Gamma-phase CsPbBr3 perovskite nanocrystals/polymethyl methacrylate electrospun nanofibrous membranes with superior photo-catalytic property.

Gamma-phase cesium lead tri-bromide perovskite nanocrystals (γ-CsPbBr3 NCs) possess potentially photo-catalytic degradation ability and long-term stability. However, their serious aggregation issue decreases their active surface area, and the recombination of photo-generated hole-electron pairs weakens their photo-catalytic property. Furthermore, these NCs can be easily absorbed on the surface of dyes [e.g., methylene blue (MB)] or dissolved in the dye solution during the photo-catalytic degradation process, thus reducing the amount of γ-CsPbBr3 NCs and their photo-catalytic degradation ability. Besides, the residual γ-CsPbBr3 NCs in the photo-catalytic degradation products also present the toxicity issue (containing Pb) and are hazardous to the ecological environment and human health. In the present study, we fabricated γ-CsPbBr3 NCs/polymethyl methacrylate electrospun nanofibrous membranes (γ-CsPbBr3 NCs/PMMA ENMs) by using electrospinning technology to solve the above problems. It is found that the synthesized γ-CsPbBr3 NCs/PMMA ENMs show a large surface area and the abundant functional groups on their surfaces, which are benefit for forming multiple kinds of chemical bonding effect between γ-CsPbBr3 NCs and PMMA ENMs. In addition, γ-CsPbBr3 NCs could disperse homogeneously in or on the surface of PMMA ENMs. These abundant chemical bonds and homogeneous distributions of γ-CsPbBr3 NCs on the surface of PMMA ENMs can significantly decrease the recombination of photo-generated hole-electron pairs and toxicity issue of γ-CsPbBr3 NCs during the photo-catalytic degradation process. Exhilaratingly, γ-CsPbBr3 NCs/PMMA ENMs could maintain a superior photo-catalytic degradation ability toward various dyes and reveal a high photo-catalytic degradation efficiency of 99.18% in 60 min for MB.

Hybrid PbS Quantum-Dot-in-Perovskite for High-Efficiency Perovskite Solar Cell.

In this study, a facile and effective approach to synthesize high-quality perovskite-quantum dots (QDs) hybrid film is demonstrated, which dramatically improves the photovoltaic performance of a perovskite solar cell (PSC). Adding PbS QDs into CH3 NH3 PbI3 (MAPbI3 ) precursor to form a QD-in-perovskite structure is found to be beneficial for the crystallization of perovskite, revealed by enlarged grain size, reduced fragmentized grains, enhanced characteristic peak intensity, and large percentage of (220) plane in X-ray diffraction patterns. The hybrid film also shows higher carrier mobility, as evidenced by Hall Effect measurement. By taking all these advantages, the PSC based on MAPbI3 -PbS hybrid film leads to an improvement in power conversion efficiency by 14% compared to that based on pure perovskite, primarily ascribed to higher current density and fill factor (FF). Ultimately, an efficiency reaching up to 18.6% and a FF of over ≈0.77 are achieved based on the PSC with hybrid film. Such a simple hybridizing technique opens up a promising method to improve the performance of PSCs, and has strong potential to be applied to prepare other hybrid composite materials.

New insights into the origin of hysteresis behavior in perovskite solar cells.

Perovskite solar cells (PSCs) have received tremendous attention due to their stunning progress in photovoltaic performance. The hysteresis behavior, however, is one of the major concerning issues accompanying the development of PSCs. In this context, we propose a new mechanism that explains the origin of hysteresis behavior by analyzing the electrical processes after changing the external electrical bias: the compensating electric field to the scanning voltage induced by drifting carriers. This is further verified by experiments, where we observed much reduced hysteresis in the current density-voltage (J-V) characteristics for the PSCs based on a thinner perovskite layer, which is a result of more evenly distributed electrons and holes. Moreover, light illumination with different wavelengths was applied to vary the initial carrier distribution inside the perovskite layer. We found that J-V curves when illuminating the device with longer wavelengths exhibited diminished hysteresis, which could be a result of more evenly generated carriers due to a smaller absorptivity than that with short wavelength illumination. Based on the proposed model, three key factors affecting the hysteresis behavior were pointed out, including the initial carrier distribution, the carrier transport properties in the perovskite layer, and the carrier extraction properties at the interfaces. Strategies to construct hysteresis-free and stable PSCs have thus been accordingly proposed.

Perovskite solar cells: must lead be replaced - and can it be done?

Perovskite solar cells have recently drawn significant attention for photovoltaic applications with a certified power conversion efficiency of more than 22%. Unfortunately, the toxicity of the dissolvable lead content in these materials presents a critical concern for future commercial development. This review outlines some criteria for the possible replacement of lead by less toxic elements, and highlights current research progress in the application of low-lead halide perovskites as optically active materials in solar cells. These criteria are discussed with the aim of developing a better understanding of the physio-chemical properties of perovskites and of realizing similar photovoltaic performance in perovskite materials either with or without lead. Some open questions and future development prospects are outlined for further advancing perovskite solar cells toward both low toxicity and high efficiency.

The effect of urbanization on carbon dioxide emissions efficiency in the Yangtze River Delta, China.

Cities have been one of the most important areas of CO2 emissions. It is increasingly important to research the effect of urbanization on CO2 emissions, especially in large emerging and developing economies, due to the indispensable need for understanding the effect of urbanization on CO2 emissions, evaluating carbon reduction tasks and providing the scientific basis for low-carbon urbanization. Utilizing a balanced panel dataset in the Yangtze River Delta (YRD), China, during the period of 2000-2010, this paper employed data envelopment analysis (DEA) window analysis and a spatial lag panel Tobit model to investigate the effect of urbanization on CO2 emissions efficiency (the ratio of the target CO2 emissions to the actual CO2 emissions). The results show that the average CO2 emissions efficiency was 0.959 in 2010, and CO2 emissions efficiency ranged from 0.816 to 1 and exhibited spatial clustering in the region. The larger potential of CO2 emissions reduction appeared in Zhenjiang and Yangzhou, indicating that more CO2 emissions reduction tasks should be allocated to these two cities. Urbanization has negative effects on improving CO2 emissions efficiency, and there is a U-curve relation between CO2 emissions efficiency and urbanization, indicating that CO2 emissions efficiency decreases at the early stage of urbanization, then increases when urbanization reach a high level. There is spatial spillover effect among the prefecture-level cities, suggesting that different prefecture-level governments should coordinate with each other to improve CO2 emissions efficiency in the whole area. Gross domestic product (GDP) per capita also plays a markedly positive role in improving CO2 emissions efficiency. This research highlights the effect of urbanization on CO2 emissions efficiency and the importance of improving CO2 emissions efficiency in developing countries.

Enhancing the Performance of Perovskite Solar Cells by Hybridizing SnS Quantum Dots with CH3 NH3 PbI3.

The combination of perovskite solar cells and quantum dot solar cells has significant potential due to the complementary nature of the two constituent materials. In this study, solar cells (SCs) with a hybrid CH3 NH3 PbI3 /SnS quantum dots (QDs) absorber layer are fabricated by a facile and universal in situ crystallization method, enabling easy embedding of the QDs in perovskite layer. Compared with SCs based on CH3 NH3 PbI3 , SCs using CH3 NH3 PbI3 /SnS QDs hybrid films as absorber achieves a 25% enhancement in efficiency, giving rise to an efficiency of 16.8%. The performance improvement can be attributed to the improved crystallinity of the absorber, enhanced photo-induced carriers' separation and transport within the absorber layer, and improved incident light utilization. The generality of the methods used in this work paves a universal pathway for preparing other perovskite/QDs hybrid materials and the synthesis of entire nontoxic perovskite/QDs hybrid structure.

Intercalating Ti2 Nb14 O39 Anode Materials for Fast-Charging, High-Capacity and Safe Lithium-Ion Batteries.

Ti-Nb-O binary oxide materials represent a family of promising intercalating anode materials for lithium-ion batteries. In additional to their excellent capacities (388-402 mAh g-1 ), these materials show excellent safety characteristics, such as an operating potential above the lithium plating voltage and minimal volume change. Herein, this study reports a new member in the Ti-Nb-O family, Ti2 Nb14 O39 , as an advanced anode material. Ti2 Nb14 O39 porous spheres (Ti2 Nb14 O39 -S) exhibit a defective shear ReO3 crystal structure with a large unit cell volume and a large amount of cation vacancies (0.85% vs all cation sites). These morphological and structural characteristics allow for short electron/Li+ -ion transport length and fast Li+ -ion diffusivity. Consequently, the Ti2 Nb14 O39 -S material delivers significant pseudocapacitive behavior and excellent electrochemical performances, including high reversible capacity (326 mAh g-1 at 0.1 C), high first-cycle Coulombic efficiency (87.5%), safe working potential (1.67 V vs Li/Li+ ), outstanding rate capability (223 mAh g-1 at 40 C) and durable cycling stability (only 0.032% capacity loss per cycle over 200 cycles at 10 C). These impressive results clearly demonstrate that Ti2 Nb14 O39 -S can be a promising anode material for fast-charging, high capacity, safe and stable lithium-ion batteries.

CH3NH3PbI3 grain growth and interfacial properties in meso-structured perovskite solar cells fabricated by two-step deposition.

Although the two-step deposition (TSD) method is widely adopted for the high performance perovskite solar cells (PSCs), the CH3NH3PbI3 perovskite crystal growth mechanism during the TSD process and the photo-generated charge recombination dynamics in the mesoporous-TiO2 (mp-TiO2)/CH3NH3PbI3/hole transporting material (HTM) system remains unexploited. Herein, we modified the concentration of PbI2 (C(PbI2)) solution to control the perovskite crystal properties, and observed an abnormal CH3NH3PbI3 grain growth phenomenon atop mesoporous TiO2 film. To illustrate this abnormal grain growth mechanism, we propose that a grain ripening process is taking place during the transformation from PbI2 to CH3NH3PbI3, and discuss the PbI2 nuclei morphology, perovskite grain growing stage, as well as Pb:I atomic ratio difference among CH3NH3PbI3 grains with different morphology. These C(PbI2)-dependent perovskite morphologies resulted in varied charge carrier transfer properties throughout the mp-TiO2/CH3NH3PbI3/HTM hybrid, as illustrated by photoluminescence measurement. Furthermore, the effect of CH3NH3PbI3 morphology on light absorption and interfacial properties is investigated and correlated with the photovoltaic performance of PSCs.

Convergence of carbon intensity in the Yangtze River Delta, China.

As China's industrialization and urbanization have grown rapidly in recent years, China's CO2 emissions rose from 3405.1799 Mt to 10,249.4630 Mt from 2000 to 2013, and it has reached the highest levels in the word since 2006. Chinese government has emphasized the importance of reducing carbon emissions and set the target of reducing carbon intensity to 60-65% of 2005 levels by 2030. Investigating the convergence of carbon intensity can identify the convergence rate, which is helpful in guiding allocations of carbon intensity reduction. The Yangtze River Delta is one of the key carbon emission regions in China, with higher urbanization levels and larger carbon emissions; thus, we employed prefecture-level panel data derived from grid data between 2000 and 2010 to examine whether the convergence of carbon intensity exists across prefecture-level cities in the Yangtze River Delta. Spatial panel data models were utilized to investigate ß-convergence of carbon intensity. The results indicated that carbon intensity showed divergence during 2002-2004 and σ-convergence over other periods (2000-2002 and 2004-2010). Carbon intensity exhibited stochastic convergence, indicating that the shocks to carbon intensity relative to the average level of carbon intensity are only transitory. There was a spatial spillover effect and ß-convergence of carbon intensity, suggesting that prefecture-level cities with higher carbon intensity would decrease rapidly in the Yangtze River Delta. Our results highlight the importance of considering the present state of carbon intensity, spatial factors, and socioeconomic factors such as industrial structure and economic levels during allocation planning for reducing carbon intensity.

Enhanced photoelectrochemical performance of quantum dot-sensitized TiO2 nanotube arrays with Al2O3 overcoating by atomic layer deposition.

While TiO2 nanotube arrays cosensitized with CdS and PbS quantum dots can achieve water splitting under visible light excitation, the use of quantum dots is limited by the relatively slow interfacial hole transfer rate and low internal quantum efficiencies in the visible region. Al2O3 overcoating by atomic layer deposition (ALD) can drastically enhance the photoelectrochemical performance of the quantum dot-sensitized TiO2 nanotube arrays. 30 ALD cycles of the Al2O3 overlayer can achieve a good balance between surface coverage and charge transfer resistance. The resulting maximum photocurrent density of 5.19 mA cm(-2) under simulated solar illumination shows a 52 times improvement over the pure TiO2 nanotube arrays, and more significantly, a 60% enhancement over bare quantum dot-sensitized TiO2 nanotube arrays. The incident photon-to-current conversion efficiency can reach the record value of 83% at 350 nm and remain above 30% up to 450 nm. A systematic examination of the role of the ALD Al2O3 overlayer indicates that surface recombination passivation, catalytic improvement in interfacial charge transfer kinetics, and chemical stabilization might synergistically enhance the photoelectrochemical performance in the visible region. These results provide a physical insight into the facile surface treatment, which could be applied to develop and optimize high-performance photoelectrodes for artificial photosynthesis.

Synergistic recombination suppression by an inorganic layer and organic dye molecules in highly photostable quantum dot sensitized solar cells.

An inorganic layer and dye molecules have synergistically suppressed the recombination in a quantum dot sensitized solar cell (QDSSC), by the design of a structure featured TiO2-CdS-ZnS-N3 (N3: RuL2(NCS)2 (L = 2,2'-bipyridyl-4,4'-dicarboxylic acid)) hybrid photoanode. When fabricated into solar cells, a cobalt complex-based electrolyte rather than an iodine-based one was employed to obtain an impressive photostability for the devices. Raman and Photoluminescence (PL) measurements revealed that not only the CdS QDs were passivated by both the inorganic layer of ZnS and dye molecule of N3, but also N3 served as an efficient hole scavenger for the CdS QDs due to a type-II energetic alignment between the two sensitizers. This role of N3 as an intermediary in hole extraction from CdS QDs to the electrolyte was further proven by the significant photovoltaic performance improvement of the CdS sensitized solar cell after ZnS deposition and N3 co-sensitization. The overall efficiency of the solar cell incorporated with TiO2-CdS-ZnS-N3 film exceeded the sum of the single CdS QDs and N3 dye sensitized solar cells. This enhancement is ascribed mainly to the synergistic recombination suppression by the inorganic layer ZnS and N3 co-sensitization, leading to inhibited recombination and increased electron lifetime, as illustrated by the electrochemical impedance spectroscopy (EIS) analysis.

Hydrothermal synthesis of tetragonal BaTiO3 nanotube arrays with high dielectric performance.

Tetragonal Barium titanate (BaTiO3) nanotube arrays have been prepared using the template-assisted hydrothermal method combined with an annealing process. The in-situ chemical conversion of TiO2 nanotube array templates ensured that BaTiO3 maintained the morphology of the nanotube architectures. Moreover, X-ray diffraction and Raman spectrum characterization were used to confirm that the BaTiO3 nanotube arrays had a tetragonal phase after the use of a simple annealing technique. Typical hysteresis loops showed their ferroelectricity, with the remanent polarization and coercive fields being 2.57 microC/cm2 and 2.52 kV/cm, respectively. The relative dielectric constant of the tetragonal BaTiO3 nanotube arrays reached up to 1000 and the dielectric loss was as low as 0.02 at 1 kHz at room temperature.

Energetic alignment in nontoxic SnS quantum dot-sensitized solar cell employing spiro-OMeTAD as the solid-state electrolyte.

An environmentally friendly solid-state quantum dot sensitized solar cell (ss-QDSSC) was prepared by combining colloidal SnS QDs as the sensitizer and organic hole scavenger spiro-OMeTAD (2,2',7,7'-tetrakis-(N,N-di-p-methoxyphenylamine)9,9'-spirobifluorene) as the solid-state electrolyte, and the energy alignment of SnS and TiO2 was investigated. The bandgap of colloidal SnS QDs increased with decreasing particle size from 14 to 4 nm due to an upshift of the conduction band and a downshift of the valence band. In TiO2/SnS heterojunctions, the conduction band minimum (CBM) difference between TiO2 and SnS was as large as ∼0.8 eV; this difference decreased with decreasing particle size, but was sufficient for electron injection from SnS nanoparticles of any size into TiO2. Meanwhile, the sensitizer regeneration driving force, that is, the difference between the valence band maximum (VBM) of SnS and the work function of the electrolyte, showed an opposite behaviour with the SnS size due to a downward shift of the SnS VB. Consequently, smaller SnS QDs should result in a more efficient charge transfer in heterojunctions, revealing the advantages of QDs vs larger particles as sensitizers. This prediction was confirmed by the improved photovoltaic performance of ss-QDSSCs modified with SnS nanoparticles, which peaked for 5-6 nm sized SnS nanoparticles due to the balance between electron injection and sunlight absorption.

Inequality characteristics and influencing factors of CO2 emissions per capita in Jiangsu Province, China.

Analyzing the inequality characteristics and influencing factors of CO2 emissions per capita (CEPC) is conducive to balancing regional development and CO2 emissions reduction. This study applied the Gini coefficient and Theil index to investigate the CEPC inequalities during 2005-2017 at the county level in Jiangsu Province, China. Considering the spatial spillover and interaction effects, the factors influencing CEPC were analyzed by a hierarchical spatial autoregressive model. The results showed that the inequalities in CEPC first increased and then decreased at the inter-regional, and inter-county levels. The spatial pattern of CEPC was stable, and there was a significantly positive spatial autocorrelation of CEPC at the county level. The High-High type counties were mainly located in Sunan (southern Jiangsu). The spatial interaction effects of the CEPC between the prefecture and county levels indicated that governments at the prefecture level should integrate their county governments to reduce the CEPC. Moreover, carbon intensity, GDP per capita, land urbanization, and industrial structure play an important role in reducing CEPC. Our findings provide a scientific basis for formulating reasonable and effective carbon emission reduction policies.

[Spatiotemporal Evolution Characteristics of Carbon Sources and Carbon Sinks and Carbon Balance Zoning in the Yangtze River Delta Region].

Mastering the spatiotemporal evolution laws of carbon sources and sinks is of great significance to promote the coordinated development of regional low-carbon, improve the science of carbon reduction and sink increase policies, and realize the goal of "double carbon." Taking 41 cities in the Yangtze River Delta Region as the research object, this study analyzed the spatiotemporal evolution characteristics of carbon sources and sinks in the Yangtze River Delta Region from 2000 to 2020 and conducted the carbon balance zoning. The results were as follows： ① The carbon emissions increased rapidly in the Yangtze River Delta Region from 2000 to 2011 but with some fluctuations after 2011. Carbon sinks increased slowly in the Yangtze River Delta Region from 2000 to 2020. The regional differences in carbon emissions and carbon sinks were significant, and the spatial pattern was relatively stable. ② The carbon compensation rate in the Yangtze River Delta Region showed a downward trend, and the carbon productivity, energy utilization efficiency, and carbon ecological support capacity were constantly enhanced. Interregional differences were the main source of carbon compensation rate in the Yangtze River Delta Region. Both the carbon compensation rate and carbon ecological support coefficient showed a spatial pattern of "high in the west and low in the east, high in the south and low in the north." The areas with high carbon economy contributive coefficient were concentrated in the central and southern areas of the Yangtze River Delta regions, and the areas with low carbon economy contributive coefficient were concentrated in Anhui Province. ③ Based on the carbon economy contributive coefficient and the carbon ecological support coefficient, cities in the Yangtze River Delta Region were classified into low-carbon maintenance areas, economic development areas, carbon sink development areas, and comprehensive optimization areas. Recommendations were proposed for each category of cities in order to promote the coordinated development of regional low-carbon and realize the goal of "double carbon".

Re-identifying farmland carbon neutrality gap under a new carbon counting and the framework of regional interactions in China.

The farmland ecosystem, with its numerous material cycles and energy flows, is an important part of the carbon cycle in terrestrial ecosystems. Focusing on the carbon neutrality of farmland is meaningful for mitigating global warming and serving national low-carbon strategies. This study enriches the carbon accounting items of farmland and establishes a new research framework to check the carbon neutrality of farmland from the aspect of regional interactions and, subsequently, the inequality among China's provinces. The results revealed that there is still a great gap in the capability of China's farmland to reach carbon neutrality, with a gap value of up to 10,503 × 104 t C. All of the provinces presented net carbon emissions, and the per unit area carbon neutrality gaps showed spatial regularity decreasing from the coastal regions to the inland areas. Anthropogenic carbon emissions on farmland played a dominant role compared with soil organic carbon. Five provinces had reduced interior-regional carbon emissions through grain trade, and the amounts were especially high for developed regions, such as Guangdong, Zhejiang, Beijing, Shanghai and Jiangsu. Sixteen provinces gained external carbon emissions through trade; these were the less developed regions located mainly in the north, such as Inner Mongolia, Hebei, Jilin, Heilongjiang and Xinjiang. Under regional inequality, 15 provinces added to the net amount of the carbon emissions generated in external regions, with China's megacities adding the highest percentage, especially Beijing, with 389.95 % compared with its original emissions. Inequality showed that most provinces had a moderate status. Sichuan and Hunan experienced weak advantages, and six provinces had disadvantages. Therefore, constructing compensation and trade-based rights and responsibilities traceability mechanisms is important.

Water-assisted chemical vapor deposition synthesis of boron nitride nanotubes and their photoluminescence property.

A novel water-assisted chemical vapor deposition (CVD) method for the efficient synthesis of boron nitride (BN) nanotubes is demonstrated. The replacement of metal oxide by water vapor could continuously generate intermediate boron oxide vapor and enhance the production of BN nanotubes. The nanotubes synthesized when an appropriate amount of water vapor was introduced had an average diameter of about 80 nm and lengths of several hundred µm. The diameter and yield of nanotubes could be controlled by tuning the amount of water vapor. This simple water-assisted CVD approach paves a new path to the fabrication of BN nanotubes in large quantities.

Co-Ni layered double hydroxides for water oxidation in neutral electrolyte.

The electrochemical properties of Co-Ni layered double hydroxides (LDHs) as efficient electrocatalysts for water oxidation were investigated in potassium phosphate electrolyte under neutral pH condition. The Co-Ni LDHs with a core-shell structure were fabricated using a facile route from a Co-Ni hydroxide precursor with iodine as a topotactic oxidizer. The unique core-shell morphology is likely due to the enrichment of Co(III) hydroxide in the inner core indicated by selected area electron diffraction and energy-dispersive spectroscopy. Through a self-assembling process at the organic/inorganic interface and dip-coating, the Co-Ni LDHs were deposited onto FTO glass substrates to prepare composite electrodes. Low over-potential and high current density was achieved in the oxygen evolution reaction. The excellent electrocatalytic activity of Co-Ni LDHs may be attributed to more accessible Co active sites and rapid movement of interlayer ions within their layered structure.

Experimental Study on the Tridacna squamosa Shell: Distinctive Structure and Mechanical Behavior.

Tridacna squamosa, Lamarck, 1819 (Bivalvia Cardiida Cardiidae, known as the fluted giant clam) is one of the largest-sized bivalve shells, which is equipped with a strong and tough bioceramic shell to effectively protect itself from the attack of predators. To better understand the mechanical defense mechanism, the relationship between the microstructure, composition, and mechanical properties of the Tridacna squamosa shell was investigated. We find that the Tridacna squamosa shell is composed of aragonite CaCO3 and a small portion of organic matter, which are well-arranged, assembling a multiscale, inhomogeneous, and anisotropic structure. Three levels of microstructure units are identified, including the smallest aragonite rods, medium sheets, and block-like lamellae. Such multiscale structures are the main contributor to creating abundant fracture surfaces much larger than the case for single mineral components, leading to multiple toughening mechanisms observed in Vickers indentation experiments, such as pulled-out of mineral platelet and crack deflection. The material inhomogeneity in the cross-sectional direction indicates that the material is stronger at the inner layer than that at the outer layer, which also facilitates an effective defense against the predator attack. This study may provide insights into the design of biomaterials with the desired mechanical properties.