Bifunctional oxygen catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with high activities and low‐cost are of prime importance and challenging in the development of ...fuel cells and rechargeable metal–air batteries. This study reports a porous carbon nanomaterial loaded with cobalt nanoparticles (Co@NC‐x/y) derived from pyrolysis of a Co/Zn bimetallic zeolitic imidazolite framework, which exhibits incredibly high activity as bifunctional oxygen catalysts. For instance, the optimal catalyst of Co@NC‐3/1 has the interconnected framework structure between porous carbon and embedded carbon nanotubes, which shows the superb ORR activity with onset potential of ≈1.15 V and half‐wave potential of ≈0.93 V. Moreover, it presents high OER activity that can be further enhanced to over commercial RuO2 by P‐doped with overpotentials of 1.57 V versus reversible hydrogen electrode at 10 mA cm−2 and long‐term stability for 2000 circles and a Tafel slope of 85 mV dec−1. Significantly, the nanomaterial demonstrates better catalytic performance and durability than Pt/C for ORR and commercial RuO2 and IrO2 for OER. These findings suggest the importance of a synergistic effect of graphitic carbon, nanotubes, exposed Co–Nx active sites, and interconnected framework structure of various carbons for bifunctional oxygen electrocatalysts.
A porous carbon nanomaterial (Co@NC‐x/y) embedded with cobalt nanoparticles and rooted with nanotubes derived from pyrolysis of a Co/Zn bimetallic zeolitic imidazolite framework is reported. The optimal catalyst of Co@NC‐3/1 shows the superb oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activities. And its mechanism is thoroughly discussed.
Developing high-performance electrocatalysts toward hydrogen evolution reaction is important for clean and sustainable hydrogen energy, yet still challenging. Herein, we report a single-atom strategy ...to construct excellent metal-organic frameworks (MOFs) hydrogen evolution reaction electrocatalyst (NiRu
-BDC) by introducing atomically dispersed Ru. Significantly, the obtained NiRu
-BDC exhibits outstanding hydrogen evolution activity in all pH, especially with a low overpotential of 36 mV at a current density of 10 mA cm
in 1 M phosphate buffered saline solution, which is comparable to commercial Pt/C. X-ray absorption fine structures and the density functional theory calculations reveal that introducing Ru single-atom can modulate electronic structure of metal center in the MOF, leading to the optimization of binding strength for H
O and H*, and the enhancement of HER performance. This work establishes single-atom strategy as an efficient approach to modulate electronic structure of MOFs for catalyst design.
Metal-organic frameworks (MOFs) have been recognized as compelling platforms for the development of miscellaneous applications because of their structural diversity and functional tunability. Here, ...we propose that the electrocatalytic properties could be well modified by incorporating missing linkers into the MOF. Theoretical calculations suggest the electronic structure of MOFs can be tuned by introducing missing linkers, which improves oxygen evolution reaction (OER) performance of the MOF. Inspired by these aspects, we introduced various missing linkers into a layered-pillared MOF Co
(OH)
(C
H
O
) (termed as CoBDC) to prepare missing-linker MOFs. Transmission electron microscope and synchrotron X-ray measurements confirmed that the missing linkers in the MOF could be introduced and well controlled by our strategy. The self-supported MOF nanoarrays with missing linkers of carboxyferrocene exhibit excellent OER performance with ultralow overpotential of 241 mV at 100 mA cm
. This work opens a new prospect to develop efficient MOF-based electrocatalysts by introducing missing linkers.
A novel 4D Einstein–Gauss–Bonnet gravity was recently formulated by Glavan and Lin Phys. Rev. Lett. 124, 081301 (2020). Although this theory may run into trouble at the level of action or equations ...of motion, the spherically symmetric black hole solution, which can be successfully reproduced in those consistent theories of 4D EGB gravity, is still meaningful and worthy of study. In this paper, we investigate Hawking radiation in the spacetime containing such a de Sitter black hole. Both the greybody factor and the power spectra of the Hawking radiation of the massless scalar are studied numerically for the full range of various parameters, including the GB coupling constant
α
, the cosmological constant
Λ
and the coupling constant related to the scalar filed
ξ
. In particular, we find a negative
α
leads to a larger greybody factor than that of a
α
≥
0
. While, for the power spectra of the Hawking radiation the situation is quite the opposite. The reason is that the temperature of the black hole would be very high when
α
<
0
. Actually, we observe that the temperature would be arbitrarily high when
α
approaches to the lower bound.
Lead halide perovskite nanocrystals (NCs) have demonstrated great potential as appealing candidates for advanced optoelectronic applications. However, the toxicity of lead and the intrinsic ...instability toward moisture hinder their mass production and commercialization. Herein, to solve such thorny problems, novel lead‐free Cs2AgBiBr6 double perovskite NCs fabricated via a simple hot‐injection method are reported, which exhibit impressive stability in moisture, light, and temperature. Such materials are then applied into photocatalytic CO2 reduction, achieving a total electron consumption of 105 µmol g−1 under AM 1.5G illumination for 6 h. This study offers a reliable avenue for Cs2AgBiBr6 perovskite nanocrystals preparation, which holds a great potential in the further photochemical applications.
Stable lead‐free Cs2AgBiBr6 double perovskite nanocrystals with a cubic shape and an average size of 9.5 nm are successfully synthesized via the hot‐injection route, and are employed as photocatalysts to convert CO2 into solar fuels (CO and CH4). This work offers a reliable avenue for Cs2AgBiBr6 perovskite nanocrystals preparation, which holds a great potential in the further photochemical applications.
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► Two general classes of metallogels developed including molecular metallogels and coordination polymer gels. ► Coordination polymer gelators developed assisted by auxiliary moieties. ...► Metal-organic gelators developed lacking auxiliary moieties. ► Metal-organic gels with novel properties in adsorption, catalysis and as templates for porous materials.
The design of metallogelators and incorporation of metals into supramolecular gels have received growing attention. Design strategies have been developed based on organogelators, including the incorporation of metal into low molecular weight organogelators (LMWGs), and coordination polymers assisted by auxiliary moieties (including lipophilic and hydrogen-bonding groups) as gelators. Additionally, a novel class of metal-organic gels lacking auxiliary moieties has recently been developed; these coordination-directed (induced) gels display novel properties e.g., in adsorption and catalysis and as templates for porous materials. This review highlights the design and properties of a diverse range of metallogelator types.
Materials with tunable long persistent luminescence (LPL) properties have wide applications in security signs, anti‐counterfeiting, data encrypting, and other fields. However, the majority of ...reported tunable LPL materials are pure organic molecules or polymers. Herein, a series of metal‐organic coordination polymers displaying color‐tunable LPL were synthesized by the self‐assembly of HTzPTpy ligand with different cadmium halides (X=Cl, Br, and I). In the solid state, their LPL emission colors can be tuned by the time‐evolution, as well as excitation and temperature variation, realizing multi‐mode dynamic color tuning from green to yellow or green to red, and are the first such examples in single‐component coordination polymer materials. Single‐crystal X‐ray diffraction analysis and theoretical calculations reveal that the modification of LPL is due to the balanced action from single molecule and aggregate triplet excited states caused by an external heavy‐atom effect. The results show that the rational introduction of different halide anions into coordination polymers can realize multi‐color LPL.
By delicate design of coordination polymers incorporating different halogens, multi‐mode color‐tunable long persistent luminescence (LPL) from green to yellow or green to red was possible. The LPL emission colors can be tuned by time, excitation, and temperature, revealing the counter‐balanced mechanisms from single‐molecule and aggregate triplet excited states resulting from an external heavy‐atom effect.
•Assembling strategies and applications of chiral MOCs were reviewed in a unique perspective.•Three types of spatial-direction strategies for chiral MOCs were addressed.•Special chiral behaviors and ...applications for stereogenic MOCs were presented.
During the past few decades, great efforts have been devoted to the design and self-assembly of discrete metal–organic cages/containers (MOCs) with increasing complexity and functionality. Among which, the incorporation of chirality into the construction of MOCs endows these supramolecular containers with unique potentials in stereochemical, nonlinear optical, biomedical and enzyme mimical fields. In this review, we give a brief survey of recent works focusing on the assembly and applications of chiral metal–organic convex polyhedra with well-defined three-dimensional (3D) outer shapes and inner cavities, including a few examples of chiral MOCs in other configurations. In general, the stereochemical origin of a chiral MOC can be generated through geometrical symmetry control pathways by removing the inherent inversion and/or mirror symmetries, in which the vertice-, edge-, and face-directed assembling approaches represent the most successful strategies to introduce stereogenic centers into and achieve absolute chiral environments in MOCs. Stereochemical memory, transfer and communication can be realized among different components of chiral MOCs in a supramolecular sense, resulting in cooperative and synergetic effects of chiral complex systems, which can be further explored for enantio-recognition, separation and asymmetric catalysis applications.
A
bstract
We compute the time-dependent complexity of the thermofield double states by four different proposals: two holographic proposals based on the “complexity-action” (CA) conjecture and ...“complexity-volume” (CV) conjecture, and two quantum field theoretic proposals based on the Fubini-Study metric (FS) and Finsler geometry (FG). We find that four different proposals yield both similarities and differences, which will be useful to deepen our understanding on the complexity and sharpen its definition. In particular, at early time the complexity linearly increase in the CV and FG proposals, linearly decreases in the FS proposal, and does not change in the CA proposal. In the late time limit, the CA, CV and FG proposals all show that the growth rate is 2
E/
(πℏ) saturating the Lloyd’s bound, while the FS proposal shows the growth rate is zero. It seems that the holographic CV conjecture and the field theoretic FG method are more correlated.
This study unpacks the environmental and social dimensions of supplier responsibility and links each dimension to distinct drivers. Using stakeholder theory and the relational view, we distinguish ...between two main drivers: stakeholder pressures (i.e., from regulatory agencies, buying firms, and nongovernmental organizations) and relational mechanisms offered by multinational companies (MNCs) (i.e., lean trainings and relational capital). We used a multi‐method research design to study how these drivers uniquely influence supplier responsibility in an emerging‐country context. An in‐depth case study with Philips Lighting and 10 of its Chinese suppliers reveals causal inferences that link stakeholder and relational drivers with each responsibility dimension (environmental vs. social). Audit and survey data from Philips Lighting's 134 Chinese suppliers, complemented with four archival databases, bolster these inferences. Overall, the results show that supplier environmental responsibility can be fostered through both stakeholder pressures and relational drivers; whereas, supplier social responsibility is much harder to address. The integrated methods offer a fuller, more comprehensive understanding of the specifics of supplier responsibility in China and also provide recommendations for MNCs that seek to improve it.
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