Rational Engineering of Multilayered Co3O4/ZnO Nanocatalysts through Chemical Transformations from Matryoshka‐Type ZIFs

Hybrid metal oxides with multilayered structures exhibit unique physical and chemical properties, particularly important to heterogeneous catalysis. However, regulations of morphology, spatial location, and shell numbers of the hybrid metal oxides still remain a challenge. Herein, binary Co₃O₄/ZnO nanocages with multilayered structures (up to eight layers) are prepared via chemical transformation from diverse Matryoshka‐type zeolitic imidazolate frameworks (ZIFs) via a straightforward and scalable calcination method. More importantly, the obtained ZIF‐derived metal oxides (ZDMOs) with versatile layer numbers exhibit remarkable catalytic activity for both gas‐phase CO oxidation and CO₂ hydrogenation reactions, which are directly related to the sophisticated shell numbers (i.e., Co₃O₄‐terminated layers or ZnO‐terminated layers). Particularly, in situ reflectance infrared Fourier transform spectroscopy (DRIFTS) results indicate that the promotional effects of the multilayered structures indeed exist in CO₂ hydrogenation, wherein the key reaction intermediates are quite different for five‐layer and six‐layer ZDMOs. For instance, *HCOO is the predominant intermediate over the six‐layer ZDMO; on the contrary, *H₃CO is the crucial species over the five‐layer ZDMO. The ZnO/Co₃O₄ interface should be the active sites for CO₂ hydrogenation to *HCOO and *H₃CO species, which are ultimately converted to the products (CH₄ or methanol). Accordingly, the work here provides a convenient way to facilely engineer multilayered Co₃O₄/ZnO nanocomposites with precisely controlled shell numbers for heterogeneous catalysis applications.     

Layered Double Hydroxide Nano‐ and Microstructures Grown Directly on Metal Substrates and Their Calcined Products for Application as Li‐Ion Battery Electrodes

Layered double hydroxide (LDH) nano‐ and microstructures with controllable size and morphology have been fabricated on “bivalent metal” substrates such as zinc and copper by a one‐step, room‐temperature process, in which metal substrates act as both reactants and supports. By manipulating the concentration of NH₃ · H₂O, the thickness and lateral size of the LDH materials can be tuned from several tens of nanometers to several hundreds of nanometers and from several hundreds of nanometers to several micrometers, respectively. This method is general and may be readily extended to any other alkali‐resisted substrate coated with Zn and Cu. As an example, Zn‐covered stainless steel foil has been shown to be effective for the growth of a Zn? Al LDH film. After calcinating the as‐grown LDH at high temperature (650 °C) in argon gas, a ZnO/ZnAl₂O₄ porous nanosheet film is obtained, which is then directly used for the first time as the anode material for Li‐ion batteries with the operating voltage window of 0.05–2.5 V (vs. Li). The result demonstrates that ZnO/ZnAl₂O₄ has higher discharge and charge capacities and considerably better cycling stability compared to pure ZnO (Li insertion/extraction rate: 200 or 500 mA g^?1). The improved electrochemical performance can be ascribed to the buffering effect of the inactive matrix ZnAl₂O₄ by relieving the stress caused by the volume change during charge–discharge cycling. This work represents a successful example for the development of promising ZnO‐based anode materials for Li‐ion batteries.     

Metal Nanocrystal‐Embedded Hollow Mesoporous TiO2 and ZrO2 Microspheres Prepared with Polystyrene Nanospheres as Carriers and Templates

Noble metal nanocrystals with different shapes and compositions are embedded in hollow mesoporous metal oxide microspheres through an ultrasonic aerosol spray. Polystyrene (PS) nanospheres are employed simultaneously as a hard template to create hollow interiors inside the oxide microspheres and as the carrier to bring pregrown metal nanocrystals, including Pd nanocubes, Au nanorods, and Au core/Pd shell nanorods, into the oxide microspheres. Calcination removes the PS template and causes the metal nanocrystals to adsorb on the inner surface of the hollow oxide microspheres. The catalytic performances of the Pd nanocube‐embedded TiO₂ and ZrO₂ microspheres are investigated using the reduction of 4‐nitrophenol as a model reaction. The presence of the mesopores in the oxide microspheres allows the reactant molecules to diffuse into the hollow interiors and subsequently interact with the Pd nanocubes. The embedding of the metal nanocrystals in the hollow oxide microspheres prevents the aggregation of the metal nanocrystals and reduces the loss of the catalyst during recycling. The Pd nanocube‐embedded ZrO₂ microspheres are found to exhibit a much higher catalytic activity, a much larger catalytic reaction rate, and a superior recyclability in comparison with a commercial Pd/C catalyst. This preparation approach could potentially be utilized to incorporate various types of mono‐ and multimetallic nanocrystals with different sizes, shapes, and compositions into hollow mesoporous oxide microspheres. Such a capability can facilitate the studies of the catalytic properties of various combinations of metal nanocrystals and metal oxide supports and therefore guide the design and creation of high‐performance catalysts.     

The Development of Yolk–Shell‐Structured Pd&ZnO@Carbon Submicroreactors with High Selectivity and Stability

Design of multicomponent yolk–shell structures is crucial for the fabrication of micro/nanoreactors for a variety of applications. This work reports the rational design and synthesis of yolk–shell‐structured submicroreactors with loaded metal nanoparticles into ZnO–microporous carbon core–shell structures. The solvothermal treatment and carbonization process of uniform zeolitic imidazolate framework‐8 (ZIF‐8)@resin polymer core–shell structures leads to the generation of yolk–shell‐structured ZnO@carbon. The synthesis conditions are optimized to track the evolution of ZIF‐8 in a confined space of resin polymer as a submicroreactor itself. It is found that nanoribbon evolution occurs via the formation of the intermediate needle‐like particles. The Pd&ZnO@carbon submicroreactor is shown to be a highly selective catalyst (selectivity >99%) for hydrogenation of phenylacetylene to phenylethylene. The excellent performance of Pd&ZnO@carbon particles is evidenced by higher conversion and selectivity than that of Pd/ZnO and Pd/C with similar Pd loading. Furthermore, Pd&ZnO@carbon submicroreactors show superior catalytic stability, and no deactivation after 25 h of reaction. The proposed strategy is promising for the design of multifunctional micro/nanoreactors or nanocontainers for construction of artificial cells.     

Strong Electronic Interaction between Amorphous MnO2 Nanosheets and Ultrafine Pd Nanoparticles toward Enhanced Oxygen Reduction and Ethylene Glycol Oxidation Reactions

Strengthening the interface interaction between metal and support is an efficient strategy to improve the intrinsic activity and reduce the amount of noble metal. Amorphization of support is an effective approach for enhancing the metal-support interaction due to the numerous surface defects in amorphous structure. In this work, a Pd/a-MnO₂ electrocatalyst containing ultrafine and well-dispersive Pd nanoparticles and amorphous MnO₂ nanosheets is successfully synthesized via a simple and rapid wet chemical method. Differing from the crystal counterpart (Pd/c-MnO₂), the flexible structure of amorphous support can be more favorable to electron transfer and further enhance the metal-support interaction. The synergism between Pd and amorphous MnO₂ results in the downshift of the d-band center, which is beneficial for the desorption of critical intermediates both in oxygen reduction reaction (ORR) and in ethylene glycol oxidation (EGOR). Due to the lower *^.OH desorption energy of Pd/a-MnO₂ surface, the rapid dissociation of *OH from Pd facilitates the formation of H₂O in ORR, thus demonstrating superior ORR performance comparable to Pt/C. For EGOR, the presence of amorphous MnO₂ promotes the formation of adsorbed OH species, which accelerates the desorption of intermediate CO from Pd sites, and thus exhibits excellent EGOR activity and stability.     

An Ultrarobust Composite Gel Electrolyte Stabilizing Ion Deposition for Long‐Life Lithium Metal Batteries

Lithium metal batteries (LMBs) possessing ultrahigh energy density are promising next‐generation battery systems, but the short cycle life and safety concerns caused by the uncontrollable growth of lithium dendrites impede their broad applications. Herein, to address these issues, an ultrarobust composite gel electrolyte (CGE) that can effectively stabilize ion deposition for LMBs is designed via fabricating a specially structured aerogel as the matrix. The gel electrolyte matrix with a 3D interconnected highly porous structures and good affinity with liquid electrolytes is fabricated via compositing bacterial cellulose (BC) and Li_0.33La_0.557TiO₃ nanowires (LLTO NWs) into an aerogel. The composite aerogel matrix demonstrates excellent wettability and liquid electrolyte uptake (586 ± 5%), and the resulting CGE presents exceptional Young's modulus of 1.15 GPa and an extremely high lithium‐ion transference number of 0.88. More significantly, the synergistic effect from the robust BC skeleton and LLTO NWs enabling stable ion deposition effectively suppresses the growth of lithium dendrites. Armed with the CGE, ultrastable symmetric Li/Li cells demonstrate a long cycle life of 1200 h and highly stable performance even at a high current density of 5 mA cm^?2. Furthermore, half cells with the CGE exhibit remarkable enhancement in capacity, cycling stability, and rate performance.     

Direct Ink Writing of Adjustable Electrochemical Energy Storage Device with High Gravimetric Energy Densities

3D printing graphene aerogel with periodic microlattices has great prospects for various practical applications due to their low density, large surface area, high porosity, excellent electrical conductivity, good elasticity, and designed lattice structures. However, the low specific capacitance limits their development in energy storage fields due to the stacking of graphene. Therefore, constructing a graphene‐based 2D materials hybridization aerogel that consists of the pseduocapacitive substance and graphene material is necessary for enhancing electrochemical performance. Herein, 3D printing periodic graphene‐based composite hybrid aerogel microlattices (HAMs) are reported via 3D printing direct ink writing technology. The rich porous structure, high electrical conductivity, and highly interconnected networks of the HAMs aid electron and ion transport, further enabling excellent capacitive performance for supercapacitors. An asymmetric supercapacitor device is assembled by two different 4‐mm‐thick electrodes, which can yield high gravimetric specific capacitance (C_g) of 149.71 F g^?1 at a current density of 0.5 A g^?1 and gravimetric energy density (E_g) of 52.64 Wh kg^?1, and retains a capacitance retention of 95.5% after 10 000 cycles. This work provides a general strategy for designing the graphene‐based mixed‐dimensional hybrid architectures, which can be utilized in energy storage fields.     

Effect of Cryogenic Temperature Deposition of Various Metal Contacts on Bulk Single-Crystal <Emphasis Type="Italic">n</Emphasis>-Type ZnO

The effect of cryogenic temperatures during metal deposition on the contact properties of Pd, Pt, Ti, and Ni on bulk single-crystal n-type ZnO has been investigated. Deposition at both room and low temperature produced contacts with Ohmic characteristics for Ti and Ni metallizations. By sharp contrast, both Pd and Pt contacts showed rectifying characteristics after deposition with barrier heights between 0.37 eV and 0.69 eV. Changes in contact behavior were measured on Pd to anneal temperatures of ∼300 °C, showing an increase in barrier height along with a decrease in ideality factor with increasing annealing temperature. This difference with annealing temperature is in sharp contrast to previous results for Au contacts to ZnO. There were no differences in near-surface stoichiometry for the different deposition temperatures; however, low temperature contacts demonstrated some peeling/cracking for Pt and Pd.     

A Versatile Light‐Switchable Nanorod Memory: Wurtzite ZnO on Perovskite SrTiO3

Integrating materials with distinct lattice symmetries and dimensions is an effective design strategy toward realizing novel devices with unprecedented functionalities, but many challenges remain in synthesis and device design. Here, a heterojunction memory made of wurtzite ZnO nanorods grown on perovskite Nb‐doped SrTiO₃ (NSTO) is reported, the electronic properties of which can be drastically reconfigured by applying a voltage and light. Despite of the distinct lattice structures of ZnO and NSTO, a consistent nature of single crystallinity is achieved in the heterojunctions via the low‐temperature solution‐based hydrothermal growth. In addition to a high and persistent photoconductivity, the ZnO/NSTO heterojunction diode can be turned into a versatile light‐switchable resistive switching memory with highly tunable ON and OFF states. The reversible modification of the effective interfacial energy barrier in the concurrent electronic and ionic processes most likely gives rise to the high susceptibility of the ZnO/NSTO heterojunction to external electric and optical stimuli. Furthermore, this facile synthesis route is promising to be generalized to other novel functional nanodevices integrating materials with diverse structures and properties.     

Single‐Step Deposition of Au‐ and Pt‐Nanoparticle‐Functionalized Tungsten Oxide Nanoneedles Synthesized Via Aerosol‐Assisted CVD,and Used for Fabrication of Selective Gas Microsensor Arrays

Tungsten oxide nanostructures functionalized with gold or platinum NPs are synthesized and integrated, using a single‐step method via aerosol‐assisted chemical vapour deposition, onto micro‐electromechanical system (MEMS)‐based gas‐sensor platforms. This co‐deposition method is demonstrated to be an effective route to incorporate metal nanoparticles (NP) or combinations of metal NPs into nanostructured materials, resulting in an attractive way of tuning functionality in metal oxides (MOX). The results show variations in electronic and sensing properties of tungsten oxide according to the metal NPs introduced, which are used to discriminate effectively analytes (C₂H₅OH, H₂, and CO) that are present in proton‐exchange fuel cells. Improved sensing characteristics, in particular to H₂, are observed at 250 °C with Pt‐functionalized tungsten oxide films, whereas non‐functionalized tungsten oxide films show responses to low concentrations of CO at low temperatures. Differences in the sensing characteristics of these films are attributed to the different reactivities of metal NPs (Au and Pt), and to the degree of electronic interaction at the MOX/metal NP interface. The method presented in this work has advantages over other methods of integrating nanomaterials and devices, of having fewer processing steps, relatively low processing temperature, and no requirement for substrate pre‐treatment.     

Catalytically Doped Semiconductors for Chemical Gas Sensing: Aerogel‐Like Aluminum‐Containing Zinc Oxide Materials Prepared in the Gas Phase

Atmospheric contamination with organic compounds is undesired in industry and in society because of odor nuisance or potential toxicity. Resistive gas sensors made of semiconducting metal oxides are effective in the detection of gases even at low concentration. Major drawbacks are low selectivity and missing sensitivity toward a targeted compound. Acetaldehyde is selected due to its high relevance in chemical industry and its toxic character. Considering the similarity between gas‐sensing and heterogeneous catalysis (surface reactions, activity, selectivity), it is tempting to transfer concepts. A question of importance is how doping and the resulting change in electronic properties of a metal‐oxide support with semiconducting properties alters reactivity of the surfaces and the functionality in gas‐sensing and in heterogeneous catalysis. A gas‐phase synthesis method is employed for aerogel‐like zinc oxide materials with a defined content of aluminum (n‐doping), which were then used for the assembly of gas sensors. It is shown that only Al‐doped ZnO represents an effective sensor material that is sensitive down to very low concentrations (<350 ppb). The advance in properties relates to a catalytic effect for the doped semiconductor nanomaterial.     

Synthesis,physical properties and antibacterial activity of metal oxides nanostructures

Metal oxides (MOs) nanostructures represent a new class of materials which have been explored for the health related applications. Highly ionic MOs nanostrucrures are important for their unique physicochemical properties as well as antibacterial activity. In this work, MOs nanostructures (ZnO, CuO, SnO₂ and CeO₂) have been synthesized by chemical co-precipitation technique and characterized by XRD, SEM, EDS, FTIR and UV–visible spectroscopy analysis. XRD results reveal the single-phase formation of all metal oxides. Spherical nanoparticles are observed in case of ZnO, SnO₂ and CeO₂ samples, while hierarchal nanostructures are observed in case of CuO sample. Antibacterial activity of four different MOs nanostructures against E. coli bacterium has been assessed by agar disc method. The antibacterial activity results have shown that the ZnO nanostructures exhibit maximum sensitivity (10 mm ZOI) towards E. coli bacterium. The order of antibacterial activity for different MOs nanostructures is found to be the following: ZnO>SnO₂>CeO₂>CuO. Our findings suggest that the particle size, morphology and type of MOs nanostructures play vital role in their antibacterial activity. It is concluded from the present findings that ZnO nanostructures can be used as an efficient antibacterial agent.     

ZnO and related materials: Plasma-Assisted molecular beam epitaxial growth, characterization and application

This paper will address features of plasma-assisted molecular beam epitaxial growth of ZnO and related materials and their characteristics. Two-dimensional, layer-by-layer growth is achieved both on c-plane sampphire by employing MgO buffer layer growth and on (0001) GaN/Al₂O₃ template by predepositing a low-temperature buffer layer followed by high-temperature annealing. Such two-dimensional growth results in the growth of high-quality heteroepitaxial ZnO epilayers. Biexciton emission is obtained from such high quality epilayers The polarity of heteroepitaxial ZnO epilayers is controlled by engineering the heterointerfaces. We achieved selective growth of Zn-polar and O-polar ZnO heteroepitaxial layers. The origin of different polarities can be successfully explained by an interface bonding sequence model. N-type conductivity in Gadoped ZnO epilayers is successfully controlled. High conductivity, enough to be applicable to devices, is achieved. Mg_xZn_1-xO/ZnO heterostructures are grown and emission from a ZnO quantum well is observed. Mg incorporation in a MgZnO alloy is determined by in-situ reflection high-energy electron diffraction intensity oscillations, which enables precise control of the composition. Homoepitaxy on commericial ZnO substrates has been examined. Reflection high-energy electron diffraction intensity oscillations during homoepitaxy growth are observed.     

Metal Single-Atom Cocatalyst on Carbon Nitride for the Photocatalytic Hydrogen Evolution Reaction: Effects of Metal Species

Single-atom (SA) catalysts exhibit high activity in various reactions because there are no inactive internal atoms. Accordingly, SA cocatalysts are also an active research fields regarding photocatalytic hydrogen (H₂) evolution which can be generated by abundant water and sunlight. Herein, it is investigated whether 10 transition metal elements can work as an SA on graphitic carbon nitride (g-C₃N₄; i.e., gCN), a promising visible-light-driven photocatalyst. A method is established to prepare SA-loaded gCN at high loadings (weight of ≈3 wt.% for Cu, Ni, Pd, Pt, Rh, and Ru) by modulating the photoreduction power. Regarding Au and Ag, SAs are formed with difficulty without aggregation because of the low binding energy between gCN and the SA. An evaluation of the photocatalytic H₂-evolution activity of the prepared metal SA-loaded gCN reveals that Pd, Pt, and Rh SA-loaded gCN exhibits relatively high H₂-evolution efficiency per SA. Transient absorption spectroscopy and electrochemical measurements reveal the following: i) Pd SA-loaded gCN exhibits a particularly suitable electronic structure for proton adsorption and ii) therefore they exhibit the highest H₂-evolution efficiency per SA than other metal SA-loaded gCN. Finally, the 8.6 times higher H₂-evolution rate per active site of Pd SA is achieved than that of Pd-nanoparticles cocatalyst.     

Simultaneous Electrical and Thermoelectric Parameter Retrieval via Two Terminal Current–Voltage Measurements on Individual ZnO Nanowires

The thermoelectric parameters, in particular the thermal conductivity and dimensionless figure of merit ZT, of ZnO nanowires, are estimated via two terminal current–voltage measurements. The measurements are carried out in situ in a transmission electron microscope and negative differential conductance is observed on individually suspended ZnO nanowires. From the low bias region of the current–voltage curve, the electrical parameters, including carrier concentration and mobility, are obtained by fitting the experimental data using a metal–semiconductor–metal model. The thermal conductivity is extracted from the high bias region of the same current–voltage curve using a self‐consistent method, which combines the self‐heating thermal conduction and electrical transport properties of ZnO nanowires. It is shown that the thermal conductivity of ZnO nanowires is suppressed significantly in comparison with that of bulk ZnO, which is attributed to the strong surface scattering of phonons. The thermal conductivity is also found to decrease more steeply than the expected $ {1 \mathord{\left/{\vphantom {1 T}} \right.} T} $ trend, but does obey a $ {1 \mathord{\left/{\vphantom {1 {\left({\alpha T + \beta T^2} \right)}}} \right. } {\left({\alpha T + \beta T^2} \right)}} $ relation; this is shown to result from four‐phonon processes at high temperatures. The dimensionless figure of merit ZT is determined to be about 0.1 at 970 K. Finally, the thermoelectric properties of individual ZnO nanowires are also discussed, indicating that ZnO nanowires are promising high temperature thermoelectric materials.     

One‐Step Synthesis of Highly Ordered Mesoporous Silica Monoliths with Metal Oxide Nanocrystals in their Channels

A simple, one‐step synthetic route to prepare ordered mesoporous silica monoliths with controllable quantities of metal oxide nanocrystals in their channels is presented. The method is based on the assisted assembly effect for mesostructure‐directing of the metal complexes formed by the interaction of metal ions with the –O– groups of copolymers. Highly ordered hexagonal silica monoliths, loaded with various metal oxide nanocrystals, including those of Cr₂O₃, MnO, Fe₂O₃, Co₃O₄, NiO, CuO, ZnO, CdO, SnO₂, and In₂O₃, can be obtained by this one‐step pathway. In the NiO/SiO₂ nanocomposite, nickel oxide nanorods with face‐centered cubic lattices are formed at low doping ratios, and they can be transformed into nanowires by increasing the quantities of the precursors. In the Fe₂O₃/SiO₂ nanocomposites, a one‐dimensional assembly of iron oxide nanoparticles is observed. In the In₂O₃/SiO₂ nanocomposites, single crystal nanowires with high aspect ratios are obtained. For the other metal oxide nanocomposites, including Cr₂O₃, MnO, Co₃O₄, CuO, ZnO, CdO, and SnO, only crystalline nanorods are obtained. N₂ sorption results of the metal oxide/SiO₂ mesostructured nanocomposites reveal that nanocrystals inside the pores do not severely decrease the pore volume or the Brunauer–Emmett–Teller (BET) surface area of the mesoporous silica host. The bandgaps of SnO₂ and In₂O₃ nanocrystals, calculated from UV‐vis spectra, are much larger than the corresponding bulk materials, implying the quantum confinement effect in the small particles. Co₃O₄/SiO₂ mesostructured nanocomposites catalyze the complete combustion of CH₄. These studies provide a new and simple method for templating synthesis of metal oxide nanostructures.     

Soft Lithography of Ceramic Patterns

Polymer‐based precursor solutions are patterned using a soft‐lithographic patterning technique to yield sub‐micrometer‐sized ceramic patterns. By using a polymer–metal‐nitrate solution as a lithographic resist, we demonstrate a micromolding procedure using a simple rubber stamp that yields a patterned precursor layer. A subsequent high‐temperature annealing step degrades the polymer giving rise to a patterned metal oxide film. This procedure is demonstrated for three different ceramic materials: Al₂O₃, ZnO, and PbTiO₃. Al₂O₃ initially forms an amorphous phase that is subsequently converted into a polycrystalline material upon electron irradiation. The formed ZnO and PbTiO₃ are polycrystalline. PbTiO₃ exhibits epitaxial alignment when cast onto a SrTiO₃(001) surface that matches its lattice periodicity. This epitaxial alignment is maintained when the PbTiO₃ phase is patterned by micromolding, giving rise to epitaxially grown PbTiO₃ patterns with feature sizes down to 300 nm.     

Overcoming Zinc Oxide Interface Instability with a Methylammonium‐Free Perovskite for High‐Performance Solar Cells

Perovskite solar cells have achieved the highest power conversion efficiencies on metal oxide n‐type layers, including SnO₂ and TiO₂. Despite ZnO having superior optoelectronic properties to these metal oxides, such as improved transmittance, higher conductivity, and closer conduction band alignment to methylammonium (MA)PbI₃, ZnO is largely overlooked due to a chemical instability when in contact with metal halide perovskites, which leads to rapid decomposition of the perovskite. While surface passivation techniques have somewhat mitigated this instability, investigations as to whether all metal halide perovskites exhibit this instability with ZnO are yet to be undertaken. Experimental methods to elucidate the degradation mechanisms at ZnO–MAPbI₃ interfaces are developed. By substituting MA with formamidinium (FA) and cesium (Cs), the stability of the perovskite–ZnO interface is greatly enhanced and it is found that stability compares favorably with SnO₂‐based devices after high‐intensity UV irradiation and 85 °C thermal stressing. For devices comprising FA‐ and Cs‐based metal halide perovskite absorber layers on ZnO, a 21.1% scanned power conversion efficiency and 18% steady‐state power output are achieved. This work demonstrates that ZnO appears to be as feasible an n‐type charge extraction layer as SnO₂, with many foreseeable advantages, provided that MA cations are avoided.     

Core–Shelled Low‐Oxidation State Oxides@Reduced Graphene Oxides Cubes via Pressurized Reduction for Highly Stable Lithium Ion Storage

Metal oxides have been regarded as promising next‐generation anode materials for rechargeable lithium ion batteries; however, their poor stability, which is caused by large volume changes during repeated lithiation/delithiation, remains a challenge. Here, conformally encapsulated low‐oxidation state oxide cubes with reduced graphene oxide (RGO) obtained via a new pressurized reduction consisting of external mechanical compression and internal thermokinetic reduction from highly porous metal oxides/RGO aerogel (RGOA) are reported. Using single crystalline (SC) cobalt oxides and iron oxide cubes as model systems, the SC‐Co₃O₄ or Fe₂O₃ cube/RGOA are pressurized into compacted xerogel along with a uniform thermokinetic reduction, which result in topotactic transformation to core‐shelled CoO/RGO or Fe₃O₄@RGO cubes. The SC‐CoO and SC‐Fe₃O₄ cubes isolated perfectly in the RGO shells have dramatically improved their cycling stabilities for lithium ion storage to hundreds of times.     

Optical Power Limiters Based on Colorless Di‐, Oligo‐, and Polymetallaynes: Highly Transparent Materials for Eye Protection Devices

The synthesis, characterization, and photophysics of a series of solution‐processable and tractable di‐, oligo‐, and polymetallaynes of some group 10–12 transition metals are presented. Most of these materials are colorless with very good optical transparencies in the visible spectral region and exhibit excellent optical power limiting (OPL) for nanosecond laser pulse. Their OPL responses outweigh those of the state‐of‐the‐art reverse saturable absorption dyes such as C₆₀, metalloporphyrins, and metallophthalocyanines that are all associated with very poor optical transparencies. On the basis of the results from photophysical studies and theoretical calculations, both the absorption of triplet and intramolecular charge‐transfer states can contribute to the enhancement of the OPL properties for these materials. Electronic influence of the type, spatial arrangement, and geometry of metal groups on the optical transparency/nonlinearity optimization is evaluated and discussed in detail. The positive contribution of transition metal ions to the OPL of these compounds generally follows the order: Pt > Au > Hg > Pd. The optical‐limiting thresholds for these polymetallaynes can be as low as 0.07 J cm^–2 at 92 % linear transmittance and these highly transparent materials manifest very impressive figure of merit σ_ex/σ_o values (up to 22.48), which are remarkably higher than those of the benchmark C₆₀ and metal phthalocyanine complexes. The present work demonstrates an attractive approach to developing materials offering superior OPL/optical transparency trade‐offs and these metallopolyynes are thus very promising candidates for use in practical OPL devices for the protection of human eyes and other delicate optical sensors.