Metal-Organic-Framework-Derived Yolk-Shell-Structured Cobalt-Based Bimetallic Oxide Polyhedron with High Activity for Electrocatalytic Oxygen Evolution

OER catalytic performance of a composite catalyst comprising multi-layer thin flake Co3O4 and PPy nanofibers

The oxygen evolution reaction (OER) plays a crucial role in energy conversion and storage processes, highlighting the significance of searching for efficient and stable OER catalysts. In this study, we have developed a composite catalyst, PPy@Co3O4, with outstanding catalytic performance for the OER. The catalyst was constructed by integrating multi-layer thin flake Co3O4 with attached PPy nanofibers, utilizing the rich active sites of Co3O4 and the flexibility and tunability of PPy nanofibers to optimize the catalyst structure. Through comprehensive characterization and performance evaluation, our results demonstrate that the PPy@Co3O4 (0.1 : 1) catalyst exhibits remarkable OER catalytic activity and stability. This research provides new strategies and insights for the development of efficient and stable OER catalysts, holding promising prospects for energy conversion and storage applications in relevant fields.

Recent strategies for constructing hierarchical multicomponent nanoparticles/metal-organic framework hybrids and their applications

Hybrid nanoparticles with unique tailored morphologies and compositions can be utilized for numerous applications owing to their combination of inherent properties as well as the structural and supportive functions of each component. Controlled encapsulation of nanoparticles within nanospaces (NPNSs) of metal-organic frameworks (MOFs) (denoted as NPNS@MOF) can generate a large number of hybrid nanomaterials, facilitating superior activity in targeted applications. In this review, recent strategies for the fabrication of NPNS@MOFs with a hierarchical architecture, tailorability, unique intrinsic properties, and superior catalytic performance are summarized. In addition, the latest and most important examples in this sector are emphasized since they are more conducive to the practical applicability of NPNS@MOF nanohybrids.

Process of metal-organic framework (MOF)/covalent-organic framework (COF) hybrids-based derivatives and their applications on energy transfer and storage

The fossil-fuel shortage and severe environmental issues have posed ever-increasing demands on clean and renewable energy sources, for which the exploration of electrocatalysts has been a big challenge toward energy transfer and storage. Some indispensable features of electrocatalysts, such as large surface area, controlled structure, high porosity, and effective functionalization, have been proved to be critical for the improvement of electrocatalytic activities. Recently, the rapid expansion of metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and porous-organic polymers has provided extensive opportunities for the development of various electrocatalysts. Moreover, combining diverse descriptions of porous-organic frameworks (such as MOFs and COFs) can generate amazing and fantastic properties, affording the formed MOF/COF (including core-shell MOF@MOF and MOF@COF and layer-on-layer MOF-on-MOF or COF-on-MOF) heterostructures wide applications in diverse fields, especially in clean energy and energy transfer. To further boosts electronic conductivity, catalytic performances, and energy storage abilities, these MOF/COF hybrid materials have been widely utilized as versatile precursors for the manufacture of transition metal catalysts embedded within mesoporous carbon nitrides (M@CN_x) and porous carbon nitride frameworks (CN_x) via a facile pyrolysis process. Given that these M@CN_x and CN_x hybrids are composed of abundant catalytic centers, rich functionalities, and large specific surface areas, vast applications in energy transfer and energy storage fields can be realized. In this mini-review, we summarize the preparation strategies of MOF/COF-based hybrids, as well as their derivatives, nanostructure formation mechanism of M@CN_x and CN_x hybrids from MOF/COF-based hybrid materials, and their applications as catalysts for driving diverse reactions and electrode materials for energy storage. Further, current challenges and future prospects of applying these derivatives into energy conversion and storage devices are also discussed.

Metal-Organic Framework-Derived Trimetallic Nanocomposites as Efficient Bifunctional Oxygen Catalysts for Zinc-Air Batteries

Transition-metal-based multifunctional catalysts have attracted increasing attention owing to high possibilities of substituting the expensive noble-metal-based catalysts in various scenarios. Multivariate metal-organic frameworks (MTV-MOFs) are ideal precursors to prepare multimetallic nanocomposites with high catalytic activity since the uniform distribution and precise regulation of mixed metal centers, as well as the consequent strong synergistic effect, could be readily achieved. Herein, a Mn/Co/Ni trimetallic catalyst (MnCoNi-C-D) with a hollow rhombic dodecahedron shape was synthesized via pyrolysis of the corresponding trimetallic-based MTV-MOF. The catalyst shows outstanding electrochemical activity toward the oxygen reduction reaction including a half-wave potential of 0.82 V and superior tolerance against methanol as well as high stability in an alkaline medium, and its oxygen evolution reaction activity also surpasses a RuO₂ catalyst. Moreover, primary and rechargeable zinc-air batteries based on MnCoNi-C-D delivered preferable performances compared with commercial Pt/C-RuO₂, including higher peak power density (116.4 mW cm^-2), higher specific capacity (841.3 mAh g^-1), higher open-circuit potential (OCV) (1.46 V), and better stability for more than 180 h. A comprehensive comparison was also conducted to prove the necessity of employing the MTV-MOF as the precursor and investigate the intrinsic superiority of the catalyst.

Formation of uniform porous yolk-shell MnCo2O4 microrugby balls with enhanced electrochemical performance for lithium storage and the oxygen evolution reaction

Mixed transition metal oxides with favorable electrochemical properties are promising electrode materials in energy storage and conversion systems. In this work, uniform porous yolk-shell MnCo₂O₄ (denoted as YSM-MCO) microrugby balls have been synthesized by simple annealing treatment of metal carbonates with a microrugby ball shape in air. Benefiting from the desired porous structure and composition, the as-synthesized YSM-MCO exhibits enhanced electrochemical performance when investigated as anode materials for lithium-ion batteries and electrocatalysts for the oxygen evolution reaction. The YSM-MCO demonstrates remarkable lithium storage properties with a good cycling stability (94% capacity retention over 200 cycles at 0.5 A g^-1) and superior rate capability (414 mA h g^-1 at 5 A g^-1). In addition, the YSM-MCO also exhibits better OER activity than most of the reported MnCo₂O₄-based electrocatalysts.

Hollow-Structured Metal Oxides as Oxygen-Related Catalysts

Metal oxide hollow structures with large surface area, low density, and high loading capacity have received great attention for energy-related applications. Acting as oxygen-related catalysts, hollow-structured transition metal oxides offer low overpotential, fast reaction rate, and excellent stability. Herein, recent progress in the oxygen-related catalysis (e.g., oxygen evolution reaction (OER), oxygen reduction reaction (ORR), and metal-air batteries) of hollow-structured transition metal oxides is discussed. Through a comprehensive outline of hollow-structured spinels, perovskites, rutiles, etc., a rational design strategy is provided for an enhanced oxygen-related catalysis performance from the viewpoint of crystal structures. Urgent challenges and further research directions are presented for hollow-structured transition metal oxides toward excellent oxygen-related catalysis.

Two-Dimensional Zeolitic Imidazolate Framework-L-Derived Iron-Cobalt Oxide Nanoparticle-Composed Nanosheet Array for Water Oxidation

Rational design of various functional nanomaterials using MOFs as a template provides an effective strategy to synthesize electrocatalysts for water splitting. In this work, we reported that an iron-cobalt oxide with 2D well-aligned nanoflakes assembling on carbon cloth (Fe-Co₃O₄ NS/CC), fabricated by an anion-exchange reaction followed by an annealing process, could serve as a high-performance oxygen-evolving catalyst. Specifically, the zeolitic imidazolate framework-L-Co nanosheet array (ZIF-L-Co NS/CC) was synthesized through a facile ambient liquid-phase deposition reaction, and then reacted with [Fe(CN)₆]^3- ions as precursors during the anion-exchange reaction at room temperature. Finally, the Fe-Co₃O₄ NS/CC was obtained via annealing treatment. On account of the compositional and structural superiority, this 3D monolithic anode exhibited outstanding electrocatalytic performance with a low overpotential of 290 mV to obtain a geometrical current density of 10 mA cm^-2 and good durability for water oxidation in base.

A Double-Buffering Strategy to Boost the Lithium Storage of Botryoid MnOx /C Anodes

Transition metal oxides (TMOs) are regarded as promising candidates for anodes of lithium ion batteries, but their applications have been severely hindered by poor material conductivity and lithiated volume expansion. As a potential solution, herein is presented a facile approach, by electrospinning a manganese-based metal organic framework (Mn-MOF), to fabricate yolk-shell MnO_x nanostructures within carbon nanofibers in a botryoid morphology. While the yolk-shell structure accomodates the lithiated volume expansion of MnO_x , the fiber confinement ensures the structural integrity during charge/discharge, achieving a so-called double-buffering for cyclic volume fluctuation. The formation mechanism of the yolk-shell structure is well elucidated through comprehensive instrumental characterizations and cogitative control experiments, following a combined Oswald ripening and Kirkendall process. Outstanding electrochemical performances are demonstrated with prolonged stability over 1000 cycles, boosted by the double-buffering design, as well as the "breathing" effect of lithiation/delithiation witnessed by ex situ imaging. Both the fabrication methodology and electrochemical understandings gained here for nanostructured MnO_x can also be extended to other TMOs toward their ultimate implementation in high-performance lithium ion batteries (LIBs).

Reaction Packaging CoSe2 Nanoparticles in N-Doped Carbon Polyhedra with Bifunctionality for Overall Water Splitting

Water electrolysis is a promising approach for green and large-scale hydrogen production; however, there are still challenges for developing efficient and stable bifunctional electrocatalysts toward the hydrogen and oxygen evolution reactions. Herein, zeolitic imidazolate framework-67 was used as the precursor for the construction of CoSe₂ nanoparticles trapped in N-doped carbon (NC) polyhedra. Among as-obtained CoSe₂-NC hybrid, highly active CoSe₂ nanoparticles in sizes of 10-20 nm are encapsulated in N-doped few-layer carbon shell, avoiding their easy aggregations of CoSe₂ nanoparticles as well as enhancing the long-term stability. The unique nanostructured CoSe₂-NC hybrid with a hierarchical porosity and 3D conductive framework thus fully exerts outstanding bifunctional catalytic activity of CoSe₂ centers. As a result, the CoSe₂-NC hybrid as bifunctional catalysts for overall water splitting delivers a high current density of 50 mA cm^-2 with an applied voltage of ∼1.73 V in an alkaline electrolyte, with a promising stability over 50 000 s.

Ultrathin carbon coated CoO nanosheet arrays as efficient electrocatalysts for the hydrogen evolution reaction

An ultrathin carbon-coated CoO composite catalyst grown on carbon cloth was developed for efficient alkaline HER.

Oxygen vacancy enriched hollow cobaltosic oxide frames with ultrathin walls for efficient energy storage and biosensing

Transition metal oxides (TMOs) with desired morphologies and atomic structures have promising applications in energy storage, catalysis, and biosensing because of their large specific surface area, high theoretical capacitance, abundant active sites, etc. In this study, hierarchical Co₃O₄ with enriched oxygen vacancies and finely tuned nanostructures, e.g. high porosity, thin wall thickness, hollow or yolk-shell structure, is prepared by dynamically balancing the decomposition and oxidation of the zeolitic imidazolate framework-67 (ZIF-67) precursor directly calcined in air at 300 °C. The optimized Co₃O₄ hollow frame inherits the original shape of the parent ZIF-67 with a high volume retention of 83% and features an ultrathin wall thickness of 10 nm, a large accessible surface area of 63.7 m² g^-1 and a high content of surface oxygen vacancies. It thus delivers an excellent specific capacitance of 770 F g^-1 at 1 A g^-1, a rate capability of 570.9 F g^-1 at 20 A g^-1 and excellent cycling stability for energy storage, and a high sensitivity of 0.7 mA mM^-1 cm^-2, a low detection limit of 0.2 μM (S/N = 3), and a wide linear detectable range of 0.005-1.175 mM for electrochemical non-enzymatic detection of glucose.

Mesoporous Hollow Nitrogen-Doped Carbon Nanospheres with Embedded MnFe2O4/Fe Hybrid Nanoparticles as Efficient Bifunctional Oxygen Electrocatalysts in Alkaline Media

Exploring sustainable and efficient electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is necessary for the development of fuel cells and metal-air batteries. Herein, we report a bimetal Fe/Mn-N-C material composed of spinel MnFe₂O₄/metallic Fe hybrid nanoparticles encapsulated in N-doped mesoporous hollow carbon nanospheres as an excellent bifunctional ORR/OER electrocatalyst in alkaline electrolyte. The Fe/Mn-N-C catalyst is synthesized via pyrolysis of bimetal ion-incorporated polydopamine nanospheres and shows impressive ORR electrocatalytic activity superior to Pt/C and good OER activity close to RuO₂ catalyst in alkaline environment. When tested in Zn-air battery, the Fe/Mn-N-C catalyst demonstrates excellent ultimate performance including power density, durability, and cycling. This work reports the bimetal Fe/Mn-N-C as a highly efficient bifunctional electrocatalyst and may afford useful insights into the design of sustainable transition-metal-based high-performance electrocatalysts.

Uniform MnCo2O4 Porous Dumbbells for Lithium-Ion Batteries and Oxygen Evolution Reactions

Three-dimensional (3D) binary oxides with hierarchical porous nanostructures are attracting increasing attentions as electrode materials in energy storage and conversion systems because of their structural superiority which not only create desired electronic and ion transport channels but also possess better structural mechanical stability. Herein, unusual 3D hierarchical MnCo₂O₄ porous dumbbells have been synthesized by a facile solvothermal method combined with a following heat treatment in air. The as-obtained MnCo₂O₄ dumbbells are composed of tightly stacked nanorods and show a large specific surface area of 41.30 m² g^-1 with a pore size distribution of 2-10 nm. As an anode material for lithium-ion batteries (LIBs), the MnCo₂O₄ dumbbell electrode exhibits high reversible capacity and good rate capability, where a stable reversible capacity of 955 mA h g^-1 can be maintained after 180 cycles at 200 mA g^-1. Even at a high current density of 2000 mA g^-1, the electrode can still deliver a specific capacity of 423.3 mA h g^-1, demonstrating superior electrochemical properties for LIBs. In addition, the obtained 3D hierarchical MnCo₂O₄ porous dumbbells also display good oxygen evolution reaction activity with an overpotential of 426 mV at a current density of 10 mA cm^-2 and a Tafel slope of 93 mV dec^-1.

Metal-Organic Framework-Derived Co3ZnC/Co Embedded in Nitrogen-Doped Carbon Nanotube-Grafted Carbon Polyhedra as a High-Performance Electrocatalyst for Water Splitting

The development of efficient, low-cost, and stable electrocatalysts for overall water splitting is of great significance for energy conversion. Transition-metal carbides (TMCs) with high catalytic activity and low cost have attracted great interests. Nevertheless, utilizing an efficient catalyst for overall water splitting is still a challenging issue for TMCs. Herein, we report the synthesis of a high-performance electrocatalyst comprising Co₃ZnC and Co nanoparticles embedded in a nitrogen-doped carbon nanotube-grafted carbon polyhedral (Co₃ZnC/Co-NCCP) by the pyrolysis of bimetallic zeolitic imidazolate frameworks in a reductive atmosphere of Ar/H₂. The Co₃ZnC/Co-NCCP exhibits remarkable electrochemical activity in catalyzing both the oxygen evolution reaction and hydrogen evolution reaction, in terms of low overpotential and excellent stability. Furthermore, the Co₃ZnC/Co-NCCP catalyst leads to a highly performed overall water splitting in the 1 M KOH electrolyte, delivering a current density of 10 mA cm^-2 at a low applied external potential of 1.65 V and shows good stability without obvious deactivation after 10 h operation. The present strategy opens a new avenue to the design of efficient electrocatalysts in electrochemical applications.

Co/Cu-MFF derived mesoporous ternary metal oxide microcubes for enhancing the catalytic activity of the CO oxidation reaction

Metal–organic framework (MOF)-based derivatives with uniform micro/mesoporous structures have attracted a great deal of interest in various research fields. Herein, we report a simple strategy to design functional mesoporous ternary metal oxides with controlled composition through direct pyrolysis of Co/Cu bimetal-formate frameworks (Co/Cu-MFFs), which were prepared by a facile one-step liquid-phase precipitation method, exhibiting uniform distribution of two different metal species and good structural integrity. The obtained mesoporous ternary metal oxide Cu_xCo_3−xO₄ (x = 0.5, 1) microcubes exhibit much better performance for CO oxidation than pure Co₃O₄, which can be mainly attributed to their larger specific surface areas, stronger reducibility, and the synergistic effect of two active metal oxide components.

The fabricated Cu_xCo_3−xO₄ microcubes with structure and component merits exhibit good performance for CO oxidation.