Aqueous Solution Process for the Synthesis and Assembly of Nanostructured One-Dimensional α‑MoO₃ Electrode Materials

A low-temperature aqueous solution synthesis of nanostructured one-dimensional (1D) molybdenum trioxide (MoO₃) was developed. The subsequent self-assembly of the fibers to form large-scale freestanding films was achieved without any assistance of organic compounds. Indeed, the whole process, from synthesis to assembly, does not require toxic organic solvents. As an example of the application of our synthesized materials, we built two types of half-cell lithium-ion batteries: (i) the cathode made out of 1D MoO₃, having the width in 50–100 nm, with the length in micro scale, and with thickness in ∼10 nm, and (ii) the anode made out of the macroscopic oxide papers consisting of 1D MoO₃ and carbon materials. As a cathode material, 1D MoO₃ showed a high rate capability with a stable cycle performance up to 20 A g^–1 as a result of a short Li⁺ diffusion path along the [101] direction and less grain boundaries. As an anode material, the composite paper compound showed a first specific discharge capacity of 800 mAh g^–1. These findings indicate not only an affordable, eco-efficient synthesis and assembly of nanomaterials but also show a new attractive strategy toward a possible full aqueous process for a large-scale fabrication of freestanding oxide paper compounds without any toxic organic solvent

Carbohydrate-Derived Nanoarchitectures: On a Synergistic Effect Toward an Improved Performance in Lithium–Sulfur Batteries

We combined the good cycle ability and rate performance of carbon-nanostructured hollow spheres with the high specific capacity at first discharge of nitrogen-doped carbon aerogels. Beneficial contributions of each constituent material, i.e., N-doped carbogel and carbon hollow spheres, led to a promising synergistic effect. A high specific capacity of more than 700 mA h g^–1 was reached with a limited fading over 25 cycles

Mesoporous Carbon Interlayers with Tailored Pore Volume as Polysulfide Reservoir for High-Energy Lithium–Sulfur Batteries

The lithium–sulfur (Li–S) battery is one of the most promising candidates for the next generation of rechargeable batteries owing to its high theoretical energy density, which is 4- to 5-fold greater than those of state-of-the-art Li–ion batteries. However, its commercial applications have been hampered due to the insulating nature of sulfur and the poor cycling stability caused by the polysulfide shuttle phenomenon. In this work, we show that Li–S batteries with a mesoporous carbon interlayer placed between the separator and the sulfur cathode not only reduces the internal resistance of the cells but also that its intrinsic mesoporosity provides a physical place for trapping soluble polysulfides as well as to alleviate the negative impact of the large volume change of sulfur. This improvement of the active material reutilization allows one to obtain a stable capacity of 1015 mAh g^–1 at 0.2 C after 200 cycles despite the use of a conventional sulfur–carbon black mixture as cathode. Furthermore, we observe an excellent capacity retention (∼0.1% loss per cycle, after the second cycle), thus making one step closer toward feasible Li–S battery technology for applications in electric vehicles and grid-scale stationary energy storage systems

Tailoring Hollow Silicon–Carbon Nanocomposites As High-Performance Anodes in Secondary Lithium-Based Batteries through Economical Chemistry

A sustainable synthesis procedure of a rational-designed silicon–carbon electrode for a high-performance rechargeable Li-based battery has been developed. It was realized by an economical approach using low-cost trichlorosilane as feedstock and without special equipment. The synthesis strategy includes polycondensation of trichlorosilane in the presence of a surfactant to selectively form spheric silicon@silica particles via a hydrogen silsesquioxane (HSQ) intermediate. After subsequent carbonization of a sucrose shell and etching the composite, we obtained an anode material based on silicon nanoparticles with 2–5-nm average diameter inside a porous carbon scaffold. The active material exhibits a high rate capability of 2000 mAh/g at a current rate of 0.5 A/g with exceptional cycle stability. After almost 1000 times of deep discharge galvanostatic cycling at 2.5 A/g current rate the capacity is still 60% of the initial 1200 mAh/g. The excellent electrochemical performance is attributed to an interaction of a stabilized solid electrolyte interface on extreme small silicon particles and a well-designed porous carbon cage which serves as efficient charge conductor

On the Role of Vapor Trapping for Chemical Vapor Deposition (CVD) Grown Graphene over Copper

The role of sample chamber configuration for the chemical vapor deposition of graphene over copper was investigated in detail. A configuration in which the gas flow is unrestricted was shown to lead to graphene with an inhomogeneous number of layers (between 1 and 3). An alternative configuration in which one end of the inner tube (in which the sample is placed) is closed so as to restrict the gas flow leads a homogeneous graphene layer number. Depending on the sample placement, either homogeneous monolayer or bilayer graphene is obtained. Under our growth conditions, the data show local conditions play a role on layer homogeneity such that under quasi-static equilibrium gas conditions not only is the layer number stabilized, but the quality of the graphene improves. In short, our data suggests vapor trapping can trap Cu species leading to higher carbon concentrations, which determines layer number and improved decomposition of the carbon feedstock (CH₄), which leads to higher quality graphene

Electrosorption of Hydrogen in Pd-Based Metallic Glass Nanofilms

As an efficient potential hydrogen storage and conversion system, hydrogen electrosorption and evolution mechanisms in Pd-based metallic glass thin films (MGTFs) are investigated. In this study, thin films of 55 nm thickness were deposited by dc magnetron sputtering. The amorphous structure of MGTFs and the atomically smooth interface between the MGTF and substrate were confirmed by transmission electron microscopy, whereas the composition-dependent surface roughness was obtained via atomic force microscopy. The shifts in the broad diffraction maxima for the Si and Cu additions were evaluated by X-ray diffraction. The Pd thin film (PdTF) and MGTF working electrodes were chronoamperometrically saturated in 0.5 M H₂SO₄ solution. The formation of palladium hydride (PdH_<i>x</i>) in the MGTFs was investigated by X-ray photoelectron spectroscopy. Cyclic voltammograms were subsequently recorded (between −0.2 and 1.4 V) at sweep rates of 0.02 V s^–1. Electrochemical impedance spectroscopy of MGTFs and PdTF was performed in full spectrum including sorption, desorption, and evolution of hydrogen in a conventional three-electrode configuration. Electrochemical circuit modeling provided the relationship between the composition-dependent hydrogen evolution and H absorption/adsorption processes. The adsorption capacitance parameter <i>Y</i>_ad corresponding to α- and β-hydride formation in the case of Pd_0.79Si_0.16Cu_0.05 MGTF is ∼5 times higher than that of the crystalline Pd thin film which is in line with the decrease in the charge-transfer resistance <i>R</i>_ct. Addition of Cu disturbs the symmetry of the glass formers, leading to remarkable changes in interfacial hydrogen bonding and diffusion of hydrogen into sublayers. Compared to other Pd- based micron-sized materials, our findings show excellent volumetric hydrogen storage capacity 4 times higher than that of the traditional counterparts of several microns, and 50% higher than the Pd thin films of the same thickness, together with high tunable capacitance, charge-transfer resistance, and diffusivity depending on the glass-forming characteristics of the nanosized MGTF

Synergistically Enhanced Polysulfide Chemisorption Using a Flexible Hybrid Separator with N and S Dual-Doped Mesoporous Carbon Coating for Advanced Lithium–Sulfur Batteries

Because of the outstanding high theoretical specific energy density of 2600 Wh kg^–1, the lithium–sulfur (Li–S) battery is regarded as a promising candidate for post lithium-ion battery systems eligible to meet the forthcoming market requirements. However, its commercialization on large scale is thwarted by fast capacity fading caused by the Achilles’ heel of Li–S systems: the polysulfide shuttle. Here, we merge the physical features of carbon-coated separators and the unique chemical properties of N and S codoped mesoporous carbon to create a functional hybrid separator with superior polysulfide affinity and electrochemical benefits. DFT calculations revealed that carbon materials with N and S codoping possess a strong binding energy to high-order polysulfide species, which is essential to keep the active material in the cathode side. As a result of the synergistic effect of N, S dual-doping, an advanced Li–S cell with high specific capacity and ultralow capacity degradation of 0.041% per cycle is achieved. Pushing our simple-designed and scalable cathode to a highly increased sulfur loading of 5.4 mg cm^–2, the Li–S cell with the functional hybrid separator can deliver a remarkable areal capacity of 5.9 mAh cm^–2, which is highly favorable for practical applications

Polymeric Frameworks as Organic Semiconductors with Controlled Electronic Properties

The rational assembly of monomers, in principle, enables the design of a specific periodicity of polymeric frameworks, leading to a tailored set of electronic structure properties in these solid-state materials. The further development of these emerging systems requires a combination of both experimental and theoretical studies. Here, we investigated the electronic structures of two-dimensional polymeric frameworks based on triazine and benzene rings by means of electrochemical techniques. The experimental density of states was obtained from quasi-open-circuit voltage measurements through a galvanostatic intermittent titration technique, which we show to be in excellent agreement with first-principles calculations performed for two- and three-dimensional structures of these polymeric frameworks. These findings suggest that the electronic properties depend not only on the number of stacked layers but also on the ratio of the different aromatic rings

Multimetallic Aerogels by Template-Free Self-Assembly of Au, Ag, Pt, and Pd Nanoparticles

Nanostructured, porous metals are of great interest for material scientists since they combine high surface area, gas permeability, electrical conductivity, plasmonic behavior, and size-enhanced catalytic reactivity. Here we present the formation of multimetallic porous three-dimensional networks by a template-free self-assembly process. Nanochains are formed by the controlled coalescence of Au, Ag, Pt, and Pd nanoparticles in aqueous media, and their interconnection and interpenetration leads to the formation of a self-supporting network. The resulting noble-metal-gels are transformed into solid aerogels by the supercritical drying technique. Compared to previously reported results, the technique is facilitated by exclusion of additional destabilizers. Moreover, temperature control is demonstrated as a powerful tool, allowing acceleration of the gelation process as well as improvement of its reproducibility and applicability. Electron microscopy shows the nanostructuring of the network and its high porosity. XRD and EDX STEM are used to investigate the alloying behavior of the bimetallic aerogels and prove the control of the alloying state by temperature induced phase modifications. Furthermore, the resulting multimetallic aerogels show an extremely low relative density (<0.2%) and a very high surface area (>50 m²/g) compared to porous noble metals obtained by other approaches. Electrically conductive thin films as well as hybrid materials with organic polymers are depicted to underline the processability of the materials, which is a key factor regarding handling of the fragile structures and integration into device architectures. Owing to their exceptional and tunable properties, multimetallic aerogels are very promising materials for applications in heterogeneous catalysis and electrocatalysis, hydrogen storage, and sensor systems but also in surface enhanced Raman spectroscopy (SERS) and the preparation of transparent conductive substrates

<i>In Situ</i> Observations of Free-Standing Graphene-like Mono- and Bilayer ZnO Membranes

ZnO in its many forms, such as bulk, thin films, nanorods, nanobelts, and quantum dots, attracts significant attention because of its exciting optical, electronic, and magnetic properties. For very thin ZnO films, predictions were made that the bulk wurtzite ZnO structure would transit to a layered graphene-like structure. Graphene-like ZnO layers were later confirmed when supported over a metal substrate. However, the existence of free-standing graphene-like ZnO has, to the best of our knowledge, not been demonstrated. In this work, we show experimental evidence for the <i>in situ</i> formation of free-standing graphene-like ZnO mono- and bilayer ZnO membranes suspended in graphene pores. Local electron energy loss spectroscopy confirms the membranes comprise only Zn and O. Image simulations and supporting analysis confirm that the membranes are graphene-like ZnO. Graphene-like ZnO layers are predicted to have a wide band gap and different and exciting properties as compared to other ZnO structures