Efficient Photocatalytic Nitrogen Fixation over Cuδ+‐Modified Defective ZnAl‐Layered Double Hydroxide Nanosheets

The photocatalytic reduction of nitrogen (N₂) with water (H₂O) as the reducing agent holds great promise as a sustainable future technology for the synthesis of ammonia (NH₃). Herein, the effect of oxygen vacancies and electron‐rich Cu^δ+ on the performance of zinc‐aluminium layered double hydroxide (ZnAl‐LDH) nanosheet photocatalysts for N₂ reduction to NH₃ under UV–vis excitation is systematically explored. Results show that a 0.5%‐ZnAl‐LDH nanosheet photocatalyst (containing 0.5 mol% Cu by metal basis) affords a remarkable NH₃ production rate of 110 µmol g^?1 h^?1 and excellent stability in pure water. The X‐ray absorption spectroscopy, electron paramagnetic resonance, and density functional theory calculations reveal that Cu addition imparts oxygen vacancies and coordinatively unsaturated Cu^δ+ (δ < 2) with electron‐rich property in the ZnAl‐LDH nanosheets, both of which readily contribute to efficient separation and transfer of photogenerated electrons and holes and promote N₂ adsorption, thereby both activating N₂ and facilitating its multielectrons reduction to NH₃.     

Ultrathin MoS2 Nanosheets as Anode Materials for Sodium‐Ion Batteries with Superior Performance

Few‐layer MoS₂ nanosheets are successfully synthesized using a simple and scalable ultrasonic exfoliation technique. The thicknesses of the MoS₂ nanosheets ares about 10 nm as measured by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The unique nanosheet architecture renders the high‐rate transportation of sodium ions due to the short diffusion paths provided by ultrathin thickness and the large interlayer space within the MoS₂ crystal structure (d₍₀₀₂₎ = 6.38 Å). When applied as anode materials in sodium‐ion batteries, MoS₂ nanosheets exhibit a high, reversible sodium storage capacity and excellent cyclability. The MoS₂ nanosheets also demonstrate good electrochemical performance at high current densities.     

Sandwich‐Like Ultrathin TiS2 Nanosheets Confined within N,S Codoped Porous Carbon as an Effective Polysulfide Promoter in Lithium‐Sulfur Batteries

As the lightest member of transition metal dichalcogenides, 2D titanium disulfide (2D TiS₂) nanosheets are attractive for energy storage and conversion. However, reliable and controllable synthesis of single‐ to few‐layered TiS₂ nanosheets is challenging due to the strong tendency of stacking and oxidation of ultrathin TiS₂ nanosheets. This study reports for the first time the successful conversion of Ti₃C₂T_x MXene to sandwich‐like ultrathin TiS₂ nanosheets confined by N, S co‐doped porous carbon (TiS₂@NSC) via an in situ polydopamine‐assisted sulfuration process. When used as a sulfur host in lithium–sulfur batteries, TiS₂@NSC shows both high trapping capability for lithium polysulfides (LiPSs), and remarkable electrocatalytic activity for LiPSs reduction and lithium sulfide oxidation. A freestanding sulfur cathode integrating TiS₂@NSC with cotton‐derived carbon fibers delivers a high areal capacity of 5.9 mAh cm^?2 after 100 cycles at 0.1 C with a low electrolyte/sulfur ratio and a high sulfur loading of 7.7 mg cm^?2, placing TiS₂@NSC one of the best LiPSs adsorbents and sulfur conversion catalysts reported to date. The developed nanospace‐confined strategy will shed light on the rational design and structural engineering of metal sulfides based nanoarchitectures for diverse applications.     

High‐Performance Ultrathin Co3O4 Nanosheet Supported PdO/CeO2 Catalysts for Methane Combustion

Efficient utilization of methane via catalytic complete combustion is a very important pathway to realize energy efficiency and pollution reduction. From the viewpoint of structural design, herein a green water‐phase route is developed to prepare ultrathin Co(OH)₂ nanosheet supported Pd catalysts. As a platform, the as‐obtained Pd/Co(OH)₂ nanosheets are able to be further used to load CeO₂ nanoparticles to form 2D nanostructured Pd/CeO₂/Co(OH)₂ multicomponent hybrids, and further calcination can result in the final well‐crystallized ultrathin Co₃O₄ nanosheet supported PdO/CeO₂ catalysts. Catalytic tests on methane combustion reveal that CeO₂ as a catalytic assistant greatly boosts the catalytic performance of PdO/Co₃O₄ via strong synergetic effects with Pd species and Co₃O₄ components. The best sample of PdO/CeO₂‐0.1/Co₃O₄ exhibits surprisingly enhanced light‐off activity, indicating that such 2D Co₃O₄ nanosheet supported nanocatalysts might show promising prospect for heterogeneous catalysis.     

Single‐Crystalline Nanomesh Tantalum Nitride Photocatalyst with Improved Hydrogen‐Evolving Performance

Tantalum nitride (Ta₃N₅) with a suitable bandgap (≈2 eV) is regarded as one of the most promising photocatalysts for efficient solar energy harvesting and conversion. However, Ta₃N₅ suffers from low hydrogen production activity due to the low carrier mobility and fast carrier recombination. Thus, the design of Ta₃N₅ nanostructures to facilitate charge carrier transport and improve photocatalytic performance remains a challenge. This study reports a new type of ultrathin (≈2 nm) Ta₃N₅ nanomesh with high specific surface area (284.6 m² g^?1) and excellent crystallinity by an innovative bottom‐up graphene oxide templated strategy. The resulting Ta₃N₅ nanomeshes demonstrate drastically improved electron transport ability and prolonged lifetime of charge carriers, due to the nature of high surface area and excellent crystallinity. As a result, when used as photocatalysts, the Ta₃N₅ nanomeshes exhibit a greater than tenfold improvement in solar hydrogen production compared to bulk counterparts. This work provides an effective and generic strategy for designing 2D ultrathin nanomesh structures for nonlayered materials with improved catalytic activity.     

Surface‐Guided Formation of Amorphous Mixed‐Metal Oxyhydroxides on Ultrathin MnO2 Nanosheet Arrays for Efficient Electrocatalytic Oxygen Evolution

Earth‐abundant amorphous nanomaterials with rich structural defects are promising alternative catalysts to noble metals for an efficient electrochemical oxygen evolution reaction; however, their inferior electrical conductivity and poor morphological control during synthesis hamper the full realization of their potency in electrocatalysis. Herein, a rapid surface‐guided synthetic approach is proposed to introduce amorphous and mixed‐metal oxyhydroxide overlayers on ultrathin Ni‐doped MnO₂ (Ni? MnO₂) nanosheet arrays via a galvanic replacement mechanism. This method results in a monolithic 3D porous catalyst with a small overpotential of only 232 mV to achieve a current density of 10 mA cm^?2 in 1 m KOH, which is much lower than the corresponding value of 307 mV for the Ni? MnO₂ reference sample. Detailed structural and electrochemical characterization reveal that the unique Ni? MnO₂ ultrathin nanosheet arrays do not only provide a large surface area to guide the formation of active amorphous catalyst layers but also ensure the effective charge transport owing to their high electron conductivity, collectively contributing to the greatly improved catalyst activity. It is envisioned that this highly operable surface‐guide synthetic strategy may open up new avenues for the design and fabrication of novel 3D nanoarchitectures integrated with functional amorphous materials for broadened ranges of applications.     

Ultrathin Li4Ti5O12 Nanosheet Based Hierarchical Microspheres for High‐Rate and Long‐Cycle Life Li‐Ion Batteries

Ultrathin Li₄Ti₅O₁₂ nanosheet based hierarchical microspheres are synthesized through a three‐step hydrothermal procedure. The average thickness of the Li₄Ti₅O₁₂ sheets is only ≈(6.6 ± 0.25) nm and the specific surface area of the sample is 178 m² g^?1. When applied into lithium ion batteries as anode materials, the hierarchical Li₄Ti₅O₁₂ microspheres exhibit high specific capacities at high rates (156 mA h g^?1 at 20 C, 150 mA h g^?1 at 50 C) and maintain a capacity of 126 mA h g^?1 after 3000 cycles at 20 C. The results clearly suggest that the utility of hierarchical structures based on ultrathin nanosheets can promote the lithium insertion/extraction reactions in Li₄Ti₅O₁₂. The obtained hierarchical Li₄Ti₅O₁₂ with ultrathin nanosheets and large specific surface area can be perfect anode materials for the lithium ion batteries applied in high power facilities, such as electric vehicles and hybrid electric vehicles.     

Fabrication of Ordered Macro‐Microporous Single‐Crystalline MOF and Its Derivative Carbon Material for Supercapacitor

Because of their good performance in diffusion‐limited processes, ordered macro‐microporous single‐crystalline metal‐organic frameworks (MOFs) have potential for use in various fields. However, there are still very few reports of the synthesis of such MOFs. A general synthesis methodology for ordered macro‐microporous single‐crystalline MOFs is highly desired. Here, a novel strategy is reported for synthesizing single‐crystalline ordered macro‐microporous MOFs by monodentate‐ligand‐induced in situ crystallization within a 3D ordered hard template in a double‐solvent system. A space‐confined growth model is proposed to clarify the shaping effect of the template; the role of the monodentate ligand is also analyzed. Moreover, a carbon material derived from the macro‐microporous MOF inherits the ordered interconnected macroporous structure. The improved diffusion and lower resistance, as well as the structural robustness, endow the derivative carbon material with superior rate performance and excellent cycling stability when prepared as electrodes for a supercapacitor. It is anticipated that the method will provide new paths to the synthesis of such macro‐microporous materials for applications in energy‐related fields and beyond.     

Ultrathin Co3O4 Layers with Large Contact Area on Carbon Fibers as High‐Performance Electrode for Flexible Zinc–Air Battery Integrated with Flexible Display

A facile and binder‐free method is developed for the in situ and horizontal growth of ultrathin mesoporous Co₃O₄ layers on the surface of carbon fibers in the carbon cloth (ultrathin Co₃O₄/CC) as high‐performance air electrode for the flexible Zn–air battery. In particular, the ultrathin Co₃O₄ layers have a maximum contact area on the conductive support, facilitating the rapid electron transport and preventing the aggregation of ultrathin layers. The ultrathin feature of Co₃O₄ layers is characterized by the transmission electron microscopy, Raman spectra, and X‐ray absorption fine structure spectroscopy. Benefiting from the high utilization degree of active materials and rapid charge transport, the mass activity for oxygen reduction and evolution reactions of the ultrathin Co₃O₄/CC electrode is more than 10 times higher than that of the carbon cloth loaded with commercial Co₃O₄ nanoparticles. Compared to the commercial Co₃O₄/CC electrode, the flexible Zn–air battery using ultrathin Co₃O₄/CC electrode exhibits excellent rechargeable performance and high mechanical stability. Furthermore, the flexible Zn–air battery is integrated with a flexible display unit. The whole integrated device can operate without obvious performance degradation under serious deformation and even during the cutting process, which makes it highly promising for wearable and roll‐up optoelectronics.     

Electronic and Defective Engineering of Electrospun CaMnO3 Nanotubes for Enhanced Oxygen Electrocatalysis in Rechargeable Zinc–Air Batteries

Rational design and massive production of bifunctional catalysts with superior oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities are essential for developing metal–air batteries and fuel cells. Herein, controllable large‐scale synthesis of sulfur‐doped CaMnO₃ nanotubes is demonstrated via an electrospinning technique followed by calcination and sulfurization treatment. The sulfur doping can not only replace oxygen atoms to increase intrinsic electrical conductivity but also introduce abundant oxygen vacancies to provide enough catalytically active sites, which is further demonstrated by density functional theory calculation. The resulting sulfur‐modified CaMnO₃ (CMO/S) exhibits better electrocatalytic activity for ORR and OER in alkaline solution with higher stability performance than the pristine CMO. These results highlight the importance of sulfur treatment as a facile yet effective strategy to improve the ORR and OER catalytic activity of the pristine CaMnO₃. As a proof‐of‐concept, a rechargeable Zn–air battery using the bifunctional catalyst exhibits a small charge–discharge voltage polarization, and long cycling life. Furthermore, a solid‐state flexible and rechargeable Zn–air battery gives superior discharge–charge performance and remarkable stability. Therefore, the CMO/S nanotubes might be a promising replacement to the Pt‐based electrocatalysts for metal–air batteries and fuel cells.     

Ultrathin Anatase TiO2 Nanosheets Embedded with TiO2‐B Nanodomains for Lithium‐Ion Storage: Capacity Enhancement by Phase Boundaries

A new form of TiO₂ microspheres comprised of anatase/TiO₂‐B ultrathin composite nanosheets has been synthesized successfully and used as Li‐ion storage electrode material. By comparison between samples obtained with different annealing temperatures, it is demonstrated that the anatase/TiO₂‐B coherent interfaces may contribute additional lithium storage venues due to a favorable charge separation at the boundary between the two phases. The as‐prepared hierarchical nanostructures show capacities of 180 and 110 mAh g^?1 after 1000 cycles at current densities of 3400 and 8500 mA g^?1. The ultrathin nanosheet structure which provides short lithium diffusion length and high electrode/electrolyte contact area also accounts for the high capacity and long‐cycle stability.     

Oxygen Reduction Reactions on Single‐ or Few‐Atom Discrete Active Sites for Heterogeneous Catalysis

The oxygen reduction reaction (ORR) is of great importance in energy‐converting processes such as fuel cells and in metal–air batteries and is vital to facilitate the transition toward a nonfossil dependent society. The ORR has been associated with expensive noble metal catalysts that facilitate the O₂ adsorption, dissociation, and subsequent electron transfer. Single‐ or few‐atom motifs based on earth‐abundant transition metals, such as Fe, Co, and Mo, combined with nonmetallic elements, such as P, S, and N, embedded in a carbon‐based matrix represent one of the most promising alternatives. Often these are referred to as single atom catalysts; however, the coordination number of the metal atom as well as the type and nearest neighbor configuration has a strong influence on the function of the active sites, and a more adequate term to describe them is metal‐coordinated motifs. Despite intense research, their function and catalytic mechanism still puzzle researchers. They are not molecular systems with discrete energy states; neither can they fully be described by theories that are adapted for heterogeneous bulk catalysts. Here, recent results on single‐ and few‐atom electrocatalyst motifs are reviewed with an emphasis on reports discussing the function and the mechanism of the active sites.     

A Robust Route to Co2(OH)2CO3 Ultrathin Nanosheets with Superior Lithium Storage Capability Templated by Aspartic Acid‐Functionalized Graphene Oxide

Two‐dimensional (2D) nanomaterials are widely recognized as an important class of functional materials possessing superior electrochemical reaction kinetics. Herein, an L‐aspartic acid (AA)‐modified graphene oxide (GO) templating strategy is developed to in situ yield ultrathin (i.e., ≈5 nm) cobalt carbonate hydroxide (Co₂(OH)₂CO₃) nanosheets as advanced anode materials of lithium ion batteries. Notably, the covalent tethering of AA on the GO surface renders a high density of carboxyl groups that impart effective loading of Co‐containing precursors and subsequent growth into Co₂(OH)₂CO₃ nanosheets bridging adjacent GO layers. The lasagna‐like Co₂(OH)₂CO₃‐GO nanocomposites exhibit an ultrahigh lithium storage capacity of 1770 mAh g^?1 after 500 cycles at 100 mA g^?1. It is noteworthy that the cycled Co₂(OH)₂CO₃ phase separates into homogeneously dispersed Co(OH)₂ and CoCO₃ phases with two different charge plateaus at ≈1.2 and 2.0 V, respectively, which effectively inhibit large‐scale homophase coarsening of Co, Li₂CO₃, and LiOH. The much shortened Li⁺/e^? transfer distance enabled by individual ultrathin Co₂(OH)₂CO₃ nanosheet together with robust layer‐by‐layer assembled nanostructure of Co₂(OH)₂CO₃‐GO confers the superior electrochemical reactivity and mechanical stability. As such, the amino acid‐modified GO templating strategy may represent a simple yet robust means of crafting a variety of 2D nanostructured composites of interest for energy storage applications.     

Citrate‐Assisted Growth of NiCo2O4 Nanosheets on Reduced Graphene Oxide for Highly Reversible Lithium Storage

Hybrid nanostructures based on graphene and transition metal oxides hold great promise as high‐performance electrode materials for next‐generation lithium‐ion batteries. In this work, the rational design and fabrication of NiCo₂O₄ nanosheets supported on reduced graphene oxide (denoted as rGO/NiCo₂O₄) is presented as a novel anode material for highly efficient and reversible lithium storage. A solution method is applied to grow Ni‐Co precursor nanosheets on rGO, in which the addition of trisodium citrate is found crucial to guide the formation of uniform Ni‐Co precursor nanosheets. Subsequent thermal treatment results in formation of crystalline NiCo₂O₄ nanosheets on rGO without damaging the morphology. The interconnected NiCo₂O₄ nanosheets form hierarchically porous films on both sides of rGO. Such a hybrid nanostructure would effectively promote the charge transport and withstand volume variation upon prolonged charge/discharge cycling. As a result, the rGO/NiCo₂O₄ nanocomposite demonstrates high reversible capacities of 954.3 and 656.5 mAh g^–1 over 50 cycles at current densities of 200 and 500 mA g^–1 respectively, and remarkable capacity retention at increased current densities.     

Highly Air‐Stable Single‐Crystalline β‐CsPbI3 Nanorods: A Platform for Inverted Perovskite Solar Cells

The synthesis of single‐crystalline β‐CsPbI₃ perovskite nanorods (NRs) using a colloidal process is reported, exhibiting their improved photostability under 45–55% humidity. The crystal structure of CsPbI₃ NRs films is investigated using Rietveld refined X‐ray diffraction (XRD) patterns to determine crystallographic parameters and the phase transformation from orthorhombic (γ‐CsPbI₃) to tetragonal (β‐CsPbI₃) on annealing at 150 °C. Atomic resolution transmission electron microscopy images are utilized to determine the probable atomic distribution of Cs, Pb, and I atoms in a single β‐phase CsPbI₃ NR, in agreement with the XRD structure and selected area electron diffraction pattern, indicating the growth of single crystalline β‐CsPbI₃ NR. The calculation of the electronic band structure of tetragonal β‐CsPbI₃ using density functional theory (DFT) reveals a direct transition with a lower band gap and a higher absorption coefficient in the solar spectrum, as compared to its γ‐phase. An air‐stable (45–55% humidity) inverted perovskite solar cell, employing β‐CsPbI₃ NRs without any encapsulation, yields an efficiency of 7.3% with 78% enhancement over the γ‐phase, showing its potential for future low cost photovoltaic devices.