Energy storage and conversion play a crucial role in modern energy systems, and the exploration of advanced electrode materials is vital but challenging. Carbon‐based nanocages consisting of sp2 ...carbon shells feature a hollow interior cavity with sub‐nanometer microchannels across the shells, high specific surface area with a defective outer surface, and tunable electronic structure, much different from the intensively studied nanocarbons such as carbon nanotubes and graphene. These structural and morphological characteristics make carbon‐based nanocages a new platform for advanced energy storage and conversion. Up‐to‐date synthetic strategies of carbon‐based nanocages, the utilization of their unique porous structure and morphology for the construction of composites with foreign active species, and their significant applications to the advanced energy storage and conversion are reviewed. Structure–performance correlations are discussed in depth to highlight the contribution of carbon‐based nanocages. The research challenges and trends are also envisaged for deepening and extending the study and application of this multifunctional material.
Carbon‐based nanocages have emerged as a new platform for advanced energy storage and conversion owing to their hollow interior cavity with microchannels across the shells, their high specific surface area with defective outer surface, and their tunable electronic structure. Up‐to‐date progress on the synthesis, encapsulating/supporting of carbon‐based nanocages and their applications is presented, along with the research challenges and trends.
Premarital cohabitation has become an increasingly popular pathway to marriage in China. However, we lack studies on its role in the timing of first birth. Motivated by the "second demographic ...transition" (SDT) theory, three questions are examined: (1) Does cohabitation accelerate the timing of first birth via premarital conceptions? (2) Are cohabitants who are not pregnant at the time of marriage more likely to delay parenthood than non-cohabitants? (3) Does the association between premarital cohabitation and the timing of first birth vary by birth cohort? Information regarding premarital cohabitational experience and age (in months) at first birth was collected from 7,310 women in the 2010-2018 China Family Panel Studies (CFPS). The role of cohabitation in the timing of first birth was evaluated using a discrete time competing-risk model. Premarital cohabitation accelerates the timing of first birth by increasing the risk of premarital conceptions, but it delays first birth conceived within marriage. The fertility-accelerating effect of premarital cohabitation rebounds in the post-1980s generation after a temporary decline between the 1960s and 1970s birth cohorts, while the fertility-delaying effect of cohabitation has been consistently observed without any sign of decline or rebound over time. The contradictory role of premarital cohabitation in the timing of first birth in China exemplifies a complex interplay between the tendency for path dependency and nonconformist value reorientations in the SDT. The rebound of the fertility-accelerating effect of cohabitation among the post-1980s generation suggests that the two contradictory roles of cohabitation will likely coexist for a long time.
Replacing precious platinum with earth‐abundant materials for the oxygen reduction reaction (ORR) in fuel cells has been the objective worldwide for several decades. In the last 10 years, the ...fastest‐growing branch in this area has been carbon‐based metal‐free ORR electrocatalysts. Great progress has been made in promoting the performance and understanding the underlying fundamentals. Here, a comprehensive review of this field is presented by emphasizing the emerging issues including the predictive design and controllable construction of porous structures and doping configurations, mechanistic understanding from the model catalysts, integrated experimental and theoretical studies, and performance evaluation in full cells. Centering on these topics, the most up‐to‐date results are presented, along with remarks and perspectives for the future development of carbon‐based metal‐free ORR electrocatalysts.
Replacing precious platinum with earth‐abundant materials in fuel cells for the oxygen reduction reaction (ORR) has been a worldwide objective for several decades. In the last 10 years, the fastest‐growing branch in this area has been carbon‐based metal‐free ORR electrocatalysts. The most up‐to‐date results of this field are presented, along with remarks and perspectives for the future development of carbon‐based metal‐free ORR electrocatalysts.
Engineering alloys are widely applied as important functional structural materials in aerospace, electronics, metallurgy, and other high-end engineering industries due to their superior properties. ...However, their further application remains notably restricted by numerous inherent limitations, including low hardness, terrible wear and high-temperature oxidation resistance. In response to this problem, the development of laser cladding (LC) technology has provided new approaches for surface modification of engineering alloys. In this review paper, the recent progress made in the preparation of engineering alloys by LC technology is thoroughly investigated. The elementary knowledge in this field is provided to establish the internal relationships among the laser processing parameters, microstructure, and significant mechanical properties. The LC processing methods and material systems are reviewed, and the critical functional coatings related to this field are also summarised and explored in detail. Furthermore, the current challenges and future efforts are presented, identifying the existing knowledge and technology gaps while also attempting to determine future research directions.
Chalcogenide aerogels are receiving widespread attention due to their unique properties. Here we comment on a recent work about amorphous Na–Mn–Sn–S chalcogels featuring local structural control, and ...provide an outlook for the development of chalcogels and the metal-organic sulfide framework.
Natural ester is considered to be a substitute of mineral oil in the future. To apply natural ester in large transformers safely, natural ester impregnated solid insulation should be proved to have ...comparable dielectric strength and thermal stability to mineral oil impregnated solid insulation. This paper mainly focuses on a comparative study of physicochemical, ac breakdown strength and thermal stability behavior of BIOTEMP natural ester/pressboard insulation and Karamay 25# naphthenic mineral oil/pressboard insulation after long term thermal ageing. The physicochemical and dielectric parameters including moisture, acids and the ac breakdown strength of these two oil/pressboard insulation systems at different ageing status were compared. The permittivity and ac breakdown strength of these two oil/pressboard insulation systems at different temperatures were also investigated. And a comparative result of the thermal stability behavior of these two oil/pressboard insulation systems with different ageing status was provided at last. Results show that though natural ester has higher absolute humidity and acidity during the long ageing period, the lower relative humidity of natural ester helps to keep its ac breakdown strength higher than mineral oil. The pressboard aged in natural ester also has higher ac breakdown strength than that aged in mineral oil. The lower relative permittivity ratio of natural ester impregnated paper to natural ester is beneficial to its dielectric strength. Using natural ester in transformer, the resistance to thermal decomposition of the oil/pressboard insulation system could be also effectively improved.
This study demonstrates the advantage of the dual metal sites for the ORR in acidic electrolyte and highlight the significance of kinetics in the theoretical study of ORR electrocatalysts.
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•The significance of kinetics in the theoretical study of ORR is highlighted.•The advantage of the dual metal sites for the ORR in acidic electrolyte is demonstrated.•The ORR activity is evaluated at the same electrode potential by tuning the surface charge.•MnCo-N-C is predicted as an electrocatalyst with high ORR activity.
In this work, the oxygen reduction reaction (ORR) process on dual-metal-nitrogen-carbon (DM-N-C) catalysts by including two important factors (potential of zero charge and potential-dependent kinetics of O-O bond cleavage) from first-principle calculations is systematically investigated. Our results reveal that the origin for the high activity of dual-metal sites can be attributed to the fact that introducing a second metal site can facilitate the O-O bond cleavage in the key OOH* intermediate during ORR and meanwhile mitigate the *OH removal issue. Importantly, we define a descriptor called “antibonding center” that simplifies the evaluation of the kinetics. Based on the advanced approach used in this work, we demonstrate that several DM-N-C electrocatalysts including FeFeN6, FeCoN6, and CoZnN6 have high ORR activity consistent with previous experiments, and also predict MnCoN6 can be more highly stable and active for acidic ORR. This study demonstrates the advantage of the dual metal sites for the ORR in acidic electrolyte and highlights the significance of kinetics in the theoretical study of ORR electrocatalysts.
Single-site catalysts feature high catalytic activity but their facile construction and durable utilization are highly challenging. Herein, we report a simple impregnation-adsorption method to ...construct platinum single-site catalysts by synergic micropore trapping and nitrogen anchoring on hierarchical nitrogen-doped carbon nanocages. The optimal catalyst exhibits a record-high electrocatalytic hydrogen evolution performance with low overpotential, high mass activity and long stability, much superior to the platinum-based catalysts to date. Theoretical simulations and experiments reveal that the micropores with edge-nitrogen-dopants favor the formation of isolated platinum atoms by the micropore trapping and nitrogen anchoring of PtCl
, followed by the spontaneous dechlorination. The platinum-nitrogen bonds are more stable than the platinum-carbon ones in the presence of adsorbed hydrogen atoms, leading to the superior hydrogen evolution stability of platinum single-atoms on nitrogen-doped carbon. This method has been successfully applied to construct the single-site catalysts of other precious metals such as palladium, gold and iridium.
High volumetric energy density combined with high power density is highly desired for electrical double‐layer capacitors. Usually the volumetric performance is improved by compressing carbon material ...to increase density but at the much expense of power density due to the deviation of the compressed porous structure from the ideal one. Herein the authors report an efficient approach to increase the density and optimize the porous structure by collapsing the carbon nanocages via capillarity. Three samples with decreasing sizes of meso‐ and macropores provide us an ideal model system to demonstrate the correlation of volumetric performance with porous structure. The results indicate that reducing the surplus macropores and, more importantly, the surplus mesopores is an efficient strategy to enhance the volumetric energy density while keeping the high power density. The optimized sample achieves a record‐high stack volumetric energy density of 73 Wh L−1 in ionic liquid with superb power density and cycling stability.
Collapsed carbon nanocages are obtained by making use of capillarity, featuring high density, large specific surface area, optimized pore distribution, and high conductivity. As supercapacitor electrode materials, such unique characteristics ensure sufficient space and efficient channels for charge storage and transport, leading to top‐level volumetric performances in both aqueous and ionic liquid electrolytes, especially the state‐of‐the‐art stack volumetric energy density with high stability in ionic liquid.
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