New chemistry for electrochemical energy storage applications

Electrochemical capacitors and batteries are two major electrochemical energy storage technologies, which have been investigated extensively to meet the rapidly-growing demand for higher energy, higher power, lower cost and enhanced safety in the past few decades. With the charge storage mechanism of electrostatic charge adsorption desorption via electrical double layers, electrochemical capacitors deliver higher power, but store less energy, compared to batteries, where redox reactions usually take place inside bulk electrode materials. Depending on the electrolytes, electrochemical capacitors can be divided into aqueous and non-aqueous capacitors. Aqueous electrolytes are more electrically conductive, non-flammable, and more sustainable, compared to non-aqueous electrolytes. However, non-aqueous electrolytes are overwhelmingly dominating the electrochemical capacitor markets, because they provide a larger electrochemical window, and consequently enable capacitors to store more energy. To take advantages of aqueous electrolytes and facilitate safer and more sustainable electrochemical capacitors, tremendous research has been conducted toincrease energy density of aqueous capacitors. Traditional approach is to utilize redox-active electrodes, e.g. metal oxide and conducting polymers in pseudocapacitors, most of which increase energy density at the expense of largely sacrificing power and cycle life. It is important to make progress in one performance aspect of electrochemical capacitors, while retaining other desirable properties as much as possible.There are two effective ways to store more energy in electrochemical capacitors. One is by increasing capacitance, and the other one is by increasing operating voltages.Higher capacitance can be obtained when introducing redox reactions in electrochemical capacitors. Instead of employing redox-active electrodes, which may experience ion diffusion in solid, aqueous redox-active electrolyte was studied to retain high power while storing more energy. The redox pair of IOx- I- in 4 M KI and 1 M KOH is reported for the first time, which enables aqueous capacitors to store a maximum energy of 7.1 Wh kg, on a par with state-of-the-art non-aqueous capacitors, while delivering a maximum power of 6222 W kg, and retaining 93% capacitance after 14,000 cycles.Higher operating voltages are realized in aqueous electrochemical capacitors by maintaining pH 1 and pH 10 at the positive and negative electrode, respectively, with a bipolar assembly of ion-exchange membranes. The theoretical electrochemical window of aqueous electrolytes is expanded from 1.23 to 1.76 V. A practical operating voltage of 1.8 V is proved to be safe for aqueous capacitors with the bipolar assembly,which allows to store a specific energy of 12.7 Wh kg, as well as retain 97% capacitance after 10,000 cycles.Although batteries, especially lithium-ion batteries, have been successful in different fields, e.g. portable electronics, electric vehicles, etc., an intrinsic drawback still exists: low abundance of lithium and therefore high cost of lithium-ion batteries. To address this issue, different types of batteries have been studied, which utilize Earth-abundant elements, such as Na, K, Al, etc. In this dissertation, a novel battery is reported, where hydronium ions perform as charge carriers. For the first time, hydronium ions are found to be reversibly stored in 3,4,9,10-perylenetetracarboxylic dianhydride crystals, contributing 85 mAh g at 1 A g after an initial conditioning process. As an aqueous battery storing hydronium ions instead of metal cations, it may deliver higher power, significantly lower the battery cost, and increase the margin of safety. Although this technology is not as mature as lithium-ion batteries, it provides new opportunities and possible solutions for future energy storage.A new deposition technology, namely ambient hydrolysis deposition, is also studied in this dissertation, which enables nanoparticles grown in porous substrate in a simple and cost-effective way. As a proof-of-concept, by controlling the amount of pre-adsorbed water vapor in the porous carbon, various amount of TiO2 nanoparticles are grown in porous carbon. The TiO2 nanoparticles can be converted into TiN nanoparticles by nitridation, which improve the electrical conductivity of porous carbon. Electrodesprepared from porous carbon with TiN nanoparticles coating exhibit enhanced rate capability in electrochemical capacitors.Keywords: electrochemical, energy, supercapacitors, batterie

Multiple Ambient Hydrolysis Deposition of Tin Oxide into Nanoporous Carbon as a Stable Anode for Lithium-Ion Batteries

We introduce a novel ambient hydrolysis deposition (AHD) methodology that, for the first time, employs sequential water adsorption followed by a hydrolysis reaction to infiltrate tiny SnO2₂ particles inside nanopores of mesoporous carbon in a conformal and controllable manner. The empty space in the SnO2₂/C composites can be adjusted by varying the number of AHD cycles. A SnO2₂/C composite with an intermediate SnO2₂ loading exhibits an initial specific delithiation capacity of 1054 mAh/g as an anode for Li-ion batteries (LIBs). The capacity contribution from SnO2₂ in the composite electrode of SnO2₂ (1494 mAh/g) when considering that both Sn alloying and SnO2₂ conversion reactions are reversible. The composite shows a specific capacity of 573 mAh/g after 300 cycles, one of the most stable cycling performances for the SnO2₂/mesoporous carbon composites. Enabled by the controllable AHD coatings, our results demonstrated the importance of the well-tuned empty space in nanostructured composites to accommodate the expansion of electrode active mass during alloying/dealloying and conversion reactions.Keywords: Sequential, Mesoporous materials, Tin, Lithium-ion batteries, Nanoparticles, SnO2₂/C composite, Electrochemistry, Hydrolysis depositio

Graphene reduced from magnesiothermic reaction

We, for the first time, employ magnesiothermic reaction to convert microwave-irradiated graphite oxide to pure graphene. The magnesiothermic reaction raises the carbon to oxygen atomic ratio from 22.2 to 165.7 and maintains a high surface area. The new strategy demonstrates an efficient method for obtaining highly pure graphene materials

Water Exchange Rate across the Blood-Brain Barrier Is Associated with CSF Amyloid-β 42 in Healthy Older Adults

INTRODUCTION: We tested if water exchange across the blood-brain barrier (BBB), estimated with a noninvasive magnetic resonance imaging (MRI) technique, is associated with cerebrospinal fluid (CSF) biomarkers of Alzheimer\u27s disease (AD) and neuropsychological function. METHODS: Forty cognitively normal older adults (67–86 years old) were scanned with diffusion‐prepared, arterial spin labeling (DP‐ASL), which estimates water exchange rate across the BBB (kw). Participants also underwent CSF draw and neuropsychological testing. Multiple linear regression models were run with kw as a predictor of CSF concentrations and neuropsychological scores. RESULTS: In multiple brain regions, BBB kw was positively associated with CSF amyloid beta (Aβ)42 concentration levels. BBB kw was only moderately associated with neuropsychological performance. DISCUSSION: Our results suggest that low water exchange rate across the BBB is associated with low CSF Aβ42 concentration. These findings suggest that kw may be a promising noninvasive indicator of BBB Aβ clearance functions, a possibility which should be further tested in future research

Plant-frugivore network simplification under habitat fragmentation leaves a small core of interacting generalists

Habitat fragmentation impacts seed dispersal processes that are important in maintaining biodiversity and ecosystem functioning. However, it is still unclear how habitat fragmentation affects frugivorous interactions due to the lack of high-quality data on plant-frugivore networks. Here we recorded 10,117 plant-frugivore interactions from 22 reservoir islands and six nearby mainland sites using the technology of arboreal camera trapping to assess the effects of island area and isolation on the diversity, structure, and stability of plant-frugivore networks. We found that network simplification under habitat fragmentation reduces the number of interactions involving specialized species and large-bodied frugivores. Small islands had more connected, less modular, and more nested networks that consisted mainly of small-bodied birds and abundant plants, as well as showed evidence of interaction release (i.e., dietary expansion of frugivores). Our results reveal the importance of preserving large forest remnants to support plant-frugivore interaction diversity and forest functionality.Fil: Li, Wande. East China Normal University; ChinaFil: Zhu, Chen. College Of Life Sciences, Zhejiang University; ChinaFil: Grass, Ingo. Universidad de Hohenheim; AlemaniaFil: Vazquez, Diego P.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Provincia de Mendoza. Instituto Argentino de Investigaciones de las Zonas Áridas. Universidad Nacional de Cuyo. Instituto Argentino de Investigaciones de las Zonas Áridas; ArgentinaFil: Wang, Duorun. East China Normal University; ChinaFil: Zhao, Yuhao. East China Normal University; ChinaFil: Zeng, Di. East China Normal University; ChinaFil: Kang, Yi. East China Normal University; ChinaFil: Ding, Ping. No especifíca;Fil: Si, Xingfeng. East China Normal University; Chin

Ambient Hydrolysis Deposition of TiO₂ in Nanoporous Carbon and the Converted TiN/Carbon Capacitive Electrode

Despite the considerable advances of deposition technologies, it remains a significant challenge to form conformal deposition on surface of nanoporous carbons. Here, we introduce a new ambient hydrolysis deposition method that employs and controls pre-adsorbed water vapor on nanoporous carbons to define the deposition of TiO₂. We converted the deposited TiO₂ into TiN via a nitridation process. The metallic-TiN-coated porous carbon exhibits superior kinetic performance as an electrode in electrical double layer capacitors. The novel deposition method provides a general solution for surface engineering on nanostructured carbons, which may result in a strong impact on the fields of energy storage and other disciplines

Land-use change interacts with island biogeography to alter bird community assembly

Anthropogenic activities have reshaped biodiversity on islands worldwide. However, it remains unclear how island attributes and land-use change interactively shape multiple facets of island biodiversity through community assembly processes. To answer this, we conducted bird surveys in various land-use types (mainly forest and farmland) using transects on 34 oceanic land-bridge islands in the largest archipelago of China. We found that bird species richness increases with island area and decreases with isolation, regardless of the intensity of land-use change. However, forest-dominated habitats exhibited lower richness than farmland-dominated habitats. Island bird assemblages generally comprised species that share more similar traits or evolutionary histories (i.e., functional and/or phylogenetic clustering) than expected if assemblages were randomly assembled. Contrary to our expectations, we observed that bird assemblages in forest-dominated habitats were more clustered on large and close islands, whereas assemblages in farmland-dominated habitats were more clustered on small islands. These contrasting results indicate that land-use change interacts with island biogeography to alter the community assembly of birds on inhabited islands. Our findings emphasize the importance of incorporating human-modified habitats when examining the community assembly of island biota, and further suggest that agricultural landscapes on large islands may play essential roles in protecting countryside island biodiversity

Land-use change interacts with island biogeography to alter bird community assembly

Anthropogenic activities have reshaped biodiversity on islands worldwide. However, it remains unclear how island attributes and land-use change interactively shape multiple facets of island biodiversity through community assembly processes. To answer this, we conducted bird surveys in various land-use types (mainly forest and farmland) using transects on 34 oceanic land-bridge islands in the largest archipelago of China. We found that bird species richness increases with island area and decreases with isolation, regardless of the intensity of land-use change. However, forest-dominated habitats exhibited lower richness than farmland-dominated habitats. Island bird assemblages generally comprised species that share more similar traits or evolutionary histories (i.e., functional and/or phylogenetic clustering) than expected if assemblages were randomly assembled. Contrary to our expectations, we observed that bird assemblages in forest-dominated habitats were more clustered on large and close islands, whereas assemblages in farmland-dominated habitats were more clustered on small islands. These contrasting results indicate that land-use change interacts with island biogeography to alter the community assembly of birds on inhabited islands. Our findings emphasize the importance of incorporating human-modified habitats when examining the community assembly of island biota, and further suggest that agricultural landscapes on large islands may play essential roles in protecting countryside island biodiversity

High Genetic Diversity and Low Differentiation of Michelia coriacea (Magnoliaceae), a Critically Endangered Endemic in Southeast Yunnan, China

Michelia coriacea, a critically endangered tree, has a restricted and fragmented distribution in Southeast Yunnan Province, China. The genetic diversity, genetic structure and gene flow in the three extant populations of this species were detected by 10 inter-simple sequence repeat (ISSR) markers and 11 simple sequence repeat (SSR) markers. Examination of genetic diversity revealed that the species maintained a relatively high level of genetic diversity at the species level (percentage of polymorphic bands) PPB = 96.36% from ISSRs; PPL (percentage of polymorphic loci) = 95.56% from SSRs, despite several fragmental populations. Low levels of genetic differentiation among the populations of M. coriacea were detected by Nei’s Gst = 0.187 for ISSR and Wright’s Fst = 0.090 for SSR markers, which is further confirmed by Bayesian model-based STRUCTURE and PCoA analysis that could not reveal a clear separation between populations, although YKP was differentiated to other two populations by ISSR markers. Meanwhile, AMOVA analysis also indicated that 22.84% and 13.90% of genetic variation existed among populations for ISSRs and SSRs, respectively. The high level of genetic diversity, low genetic differentiation, and the population, structure imply that the fragmented habitat and the isolated population of M. coriacea may be due to recent over-exploitation. Conservation and management of M. coriacea should concentrate on maintaining the high level of genetic variability through both in and ex-situ conservation actions

Efficient Fabrication of Nanoporous Si and Si/Ge Enabled by a Heat Scavenger in Magnesiothermic Reactions

Magnesiothermic reduction can directly convert SiO₂ into Si nanostructures. Despite intense efforts, efficient fabrication of highly nanoporous silicon by Mg still remains a significant challenge due to the exothermic reaction nature. By employing table salt (NaCl) as a heat scavenger for the magnesiothermic reduction, we demonstrate an effective route to convert diatom (SiO₂) and SiO₂/GeO₂ into nanoporous Si and Si/Ge composite, respectively. Fusion of NaCl during the reaction consumes a large amount of heat that otherwise collapses the nano-porosity of products and agglomerates silicon domains into large crystals. Our methodology is potentially competitive for a practical production of nanoporous Si-based materials.Keywords: Energy storage, Nanoparticles, Porous silicon, Nanowires, Chemical reduction, Dioxide, Electrodes, Anode materials, Lithium ion batteries, Crystallin