In Situ Spontaneous Construction of Zinc Phosphate Coating Layer Toward Highly Reversible Zinc Metal Anodes.

Aqueous zinc ion batteries have received widespread attention due to their merits of high safety, high theoretical specific capacity, low cost, and environmental benignity. Nevertheless, the irreversible issues of Zn anode deriving from side reactions and dendrite growth have hindered its commercialization in large-scale energy storage systems. Herein, a zinc phosphate tetrahydrate (Zn3 (PO4 )2 ·4H2 O, ZnPO) coating layer is in situ formed on the bare Zn by spontaneous redox reactions at room temperature to tackle the above issues. Particularly, the dense and brick-like ZnPO layer can effectively separate the anode surface from the aqueous electrolyte, thus suppressing the serious side reactions. Moreover, the ZnPO layer with high ionic conductivity, high Zn2+ transference number, and low nucleation barrier permits rapid Zn2+ transport and enables uniform Zn deposition, ensuring dendrite-free Zn deposition. As a result, the ZnPO@Zn symmetric battery achieves a high Coulombic efficiency of 99.8% and displays ultrahigh cycle stability over 6000 h (> 8 months), far surpassing its counterparts. Furthermore, the ZnPO@Zn||MnO2 full battery exhibits excellent electrochemical performances. Therefore, this work provides a new reference for simple and large-scale preparation of highly reversible Zn metal anodes, and has great potential for practical applications.

Tough Bonding of PVA Hydrogel-on-Textured Titanium Alloy with Varying Texture Densities in Swollen State.

Cartilage defects in large joints are a common occurrence in numerous degenerative diseases, especially in osteoarthritis. The hydrogel-on-metal composite has emerged as a potential candidate material, as hydrogels, to some extent, replicate the composition of human articular cartilage consisting of collagen fibers and proteoglycans. However, achieving tough bonding between the hydrogel and titanium alloy remains a significant challenge due to the swelling of the hydrogel in a liquid medium. This swelling results in reduced interfacial toughness between the hydrogel and titanium alloy, limiting its potential clinical applications. Herein, our approach aimed to achieve durable bonding between a hydrogel and a titanium alloy composite in a swollen state by modifying the surface texture of the titanium alloy. Various textures, including circular and triangular patterns, with dimple densities ranging from 10 to 40%, were created on the surface of the titanium alloy. Subsequently, poly(vinyl alcohol) (PVA) hydrogel was deposited onto the textured titanium alloy using a casting-drying method. Our findings revealed that PVA hydrogel on the textured titanium alloy with a 30% texture density exhibited the highest interfacial toughness in the swollen state, measuring at 1300 J m-2 after reaching equilibrium swelling in deionized water, which is a more than 2-fold increase compared to the hydrogel on a smooth substrate. Furthermore, we conducted an analysis of the morphologies of the detached hydrogel from the textured titanium alloy after various swelling durations. The results indicated that interfacial toughness could be enhanced through mechanical interlocking, facilitated by the expanded volume of the hydrogel protrusions as the swelling time increased. Collectively, our study demonstrates the feasibility of achieving tough bonding between a hydrogel and a metal substrate in a liquid environment. This research opens up promising avenues for designing soft/hard heterogeneous materials with strong adhesive properties.

Clay-Originated Two-Dimensional Holey Silica Separator for Dendrite-Free Lithium Metal Anode.

Lithium metal anode is the ultimate choice to obtain next-generation high-energy-density lithium batteries, while the dendritic lithium growth owing to the unstable lithium anode/electrolyte interface largely limits its practical application. Separator is an important component in batteries and separator engineering is believed to be a tractable and effective way to address the above issue. Separators can play the role of ion redistributors to guide the transport of lithium ions and regulate the uniform electrodeposition of Li. The electrolyte wettability, thermal shrinkage resistance, and mechanical strength are of importance for separators. Here, clay-originated two-dimensional (2D) holey amorphous silica nanosheets (ASN) to develop a low-cost and eco-friendly inorganic separator is directly adopted. The ASN-based separator has higher porosity, better electrolyte wettability, much higher thermal resistance, larger lithium transference number, and ionic conductivity compared with commercial separator. The large amounts of holes and rich surface oxygen groups on the ASN guide the uniform distribution of lithium-ion flux. Consequently, the Li//Li cell with this separator shows stable lithium plating/stripping, and the corresponding Li//LiFePO4 , Li//LiCoO2, and Li//NCM523 full cells also show high capacity, excellent rate performance, and outstanding cycling stability, which is much superior to that using the commercial separator.

Graphene mitigated fracture and interfacial delamination of silicon film anodes through modulating the stress generation and development.

Silicon film is an attractive anode candidate in lithium ion batteries due to its two-dimensional (2D) morphology that is beneficial to buffer the large volume expansion of traditional silicon anodes. Even so, the generation of stress during the lithiation/delithiation process can still lead to the cracking and delamination of the silicon film from the current collector, ultimately resulting in the fast failure of the electrode. Laying a graphene layer between the silicon film and the current collector has been demonstrated to alleviate the stress generated during the battery cycling, but its universal application in commercial silicon structures with other dimensionalities remains technically challenging. Putting graphene on top of a 2D silicon film is more feasible and has also been shown with enhanced cycling stability, but the underneath mechanical mechanisms remain unclear. Herein, using the combination of 2D graphene and 2D silicon films as a model material, we investigate the stress generation and diffusion mode during the battery cycling to disclose the mechanical and electrochemical optimization of a silicon anode experimentally and theoretically. As a result, the optimum thickness of the silicon film and the coated graphene layers are obtained, and it is found the in-plane cracking and out-of-plane delamination of the silicon film could be mitigated by coating graphene due to the slow transfer of the normal and shear stresses. This work provides some understanding of the electrochemically derived mechanical behaviors of the graphene-coated battery materials and guidelines for developing stable high-energy-density batteries.

Graphene Emerges as a Versatile Template for Materials Preparation.

Graphene and its derivatives are emerging as a class of novel but versatile templates for the controlled preparation and functionalization of materials. In this paper a conceptual review on graphene-based templates is given, highlighting their versatile roles in materials preparation. Graphene is capable of acting as a low-dimensional hard template, where its two-dimensional morphology directs the formation of novel nanostructures. Graphene oxide and other functionalized graphenes are amphiphilic and may be seen as soft templates for formatting the growth or inducing the controlled assembly of nanostructures. In addition, nanospaces in restacked graphene can be used for confining the growth of sheet-like nanostructures, and assemblies of interlinked graphenes can behave either as skeletons for the formation of composite materials or as sacrificial templates for novel materials with a controlled network structure. In summary, flexible graphene and its derivatives together with an increasing number of assembled structures show great potentials as templates for materials production. Many challenges remain, for example precise structural control of such novel templates and the removal of the non-functional remaining templates.

Mixed-Dimensional Assembly Strategy to Construct Reduced Graphene Oxide/Carbon Foams Heterostructures for Microwave Absorption, Anti-Corrosion and Thermal Insulation.

Considering the serious electromagnetic wave (EMW) pollution problems and complex application condition, there is a pressing need to amalgamate multiple functionalities within a single substance. However, the effective integration of diverse functions into designed EMW absorption materials still faces the huge challenges. Herein, reduced graphene oxide/carbon foams (RGO/CFs) with two-dimensional/three-dimensional (2D/3D) van der Waals (vdWs) heterostructures were meticulously engineered and synthesized utilizing an efficient methodology involving freeze-drying, immersing absorption, secondary freeze-drying, followed by carbonization treatment. Thanks to their excellent linkage effect of amplified dielectric loss and optimized impedance matching, the designed 2D/3D RGO/CFs vdWs heterostructures demonstrated commendable EMW absorption performances, achieving a broad absorption bandwidth of 6.2 GHz and a reflection loss of - 50.58 dB with the low matching thicknesses. Furthermore, the obtained 2D/3D RGO/CFs vdWs heterostructures also displayed the significant radar stealth properties, good corrosion resistance performances as well as outstanding thermal insulation capabilities, displaying the great potential in complex and variable environments. Accordingly, this work not only demonstrated a straightforward method for fabricating 2D/3D vdWs heterostructures, but also outlined a powerful mixed-dimensional assembly strategy for engineering multifunctional foams for electromagnetic protection, aerospace and other complex conditions.

The promotion of vascular reconstruction by hierarchical structures in biodegradable small-diameter vascular scaffolds.

Tissue engineering of small-diameter vessels remains challenging due to the inadequate ability to promote endothelialization and infiltration of smooth muscle cells (SMCs). Ideal vascular graft is expected to provide the ability to support endothelial monolayer formation and SMCs infiltration. To achieve this, vascular scaffolds with both orientation and dimension hierarchies were prepared, including hierarchically random vascular scaffold (RVS) and aligned vascular scaffold (AVS), by utilizing degradable poly(ε-caprolactone)-co-poly(ethylene glycol) (PCE) and the blend of PCE/gelatin (PCEG) as raw materials. In addition to the orientation hierarchy, dimension hierarchy with small pores in the inner layer and large pores in the outer layer was also constructed in both RVS and AVS to further investigate the promotion of vascular reconstruction by hierarchical structures in vascular scaffolds. The results show that the AVS with an orientation hierarchy that consists with the natural vascular structure had better mechanical properties and promotion effect on the proliferation of vascular cells than RVS, and also exhibited excellent contact guidance effects on cells. While the dimension hierarchy in both RVS and AVS was favorable to the rapid infiltration of SMCs in a short culture time in vitro. Besides, the results of subcutaneous implantation further demonstrate that AVS achieved a fully infiltrated outer layer with wavy elastic fibers-mimic strips formation by day 14, ascribing to hierarchies of aligned orientation and porous dimension. The results further indicate that the scaffolds with both orientation and dimension hierarchical structures have great potential in the application of promoting the vascular reconstruction.

A Cu-Ag double-layer coating strategy for stable and reversible Zn metal anodes.

Structuring a stable artificial coating to mitigate dendrite growth and side reactions is an effective strategy for protecting the Zn metal anode. Herein, a Cu-Ag double-layer metal coating is constructed on the Zn anode (Zn@Cu-Ag) by simple and in-situ displacement reactions. The Cu layer enhances the bond between the Ag layer and Zn substrate by acting as an intermediary, preventing the Ag coating from detachment. Concurrently, the Ag layer serves to improve the corrosion resistance of Cu metal. During plating, the initial Cu sheets and Ag particles on the surface of Zn@Cu-Ag electrode gradually transform into a flat and smooth layer, resulting in the formation of AgZn, AgZn3, and (Ag, Cu)Zn4 alloys. Alloys play a multifunctional role in inhibiting dendrite growth and side reactions due to decreased resistance, low nucleation barrier, enhanced zincophilicity, and strong corrosion resistance. Consequently, the Zn@Cu-Ag symmetric cell exhibits continuous stable performance for 3750 h at 1 mA cm-2. Furthermore, the Zn@Cu-Ag||Zn3V3O8 full cell achieves an initial capacity of 293.4 mAh g-1 and realizes long cycling stability over 1200 cycles. This work provides new insight into the engineering of an efficient artificial interface for highly stable and reversible Zn metal anodes.

Approach to Significantly Enhancing the Electrochromic Performance of PANi by In Situ Electrodeposition of the PANi@MXene Composite Film.

Electrochromic materials (ECMs) are capable of reversibly adjusting their transmittance or reflectance properties in response to changes in the external biasing voltages. In this study, we enhanced the electrochromic and electrochemical properties of polyaniline (PANi) effectively through the incorporation of MXene Ti2CTx using an in situ composite strategy. This improvement in the electrochromic and electrochemical properties observed can be attributed to the intermolecular forces between the aniline group of PANi and the terminal groups of MXene Ti2CTx sheets. The presence of hydrogen bonds between the PANi monomers and the MXene sheets was confirmed through theoretical calculations and photoluminescence results, which effectively improved the composite interfaces. Additionally, the PANi@MXene composite films were successfully prepared through a simple one-step in situ polymerization process, as verified by SEM and XPS characterization. The electrochemical studies revealed enhanced electronic conductivity, a high ion diffusion coefficient, and a narrow energy redox gap, all contributing to the excellent electrochemical properties observed. Overall, our results demonstrate that the MXene Ti2CTx composition effectively enhances the electrochromic performance of PANi. The PANi@MXene composite films exhibited a high optical modulation range, rapid switching response time, good thermal radiation regulation, and excellent operational stability. This composite strategy significantly improves the performance and practical applicability of ECMs.

In-situ formed Cyclodextrin-functionalized graphene oxide / poly (N-isopropylacrylamide) nanocomposite hydrogel as an recovery adsorbent for phenol and microfluidic valve.

Phenolic compounds are important industrial raw materials for various industrial applications, but phenol-containing wastewater creates significant environmental and biological hazards. To address these issues, a three-dimensional network graphene oxide-cyanoethyltriethoxysilane-ß-cyclodextrin/poly (N-isopropylacrylamide) (GO-CTES-ß-CD/PNIPAM) nanocomposite hydrogel as a phenol recovery adsorbent is prepared herein by in-situ polymerization. Double graft modification on the graphene oxide (GO) via the silane coupling agent 2-cyanoethyltriethoxysilane (CTES) and single (6-tetraethylenepentamine-6-deoxy)-ß-cyclodextrin (NH-ß-CD) compensated the loss of the active sites on both GO and N-isopropylacrylamide (NIPAM), and the hydrogel shows excellent mechanical properties as the chemical crosslinking and physical entanglement of the two components. Consequently, the composite hydrogel achieved an adsorption capacity of 131.64 mg·g-1 for the common environmental toxin 4-NP. After five repeated adsorption-desorption cycles, the hydrogel retained 74% of the initial 4-NP removal ratio. The adsorption results followed pseudo-first-order kinetics, corresponding to heterogeneous multilayer adsorption, which was regulated by a combination of surface adsorption and intra-particle diffusion mechanisms. In general, the nanocomposite hydrogel shows promising application in the field of recycling phenols from wastewater. Also, high photothermal conversion and temperature-sensitive properties are also demonstrated, which makes the hydrogel possessing great potential to be applied in smart microvalves.

Solid Carbon Spheres with Interconnected Open Pore Channels Enabling High-Efficient Polysulfide Conversion for High-Rate Lithium-Sulfur Batteries.

Hollow carbon spheres or core-sheath porous carbon spheres have been widely used in the S cathode of lithium-sulfur batteries. However, the sphere shells or the pore walls may block the free transport of active species to a certain extent and may have a negative influence on the effective accommodation of elemental sulfur. Herein, solid but porous carbon spheres (PNCS) with large porosity and high specific surface area are developed, which enable high sulfur loading and ample cathode/electrolyte contact area, and the interconnected open pore channels significantly shorten the ion/electron transport pathways. Together with high-conducting nitrogen-doped graphene (NG), facilitated polysulfide conversion kinetics is realized in the as-assembled Li-S batteries, which deliver a high initial discharge capacity of 1445 mAh g-1 at 0.2 C, excellent rate capability of 872 mAh g-1 at 4 C, and low capacity decay of 0.047% per cycle for 500 cycles at 1 C. Even under high sulfur loading of 5.5 mg cm-2 and low electrolyte/sulfur (E/S) ratio of 5 µL mg-1, the Li-S batteries still display high specific capacities of 896 mAh g-1 and 4.96 mAh cm-2. The real application of PNCS/NG is also demonstrated by the corresponding Li-S pouch cells showing high discharging capacity and stable open circuit voltage. This work exhibits the promising application of the solid carbon spheres as the S host for effectively addressing the polysulfide shuttle and propelling the development of high-performance Li-S batteries.

Cation Vacancy-Boosted Lewis Acid-Base Interactions in a Polymer Electrolyte for High-Performance Lithium Metal Batteries.

Polymer electrolytes have gained extensive attention owing to their high flexibility, easy processibility, intrinsic safety, and compatibility with current fabrication technologies. However, their low ionic conductivity and lithium transference number have largely impaired their real application. Herein, novel two-dimensional clay nanosheets with abundant cation vacancies are created and incorporated in a poly(ethylene oxide) (PEO)/poly(vinylidene fluoride-co-hexafluoropropylene)-blended polymer-based electrolyte. The characterization and simulation results reveal that the cation vacancies not only provide lithium ions with additional Lewis acid-base interaction sites but also protect the PEO chains from being oxidized by excess lithium ions, which enhances the dissociation of lithium salts and the hopping mechanism of lithium ions. Benefiting from this, the polymer electrolyte shows a high ionic conductivity of 2.6 × 10-3 S cm-1 at 27 °C, a large Li+ transference number up to 0.77, and a wide electrochemical stability window of 4.9 V. Furthermore, the LiFePO4∥Li coin cell with such a polymer electrolyte delivers a high specific capacity of 145 mA h g-1 with an initial Coulombic efficiency of 99.9% and a capacity retention of 97.3% after 100 cycles at ambient temperature, as well as a superior rate performance. When pairing with high-voltage cathodes LiCoO2 and LiNi0.5Mn1.5O4, the corresponding cells also exhibit favorable electrochemical stability and a high capacity retention. In addition, the LiFePO4∥Li pouch cells display high safety even under rigorous conditions including corner-cut, bending, and nail-penetration.

Two-Dimensional Nanochannel Arrays Based on Flexible Montmorillonite Membranes.

Two-dimensional (2D) nanochannel arrays are constructed by bottom-up reassembly of montmorillonite monolayers that are obtained by liquid-phase exfoliation of its layered crystals, and the as-constructed interstitial space between these monolayers is uniform and provides ions with nanoscale transport channels. Surface-charge-controlled ion transport behavior is observed through these nanochannels as the electrolyte concentration reduces to 10-4 M at room temperature. Furthermore, the nanochannel structure remains even after 400 °C heat treatment, and nanofluidic devices based on the annealed nanochannel arrays still exhibit surface-charge-governed ion transport at low electrolyte concentrations. In addition, a drift-diffusion experiment is conducted to investigate the mobility ratio of cations/anions through the nanochannels with asymmetric bulk electrolyte concentrations, and the results show that the mobility of cations is about eight to nine times that of anions, which is consistent with the fact that the montmorillonite monolayers are negatively charged and the nanochannels are permselective. Last, ionic current rectification is observed in the nanofluidic system of asymmetric geometric shape, and rectification factors of ∼2.6 and ∼3.5 can be obtained in KCl and HCl electrolytes, respectively, at a bias between -1 and +1 V because of the asymmetric electrostatic potential through the nanochannels.

Self-assembled two-dimensional nanofluidic proton channels with high thermal stability.

Exfoliated two-dimensional (2D) sheets can readily stack to form flexible, free-standing films with lamellar microstructure. The interlayer spaces in such lamellar films form a percolated network of molecularly sized, 2D nanochannels that could be used to regulate molecular transport. Here we report self-assembled clay-based 2D nanofluidic channels with surface charge-governed proton conductivity. Proton conductivity of these 2D channels exceeds that of acid solution for concentrations up to 0.1 M, and remains stable as the reservoir concentration is varied by orders of magnitude. Proton transport occurs through a Grotthuss mechanism, with activation energy and mobility of 0.19 eV and 1.2 × 10(-3) cm(2) V(-1) s(-1), respectively. Vermiculite nanochannels exhibit extraordinary thermal stability, maintaining their proton conduction functions even after annealing at 500 °C in air. The ease of constructing massive arrays of stable 2D nanochannels without lithography should prove useful to the study of confined ionic transport, and will enable new ionic device designs.

Self-assembly of graphene oxide at interfaces.

Due to its amphiphilic property, graphene oxide (GO) can achieve a variety of nanostructures with different morphologies (for example membranes, hydrogel, crumpled particles, hollow spheres, sack-cargo particles, Pickering emulsions, and so on) by self-assembly. The self-assembly is mostly derived from the self-concentration of GO sheets at various interfaces, including liquid-air, liquid-liquid and liquid-solid interfaces. This paper gives a comprehensive review of these assembly phenomena of GO at the three types of interfaces, the derived interfacial self-assembly techniques, and the as-obtained assembled materials and their properties. The interfacial self-assembly of GO, enabled by its fantastic features including the amphiphilicity, the negatively charged nature, abundant oxygen-containing groups and two-dimensional flexibility, is highlighted as an easy and well-controlled strategy for the design and preparation of functionalized carbon materials, and the use of self-assembly for uniform hybridization is addressed for preparing hybrid carbon materials with various functions. A number of new exciting and potential applications are also presented for the assembled GO-based materials. This contribution concludes with some personal perspectives on future challenges before interfacial self-assembly may become a major strategy for the application-targeted design and preparation of functionalized carbon materials.

Graphene oxide assisted hydrothermal carbonization of carbon hydrates.

Hydrothermal carbonization (HTC) of biomass such as glucose and cellulose typically produces micrometer-sized carbon spheres that are insulating. Adding a very small amount of Graphene oxide (GO) to glucose (e.g., 1:800 weight ratio) can significantly alter the morphology of its HTC product, resulting in more conductive carbon materials with higher degree of carbonization. At low mass loading level of GO, HTC treatment results in dispersed carbon platelets of tens of nanometers in thickness, while at high mass loading levels, free-standing carbon monoliths are obtained. Control experiments with other carbon materials such as graphite, carbon nanotubes, carbon black, and reduced GO show that only GO has significant effect in promoting HTC conversion, likely due to its good water processability, amphiphilicity, and two-dimensional structure that may help to template the initially carbonized materials. GO offers an additional advantage in that its graphene product can act as an in situ heating element to enable further carbonization of the HTC products very rapidly upon microwave irradiation. Similar effect of GO is also observed for the HTC treatment of cellulose.

On the origin of the stability of graphene oxide membranes in water.

Graphene oxide (GO) films are known to be highly stable in water and this property has made their use in membrane applications in solution possible. However, this state of affairs is somewhat counterintuitive because GO sheets become negatively charged on hydration and the membrane should disintegrate owing to electrostatic repulsion. We have now discovered a long-overlooked reason behind this apparent contradiction. Our findings show that neat GO membranes do, indeed, readily disintegrate in water, but the films become stable if they are crosslinked by multivalent cationic metal contaminants. Such metal contaminants can be introduced unintentionally during the synthesis and processing of GO, most notably on filtration with anodized aluminium oxide filter discs that corrode to release significant amounts of aluminium ions. This finding has wide implications in interpreting the processing-structure-property relationships of GO and other lamellar membranes. We also discuss strategies to avoid and mitigate metal contamination and demonstrate that this effect can be exploited to synthesize new membrane materials.

Nanospace-confined formation of flattened Sn sheets in pre-seeded graphenes for lithium ion batteries.

Flattened Sn sheets are prepared from the pre-seeded Sn salt in the interlayer nanospace of a graphene membrane, which acts as a template to shape Sn crystals and prevent the aggregation. The sandwich structure clamping Sn sheets accommodates the volume change during charge/discharge. We show that the hybrid possesses excellent rate performance and cycling stability as an anode for lithium ion batteries.

Hybridization of graphene oxide and carbon nanotubes at the liquid/air interface.

The liquid/air interface provides an ideal platform for the uniform hybridization of multi-components in a thin graphene-based membrane through self-assembly. This study presents the first example for such a hybrid membrane which combines chemically active GO layers with highly conductive carbon nanotubes.