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Transition metal oxides are considered promising anode materials for high performance flexible electrodes due to their abundant reserves and excellent specific capacity. However, their inherent low conductivity, large volume effect, and poor cycling performance limit their applications. Herein, we report a novel "spontaneous complexation and exfoliation" strategy for the fabrication of flexible MnO NCs@rGO thin-film electrodes, which overcomes the aforementioned drawbacks and pushes the mechanical flexibility and lithium-ion (Li + ) storage performance to a higher level. The combination of large-area few-layer reduced graphene oxide (rGO) films and ultrafine MnO nanocrystals (MnO NCs) provides a high density of electrochemical active sites. Notably, the layer-by-layer embedded structure not only enables the MnO NCs@rGO electrodes to withstand various mechanical deformations but also produces a strong synergistic effect of enhanced reaction kinetics by providing an enlarged electrode/electrolyte contact area and reduced electron/ion transport resistance. The elaborately designed flexible MnO NCs@rGO anode provides a specific capacity of about 1220 mAh g -1 over 1000 cycles, remarkable high-rate capacity (50.0 A g -1 ), and exceptional cycling stability. Finally, the assembled flexible lithium-ion full cells achieve zero capacity loss during repeated large-angle bending, demonstrating immense potential as a high-performance flexible energy storage device. This work provides valuable insights into unique structural designs for durable and ultra-fast lithium ion batteries.

Cells coordinate their activity and regulate biological processes in response to chemical signals. Mimicking natural processes, control over the formation of artificial supramolecular materials is of high interest for their application in biology and medicine. Supramolecular material that can form in response to chemical signals is important for the development of autonomously responsive materials. Herein, a supramolecular hydrogel system is reported enabling in situ generation of hydrogelators in response to a specific chemical signal. Using self-immolative chemistry, spatial control over the formation of supramolecular hydrogel material and structured free-standing hydrogel objects via providing H 2 O 2 locally is demonstrated. In addition, a hybrid system is developed enabling in situ generation of the H 2 O 2 by the action of an enzyme and glucose, providing an extra handle for the development of an intelligent soft material. This generic design should enable the use of various (chemical)stimuli that can be obtained via coupling different stimuli and various chemical and/or biological markers and appears a versatile approach for the design of smart artificial soft materials that can find application in theranostic purposes., (© 2024 Wiley‐VCH GmbH.)

Free-standing micro-supercapacitor (MSC) devices without substrate or current collectors are promising for practical applications. However, it is still difficult to prepare high-performance free-standing MSC devices because of the requirement of optimized active sites, conductivity, ion diffusion, controlled patterns, moisture susceptibility, etc. Here, it is proposed that the optimization of oxygen level on graphene is promising to solve these requirements because of the balance of sp 2 and sp 3 hybridization. Using the medium-oxidized graphene, the flexible, conductive, hydro-stable, easy-processing film can be facilely obtained, which facilitates the preparation of free-standing MSC electrodes. After constructing with gel electrolyte, the free-standing MSC device shows a high capacitance of 898.4 mF cm -2 using aqueous-gel electrolyte and 383.6 mF cm -2 using ion-gel electrolyte with mass loading of ca. 10 mg cm -2 . Correspondingly, the MSC device can achieve a landmark energy density of 42.6 µWh cm -2 at 0.85 mW cm -2 (7.1 mWh cm -3 at 141.7 mW cm -3 ). The advantages of high performance, facile preparation, and low inactive components make the free-standing MSC device promising for practical applications., (© 2024 Wiley‐VCH GmbH.)

Understanding of the structure and interfacial merits that reactive metal-organic frameworks (MOFs) undergo is critical for constructing efficient catalysts for non-thermal plasma-assisted conversion of greenhouse gases. Herein, we proposed a free-standing bimetallic (Co/Ni) MOFs supported on bacterial cellulose (BC) foams (Co/Ni-MOF@BC) toward the coaxial dielectric barrier discharge (DBD) plasma-catalytic system, of which the Co/Ni ions coordination demonstrated an intriguing textual uplifting of the malleable BC nanofiber network with abundant pores up to micrometer-scale, which could impart a more intensive predominant filamentary microdischarge current to 180 mA with stronger plasma-catalytic interaction. Remarkably, compared to the monometallic MOF@BC foams, this bimetallic Co/Ni-MOF@BC also delivered a substantially improved alkaline absorption ability as further confirmed by the CO 2 - temperature-programmed desorption (TPD) result. Benefiting from its 3D superiority and synergy of Co/Ni dual-regulation, the Co/Ni-MOF@BC, therefore, displayed the highest CO 2 and CH 4 conversion rates to 52.31 % and 71.50 %, which was above 1.5 and 1.3 times higher than those of monometallic counterparts and Co/Ni-MOF powder. Additionally, its robust cycling performance has also been evidenced by the excellent long-time DRM performance, unchanged crystallinity, morphology, and surface chemical states. By taking both the catalyst existing form and interfacial optimization of MOFs into consideration for designing a unique DRM catalyst, we believed this free-standing 3D Co/Ni-MOF@BC foams could inspire more research outputs on the design of functional catalysts with abundant pores and alkaline absorption sites to accelerate the redox kinetics of CO 2 /CH 4 conversion., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Developing thermoelectric films without substrates-free-standing films-eliminates substrate-induced effects on performance and meets the flexibility requirements of emerging wearable thermoelectric applications. This study investigates Gallium-doped Zinc Oxide (GZO), composed of abundant and non-toxic elements, to fabricate a substrate-free GZO film via 3D printing and compares its structural, chemical, and thermoelectric properties with those of a substrate-constrained GZO film produced through chemical deposition. Both films exhibited uniform crystal structures and phase purity; however, the substrate-constrained film displayed additional diffraction peaks, suggesting potential substrate interactions. The 3D-printed free-standing film effectively eliminated the tensile stresses observed in the substrate-constrained film. FE-STEM analysis revealed nanostructures with homogeneous elemental distribution in both films, though the substrate-constrained film showed discontinuities, such as pores, likely caused by post-deposition annealing treatment. XPS analysis highlighted differences in chemical states and elemental compositions between the films, influenced by fabrication methods, substrate-induced stresses, and surface energy mismatches. The free-standing GZO film developed through 3D printing exhibited a more balanced incorporation of Zn and O, as it was not subject to substrate or post-deposition annealing constraints. Consequently, it demonstrated a 14 % increase in electrical conductivity and a 91 % improvement in the Seebeck coefficient compared to the substrate-constrained film, resulting in a higher room-temperature power factor of 261 nW/m·K 2 . These findings underscore the potential of 3D-printed free-standing GZO films to advance thermoelectric applications, offering a promising alternative to overcome the challenges of substrate-constrained films and further drive innovation in the field., Competing Interests: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (© 2024 Published by Elsevier Ltd.)

In recent years, the automotive industry has made significant progress in integrating multifunctional sensors to improve vehicle performance, safety, and efficiency. As the number of integrated sensors keeps increasing, there is a growing interest in alternative energy sources. Specifically, self-powered sensor systems based on energy harvesting are drawing much attention, with a main focus on sustainability and reducing reliance on typical batteries. This paper demonstrates the use of triboelectric nanogenerators (TENGs) in a computer mouse for efficient energy harvesting and in automobile braking systems for safety applications using SrBi 2 Ta 2 O 9 (SBTO) perovskite, blended PDMS composite operating in free-standing mode with an interdigitated patterned aluminum electrode. This self-powered sensor is capable of distinguishing between normal and abnormal braking patterns using digital signal processing techniques. It is noteworthy that the addition of 15% wt. of the SBTO in PDMS composite-based TENG delivered 13.5 V, 45 nA, and an output power of 0.98 µW. This new combination of energy harvesting and safety applications enables real-time monitoring and predictive maintenance in the automotive industry., (© 2024 Wiley‐VCH GmbH.)

Developing a facile strategy to synthesize free-standing defect-free metal-organic framework (MOF) membranes with high separation selectivity and good mechanical stability is very appealing but challenging. Herein, by confining the reaction of metal and ligand at the quasi-interface, a representative membrane composed of a continuous ZIF-8 layer and poly(vinyl alcohol) (PVA) was fabricated. The continuous ZIF-8 layer endowed the membrane with high separation efficiency, while PVA acted as a filler to eliminate the defection, synergistically achieving high selective ion transport and good mechanical stability. The continuous defect-free ZIF-8/PVA membrane showed excellent separation performance of selective ion transport with high Li + permeance of 17.83 mol·m -2 ·h -1 as well as decent Li + /Mg 2+ and Li + /Ca 2+ selectivities of 24.60 and 244.58, respectively. The separation performance of the ZIF-8/PVA membrane remained stable after 10% strain, indicating its good mechanical stability. This work will promote the development of MOF-based membranes in practical applications.

Beyond traditional paper, multifunctional nanopaper has received much attention in recent years. Currently, many nanomaterials have been successfully used as building units of nanopaper. However, it remains a great challenge to prepare flexible and freestanding metal-organic framework (MOF) nanopaper owing to the low aspect ratio and brittleness of MOF nanocrystals. Herein, this work develops a flexible and free-standing MOF nanopaper with MOF nanowires as building units. The manganese-based MOF (Mn-MOF) nanowires with lengths up to 100 μm are synthesized by a facile solvothermal method. Through a paper-making technique, the Mn-MOF nanowires interweave with each other to form a three-dimensional architecture, thus creating a flexible and free-standing Mn-MOF nanowire paper. Furthermore, the surface properties can be engineered to obtain high hydrophobicity by modifying polydimethylsiloxane (PDMS) on the surfaces of the Mn-MOF nanowire paper. The water contact angle reaches 130°. As a proof of concept, this work presents two potential applications of the Mn-MOF/PDMS nanowire paper: (i) The as-prepared Mn-MOF/PDMS nanowire paper is compatible with a commercial printer. The as-printed colorful patterns are of high quality, and (ii) benefiting from the highly hydrophobic surfaces, the Mn-MOF/PDMS nanowire paper is able to efficiently separate oil from water.

The NASICON-structured Na 3 MnZr(PO 4 ) 3 compound is a promising high-voltage cathode material for sodium-ion batteries (SIBs). In this study, an easy and scalable electrospinning approach was used to synthesize self-standing cathodes based on Na 3 MnZr(PO 4 ) 3 loaded into carbon nanofibers (CNFs). Different strategies were applied to load the active material. All the employed characterization techniques (X-ray powder diffraction (XRPD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), thermal gravimetric analysis (TGA), and Raman spectroscopy) confirmed the successful loading. Compared to an appositely prepared tape-cast electrode, Na 3 MnZr(PO 4 ) 3 /CNF self-standing cathodes demonstrated an enhanced specific capacity, especially at high C-rates, thanks to the porous conducive carbon nanofiber matrix. Among the strategies applied to load Na 3 MnZr(PO 4 ) 3 into the CNFs, the electrospinning (vertical setting) of the polymeric solution containing pre-synthesized Na 3 MnZr(PO 4 ) 3 powders resulted effective in obtaining the quantitative loading of the active material and a homogeneous distribution through the sheet thickness. Notably, Na 3 MnZr(PO 4 ) 3 aggregates connected to the CNFs, covered their surface, and were also embedded, as demonstrated by TEM and EDS. Compared to the self-standing cathodes prepared with the horizontal setting or dip-drop coating methods, the vertical binder-free electrode exhibited the highest capacity values of 78.2, 55.7, 38.8, 22.2, 16.2, 12.8, 10.3, 9.0, and 8.5 mAh/g at C-rates of 0.05C, 0.1C, 0.2C, 0.5C, 1C, 2C, 5C, 10C, and 20C, respectively, with complete capacity retention at the end of the measurements. It also exhibited a good cycling life, compared to its tape-cast counterpart: it displayed higher capacity retention at 0.2C and 1C, and, after cycling 1000 cycles at 1C, it could be further cycled at 5C, 10C, and 20C.

Sodium-ion batteries (SIBs) have demonstrated remarkable development potential and commercial prospects. However, in the current state of research, the development of high-energy-density, long-cycle-life, high-rate-performance anode materials for SIBs remains a huge challenge. Free-standing flexible electrodes, owing to their ability to achieve higher energy density without the need for current collectors, binders, and conductive additives, have garnered significant attention across various fields. In this work, we designed and fabricated a free-standing three-dimensional flexible Nb 2 O 5 @WS 2 @C carbon nanofiber (CNF) anode based on a hybrid adsorption-intercalation-conversion mechanism of sodium storage, using electrospinning and hydrothermal synthesis processes. The hybrid structure, aided by synergistic effects, releases the advantages of all materials, demonstrating a superior rate performance (288, 248, 211, 158, 90, and 48 mA h g -1 at the current density of 0.2, 0.5, 1, 2, 5, and 10 A g -1 , respectively) and good cycling stability (160 mA h g -1 after 200 cycles at 1 A g -1 ). This work provides certain guiding significance for future research on hybrid and flexible anodes of SIBs.

Tin selenides possess layered structure and high theoretical capacity, which is considered as desirable anode material for lithium-ion batteries. However, its further development is limited by the low intrinsic electrical conductivity and sluggish reaction kinetics. Herein, a well-designed structure of SnSe 2 nanosheet attached on N, Se co-doped carbon nanofibers (SnSe 2 @CNFs) is fabricated as self-standing anodes for lithium-ion batteries. The integration of structural engineering and heteroatom doping enables accelerated electrons transfer and rapid ion diffusion for boosting Li + storage performance. Impressively, the flexible SnSe 2 @CNFs anodes exhibit inspiring capacity of 837.7 mAh g -1 after 800 cycles at 1.2 C with coulombic efficiency almost 100% and superior rate performance 419.5 mAh g -1 at 2.4 C. The kinetics analysis demonstrates the pseudocapacitive characteristic of SnSe 2 @CNFs promotes the storage property. This work sheds light on the hierarchical electrode construction towards high-performance energy storage applications., (© 2024 IOP Publishing Ltd.)

The biomedical field has the potential to significantly benefit from the use of flexible free-standing Ag nanostructures due to their outstanding mechanical and antibacterial properties. However, the intricate process of synthesizing these nanostructures, as well as the potential toxicity of nanostructured Ag, pose significant challenges. This study used a facile etching method to synthesize the free-standing nanoporous Ag (NP-Ag) ribbons with a homogeneous and bicontinuous three-dimensional ligament structure. The free-standing NP-Ag ribbons demonstrated stable mechanical performance and excellent flexibility when subjected to various deformation states on artificial fingers. Additionally, the NP-Ag ribbons exhibited remarkable antibacterial capacity with rates of 99.81 ± 0.14% against Escherichia coli, 96.11 ± 1.49% against Staphylococcus aureus, and 95.37 ± 1.24% against methicillin-resistant Staphylococcus aureus. The antibacterial mechanism of NP-Ag is attributed to the rapid release of Ag ions (Ag + ) in 24 h, causing damage to the bacterial membrane. Moreover, the in vivo results demonstrate that the NP-Ag ribbons provide rapid antibacterial efficacy and are biosafe due to the long-term stable Ag + release of NP-Ag. The development of these free-standing flexible NP-Ag ribbons offers a new avenue for wearable antibacterial applications., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Inc. All rights reserved.)

Metal-organic frameworks (MOFs) are promising candidates for the advanced membrane materials based on their diverse structures, modifiable pore environment, precise pore sizes, etc. Nevertheless, the use of supports and large amounts of solvents in traditional solvothermal synthesis of MOF membranes is considered inefficient, costly, and environmentally problematic, coupled with challenges in their scalable manufacturing. In this work, we report a solvent-free space-confined conversion (SFSC) approach for the fabrication of a series of free-standing MOF (ZIF-8, Zn(EtIm) 2 , and Zn 2 (BIm) 4 ) membranes. This approach excludes the employment of solvents and supports that require tedious pretreatment and, thus, makes the process more environment-friendly and highly efficient. The free-standing membranes feature a robust and unique architecture, which comprise dense surface layers and highly porous interlayer with large amounts of irregular-shaped micron-scale pore cavities, inducing satisfactory H 2 /CO 2 selectivities and exceptional H 2 permeances. The ZIF-8 membrane affords a considerable H 2 permeance of 2653.7 GPU with a competitive H 2 /CO 2 selectivity of 17.1, and the Zn(EtIm) 2 membrane exhibits a high H 2 /CO 2 selectivity of 22.1 with an excellent H 2 permeance (6268.7 GPU). The SFSC approach potentially provides a new pathway for preparing free-standing MOF membranes under solvent-free conditions, rendering it feasible for scale-up production of membrane materials for gas separation.

In order to subdue the obvious problem of uneven electric field distribution on regularly used copper/aluminum current collectors for alkali metal batteries, graphene on porous stainless steel (pSS_Gr) was fabricated using the ion etching technique that is employed as an effective host for lithium and sodium metal anodes. The binder-free pSS_Gr demonstrated stable Li plating and stripping at areal current and capacity of 6 mA cm -2 and 2.54 mAh cm -2 , respectively, for over 1000 cycles with 98% coulombic efficiency (C.E.). Also, in the case of Na metal anode, the host has shown stable performance at 4 mA cm -2 and 1 mAh cm -2 over 1000 cycles with ∼100% C.E.. Further, a full cell composed of Li-plated pSS_Gr as an anode and LiFePO 4 as a cathode is electrochemically tested at 50 mA g -1 current density with stable 100 cycles., (© 2023 Wiley-VCH GmbH.)

Potassium-ion batteries (PIBs) have attracted enormous attention due to the increasing lithium battery cost, but their development is still in the pre-mature stage due to the limited selection of electrodes. Herein, a free-standing current-collector-integrated electrode, composed of mixed-phase WS 2 nanosheets with nitrogen-doped multichannel carbon nanofibers (N-MCNFs) membrane, is reported for high-performance potassium ion batteries anode. Benefiting the unique multichannel carbon nanostructure as a current collector-integrated electrode as well as mixed-phase lamellar structure WS 2 for enhanced potassium ion entry, the 1T/2H-WS 2 /N-MCNFs hybrid current-collector-free anode delivers an outstanding areal capacity of 2.88 mAh cm -2 (corresponding to 411 mAh/g based on the mass of both electrode and current collector) at a current of 0.7 mA cm -2 as well as long-term cycling stability for over 1000 cycles at a high current of 14 mA cm -2 , surpassing the current state-of-art PIB anode. It is believed that our findings based on the high energy current collector integrated electrode at high mass loading would boost future research on practical metal ion batteries., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Currently available commercial nerve guidance conduits have been applied in the repair of peripheral nerve defects. However, a conduit exhibiting good biocompatibility remains to be developed. In this work, a series of chitosan/graphene oxide (GO) films with concentrations of GO varying from 0-1 wt% (collectively referred to as CHGF-n) were prepared by an electrodeposition technique. The effects of CHGF-n on proliferation and adhesion abilities of Schwann cells were evaluated. The results showed that Schwann cells exhibited elongated spindle shapes and upregulated expression of nerve regeneration-related factors such as Krox20 (a key myelination factor), Zeb2 (essential for Schwann cell differentiation, myelination, and nerve repair), and transforming growth factor β (a cytokine with regenerative functions). In addition, a nerve guidance conduit with a GO content of 0.25% (CHGFC-0.25) was implanted to repair a 10-mm sciatic nerve defect in rats. The results indicated improvements in sciatic functional index, electrophysiology, and sciatic nerve and gastrocnemius muscle histology compared with the CHGFC-0 group, and similar outcomes to the autograft group. In conclusion, we provide a candidate method for the repair of peripheral nerve defects using free-standing chitosan/GO nerve conduits produced by electrodeposition.

The design and discovery of free-standing hybrid electrode materials with large absolute capacity and high cycling stability for energy storage become desirable and are still challenging. In this work, we demonstrate that the hybrid supercapacitor (HSC) device is assembled by 3D core-shell hierarchical nanorod arrays of Ni 3 S 2 @NiCoP nanocomposite for the first time. The Ni 3 S 2 @NiCoP nanocomposite is successfully synthesized through a facile stratagem containing hydrothermal process and the subsequent electrodeposition method. The 3D architecture of Ni 3 S 2 @NiCoP hybrid electrode composed of vertically aligned "hyperchannel" 1D Ni 3 S 2 nanorods and highly conductive interconnected 2D nanosheets of NiCoP is beneficial to fast electron transfer kinetics, thus leading to enhancing the ionic and electronic conductivity, kinetics of redox reaction, and synergistic behavior of active species. The fabricated HSC device with Ni 3 S 2 @NiCoP electrode delivers outstanding areal capacity of 109 µAh cm -2 at a current density of 1 mA cm -2 , brilliant energy density of 74.9 Wh kg -1 at a power density of 700 W kg -1 , and prominent cyclic performance of 92% capacity retention even after 144-h floating test. This work demonstrates that the core-shell hierarchical nanorod arrays of Ni 3 S 2 @NiCoP can be viewed as one of the novel battery-type electrode materials for high-performance HSCs., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Inc. All rights reserved.)

In virtue of the high electrochemical activity and inherent flexibility, polyaniline (PANI) is an ideal electrode material for flexible supercapacitors (SCs). However, in practical applications, the inevitable agglomeration of PANI leads to low capacitance, poor rate performance, and cycling stability. Here, antimonene (Sb) nanosheets with ultrathin thickness, excellent mechanical strength, and flexibility are introduced into the carbon nanotube (CNT) framework for PANI electrodeposition via simple vacuum filtration, which enables the continuous and uniform growth of PANI. The resultant free-standing Sb/CNT/PANI electrode can thus exhibit a high specific capacitance of 578.57 F g -1 together with a high rate capability. Besides, thanks to the introduction of Sb nanosheets, the agglomeration of PANI during the electrodeposition is improved, which correspondingly alleviates the structural deterioration of PANI during repeated charge/discharge. Thus, the flexible SC assembled by Sb/CNT/PANI electrodes demonstrates both an impressive specific capacitance of 416 F g -1 and outstanding cycling stability over 12 000 cycles. Moreover, this SC device can have a practical self-healing function by employing self-healable polyurethane. The facile strategy reported herein sheds light on the design of high-performance flexible SCs, catering to the needs of portable and wearable electronics., (© 2022 Wiley-VCH GmbH.)

Hydrogen evolution reaction (HER) has a dominant function in energy conversion and storage because it supplies a most effective way for converting electricity into sustainable high-purity hydrogen. Layered double hydroxides (LDHs) have shown promising performance in the process of electrochemical water oxidation (a half-reaction for water splitting). Nevertheless, HER properties have not been well released due to the structural characteristics of related materials. Herein, a simple and scalable tactics is developed to synthesize chromium-doped CoFe LDH (CoFeCr LDH). Thanks to oxygen vacancy, optimized electronic structure and interconnected array hierarchical structure, our developed ternary CoFeCr-based layered double hydroxide catalysts can provide 10 mA cm -2 current density at -0.201 V vs. RHE with superior long-term stability in alkaline electrolyte. We anticipate that the simple but feasible polymetallic electronic modulation strategy can strengthen the electrocatalytic property of the layered double hydroxides established in the present study, based on a carbon neutral and hydrogen economy.

Flexible electrode plays a key role in flexible energy storage devices. The SnTe/C nanofibers membrane (SnTe/CNFM) with excellent mechanical flexibility has been successfully synthesized for the first time through electrospinning, and it demonstrates outstanding electrochemical performance as free-standing anode for lithium/sodium-ion batteries. The SnTe/CNFM electrode delivers a discharge capacity of 526.7 mAh g -1 at 1000 mA g -1 after 1000 cycles in lithium-ion half-cells and a discharge capacity of 236.5 mAh g -1 at 500 mA g -1 after 80 cycles in lithium-ion full-cells with a LiFePO 4 cathode. Not only that, it shows a discharge capacity of 182.7 mAh g -1 at 200 mA g -1 after 200 cycles in sodium-ion half-cells and a high discharge capacity of 207.0 mAh g -1 at 500 mA g -1 after 50 cycles in sodium-ion full-cells with a Na 0.44 MnO 2 cathode. Moreover, the prepared SnTe/CNFM exhibits good mechanical flexibility. The SnTe/CNFM can still return to its original state without any breakage after bending, curling, folding and kneading. These results indicate that SnTe/CNFM is expected to become one of the promising free-standing anodes for lithium/sodium-ion batteries., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Background: Evidence is emerging for the use of overground lower limb robotic exoskeletons in the rehabilitation of people with spinal cord injury (SCI), with suggested benefits for gait speed, bladder and bowel function, pain management and spasticity. To date, research has focused on devices that require the user to support themselves with a walking aid. This often precludes use by those with severe trunk, postural or upper limb deficits and places the user in a suboptimal, flexed standing position. Free-standing exoskeletons enable people with higher level injuries to exercise in an upright position. This study aimed to evaluate the feasibility of therapy with a free-standing exoskeleton for those with SCI, and to determine the potential health-related benefits of this intervention., Methods: This 12-week intervention study with 12-week waitlist control and 12-week follow up, provided people with SCI scoring < 5 on the mobility section of the spinal cord independence measure (SCIM-III) twice weekly therapy in the REX (Rex Bionics, Auckland, NZ), a free-standing lower limb robotic exoskeleton. The primary outcome measure of interest was function, as measured on the SCIM-III. A battery of secondary outcomes was included. Participants also completed a survey on their perceptions of this treatment modality, to determine acceptability., Results: Forty-one potential participants were screened for eligibility. Two females (one ASIA A, one ASIA C) and one male (ASIA B) completed all 24 intervention sessions, and the follow up assessment. One participant showed positive trends in function, fatigue, quality of life and mood during the intervention phase. Grip and quadriceps strength, and lower limb motor function improved in another. Two improved their percentage of lean body mass during the intervention phase. Remaining results were varied across patients, time points and outcomes. The intervention was highly acceptable to all participants., Conclusion: With three of 41 potential participants being eligible and completing this study, our results show that there are potential benefits of exercise in a free-standing exoskeleton for people with severe mobility impairment due to SCI, for a small subset of patients. Further research is warranted to determine those most likely to benefit, and the type of benefit depending on the patient characteristics. Trial registration The trial was registered prospectively on 20 April 2018 at www.anzctr.org.au/ (ACTRN12618000626268)., (© 2021. The Author(s).)

Introduction: Robotic exoskeletons facilitate therapy in upright postures. This study aimed to evaluate potential health-related effects of this therapy for people with severe mobility impairment due to chronic stroke., Methods: This quasi-controlled trial with 12 weeks of twice weekly therapy in a free-standing exoskeleton, and 12 weeks follow up, included people dependent for mobility, with stroke at least 3 months prior. The primary outcome was lower limb motor function. A battery of secondary outcomes was evaluated., Results: Nine participants were enrolled. There was no change in motor function. There was a significant between phase difference in level of independence with activities of daily living (median post-intervention change = 5, IQR = 0, 10, p = 0.01), and grip strength (affected limb) (median post-intervention change = 1, IQR = 0, 2, p = 0.03). A significant difference was found for quadriceps strength (affected limb) (median change in wait phase = 4, IQR = 2, 7.5, p = 0.01). Participants consistently reported positive perceptions of the therapy., Conclusions: Therapy with a free-standing exoskeleton is acceptable to participants and can facilitate improvements in level of independence and grip strength. Restrictions regarding eligibility to use the device, may reduce the clinical application of this therapy for people with stroke., Competing Interests: Declaration of conflicting interests: The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article., (© The Author(s) 2021.)

Patterned conducting polymer films with unique structures have promising prospects for application in various fields, such as actuation, water purification, sensing, and bioelectronics. However, their practical application is hindered because of the limitations of existing construction methods. Herein, a strategy is proposed for the superhydrophobic-substrate-assisted construction of free-standing 3D microcavity-patterned conducting polymer films (McPCPFs) at micrometer resolution. Easy-peeling and nondestructive transfer properties are achieved through electrochemical polymerization along the solid/liquid/gas triphase interface on micropillar-structured substrates. The effects of the wettability and geometrical parameters of the substrates on the construction of McPCPFs are systematically investigated in addition to the evolution of the epitaxial growth along the triphase interface at different polymerization times. The McPCPFs can be easily peeled from superhydrophobic surfaces using ethanol because of weak adhesion and nondestructively transferred to various substrates taking advantage of the capillarity. Furthermore, sensitive light-driven McPCPF locomotion on organic liquid surfaces is demonstrated. Ultimately, a facile strategy for the construction of free-standing 3D microstructure-patterned conducting polymer films is proposed, which can improve productivity and applicability of the films in different fields and expand the application scope of superwettable interfaces., (© 2021 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Supercapacitors are increasingly used in short-distance electric transportation due to their long lifetime (≈15 years) and fast charging capability (>10 A g -1 ). To improve their market penetration, while minimizing onboard weight and maximizing space-efficiency, materials costs must be reduced (<10 $ kg -1 ) and the volumetric energy-density increased (>8 Wh L -1 ). Carbon nanofibers display good gravimetric capacitance, yet their marketability is hindered by their low density (0.05-0.1 g cm -3 ). Here, the authors increase the packing density of low-cost, free-standing carbon nanofiber mats (from 0.1 to 0.6 g cm -3 ) through uniaxial compression. X-ray computed tomography reveals that densification occurs by reducing the inter-fiber pore size (from 1-5 µm to 0.2-0.5 µm), which are not involved in double-layer capacitance. The improved packing density is directly proportional to the volumetric performances of the device, which reaches a volumetric capacitance of 130 F cm -3 and energy density of 6 Wh L -1 at 0.1 A g -1 using a loading of 3 mg cm -2 . The results outperform most commercial and lab-scale porous carbons synthesized from bioresources (50-100 F cm -3 , 1-3 Wh L -1 using 10 mg cm -2 ) and contribute to the scalable design of sustainable electrodes with minimal 'dead volume' for efficient supercapacitors., (© 2021 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Iron phosphide with high specific capacity has emerged as an appealing candidate for next-generation lithium-ion battery anodes. However, iron phosphide could undergo conversion reactions and generally suffer from a rapid capacity degradation upon cycling due to its structure pulverization. Chemomechanical breakdown of iron phosphide due to its rigidity has been a challenge to fully realizing its electrochemical performance. To address this challenge, we report here on an enticing opportunity: a flexible, free-standing iron phosphide anode with Fe 2 P nanoparticles confined in carbon nanofibers may overcome existing challenges. For the synthesis, we introduce a facile electrospinning strategy that enables in situ formation of Fe 2 P within a carbon matrix. Such a carbon matrix can effectively minimize the structure change of Fe 2 P particles and protect them from pulverization, allowing the electrodes to retain a free-standing structure after long-term cycling. The produced electrodes showed excellent electrochemical performance in lithium-ion half and full cells, as well as in flexible pouch cells. These results demonstrate the successful development of iron phosphide materials toward high capacity, light weight, and flexible energy storage.

The realization of a large low-field magnetoresistance (LFMR) effect in free-standing magnetic oxide films is a crucial goal toward promoting the development of flexible, low power consumption, and nonvolatile memory devices for information storage. La 0.7 Sr 0.3 MnO 3 (LSMO) is an ideal material for spintronic devices due to its excellent magnetic and electronic properties. However, it is difficult to achieve both a large LFMR effect and high flexibility in LSMO films due to the lack of research on LFMR-related mechanisms and the strict LSMO growth conditions, which require rigid substrates. Here, we induced a large LFMR effect in an LSMO/mica heterostructure by utilizing a disorder-related spin-polarized tunneling effect and developed a simple transfer method to obtain free-standing LSMO films for the first time. Electrical and magnetic characterizations of these free-standing LSMO films revealed that all of the principal properties of LSMO were sustained under compressive and tensile conditions. Notably, the magnetoresistance of the processed LSMO film reached up to 16% under an ultrasmall magnetic field (0.1 T), which is 80 times that of a traditional LSMO film. As a demonstration, a stable nonvolatile multivalue storage function in flexible LSMO films was successfully achieved. Our work may pave the way for future wearable resistive memory device applications.

A flexible free-standing electrochemical biosensor to detect carcinoembryonic antigen (CEA) is described based on a conducting polypyrrole (PPy) nanocomposite film electrode. The conducting PPy composite was constructed by the sandwiched structure formed by PPy doped with pentaerythritol ethoxylate (PEE) and 2-naphthalene sulfonate (2-NS-PPy) separately via electropolymerization. Gold nanoparticles (AuNPs) were fixed on the PPy composite film by electrodeposition and then connected to CEA aptamer through self-assembly to construct a free-standing electrochemical biosensor breaking away from additional soft substrates and current collector. This PPy composite film-based electrochemical biosensor exhibits satisfying sensing performance for CEA detection, with a linear range from 10 -10  g/mL to 10 -6  g/mL and a detection limit of 0.033 ng/mL, good specificity and long-term sensing stability (96.8% of the original signal after 15 days). The biosensor also presents acceptable reproducibility with 1.7% relative standard deviation. Moreover, this electrochemical biosensor owns the deformation stability that could bear various deformations (twisting, folding, and knotting) without affecting device's sensing performance. It can even maintain 99.4% of the original signal under 25% strain deformation. Due to the superior sensing performance, high stability (mechanical deformation and long-term storage), and flexibility, this free-standing electrochemical biosensor proves huge potential in application of flexible and wearable electronics.

In this study, we have successfully prepared a free-standing Si/void/rGO yolk-shell structured electrode via the electrostatic self-assembly using protonated chitosan. When graphene oxide (GO) is dispersed in water, its carboxyl and hydroxyl groups on the surface are ionized, resulting in the high electronegativity of GO. Meanwhile, chitosan monomer contains -NH 2 and -OH groups, forming highly electropositive protonated chitosan in acidic medium. During the electrostatic interaction between GO and chitosan, which results in a rapid coagulation phenomenon, Si/SiO 2 nanoparticles dispersed in GO can be uniformly encapsulated between GO sheets. The free-standing Si/void/rGO film can be obtained by freeze-drying, high-pressure compression, thermal reduction and HF etching technology. Our investigation shows that after 200 charge/discharge cycles at the current density of 200 mA·g -1 , the specific discharge capacity of the free-standing electrode remains at 1129.2 mAh·g -1 . When the current density is increased to 4000 mA·g -1 , the electrode still has a specific capacity of 469.2 mAh·g -1 , showing good rate performance. This free-standing electrode with a yolk-shell structure shows potential applications in the field of flexible lithium-ion batteries.

The internal concentration polarization (ICP) of asymmetric osmotic membranes with support layers greatly reduced membrane water permeability, therefore compromising membrane performance. In this study, a series of free-standing symmetric hybrid forward osmosis (FO) membranes without experiencing ICP were fabricated by covalently linking metal-organic framework (MOF) nanofillers with a polymer matrix. Owing to the introduction of MOFs, which allow only water permeation but reject salts by steric hindrance, the prepared hybrid membranes could approach the empirical permeability-selectivity trade-off. The optimized hybrid membrane displayed an outstanding water/Na 2 SO 4 selectivity of ∼1208.4 L mol -1 , compared with that of conventional membranes of ∼375.6 L mol -1 . Additionally, the fabricated hybrid membranes showed excellent mechanical robustness, maintaining structural integrity during the long-term FO separation of high-salinity solution. This work provides an effective methodology to fabricate high-performance, symmetric MOF-based membranes for osmotic separation processes such as seawater desalination and water purification.

Porous polymer membranes are widely desired as catalyst supports, sensors, and active layers for separation membranes. We demonstrate that electron beam irradiation of freely suspended gold or Fe 3 O 4 nanoparticle (NP) monolayer sheets followed by wet chemical etching is a high-fidelity strategy to template two-dimensional (2D) porous cross-linked hydrocarbon membranes. This approach, which relies on secondary electrons generated by the NP cores, can further be used to transform three-dimensional (3D) terraced gold NP supercrystals into 3D porous hydrocarbon membranes. We utilize electron tomography to show how the number of NP layers (monolayer to pentalayer) controls attenuation and scattering of the primary e-beam, which in turn determines ligand cross-link density and 3D pore structure. Electron tomography also reveals that many nanopores are vertically continuous because of preferential sintering of NPs. This work demonstrates new routes for the construction of functional nanoporous media.

Electrophoresis of chitosan and its composites are widely used to form a coating on selective substrates, but the parasitic water electrolysis causes structural defects that weaken the resulting film. In this work, we demonstrate a bipolar electrophoresis technique that leverages the water electrolysis to produce a chitosan film with less porosity and surface cavities. The process involves a negative bias to deposit the protonated chitosan molecules from the solution, followed by a positive bias to remove the entrapped hydrogen bubbles via the re-protonation of chitosan deposit. Since water electrolysis occurs for both positive and negative bias, the bipolar profile is designed to engender pH changeup near the electrode for "surface conditioning" of chitosan film. The bipolar electrophoresis route demonstrates better coulomb efficiency than that of conventional potentiostatic electrophoresis, resulting in a free-standing chitosan film with sufficient mechanical strength and large area., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

A high filler content is often needed in polymer composite-based thermoelectric (TE) films to improve their performance. Nevertheless, this often leads to poor processability and poor mechanical performance. Herein, a biomimetic approach is adopted to facilitate the filler content up to 90.5 wt % in free-standing and flexible n-type PVDF/Ag 2 Se TE films, where PVDF dendricolloids are a solution mixed with Ag 2 Se nanowires (NWs), followed by filtration. These soft dendric nanoparticles within PVDF dendricolloids have high adhesivity and strong network-building ability, which allows the formation of "grapevine-grape"-like networks with soft dendritic particles and inorganic TE fillers as "grapevine" and "manicure finger grapes", respectively. The maximum power factor of 189.02 μW m -1 K -2 is achieved for a PVDF/Ag 2 Se mass ratio of 1:9.5 at 300 K. Meanwhile, excellent flexibility with only 15.8% decrease in electrical conductivity after 1000 bending cycles was observed. These properties at such a high filler content are attributed to the long-range grapevine-like network of soft PVDF dendritic particles and entanglement between numerous Ag 2 Se NWs. This work carves a path to fabricate high-performance free-standing flexible n-type TE composite films as well as other functional polymer composites requiring high inorganic filler loading.

Recently, Li-ion batteries (LIBs) have attracted extensive attention owing to their wide applications in portable and flexible electronic devices. Such a huge market for LIBs has caused an ever-increasing demand for excellent mechanical flexibility, outstanding cycling life, and electrodes with superior rate capability. Herein, an anode of self-supported Fe 3 O 4 @C nanotubes grown on carbon fabric cloth (CFC) is designed rationally and fabricated through an in situ etching and deposition route combined with an annealing process. These carbon-coated nanotube structured Fe 3 O 4 arrays with large surface area and enough void space can not only moderate the volume variation during repeated Li + insertion/extraction, but also facilitate Li + /electrons transportation and electrolyte penetration. This novel structure endows the Fe 3 O 4 @C nanotube arrays stable cycle performance (a large reversible capacity of 900 mA h g -1 up to 100 cycles at 0.5 A g -1 ) and outstanding rate capability (reversible capacities of 1030, 985, 908, and 755 mA h g -1 at 0.15, 0.3, 0.75, and 1.5 A g -1 , respectively). Fe 3 O 4 @C nanotube arrays still achieve a capacity of 665 mA h g -1 after 50 cycles at 0.1 A g -1 in Fe 3 O 4 @C//LiCoO 2 full cells., (© 2020 Wiley-VCH GmbH.)

One of the challenges in 3D-bioprinting is the realization of complex, volumetrically defined structures, that are also anatomically accurate and relevant. Towards this end, in this study we report the development and validation of a carboxylated agarose (CA)-based bioink that is amenable to 3D printing of free-standing structures with high stiffness at physiological temperature using microextrusion printing without the need for a fugitive phase or post-processing or support material (FRESH). By blending CA with negligible amounts of native agarose (NA) a bioink formulation (CANA) which is suitable for printing with nozzles of varying internal diameters under ideal pneumatic pressure was developed. The ability of the CANA ink to exhibit reproducible sol-gel transition at physiological temperature of 37 °C was established through rigorous characterization of the thermal behavior, and rheological properties. Using a customized bioprinter equipped with temperature-controlled nozzle and print bed, high-aspect ratio objects possessing anatomically-relevant curvature and architecture have been printed with high print reproducibility and dimension fidelity. Objects printed with CANA bioink were found to be structurally stable over a wide temperature range of 4 °C to 37 °C, and exhibited robust layer-to-layer bonding and integration, with evenly stratified structures, and a porous interior that is conducive to fluid transport. This exceptional layer-to-layer fusion (bonding) afforded by the CANA bioink during the print obviated the need for post-processing to stabilize printed structures. As a result, this novel CANA bioink is capable of yielding large (5-10 mm tall) free-standing objects ranging from simple tall cylinders, hemispheres, bifurcated 'Y'-shaped and 'S'-shaped hollow tubes, and cylinders with compartments without the need for support and/or a fugitive phase. Studies with human nasal chondrocytes showed that the CANA bioink is amenable to the incorporation of high density of cells (30 million/mL) without impact on printability. Furthermore, printed cells showed high viability and underwent mitosis which is necessary for promoting remodeling processes. The ability to print complex structures with high cell densities, combined with excellent cell and tissue biocompatibility of CA bodes well for the exploitation of CANA bioinks as a versatile 3D-bioprinting platform for the clinical translation of regenerative paradigms.

Layer-structured black phosphorus (BP) demonstrating high specific capacity has been viewed as a very promising anode material for future high-energy-density Li-ion batteries (LIBs). However, its practical application is hindered by large volume change of BP and poor mechanical stability of BP anodes by traditional slurry casting technology. Here, a free-standing flexible anode composed of BP nanosheets and nanocellulose (NC) nanowires is fabricated via a facile vacuum-assisted filtration approach. The constructed free-standing BP@NC composite anode offers three-dimensional (3D) mixed-conducting network for Li + /e - transports. The substrate of NC film has a certain flexibility up to 10.2% elongation that can restrain the volume change of BP and electrode during operation. In addition, molecular dynamic (MD) simulation and density function theory (DFT) show the greatly enhanced Li + diffusion in BP@NC composite where the Li ions receive less repulsive force at the interface of BP interlayer and nanocellulose. Benefiting from above multifunction of nanocellulose, the BP@NC composite exhibits high capacities of 1020.1 mAh g -1 at 0.1 A g -1 after 230 cycles and 994.4 mAh g -1 at 0.2 A g -1 after 400 cycles, corresponding to high capacity retentions of 87.1% and 84.9%, respectively. Our results provide a low-cost and effective strategy to develop advanced electrodes for next-generation rechargeable batteries.

Structural DNA nanotechnology can produce a wide range of 3D nanostructures with programmable structure and size at <5 nm resolution. However, it is challenging to dry these structures without capillary force-induced damage. As a result, the applications of 3D DNA nanostructures have long been limited in aqueous environments. Ready access to free-standing 3D DNA nanostructures in the dry state could revolutionize many research areas, especially in the development of low-density, high-strength materials. Here we report a method to obtain free-standing wireframe 3D DNA tetrahedra in air on a solid substrate, such as SiO 2 and mica, by absorbing uranyl acetate and lyophilization. The dried DNA tetrahedron structure, 93 ± 2 nm in height, withstands 42 ± 22 nN of loading force. The effective hardness (9.1 ± 5.1 MPa) and Young's modulus (77 ± 48 MPa) of this low-density (70.7 kg/m 3 ) DNA-inorganic hybrid nanostructure are comparable to other reported low-density high-strength materials.

Electrocatalytic nitrogen reduction reaction is a carbon-free and energy-saving strategy for efficient synthesis of ammonia under ambient conditions. Here, we report the synthesis of nanosized Bi 2 O 3 particles grown on functionalized exfoliated graphene (Bi 2 O 3 /FEG) via a facile electrochemical deposition method. The obtained free-standing Bi 2 O 3 /FEG achieves a high Faradaic efficiency of 11.2% and a large NH 3 yield of 4.21 ± 0.14 [Formula: see text] h -1  cm -2 at - 0.5 V versus reversible hydrogen electrode in 0.1 M Na 2 SO 4 , better than that in the strong acidic and basic media. Benefiting from its strong interaction of Bi 6p band with the N 2p orbitals, binder-free characteristic, and facile electron transfer, Bi 2 O 3 /FEG achieves superior catalytic performance and excellent long-term stability as compared with most of the previous reported catalysts. This study is significant to design low-cost, high-efficient Bi-based electrocatalysts for electrochemical ammonia synthesis.

Long-term, real-time, and comfortable epidermal electronics are of great practical importance for healthcare monitoring and human-machine interaction. However, traditional physiological signal monitoring confined by the specific clinical sites and unreliability of the epidermal electrodes leads to great restrictions on its application. Herein, we constructed a solution-processed submicron (down to 230 nm), free-standing, breathable sandwich-structured hybrid electrode composed of a silver nanowire network with a conductive polymer film, which is conformal, water-permeable, and noninvasive to the skin while achieving good signal acquisition ability. The free-standing hybrid electrode is prepared via an in situ capillary force lift-off process and can be transferred onto complex surfaces. The whole process is a complete solution process that facilitates large-area preparation and application. The light-weight hybrid electrodes exhibit high optical transmittance, high electrical conductivity, and high gas/ion permeability. When the hybrid electrodes are attached onto the skin, the imperceptible films show high conformality with low electrical impedance, thus exhibiting significantly improved electrocardiology and electromyogram signal monitoring performance compared to that of the commercial gel electrodes.

We designed and tested a highly sensitive metasurface device based on free-standing complementary asymmetric split-ring resonators at terahertz frequencies. It is utilized for sensing a galactose film. We characterized the device using the induced red shift of a Fano resonance observed in the THz transmission. The sensor has a high sensitivity of 91.7 GHz/RIU due to a significant interaction between the galactose overlayer and the metasurface.

A number of inherent and thorny obstacles still stand in the way of the practical application of Li-O 2 batteries, which require development of an advanced lithium anode and O 2 cathode. Herein, the strategy of a symmetrical Li-O 2 battery is presented. Specifically, Cu nanoneedle arrays with a nanoengineered Au coating are grown directly on a Cu foam substrate (Au/Cu@FCu), which can act as both the anode backbone and the cathode in a Li-O 2 battery. The excellent conductivity, high porosity, large specific surface, and superior lithiophilicity as well as high catalytic activity of the Au/Cu@FCu electrodes can simultaneously regulate the deposition behavior of the lithium metal in the anode and catalyze the formation/decomposition of Li 2 O 2 in the cathode. As a result, the Li uniformly deposited on the Au/Cu@FCu anode without Li dendrites, showing a high Coulombic efficiency over 96% and a long and stable cycle lifetime over 970 h. At the same time, the Au/Cu@FCu cathode demonstrates extremely low overpotentials (0.64 V) and a much higher specific capacity of 27 270 mAh g -1 compared to the Li-O 2 batteries with a carbon-free cathode reported to date. Moreover, the "ebb and flow" phenomenon of the anode and cathode morphology is also observed in the Li-O 2 battery.

Constructing high-efficiency electrocatalysts is vital towards electrocatalytic water splitting, but it remains a challenge. Although Ni-based materials have drawn extensive attention as highly active catalysts, the relatively limited electroactive sites in Ni-based catalysts still remains a great issue. In order to further boost the electrocatalytic performances, heteroatom doping and interface engineering are usually adopted for modification. Here, a new strategy is developed to construct W doped NiO/NiS 2 interfaced nanosheets directly on carbon sheet, which is working as efficient and bifunctional electrocatalysts for overall water splitting. W doped NiO nanosheets are directly constructed on the carbon sheet by the hydrothermal and annealing processes. After that, W-NiO was subjected to Ar plasma assisted sulfuration treatment for forming W doped NiO/NiS 2 interfaced nanosheets. Based on systematic investigations, we find that W doping can effectively induce the modified electronic structure of Ni to boost the intrinsic activities in NiO/NiS 2 . Further, forming NiO/NiS 2 nanointerfaces can also provide rich electroactive sites and boost the charge transfer rate. Consequently, W doped NiO/NiS 2 exhibits the much enhanced performances for overall water splitting. As a bifunctional electrode, W-NiO/NiS 2 demonstrates a remarkable activity with a 1.614 V cell voltage at 10 mA cm -2 for overall water splitting., (Copyright © 2019 Elsevier Inc. All rights reserved.)

We propose a flexible, binder-free and free-standing carbonaceous paper fabricated via electrostatic spray deposition using reduced graphene oxide/carbon nanotube (rGO/CNT) as a promising electrode material for flexible sodium-ion batteries (NIBs). The as-prepared rGO/CNT paper exhibits a three-dimensional (3D) layered structure by employing rGO as conductive frameworks to provide sodium-storage active sites and CNT as spacer to increase rGO interlayer distance and benefit the diffusion kinetics of sodium ions. Consequently, the rGO/CNT paper delivers an enhanced sodium ion storage capacity of 166.8 mAh g -1 at 50 mA g -1 , retaining an average capacity of 101.4 mAh g -1 when current density sets back 100 mA g -1 after cycling at various current rates. An average capacity of 50 mAh g -1 at 200 mA g -1 was stabilized when cycling up to 300 cycles. The well-maintained electrochemical performance of free-standing rGO/CNT paper is due to the well-established hybrid 3D nanostructures, which demonstrates our carbon based material fabricated by a facile approach can be applied as one of the high-performance and low-cost electrode materials for applications in flexible energy storage devices., Competing Interests: The authors declare no conflicts of interest.

Rechargeable Zn/MnO 2 batteries using mild aqueous electrolytes are attracting extensive attention due to their low cost, high safety, and environmental friendliness. However, the charge-storage mechanism involved remains a topic of controversy so far. Also, the practical energy density and cycling stability are still major issues for their applications. Herein, a free-standing α-MnO 2 cathode for aqueous zinc-ion batteries (ZIBs) is directly constructed with ultralong nanowires, leading to a rather high energy density of 384 mWh g -1 for the entire electrode. Greatly, the H + /Zn 2+ coinsertion mechanism of α-MnO 2 cathode for aqueous ZIBs is confirmed by a combined analysis of in situ X-ray diffractometry, ex situ transmission electron microscopy, and electrochemical methods. More interestingly, the Zn 2+ -insertion is found to be less reversible than H + -insertion in view of the dramatic capacity fading occurring in the Zn 2+ -insertion step, which is further evidenced by the discovery of an irreversible ZnMn 2 O 4 layer at the surface of α-MnO 2 . Hence, the H + -insertion process actually plays a crucial role in maintaining the cycling performance of the aqueous Zn/α-MnO 2 battery. This work is believed to provide an insight into the charge-storage mechanism of α-MnO 2 in aqueous systems and paves the way for designing aqueous ZIBs with high energy density and long-term cycling ability., (© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In this work, a free-standing sodium titanate ultralong nanotube membrane for multifunctional water purification has been prepared. For obtaining this free-standing membrane with good tenacity, one-dimensional (1D) sodium titanate ultralong nanotubes with a diameter of about 48 nm and length of hundreds of micrometers were prepared from TiO 2 nanoparticles by a stirring hydrothermal method, which can be easily assembled into 2D membranes by facile vacuum filtration. After modified with methyltrimethoxysilane (MTMS), the free-standing membrane with hydrophobic surface possesses oil-water separation, self-cleaning and photocatalytic functions at the same time, which is favorable for the recovery of membrane and decontamination of various pollutants including oils, dust, and organic dyes from water. Furthermore, this membrane also exhibits excellent alkaline, acid, and corrosive salt resistance. This free-standing sodium titanate membrane with multifunction has potential applications in efficient wastewater purification and environmental remediation.

Rechargeable potassium-ion batteries (PIBs) have attracted tremendous attention as potential electrical energy storage systems due to the special merit of abundant resources and low cost of potassium. However, one critical barrier to achieve practical application of PIBs has been the lack of suitable electrode materials. Here, a novel flexible membrane consisting of N, P codoped carbon nanofibers decorated with MoP ultrafine nanoparticles (MoP@NPCNFs) is fabricated via a simple electrospinning method combined with the later carbonization and phosphorization process. The 3D porous CNF structure in the as-synthesized composite can shorten the transport pathways of K-ions and improve the conductivity of electrons. The ultrafine MoP nanoparticles can guarantee high specific capacity and the N, P co-doping could improve wettability of electrodes to electrolytes. As expected, the free-standing MoP@NPCNF electrode demonstrates a high capacity of 320 mAh g -1 at 100 mA g -1 , a superior rate capability maintaining 220 mAh g -1 at 2 A g -1 , as well as a capacity retention of more than 90% even after 200 cycles. The excellent rate performance, high reversible capacity, long-term cycling stability, and facile synthesis routine make this hybrid membrane promising anode for potassium-ion batteries., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Owing to low-cost and 3d electronic configurations, Co 3 O 4 material is considered as promising candidate for oxygen evolution reaction (OER) electrocatalyst, but the intrinsically low conductivity and limited active site exposure greatly limit the electrocatalytic performances, Herein, we successfully achieve modulation of Co 3 O 4 arrays by Mn and S dual-doping for OER. Results demonstrate that Mn doping modifies the electronic structure of Co center to boost the intrinsic activity of active site in Co 3 O 4 , while inducing S in Co 3 O 4 increases the electrical conductivity and provides ample S sites for proton adsorption. In addition, Mn and S dual-doping effectively increase the proportion of Co 3+ , resulting in facilitating the four-electron transfer and thus higher electrochemical activities. Consequently, the optimal Mn and S dual-doping Co 3 O 4 presents low overpotentials of 330, 407 and 460 mV at 10, 100 and 300 mA cm -2 for OER, as well as a low Tafel slope of 68 mV dec -1 and a good durability after 20 h. Current work highlights a feasible strategy to design electrocatalysts via dual-doping and maximizing the high-valence transition metal ions., (Copyright © 2019 Elsevier Inc. All rights reserved.)

Lithium-oxygen (Li-O 2 ) batteries have been widely recognized as appealing power systems for their extremely high energy density versus common Li-ion batteries. However, there are still lots of issues that need to be addressed toward the practical application. Here, free-standing Co-doped NiO three-dimensional nanosheets were prepared by a hydrothermal synthesis method and directly employed as the air-breathing cathode of the Li-O 2 battery. The morphological phenomenon and electrochemical performance of the as-prepared cathode material were characterized by high-resolution scanning electron microscopy, X-ray diffraction, cyclic voltammetry, galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy measurements. The Co-doped NiO electrode delivered a maximum discharge capacity of around 12 857 mA h g -1 with a low overpotential (0.82 V) at 200 mA g -1 . Under upper-limit specific capacities of 500 mA h g -1 at 400 mA g -1 , the Li-O 2 batteries exhibited a long cycle life of 165 cycles. Compared with the undoped NiO electrode, the Li-O 2 battery based on the Co-doped NiO cathode showed significantly higher oxygen reduction reaction and oxygen evolution reaction activities. This superior electrochemical performance is because of the partial substitution of Ni 2+ in the NiO matrix by Co 2+ to improve the p-type electronic conductivity of NiO. In addition, the morphology and specific surface area of NiO are affected by Co doping, which can expand the electrode-electrolyte contact area and lead to sufficient space for Li 2 O 2 deposition. This approach harnesses the great potential of Co-doped NiO nanosheets for practical applications as advanced electrodes for rechargeable Li-O 2 batteries.

Dendrite growth of metal anodes is one of the key hindrances for both secondary aqueous metal batteries and nonaqueous metal batteries. In this work, a freestanding Ti 3 C 2 T x MXene@Zn paper is designed as both zinc metal anode and lithium metal anode host to address the issue. The binder-free Ti 3 C 2 T x MXene@Zn paper exhibits merits of good mechanical flexibility, high electronic conductivity, hydrophilicity, and lithiophilicity. The crystal growth mechanism of Zn metal on common Zn foil and Ti 3 C 2 T x MXene@Zn composite is also studied. It is found that the Ti 3 C 2 T x MXene@Zn paper can effectively suppress the dendrite growth of Zn, enabling reversible and fast Zn plating/stripping kinetics in an aqueous electrolyte. Moreover, the Ti 3 C 2 T x MXene@Zn paper can be used as a 3D host for a lithium metal anode. In this host, Zn is utilized as a nucleation agent to suppress the Li dendrite growth. The freestanding Ti 3 C 2 T x MXene@Zn@Li anode exhibits superior reversibility with high Coulombic efficiency (97.69% over 600 cycles at 1.0 mA cm -2 ) and low polarization compared with the Cu@Li anode. These findings may be useful for the design of dendrite-free metal-based energy storage systems.

Two-dimensional (2D) bismuth oxide (Bi 2 O 3 ) heterostructured nanosheets (BOHNs) were first fabricated by a solution-based molecular self-assembly approach. The synthesized BOHNs nanosheets feature mixed α- and β-phases and rich surface/edge-active sites. When utilized as anode materials for rechargeable batteries, dual-phase BOHNs deliver an initial discharge capacity as high as 647.6 mAh g -1 and an increased capacity of over 200 mAh g -1 remained after 260 cycles for lithium-ion batteries (LIBs), and a stable cycling capacity at ∼50 mAh g -1 after 500 cycles for sodium-ion batteries (SIBs). A novel flexible 2D/1D/2D structure is further developed by implanting 2D BOHNs into conductive 1D carbon nanotubes and 2D graphene to form composite (BOHNCG) paper as free-standing anodes for both LIBs and SIBs. The capacity of 2D/1D/2D BOHNCG as a LIB anode reaches 823.5 mAh g -1 , corresponding to an enhancement of ∼27%, and remains at >110 mAh g -1 after 80 cycles as a SIB anode with greatly improved cycling stability. This work verifies the promising potential of 2D BOHNs for practical energy-related devices and enriches the current research on emerging 2D nanomaterials.

Droplets suspended by acoustic levitation provide genuine substrate-free environments for understanding unconventional fluid dynamics, evaporation kinetics, and chemical reactions by circumventing solid surface and boundary effects. Using a fully levitated air-water interface by acoustic levitation in conjunction with drying-mediated nanoparticle self-assembly, here, we demonstrate a general approach to fabricating free-standing nanoassemblies, which can totally avoid solid surface effects during the entire process. This strategy has no limitation for the sizes or shapes of constituent metallic nanoparticle building blocks and can also be applied to fabricate free-standing bilayered and trilayered nanoassemblies or even three-dimensional hollow nanoassemblies. We believe that our strategy may be further extended to quantum dots, magnetic particles, colloids, etc. Hence, it may lead to a myriad of homogeneous or heterogeneous free-standing nanoassemblies with programmable functionalities.