Graphene, with unique two-dimensional form and numerous appealing properties, promises to remark- ably increase the energy density and power density of electrochemical energy storage devices （EESDs）, ...ranging from the popular lithium ion batteries and supercapacitors to next-generation high-energy bat- teries. Here, we review the recent advances of the state-of-the-art graphene-based materials for EESDs, including lithium ion batteries, supercapacitors, micro-supercapacitors, high-energy lithium-air and lithium-sulfur batteries, and discuss the importance of the pore, doping, assembly, hybridization and functionalization of different nano-architectures in improving electrochemical performance. The major roles of graphene are highlighted as （1） a superior active material, （2） ultrathin 2D flexible support, and （3） an inactive yet electrically conductive additive. Furthermore, we address the enormous potential of graphene for constructing new-concept emerging graphene-enabled EESDs with multiple functional- ities of lightweight, ultra-flexibility, thinness, and novel cell configurations. Finally, future perspectives and challenges of graphene-based EESDs are briefly discussed.
MXene-Ti3C2, as a new class of two-dimensional (2D) transition metal carbides (or nitrides), has been synthesized by exfoliating pristine Ti3AlC2 phases with hydrofluoric acid. The SEM and XRD images ...show that the resultant MXene possesses a graphene-like 2D nanostructure. and the surface of MXene has been partially terminated with -OH, thus providing a favorable microenvironment for enzyme immobilization and retaining their bioactivity and stability. Considering the unique metallic conductivity, biocompatibility and good dispersion in aqueous phase, the as-prepared MXene was explored as a new matrix to immobilize tyrosinase (a model enzyme) for fabricating a mediator-free biosensor for ultrasensitive and rapid detection of phenol. The varying electrochemical measurements were used to investigate the electrochemical performance of MXene-based tyrosinase biosensors. The results revealed that the direct electron transfer between tyrosinase and electrode could be easily achieved via a surface-controlled electrochemical process. The fabricated MXene-based tyrosinase biosensors exhibited good analytical performance over a wide linear range from 0.05 to 15.5 μmol L−1, with a low detection limit of 12 nmol L−1 and a sensitivity of 414.4 mA M−1. The proposed biosensing approach also demonstrated good repeatability, reproducibility, long-term stability and high recovery for phenol detection in real water samples. With those excellent performances, MXene with graphene-like structure is proved to be a robust and versatile electrochemical biosensing platform for enzyme-based biosensors and biocatalysis, and has wide potential applications in biomedical detection and environmental analysis.
•Graphene-like MXene-Ti3C2 was prepared by exfoliating pristine Ti3AlC2 with HF.•MXene-Ti3C2 possesses unique metallic conductivity, biocompatibility and good dispersion in aqueous phase.•MXene was explored as a new biosensing platform for tyrosinase immobilization and phenol detection.•The nanostructure and surface -OH provide favorable microenvironments for retaining enzyme bioactivity and stability.•The MXene-Ti3C2 based biosensor exhibited excellent analytical performances.
Ultrafine SnS2 nanocrystals–reduced graphene oxide nanoribbon paper (SnS2–RGONRP) has been created by a well-designed process including in situ reduction, evaporation-induced self-assembly, and ...sulfuration. The as-formed SnS2 nanocrystals possess an average diameter of 2.3 nm and disperse on the surface of RGONRs uniformly. The strong capillary force formed during evaporation leads to a compact assembly of RGONRs to give a flexible paper structure with a high density of 0.94 g cm–3. The as-prepared SnS2–RGONRP composite could be directly used as free-standing electrode for sodium ion batteries. Due to the synergistic effects between the ultrafine SnS2 nanocrystals and the conductive, tightly connected RGONR networks, the composite paper electrode exhibits excellent electrochemical performance. A high volumetric capacity of 508–244 mAh cm–3 was obtained at current densities in the range of 0.1–10 A g–1. Discharge capacities of 334 and 255 mAh cm–3 were still kept, even after 1500 cycles tested at current densities of 1 and 5 A g–1, respectively. This strategy provides insight into a new pathway for the creation of free-standing composite electrodes used in the energy storage and conversion.
Topside total electron content (TEC) data measured by COSMIC/FORMAT-3 during 2008 and 2016 were used to analyze and model the global plasmaspheric electron content (PEC) above 800 km with the help of ...the empirical orthogonal function (EOF) analysis method, and the potential role of the proposed PEC model in helping Global Navigation Satellite System (GNSS) users derive accurate slant TEC (STEC) from existing high-precision vertical TEC (VTEC) products was validated. A uniform gridded PEC dataset was first obtained using the spherical harmonic regression method, and then, it was decomposed into EOF basis modes. The first four major EOF modes contributed more than 99% of the total variance. They captured the pronounced latitudinal gradient, longitudinal differences, hemispherical differences, diurnal and seasonal variations, and the solar activity dependency of global PEC. A second-layer EOF decomposition was conducted for the spatial pattern and amplitude coefficients of the first-layer EOF modes, and an empirical PEC model was constructed by fitting the second-layer basis functions related to latitude, longitude, local time, season, and solar flux. The PEC model was designed to be driven by whether solar proxy or parameters derived from the Klobuchar model meet the real-time requirements. The validation of the results demonstrated that the proposed PEC model could accurately simulate the major spatiotemporal patterns of global PEC, with a root-mean-square (RMS) error of 1.53 and 2.24 TECU, improvements of 40.70% and 51.74% compared with NeQuick2 model in 2009 and 2014, respectively. Finally, the proposed PEC model was applied to conduct a vertical-slant TEC conversion experiment with high-precision Global Ionospheric Maps (GIMs) and dual-frequency carrier phase observables of more than 400 globally distributed GNSS sites. The results of the differential STEC (dSTEC) analysis demonstrated the effectiveness of the proposed PEC model in aiding precise vertical-slant TEC conversion. It improved by 18.52% in dSTEC RMS on a global scale and performed better in 90.20% of the testing days compared with the commonly used single-layer mapping function.
Many studies have reported that there is a coupling mechanism between ionosphere and earthquake (EQ). Ionospheric anomalies in the form of abnormal increases and decreases of ionospheric Total ...Electron Content (TEC) are even regarded as precursors to EQs. In this paper, TEC anomalies associated with three major EQs were investigated by Global Ionospheric Maps (GIMs) and GPS-TEC, including Kumamoto-shi, Japan—EQ occurred on 15 April 2016 with Mw = 7.0; Jinghe, China—EQ occurred on 8 August 2017 with Mw = 6.3; and Lagunas, Peru—EQ occurred on 26 May 2019 with Mw = 8.0. It was found that the negative ionospheric anomalies linger above or near the epicenter for 4–10 h on the day of the EQ. For each EQ, the 10-min sampling interval of TEC was extracted from three permanent GPS stations around the epicenter within 10 days before and after the EQ. Variations of TEC manifest that the negative ionospheric anomalies first appear 10 days before the EQ. From 5 days before to 2 days after the main shock, the negative ionospheric anomalies were more prominent than the other days, with the amplitude of negative ionospheric anomaly reaching −3 TECu and the relative ionospheric anomaly exceeding 20%. In case of Kumamoto-shi EQ, the solar-geomagnetic conditions were not quiet (Dst < −30 nT, Kp > 4, and F10.7 > 100 SFU) on the suspected EQ days. We discussed the differences between ionospheric anomalies caused by active solar-geomagnetic conditions and EQ. Combining the analysis results of Jinghe EQ and Lagunas EQ, under quiet solar-geomagnetic conditions (Dst > −30 nT, Kp < 4, and F10.7 < 100 SFU), it can be found that TEC responds to various solar-geomagnetic conditions and EQ differently. The negative ionospheric anomalies could be considered as significant signals of upcoming EQs. These anomalies under different solar-geomagnetic conditions may be effective to link the lithosphere and ionosphere in severe seismic zones to detect EQ precursors before future EQs.
Nitrogen-doped graphene nanoribbon aerogels (N-GNRAs) are fabricated through the self-assembly of graphene oxide nanoribbons (GONRs) combined with a thermal annealing process. Amino-groups are ...grafted to the surface of graphene nanoribbons (GNRs) by an epoxy ring-opening reaction. High nitrogen doping level (7.6 atm% as confirmed by elemental analysis) is achieved during thermal treatment resulting from functionalization and the rich edge structures of GNRs. The three dimensional (3D) N-GNRAs feature a hierarchical porous structure. The quasi-one dimensional (1D) GNRs act as the building blocks for the construction of fishnet-like GNR sheets, which further create 3D frameworks with micrometer-scale pores. The edge effect of GNRs combined with nitrogen doping and porosity give rise to good electrical conductivity, superhydrophilic, highly compressible and low density GNRAs. As a result, a high capacity of 910 mA h g(-1) is achieved at a current density of 0.5 A g(-1) when they are tested as anode materials for lithium ion batteries. Further cell culture experiments with the GNRAs as human medulloblastoma DAOY cell scaffolds demonstrate their good biocompatibility, inferring potential applications in the biomedical field.
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•There are significant regional differences in the development level of UGI in the YREB.•Cities with high UGI development are mostly concentrated in economically developed areas.•The ...level of UGI development in the YREB region has been shown to be influenced by a combination of diverse conditions.•The high level UGI groupings of cities are more consistent, and the development paths of non-high level UGI are more diverse.
In cities, green infrastructure (GI) is a vital natural life support system that is intimately linked to the daily lives of citizens. High levels of Urban Green Infrastructure (UGI) can help mitigate a series of ecological problems faced by cities, which is extremely important for preserving the stability of urban ecosystems and promoting sustainable urban development. However, current research has not fully explored the influencing factors of UGI and the interaction effect between them. Therefore, in order to better explore the results of China’s proposed policy to promote GI development, data from 110 cities in China’s Yangtze River Economic Belt (YREB) region during the 12th Five-Year Plan and 13th Five-Year Plan periods were measured separately, and natural and geographic environmental conditions, quality of urban construction, level of economic development, socio-cultural development, and eco-environmental quality were selected as the influencing factors. The entropy TOPSIS was used to evaluate the development trend of UGI in the two periods of the region, and the relationship between influencing factors and UGI development was investigated through the use of fs/QCA, and the high-level development path of each city to achieve GI was explained. The results show that (1) Cities with high UGI development are mostly concentrated in economically developed areas, while cities in the YREB’s central and western regions have relatively low levels of UGI development. (2) According to the spatial and temporal differences, the factors driving the high level and non-high level of UGI development in prefecture-level cities in the YREB showed several different configurations, confirming that the development level of UGI was affected by a variety of conditions. (3) During the 12th Five-Year Plan to 13th Five-Year Plan periods, the configuration of urban high-level UGI was found to be more consistent, while the development path of non-high-level UGI is more diversified. The study explores the overall development level and trend of green infrastructure in different cities, and the citation of fs/QCA provides a better understanding of the complex mechanisms of the interactions between these variables, with a view to providing some guidance and enlightenment for enhancing the future urban UGI development and urban high-quality development in the Yangtze River Economic Belt.
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