Exploring the non-linear relationship and synergistic effect between urban built environment and public sentiment integrating macro- and micro-level perspective: a case study in San Francisco.

Public sentiment can effectively evaluate the public's feelings of well-being in the urban environment and reflect the quality of the spatial environment to a certain extent. Previous studies on the relationship between public sentiment and urban built environmental factors have yielded meaningful results. However, few studies have focused on the effect of micro-built environment on public sentiment at the street level, which directly shapes people's perceptions. In addition, the nonlinear relationship and synergistic effect among urban built environmental factors have been commonly disregarded in previous studies, resulting in an incomplete understanding of the impact of urban built environment on public emotions. Therefore, this paper takes San Francisco as a study case to explore the complex relationship between urban built environmental factors and public emotions. Specifically, this paper measures the polarity of public emotions through sentiment analysis on Twitter data, establishes a comprehensive built environment index system from both macro- and micro- perspectives, and subsequently explores the complex relationship between the urban built environment and public sentiment through the OLS model and Shapley Additive Explanation algorithm. Results show that: (1) micro-built environmental factors have a significant influence on public emotion, although they have been frequently ignored. (2) Public sentiment tends to be more positive in areas with recreation facilities, mixed land use, rich street view visual environment, suitable thermal and acoustic environment, balanced income, and a suitable degree of high population density. (3) A nonlinear relationship and threshold effect exist between the built environmental variables and the semantic orientations of public emotion. Environment improvement strategies based on the synergic effect between variables can effectively promote the generation of positive emotions. Our empirical findings can offer valuable insights to promote feelings of well-being and foster an urban development approach through strategic interventions within the urban built environment.

Stabilized Multi-Electron Reactions in a High-Energy Na4 Mn0.9 CrMg0.1 (PO4 )3 Sodium-Storage Cathode Enabled by the Pinning Effect.

Na superionic conductor (NASICON)-type Na4 MnCr(PO4 )3 has attracted extensive attention among the phosphate sodium-storage cathodes due to its ultra-high energy density originating from three-electron reactions but it suffers from severe structural degradation upon repeated sodiation/desodiation processes. Herein, Mg is used for partial substitution of Mn in Na4 MnCr(PO4 )3 to alleviate Jahn-Teller distortions and to prolong the cathode cycling life by virtue of the pinning effect induced by implanting inert MgO6 octahedra into the NASICON framework. The as-prepared Na4 Mn0.9 CrMg0.1 (PO4 )3 /C cathode delivers high capacity retention of 92.7% after 500 cycles at 5 C and fascinating rate capability of 154.6 and 70.4 mAh g-1 at 0.1 and 15 C, respectively. Meanwhile, it can provide an admirable energy density of ≈558.48 Wh kg-1 based on ≈2.8-electron reactions of Mn2+ /Mn3+ , Mn3+ /Mn4+ , and Cr3+ /Cr4+ redox couples. In situ X-ray diffraction reveals the highly reversible single-phase and bi-phase structural evolution of such cathode materials with a volume change of only 6.3% during the whole electrochemical reaction. The galvanostatic intermittent titration technique and density functional theory computations jointly demonstrate the superior electrode process kinetics and enhanced electronic conductivity after Mg doping. This work offers a new route to improve the cycling stability of the high-energy NASICON-cathodes for sodium-ion batteries.

Bridging the gap between atomically thin semiconductors and metal leads.

Electrically interfacing atomically thin transition metal dichalcogenide semiconductors (TMDSCs) with metal leads is challenging because of undesired interface barriers, which have drastically constrained the electrical performance of TMDSC devices for exploring their unconventional physical properties and realizing potential electronic applications. Here we demonstrate a strategy to achieve nearly barrier-free electrical contacts with few-layer TMDSCs by engineering interfacial bonding distortion. The carrier-injection efficiency of such electrical junction is substantially increased with robust ohmic behaviors from room to cryogenic temperatures. The performance enhancements of TMDSC field-effect transistors are well reflected by the low contact resistance (down to 90 Ωµm in MoS2, towards the quantum limit), the high field-effect mobility (up to 358,000 cm2V-1s-1 in WSe2), and the prominent transport characteristics at cryogenic temperatures. This method also offers possibilities of the local manipulation of atomic structures and electronic properties for TMDSC device design.

Oxide Inhibitor-Assisted Growth of Single-Layer Molybdenum Dichalcogenides (MoX2, X = S, Se, Te) with Controllable Molybdenum Release.

Though chemical vapor deposition (CVD) methods have been widely used in the growth of two-dimensional transition-metal dichalcogenides (2D TMDCs), the controllable fabrication of 2D TMDCs is yet hard to achieve because of the great challenge of concisely controlling the release of precursors vapor, one of the most critical growth kinetic factors. To solve this important issue, here we report the utilization of oxide inhibitors covering Mo source during CVD reactions to manipulate the release of Mo vapor. In contrast to the lack of capability of conventional CVD methods, 2D molybdenum dichalcogenide (MoX2, X = S, Se, Te) monolayers were successfully fabricated through the proposed CVD protocol with the oxide-inhibitor-assisted growth (OIAG) strategy. In this way, despite the fact that only separated MoTe2 flakes were prepared, both MoS2 (continuous and clean) and MoSe2 (continuous but dotted) monolayer films at the scale of centimeter were obtained. The presented OIAG method enables a comprehensive understanding and precise control of the reaction kinetics for improved growth of 2D MoX2.

Effect of Sodium Content on the Electrochemical Performance of Li-Substituted, Manganese-Based, Sodium-Ion Layered Oxide Cathodes.

Li-substituted, manganese-based, layered oxides NaxLi0.18Mn0.66Co0.17Ni0.17O2+δ (x = 0.54, 0.66, 0.78, and 0.90) have been investigated as one kind of high-performance cathode materials for sodium ion batteries (SIBs). Phase compositions and local structures of the cathode materials with varying sodium content were elucidated by powder X-ray diffraction (PXRD) and atomic-scale high angle annular dark field scanning transmission electron microscope (HAADF-STEM), which demonstrates that a Li-O'3 phase was aroused in P2-type sodium layered oxide matrix forming a Na-P2/Li-O'3 hybrid structure. More importantly, the effect of sodium content on the preferential exposure of (102) and (104) facets and surface morphology of the cathode particles has been comprehensively studied, as well as their relationship with electrochemical performance. It reveals that, in addition to the preferential growth of (102) and (104) facets that has been proved to enhance the capacity and rate performance of the layered oxides, the smooth surface finish of the particles also plays a vital role in deciding the electrochemical performance. The layered sodium cathode material with a sodium content of 0.66 possesses sufficient exposure of (102) and (104) facets and smooth side surface, resulting in the superior capacities under various C rates (187 mAh/g at 0.2 C and 114 mAh/g at 5 C) comparing to the cathode materials with all other sodium contents. The mechanism has also been proposed in this study. These findings presented herein open up new strategies to design high performance sodium layered oxide cathode.

Single-Crystal α-Fe2O3 with Engineered Exposed (001) Facet for High-Rate, Long-Cycle-Life Lithium-Ion Battery Anode.

Designing electrode materials with engineered exposed facets provides a novel strategy to improve their electrochemical properties. However, the controllability of the exposed facet remains a daunting challenge, and a deep understanding of the correlation between exposed facet and Li+-transfer behavior has been rarely reported. In this work, single-crystal α-Fe2O3 hexagonal nanosheets with an exposed (001) facet are prepared with the assistance of aluminum ions through a one-step hydrothermal process, and structural characterizations reveal an Al3+-concentration-dependent-growth mechanism for the α-Fe2O3 nanosheets. Furthermore, such α-Fe2O3 nanosheets, when used as lithium-ion battery anodes, exhibit high specific capacity (1261.3 mAh g-1 at 200 mA g-1), high rate capability (with a reversible capacity of approximately 605 mAh g-1 at 10 A g-1), and excellent cyclic stability (with a capacity of over 900 mAh g-1 during 500 cycles). The superior electrochemical performance of α-Fe2O3 nanosheets is attributed to the pseudocapacitive behavior, Al-doping in the α-Fe2O3 structure, and improved Li+-transfer property across the (001) facet, as elucidated by first-principles calculations based on density functional theory. These results reveal the underlying mechanism of Li+ transfer across different facets and thus provide insights into the understanding of the excellent electrochemical performance.

Improving the Electrochemical Properties of the Manganese-Based P3 Phase by Multiphasic Intergrowth.

Layered transition-metal oxides are one kind of the most promising cathode materials for sodium-ion batteries. In this study, we propose a strategy to enhance the electrochemical properties of P3-type manganese-based layered oxide cathode by introducing a small amount of layered P2 and Li-O'3 phases. Powder X-ray diffraction (PXRD) structural refinement and aberration-corrected scanning transmission electron microscopy (STEM) are performed to confirm the microstructures of different samples. PXRD refinement results show that the elevated annealing temperature leads to a partial conversion of the P3 phase to the P2 phase and the addition of lithium results in the formation of a new O'3 phase in the P3/P2-layered matrix. STEM results identify the intergrowth of P3/P2 and P3/P2/O'3 in biphasic and triphasic materials, respectively. Electron energy loss spectroscopy verifies that the alkali metal layer in the O'3 phase is occupied by the lithium ion. The intergrowth of biphasic and triphasic materials in these layered P3/P2 and P3/P2/O'3 hybrid structures brings forth a positive effect on the electrochemical properties. In particular, the formation of P3/P2/O'3-intergrown hybrid structures greatly improves the cycling stability of the P3 phase that the capacity retention of P3/P2/O'3 hybrid structures remains 78%, while capacity retention of the pure P3 phase is only 54.1% after 50 cycles at a rate of 0.2 C, and the rate performance of the P3 phase has also been enhanced.

Bioinspired leaves-on-branchlet hybrid carbon nanostructure for supercapacitors.

Designing electrodes in a highly ordered structure simultaneously with appropriate orientation, outstanding mechanical robustness, and high electrical conductivity to achieve excellent electrochemical performance remains a daunting challenge. Inspired by the phenomenon in nature that leaves significantly increase exposed tree surface area to absorb carbon dioxide (like ions) from the environments (like electrolyte) for photosynthesis, we report a design of micro-conduits in a bioinspired leaves-on-branchlet structure consisting of carbon nanotube arrays serving as branchlets and graphene petals as leaves for such electrodes. The hierarchical all-carbon micro-conduit electrodes with hollow channels exhibit high areal capacitance of 2.35 F cm-2 (~500 F g-1 based on active material mass), high rate capability and outstanding cyclic stability (capacitance retention of ~95% over 10,000 cycles). Furthermore, Nernst-Planck-Poisson calculations elucidate the underlying mechanism of charge transfer and storage governed by sharp graphene petal edges, and thus provides insights into their outstanding electrochemical performance.

Vertically-oriented graphene nanosheet as nano-bridge for pseudocapacitive electrode with ultrahigh electrochemical stability.

A hierarchical structure consisting of Ni-Co hydroxide nanosheets (NCHN) electrodeposited on vertically-oriented graphene nanosheets (GN) on carbon cloth (CC) was fabricated for high-performance pseudocapacitive electrodes. NCHN was uniformly distributed on GN, forming a sheet-on-sheet hierarchical structure. Such NCHN/GN/CC hybrid electrodes exhibit high capacitance and ultrahigh electrochemical-stability that structure and electrochemical properties of hybrid electrodes are not affected by the cyclic low-rate scanning (at 5 mV s-1 even over 1000 cycles). GN vertically grown on CC is used as nano-bridge between NCHN active materials and CC current collector, which effectively facilitates ion/charge transfer between the electrolyte and electrode, consequently leading to the ultrahigh electrochemical-stability of hybrid electrodes. To assess functional behavior, two-terminal flexible asymmetric supercapacitor devices with NCHN/GN/CC as positive electrode and GN/CC as negative electrode were assembled and electrochemically treated to demonstrate the ultrahigh electrochemical stability.