Li-ion batteries play important roles in this mobile society. The ever-increasing demand for energy storage, particularly from electric vehicles, requires next-generation Li batteries with higher energy density and better safety. In contrast to existing Li-ion batteries using lithiated cathodes and Li-free anodes, we explore Li-free cathodes coupled with lithium/ lithiated anodes in order to construct new Li batteries assembled in a charged state. Two highly promising Li-free cathode materials of 1-D FeOF nanorods and 2-D monolayer MnO2 nanosheets are integrated to make FeOF@MnO2 nanocomposites. FeOF nanorods are sandwiched by monolayer MnO2 nanosheets where FeOF nanoparticles could prevent the restacking of the monolayer MnO2 nanosheets and the presence of monolayer MnO2 nanosheets could enhance the electrical integration of the FeOF nanorods. Synergistic effects of the binary Fe/Mn-based cathodes can lead to both high voltage and high capacity, compared to individual components. Electrochemical evaluation reveals that binary Fe/Mn-based Li-free cathodes demonstrate promising performances and are worthy of further investigation and optimization.

Theoretically monolayer MnO2 sheets have an impressive high capacity of 616 mAh/g, but practically monolayer MnO2 sheets have poor performances due partially to monolayer restacking. In this paper, we report the preparation of three-dimensional porous NiO nanorod pillared delta-MnO2 nanosheets as integrated nanoarchitectures as lithium-free cathode materials. The as-synthesized NiO pillared delta-MnO2 nanosheets have resulted in a moderately high specific capacity of 185 mA h g(-1), with more than 63% capacity retention after 200 cycles. In comparison, 2D MnO2 nanosheets without NiO pillared structures only achieved a low initial capacity of 137 mA h g(-1), with just 17% capacity retention after 200 cycles. The dramatically improved electrochemical performances could be attributed to high surface areas with excellent porosity which provides more electrochemically active sites and thermodynamically favorable insertion pathways for the lithium ions. Our results reveal that insertion of pillars is a promising strategy to explore in order to mitigate the restacking issues and achieve electrochemical performances close to theoretical values for monolayer MnO2. (C) 2021 Elsevier Ltd. All rights reserved.

It is still a challenging task to prepare highly porous nanorod arrays of metals formed on substrates for optical and energy storage applications. Herein, we demonstrate the design and synthesis of black color, metallic and highly porous Ti nanorod arrays as novel current collectors for dendrite-free and highly stable Li-metal anodes. The high porosity of metallic nanorod arrays provides numerous heterogeneous nucleation sites and huge contact area and large space for the accommodation of Li metal. The conductive metallic Ti nanorod arrays enhance electrode integration. Effectively, it eliminates formation Li dendrites and demonstrates superior cycling stability over 300 cycles. Additionally, the unique porous structures of the nanorod arrays can decrease the amplitude of forced vibration in narrow space leading to light absorption. Interestingly, the metal is black instead of metallic color. The black metallic nanorod arrays can absorb more than 96% of both visible and infra-red lights. This black color metallic porous nanorod arrays may find additional applications in aerospace, energy, biomedical, defence, and chemical industries.

To provide reference for optimizing the photoelectric conversion efficiency, we studied the effects of salt–alkali molar ratio on the properties of tin oxide nanofilms. We found that when the hydrothermal temperature was increased to 80 °C, the film growth was not complete. With a hydrothermal temperature of 120 °C, the film became more complete and structured. However, at 160 °C, thick and very irregular tin dioxide (SnO2) crystal particles were deposited on the FTO conductive glass surface. With the increase in heat treatment temperature, crystallization became more and more dense and complete. At 80 °C hydrothermal temperature, the simulated peak of the surface and number of peaks became smaller. However, they significantly increased with a hydrothermal temperature of 120 °C. When the hydrothermal temperature was at 160 °C, the surface simulated peak increased, but the number of peaks decreased. Moreover, the diameter of each peak was greatly increased. The film obtained via the hydrothermal method was relatively pure, and Sn(OH)3 was not completely converted into SnO2.

To meet the increasing demand for energy storage, it is very urgent and crucial to develop next-generation lithium ion batteries (LIBs) using carbon alternative electrode materials. The theoretical capacity of graphite (372 mA h g− 1) is almost achieved and becomes one of the bottlenecks to further increase the energy density of LIBs based on carbon. Therefore, there is an urgent need to develop higher capacity materials to meet the increasing demand for energy storage. Many carbon-alternative electrode materials have been proposed. However, poor cyclability, large volume variation during cycling, and poor conductivity are known issues associated with those high-capacity carbon-alternative electrode materials. One strategy is to design and tailor nano/microstructures of those materials in order to address the challenges. Anisotropic particles, using iron oxides as the model, have been prepared in various sizes, shapes, and structures, which demonstrated impressive electrochemical performances. Therefore, anisotropic particles can find promising application in next-generation LIBs.

Composite nanowires incorporating both metal oxide and metal nanoparticles as the basic building units are attracting much attention recently. We report here a facile approach to synthesize 3D networks of 1D nanowires of formed by both NiO and Ni nanoparticle. The composite nanowires were in-situ synthesized on carbonized eggshell membrane. Here, alpha-Ni(OH)(2) nanowire precursor was synthesized on eggshell membrane under mild conditions in a diaphragm-assisted reactor first. Then the precursor was transformed into composite of NiO-Ni nanowires on carbonized eggshell membrane under heat treatment in argon. The eggshell membrane played multiple roles as the substrate to collect the alpha-Ni(OH)(2) nanowire precursor and then as the source of reducing agents to partially reduce to Ni2+ to Ni-0. When tested for lithium-ion batteries, the composite of 3D networks NiO-Ni nanowires attached on carbonized eggshell membrane demonstrated impressively improved rate and cycling performances, as compared to that of bare NiO nanowires. The idea and method outline here based on bio-inspired synthesis using bio-template to prepare composites could be applied to synthesize other functional materials. (C) 2018 Elsevier Ltd. All rights reserved.

Sophisticated biological systems developed over millions of years of evolution can be rich sources of inspiration for engineers and scientists. There is increasing interest in the synthesis and applications of metallic hydroxy salts, for example Co-2(OH)(3)Cl. It is not an easy task to prepare phase-pure structured Co-2(OH)(3)Cl by direct mixing aqueous solutions of CoCl2 salts and NaOH in a flask. We demonstrate that crystalline Co-2(OH)(3)Cl microparticles with unique morphology can be synthesized in eggshell reactor systems. The eggshell reactor system can provide the unique reaction environment for the formation of crystalline Co-2(OH)(3)Cl microparticles with relatively well-defined shapes. Time-course experiments and intensive characterization helped us to propose a plausible formation mechanism. Our preliminary results suggest that the microscale Co-2(OH)(3)Cl particles synthesized from the eggshell reactor system can be used for lithium-ion batteries, although its performance may still need to be further optimized and improved. In another attempt, we transformed the as-prepared Co-2(OH)(3)Cl microparticle precursor into high-order structured Co3O4 microparticles preserving the same microscale morphology but with small Co3O4 nanoparticles as the basic building units. The as-prepared high-order structured Co3O4 microparticles demonstrate reasonably good electrochemical performance with a capacity of 900 mA h g(-1) in reversible lithium ion storage.

Room-temperature synthesis of alpha-phase bimetallic nickel-cobalt layered double hydroxides (Ni-Co LDHs) nanosheets in the forms of arrays grown on arbitrary substrates is still a challenging task. We demonstrate a facile diaphragm-assisted approach to grow alpha-phase Ni-Co LDHs nanosheet arrays on various substrates at room temperature. The as-synthesized nanosheet arrays can induce high surface roughness at the microscale, achieving both superoleophobicity underwater and superhydrophobicity in air, with contact angles measured for oil at 160 degrees and for water at 154 degrees, respectively. The nanosheet arrays of Ni-Co LDHs formed directly on 3D nickel foam substrates can be used as binder-free electrodes for rechargeable batteries, achieving a specific capacity of 177mAhg(-1) when tested at 2000mAg(-1). In contrast to literature reports, in which LDHs are often considered for pseudocapacitors, we suggest our electrodes are good for rechargeable alkaline secondary batteries or as battery electrodes in hybrid supercapacitors, based on battery behavior observed in our electrochemical tests. Other substrates, including titanium wires and carbon fiber papers, can be used as substrates. The as-prepared alpha-phase Ni-Co LDHs nanosheet arrays coated substrates and their derivatives (e.g., oxides, sulfides) can find many potential applications, including wastewater treatment, separation, electrochromic devices, catalysis and electrocatalysis, as well as energy storage.

Transition metal oxyfluorides are attracting much attention for next-generation rechargeable batteries, including lithium-ion batteries and those beyond lithium-ion batteries. Mixed-anion transition metal oxyfluorides offer the combined advantages of fluorides and the beneficial effects of oxides achieving improved capacity, high voltage, good conductivity and good cycling stability. Oxygen-fluorine substitution can be employed to manipulate the physiochemical properties of those corresponding transition metal oxides and/or fluorides for rechargeable batteries, as cathode and/or anode materials, achieving improved electrochemical performances. However, it is still a challenging task to develop facile procedures to produce transition metal oxyfluorides, particularly difficult on a large scale and with high purity. Various methods and approaches have been developed over the years, typically based on solid state reactions. Recently, liquid-based approaches under mild conditions for the preparation of transition metal oxyfluorides are attracting much attention. In this review, a number of transition metal oxyfluorides reported for rechargeable batteries, including VO2F, BiOF, FeOF, TiOF2, NbO2F, are discussed. Their synthetic ap-proaches, limitations and electrochemical performances are reviewed. Transition metal oxyfluorides with the presence of strong electronegativity of fluorides are often suitable as positive electrode materials. For cathode applications, the author suggests that lithium-free cathodes of transition metal oxyfluorides can be coupled with lithiated anodes to make as-assembled charged-state lithium-ion batteries. The same concept can be employed to prepare charged state sodium-ion batteries and other batteries using transition metal oxyfluorides as cathodes. The author suggests that asassembled batteries in charged state based on transition metal oxyfluorides (e.g., FeOF) as cathodes coupled with lithiated anodes will eventually be commercialized. The development of next-generation lithium-ion batteries and those so-called beyond lithium-ion batteries will depend on the capability to synthesize and produce high-quality transition metal oxyfluorides on a large scale. Those transition metal oxyfluorides not only can find practical applications in batteries, but also can be employed as model electrode systems for fundamental mechanism studies.

It is still a challenging task to facilely grow microscale arrays on arbitrary substrates at low temperature conditions in solutions. Here, we have successfully formed ZnO microrod arrays on various substrates, including glass, gold coated glass, silicon wafer, and Teflon, by a single-step wet-chemical synthesis approach. We employ ammonia as the multifunctional reactant to modify the surface properties of the substrates and to regulate the pH of the reaction environment. Compared to other methods, no preloaded additives or seeds are required. The surface wettability of the ZnO microrod coated substrates can be tuned, achieving both hydrophilic and hydrophobic properties in air. We have studied both static wettability and dynamic behaviors of droplet impact or rebound on the modified substrates. We demonstrate that it is possible to achieve micromass transfer by using the hydrophobic substrate to repel water microdroplet while using the hydrophilic substrate to capture the water microdroplets utilizing their different dynamic wettability-induced responses to water droplets. We believe that the ZnO microrod array coated substrates with different static/dynamic wettability may find many potential applications, such as antiwetting, self-cleaning, inject printing, micromass transfer and capture, biomedical diagnosis, microanalysis, and so forth.

Bioinspired synthesis has been attracting much attention. Here, we demonstrate a novel approach to directly use waste eggshells as a reactor system for controlled synthesis of nanostructures formed on different substrates. This approach can recycle and transform the "trash" of waste eggshells into "treasure" of unique reactor systems for nanofabrication. The eggshell reactor system can provide unique conditions for the formation of nanostructures on various substrates. Using Co(OH)2 as a model, amorphous Co(OH)2 nanorod arrays, which cannot be synthesized conventionally by direct mixing of precursors, have been successfully formed on various substrates, including Ni foam, metal foil, and glass. To illustrate their potential applications, we use the as-fabricated amorphous Co(OH)2 nanorod arrays on Ni foam as (1) binder-free electrodes for rechargeable alkaline batteries, demonstrating impressively good electrochemical performances, and (2) electrocatalyst for oxygen evolution reaction, demonstrating improved electrocatalytic performances as compared to their crystalline counterpart. We believe the idea outlined here, using eggshell reactor system, can be further expanded to synthesize many different functional materials and precursors which can find additional applications, including self-cleaning, catalysis, sensor, electrochromic devices, etc.

A family of Pocket Cubes with different chemical compositions but with the same overall mesoscale microstructures was prepared for potential applications in energy storage and water treatment.

Hierarchical microscale materials have received much attention recently. They can find many important applications, including wastewater treatment and energy storage. However, it is still a challenging task to facilely synthesize microscale structures with good size distribution, unique structures and, particularly, tunable composition. Herein, we have prepared a family of 2 × 2 × 2 Pocket Cube-like hierarchical microparticles, with different chemical compositions, including bimetal hydroxide (ZnSn(OH)6), mixed bimetal oxide and metal oxide (Zn2SnO4u0026SnO2), carbon coated bimetal oxide and metal (Zn2SnO4u0026Sn@C), all with the same overall mesoscale microstructures. This family of microscale Pocket Cubes, with different chemical compositions and their associated different physiochemical properties, may offer a set of functional materials for many applications. In order to demonstrate their potential applications, we have preliminarily studied their performances in rechargeable batteries and water remediation. Interestingly, these selected Pocket Cubes are electrochemically active toward the reversible storage of both sodium and lithium with comparable performances to those nanoparticles reported, although their sizes are remarkably large on the microscale. We found that the shapes of the microparticles can influence their photocatalytic performances. Our preliminary results suggest that this family of microscale Pocket Cubes, with further optimization and improvement, can find many promising applications, including wastewater treatment and energy storage.

Nanoparticle‐based electrodes often suffer from poor electrical properties due to high interparticle resistance, as well as low Coulombic efficiency attributed to large surface area induced parasitic reactions. In order to address this issue, a strategy of encapsulating two kinds of nanoparticles of both metal oxide and metallic nanoparticles is attempted, simultaneously, in microscale carbon cubic shells for highly reversible lithium storage. The unique structure is synthesized by simultaneous reactions of (1) decomposition of crystalline Co2(OH)3Cl microparticle precursor, synthesized in unique eggshell reactor systems, into nanoparticles, (2) partial reduction of CoO into metallic Co by eggshell membrane, (3) carbon coating by chemical vapor deposition facilitated by presence of catalytic Co with carbon released from the eggshell membrane, and (4) microscale carbon shell formed using the Co2(OH)3Cl particles as microtemplates. The carbon shells can prevent the encapsulated mixed nanoparticles from direct contact with electrolyte and reduce undesirable parasitic reactions, and accommodate volumetric variation during cycling. The introduction of metallic Co nanoparticles can reduce interparticle resistance. When evaluated for lithium storage, the unique structures of CoO–Co@C demonstrate superior electrochemical performances in terms of electrode stability and rate performance, as compared to that of pure CoO.

Single-crystalline α-Fe2O3 void@frame open microframes with perforated shells and high accessibility exhibited improved Li-ion storage properties as compared to solid microparticles.

It is still a challenging task to develop facile top-down methods to carve microparticles into nanostructures on a large scale. We demonstrate a top-down electrochemical method based on a sodium-ion battery system to machine rhombohedral microparticles into hierarchical flower-like nanostructures on a large scale, using Fe2O3 as a model. Electrochemical parameters, such as current, and number of cycles can be employed to tune the morphology of the as-derived nanostructures, which can be used to tune magnetization properties. This Na-ion electrochemical nanomachining (ECNM) provides an alternative top-down route to manipulate microparticles into substructures. Particularly interesting, the magnetic properties could be tuned by this ECNM method. It will be interesting to further study electrochemically induced reorganization to change material properties. The concept and methods outlined here could be extended to use other ion-based ECNM, including Mg2+, Ca2+, Al3+, for electrochemical manipulation of structures, opening up additional opportunities for functional materials.

It is still a challenging task to develop reliable electrodes for sodium ion batteries. Herein, a facile procedure is formulated to synthesize a 3-D composite of 1-D SnO2 nanorods anchored on 2-D graphene sheets for reversible sodium storage. The nanorods are uniformly distributed on the graphene sheets with only one end anchored on graphene, which could be attributed to the unique surface properties of graphene oxide precursor with abundant oxygenate groups. Relatively improved electrochemical performances with a specific capacity of ~200mAh/g for at least 100 cycles, and good rate performance at current of five times of the original current have been achieved for the SnO2 nanorods@Graphene composite. The improved performance as compared to bare SnO2 nanorods could be attributed to the unique structures that prevent the restacking of graphene, avoid the agglomeration of SnO2 nanorods and accommodate the volume changes.

A facile bio-inspired, diaphragm-assisted method is demonstrated for effective synthesis of nanostructures on substrates.

The disposal of eggshell waste is an environmentally and economically challenging problem. We demonstrate here a novel application of waste eggshell as a multifunctional reaction system to regulate the reactants and pH inside the reactor and using eggshell membrane as protein-based and active substrates to collect the nanostructures formed in a controlled environment. We outline an idea of transferring waste eggshell (or "trash") into a unique reaction system (or "treasure") for the synthesis of 1-D nanorod arrays on eggshell membrane protein fibers. Subsequently, the intrinsic sulfur element contained in the eggshell membrane protein fibers is utilized to transform the Co(OH)(2) nanorod arrays into Co9S8 nanorod arrays. Meanwhile, the protein fibers are in situ carbonized into carbon fibers. The as-synthesized composite of crystalline Co9S8 nanorod arrays on carbon fibers is demonstrated to be a potential electrode for both lithium-ion and sodium-ion batteries. The idea of in situ carbonization and sulfurization based on proteins could be generalized for the synthesis of a composite of carbon and sulfides.

Sodium-ion batteries (SIBs) are, arguably, one of the most promising candidates for post-lithium ion battery era. The success of sodium-ion batteries is dependent on electrode materials developed. We reported here the facile preparation of carbonized filter paper decorated with Sn@C nanospheres as negative electrode materials for SIBs. The carbonized filter paper decorated with Sn@C nanospheres were obtained by in-situ carbonization of the cellulose paper fibers and the reduction of SnO2 to metallic Sn which were encapsulated with carbon sheaths by chemical vapor deposition (CVD). Particularly, both the carbon sheaths and the encapsulated Sn cores are spherical. The formation mechanism of the spherical Sn@C nanospheres was proposed based on unique properties of molten tin with high surface tension forming spherical droplets. The carbonized filter paper decorated with Sn@C nanospheres in the form of slices can be directly assembled into electrochemical cells without any further treatment or additives. Higher capacities and better Coulombic efficiencies than that of bare carbonized filter paper were achieved. The mechanism of capacity fading was investigated systematically by cyclic voltammetry (CV) and post-test analysis. This understanding will be helpful to design better Sn based electrodes for SIBs. (C) 2015 Elsevier Ltd. All rights reserved.