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Due to strong van der Waals interactions, graphene nanosheets stack together, resulting in inefficient charge storage, which significantly compromises their performance as electrodes in supercapacitors. Herein, we design a hybrid material by interacting covalent organic frameworks (COFs) into reduced graphene oxide (rGO) films or fibers. The 2D COF nanosheets contain abundant mesopores, which prevents the stacking of rGO nanosheets, enabling the efficient electrolyte ion mass transfer. The optimal COF/rGO hybrid delivers a high gravimetric specific capacitance of 321 ​F ​g−1 and volumetric specific capacitance of 237 ​F ​cm−3 in an aqueous electrolyte measured in the three-electrode configuration, representing a breakthrough in capacitive graphene electrodes. Consequently, the fabricated 2D thin-film and 1D fiber supercapacitors deliver a high device energy density of 10.3 ​Wh kg−1 or 7.9 ​mWh cm−3 in aqueous and gel electrolytes, respectively. Moreover, an ultrahigh stack energy density of 87 ​Wh L−1 ​at the power density of 638 ​W ​L−1 is achieved using an ionic liquid electrolyte, which is superior to most of the carbon-based supercapacitors reported so far, as well as commercial lead-acid and lithium thin-film batteries. Overall, this study demonstrates 2D COFs as a critical enabler to realize high-performance graphene supercapacitors. 2D COFs also have the potential to enable unique architectures for many other 2D materials.

Graphene hydrogel fibers are promising electrode materials for emerging wearable energy storage devices. They shrink significantly (up to 10 times in volume) during drying when trapped solvents are removed, accompanied by complex internal structural transformation. This vital drying process has been ignored in previous research. Here, we present a comprehensive study to correlate the drying of graphene hydrogel fibers with their porous structures and electrochemical properties. Five representative drying conditions involving different temperatures, pressures, and solvent exchanging conditions were compared. We found that first, the average interlayer spacing of stacked graphene nanosheets measured by X-ray diffraction is determined during hydrothermal assembly. During drying, the fast solvent removal causes significant pore closure and creates randomly oriented tortuous pores. On the other hand, the evaporation of solvents provides capillary forces to drive the rearrangement of stacked rGO. Trapping non-volatile solvents in hydrogel rGO fibers can preserve interconnected pores, while freeze-drying leads to non-interconnected pores. Subsequently, different dried graphene fibers have dramatically different specific volumetric capacitance ranging from 5 to 120 F cm−3 and diverse rate capability in capacitive energy storage. These new fundamental insights provide useful guides for controllable assembly of 2D materials into fiber architectures for energy storage applications and beyond.

As an emerging clean coal combustion technology, Moderate or Intense Low-Oxygen Dilution (MILD) combustion or oxy-fuel combustion, compared with traditional coal combustion, has many advantages. However, compared with MILD combustion and oxy-fuel combustion, MILD-oxy combustion is believed more attractive. In this work, MILD-oxy combustion characteristics with oxygen concentrations from 10% to 50% are studied numerically. The results show that within a certain range, increasing the oxygen concentration is in favor of MILD-oxy combustion performance close to that of MILD-air combustion. When the oxygen concentration is higher enough, the momentum reduced by the increase of oxygen concentration has a great influence on the furnace temperature. With the increase of oxygen concentration, the radiation heat transfer is enhanced and the convective heat transfer is weakened. The increase of oxygen concentration can promote the occurrence of char gasification reaction with CO2. In addition, MILD-oxy combustion has a large impact on CO emission.

Many engineering applications demand lightweight materials with multifunctional mechanical properties. Graphene aerogels (GAs) have emerged as a potential candidate. However, GAs reported so far exhibit weak mechanical strength. Here, we report a two-step freezing method with assistance of borate cross-linkers to synthesize a core-shell structured GA. The large temperature gradient can control the nucleation and growth of ice crystals, leading to the formation of a densely packed core and sparsely packed shell. This unique structure can be turned for high compressive strength (43.43 kPa at 50% strain) and elasticity through consecutive distribution of mechanical loads between the core and shell. It can fully recover from 70% strain and 100 compression cycles under 50% strain. The GA also shows excellent compression sensitivity to electrical resistance, and the first-ever reported creep resistance for GAs with negligible residual strain under a static force of 4 kPa up to 200 °C in the air. The as-formed core-shell GAs exhibit stable piezoelectric effects, ultralow thermal conductivity (∼0.023 W m−1K−1) and superior electrical conductivities (up to 52.99 S/m at 70% strain). The unique architecture and its multifunctional mechanical properties make it promising for a range of applications, including flexible sensors, actuators, thermal insulation, and electronics.

Flexible zinc-air batteries (ZAB) are a promising battery candidate for emerging flexible electronic devices, but the catalysis-based working principle and unique semi-opened structure pose a severe challenge to their overall performance at cold temperature. Herein, we report the first flexible rechargeable ZAB with excellent low-temperature adaptability, based on the innovation of an efficient electrocatalyst to offset the electrochemical performance shrinkage caused by decreased temperature and a highly conductive hydrogel with a polarized terminal group to render the anti-freezing property. The fabricated ZABs show excellent electrochemical performances that outperform those of many aqueous ZABs at room temperature. They also deliver a high capacity of 691 mAh g-1 and an energy density of 798 Wh kg-1 at -20 °C (92.7 % and 87.2 % retention of the room temperature counterparts, respectively), together with excellent flexibility and reverting capability.

The sluggish oxygen evolution reaction (OER) is a crucial limiting factor in many renewable energy conversion and storage devices. Multi-metal oxides have been explored as efficient electrocatalysts for the OER; however, the ideal elemental composition for multi-metal oxides is unknown. We first performed density functional theory calculations, which predicted that Co oxyhydroxides doped with Fe and V have excellent catalytic activity. We synthesized a series of amorphous Co–Fe–V ternary metal oxides with a precisely controlled metal molar composition (denoted as CoaFebVcOx, where a + b + c = 10), uniformly distributed elements and identical morphologies by using Prussian blue analogues (PBAs) as novel metal precursors. A systematic investigation was carried out to establish correlations between the elemental compositions and the OER activity for CoaFebVcOx, resulting in a comprehensive catalytic activity atlas of ternary Co–Fe–V metal oxides for the OER, which can serve as a roadmap for electrocatalyst development. In particular, Co3Fe4V3Ox with an elemental composition of Co : Fe : V = 3 : 4 : 3 shows the best performance, with an overpotential of merely 249 mV to reach a current density of 10 mA cm−2, and a low Tafel slope of 41 mV dec−1, outperforming a commercial IrOx catalyst. X-ray photoelectron spectroscopy analysis reveals strong electronic synergies among the metal cations in CoaFebVcOx. The V and Fe doping can affect the electronic structure of Co to yield nearly optimal adsorption energies for OER intermediates, giving rise to the superior activity. Furthermore, composition-tuneable and uniform PBAs may serve as versatile and efficient metal precursors to produce many more multi-metal oxides for various renewable energy applications.

Synthesis of structurally controlled graphene materials is critical for realizing their practical applications. The electrochemical exfoliation of graphite has emerged as a simple method to produce graphene materials. This review examines research progress in the last 5 years, from 2015 to 2019. Graphene material synthesis methods generally have a trade‐off between increasing production yield and achieving better material property control. The synthesis conditions for synthesizing pristine graphene, graphene oxide (GO), and graphene composites are significantly different. Thus, in this review, we first discuss synthesis methods for graphene materials with high C/O ratios from four aspects: graphite electrodes, equipment engineering, electrolytes, and additional reduction methods. Next, we survey synthesis methods for GO and examine how the pretreatment of the graphite electrodes, electrolytes, and operation parameters, such as applied voltages, electrolyte temperatures, and mechanical forces, affect the quality of GO. Further, we summarize electrochemical exfoliation methods used to dope graphene materials, introduce covalent functional groups, incorporate various nanoparticles, and assembly of graphene architectures. For all synthesis methods, we compare the properties of resulting graphene materials such as C/O ratios, lateral size, layer numbers, and quality characterized by Raman spectroscopy. Lastly, we propose our perspectives on further research. We hope this review stimulates more studies to realize the on‐demand production of graphene materials with desired properties using electrochemical exfoliation methods.

One-dimensional fiber-shaped supercapacitors have recently attracted lots of attention as a potential energy storage solution for emerging wearable devices. However, fiber supercapacitors often exhibit low energy storage capacity and poor rate capability due to their small volume, low specific volumetric capacitance, and poor electrode electrical conductivity. Here we demonstrate a novel hydrothermally assembled core-sheath fiber comprised of a graphite fiber core and a MoS2 nanosheet intercalated holey graphene oxide (HGO) sheath as electrodes for fiber supercapacitors. HGO and MoS2 nanosheets self-assemble around the graphite fiber core in a space-confined reactor during the hydrothermal synthesis. HGO nanosheets supply abundance channels for electrolyte ion transfer, MoS2 nanosheets provide large pseudocapacitance, and graphite fibers serve as faster electron transfer highways. The mass loading of MoS2 is easily tunable. The optimized composite fiber with 34.9 wt% MoS2 delivers a high volumetric capacitance 421 F cm−3 at the CV scan rate of 5 mV s−1 and the capacitance retention of 51.0% when the scan rate increases from 2 to 100 mV s−1. The core-sheath fiber enables fast reversible redox kinetics, and its surface capacitive energy storage contributes ∼75–80% of its total energy storage. The assembled solid-state fiber supercapacitor delivers a high device volumetric capacitance of 94 F cm−3 at 0.1 A cm−3 and an energy density of 8.2 mWh cm−3 at the power density of 40 mW cm−3, outperforming many recently reported fiber supercapacitors. The core-sheath fiber electrode design based on HGO, MoS2 and graphite fiber cores provides an efficient platform for designing various novel fiber electrodes for potential electrochemical applications.

The reasonably accurate numerical simulation of methane–air combustion is important for engineering purposes. In the present work, the validations of sub-models were carried out on a laboratory-scale turbulent jet flame, Sandia Flame D, in comparison with experimental data. The eddy dissipation concept (EDC), which assumes that the molecular mixing and subsequent combustion occur in the fine structures, was used for the turbulence–chemistry interaction. The standard k-ε model (SKE) with the standard or the changed model constant C1ε, the realizable k-ε model (RKE), the shear-stress transport k-ω model (SST), and the Reynolds stress model (RSM) were compared with the detailed chemical kinetic mechanism of GRI-Mech 3.0. Different reaction treatments for the methane–air combustion were also validated with the available experimental data from the literature. In general, there were good agreements between predictions and measurements, which gave a good indication of the adequacy and accuracy of the method and its further applications for industry-scale turbulent combustion simulations. The differences between predictions and measured data might have come from the simplifications of the boundary settings, the turbulence model, the turbulence–reaction interaction, and the radiation heat transfer model. For engineering predictions of methane–air combustion, the mixture fraction probability density function (PDF) model for the partially premixed combustion with RSM is recommended due to its relatively low simulation expenses, acceptable accuracy predictions, and quantitatively good agreement with the experiments.

Two-dimensional covalent organic frameworks (2D-COFs) are an emerging family of catalytical materials with well-defined molecular structures. The stacking of 2D nanosheets and large intrinsic bandgaps significantly impair their performance. Here, we report coaxial one-dimensional van der Waals heterostructures (1D vdWHs) comprised of a carbon nanotube (CNT) core and a thickness tunable thienothiophene-pyrene COF shell using a solution based in situ wrapping method. Density functional theory calculations and in-operando and ex-situ spectroscopic analysis show that the carbon-sulfur region in the thienothiophene groups is the active catalytic site. The unique coaxial structure enables controllable n-doping from the CNT core to the COF shell depending on COF shell thickness, which lowers the bandgap and work function of COF. Consequently, the charge transfer barrier between the active catalytic site and adsorbed oxygen intermediates becomes lower, resulting in a dramatic enhancement in their catalytic activity for oxygen redox reactions. It enables a high-performance rechargeable zinc-air battery with a specific capacity of 696 mAh gZn-1 under a high current density of 40 mA cm-2 and excellent cycling stability. 1D vdWHs open the door to create multi-dimensional vdWHs for exploring fundamental physics and chemistry, as well as practical applications in electrochemistry, electronics, photonics, and beyond., Comment: 47 pages and 34 figures

A combined severity factor (RCSF) which is usually used to evaluate the effectiveness of hydrothermal pretreatment at above 100 °C had been developed to assess the influence of temperature, time, and alkali loading on pretreatment and enzymatic hydrolysis of lignocellulose. It is not suitable for evaluating alkaline pretreatment effectiveness at lower than 100 °C. According to the reported deducing process, this study modified the expression of $$ {R}_{\mathrm{CSF}}=\log \left[{C}_{OH^{-}}^n\times t\times {e}^{\left({T}_r-{T}_b\right)/14.75}\right] $$ as $$ {R}_{\mathrm{CSF}}=\log \left\{{C}_{OH^{-}}\times t\times {e}^{\left[-13700/\left( Tr+273\right)+36.2\right]}\right\} $$ which is easier and more reasonable to assess the effectiveness of alkaline pretreatment. It showed that RCSF exhibited linear trend with lignin removal, and quadratic curve relation with enzymatic hydrolysis efficiency (EHE) at the same temperature. The EHE of alkali-treated SCB could attain the maximum value at lower RCSF, which indicated that it was not necessary to continuously enhance strength of alkaline pretreatment for improving EHE. Within a certain temperature range, the alkali loading was more important than temperature and time to influence pretreatment effectiveness and EHE. Furthermore, the contribution of temperature, time, and alkali loading to pretreatment cost which was seldom concerned was investigated in this work. The alkali loading contributed more than 70% to the pretreatment cost. This study laid the foundation of further optimizing alkaline pretreatment to reduce cost for its practical application.

A viscosity-sensitive fluorescent probe is demonstrated by grafting a rotatable 4-N,N'-dimethylaniline group on (6,5) single-walled carbon nanotubes. The rotation of the grafted group is constricted by solution viscosity, causing changes in the photoluminescence behaviors of the nanotubes. This enables a highly sensitive fluorescent probe for determining solution ratiometric viscosity in the biologically transparent second near-infrared region.

Herein, we report a facile process to massively synthesize three-dimensional (3D) boron and nitrogen co-doped carbon@Fe 2 O 3 /Fe 3 C/Fe nanoparticle decorated carbon nanotubes (B/N co-doped C@Fe 2 O 3 /Fe 3 C/Fe-CNTs). The fabrication involved a simple one-step chemical vapor deposition process. These as-synthesized 3D B/N co-doped C@Fe 2 O 3 /Fe 3 C/Fe-CNTs based absorbers exhibited excellent microwave absorption properties with tunable strong absorption wavebands in the frequency range of 2–18 GHz. A minimum reflection loss (RL) value of −42.6 dB was observed at 6.88 GHz with absorber thickness of 3.5 mm. Moreover, the absorption bandwidth for RL less than −10 dB was as large as 4.14 GHz when the absorber thickness dropped to 2.0 mm. A possible absorption mechanism was proposed in detail, which can be attributed to the synergy of the impedance matching and enhancement of multiple reflection among 3D B/N co-doped C@Fe 2 O 3 /Fe 3 C/Fe nanoparticles.

In this study, water-responsive elastomer nanocomposites were designed and prepared by simultaneously introducing cellulose nanocrystals (CNCs) and fibrillar silicate (FS) into epoxidized natural rubber (ENR) via latex compounding followed by in-situ drying and filming. The simultaneous presence of CNCs and FS reduces the dense packing of both FS and CNCs because the initial dispersion of FS and CNCs in the latex is homogeneous and mutually separated, and the interaction between FS and CNCs is weaker than that between CNCs. More importantly, the longer FS forms network framework, and some of the shorter CNCs are assembled with FS through hydrogen bonding interaction, forming the much stronger network in CNC/FS/ENR composites. As a result, CNCs and FS show a synergistic effect on the water-responsive sensitivity. Among various ENR composites with the same volume fraction of fillers, 2CNC/4FS/ENR composite exhibits the strongest network, and its storage modulus and reversible water responsive sensitivity are approximately 11.5 times and 3 times that of 6CNC/ENR composite, respectively.

Moderate or intensive low-oxygen dilution (MILD) combustion is a novel combustion technology with high efficiency and low emissions. The turbulence-chemistry interaction is crucial in the numerical research of MILD combustion. In this paper, the MILD and conventional combustions are investigated numerically with the original and the modified Eddy Dissipation Concept (EDC) parameters. The results show that the original EDC constants are suitable for conventional combustion prediction. While, the predicted temperature, and therefore the NOx production in MILD combustion, are overestimated with the original EDC constants. MILD combustion can be reasonably predicted with the modified EDC constants. However, it is worth noting that, the numerical results of conventional combustion with the modified EDC parameters are similar to those of MILD combustion, so it is difficult to judge whether the combustion mode is MILD combustion only with the numerical results at this state. In addition, although conventional combustion with the modified EDC parameters is incorrectly predicted for the distributions of temperature and species, the flow field is basically unchanged with different EDC parameters. Therefore, the flow characteristics can be used to numerically distinguish between MILD combustion and conventional combustion.

Covalent organic frameworks (COFs) with redox-active moieties are potential capacitive energy storage materials. However, their performance is limited by their poor electrical conductivity and sluggish ion diffusion in their nanopores. Herein, we report coaxial one-dimensional van der Waals heterostructures (vdWHs) comprised of a carbon nanotube (CNT) core and a pyrene–pyridine COF shell synthesized by an in situ wrapping method. The coaxial structure allows efficient electronic interaction between the CNT core and COF shell and improves the electrical conductivity significantly. It also improves electrolyte ion accesses to redox-active pyridine groups in the COF, resulting in excellent capacitive energy storage performance with a high specific capacitance of ∼360 F g−1, an excellent rate capability of ∼80%, and a good stability of 92% capacitance retention after 20 000 charge/discharge cycles. Our strategy opens the door to create other multi-dimensional vdWHs for various potential applications.

We demonstrate that novel three-dimensional (3D) B(OH)3 and α-Fe2O3 nanoparticles decorated carbon microspheres (B(OH)3/α-Fe2O3-CMSs) can be fabricated via a facile thermal treatment process. The carbon microspheres with diameter of 1-3μm and decorated B(OH)3 and α-Fe2O3 nanoparticles with diameters of several to tens of nanometers are successfully fabricated. These novel 3D B(OH)3/α-Fe2O3-CMS composites exhibit enhanced microwave absorption with tunable strong absorption wavebands in the frequency range of 2-18GHz. They have a minimum reflection loss (RL) value of -52.69dB at a thickness of 3.0mm, and the effective absorption bandwidth for RL less than -10dB is as large as 5.64GHz. The enhanced microwave absorption performance arises from the synergy of the impedance matching caused by the B(OH)3 nanoparticles, dielectric loss as well as the enhancement of multiple reflection among 3D α-Fe2O3 nanocrystals. These results provide a new strategy to tune electromagnetic properties and enhance the capacity of high-efficient microwave absorbers.

Since the oxidant in the MILD combustion is diluted by recirculated flue gas, the combustion characteristics of the pulverized coal in the MILD combustion are significantly different from the conventional combustion. In this work, thermogravimetric analysis is used to study the combustion characteristics and kinetic characteristics of pulverized coal under low oxygen concentration atmosphere. The results show that pulverized coal has a higher burnout temperature under low oxygen concentrations. Increasing the heating rate or replacing N2 with CO2 improves the combustibility of pulverized coal. In the O2/CO2 atmosphere, due to the low oxygen concentration and the high burnout temperature, the high heating rate may make the contribution of coal gasification greater than that of oxidation. In addition, the Coats-Redfern method is used to calculate the kinetic parameters of pulverized coal MILD combustion under different conditions, and the activation energy ranges from 27.22 kJ/mol to 162.53 kJ/mol.

Emerging wearable electronics require flexible energy storage devices with high volumetric energy and power densities. Fiber-shaped capacitors (FCs) offer high power densities and excellent flexibility but low energy densities. Zn-ion capacitors have high energy density and other advantages, such as low cost, nontoxicity, reversible Faradaic reaction, and broad operating voltage windows. However, Zn-ion capacitors have not been applied in wearable electronics due to the use of liquid electrolytes. Here, the first quasisolid-state Zn-ion hybrid FC (ZnFC) based on three rationally designed components is demonstrated. First, hydrothermally assembled high surface area and conductive reduced graphene oxide/carbon nanotube composite fibers serve as capacitor-type positive electrodes. Second, graphite fibers coated with a uniform Zn layer work as battery-type negative electrodes. Third, a new neutral ZnSO4 -filled polyacrylic acid hydrogel act as the quasisolid-state electrolyte, which offers high ionic conductivity and excellent stretchability. The assembled ZnFC delivers a high energy density of 48.5 mWh cm-3 at a power density of 179.9 mW cm-3 . Further, Zn dendrite formation that commonly happens under high current density is efficiently suppressed on the fiber electrode, leading to superior cycling stability. Multiple ZnFCs are integrated as flexible energy storage units to power wearable devices under different deformation conditions.

1D supercapacitors (SCs) have emerged as promising candidates to power emerging electronics in recent years because of their unique advantages in energy storage and mechanical flexibility. There are four main research fronts in the development of 1D SCs: 1) enhancing mechanical characteristics, 2) achieving superior electrochemical performance, 3) enabling multiple device integration, and 4) demonstrating multifunctionality. Here, a brief history of 1D SCs is presented and significant research achievements regarding the four fronts identified as the main pillars of the development of 1D SCs are highlighted. The current challenges of the fabrication and utilization of 1D SCs are critically examined and potential solutions are analyzed. Plus, the performance inconsistencies arising from the improper use and extreme diversity of performance evaluation and reporting methods are highlighted. Beyond, perspectives on future efforts are provided and goals regarding the four research fronts are set, to further push 1D SCs toward practical applications. The development of 1D SCs is summarized here, with existing obstacles diagnosed, corresponding solutions proposed, and future directions indicated accordingly.

One-dimensional (1D) electrochemical energy storage devices, such as fiber supercapacitors and cable-shaped batteries, are promising energy storage solutions for emerging wearable electronics due to their advantages in flexibility, weavability, and wearability. Two-dimensional (2D) materials with unique structures and properties can be used to create novel 1D electrochemical energy storage devices. Here, we reviewed recent research efforts in using various 2D materials, such as graphene, transitional metal dichalcogenides, transition metal oxides, transition metal hydroxides, and transitional metal carbides and carbonitrides, to construct fiber supercapacitors and cable-shaped batteries. For every 2D material, we first examined its intrinsic properties and their impacts on its energy storage performance. Next, we reviewed several universal approaches which have been used to enhance its performance, including creating nanostructures, controlling the stacking/alignment, modulating chemical properties via doping or phase engineering, forming nanocomposites to increase electrical conductivity or stability, and designing fiber/cable electrode architectures. Further, we also compared the key characteristics and energy storage performance of recently reported 1D electrochemical energy storage devices containing 2D materials. Last, we offer our perspectives on the challenges and potential future research directions in this area. We hope this review can stimulate more research to realize the applications of 2D materials in practical 1D electrochemical energy storage devices. Accepted version The authors acknowledge financial support from the Australian Research Council under the Future Fellowships scheme (FT160100107) and Discovery Project (DP180102210).

Full-spectrum k-distribution (FSK) look-up tables provide great accuracy combined with outstanding numerical efficiency for the evaluation of radiative transfer in nonhomogeneous gaseous media. However, previously published tables cannot be used for gas–soot mixtures that are found in most combustion scenarios since it is impossible to assemble k-distributions for a gas mixed with nongray absorbing particles from gas-only full-spectrum k-distributions. Consequently, a new FSK look-up table has been constructed by optimizing the previous table recently published by the authors and then adding one soot volume fraction to this optimized table. Two steps comprise the optimization scheme: (1) direct calculation of the nongray stretching factors (a-values) using the k-distributions (k-values) rather than tabulating them; (2) deletion of unnecessary mole fractions at many thermodynamic states. Results show that after optimization, the size of the new table is reduced from 5 GB (including the k-values and the a-values for gases only) to 3.2 GB (including the k-values for both gases and soot) while both accuracy and efficiency remain the same. Two scaled flames are used to validate the new table. It is shown that the new table gives results of excellent accuracy for those benchmark results together with cheap computational cost for both gas mixtures and gas–soot mixtures.

The inlet velocity is an important parameter in the Moderate or Intense Low-Oxygen Dilution (MILD) combustion. Different inlet velocities not only change the flow of the flue gas, but also affect the dilution effect of the circulating flue gas and the temperature distribution of the furnace. In coal MILD-oxy combustion, different oxygen concentrations change the amount of flue gas and inlet velocity when the excess oxygen coefficient is fixed. Therefore, the change of inlet velocity is worthy of attention in MILD-oxy combustion. In this work, the MILD combustion characteristics with different inlet velocities at different oxygen concentrations are discussed by changing the burner diameter. The results show that increasing the inlet velocity suppresses the temperature peaks in both MILD-air and MILD-oxy combustion. When the inlet velocity is fixed, the flame temperature is increased with the O2 concentration. The facilitation of char gasification reaction with increasing oxygen concentration is also partly due to the increase of temperature and char gasification is also partially affected by the O2 concentration. In terms of heat transfer, the inlet velocity has a large effect on convective heat transfer.

Translating the advantages of carbon nanomaterials into macroscopic energy storage devices is challenging because the desirable nanoscale properties often disappear during assembly processes. Here we describe a new nonequilibrium subcritical hydrothermal method capable of independently manipulating the temperature and pressure to create unique assembly conditions crossing the commonly used liquid-vapor boundary. Highly conductive and dense-packed yet ion-accessible nanocarbon microfibers can be obtained from graphene oxide sheets, single-walled carbon nanotubes, and a nitrogen-doping crosslinker under 20 min of hydrothermal assembly, 80% energy saving compared to standard hydrothermal methods, and one of the shortest time in the field of hydrothermal processing of carbon nanomaterials. Using those microfibers, we built microsupercapacitors that reach a high volumetric capacitance of 52 F cm−3, energy density of 7.1 mWh cm−3, and power density of 1645.7 mW cm−3, respectively. We further demonstrate the 3D integration of multiple fiber microsupercapacitors that reduces the device footprint by 75% while expanding the operational voltage and current window. This strategy is a promising tool for harmoniously assembling carbon nanostructures as energy storage components for various energy applications.

Novel turbostratic BN thin films have been fabricated via a facile chemical vapor deposition route on SiO2/Si substrates. The BN thin film grew continuously on the entire SiO2/Si surface and the region with uniform thickness (~150 nm) can be up to several centimeters in lateral size which is only limited by the size of the substrate. The thin film exhibited a novel turbostratic graphite-like structure. Moreover, the micro-Raman spectrum of the thin film was found unexpectedly broadened and blue-shifted relative to that of the bulk hexagonal BN. The reason for the peculiar Raman scattering behavior of the turbostratic BN thin films was briefly discussed.

Highlights: • BN hollow nanospheres are fabricated in large scale via a new CVD method. • Morphology and structure are elucidated by complementary analytical techniques. • Formation mechanism is proposed based on experimental observations. • Dielectric properties are investigated in the X-band microwave frequencies. • BN hollow nanospheres show lower dielectric loss than regular BN powders. - Abstract: Boron nitride (BN) hollow nanospheres have been successfully fabricated by pyrolyzing vapors decomposed from ammonia borane (NH{sub 3}BH{sub 3}) at 1300 °C. The final products have been extensively characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The BN hollow nanospheres were ranging from 100 to 300 nm in diameter and around 30–100 nm in thickness. The internal structure of the products was found dependent on the reaction temperatures. A possible formation mechanism of the BN hollow nanospheres was proposed on the basis of the experimental observations. Dielectric measurements in the X-band microwave frequencies (8–12 GHz) showed that the dielectric loss of the paraffin filled by the BN hollow nanospheres was lower than that filled by regular BN powders, which indicated that the BN hollow nanospheres could be potentially used as low-density fillers for microwave radomes.

Coal hydropyrolysis (CHP) and coal hydrogasification (CHG) are two important processes during coal conversion in a hydrogen atmosphere. Much attention has been paid on this clean coal conversion technology because of its advantages. In this work, the CHP and CHG kinetic characteristics of a bituminous coal are studied in a pressurized thermogravimetric analyzer (P-TGA). The effects of the pressure on the CHP and CHG kinetics of the bituminous coal are detected with the non-isothermal thermogravimetric method. In addition, the kinetic compensation effect (KCE) and isokinetic points of the two processes are investigated. Besides, the kinetic triplets, including the pre-exponent factor, the activation energy and mechanism function are also calculated and defined for all of the cases during the CHP and CHG processes. Meaningful and interesting conclusions are finally obtained from this study. The initial pyrolysis temperature will increase with the reaction pressure when the pressure is within 3 MPa. The appe...

Five percent Nb-doped TiO 2 (Nb:TiO 2 ) films on glass substrates were prepared with pulsed laser deposition in 10 mTorr at room temperature, and then, they were annealed at various temperatures from 250 to 550 °C in vacuum ( −5 Torr). The X-ray diffraction data suggest that the as-prepared amorphous Nb:TiO 2 film on glass was transformed to the (1 0 1) oriented anatase phase above ∼350 °C. For the anatase Nb:TiO 2 samples, the temperature dependence of the resistance exhibited a metallic behavior. As the post-deposition annealing temperature increased up to 550 °C, the resistivity (∼3.9 × 10 −4 Ω cm) was minimum at 450 °C while the Hall mobility (2.6 cm 2 /(V s)) and carrier density (4.7 × 10 21 cm −3 ) were maximum. The optical transmittance in the visible light range was about 70–80%, and the optical band gaps gradually decreased from 3.64 to 3.28 eV as the post-deposition annealing temperature increased.

A Nd : YAG / Cr4 + : YAG composite crystal passively Q-switched laser with high-output pulse energy is studied both theoretically and experimentally. According to the characteristics of flash lamp pump, the rate equations of nonuniform pump are established. The pulse interval, pulse energy, and pulse width of the output pulse train are analyzed accurately by nonuniform pump. The experimental parameters are optimized by numerical simulation, with Cr4 + : YAG saturable absorber initial transmittance of 14%, output coupling mirror reflectivity of 30%, and cavity length of 9.7 cm. Under the same conditions, the maximum static energy is 954.34 mJ without Q-switch. An output pulse train with four pulses can be obtained at the same pump condition in experimental study. The four pulses energy are 156.5, 151, 149.74, and 145.76 mJ in turn with corresponding intervals of 20.81, 24.16, and 46.03 μs. The average pulse width is 5.72 ns. The Q-switch efficiency is 63.2%. The energy of the four pulses decreases, the pulse interval increases, and the pulse width is basically unchanged. The nonuniform pump theoretical and experimental results are in good agreement.

Coal hydrogasification (CHG) is a promising technology for clean and efficient coal utilization. However, the kinetic mechanism of CHG has not been fully understood, and multidimensional numerical simulations of CHG in entrained-flow gasifiers are still rarely reported. To evaluate and optimize hydrogasification parameters in an entrained-flow-bed gasifier, it is necessary to develop a reasonable CHG kinetic model and carry out the corresponding numerical simulations. In this work, a CHG kinetic model, including five homogeneous reactions and three heterogeneous reactions, is established. Thereinto, for the heterogeneous reactions, a novel combined random pore and shrinking-core model with pressure correction (CRPSC–PC) is put forward to predict the char–gas reaction process. When the CHG model is set up, it is then loaded to the commercial computational fluid dynamics (CFD) package, Fluent, via the user-defined function (UDF), and the simulation results are validated against literature-available experime...

Nb-doped TiO 2 (Nb:TiO 2 ) films were grown on a hexagonal (0001)Al 2 O 3 substrate at 650 °C and ∼10 −5 Torr. The Nb:TiO 2 film had a small resistivity of ∼8×10 −4 Ω cm at room temperature and a behavior of a slightly increasing resistance upon cooling. In addition, the Nb:TiO 2 film had an optical transmittance of about 60% in the visible range. A careful analysis of the in-plane atomic structure suggests that the rutile Nb:TiO 2 film on the hexagonal (0001)Al 2 O 3 can be re-interpreted by a certain pseudo-hexagonal structure, which is discriminated from the in-plane rectangular one of the tetragonal (100)Nb:TiO 2 . The pseudo-hexagonal properties of the Nb:TiO 2 film were characterized by negligible mosaic structure at the interface, the same electron diffraction pattern as the hexagonal Al 2 O 3 substrate, and perfect six-fold symmetries in the pole figure and ϕ-scan XRD patterns.

In this paper, a series of hybrid star PLLA (sPLLA) with different arm lengths was synthesized via the hydrosilylation between octakis(dimethylsiloxy) silsesquioxane (Q8M8) and functionalized PLLA macromolecules with vinyl end groups (mPLLA). mPLLA was synthesized by ring-opening polymerization of l-lactide using 2-hydroxyethylmethacryl as an initiator in the presence of stannous 2-ethylhexanoate as a catalyst. The obtained sPLLA has low polydispersity with polydispersity index values from 1.29 to 1.30. The arm numbers of sPLLA vary from 5 to 7 and decrease with the increase in the length of the mPLLA arm due to the steric hindrance, which are estimated by 1H NMR analysis. The branched structure of sPLLA is also evidenced by the lower intrinsic viscosity when compared with the linear mPLLA with similar molecular weight. Both the glass transition temperatures (T g’s) and melting temperatures (T m’s) of sPLLAs are higher than those of the mPLLA arms. The incorporation of polyhedral oligomeric silsesquioxane (POSS) does not change the crystalline structure of PLLA, while the crystallinity of sPLLA is enhanced as the result that the POSS core acts as a heterogeneous nucleating agent in the matrix to promote the crystallization ability of PLLA. High-resolution transmission electron microscopy observation suggests that POSS disperses in the crystalline PLLA matrix as 5–20 nm aggregates. Microspheres of sPLLA with mean diameter 1 to 2 μm were prepared via emulsion solvent evaporation method. The sPLLA microspheres have higher loading capacity and encapsulation efficiency and lower drug release rate than mPLLA microspheres.

In this paper, polyhedral oligomeric silsesquioxanes (POSS) with three different substituents are blended with poly(L-lactic acid) (PLLA) solution to prepare the hybrid films. The three types of POSS are octa(3-chloroammoniumpropyl)silsesquioxane (OCAPS), octa(3-chloropropyl)silsesquioxane (OCPS) and octavinylsilsesquioxane (OVPS). The effects of POSS substituents on the dispersion and properties of PLLA are investigated by means of SEM, XRD, DSC, DMA, POM, TGA, tensile and in vitro tests. The results show that OCAPS and OCPS have better dispersion states than OVPS, supported by the fact that an obvious phase separation is observed in OVPS/PLLA hybrid film. OCAPS and OVPS hybrid materials show higher T gs than that of PLLA, whereas OCPS acts as a plasticizer to decrease the T g of PLLA. Meanwhile, the T ms of PLLA are all decreased by the incorporation of the three POSS. The thermal stability of PLLA has been improved by the presence of OCPS and OVPS. The addition of POSS does not change the crystalline s...

Compactness and versatility of fiber-based micro-supercapacitors (FMSCs) make them promising for emerging wearable electronic devices as energy storage solutions. But, increasing the energy storage capacity of microscale fiber electrodes, while retaining their high power density, remains a significant challenge. Here, this issue is addressed by incorporating ultrahigh mass loading of ruthenium oxide (RuO2 ) nanoparticles (up to 42.5 wt%) uniformly on nanocarbon-based microfibers composed largely of holey reduced graphene oxide (HrGO) with a lower amount of single-walled carbon nanotubes as nanospacers. This facile approach involes (1) space-confined hydrothermal assembly of highly porous but 3D interconnected carbon structure, (2) impregnating wet carbon structures with aqueous Ru3+ ions, and (3) anchoring RuO2 nanoparticles on HrGO surfaces. Solid-state FMSCs assembled using those fibers demonstrate a specific volumetric capacitance of 199 F cm-3 at 2 mV s-1 . Fabricated FMSCs also deliver an ultrahigh energy density of 27.3 mWh cm-3 , the highest among those reported for FMSCs to date. Furthermore, integrating 20 pieces of FMSCs with two commercial flexible solar cells as a self-powering energy system, a light-emitting diode panel can be lit up stably. The current work highlights the excellent potential of nano-RuO2 -decorated HrGO composite fibers for constructing micro-supercapacitors with high energy density for wearable electronic devices.