Formation of NixCo3−xS4 Hollow Nanoprisms with Enhanced Pseudocapacitive Properties

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_xCo_3?xS₄ 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_xCo_3?xS₄ hollow nanoprisms with a well‐defined hollow interior. The intriguing structural and compositional features are beneficial for electrochemical applications. Impressively, the resultant Ni_xCo_3?xS₄ hollow prisms manifest a high specific capacitance with enhanced cycling stability, making them potential electrode materials for supercapacitors.     

Hierarchical Hollow Nanoprisms Based on Ultrathin Ni‐Fe Layered Double Hydroxide Nanosheets with Enhanced Electrocatalytic Activity towards Oxygen Evolution

The oxygen evolution reaction (OER) is involved in various renewable energy systems, such as water‐splitting cells and metal–air batteries. Ni‐Fe layered double hydroxides (LDHs) have been reported as promising OER electrocatalysts in alkaline electrolytes. The rational design of advanced nanostructures for Ni‐Fe LDHs is highly desirable to optimize their electrocatalytic performance. Herein, we report a facile self‐templated strategy for the synthesis of novel hierarchical hollow nanoprisms composed of ultrathin Ni‐Fe LDH nanosheets. Tetragonal nanoprisms of nickel precursors were first synthesized as the self‐sacrificing template. Afterwards, these Ni precursors were consumed during the hydrolysis of iron(II) sulfate for the simultaneous growth of a layer of Ni‐Fe LDH nanosheets on the surface. The resultant Ni‐Fe LDH hollow prisms with large surface areas manifest high electrocatalytic activity towards the OER with low overpotential, small Tafel slope, and remarkable stability.     

Nickel Hydroxide Supercapacitor with a Theoretical Capacitance and High Rate Capability Based on Hollow Dendritic 3D‐Nickel Current Collectors

A straightforward way to attain the theoretical capacitance and high rate capability of nickel hydroxide supercapacitors, by utilizing a mesoporous hollow dendritic three‐dimensional‐nickel (3D‐Ni) current collector is proposed. A facile electrodeposition method employing a hydrogen bubble template was chosen for rapid fabrication of the dendritic 3D‐nickel structure. After nickel hydroxide was deposited on the hollow 3D‐nickel current collector, it exhibited a highest capacitance of 3637 F g⁻¹ at a current density of 1 A g⁻¹, and retained 97 % of capacitance at a high current density of 100 A g⁻¹ with a cycle stability of over 80 % after 10 000 cycles. The enhanced performance could be attributed to the large surface area and high conductivity of the moss‐like dendritic 3D‐Ni current collector, which allowed direct contact between the active materials and the current collector, and reduced diffusion resistance between the surface of the active materials and the electrolyte. These results not only confirmed a facile fabrication method for high‐performance 3D metal nanostructures, but also offer a promising solution for state‐of‐the‐art energy storage systems.     

MoS2‐on‐MXene Heterostructures as Highly Reversible Anode Materials for Lithium‐Ion Batteries

Two‐dimensional (2D) heterostructured materials, combining the collective advantages of individual building blocks and synergistic properties, have spurred great interest as a new paradigm in materials science. The family of 2D transition‐metal carbides and nitrides, MXenes, has emerged as an attractive platform to construct functional materials with enhanced performance for diverse applications. Here, we synthesized 2D MoS₂‐on‐MXene heterostructures through in situ sulfidation of Mo₂TiC₂T_x MXene. The computational results show that MoS₂‐on‐MXene heterostructures have metallic properties. Moreover, the presence of MXene leads to enhanced Li and Li₂S adsorption during the intercalation and conversion reactions. These characteristics render the as‐prepared MoS₂‐on‐MXene heterostructures stable Li‐ion storage performance. This work paves the way to use MXene to construct 2D heterostructures for energy storage applications.     

Dispersed Nickel Nanoparticles on Flower‐like Layered Nickel‐Cobalt Double Hydroxides for Non‐enzymic Amperometric Sensing of Glucose

The article describes the preparation of supported nickel nanoparticles (NiNPs) by partial reduction of Ni,Co‐layered double hydroxide (NiCo‐LDH). The nanocomposites were characterized by X‐ray diffraction and their morphology and composition were characterized by scanning electron microscopy and transmission electron microscopy. The electrochemical properties of the nanocomposite were explored by cyclic voltammetry and amperometry, which revealed significant electrocatalytic behavior towards the oxidation of glucose. The resulted non‐enzymatic glucose sensor has a linear response to glucose in the 5.0 μM to 14.8 mM concentration range, a low detection limit of 1.6 μM, high sensitivity, and excellent selectivity.     

Multielectron‐Transfer‐based Rechargeable Energy Storage of Two‐Dimensional Coordination Frameworks with Non‐Innocent Ligands

The metallically conductive bis(diimino)nickel framework (NiDI), an emerging class of metal–organic framework (MOF) analogues consisting of two‐dimensional (2D) coordination networks, was found to have an energy storage principle that uses both cation and anion insertion. This principle gives high energy led by a multielectron transfer reaction: Its specific capacity is one of the highest among MOF‐based cathode materials in rechargeable energy storage devices, with stable cycling performance up to 300 cycles. This mechanism was studied by a wide spectrum of electrochemical techniques combined with density‐functional calculations. This work shows that a rationally designed material system of conductive 2D coordination networks can be promising electrode materials for many types of energy devices.     

Two‐Dimensional Cobalt‐/Nickel‐Based Oxide Nanosheets for High‐Performance Sodium and Lithium Storage

Two‐dimensional (2D) nanomaterials are one of the most promising types of candidates for energy‐storage applications due to confined thicknesses and high surface areas, which would play an essential role in enhanced reaction kinetics. Herein, a universal process that can be extended for scale up is developed to synthesise ultrathin cobalt‐/nickel‐based hydroxides and oxides. The sodium and lithium storage capabilities of Co₃O₄ nanosheets are evaluated in detail. For sodium storage, the Co₃O₄ nanosheets exhibit excellent rate capability (e.g., 179 mA h g^?1 at 7.0 A g^?1 and 150 mA h g^?1 at 10.0 A g^?1) and promising cycling performance (404 mA h g^?1 after 100 cycles at 0.1 A g^?1). Meanwhile, very impressive lithium storage performance is also achieved, which is maintained at 1029 mA h g^?1 after 100 cycles at 0.2 A g^?1. NiO and NiCo₂O₄ nanosheets are also successfully prepared through the same synthetic approach, and both deliver very encouraging lithium storage performances. In addition to rechargeable batteries, 2D cobalt‐/nickel‐based hydroxides and oxides are also anticipated to have great potential applications in supercapacitors, electrocatalysis and other energy‐storage‐/‐conversion‐related fields.     

A Hydrogen‐Deficient Nickel–Cobalt Double Hydroxide for Photocatalytic Overall Water Splitting

Developing highly efficient and low‐cost photocatalysts for overall water splitting has long been a pursuit for converting solar power into clean hydrogen energy. Herein, we demonstrate that a nonstoichiometric nickel–cobalt double hydroxide can achieve overall water splitting by itself upon solar light irradiation, avoiding the consumption of noble‐metal co‐catalysts. We employed an intensive laser to ablate a NiCo alloy target immersed in alkaline solution, and produced so‐called L‐NiCo nanosheets with a nonstoichiometric composition and O^2?/Co³⁺ ions exposed on the surface. The nonstoichiometric composition broadens the band gap, while O^2? and Co³⁺ ions boost hydrogen and oxygen evolution, respectively. As such, the photocatalyst achieves a H₂ evolution rate of 1.7 μmol h^?1 under AM 1.5G sunlight irradiation and an apparent quantum yield (AQE) of 1.38 % at 380 nm.     

Carbon‐Incorporated Nickel–Cobalt Mixed Metal Phosphide Nanoboxes with Enhanced Electrocatalytic Activity for Oxygen Evolution

Hollow nanostructures have attracted increasing research interest in electrochemical energy storage and conversion owing to their unique structural features. However, the synthesis of hollow nanostructured metal phosphides, especially nonspherical hollow nanostructures, is rarely reported. Herein, we develop a metal–organic framework (MOF)‐based strategy to synthesize carbon incorporated Ni–Co mixed metal phosphide nanoboxes (denoted as NiCoP/C). The oxygen evolution reaction (OER) is selected as a demonstration to investigate the electrochemical performance of the NiCoP/C nanoboxes. For comparison, Ni–Co layered double hydroxide (Ni–Co LDH) and Ni–Co mixed metal phosphide (denoted as NiCoP) nanoboxes have also been synthesized. Benefiting from their structural and compositional merits, the as‐synthesized NiCoP/C nanoboxes exhibit excellent electrocatalytic activity and long‐term stability for OER.     

Particle‐in‐a‐Frame Nanostructures with Interior Nanogaps

Designing plasmonic hollow colloids with small interior nanogaps would allow structural properties to be exploited that are normally linked to an ensemble of particles but within a single nanoparticle. Now, a synthetic approach for constructing a new class of frame nanostructures is presented. Fine control over the galvanic replacement reaction of Ag nanoprisms with Au precursors gave unprecedented Au particle‐in‐a‐frame nanostructures with well‐defined sub‐2 nm interior nanogaps. The prepared nanostructures exhibited superior performance in applications, such as plasmonic sensing and surface‐enhanced Raman scattering, over their solid nanostructure and nanoframe counterparts. This highlights the benefit of their interior hot spots, which can highly promote and maximize the electric field confinement within a single nanostructure.     

Double‐Shelled Nanocages with Cobalt Hydroxide Inner Shell and Layered Double Hydroxides Outer Shell as High‐Efficiency Polysulfide Mediator for Lithium–Sulfur Batteries

Lithium–sulfur (Li‐S) batteries have been considered as a promising candidate for next‐generation electrochemical energy‐storage technologies because of their overwhelming advantages in energy density. Suppression of the polysulfide dissolution while maintaining a high sulfur utilization is the main challenge for Li–S batteries. Here, we have designed and synthesized double‐shelled nanocages with two shells of cobalt hydroxide and layered double hydroxides (CH@LDH) as a conceptually new sulfur host for Li–S batteries. Specifically, the hollow CH@LDH polyhedra with complex shell structures not only maximize the advantages of hollow nanostructures for encapsulating a high content of sulfur (75 wt %), but also provide sufficient self‐functionalized surfaces for chemically bonding with polysulfides to suppress their outward dissolution. When evaluated as cathode material for Li–S batteries, the CH@LDH/S composite shows a significantly improved electrochemical performance.     

Core‐Shell Structured Cobalt Sulfide/Cobalt Aluminum Hydroxide Nanosheet Arrays for Pseudocapacitor Application

The direct synthesis of nanostructured electrode materials on three‐dimensional substrates is important for their practical application in electrochemical cells without requiring the use of organic additives or binders. In this study, we present a simple two‐step process to synthesize a stable core–shell structured cobalt sulfide/cobalt aluminum hydroxide nanosheet (LDH‐S) for pseudocapacitor electrode application. The cobalt aluminum layered double hydroxide (CoAl‐LDH) nanoplates were synthesized in basic aqueous solution with a kinetically‐controlled thickness. Owing to the facile diffusion of electrolytes through the nanoplates, thin CoAl‐LDH nanoplates have higher specific capacitance values than thick nanoplates. The as‐grown CoAl‐LDH nanoplates were transformed into core–shell structured LDH‐S nanosheets by a surface modification process in Na₂S aqueous solution. The chemically robust cobalt sulfide (CoS) shell increased the electrochemical stability compared to the sulfide‐free CoAl‐LDH electrodes. The LDH‐S electrodes exhibited high electrochemical performance in terms of specific capacitance and rate capability with a galvanostatic discharge of 1503 F g^?1 at a current density of 2 A g^?1 and a specific capacitance of 91 % at 50 A g^?1.     

Nano‐Sized Inorganic Energy‐Materials by the Low‐Temperature Molecular Precursor Approach

The low‐temperature synthesis of inorganic materials and their interfaces at the atomic and molecular level provides numerous opportunities for the design and improvement of inorganic materials in heterogeneous catalysis for sustainable chemical energy conversion or other energy‐saving areas. Using suitable molecular precursors for functional inorganic nanomaterial synthesis allows for facile control over uniform particle size distribution, stoichiometry, and leads to desired chemical and physical properties. This Minireview outlines some advantages of the molecular precursor approach in light of selected recent developments of molecule‐to‐nanomaterials synthesis for renewable energy applications, relevant for the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and overall water‐splitting.     

Wall‐ and Hybridisation‐Selective Synthesis of Nitrogen‐Doped Double‐Walled Carbon Nanotubes

Controlled nitrogen‐doping is a powerful methodology to modify the properties of carbon nanostructures and produce functional materials for electrocatalysis, energy conversion and storage, and sensing, among others. Herein, we report a wall‐ and hybridisation‐selective synthetic methodology to produce double‐walled carbon nanotubes with an inner tube doped exclusively with graphitic sp²‐nitrogen atoms. Our measurements shed light on the fundamental properties of nitrogen‐doped nanocarbons opening the door for developing their potential applications.     

基于金属有机框架中空材料的研究进展

金属有机框架(MOFs)中空材料因其大的比表面积、低密度、较高的负载能力和良好的离子渗透性,如氢氧化物、磷化物、硫化物等纳米材料,在能源储存与转换领域有良好的发展前景。 本文主要总结了基于不同形貌MOFs中空材料的制备途径和形成机理,着重介绍了其在超级电容器、锂离子电池和电催化等方面的应用,最后论述了基于MOFs中空材料的未来发展前景和挑战。     

Hierarchical Structures Based on Functionalized Magnetic Cores and Layered Double‐Hydroxide Shells: Concept,Controlled Synthesis,and Applications

The combination of magnetic particles and layered double hydroxide (LDHs) materials leads to the formation of hierarchical composites that can take full advantages of each component; this is an effective approach for achieving multifunctional materials with intriguing properties. This Concept article summarizes several important strategies for the fabrication of magnetic‐core/LDH‐shell hierarchical nanocomposites, including direct coprecipitation, layer‐by‐layer assembly, and in situ growth methods. The obtained nanocomposites exhibit excellent performance as multifunctional materials for promising applications in targeted drug delivery, efficient separation, and catalysis. The fabrication and application of magnetic‐core/LDH‐shell nanocomposite materials represent a new direction in the development of LDH‐based multifunctional materials, which will contribute to the progress of chemistry and material science.     

Well‐Defined Metal–Organic Framework Hollow Nanocages

Metal–organic frameworks (MOFs) have demonstrated great potentials in a variety of important applications. To enhance the inherent properties and endow materials with multifunctionality, the rational design and synthesis of MOFs with nanoscale porosity and hollow feature is highly desired and remains a great challenge. In this work, the formation of a series of well‐defined MOF (MOF‐5, Fe^II‐MOF‐5, Fe^III‐MOF‐5) hollow nanocages by a facile solvothermal method, without any additional supporting template is reported. A surface‐energy‐driven mechanism may be responsible for the formation of hollow nanocages. The addition of pre‐synthesized poly(vinylpyrrolidone)‐ (PVP) capped noble‐metal nanoparticles into the synthetic system of MOF hollow nanocages yields the yolk–shell noble metal@MOF nanostructures. The present strategy to fabricate hollow and yolk–shell nanostructures is expected to open up exciting opportunities for developing a novel class of inorganic–organic hybrid functional nanomaterials.     

钼酸根阴离子在增强聚苯胺包覆的镍钴层状氢氧化物的电容和析氧行为中的关键作用

理论容量大且过电位低的层状氢氧化物(LDHs)是极有前景的超级电容电池和析氧反应的电极材料;然而,体相LDHs的低电导率和活性位点不足增加了电极的内阻,降低了电极容量和产氧效率.本文采用两步法制备了聚苯胺包覆的MoO42?插层的镍钴层状双金属氢氧化物复合电极(M-LDH@PANI).随着LDH中MoO42?含量的增加,针状的LDH微球逐渐演化为具有较高比表面积的片状M-LDH微球,这为整个电极提供了更多的电化学位点.此外,非晶态的聚苯胺包覆提高了复合电极的电导率.在引入适量MoO42?插层离子时,M-LDH@PANI表现出显著强化的储能和催化性能.所获得的M-LDH@PANI-0.5在析氧反应中表现出优越的电催化活性(10 mA cm?2时的过电位为266 mV),作为超级电容电池电极则具有864.8 C g?1的高容量.采用M-LDH@PANI-0.5作为正极及以活性炭作为负极组装的超级电容电池在功率密度为8,300.0 W kg?1时能量密度为44.6 Wh kg?1,且具有优异的循环稳定性(10000次循环后保留83.9％的初始容量).本文为LDH基材料的阴离子插层改性增强材料性能的机理提供了一个非传统的解释.在上述研究基础上,采用射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、高分辨透射电镜(HRTEM)和比表面积测试(BET)等手段对样品进行了深入表征.XRD结果表明,MoO42?插层的LDH材料的层间晶面(003)的峰随着MoO42?含量的增加而逐渐消失,这是由于晶面间距越大越容易受到晶粒细化的影响,间距大的晶格更容易受到破坏,导致晶格的展宽和弱化,从而间接证明MoO42?的成功插层.SEM、HRTEM和BET测试结果表明,MoO42?的含量对材料的形貌和比表面积具有重大影响.利用XPS对样品的价态进行了研究,发现随着MoO42?含量的增加,Co和Ni的价态没有明显变化.电化学测试结果表明,电极的储能和催化性能随MoO42?含量的增加而先增加后减小.利用理论计算分析了MoO42?在LDH中的插层行为,发现少量的MoO42?有利于扩大LDH的层间间距,而过量的MoO42?则会与LDH的H原子结合,从而与电解液中的OH?竞争,导致复合电极的电化学性能下降.此外,MoO42?插层的片状微球能有效调节材料的去质子化能,大大加速电极表面的氧化还原反应.因此,MoO42?插层能够显著强化LDH基材料的超级电容电池电极和OER催化剂电化学性能.     

钼酸根阴离子在增强聚苯胺包覆的镍钴层状氢氧化物的电容和析氧行为中的关键作用

理论容量大且过电位低的层状氢氧化物(LDHs)是极有前景的超级电容电池和析氧反应的电极材料;然而,体相LDHs的低电导率和活性位点不足增加了电极的内阻,降低了电极容量和产氧效率.本文采用两步法制备了聚苯胺包覆的MoO42?插层的镍钴层状双金属氢氧化物复合电极(M-LDH@PANI).随着LDH中MoO42?含量的增加,针状的LDH微球逐渐演化为具有较高比表面积的片状M-LDH微球,这为整个电极提供了更多的电化学位点.此外,非晶态的聚苯胺包覆提高了复合电极的电导率.在引入适量MoO42?插层离子时,M-LDH@PANI表现出显著强化的储能和催化性能.所获得的M-LDH@PANI-0.5在析氧反应中表现出优越的电催化活性(10 mA cm?2时的过电位为266 mV),作为超级电容电池电极则具有864.8 C g?1的高容量.采用M-LDH@PANI-0.5作为正极及以活性炭作为负极组装的超级电容电池在功率密度为8,300.0 W kg?1时能量密度为44.6 Wh kg?1,且具有优异的循环稳定性(10000次循环后保留83.9％的初始容量).本文为LDH基材料的阴离子插层改性增强材料性能的机理提供了一个非传统的解释.在上述研究基础上,采用射线衍射(XRD)、X射线光电子能谱(XPS)、扫描电子显微镜(SEM)、高分辨透射电镜(HRTEM)和比表面积测试(BET)等手段对样品进行了深入表征.XRD结果表明,MoO42?插层的LDH材料的层间晶面(003)的峰随着MoO42?含量的增加而逐渐消失,这是由于晶面间距越大越容易受到晶粒细化的影响,间距大的晶格更容易受到破坏,导致晶格的展宽和弱化,从而间接证明MoO42?的成功插层.SEM、HRTEM和BET测试结果表明,MoO42?的含量对材料的形貌和比表面积具有重大影响.利用XPS对样品的价态进行了研究,发现随着MoO42?含量的增加,Co和Ni的价态没有明显变化.电化学测试结果表明,电极的储能和催化性能随MoO42?含量的增加而先增加后减小.利用理论计算分析了MoO42?在LDH中的插层行为,发现少量的MoO42?有利于扩大LDH的层间间距,而过量的MoO42?则会与LDH的H原子结合,从而与电解液中的OH?竞争,导致复合电极的电化学性能下降.此外,MoO42?插层的片状微球能有效调节材料的去质子化能,大大加速电极表面的氧化还原反应.因此,MoO42?插层能够显著强化LDH基材料的超级电容电池电极和OER催化剂电化学性能.     

A Linker‐Mediated Self‐Assembly Method to Couple Isocharged Nanostructures: Layered Double Hydroxide–CdS Nanohybrids with High Activity for Visible‐Light‐Induced H2 Generation

The electrostatically derived self‐assembly of cationic Zn‐Cr‐layered double hydroxide (LDH) nanosheets and cationic CdS quantum dots (QDs) with anionic linkers leads to the formation of strongly coupled Zn‐Cr‐LDH–CdS nanohybrids. The hybridization with Zn‐Cr‐LDH leads to significant enhancement of the photocatalytic activity of CdS for visible‐light‐induced H₂ generation, a property that is attributed to the depression of electron–hole recombination. In comparison with a direct hybridization method between oppositely charged species, this linker‐mediated method provides greater flexibility in controlling the chemical composition and electronic coupling of the nanohybrids. The present hybridization strategy provides a useful method not only to couple two kinds of isocharged nanostructured materials, but also to explore efficient hybrid‐type photocatalysts.