Identifying effective means to improve the electrochemical performance of oxygen‐evolution catalysts represents a significant challenge in several emerging renewable energy technologies. Herein, we ...consider metal–nitrogen–carbon sheets which are commonly used for catalyzing the oxygen‐reduction reaction (ORR), as the support to load NiO nanoparticles for the oxygen‐evolution reaction (OER). FeNC sheets, as the advanced supports, synergistically promote the NiO nanocatalysts to exhibit superior performance in alkaline media, which is confirmed by experimental observations and density functional theory (DFT) calculations. Our findings show the advantages in considering the support effect for designing highly active, durable, and cost‐effective OER electrocatalysts.
Sitting on the FeNC: Metal–nitrogen–carbon sheets are used as the supports for metal oxide catalysts for the oxygen‐evolution reaction (OER). Iron–nitrogen–carbon (FeNC) sheets loaded with NiO nanoparticles give superior performance in alkaline media. The improved performance originates from a synergistic effect between the FeNC sheets and NiO.
Between 15 and 27 kyr b2k (thousands of years before 2000 CE) during the last glacial, Greenland experienced a prolonged cold stadial phase, interrupted by two short-lived warm interstadials. ...Greenland ice-core calcium data show two periods, preceding the interstadials, of anomalously high atmospheric dust loading, the origin of which is not well understood. At approximately the same time as the Greenland dust peaks, the Chinese Hulu Cave speleothems exhibit a climatic signal suggested to be a response to Heinrich Event 2, a period of enhanced ice-rafted debris deposition in the North Atlantic. In the climatic signal of Antarctic ice cores, moreover, a relative warming occurs between 23 and 24.5 kyr b2k that is generally interpreted as a counterpart to a cool climate phase in the Northern Hemisphere. Proposed centennial-scale offsets between the polar ice-core timescales and the speleothem timescale hamper the precise reconstruction of the global sequence of these climatic events. Here, we examine two new .sup.10 Be datasets from Greenland and Antarctic ice cores to test the agreement between different timescales, by taking advantage of the globally synchronous cosmogenic radionuclide production rates.
Statistical and case studies, as well as data‐mining reconstructions suggest that the magnetotail current in the substorm growth phase has a multiscale structure with a thin ion‐scale current sheet ...embedded into a much thicker sheet. This multiscale structure may be critically important for the tail stability and onset conditions for magnetospheric substorms. The observed thin current sheets are found to be too long to be explained by the models with isotropic plasmas. At the same time, plasma observations reveal only weak field‐aligned anisotropy of the ion species, whereas the anisotropic electron contribution is insufficient to explain the force balance discrepancy. Here we elaborate a self‐consistent equilibrium theory of multiscale current sheets, which differs from conventional isotropic models by weak ion anisotropy outside the sheet and agyrotropy caused by quasi‐adiabatic ion orbits inside the sheet. It is shown that, in spite of weak anisotropy, the current density perturbation may be quite strong and localized on the scale of the figure‐of‐eight ion orbits. The magnetic field, current and plasma density in the limit of weak field‐aligned ion anisotropy and strong current sheet embedding, when the ion scale thin current sheet is nested in a much thicker Harris‐like current sheet, are investigated and presented in an analytical form making it possible to describe the multiscale equilibrium in sharply stretched 2D magnetic field configurations and to use it in kinetic simulations and stability analysis.
Plain Language Summary
Conventional kinetic equilibria with isotropic pressures for ions and electrons aimed to describe the current sheet in Earth's magnetotail cannot reproduce its multiscale structure with the proton gyroradius‐scale current sheet being embedded into a much thicker sheet. They cannot explain either the formation of such thin current sheets sufficiently far from Earth. The embedding effect can be reproduced in case of anisotropic and agyrotropic plasmas because orbits of weakly magnetized ions near the current sheet deviate from the Larmor circle and become more like a figure of eight. However, the corresponding multiscale current sheet models have been studied so far for substantial and strong plasma anisotropy, while observations suggest that the tail plasmas are weakly anisotropic. Here we perform an analysis of a weakly anisotropic current sheet model, which transforms in the isotropic limit into a classical Harris sheet model, and show that the key observed embedding features can be reproduced.
Key Points
Kinetic equilibria of ion‐scale current sheets embedded into a thicker weakly anisotropic Harris‐like current sheet are investigated
The current density increase due to quasi‐adiabatic ion motions may be substantial in spite of weak plasma anisotropy
2D thin current sheets have aspect ratios consistent with observations and controlled by the embedding strength
The future response of the Antarctic ice sheet to rising temperatures remains highly uncertain. A useful period for assessing the sensitivity of Antarctica to warming is the Last Interglacial (LIG) ...(129 to 116 ky), which experienced warmer polar temperatures and higher global mean sea level (GMSL) (+6 to 9 m) relative to present day. LIG sea level cannot be fully explained by Greenland Ice Sheet melt (~2 m), ocean thermal expansion, and melting mountain glaciers (~1 m), suggesting substantial Antarctic mass loss was initiated by warming of Southern Ocean waters, resulting from a weakening Atlantic meridional overturning circulation in response to North Atlantic surface freshening. Here, we report a blue-ice record of ice sheet and environmental change from theWeddell Sea Embayment at the periphery of the marine-based West Antarctic Ice Sheet (WAIS), which is underlain by majormethane hydrate reserves. Constrained by awidespread volcanic horizon and supported by ancient microbial DNA analyses, we provide evidence for substantial mass loss across the Weddell Sea Embayment during the LIG, most likely driven by ocean warming and associated with destabilization of subglacial hydrates. Ice sheet modeling supports this interpretation and suggests that millennial-scale warming of the Southern Ocean could have triggered a multimeter rise in global sea levels. Our data indicate that Antarctica is highly vulnerable to projected increases in ocean temperatures and may drive ice–climate feedbacks that further amplify warming.
Electrical devices generate heat at work. The heat should be transferred away immediately by a thermal manager to keep proper functions, especially for high‐frequency apparatuses. Besides high ...thermal conductivity (K), the thermal manager material requires good foldability for the next generation flexible electronics. Unfortunately, metals have satisfactory ductility but inferior K (≤429 W m−1 K−1), and highly thermal‐conductive nonmetallic materials are generally brittle. Therefore, fabricating a foldable macroscopic material with a prominent K is still under challenge. This study solves the problem by folding atomic thin graphene into microfolds. The debris‐free giant graphene sheets endow graphene film (GF) with a high K of 1940 ± 113 W m−1 K−1. Simultaneously, the microfolds render GF superflexible with a high fracture elongation up to 16%, enabling it more than 6000 cycles of ultimate folding. The large‐area multifunctional GFs can be easily integrated into high‐power flexible devices for highly efficient thermal management.
An atomic crystal‐folding principle is proposed for designing highly thermal‐conductive yet superflexible graphene film. Debris‐free, giant graphene sheets and folded atomic thin crystals afford macroscopic assembled graphene film a high thermal conductivity 1940 W m−1 K−1 and fracture elongation 16%, respectively. This principle opens the door for high‐performance yet flexible inorganic/ceramic macroscopic materials and devices.
This is the first textbook to address all the components of the Earth's cryosphere – all forms of snow and ice, both terrestrial and marine. It provides a concise but comprehensive summary of snow ...cover, glaciers, ice sheets, lake and river ice, permafrost, sea ice and icebergs – their past history and projected future state. It is designed for courses at upper undergraduate and graduate level in environmental science, geography, geology, glaciology, hydrology, water resource engineering and ocean sciences. It also provides a superb up-to-date summary for researchers of the cryosphere. The book includes an extensive bibliography, numerous figures and color plates, thematic boxes on selected topics and a glossary. The book builds on courses taught by the authors for many decades at the University of Colorado and the University of Alberta. Whilst there are many existing texts on individual components of the cryosphere, no other textbook covers the whole cryosphere.
Despite the desirable advancement in synthesizing transition‐metal phosphides (TMPs)‐based hybrid structures, most methods depend on foreign‐template‐based multistep procedures for tailoring the ...specific structure. Herein, a self‐template and recrystallization–self‐assembly strategy for the one‐step synthesis of core–shell‐like cobalt phosphide (CoP) nanoparticles embedded into nitrogen and phosphorus codoped porous carbon sheets (CoP⊂NPPCS), is first proposed. Relying on the unusual coordination ability of melamine with metal ions and the cooperative hydrogen bonding of melamine and phytic acid to form a 2D network, a self‐synthesized single precursor can be attained. Importantly, this approach can be easily expanded to synthesize other TMPs⊂NPPCS. Due to the unique compositional and structural characteristics, these CoP⊂NPPCSs manifest outstanding electrochemical performances as anode materials for both lithium‐ and potassium‐ion batteries. The unusual hybrid architecture, the high specific surface area, and porous features make the CoP⊂NPPCS attractive for other potential applications, such as supercapacitors and electrocatalysis.
A two‐dimensional (2D) core–shell‐like material comprising nitrogen/phosphorus‐codoped porous carbon sheets and embedded cobalt phosphide (CoP) nanoparticles is designed and fabricated by a self‐template and recrystallization‐self‐assembly strategy. Due to this advantageous architecture design, the 2D hybrid indicates excellent electrochemical performance in terms of high reversible capacity, good rate capability, and excellent cycle stability as anode materials for lithium‐ion and potassium‐ion batteries.
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