying the reaction time i.e. nanospheres, hexagon and nanocubes. Their catalytic activity has been explored towards OER in 1.0 M alkaline KOH solution. The catalyst Co₃O₄-24 h nanoparticles synthesized in 24 h reaction time shows the lowest overpotential (η) value of 296 mV at 10 mA cm^-2 current density, in comparison to that of other as-prepared catalysts i.e. Co₃O₄-pH9 (311 mV), Co₃O₄-12 h (337 mV), and Co₃O₄-6 h (342 mV) with reference to commercially available IrO₂ (415 mV). Moreover, Co₃O₄-24 h sample shows the outstanding electrochemical stability up to 25 h time.

Molecular and heterogeneous water oxidation catalysts: recent progress and joint perspectives

The recent synthetic and mechanistic progress in molecular and heterogeneous water oxidation catalysts highlights the new, overarching strategies for knowledge transfer and unifying design concepts.