Improved-quality graphene films via the synergism of large nanosheet aligning and nanotube bridging for flexible supercapacitors.

Scalable production of reduced graphene oxide (rGO) films with high mechanical-electrical properties is desirable as these films are candidates for wearable electronics devices and energy storage applications. Removing structural incompleteness such as wrinkles or voids in the graphene films, which are generated from the assembly process, would greatly optimize their mechanical properties. However, the densely stacked graphene sheets in the films degrade their ionic kinetics and thus limit their development. Here, a horizontal-longitudinal-structure modulating strategy is demonstrated to produce enhanced mechanical, conductive, and capacitive graphene films. Typically, two-dimensional large graphene sheets (LGS) induce regular stacking of graphene oxide (GO) during the assembly process to reduce wrinkles, while one-dimensional single-walled carbon nanotubes (SWCNT) bridge with graphene sheets to strengthen the multidirectional intercalation and reduce GO layer restacking. The simultaneous incorporation of LGS and SWCNT synergistically creates a fine microstructure by improving the alignment of graphene sheets, increasing continuous conductive pathways to facilitate electron transport, and enlarging interlayer spacing to promote electrolyte ion diffusion. As a result, the obtained graphene films are flat and exhibit signally reinforced mechanical properties, electrical conductivity (38727 S m-1), as well as specific capacitance (232 F g-1) as supercapacitor electrodes compared to those of original rGO films. Moreover, owing to the comprehensive improved properties, a flexible gel supercapacitor assembled by the graphene film-based electrodes shows high energy density, good flexibility, and excellent cycling stability (93.8% capacitance retention after 10 000 cycles). This work provides a general strategy to manufacture robust graphene structural materials for energy storage applications in flexible and wearable electronics.

Combined assisted bone age assessment and adult height prediction methods in Chinese girls with early puberty: analysis of three artificial intelligence systems.

BACKGROUND: The applicability and accuracy of artificial intelligence (AI)-assisted bone age assessment and adult height prediction methods in girls with early puberty are unknown. OBJECTIVE: To analyze the performance of AI-assisted bone age assessment methods by comparing the corresponding methods for predicted adult height with actual adult height. MATERIALS AND METHODS: This retrospective review included 726 girls with early puberty, 87 of whom had reached adult height at last follow-up. Bone age was evaluated using the Greulich-Pyle (GP), Tanner-Whitehouse (TW3-RUS) and China 05 RUS-CHN (RUS-CHN) methods. Predicted adult height was calculated using the China 05 (CH05), TW3 and Bayley-Pinneau (BP) methods. RESULTS: We analyzed 1,663 left-hand radiographs, including 155 from girls who had reached adult height. In the 6-8- and 9-11-years age groups, bone age differences were smaller than those in the 12-14-years group; however, the differences between predicted adult height and actual adult height were larger than those in the 12-14-years group. TW3 overestimated adult height by 0.4±2.8 cm, while CH05 and BP significantly underestimated adult height by 2.9±3.6 cm and 1.3±3.8 cm, respectively. TW3 yielded the highest proportion of predicted adult height within ±5 cm of actual adult height (92.9%), with the highest correlation between predicted and actual adult heights. CONCLUSION: The differences in measured bone ages increased with increasing bone age. However, the corresponding method for predicting adult height was more accurate when the bone age was older. TW3 might be more suitable than CH05 and BP for predicting adult height in girls with early puberty. Methods for predicting adult height should be optimized for populations of the same ethnicity and disease.

Surface amorphous coating for an economical and high-stability current collector for rechargeable aluminum-ion batteries.

Rechargeable aluminum-ion batteries (AIBs) are regarded as the next-generation energy storage devices due to their low flammability, low cost and high power density as well as abundant aluminum (Al) reserves. However, these popular ionic liquid electrolytes contain highly corrosive acid, which always corrodes the most used positive current collector, thus hindering the commercialization of AIBs. This study proposes an efficient and economical method of coating amorphous Ni3S2compound on a nickel metal current collector (Ni-S/Ni). The conductivity and the onset oxidation potential of amorphous Ni3S2coating can be up to 2.3 × 106S m-1and 2.7 V respectively. A Ni-S/Ni current collector can provide excellent cycling stability with no electrochemical corrosion in the AIBs. The AIBs fabricated using a Ni-S/Ni current collector exhibits a specific capacity of 65 mAh/g at 1 A g-1, high coulombic efficiency of 99% and cyclability of at least 2000 cycles. Moreover, the total cost of the Ni-S/Ni current collector can be limited to less than 3.3 USD/m2. The comprehensive performances of these AIBs are better than most reported results so far, which indicates that this method can advance the commercialization of AIBs.

Effects of electrode thickness and crystal water on pseudocapacitive performance of layered birnessite MnO2.

Manganese dioxide (MnO2) nanomaterials with two-dimensional (2D) layered birnessite structures are promising pseudocapacitive electrode materials. However, the effects of structural factors on their electrochemical performance is not fully understood. We synthesize alkali-free crystal water containing 2D layered birnessite MnO2 electrodes with controllable mass loading from 0.1 to 19.3 mg cm-2 to investigate the effects of electrode thickness and crystal water functions on crystal structure and pseudocapacitive behavior, to promote its industrialization. We find that the crystal water enlarges the interlayer space of birnessite MnO2 with electrolyte ions transported much more easily, resulting in higher specific capacitance of 702 F g-1 (70.2 mF cm-2) and excellent cycling stability of 20 000 charge-discharge cycles even at a mass loading of up to 10.8 mg cm-2. Such gains in specific capacitance are weakened significantly with raised mass loading. Thus, compared to a carbon cloth substrate, a carbon nanotube film with enhanced electron space transport capability presents better performance, indicating an effective strategy for higher mass loading cases. The present work sheds light on an efficient method for achieving high capacitance and mass loading together, for practical applications.

ZIF-derived carbons as highly efficient and stable ORR catalyst.

To develop highly efficient none-precious metal catalysts in lieu of Pt/C for catalyzing oxygen reduction reaction (ORR), ZIF-67 derived carbons are fabricated rationally in combination with reduced graphene oxide (rGO) integration and further KOH etching respectively. ZIF-C/rGO presents excellent ORR activity especially in alkali media with onset potential, half-wave potential and limited current density being 1.00 V, 0.87 V and 5.92 mA cm-2, respectively, which are close approaching or superior to those of commercial Pt/C. Although the ORR activity in acid media is still a little inferior to that of the Pt/C, the durability of ZIF-C/rGO is better in both alkali and acid electrolytes. Further KOH etching (ZIF-C/rGO-KOH) reduces active N sites and destroys the micropores with resulting in reduced ORR performances, though more mesopore Brunauer-Emmett-Teller surface and volume are obtained. Through comparable study, huge performance enhancements form rGO integration is attributed to the attained higher charge transfer channels, more micropores with avoiding great losses of N and Co active sites can depress over polarization of electrolyte, aggregation of active components and collapsing of mass transport channels, on which the ORR activity is boosted to the extreme due to the resulted synergistic effect.

The Solvent Induced Inter-Dimensional Phase Transformations of Cobalt Zeolitic-Imidazolate Frameworks.

Studying inter-dimensional phase transitions of zeolitic-imidazolate frameworks (ZIFs) is essential for developing strategies in controlling morphology and properties. Herein, the inter-dimensional topotactic phase transformations of 3D ZIF-67 to 2D ZIF-L are investigated in detail by employing a simple and efficient solvent-induced growth method. In addition to ZIF-67 and ZIF-L, a series of novel core-shell composites of ZIF-67@ZIF-L, with unprecedented morphologies, are also obtained and well-defined. The different behaviors of the amine hydrogen of 2-MIM in the solvents play a pivotal role for inter-dimensional phase transformations, and in combination with the concentration of 2-MIM, the 2D to 3D phase transformations are also revealed. The findings are very beneficial for morphological design of the ZIFs, along with exploration of the corresponding properties. Impressively, Co-ZIFs exhibit interesting tunable CO2 adsorption behaviors with the phase evolution, which might bring broader understanding for designing CO2 detection and adsorption devices.

High-efficiency piezoelectric micro harvester for collecting low-frequency mechanical energy.

A single-layer zinc oxide (ZnO) nanorod array-based micro energy harvester was designed and integrated with a piezoelectric metacapacitor. The device presents outstanding low-frequency (1-10 Hz) mechanical energy harvesting capabilities. When compared with conventional pristine ZnO nanostructured piezoelectric harvesters or generators, both open-circuit potential and short-circuit current are significantly enhanced (up to 3.1 V and 124 nA cm-2) for a single mechanical knock (∼34 kPa). Higher electromechanical conversion efficiency (1.3 pC/Pa) is also observed. The results indicate that the integration of the piezoelectric metacapacitor is a crucial factor for improving the low-frequency energy harvesting performance. A double piezoelectric-driven mechanism is proposed to explain current higher output power, in which the metacapacitor plays the multiple roles of charge pumping, storing and transferring. An as-fabricated prototype device for lighting an LED demonstrates high power transference capability, with over 95% transference efficiency to the external load.

Structure and performance of dielectric films based on self-assembled nanocrystals with a high dielectric constant.

Self-assembled films built from nanoparticles with a high dielectric constant are attractive as a foundation for new dielectric media with increased efficiency and range of operation, due to the ability to exploit nanofabrication techniques and emergent electrical properties originating from the nanoscale. However, because the building block is a discrete one-dimensional unit, it becomes a challenge to capture potential enhancements in dielectric performance in two or three dimensions, frequently due to surface effects or the presence of discontinuities. This is a recurring theme in nanoparticle film technology when applied to the realm of thin film semiconductor and device electronics. We present the use of chemically synthesized (Ba,Sr)TiO3 nanocrystals, and a novel deposition-polymerization technique, as a means to fabricate the dielectric layer. The effective dielectric constant of the film is tunable according to nanoparticle size, and effective film dielectric constants of up to 34 are enabled. Wide area and multilayer dielectrics of up to 8 cm(2) and 190 nF are reported, for which the building block is an 8 nm nanocrystal. We describe models for assessing dielectric performance, and distinct methods for improving the dielectric constant of a nanocrystal thin film. The approach relies on evaporatively driven assembly of perovskite nanocrystals with uniform size distributions in a tunable 7-30 nm size range, coupled with the use of low molecular weight monomer/polymer precursor chemistry that can infiltrate the porous nanocrystal thin film network post assembly. The intercrystal void space (low k dielectric volume fraction) is minimized, while simultaneously promoting intercrystal connectivity and maximizing volume fraction of the high k dielectric component. Furfuryl alcohol, which has good affinity to the surface of (Ba,Sr)TiO3 nanocrystals and miscibility with a range of solvents, is demonstrated to be ideal for the production of nanocomposites. The nanocrystal/furfuryl alcohol dispersions are suitable for the fabrication of thin films by chemical deposition techniques, including spin-coating, printing or a spraying process. To demonstrate the application of this technique to device fabrication, a multilayer capacitor with capacitance of 0.83 nF mm(-2) at 1 MHz is presented.

Pattern of linear growth and progression of bone maturation for girls with early-onset puberty: A mixed longitudinal study.

Background and objective: With a worldwide trend to earlier age of onset of puberty, the prevalence of early-onset puberty (EP) among girls has increased. The impact of EP on the pattern of linear growth and bone maturation is unclear. Accordingly, the objective of our study was to describe this pattern for girls with EP in Shenzhen, China. Methods: A total of 498 untreated girls diagnosed with EP at Shenzhen Children's Hospital, China, between January 2016 and December 2021. A total of 1,307 anthropometric measurements and 1,307 left-hand radiographs were available for analysis. Artificial intelligence (AI) was used to determine bone age (BA). Participants were classified into groups according to chronological age (CA) and BA. The pattern of linear growth (height) and progression of bone maturation was described between groups using the Lambda-Mu-Sigma (LMS) method. Published height-for-CA and height-for-BA norm references for a healthy Chinese population were used for age-appropriate comparisons. Results: The mean CA of appearance of first pubertal signs (breast buds) was 8.1 ± 0.5 years. Compared to norm-referenced data, girls with EP were significantly taller at a CA of 7-10 years. This was followed by a slowing in linear growth after a CA of 10 years, with 71 girls with EP having already achieved their target adult height. From 7 to 10 years of BA, the linear growth was slower in the EP group compared to norm-reference values. This was followed by a period of catch-up growth at 11.2 years of BA, with growth curves approaching norm-referenced values. The BA progressed rapidly from 7 to 8 years of age in about half of the girls with EP (median ΔBA/ΔCA >1.9), slowing, thereafter, until the period of catch-up growth at 11.2 years of BA. Conclusions: BA provides a more reliable reference than CA to assess growth parameters among girls with EP. Our limited data set does indicate that EP does not negatively impact final adult height. Therefore, the growth curves from our study are relevant, providing a reference for pediatricians in this clinical population and, thus, preventing over-treatment for EP.

Tremella-like 2D Nickel-Copper Disulfide with Ultrahigh Capacity and Cyclic Retention for Hybrid Supercapacitors.

Two-dimensional (2D) disulfides possess unique physical and chemical properties and are widely used in electronic and photoelectric devices. Tuning the composition and optimizing the structure of the disulfides are feasible approaches to designing target sulfides for hybrid supercapacitors. This work synthesizes the tremella-like nanosheet-connected (CuxNi1-x)S2 via solvothermal and sulfur-vapor vulcanization. The 2D (CuxNi1-x)S2 electrode performs a high reversible capacity (526.0 mA h g-1 at 1 A g-1), decent capacity retention (75.6%) at 10 A g-1, and prolonged cyclic retention (94.4% over 15,000 cycles), which is higher than that of (CuxNi1-x)O and monometallic sulfides of NiS2 and CuS. The elevated electrochemical properties of (CuxNi1-x)S2 are attributed to the optimized composition with increased redox reaction, enlarged lattice distance, abundant active sites, and attractive electronic and ionic conductivity. Also, (CuxNi1-x)S2 and active carbon (AC) are assembled to form a hybrid supercapacitor (HSC). The (CuxNi1-x)S2//AC HSC demonstrates a maximum specific capacitance of 231.0 F g-1 at 1 A g-1 and a high energy density of 82.4 W h kg-1 at a power density of 1.82 kW kg-1. Outstanding cyclic retentions of 94.9 and 84.5% after 8000 and 10,000 cycles are also obtained. In conclusion, this result suggests a facile routine for preparing a novel 2D layer material of (CuxNi1-x)S2 with outstanding specific capacity and cycling performance for hybrid supercapacitors.

Dynamic charge acceptance and hydrogen evolution of a new MXene additive in advanced lead-acid batteries via a rapid screening three-electrode method.

A methodology to screen additives in lead-acid batteries is critical. We developed a three-electrode system that can rapidly check the dynamic charge acceptance (DCA) and hydrogen evolution of electrodes. The electrode with 2% MXene and 0.2% carbon black shows a better DCA, which indicates its great potential in the start-stop technology.

A scaling law for distinct electrocaloric cooling performance in low-dimensional organic, relaxor and anti-ferroelectrics.

Electrocaloric (EC) materials show promise in eco-friendly solid-state refrigeration and integrable on-chip thermal management. While direct measurement of EC thin-films still remains challenging, a generic theoretical framework for quantifying the cooling properties of rich EC materials including normal-, relaxor-, organic- and anti-ferroelectrics is imperative for exploiting new flexible and room-temperature cooling alternatives. Here, we present a versatile theory that combines Master equation with Maxwell relations and analytically relates the macroscopic cooling responses in EC materials with the intrinsic diffuseness of phase transitions and correlation characteristics. Under increased electric fields, both EC entropy and adiabatic temperature changes increase quadratically initially, followed by further linear growth and eventual gradual saturation. The upper bound of entropy change (∆Smax) is limited by distinct correlation volumes (V cr ) and transition diffuseness. The linearity between V cr and the transition diffuseness is emphasized, while ∆Smax = 300 kJ/(K.m3) is obtained for Pb0.8Ba0.2ZrO3. The ∆Smax in antiferroelectric Pb0.95Zr0.05TiO3, Pb0.8Ba0.2ZrO3 and polymeric ferroelectrics scales proportionally with V cr-2.2, owing to the one-dimensional structural constraint on lattice-scale depolarization dynamics; whereas ∆Smax in relaxor and normal ferroelectrics scales as ∆Smax ~ V cr-0.37, which tallies with a dipolar interaction exponent of 2/3 in EC materials and the well-proven fractional dimensionality of 2.5 for ferroelectric domain walls.

Electrical Properties of New Hollandite Complex Oxide Nanocrystals.

A new class of hollandite Ba-Mn-Ti oxide nanocrystals was synthesized. They are synthetic min- erals exclusively composed of Ba, Ti, Mn, and O elements. The BaMn3Ti4O14.25 nanocrystals (designated BMT-134), a typical member of this newly discovered hollandite oxide group, possess a giant dielectric constant and multiferroic properties. In the present paper, electrical properties of nanocrystals of BMT-134 are studied and compared with BMT-125 (BaMn2TiO14.5). We studied the combined complex impedance and temperature dependent conductivity behaviors. The results prove that electron hopping plays a significant role in the electrical properties of the new hollandite BMT nanocrytals. In addition, the dielectric behavior and generation of ferroelectricity can be interpreted on the basis of Mott polaron theory.

A three-dimensional interconnected hierarchical FeOOH/TiO2/ZnO nanostructural photoanode for enhancing the performance of photoelectrochemical water oxidation.

A novel ZnO/TiO2/FeOOH hierarchical nanostructure has been synthesized by a low temperature chemical bath deposition method. The integrated three-dimensional (3D) nanostructure consists of one-dimensional (1D) ZnO/TiO2 core-shell nanowire arrays and two-dimensional (2D) interconnected FeOOH nanosheets. By applying such a hierarchical nanostructure as a photoanode for photoelectrochemical water reaction, higher photostability and photocurrent density are gained compared with the reported ZnO based nanostructures. It is concluded that the giant enhancement of the properties is because, in the process of photoelectrochemical reaction, electron-hole separation and transfer are enhanced efficiently through the ZnO/TiO2 heterojunction, and in the meanwhile, terminal interconnected FeOOH nanosheets play both the roles of a surface catalyst and a protective layer effectively to accelerate water splitting reaction and enhance photostability. Based on such an environmentally friendly hierarchical nanostructure, photoelectrochemical water splitting and other similar reactions could be performed effectively and economically.

Green and scalable production of colloidal perovskite nanocrystals and transparent sols by a controlled self-collection process.

Colloidal perovskite oxide nanocrystals have attracted a great deal of interest owing to the ability to tune physical properties by virtue of the nanoscale, and generate thin film structures under mild chemical conditions, relying on self-assembly or heterogeneous mixing. This is particularly true for ferroelectric/dielectric perovskite oxide materials, for which device applications cover piezoelectrics, MEMs, memory, gate dielectrics and energy storage. The synthesis of complex oxide nanocrystals, however, continues to present issues pertaining to quality, yield, % crystallinity, purity and may also suffer from tedious separation and purification processes, which are disadvantageous to scaling production. We report a simple, green and scalable "self-collection" growth method that produces uniform and aggregate-free colloidal perovskite oxide nanocrystals including BaTiO3 (BT), Ba(x)Sr(1-x)TiO3 (BST) and quaternary oxide BaSrTiHfO3 (BSTH) in high crystallinity and high purity. The synthesis approach is solution processed, based on the sol-gel transformation of metal alkoxides in alcohol solvents with controlled or stoichiometric amounts of water and in the stark absence of surfactants and stabilizers, providing pure colloidal nanocrystals in a remarkably low temperature range (15 °C-55 °C). Under a static condition, the nanoscale hydrolysis of the metal alkoxides accomplishes a complete transformation to fully crystallized single domain perovskite nanocrystals with a passivated surface layer of hydroxyl/alkyl groups, such that the as-synthesized nanocrystals can exist in the form of super-stable and transparent sol, or self-accumulate to form a highly crystalline solid gel monolith of nearly 100% yield for easy separation/purification. The process produces high purity ligand-free nanocrystals excellent dispersibility in polar solvents, with no impurity remaining in the mother solution other than trace alcohol byproducts (such as isopropanol). The afforded stable and transparent suspension/solution can be treated as inks, suitable for printing or spin/spray coating, demonstrating great capabilities of this process for fabrication of high performance dielectric thin films. The simple "self-collection" strategy can be described as green and scalable due to the simplified procedure from synthesis to separation/purification, minimum waste generation, and near room temperature crystallization of nanocrystal products with tunable sizes in extremely high yield and high purity.

Hollandites as a new class of multiferroics.

Discovery of new complex oxides that exhibit both magnetic and ferroelectric properties is of great interest for the design of functional magnetoelectrics, in which research is driven by the technologically exciting prospect of controlling charges by magnetic fields and spins by applied voltages, for sensors, 4-state logic, and spintronics. Motivated by the notion of a tool-kit for complex oxide design, we developed a chemical synthesis strategy for single-phase multifunctional lattices. Here, we introduce a new class of multiferroic hollandite Ba-Mn-Ti oxides not apparent in nature. BaMn3Ti4O14.25, designated BMT-134, possesses the signature channel-like hollandite structure, contains Mn(4+) and Mn(3+) in a 1:1 ratio, exhibits an antiferromagnetic phase transition (TN ~ 120 K) with a weak ferromagnetic ordering at lower temperatures, ferroelectricity, a giant dielectric constant at low frequency and a stable intrinsic dielectric constant of ~200 (1-100 MHz). With evidence of correlated antiferromagnetic and ferroelectric order, the findings point to an unexplored family of structures belonging to the hollandite supergroup with multifunctional properties, and high potential for developing new magnetoelectric materials.

Magnetoelectricity in CoFe2O4 nanocrystal-P(VDF-HFP) thin films.

Transition metal ferrites such as CoFe2O4, possessing a large magnetostriction coefficient and high Curie temperature (Tc > 600 K), are excellent candidates for creating magnetic order at the nanoscale and provide a pathway to the fabrication of uniform particle-matrix films with optimized potential for magnetoelectric coupling. Here, a series of 0-3 type nanocomposite thin films composed of ferrimagnetic cobalt ferrite nanocrystals (8 to 18 nm) and a ferroelectric/piezoelectric polymer poly(vinylidene fluoride-co-hexafluoropropene), P(VDF-HFP), were prepared by multiple spin coating and cast coating over a thickness range of 200 nm to 1.6 µm. We describe the synthesis and structural characterization of the nanocrystals and composite films by XRD, TEM, HRTEM, STEM, and SEM, as well as dielectric and magnetic properties, in order to identify evidence of cooperative interactions between the two phases. The CoFe2O4 polymer nanocomposite thin films exhibit composition-dependent effective permittivity, loss tangent, and specific saturation magnetization (Ms). An enhancement of the effective permittivity and saturation magnetization of the CoFe2O4-P(VDF-HFP) films was observed and directly compared with CoFe2O4-polyvinylpyrrolidone, a non-ferroelectric polymer-based nanocomposite prepared by the same method. The comparison provided evidence for the observation of a magnetoelectric effect in the case of CoFe2O4-P(VDF-HFP), attributed to a magnetostrictive/piezoelectric interaction. An enhancement of Ms up to +20.7% was observed at room temperature in the case of the 10 wt.% CoFe2O4-P(VDF-HFP) sample.

Enhanced electrochemical stability and ion transfer rate: A polymer/ceramic composite electrolyte for high-performance all-solid-state lithium-sulfur batteries.

All-solid-state (ASS) lithium-sulfur (LiS) batteries utilizing composite polymer electrolytes (CPEs) represent a promising avenue in the domain of electric vehicles and large-scale energy storage systems, leveraging the combined benefits of polymer electrolytes (PEs) and ceramic electrolytes (CEs). However, the inherent weak interface compatibility between PEs and CEs often leads to phase separation, thereby impeding the transposition of Li+. In this study, the trimethoxy-[3-(2-methoxyethoxy)propyl]silane (TM-MES) is introduced as a chemical agent to form bonds with polyethylene oxide (PEO) and Li10GeP2S12 (LGPS), resulting in the development of a novel composite polymer electrolyte (CPETM-MES). This innovative approach mitigates phase separation between PEs and CEs while concurrently enhancing the protective capabilities of LGPS against decomposition at the interfaces of both the Li anode and sulfur cathode. Moreover, the CPETM-MES exhibits superior mechanical toughness, an expanded electrochemical window, and elevated ionic conductivity. In the symmetric cell, it demonstrates an extended operational lifespan exceeding 1800 h, and the current density can reach up to 1.05 mA/cm2. Furthermore, the initial discharge capacity of ASS LiS batteries utilizing CPETM-MES attains 1227 mAh/g and maintains a capacity of 904 mAh/g after 100 cycles. Notably, a high-energy-density of 2454 Wh/kg is achieved based on the sulfur cathode.