Lithium–sulfur (Li–S) batteries have been regarded as a promising next‐generation energy storage technology for their ultrahigh theoretical energy density compared with those of the traditional ...lithium‐ion batteries. However, the practical applications of Li–S batteries are still blocked by notorious problems such as the shuttle effect and the uncontrollable growth of lithium dendrites. Recently, the rapid development of electrospinning technology provides reliable methods in preparing flexible nanofibers materials and is widely applied to Li–S batteries serving as hosts, interlayers, and separators, which are considered as a promising strategy to achieve high energy density flexible Li–S batteries. In this review, a fundamental introduction of electrospinning technology and multifarious electrospinning‐based nanofibers used in flexible Li–S batteries are presented. More importantly, crucial parameters of specific capacity, electrolyte/sulfur (E/S) ratio, sulfur loading, and cathode tap density are emphasized based on the proposed mathematic model, in which the electrospinning‐based nanofibers are used as important components in Li–S batteries to achieve high gravimetric (WG) and volume (WV) energy density of 500 Wh kg−1 and 700 Wh L−1, respectively. These systematic summaries not only provide the principles in nanofiber‐based electrode design but also propose enlightening directions for the commercialized Li–S batteries with high WG and WV.
A mathematic model is proposed using the electrospinning‐based nanofibers serve as a cathode and anode host, and separator to achieve high gravimetric (WG) and volume (WV) energy density of 500 Wh kg−1 and 700 Wh L−1 in Li–S batteries, respectively, by emphasizing the crucial parameters of specific capacity, electrolyte/sulfur (E/S) ratio, sulfur loading, and cathode tap density in the cell.
Photoelectron transfer between heterojuctions is an important process for photocatalysis, and identification of the electron transfer process provides valuable information for catalyst design. ...Herein, Ti3C2, one of the widely used two‐dimensional materials, is used to produce a heterojunction of TiO2 and Ti3C2 by an in situ growth method and the photogenerated electrons transfer between the two components for photocatalytic water splitting to hydrogen is investigated. Theoretical simulation and experimental tests proclaim that electrons transfer from Ti3C2 to TiO2 forms an internal electric field, which implies that there exists the driving force of electronic movement from TiO2 to Ti3C2. In situ irradiation X‐ray photoelectron spectroscopy shows the binding energies of TiC (in Ti3C2) and TiO (in TiO2) move toward negative and positive positions, respectively, verifying the photogenerated electrons produced from TiO2 and transferring to Ti3C2 driven by the internal electric field. In addition, the amount of TiO2 nanoparticles also affects the hydrogen evolution rate. Several parallel experiments are designed to uncover the fact that less or excess amount of TiO2 nanoparticles leads to a tinier shift of binding energy, which hints the quantity of heterojunction is a considerable factor in photocatalytic performance. This work develops a new method to directly monitor the photoelectron transfer process between heterojuctions.
An in situ irradiation X‐ray photoelectron spectroscopy coupled with UV light optical fiber measurement setup is developed to monitor the photoelectron transfer process between heterojuctions.
Given the overload trip of a slag conveyor caused by slag falling in a critical coal-fired boiler using blended Zhundong coal， the diagnosis and analysis were carried out from five aspects of coal ...quality analysis， slag falling location， furnace soot blowing test， aerodynamics field and burner nozzle. The causes of slagging and its falling were deduced. Moreover， the furnace was shut down and inspected to verify the inference. The results indicate that the blended Zhundong leads to a moderate slagging tendency. Under the influence of deformation and blockage of the peripheral air nozzles of the burner， ash from combustion deposits as slag on the side water-cooled wall， accumulating into slags that， upon falling， trigger the overload trip of the conveyor. In view of the coal quality characteristics of the blended Zhundong coal， the paper proposes preventive measures from both operational and maintenance perspectives， providing insights for the operation of boilers facing similar situations.
Rapid climate variability and intense human activities generate obvious impacts on the Qilian Mountains ecosystem. The time series of fractional vegetation coverage (FVC) from 1986 to 2021 were used ...to quantify the impact of climate variability and human activities on vegetation variations in the Qilian Mountain National Nature Reserve (QMNNR), using 3147 land satellite images based on the Google Earth Engine cloud platform. The contributions of climate variability and human activities to FVC were quantified using multiple regression residual analysis. Partial correlation and correlation methods were used to quantify the impact of temperature, precipitation, and human activity footprints on FVC. The results showed that from 1986 to 2021, the increase rate of FVC was 1.7 × 10−3 y−1, and the high vegetation coverage of the FVC was mainly distributed in the southeastern part of the reserve. In contrast, the low vegetation coverage was mainly distributed in the northwest part of the reserve. The Mann–Kendall mutation test found that the year of 2009 was the year of the mutation. The growth rate of FVC from 2010 to 2021 was greater than that from 1986 to 2009. In addition, climate variability and human activities exhibited a remarkable spatial heterogeneity in FVC changes. Climate variability and human activities contributed 49% and 51% to the increase in FVC in the reserve, respectively, and the contribution of human activities was greater than that of climate variability. The warming and humidification phenomena in the reserve were obvious. However, precipitation was the dominant factor affecting the dynamic changes in FVC. This study improves our understanding of the response of vegetation dynamics to the climate and human activities in the QMNNR.
The utilization of powdery semi-coke as a power fuel in pulverized coal-fired power plants has become a new and potential technique to consume the excess powdery semi-coke. The characteristic of low ...volatile results in poor combustion performance and high NO
x
emission, and to co-fire with bituminous coal is a practical strategy to address this problem. However, the co-combustion characteristics and the inherent interaction between semi-coke and coal remain insufficiently understood. In addition, the influences of secondary air arrangement, the boiler operation load, and the fuel type on co-combustion process are still unclear, which is urgent to be further explored. In the present study, experiments and numerical simulations were jointly utilized to inquire into the co-combustion behaviors and NO
x
emission features of semi-coke and coal. The results demonstrated that the “out-furnace method” was a suitable choice for small-capacity boiler when the proportion of semi-coke was 33%, due to the limited combinations of the semi-coke injection position. It was recommended that semi-coke was preferred to be injected from the middle layers of the furnace under the “in-furnace method” to improve the overall co-combustion performance. The critical value of the separated over fire air ratio in this study was 27.5%, over which a slight drop of carbon content in fly ash could come about. Moreover, the elevation in the proportion of separated over fire air gave rise to the significant decline of NO
x
concentration. The constricted secondary air arrangement was preferred to be employed due to the high boiler efficiency. The separated over fire air and the surrounding air needed to maintain a wide-open degree to prevent the increase of NO
x
emissions and the coking of nozzles. For the load reduction regulation method adopted in this study, the NO
x
concentration first rose and then dropped, while the burnout ratio decreased obviously as the operation load was reduced. Different combinations of coal and semi-coke generated significant influences on co-combustion behaviors within the furnace. The NO
x
generated by high-volatile fuel (bituminous coal) combustion was mainly affected by volatile-N, while the NO
x
generated by low-volatile fuel (semi-coke) was mainly impacted by char-N. This study is of guiding significance for the efficient and clean utilization and beneficial to the large-scale application of powder semi-coke in power plants.
The practical exploitation of lithium–sulfur batteries is hindered by a multitude of obstacles, including sluggish redox kinetics and the shuttling of soluble lithium polysulfide (LiPS) during ...long-term cycling. Here, we report the construction of a continuous three-dimensional conductive carbon nanofiber supported TiO2–MXene heterojunction framework (TM-CNFs) via a one-step electrospinning–carbonization strategy, with MXene as the “energy band bridge” between the carbon substrate and TiO2 to reduce the barrier for electron transfer. Theoretical simulations and experimental tests clearly indicate that the TiO2–MXene heterojunction can accelerate the mass transfer process of LiPS at the interface. Meanwhile, the redistribution of electrons at the heterojunction interfaces accelerates the surface electron reversible exchange. Based on the enhanced conductivity, the strong chemisorption for LiPS, and the remarkable catalysis for the simultaneous conversion of the sulfur species, Li–S cells with a flexible TM-CNFs host demonstrate excellent rate performance and cycling stability (807.3 mA h g−1 at 0.5C after 200 cycles, and 723.3 mA h g−1 at 1C after 500 cycles), a high areal capacity and energy density (10.85 mA h cm−2 and 1909.86 W h kg−1 at a high sulfur area loading of 10.5 mg cm−2), and a high gravimetric full-cell energy density over 300 W h kg−1. The present work provides a novel perspective on the design of electrocatalysts for LiPS redox and a feasible strategy to improve the electrochemical performance of practical lithium–sulfur batteries.
The major challenge for realistic application of Li-S batteries lies in the great difficulty in breaking through the obstacles of the sluggish kinetics and polysulfides shuttle of the sulfur cathode ...at high sulfur loading for continuously high sulfur utilization during prolonged charge-discharge cycles. Here we demonstrate that large percentage of sulfur can be effectively incorporated within a three-dimensional (3D) nanofiber network of high quality graphene from chemical vapor deposition (CVD), through a simple ball-milling process. While high quality graphene network provided continuous and durable channels to enable efficient transport of lithium ions and electrons, the in-situ sulfur doping from the alloying effect of ball milling facilitated desirable affinity with entire sulfur species to prevent sulfur loss and highly active sites to propel sulfur redox reactions over cycling. This resulted in remarkable rate-performance and excellent cycling stability, together with large areal capacity at very high sulfur mass loading (Specific capacity over 666 mAh g−1 after 300 cycles at 0.5 C, and areal capacity above 5.2 mAh cm−2 at 0.2 C at sulfur loading of 8.0 mg cm−2 and electrolyte/sulfur (E/S) ratio of 8 µL mg−1; and high reversible areal capacities of 13.1 mAh cm−2 at a sulfur load of 15 mg cm−2 and E/S of 5 µL mg−1).
In situ sulfur-doped graphene network as efficient metal-free electrocatalyst for polysulfides redox reactions to enable high area capacity lithium-sulfur batteries. Display omitted
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•A facile SiO2/Ni2P/rGO/Cd0.5Zn0.5S yolk-shell structural nanoreactor was prepared.•The H2 evolution rate of optimal sample was 14 times higher than pure Cd0.5Zn0.5S.•The directional ...transfer and migration of photo-induced electrons was achieved.•The dynamic behaviors of photo-induced charges were uncovered by ISI-XPS results.
High-efficiency light utilization and prolonged lifetime of photo-induced charge carriers is a key step towards superior photocatalytic H2 evolution. Herein, the design of a novel spatially separated Ni2P co-catalyst decorated SiO2/rGO/Cd0.5Zn0.5S yolk-shell structural photocatalytic nanoreactor is reported. In this system, the advantages of ultrathin mesoporous shell and yolk-shell structure not only facilitate the mass diffusion with short length, but also allow broad-spectrum light absorption and increase the density of catalytic active sites. Importantly, the photo-generated electrons can be directionally injected from the outermost Cd0.5Zn0.5S shell to the spatially separated Ni2P co-catalyst. The dynamic behaviors of photo-induced charge carriers can be rationally regulated by the suitable energy level alignment and the built-in electric fields derived from both sides of embedded rGO interlayer. The synergistic effects of the excellent light-harvesting ability, more exposed active sites and improved charge separation efficiency significantly boosted the photocatalytic performances of hydrogen evolution. As a result, the optimal SiO2/Ni2P/rGO/Cd0.5Zn0.5S composite exhibited the highest hydrogen generation of 11.65 mmoL‧g−1‧h−1, even after five cycles. This work proposes new insights into the design of the efficient hollow sphere structural heterojunctions for photocatalytic water splitting applications.
•A free-standing film composed of yolk-shell nanofibers was synthesized by a typical hard-templating method.•The TiO2-CNFs@void@TiN@C composite shows an excellent sulfur affinity and a cathode with ...68 wt% sulfur was obtained.•The unique structure and asymmetric polar groups can effectively retard the ‘shuttle effect’ of soluble LIPSs.•Stable cyclic performance with ~0.054% capacity decay per cycle over 1000 cycles at 1C was obtained.•The cathode with 9.5 mg cm−2 sulfur loading could deliver an extremely high areal capacity of 8.2 mAh cm−2at 1.5 mA cm−2.
Nanostructure design holds great potential in fabricating sulfur electrodes that host a high sulfur loading and still attain high electrochemical utilization for the developing of high-energy-density lithium-sulfur (Li-S) batteries. In this contribution, we introduce the yolk-shell structure into a freestanding carbon nanofibers film and construct a complete hollow yolk-shell TiO2/carbon nanofibers@void@TiN@carbon (TiO2-CNFs@void@TiN@C) composite. With inherent double conductive network and strong adsorption capability for polysulfides, the TiO2-CNFs@void@TiN@C composite can not only provide sufficient electrical contact for the insulating sulfur, but also effectively entrap polysulfides for prolonged cycle life. As a result, an excellent capacity retention ratio of 60.9% after 1000 cycles at 1 C as well as a high capacity of 688.5 mAh g−1 at 5 C rate is accomplished with the cells employing TiO2-CNFs@void@TiN@C as a cathode substrate for sulfur. Moreover, the TiO2-CNFs@void@TiN@C composite, with a high S mass loading of 9.5 mg cm−2, delivers a superb areal capacity of 8.2 mAh cm−2.
Intact coaxial multilayered yolk-shell TiO2-CNFs@void@TiN@C composite serves as a freestanding sulfur host. Display omitted
In order to obtain the maximum green up-conversion luminescence intensity of Ho
3+
/Yb
3+
co-doped YNbO
4
, a uniform design and a quadratic general rotation combination design were applied to ...optimize the doping concentration. The concentration of the rare earth corresponding to the strongest green luminescence intensity was determined to be 10% Ho
3+
/34.9% Yb
3+
. Maximum luminous intensity of green light tested under 980 nm excitation was 157373.266, which was close to the theoretical calculated integral intensity value of 157290.825. The variation of the up-conversion luminescence spectra at different power density of the 980 nm laser was characterized. According to the formula fitting, the up-conversion luminescence process is a two-photon process. Meanwhile, the temperature sensing characteristic of the samples has been discussed. Finally, the CIE coordinates were analyzed and calculated to be (0.297, 0.692).
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