Free-standing 3D Research Articles

Diffusion-Mediated Nucleation and Growth of fcc and bcc Nanocrystal Superlattices with Designable Assembly of Freestanding 3D Supercrystals.

Diffusion-mediated assembly of octahedral PbS nanocrystals (NCs) in a confined antisolvent environment displays a primary burst nucleation and Ostwald ripening growth of rhombic bcc supercrystals, followed by a secondary seed-based nucleation and oriented attachment growth of triangle fcc supercrystals. As the diffusion proceeds from ethanol across a sharp interface into NC-suspended toluene, a burst nucleation of supercrystal seeds occurs, and such supercrystals are quickly developed into rhombic grains that have a bcc structure. At a critical size of 10 μm, an Ostwald ripening event appears to guide the supercrystal growth. Upon grain growth above 30 μm, the fcc supercrystals start a nucleation at two symmetrical tips of individual rhombic crystals. Such fcc supercrystals are developed with a triangle shape, and two triangles are combined with one bcc rhombus in-between to form a butterfly-like bowtie stacking structure. The fcc triangle wings grow larger at a reduction of bcc rhombus cores. As the bcc cores gradually fade, such butterfly-like bowtie crystals aggregate and undergo an oriented attachment process, leading to the formation of freestanding 3D triangle crystals that have a single fcc lattice. Analysis of experimental observations and defined diffusion parameters reveals that fast solvent diffusion and high-NC concentration promote the growth of rhombic bcc supercrystals, while slow solvent diffusion and low-NC concentration accelerate the development of triangle fcc supercrystals. Upon succeeding in designable growth of 3D fcc supercrystals, this study provides designing principles for controlled fabrication of supercrystals with desired superlattices for additional engineering and applications.

3D Free-Standing Graphene: Influence of Etching Solution and Etching Time on Chemical Vapor Deposition on the Graphene/Nickel Foam

Three-dimensional (3D) structures made of graphene sheets have been developed recently, and have resulted in the development of a new class of graphene materials known as 3D graphene materials. High-quality free-standing 3D graphene foam has been synthesized by chemical vapor deposition (CVD) on nickel foam followed by a chemical etching process to remove the nickel foam as a template. Field-emission scanning electron microscopy (FESEM), x-ray diffraction (XRD), and Raman spectroscopy measurements were performed to investigate the morphologies, crystal phase, and the structure of nickel foam (NF), graphene/nickel foam (Gr/NF), and 3D graphene (3D Gr). In this study, the influence of etching solution and etching time on Gr/NF to produce free-standing 3D Gr was investigated. XRD spectroscopy showed that the mixed solutions of 1M FeCl<sub>3</sub>:1M HCl at 80 °C for 3 h can significantly remove the NF and no peaks of NF are observed, thus indicating a high crystal quality of 3D Gr was obtained. In addition, XRD spectroscopy revealed that by increasing the etching time beyond 3 h, the intensity of diffraction peaks decreases, thus degrading graphene quality. This research emphasizes the significance of proper selections of etching solution and etching time in removing the NF to maintain the characteristic, quality, and surface morphology of 3D Gr after the etching process.

Mechanical properties characterization of 2D materials via pressure bulge testing

Pressure bulge testing is one of the standard techniques for characterizing the mechanical properties of thin films, whereas it is far less often used to characterize the mechanical properties of 2D materials. In the present work, the effectiveness of bulge testing on determining the mechanical properties of 2D materials is systematically investigated using numerical analysis. After assuming 2D materials as continuum thin films, we start by simulating the relationship between the pressure difference across the suspended film and the film deflection, and then fit the results with analytical models to extract the elastic modulus of the film. It should be noted that the clamped, pre-stretched film widely assumed in the existing analytical model is not appropriate for atomically thin materials; instead, freestanding 2D materials are actually slack in bulge testing due to the delamination of their adhesive boundary condition. Therefore, the initially unstressed flat films, pre-stretched films and slack films are investigated in the present work, and the Poisson’s ratio effect is considered to investigate the effectiveness of bulge testing for most 2D materials. It is found that bulge testing can be an effective approach to characterize the mechanical properties of 2D materials.

Back Cover Image, Volume 2, Issue 1, January 2023

Battery EnergyVolume 2, Issue 1 12092 COVEROpen Access Back Cover Image, Volume 2, Issue 1, January 2023 First published: 18 January 2023 https://doi.org/10.1002/bte2.12092AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Graphical Abstract Back Cover: In article number BTE2.20220032, Wenbo Liu and co-workers develop a simple and effective strategy to achieve PANI-modified freestanding 3D dendritic hierarchical porous Cu-Sn nanocomposites, which shows ultrahigh areal capacity and good cycling stability as additive-free thick anodes for LIBs. The Sn content and areal capacity can be tuned easily by changing the dealloying time of initial alloy for 3D tin-based thick anodes with adjustable capacities toward high-performance LIBs. Volume2, Issue1January 202312092 RelatedInformation

Designing free-standing 3D lamellar/pillared RGO/CNTs aerogels with ultra-high conductivity and compressive strength for elastic energy devices

We here demonstrate a lamellar/pillared RGO/CNTs composite aerogel with high conductivity and compressive strength. By using the RGO/CNTs aerogel derived composite electrodes, high performance energy storage and conversion devices are developed.

Few-layered Ti3C2TXcoupled with Fe3O4nanoparticles assembled in a reduced graphene oxide hydrogel as advanced electrodes for high-energy supercapacitors

A high-performance symmetric supercapacitor device based on free-standing 3D porous Fe3O4@Ti3C2TX–rGO heterostructure hydrogel electrodes is built.

Binder-Free Freestanding 3D Zn-Graphene Anode Induced from Commercial Zinc Powders and Graphene Oxide for Zinc Ion Battery with High Utilization Rate

Aqueous zinc-ion batteries (AZIBs) have received widespread attention owing to the increasing demand for safety and inexpensive batteries. However, a zinc metal anode suffers from dendrite growth during continuous cycling, and side reactions occurred on anode surface such as hydrogen evolution reaction (HER) and passivation. Moreover, the low utilization of Zn metal is also a neglected issue leading to a low energy density at the cell-level. Herein, a nondendrite Zn anode with high utilization was designed by spontaneous reaction of commercial Zn powders and graphene oxide (GO). The formed binder-free three-dimensional (3D) anode Zn_G achieves a cycling time over 550 h and extremely low voltage hysteresis of ∼20 mV with 7.4% DOD (130 h for Zn foil with 1.3% DOD and 80 h for Zn powders with 7.4% DOD) at a current density of 1 mA cm–2 in a symmetric cell. In Zn||MnO2 full batteries, Zn_G greatly enhances the gravimetric energy density on the cell level and achieved more than 1600 cycles much higher than Zn foil (Zn_F) with 700 cycles and Zn powders (Zn_P) with 500 cycles. The low N/P ratio of 3 also achieved high stability with 126 mAh g–1 and 74.5% retention after 1000 cycles.

Cataloguing MoSi2N4 and WSi2N4 van der Waals Heterostructures: An Exceptional Material Platform for Excitonic Solar Cell Applications

Abstract2D materials van der Waals heterostructures (vdWHs) provide a revolutionary route toward high‐performance solar energy conversion devices beyond the conventional silicon‐based pn junction solar cells. Despite tremendous research progress accomplished in recent years, the searches of vdWHs with exceptional excitonic solar cell conversion efficiency and optical properties remain an open theoretical and experimental quest. Here, this study shows that the vdWH family composed of MoSi2N4 and WSi2N4 monolayers provides a compelling material platform for developing high‐performance ultrathin excitonic solar cells and photonics devices. Using first‐principle calculations, 51 types of MoSi2N4 and WSi2N4‐based [(Mo,W)Si2N4] vdWHs composed of various metallic, semimetallic, semiconducting, insulating, and topological 2D materials are constructed and classified. Intriguingly, MoSi2N4/(InSe, WSe2) are identified as Type II vdWHs with exceptional excitonic solar cell power conversion efficiency reaching well over 20%, which are competitive to state‐of‐the‐art silicon solar cells. The (Mo,W)Si2N4 vdWH family exhibits strong optical absorption in both the visible and UV regimes. Exceedingly large peak UV absorptions over 40%, approaching the maximum absorption limit of a freestanding 2D material, can be achieved in (Mo,W)Si2N4/α2‐(Mo,W)Ge2P4 vdWHs. The findings unravel the enormous potential of (Mo,W)Si2N4 vdWHs in designing ultimately compact excitonic solar cell device technology.

Effectiveness of the analytical models used in standard techniques for mechanical property characterization of 2D materials

Two dimensional (2D) materials are usually assumed to be continuum thin films to study their mechanical behavior. Freestanding indentation testing and pressure bulge testing are two standard techniques for characterizing the mechanical properties of thin films. Compared with the former, the latter is far less often used to characterize the elastic moduli of 2D materials, even though there is no solid evidence to show that the former is more effective than the latter. In the present work, the effectiveness of the analytical models adopted in both approaches on determining the elastic moduli of 2D materials are investigated using numerical analysis, which can be evaluated based upon the accuracy of the determined elastic moduli, and the effects of Poisson’s ratio and the applied loading range are also considered. To account for the effect of the adhesive boundary condition of freestanding 2D materials in the testing, the numerical simulations of the initially unstressed samples, pre-stretched samples and slack samples are all analyzed in the present work. It is found that the bulge testing model is actually more effective than the indentation model on determining the mechanical properties of 2D materials.

Shape morphing of plastic films

Three-dimensional (3D) architectures have qualitatively expanded the functions of materials and flexible electronics. However, current fabrication techniques for devices constrain their substrates to 2D geometries and current post-shape transformation strategies are limited to heterogenous or responsive materials and are not amenable to free-standing inert plastic films such as polyethylene terephthalate (PET) and polyimide (PI), which are vital substrates for flexible electronics. Here, we realize the shape morphing of homogeneous plastic films for various free-standing 3D frameworks from their 2D precursors by introducing a general strategy based on programming the plastic strain in films under peeling. By modulating the peeling parameters, previously inaccessible free-standing 3D geometries ranging from millimeter to micrometer were predicted theoretically and obtained experimentally. This strategy is applicable to most materials capable of plastic deformation, including polymers, metals, and composite materials, and can even enable 4D transformation with responsive plastic films. Enhanced performance of 3D circuits and piezoelectric systems demonstrates the enormous potential of peeling-induced shape morphing for 3D devices.

One-step electrodeposition of Ni-Mo electrode with column-pyramid hierarchical structure for highly-efficient hydrogen evolution

The construction of transition metal alloys with 3D structure facilitates their catalytic activity towards hydrogen evolution reaction. Although this can be achieved by the wet chemical and template strategies, the uncertainty of reaction process inevitably results in the difficulty of the repeatability of product synthesis. Herein, we present the rationally designed 3D Ni-Mo with a typical hierarchical structure on Ni foam by combing ‘hydrogen bubble template’ and ‘tip effect’ via one-step electrodeposition. This 3D Ni-Mo/NF has both regular columnar structures of micron level and widespread pyramidal-like nanoparticles, which only needs an overpotential of 53 mV and 161 mV to afford 10 mA cm−2 and 100 mA cm−2 for HER in 1 M KOH, respectively. In addition, a small Tafel slope (42.6 mV dec-1), and long-term operational stability are achieved on the catalyst. The excellent performance can be traced to the amorphous and hierarchical structure with favorable active sites. Furthermore, the network structure of the nickel foam substrate can promote the diffusion and infiltration of electrolyte. Impressively, this electrode exhibits super hydrophilic, which facilitates the detachment of bubbles. The free-standing 3D catalysts in this study can be synthesized in a facile and viable way, indicating their promising tactic for scaled-up water electrolysis.

TaIrTe4 Monolayer with Topological Insulator Characteristic: A New and Highly Efficient Electrocatalyst toward Oxygen Reduction Reaction

Topological materials with robust topological surface states can be a class of very promising catalysts in electrocatalysis. In this study, a freestanding 2D topological insulator (TI) nanomaterial, namely, TaIrTe4 monolayer with low Ir-loading, which can be exfoliated from the bulk phase with the layered structure, is demonstrated to be dynamically, mechanically, and thermodynamically stable under the first-principles calculations. More intriguingly, coupled with good conductivity, a 2D TaIrTe4 monolayer can be considered as an alternative to noble metal Pt-based electrocatalyst for the oxygen reduction reaction (ORR). Our calculations revealed that on the surface of the TaIrTe4 monolayer, the adsorbed O2 molecules can be effectively activated and dissociated into two separated O* species through a very small energy barrier (0.28 eV, even lower than that of Pt(111)). When the four-electron (4e) dissociation path of ORR occurs on the TaIrTe4 monolayer, a very small overpotential of 0.47 V can be observed, which can be even comparable to the Pt(111) surface. In addition, the 2D TaIrTe4 monolayer can also exhibit high selectivity, effectively inhibiting the formation of byproduct H2O2. It can be revealed that the TI topological states can have an important effect on the excellent ORR catalytic activity of the 2D TaIrTe4 monolayer. Undoubtedly, the design of ORR electrocatalysts based on the fascinating topological materials can be a new and effective way to replace the precious metal Pt-based ORR electrocatalysts.

Subaqueous free-standing 3D cell culture system for ultrafast cell compaction, mechano-inductive immune control, and improving therapeutic angiogenesis.

Conventional 3D cell culture methods require a comprehensive complement in labor-intensive and time-consuming processes along with in vivo circumstantial mimicking. Here, we describe a subaqueous free-standing 3D cell culture (FS) device that can induce the omnidirectional environment and generate ultrafast human adipose-derived stem cells (hADSCs) that efficiently aggregate with compaction using acoustic pressure. The cell culture conditions were optimized using the FS device and identified the underlying molecular mechanisms. Unique phenomena in cell aggregation have led to extraordinary cellular behavior that can upregulate cell compaction, mechanosensitive immune control, and therapeutic angiogenesis. Therefore, we designated the resulting cell aggregates as "pressuroid." Notably, external acoustic stimulation produced by the FS device affected the pressuroids. Furthermore, the pressuroids exhibited upregulation in mechanosensitive genes and proteins, PIEZO1/2. CyclinD1 and PCNA, which are strongly associated with cell adhesion and proliferation, were elevated by PIEZO1/2. In addition, we found that pressuroids significantly increase angiogenic paracrine factor secretion, promote cell adhesion molecule expression, and enhance M2 immune modulation of Thp1 cells. Altogether, we have concluded that our pressuroid would suggest a more effective therapy method for future cell therapy than the conventional one.

Corrugations in Free-Standing Graphene.

Although both the tendency of 2D materials to bend out of plane as well as its effect on materials’ properties are well known, the factors influencing this phenomenon have not been extensively studied. Graphene, the one-atom-thick membrane of carbon atoms, is both arguably the best known 2D material, as well as the most prone to spontaneous corrugations. Here, we use electron diffraction to systematically study the factors influencing corrugations in graphene, including the size of the free-standing area, the preparation method, the amount of surface contamination, and electron-beam-induced structural disorder. We find that mechanically exfoliated graphene is less corrugated than graphene grown via chemical vapor deposition (corrugation amplitude of Å compared to Å for a free-standing area with a diameter of m). Similarly, corrugation amplitude grows by more than a factor of two when the diameter of the free- standing area is increased from m to ca. m. Electron beam irradiation affects the corrugation in two ways, firstly by removing the hydrocarbon contamination, which decreases corrugation, and secondly by creating increasing amounts of disorder into the material, which again increases corrugation. Overall, our results show that control over the sample during both initial preparation and post-preparation treatment allows for a change in the amount of corrugation in free-standing 2D materials, which may lead to new advances in their use in applications.

Carbonized Bacterial Cellulose Decorated with ZIF-8 Derived Iron Single-Atom Catalyst Nanocages As a Cathode Host for Lithium-Sulfur Batteries

Li-S chemistry is regarded as promising next-generation battery technology. However, its complex redox process and long-chain lithium polysulfides shuttling are hindering the development of practical Li-S battery technology. Various electrocatalysts are being investigated to address the problem by expediting reaction kinetics. Here we report Fe single metal atom catalyst (Fe-SAC) used in the sulfur cathode of Li-S batteries.Fe-SAC is synthesized using a modified metal-organic framework (MOF)-based approach, in which the low vapor pressure Fe element substitutes Zn during pyrolysis of ZIF-8 to attain Fe-N4 moieties by being coordinated with four substitutional nitrogen atoms in the graphene lattice. A freestanding 3D structure with Fe-SAC-functionalized carbon nanocages linked by a carbon nanofiber network is applied as the sulfur cathode scaffold. Here the nanocages are derived from Fe-doped ZIF with Fe-N4 SAC moieties embedded on the inside and outside surfaces. The carbon nanofiber network is derived from the carbonization of bacterial cellulose.We report several methods for assessing Fe-SAC catalytic function on sulfide redox reactions for the prepared electrode in cells with lithium polysulfides electrolytes. Electrochemical studies compare the performance of the nanostructured electrodes with or without Fe-SAC to confirm the catalytic effects in improving the Li-S battery performance. Accordingly, the prepared composite cathode delivers a high initial capacity of 1338 mAh/g at 0.1C and excellent rate capability at 2C with a reversible capacity of 840 mAh/g.

3D printed freestanding ZnSe/NC anodes for Li-ion microbatteries

The rapid development of micro/nanomanufactured integrated microsystems in recent years requires high performance micro energy storage devices (MESDs). Li-ion microbatteries (LIMBs) are the most studied MESDs, but the low mass loading of active materials and the less-than-perfect energy density hinder their further application. A 3D printed ZnSe/N-doped carbon (ZnSe/NC) electrode was designed and fabricated by extrusion-based 3D printing and a post-treatment strategy as the anode of LIMBs. The high-capacity ZnSe nanoparticles are confined in the NC, where the NC not only improves the conductivity but also acts as a buffer layer to reduce the volume expansion and provide additional active sites for electrochemical reactions. The interconnected design of the 3D printed electrode is good for fast mass transfer and ion transport. A freestanding 3D printed ZnSe/NC electrode with a high mass loading of 3.15 mg cm−2 was achieved by direct ink printing, which had a superior energy density and decent reversibility in high-power LIMBs. This strategy can be used for other high-performance electrodes to achieve a high-mass-loading of active materials for microbatteries, opening up a new way to construct advanced MESDs.

Chemically exfoliated nanosheets of β-Bi2O3

Exploring two dimensional (2D) materials is important for further developing the field of quantum materials. However, progress in 2D material development is limited by difficulties with their production. Specifically, freestanding 2D materials with bulk non-layered structures remain particularly challenging to prepare. Traditionally, chemical or mechanical exfoliation is employed for obtaining freestanding 2D materials, but these methods typically require layered starting materials. Here we put forth a method for obtaining thin layers of β-Bi2O3, which has a three-dimensional covalent structure, by using chemical exfoliation. In this research, Na3Ni2BiO6 was exfoliated with acid and water to obtain β-Bi2O3 nanosheets less than 10 nm in height and over 1 µm in lateral size. Our results open the possibility for further exploring β-Bi2O3 nanosheets to determine whether their properties change from the bulk to the nanoscale. Furthermore, this research may facilitate further progress in obtaining nanosheets of non-layered bulk materials using chemical exfoliation.

Ultrathin Metal-Organic Framework Nanosheets Exhibiting Exceptional Catalytic Activity.

Two-dimensional (2D) metal-organic framework nanosheets (MONs) or membranes are classes of periodic, crystalline polymeric materials that may show unprecedented physicochemical properties due to their modular structures, high surface areas, and high aspect ratios. Yet preparing 2D MONs from multiple components and two different types of polymerization reaction remains challenging and less explored. Here, we report the synthesis of MOF films via interfacial polymerization, which involves three active monomers for simultaneous polycondensation and polycoordination taking place in a confined interface. The well-defined lamellar structure of the MOF films allowed feasible and scalable exfoliation to produce free-standing 2D MONs with high aspect ratio up to 2000:1 and ultrathin thickness (∼1.7 nm). The pore structure was revealed by high-resolution TEM images with near-atomic precision. The imide-linkage of MONs provided superior thermal (up to 530 °C) and good chemical stability in the pH range from 3 to 12. More importantly, the MONs exhibited exceptional catalytic activity and superior reusability for the hydroboration reactions of alkynes, in which the turnover frequency (TOF) reached 41734 h-1, which is 2-4 orders of magnitude greater than that reported for homogeneous and heterogeneous catalysts.

Free-standing 3D porous energy hydrogels enabled by ion-induced gelation strategy for High-performance supercapacitors

Two-dimensional (2D) materials, such as MXene and graphene, are considered as the ideal alternative electrode materials for high energy density supercapacitors. However, the inevitable collapsing and restacking problems caused by the van der Waals force will reduce their active surface sites and slow down the rate of ion transportation and thus cause the degradation of electrochemical performance. Hence, in this paper, we reported a facile and environment-friendly method to synthesize 3D Ti3C2Tx/rGO hybrid composite through an ion-induced gelation approach. With the assistance of Fe2+, Ti3C2Tx and rGO nanosheets converge to form a 3D porous Ti3C2Tx/rGO-Fe hydrogel with a high specific surface area of 59.5 m2 g−1. By optimizing the ratio of MXene and rGO, the resultant Ti3C2Tx/rGO-Fe electrode displays a maximum specific capacitance of 3194 mF cm−2 at 1 mA cm−2. Meanwhile, the assembled Ti3C2Tx/rGO-Fe//Ti3C2Tx/rGO-Fe symmetric supercapacitor delivers a maximum energy density of 76.3 μWh cm−2 at a power density of 500 μW cm−2 and unparalleled cycling performance with 95.6 % capacitance retention after 5000 cycles at 6 mA cm−2. This work demonstrates that the ion-induced gelation method for preparing 3D MXene/rGO hydrogel has great potential in applying high-performance electrode materials for supercapacitors.

Thermally Chargeable Supercapacitor with 3D Ti3C2Tx MXene Hollow Sphere Based Freestanding Electrodes

AbstractThermally chargeable supercapacitors (TCSCs) are emerging and promising devices that could convert thermal energy spontaneously existing in nature into electricity and then store energy for further utilization. Herein, this work reports on the freestanding 3D Ti3C2Tx MXene‐based TCSC, where lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), poly(ethylene oxide) (PEO), and polyvinylidene fluoride‐hexafluoropropylene (PVDF‐HFP) serve as gel electrolyte. Different from the semiconductor‐based thermoelectric materials, the fabricated Ti3C2Tx TCSC exhibits a high Seebeck coefficient of 78.4 mV K−1. Moreover, when applying a temperature difference (ΔT) of 5.8 K between the cold and hot sides, the Ti3C2Tx TCSC devices provide a stable high voltage of 400.6 mV. The charging/discharging cycles of the Ti3C2Tx TCSC devices upon periodic ΔT of 3.3 and 5.8 K demonstrate their excellent stability. To realize the practical application, the four Ti3C2Tx TCSCs devices connected in series are charged by supplying a ΔT of 5.8 K and used to power a digital timer, demonstrating the possibility and application of the TCSCs in self‐powered integrated electronics.