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A novel bipolar battery architecture using an integrated Al electrode as both the high-capacity anode and bipolar plate is proposed to construct bipolar Li batteries, leading to high energy density and simple architecture/manufacturing.

Mesoporous silicas tethered with anions were developed as quasi-solid electrolytes. The high grafted density of –NTf− groups and their uniformly distributed negative charge endow MCM41-NLiTf with single Li-ion conductivity up to 2.4 × 10−4 S cm−1.

Developing highly efficient and low-cost electrocatalysts for the hydrogen evolution reaction (HER) in neutral media is crucial but still a significant challenge on account of the sluggish multistep reaction kinetics involved. Theoretically, constructing a metal/metal hydroxide interface with a metal hydroxide acting as a water dissociation promotor and a metal as the subsequent hydrogen adsorption site is expected to accelerate the HER kinetics in neutral media. We found that the intercalation of tungstate into Ni(OH)2 can tune the electronic structure of the Ni/Ni(OH)2 interface, decrease the energetic barrier for the Volmer step, and thus optimize the HER performance of Ni/Ni(OH)2 hybrid. Herein, a heterostructured Ni/Ni(OH)2 nanosheet array on Cu foam is designed and constructed via a simple hydrothermal and subsequent plasma reduction strategy. The HER performance can be further enhanced by assembling tungstate-intercalated Ni/Ni(OH)2 hybrid nanosheets on Cu2O nanotube arrays, exhibiting a low overpotential (39 mV @ 10 mA cm−2) and excellent stability (48 h).

Transition metal phosphides (TMPs) have been reported as efficient pre-catalysts for the oxygen evolution reaction (OER) in alkaline media. In situ generated metal oxyhydroxides on the surface of TMPs serve as real active sites. However, the reconstruction of most of the reported TMPs is incomplete and the active components cannot be fully used. Herein, hollow nanostructured Ni5P2/FeP4 nanoboxes (NiFeP NBs) are designed and synthesized as pre-catalysts. During the OER, the NiFeP NBs deeply reconstruct into low-crystalline and ultrathin NiOOH/FeOOH nanosheet assembled nanoboxes (NiOOH/FeOOH NBs). In situ Raman spectroscopy and ex situ characterization studies provide evidence that the hollow nanostructure facilitates the deep reconstruction of NiFeP NBs. Benefiting from the hierarchical hollow structure, the abundant interface between NiOOH and FeOOH, and plentiful defects, the reconstructed NiOOH/FeOOH NBs exhibit superior OER activity and excellent stability. Density functional theory (DFT) calculations reveal that the Fe–Ni dual sites in the NiOOH/FeOOH interface may be the possible active sites.

The sluggish electrochemical kinetics of sulfur species has impeded the wide adoption of lithium-sulfur battery, which is one of the most promising candidates for next-generation energy storage system. Here, we present the electronic and geometric structures of all possible sulfur species and construct an electronic energy diagram to unveil their reaction pathways in batteries, as well as the molecular origin of their sluggish kinetics. By decoupling the contradictory requirements of accelerating charging and discharging processes, we select two pseudocapacitive oxides as electron-ion source and drain to enable the efficient transport of electron/Li+ to and from sulfur intermediates respectively. After incorporating dual oxides, the electrochemical kinetics of sulfur cathode is significantly accelerated. This strategy, which couples a fast-electrochemical reaction with a spontaneous chemical reaction to bypass a slow-electrochemical reaction pathway, offers a solution to accelerate an electrochemical reaction, providing new perspectives for the development of high-energy battery systems., The sluggish electrochemical kinetics of sulfur species remains a major hurdle for the broad adoption of lithium-sulfur batteries. Here, the authors construct an energy diagram of sulfur species to unveil their reaction pathways and propose a general strategy to accelerate electrochemical reactions.

Developing drug delivery platforms that can modulate a tumor microenvironment and deliver multiple therapeutics to targeted tumors is critical for efficient cancer treatment. Achieving these platforms still remains a great challenge. Herein, biodegradable nanocapsules based on MnFe hydroxides (H-MnFe(OH)x) have been developed as a new type of cargo delivery with high loading capacity and catalytic activity, enabling synergetic therapy with promoted efficacy by relieving hypoxia in tumor tissues. As a proof of concept, a photosensitizer (indocyanine green, ICG) and a chemotherapeutic drug (doxorubicin, DOX) are co-loaded in nanocapsules and selectively released upon degradation of the nanocapsules in the acidic tumor microenvironment, and are promoted by near infrared irradiation. Meanwhile, Mn2+/Fe3+ ions released from the degradation of nanocapsules catalyze the conversion of H2O2 in a tumor microenvironment into oxygen, which modulates tumor hypoxia and dramatically boosts multimodal therapies. Remarkable synergistic anticancer outcomes have been demonstrated both in vitro and in vivo, paving the way towards future multifunctional therapeutic platforms.

Conventional liquid electrolytes for lithium batteries usually suffer from irreversible decomposition and safety concerns. Solid state electrolytes (SSEs) have been considered as the key for advanced lithium batteries with improved energy density and safety, whereas challenges remain for polymer and inorganic SSEs. Recently, hybrid solid-state electrolytes (HSSEs) that integrate the merits of different electrolyte systems have been under intensive study. Herein, we summarize the recent progress of HSSEs with different compositions and structures. The design principle of each type of HSSEs are discussed, as well as their ionic conducting mechanism, electrochemical performance and effects of compositional/structural control. Finally, challenges and perspectives are provided for the future development of HSSEs and solid-state lithium batteries.

To circumvent the imbalances of electrochemical kinetics and capacity between Li+ storage anodes and capacitive cathodes for lithium-ion capacitors (LICs), we herein demonstrate an efficient solution by boosting the capacitive charge-storage contributions of carbon electrodes to construct a high-performance LIC. Such a strategy is achieved by the in situ and high-level doping of nitrogen atoms into carbon nanospheres (ANCS), which increases the carbon defects and active sites, inducing more rapidly capacitive charge-storage contributions for both Li+ storage anodes and PF6– storage cathodes. High-level nitrogen-doping-induced capacitive enhancement is successfully evidenced by the construction of a symmetric supercapacitor using commercial organic electrolytes. Coupling a pre-lithiated ANCS anode with a fresh ANCS cathode enables a full-carbon LIC with a high operating voltage of 4.5 V and high energy and power densities thereof. The assembled LIC device delivers high energy densities of 206.7 and 115.4 W...

Construction of metal–organic frameworks with sophisticated nanostructures remains a considerable challenge. Herein, we report the rational design and synthesis of ZIF-67 nanoscaffolds and defected nanocubes co-mediated by dopamine and polyoxometalate. The formation of these sophisticated ZIF-67 nanostructures is achieved through the protection of dopamine and etching of polyoxometalate. As a demonstration, we have converted the ZIF-67 nanoscaffolds incorporated with molybdenum into carbon-coated cobalt–molybdenum mixed selenides (denoted as CoMoSe@C nanoscaffolds) with little alteration in the structure by reacting the ZIF-67 nanoscaffolds with selenium powder at high temperature. Benefiting from their unique structural merits, the CoMoSe@C nanoscaffolds exhibit enhanced lithium storage properties in terms of good cycling performance and superior rate capability.

By virtue of high theoretical sodium storage capacities and low cost, FeP is a prospective anode material for sodium-ion batteries (SIBs). Nevertheless, poor cycling and rate performance greatly limit the application of FeP in practice. Herein, a facile template-engaged method is employed to synthesize copper and carbon-incorporated yolk-shelled FeP (denoted as YS-Cu-FeP@C) spheres. The copper is doped into FeP, while the carbon layer with N-doping is coated on the surface of yolk-shelled FeP spheres. Aided by the unique compositional and structural advantages, the as-synthesized YS-Cu-FeP@C spheres exhibit enhanced electrochemical performance for SIBs, including excellent rate capability (145 mAh g−1 at 10 A g−1) and remarkable long-term cycle performance (up to 900 cycles at 1 A g−1). This work provides a rational design and synthetic strategy to boost the sodium storage properties of metal phosphide-based electrode materials.

Commercialization of ZnO-based anodes remains hampered by their rapid capacity fading upon cyclical charge and discharge. Design and synthesis of suitable carbon scaffolds for coating ZnO active materials has been regarded as the most effective strategy to overcome this problem. We herein report a confined growth strategy for the synthesis of a novel ZnO/carbon mesoporous composite that consists of small ZnO nanoparticles whose growth is confined in rationally designed N-rich carbon spheres (referred to as ZnO-NMPCS). Such a mesoporous nanocomposite has several structural merits such as small ZnO nanoparticles, a homogeneous distribution, an interconnected spherical framework with a large surface area, and a N-rich carbon lattice; these merits not only provide a robust scaffold for stable lithiation/delithiation of ZnO active materials but also ensure sufficient Li+ storage space/sites and fast ions/electrons transport. As a result, the developed nanocomposite exhibits excellent Li+ storage properties in terms of high capacity, fast rate capability, and long cycling lifespan (425 mAh g−1 after 1800 cycles at 5 A g−1). This work offers an effective confined growth strategy to overcome the long-term roadblock to ZnO-based anodes; the carbon scaffold also provides a general platform for the confined growth of other metal oxide nanocrystals.

Building nanocomposite architectures based on carbon nanotubes (CNTs) and active nanoparticles (NPs) with an engineered interface is of great interest for developing the ability to store electrochemical energy. The use of cellulose to direct hetero-assembly was achieved by in situ regenerating an ionic liquid mixture (CNTs, NPs, cellulose) in water, and was applied to the fabrication of flexible anodes consisting of CNTs and NPs. These anodes showed CNTs threading through their structures and exhibited strong interfacial contacts, which provided a relatively short lithium-ion diffusion length and continuous electron conduction pathway as well as high mechanical stability. When evaluated as an anode material for a lithium-ion battery, the flexible nanocomposites showed high reversible capacity and good rate performance compared to traditionally made electrodes, demonstrating a simple and green strategy for the industrial-scale production of energy-storage devices.

Proton exchange membrane fuel cells have been regarded as the most promising candidate for fuel cell vehicles and tools. Their broader adaption, however, has been impeded by cost and lifetime. By integrating a thin layer of tungsten oxide within the anode, which serves as a rapid-response hydrogen reservoir, oxygen scavenger, sensor for power demand, and regulator for hydrogen-disassociation reaction, we herein report proton exchange membrane fuel cells with significantly enhanced power performance for transient operation and low humidified conditions, as well as improved durability against adverse operating conditions. Meanwhile, the enhanced power performance minimizes the use of auxiliary energy-storage systems and reduces costs. Scale fabrication of such devices can be readily achieved based on the current fabrication techniques with negligible extra expense. This work provides proton exchange membrane fuel cells with enhanced power performance, improved durability, prolonged lifetime, and reduced cost for automotive and other applications., Proton exchange membrane fuel cells often suffer from low lifetimes and high cost. Here, the authors enhance the transient power performance and durability of these fuel cells by integrating a thin layer of tungsten oxide within the anode, which acts as a hydrogen reservoir, oxygen scavenger, and a regulator for the hydrogen-disassociation reaction.

Silicon holds great promise as an anode material for lithium-ion batteries with higher energy density; its implication, however, is limited by rapid capacity fading. A catalytic growth of graphene cages on composite particles of magnesium oxide and silicon, which are made by magnesiothermic reduction reaction of silica particles, is reported herein. Catalyzed by the magnesium oxide, graphene cages can be conformally grown onto the composite particles, leading to the formation of hollow graphene-encapsulated Si particles. Such materials exhibit excellent lithium storage properties in terms of high specific capacity, remarkable rate capability (890 mAh g-1 at 5 A g-1 ), and good cycling retention over 200 cycles with consistently high coulombic efficiency at a current density of 1 A g-1 . A full battery test using LiCoO2 as the cathode demonstrates a high energy density of 329 Wh kg-1 .

A simple and scalable melt infiltration method has been developed to encapsulate SnO2 nanocrystals into a hierarchically porous carbon matrix as a high-capacity lithium storage material. SnO2 nanocrystals in a three-dimensional carbonaceous network are obtained via melt infiltration of SnCl2 and subsequent in situ conversion. The SnO2–carbon composite delivers high capacity with a long lifespan of over 800 cycles. Such a method provides an efficient strategy to encapsulate active materials into porous carbons with superior electrochemical performance.

Hollow structures of rutile TiO2 , and especially with non-spherical shape, have rarely been reported. Herein, high-quality rutile TiO2 submicroboxes have been synthesized by a facile templating method using Fe2 O3 submicrocubes as removable templates. Compared to other rutile TiO2 nanomaterials, the as-prepared rutile TiO2 submicroboxes manifest superior lithium storage properties in terms of high specific capacity, long-term cycling stability, and excellent rate capability.

Three-dimensional (3D) Pt-based alloy nanostructures composed of one-dimensional (1D) nanowires/nanorods have recently attracted significant interest as electrocatalysts. In this work, we report an effective solvothermal method for the direct preparation of 3D Pt–Co nanowire assemblies (NWAs) with tunable composition. The composition- and structure-dependent electrocatalytic performance is thoroughly investigated. Because of the bimetallic synergetic effect and unique structural advantage, the as-prepared 3D Pt3Co NWA outperforms commercial Pt/carbon and Pt black catalysts and even 3D Pt NWA. The electrochemical results demonstrate that the 3D Pt3Co NWA is indeed a promising electrocatalyst with enhanced catalytic activity and improved durability for practical electrocatalytic applications.

Despite the great advantages of hollow structures as electrodes for lithium-ion batteries, one apparent common drawback which is often criticized is their compromised volumetric energy density due to the introduced hollow interior. Here, we design and synthesize bowl-like SnO2 @carbon hollow particles to reduce the excessive hollow interior space while retaining the general advantages of hollow structures. As a result, the tap density can be increased about 30 %. The as-prepared bowl-like SnO2 @carbon hollow particles with conformal carbon support exhibit excellent lithium storage properties in terms of high capacity, stable cyclability and excellent rate capability.

Semiconductor heterostructures are of great interest in a wide range of applications. In this work, we design and synthesize a novel heteronanostructure with controlled relative composition, i.e., BiVO4/Bi2S3 hollow discoid-like particles with mesoporous shell. The synthesis involves a facile anion exchange process by reacting pre-synthesized BiVO4 discoid-like particles with Na2S in an aqueous solution. Benefiting from the unique structural features and the formation of heterostructure, the as-prepared BiVO4/Bi2S3 hollow discoids exhibit significantly enhanced photoelectrochemical current response and photocatalytic activity for reduction of Cr(VI) under visible-light illumination.

Hollow nanostructures are of great interest for a wide variety of applications. Despite the great advances, synthesis of anisotropic hollow structures is still very challenging. In this work, we have developed a simple sacrificial template method to synthesize uniform Ni(x)Co(3-x)S4 hollow nanoprisms with tunable composition. Tetragonal nanoprisms of nickel-cobalt acetate hydroxide precursors with controllable Ni/Co molar ratios are first synthesized and used as the sacrificial templates. After a sulfidation process with thioacetamide (TAA) in ethanol, the solid precursor prisms can be transformed into the corresponding Ni(x)Co(3-x)S4 hollow nanoprisms with a well-defined hollow interior. The intriguing structural and compositional features are beneficial for electrochemical applications. Impressively, the resultant Ni(x)Co(3-x)S4 hollow prisms manifest a high specific capacitance with enhanced cycling stability, making them potential electrode materials for supercapacitors.

CoSe2 is a potential anode material for sodium-ion batteries in terms of their high sodium storage capacity and tunable properties. However, structural degradation and unstable interphase during the reversible sodiation and de-sodiation lead to fast capacity decay. In this work, we develop a nanocomposite architecture based on CoSe2 nanoparticles embedded in N-doped carbon matrix with conformal TiO2 coating (CoSe2@NC@TiO2) by using a metal-organic framework-assisted strategy. The small CoSe2 nanoparticles and N-doped carbon matrix facilitate charge transport and suppress the structural degradation, while the redox-active TiO2 shell further strengthens the structural and interfacial stability without decreasing the capacity. The as-prepared CoSe2@NC@TiO2 nanocomposite particles deliver a reversible sodium storage capacity of 520 mAh g−1 at 0.1 A g−1 with a capacity retention of 78% after 200 cycles, in contrast to the rapid capacity fading after 50 cycles of the pristine CoSe2@NC particles without TiO2 shell.

Increasing the complexity of hollow structures, in terms of chemical composition and shell architecture, is highly desirable for both fundamental studies and realization of various functionalities. Starting with metal-organic frameworks (MOFs), we demonstrate a general approach toward the large-scale and facile synthesis of complex hollow microboxes via manipulation of the template-engaged reactions between the Prussian blue (PB) template and different alkaline substances. The reaction between PB microcubes with NaOH solution leads to the formation of Fe(OH)3 microboxes with controllable multishelled structure. In addition, PB microcubes will react with the conjugate bases of metal oxide based weak acids, generating multicompositional microboxes (Fe2O3/SnO2, Fe2O3/SiO2, Fe2O3/GeO2, Fe2O3/Al2O3, and Fe2O3/B2O3), which consist of uniformly dispersed oxides/hydroxides of iron and another designed element. Such complex hollow structures and atomically integrated multiple compositions might bring the usual physiochemical properties. As an example, we demonstrate that these complex hollow microboxes, especially the Fe2O3/SnO2 composite microboxes, exhibit remarkable electrochemical performance as anode materials for lithium ion batteries.

As alike as two peas in a pod: Hollow iron-containing microspheres composed of nanoplate-like building blocks were synthesized by a straightforward strategy and readily converted into magnetic Fe3O4 hollow microspheres (see images) without noticeable structural deformation. These Fe3O4 microspheres exhibited high reversible capacity and excellent cycling performance when evaluated as an anode material for lithium-ion batteries.

The rational design and synthesis of hollow structured functional materials are of great significance as both fundamental challenges in materials science and practical solutions for efficient energy utilization in modern society. The unique structural features of hollow functional materials bring outstanding electrochemical properties for both energy storage and electrocatalysis. However, conventional templating methods are normally less efficient in constructing hollow structures with desirable compositions and architectures. In the past decade, many novel synthetic approaches directly converting templates into hollow structures have been developed. Collectively termed as the "self-templated" strategy, it makes use of various physical/chemical processes to transform solid templates into hollow structures of target materials. Of particular note is the outstanding capability to construct complex hollow architectures of a wide variety of inorganic or hybrid functional materials, thus providing effective solutions for various electrochemical energy applications. In this Account, we present the recent progress in self-templated formation of hollow structures especially with complex architectures, and their remarkable performance in electrochemical energy-related technologies. These advanced self-templated methods are summarized as three categories. "Selective etching" creates hollow structures from solid templates of same materials by removing some of the internal parts, forming multishelled or unusual hollow architectures. "Outward diffusion" utilizes the relocation of mass in templates from inner region to outer region driven by various mechanisms, to construct hollow structures with multiple or hierarchical shells. "Heterogeneous contraction" typically applies to thermally decomposable templates and generates various hollow structures under nonequilibrium heating conditions. We further demonstrate some remarkable electrochemical properties of such hollow structures in virtue of their exceptional composition-/structure-induced merits. As electrode materials for lithium-ion batteries, hybrid or multishelled metal oxides exhibit high cyclability because of their capability to well accommodate the lithium insertion strain. Also the rate capability is effectively improved by the fast lithium insertion/deinsertion in multishelled or hierarchical hollow structures. These exceptional structural merits also significantly enhance the reaction kinetics and prolong the cycling lifetime of metal-sulfides-based electrodes, which enables the assembly of hybrid supercapacitors with high energy and power densities. On the other hand, multicompositional hollow structures with large exposed surface area and rich open pore channels offer abundant robust active sites and fast charge/mass transport for electrocatalytic reactions. These studies demonstrate that the versatility and superiority of self-templated methods for hollow structured functional materials have greatly promoted their applications for electrochemical energy storage and conversion. With continued research efforts, we are expecting greater and broader impacts brought by the rapidly growing family of hollow structures formed by self-templated methods.

Brought to light: Ag2S–Ag hybrid nanotubes were synthesized by rapid microwave-assisted sulfidation of Ag2CO3 nanorods. The relative amounts of Ag2S and Ag in the hybrid structure can be controlled easily by varying the concentration of the sulfur precursor. The optimized Ag2S–Ag hybrid structure has superior photocatalytic activity (yellow) for both degradation of methyl orange (see graph) and reduction of aqueous CrVI under visible-light irradiation.

Layered protonated titanates (LPTs), a class of interesting inorganic layered materials, have been widely studied because of their many unique properties and their use as precursors to many important TiO(2)-based functional materials. In this work, we have developed a facile solvothermal method to synthesize hierarchical spheres (HSs) assembled from ultrathin LPT nanosheets. These LPT hierarchical spheres possess a porous structure with a large specific surface area and high stability. Importantly, the size and morphology of the LPT hierarchical spheres are easily tunable by varying the synthesis conditions. These LPT HSs can be easily converted to anatase TiO(2) HSs without significant structural alteration. Depending on the calcination atmosphere of air or N(2), pure anatase TiO(2) HSs or carbon-supported TiO(2) HSs, respectively, can be obtained. Remarkably, both types of TiO(2) HSs manifest excellent cyclability and rate capability when evaluated as anode materials for high-power lithium-ion batteries.

High-stability Pt electrocatalysts have been prepared using hierarchical CNT@TiO2 structures composed of TiO2 nanosheets grafted on the CNT backbone as the support. The as-prepared Pt/CNT@TiO2 electrocatalysts manifest high electrocatalytic activity with greatly improved stability compared to conventional CNT or carbon black supported Pt electrocatalysts.

Production of hydrogen by electrochemical water splitting has been hindered by the high cost of precious metal catalysts, such as Pt, for the hydrogen evolution reaction (HER). In this work, novel hierarchical β-Mo2 C nanotubes constructed from porous nanosheets have been fabricated and investigated as a high-performance and low-cost electrocatalyst for HER. An unusual template-engaged strategy has been utilized to controllably synthesize Mo-polydopamine nanotubes, which are further converted into hierarchical β-Mo2 C nanotubes by direct carburization at high temperature. Benefitting from several structural advantages including ultrafine primary nanocrystallites, large exposed surface, fast charge transfer, and unique tubular structure, the as-prepared hierarchical β-Mo2 C nanotubes exhibit excellent electrocatalytic performance for HER with small overpotential in both acidic and basic conditions, as well as remarkable stability.

Uniform ZnMn2O4 hollow microspheres have been synthesized by a facile coprecipitation and annealing method. The resultant ZnMn2O4 hollow microspheres exhibit high specific discharge capacity, good rate capability, and excellent cycling stability. The improved electrochemical performance may be attributed to the beneficial features of reduced diffusion length for Li+ ions and enhanced structural integrity with sufficient void space for buffering the volume variation during the Li+ insertion/extraction.

Electrochemical water splitting has been considered as a promising approach to produce clean and sustainable hydrogen fuel. However, the lack of high-performance and low-cost electrocatalysts for hydrogen evolution reaction hinders the large-scale application. As a new class of porous materials with tunable structure and composition, metal-organic frameworks have been considered as promising candidates to synthesize various functional materials. Here we demonstrate a metal-organic frameworks-assisted strategy for synthesizing nanostructured transition metal carbides based on the confined carburization in metal-organic frameworks matrix. Starting from a compound consisting of copper-based metal-organic frameworks host and molybdenum-based polyoxometalates guest, mesoporous molybdenum carbide nano-octahedrons composed of ultrafine nanocrystallites are successfully prepared as a proof of concept, which exhibit remarkable electrocatalytic performance for hydrogen production from both acidic and basic solutions. The present study provides some guidelines for the design and synthesis of nanostructured electrocatalysts., There is extensive research into non-platinum electrocatalysts for hydrogen evolution. Here, the authors report a molybdenum carbide catalyst, prepared via the carburization of a copper metal-organic framework host/molybdenum-based polyoxometalates guest system, and demonstrate its catalytic activity.

Nanoframe-like hollow structures with unique three-dimensional (3D) open architecture hold great promise for various applications. Current research efforts mainly focus on frame-like noble metals and metal oxides. However, metal sulfides with frame-like nanostructures have been rarely reported. Starting from metal-organic frameworks (MOFs), we demonstrate a novel structure-induced anisotropic chemical etching/anion exchange method to transform Ni-Co Prussian blue analogue (PBA) nanocubes into NiS nanoframes with tunable size. The reaction between Ni-Co PBA nanocube templates and Na2 S in solution leads to the formation of well-defined NiS nanoframes. The different reactivity between the edges and the plane surface of the Ni-Co PBA nanocubes is found to be the key factor for the formation of NiS nanoframes. Benefitting from their structural merits including 3D open structure, small size of primary nanoparticles, high specific surface area, and good structural robustness, the as-derived NiS nanoframes manifest excellent electrochemical performance for electrochemical capacitors and hydrogen evolution reaction in alkaline electrolyte.

While the synthesis of hollow structures of transition metal oxides is well established, it is extremely challenging to fabricate complex hollow structures for mixed transition metal sulfides. Here we report an anion exchange method to synthesize a complex ternary metal sulfides hollow structure, namely nickel cobalt sulfide ball-in-ball hollow spheres. Uniform nickel cobalt glycerate solid spheres are first synthesized as the precursor and subsequently chemically transformed into nickel cobalt sulfide ball-in-ball hollow spheres. When used as electrode materials for electrochemical capacitors, these nickel cobalt sulfide hollow spheres deliver a specific capacitance of 1,036 F g(-1) at a current density of 1.0 A g(-1). An asymmetric supercapacitor based on these ball-in-ball structures shows long-term cycling performance with a high energy density of 42.3 Wh kg(-1) at a power density of 476 W kg(-1), suggesting their potential application in high-performance electrochemical capacitors.

A high-performance electrode for supercapacitors is designed and synthesized by growing electroactive NiCo2 O4 nanosheets on conductive Ni nanofoam. Because of the structural advantages, the as-prepared Ni@NiCo2 O4 hybrid nanostructure exhibits significantly improved electrochemical performance with high capacitance, excellent rate capability, and good cycling stability.

While the synthesis of TiO2 hollow structures is well-established, in most cases it is particularly difficult to control the crystallization of TiO2 in solution or by calcination. As a result, TiO2 hollow structures do not really exhibit enhanced lithium storage properties. Herein, we report a simple and cost-effective template-assisted method to synthesize anatase TiO2 hollow spheres composed of highly crystalline nanocrystals, in which carbonaceous (C) spheres are chosen as the removable template. The release of gaseous species from the combustion of C spheres may inhibit the growth of TiO2 crystallites so that instead small TiO2 nanocrystals are generated. The small size and high crystallinity of primary TiO2 nanoparticles and the high structural integrity of the hollow spheres gives rise to significant improvements in the cycling stability and rate performance of the TiO2 hollow spheres.

Pt nanocubes/rGO in one pot: Pt nanocubes/rGO hybrids are successfully ­synthesized via a facile one-pot approach. The resultant Pt nanocubes/rGO hybrid exhibits enhanced catalytic activity and excellent electrochemical stability in comparison with commercial Pt/CB electrocatalysts, which can be ascribed to the abundant Pt(100) ­surface and its uniform distribution on rGO.

A promising family of mixed transition-metal oxides (MTMOs) (designated as Ax B3-x O4 ; A, B=Co, Ni, Zn, Mn, Fe, etc.) with stoichiometric or even non-stoichiometric compositions, typically in a spinel structure, has recently attracted increasing research interest worldwide. Benefiting from their remarkable electrochemical properties, these MTMOs will play significant roles for low-cost and environmentally friendly energy storage/conversion technologies. In this Review, we summarize recent research advances in the rational design and efficient synthesis of MTMOs with controlled shapes, sizes, compositions, and micro-/nanostructures, along with their applications as electrode materials for lithium-ion batteries and electrochemical capacitors, and efficient electrocatalysts for the oxygen reduction reaction in metal-air batteries and fuel cells. Some future trends and prospects to further develop advanced MTMOs for next-generation electrochemical energy storage/conversion systems are also presented.

Carbon-coated NiCo2 O4 @SnO2 core-shell hetero-nanostructures are synthesized by a facile hydrothermal process and subsequent carbon nano-coating. When evaluated as anode materials for lithium-ion batteries, the 3D hetero-nanostructures exhibit enhanced lithium storage properties due to advantageous structural features.

Deeply excavated: Platinum nanoframes with highly concave {740} facets are synthesized directly by a facile oleylamine-assisted solvothermal method. Because of the unique structure and exposed high-index facets, the as-prepared Pt nanoframes exhibit very high electrocatalytic activity and remarkable stability for the oxygen reduction reaction and the oxidation of methanol and formic acid.

As a promising rechargeable battery system, lithium– sulfur (Li–S) batteries can deliver an exceptionally high theoretical specific capacity of 1672 mAhg 1 and an energy density of 2500 Whkg 1 with the low-cost and environmentfriendly sulfur as the cathode material. Although the potential use of sulfur as a cathode material has long been discovered, several severe drawbacks have hindered the realization of Li–S batteries. One limitation is the insulating nature of sulfur with a very low conductivity of 5 10 30 Scm , which results in low utilization of sulfur. Another well-known problem is associated with the easy dissolution of polysulfides, the intermediate products formed during the electrochemical reaction, in organic electrolytes. The dissolved polysulfides “shuttle” between the electrodes, leading to the low Coulombic efficiency and deposition of a highly resistive layer on the surface of electrodes. These detrimental issues result in unsatisfactory electrochemical performance with rapid fading of capacity. Several approaches have been proposed to overcome the above-mentioned challenges in Li–S batteries, such as developing novel electrolytes and electrode materials. Among these efforts, using sulfur-containing composites instead of pure sulfur as the cathode materials has been demonstrated as an effective way towards high-performance Li–S batteries. Polymers and porous carbons are the common candidates to form composites with sulfur, which immobilize the loaded sulfur, and probably also the derived polysulfides via physical and/or chemical interactions. In addition, the electrical conductivity of composite materials is also better than that obtained with pristine sulfur. In particular, porous carbon materials have attracted intensive attention due to their good compatibility with sulfur, easy accessibility, and the abundance of candidates with diverse porosity and structures. Mesoporous carbon materials have been widely studied as the host materials to confine sulfur. For example, nanocomposites consisting of sulfur and ordered mesoporous carbon or mesoporous hollow carbon spheres have shown improved sulfur utilization and cycling stability. Nonetheless, continuous capacity fading upon prolonged cycling is still commonly observed, and the use of optimized ether-based electrolytes seems to be indispensable. Recent reports on carbon materials with rich micropores have revealed distinct characteristics. 25] Sulfur embedded in microporous carbon shows a pronounced discharge plateau at a lower potential of about 1.8 V versus Li/Li, which is different from the two plateaus of a typical sulfur cathode. More importantly, these microporous carbon/sulfur nanocomposites generally show outstanding capacity retention upon cycling and good compatibility with conventional carbonate-based electrolytes. However, the origins of the unusual characteristics of microporous carbon are not fully understood yet. In recently years, syntheses of porous carbon materials from metal-organic frameworks (MOFs) or porous coordination polymers (PCPs) have attracted growing attention due to the facile preparation procedures, high carbon yield, and unique porous structures. For example, carbonization of MOF-5 with furfuryl alcohol results in nanoporous carbon, which shows excellent supercapacitive performance. The carbon materials with fiber-like morphology prepared from Al-based PCPs exhibit remarkably high porosity. In particular, MOFs and PCPs are very attractive as both the template and the precursor for the fabrication of microporous carbon. Compared with many other highly porous carbon materials, such as those prepared by post-activation processes, the porous carbon derived from MOFs and PCPs exhibits highly uniform porosity, largely originating from the ordered crystalline structures of the MOFs and PCPs. However, the interesting application of these carbon materials derived from MOFs and PCPs for Li–S batteries needs to be further explored. Herein, we report the facile synthesis of microporous carbon polyhedrons (MPCPs) using unique MOF polyhedrons as both the template and precursor, and their use as carbon host to incorporate sulfur for Li–S batteries. The asprepared MPCPs with abundant and uniform micropores serve as an ideal model system for investigating the electrochemical behaviors of sulfur embedded in microporous [a] H. B. Wu, S. Wei, Dr. L. Zhang, Prof. R. Xu, Prof. X. W. Lou School of Chemical and Biomedical Engineering Nanyang Technological University 62 Nanyang Drive, Singapore 637459 (Singapore) E-mail : rxu@ntu.edu.sg xwlou@ntu.edu.sg Homepage: http://www.ntu.edu.sg/home/xwlou [b] H. B. Wu, Prof. H. H. Hng School of Materials Science and Engineering Nanyang Technological University 50 Nanyang Avenue, Singapore 639798 (Singapore) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201301689.

Novel nano-heterostructures composed of Fe2O3 hollow nanorods on both the outer and inner surface of the aligned TiO2 nanotube arrays (TNAs) have been fabricated by growing FeOOH nanospindles onto the TNAs, and then followed by thermal transformation in air. Owing to their structural advantages, such a hierarchical architecture exhibits superior electrochemical performance with a remarkable areal capacity of over 600 μA h cm−2 at a current density of 100 μA cm−2 for 50 cycles (∼680 μA h cm−2 at 100 μA cm−2). This hierarchal structure might be easily integrated as a binder-free electrode for microscale lithium-ion batteries considering the improved performance and the simple synthesis.

Nanosheet-assembled hierarchical V(2)O(5) hollow microspheres are successfully obtained from V-glycolate precursor hollow microspheres, which in turn are synthesized by a simple template-free solvothermal method. The structural evolution of the V-glycolate hollow microspheres has been studied and explained by the inside-out Ostwald-ripening mechanism. The surface morphologies of the hollow microspheres can be controlled by varying the mixture solution and the solvothermal reaction time. After calcination in air, hierarchical V(2)O(5) hollow microspheres with a high surface area of 70 m(2) g(-1) can be obtained and the structure is well preserved. When evaluated as cathode materials for lithium-ion batteries, the as-prepared hierarchical V(2)O(5) hollow spheres deliver a specific discharge capacity of 144 mA h g(-1) at a current density of 100 mA g(-1), which is very close to the theoretical capacity (147 mA h g(-1)) for one Li(+) insertion per V(2)O(5) . In addition, excellent rate capability and cycling stability are observed, suggesting their promising use in lithium-ion batteries.

Ultrathin one-dimensional (1D) nanostructures such as nanowires and nanorods have drawn considerable attention due to their promising applications in various fields. Despite the numerous reports on 1D nanostructures of noble metals, one-pot solution synthesis of Pt 1D nanostructures still remains a great challenge, probably because of the intrinsic isotropic crystal growth behavior of Pt. Herein, we demonstrate the facile solvothermal synthesis of nanowire assemblies composed of ultrathin (ca. 3 nm) and ultralong (up to 10 μm) Pt nanowires without involving any template. The oriented attachment mechanism is found to be partially responsible for the formation of such ultrathin Pt nanowires. The amine molecules generated during the reaction might assist the formation of nanowire assemblies. Importantly, the present system can be extended to synthesize Pt-based alloy nanowire assemblies such as Pt-Au and Pt-Pd. These Pt nanowires can be easily cast into a free-standing membrane, which exhibits excellent electrocatalytic activity and very high stability for formic acid and methanol oxidation and the oxygen reduction reaction.

Hollow microand nano-structures have attracted great interest because of their promising applications in a wide range of areas. Substantial efforts have been dedicated to the facile synthesis of hollow structures with different complex interiors, such as core-shelled, yolk-shelled, and multi-shelled hollow structures, in view of their fantastic architectures and tunable physical and chemical properties, which are attractive for many applications, such as drug delivery, 8] photocatalysis, dye-sensitized solar cells, gas sensors, and lithium-ion batteries (LIBs). A common synthetic strategy for the fabrication of hollow structures with complex interiors employs sacrificial templates, such as uniform polymer, silica, carbon, and metal oxide nanoparticles. For example, multi-shelled metal oxide hollow spheres, including TiO2, iron oxides, and SnO2, have been synthesized by employing sacrificial templates. Multi-shelled Cu2O hollow spheres have also been prepared through vesicle templating and an intermediate-templating phase-transformation process by Xu et al. However, templating methods for constructing complex hollow structures are usually time consuming and costly because of the need for the synthesis of the templates and the multi-step templating process. Therefore, it is highly desirable to develop facile, scalable template-free approaches for the rational synthesis of hollow structures with designed multilevel interior structures. Vanadium oxides, especially vanadium pentoxide (V2O5), have been extensively studied as high capacity cathode materials for LIBs in the past decades. In particular, porous or hollow-structured V2O5 materials have drawn special interest because of their advantageous features for facile Li ion insertion and good cycling stability. However, the controllable fabrication of V2O5 hollow structures with high uniformity and complex interiors through simple synthesis procedures still remains very challenging. Herein, we report the controllable synthesis of uniform VO2 microspheres with various hollow structures, including yolkshelled, multi-shelled, and single-shelled structures, through a one-step template-free solvothermal method (for detailed experimental procedures, see the Supporting Information). The complex interior structures can be simply tailored by adjusting the solvothermal reaction duration and the concentration of the VOC2O4 precursor solution. The resulting VO2 hollow complex structures are robust and could be readily transformed into V2O5 hollow microspheres, which manifest high capacity and good cycling stability when evaluated as cathode materials for LIBs. The powder X-ray diffraction (XRD) pattern of a representative sample prepared by solvothermal synthesis is shown in Figure 1a. The pattern can be assigned to the recently

Noble metals such as platinum (Pt) are widely used as catalysts in fuel cells and other heterogeneous catalytic processes. However, there is an urgent need to develop substitutes for pure Pt catalysts to reduce the overall use of precious Pt and at the same time to enhance poisoning resistance. A promising strategy is to design Pt based bi- or trimetallic nanostructures because their unique structures and compositions would enhance their catalytic performance. In this study, we report the synthesis, characterization, and electrochemical evaluation of cubic intermetallic PtCu(3) nanocages. The influential effects of several important experimental parameters on the final products have been explored through systematic studies on the growth of PtCu(3) nanocages. Relative to the current commercial Pt electrocatalyst, these PtCu(3) nanocages possess a more accessible surface area and a unique hollow structure, which contribute to improved electrocatalytic activity in the methanol oxidation reaction.

Ultra-light Ni nanofoams composed of nanowires have been synthesized on a large scale by a facile reflux approach. From the Ni nanofoam, many other functional nanofoams, composed of semi-hollow NiO nanowires, multi-generation Ni nanowires, and noble metal nanotubes, can be easily derived for many important applications. As an example, the promising application of the NiO nanofoam in lithium-ion batteries is demonstrated.