Triple‐Shelled Manganese–Cobalt Oxide Hollow Dodecahedra with Highly Enhanced Performance for Rechargeable Alkaline Batteries

Design and Self-Assembly of Polyhedron Particles to Construct Iridescent Structural Colors

Polyhedron particles exhibit unique physical properties in constructing novel materials. Here, the polystyrene (PS) polyhedron particles were fabricated via dispersion polymerization, and their morphologies can be controlled by tuning the divinylbenzene (DVB) content and polarity of the reaction medium. The possible formation mechanism is the asymmetric distribution of cross-linked networks during the phase separation process. In addition, the large-scale iridescent structural colors based on polyhedrons were obtained and further explored their applications in smart displays. This presented method guides the fabrication of anisotropic particles and their further assembly to construct novel materials.

Rationally Designed Mn2 O3 -ZnMn2 O4 Hollow Heterostructures from Metal-Organic Frameworks for Stable Zn-Ion Storage

Mn-based oxides have sparked extensive scientific interest for aqueous Zn-ion batteries due to the rich abundance, plentiful oxidation states, and high output voltage. However, the further development of Mn-based oxides is severely hindered by the rapid capacity decay during cycling. Herein, a two-step metal-organic framework (MOF)-engaged templating strategy has been developed to rationally synthesize heterostructured Mn₂ O₃ -ZnMn₂ O₄ hollow octahedrons (MO-ZMO HOs) for stable zinc ion storage. The distinctive composition and hollow heterostructure endow MO-ZMO HOs with abundant active sites, enhanced electric conductivity, and superior structural stability. By virtue of these advantages, the MO-ZMO HOs electrode shows high reversible capacity, impressive rate performance, and outstanding electrochemical stability. Furthermore, ex situ characterizations reveal that the charge storage of MO-ZMO HOs mainly originates from the highly reversible Zn²⁺ insertion/extraction reactions.

Pseudocapacitive Lithium Storage of Cauliflower-Like CoFe2 O4 for Low-Temperature Battery Operation

Binary transition-metal oxides (BTMOs) with hierarchical micro-nano-structures have attracted great interest as potential anode materials for lithium-ion batteries (LIBs). Herein, we report the fabrication of hierarchical cauliflower-like CoFe₂ O₄ (cl-CoFe₂ O₄ ) via a facile room-temperature co-precipitation method followed by post-synthetic annealing. The obtained cauliflower structure is constructed by the assembly of microrods, which themselves are composed of small nanoparticles. Such hierarchical micro-nano-structure can promote fast ion transport and stable electrode-electrolyte interfaces. As a result, the cl-CoFe₂ O₄ can deliver a high specific capacity (1019.9 mAh g^-1 at 0.1 A g^-1 ), excellent rate capability (626.0 mAh g^-1 at 5 A g^-1 ), and good cyclability (675.4 mAh g^-1 at 4 A g^-1 for over 400 cycles) as an anode material for LIBs. Even at low temperatures of 0 °C and -25 °C, the cl-CoFe₂ O₄ anode can deliver high capacities of 907.5 and 664.5 mAh g^-1 at 100 mA g^-1 , respectively, indicating its wide operating temperature. More importantly, the full-cell assembled with a commercial LiFePO₄ cathode exhibits a high rate performance (214.2 mAh g^-1 at 5000 mA g^-1 ) and an impressive cycling performance (612.7 mAh g^-1 over 140 cycles at 300 mA g^-1 ) in the voltage range of 0.5-3.6 V. Kinetic analysis reveals that the electrochemical performance of cl-CoFe₂ O₄ is dominated by pseudocapacitive behavior, leading to fast Li⁺ insertion/extraction and good cycling life.

Aerobic Oxidation of 5-Hydroxymethylfurfural to 2,5-Furandicarboxylic Acid over Holey 2 D Mn2 O3 Nanoflakes from a Mn-based MOF

The aerobic oxidation of 5-hydroxymethylfurfural (HMF) to 2,5-furandicarboxylic acid (FDCA), a promising renewable monomer to produce bio-based polymers such as polyethylene furanoate (PEF), has recently emerged as the subject of increasing interest. Here, holey 2 D Mn₂ O₃ nanoflakes were obtained by a facile thermal treatment of a Mn-based metal-organic framework (MOF) precursor. The structural and morphological properties of the nanoflakes were characterized by powder XRD, FTIR, SEM and TEM to explore the formation process. It was inferred that the linker loss in the MOF precursor and the oxidation of the Mn cation induced by the heat-treatment in air were responsible for the formation of holey 2 D Mn₂ O₃ nanoflakes. The specific morphology and redox cycle of the Mn cation on the surface endowed the synthesized nanoflakes with promising performance on the selective oxidation. The obtained nanoflakes calcined at 400 °C (M400) afforded over 99.5 % yield of FDCA at complete conversion of HMF, which is superior to the catalytic activity of commercial Mn₂ O₃ and activated MnO₂ . To our knowledge, Mn₂ O₃ exhibiting such a high performance on the aerobic oxidation of HMF to FDCA has not yet been reported. Based on the investigation of the experimental parameters, a plausible reaction mechanism was proposed.

Construction of MnO2 Artificial Leaf with Atomic Thickness as Highly Stable Battery Anodes

The leaf-like structure is a classic and robust structure and its unique vein support can reduce structural instability. However, biomimetic leaf structures on the atomic scale are rarely reported due to the difficulty in achieving a stable vein-like support in a mesophyll-like substrate. A breathable 2D MnO₂ artificial leaf is first reported with atomic thickness by using a simple and mild one-step wet chemical method. This homogeneous ultrathin leaf-like structure comprises of vein-like crystalline skeleton as support and amorphous microporous mesophyll-like nanosheet as substrate. When used as an anode material for lithium ion batteries, it first solves the irreversible capacity loss and poor cycling issue of pure MnO₂ , which delivers high capacity of 1210 mAh g^-1 at 0.1 A g^-1 and extremely stable cycle life over 2500 cycles at 1.0 A g^-1 . It exhibits the most outstanding cycle life of pure MnO₂ and even comparable to the most MnO₂ -based composite electrode materials. This biomimetic design provides important guidelines for precise control of 2D artificial systems and gives a new idea for solving poor electrochemical stability of pure metal oxide electrode materials.

Synthesis of Well-Defined Internal-Space-Controllable UiO-66 Spherical Nanostructures Used as Advanced Nanoreactor

Controllable well-defined metal-organic frameworks (MOFs) spherical structures are expected to be potential good platforms for the heterogeneous catalysis, guest storage, and drug delivery. However, the synthesis faces a challenge. In this paper, a series of well-defined MOFs spherical structures including core-shell, yolk-shell, and hollow spheres were successfully constructed with colloidal carbon as template. Meanwhile, the shapes of MOFs unit (bricklike or octahedral) and sizes of the formed internal space can be controlled simultaneously by rationally changing the modulator and removing template in a good manner. The as-prepared structures could not only keep intact crystal textures but also be used as advanced nanoreactors for enhancing raw materials conversion in the heterogeneous reaction of synthesizing benzoin ethyl ether. Particularly, by our internal-space-controllable nanoreactors, for the first time, the quantifiable relation between nanoreactors' internal space sizes and raw material conversion was revealed.

Synthesis of Single-Component Metal Oxides with Controllable Multi-Shelled Structure and their Morphology-Related Applications

Multi-shelled hollow spheres metal oxides, namely materials with more than three shells, have attracted increasing attention due to their unique structure. The preparation methods of typical metal oxides including NiO, Co₃ O₄ and ZnO etc. have been summarized in this review. Simultaneously, the parameters that influence the ultimate morphologies, shell number as well as the compositions have also been discussed. The potential application fields in energy conversion and storage, electromagnetic wave absorption, photocatalysis that related to the unique structure are also highlighted. Finally, the future researches of multi-shelled hollow spheres metal oxides are further discussed.