The electrochemical hydrogen evolution reaction (HER) is an attractive technology for the mass production of hydrogen. Ru‐based materials are promising electrocatalysts owing to the similar bonding ...strength with hydrogen but much lower cost than Pt catalysts. Herein, an ordered macroporous superstructure of N‐doped nanoporous carbon anchored with the ultrafine Ru nanoclusters as electrocatalytic micro/nanoreactors is developed via the thermal pyrolysis of ordered macroporous single crystals of ZIF‐8 accommodating Ru(III) ions. Benefiting from the highly interconnected reticular macro–nanospaces, this superstrucure affords unparalleled performance for pH‐universal HER, with order of magnitude higher mass activity compared to the benchmark Pt/C. Notably, an exceptionally low overpotential of only 13 mV@10 mA cm−2 is required for HER in alkaline solution, with a low Tafel slope of 40.41 mV dec−1 and an ultrahigh turnover frequency value of 1.6 H2 s−1 at 25 mV, greatly outperforming Pt/C. Furthermore, the hydrogen generation rates are almost twice those of Pt/C during practical overall alkaline water splitting. A solar‐to‐hydrogen system is also demonstrated to further promote the application. This research may open a new avenue for the development of advanced electrocatalytic micro/nanoreactors with controlled morphology and excellent performance for future energy applications.
An ordered macroporous superstructure of nitrogen‐doped nanoporous carbon implanted with ultrafine Ru nanoclusters is developed via thermal pyrolysis of the ordered macroporous single crystals of ZIF‐8 accommodating Ru(III) ions, which affords unparalleled performance for the pH‐universal hydrogen evolution reaction, with order of magnitude higher mass activity compared to the benchmark Pt/C.
Herein, the authors report, for the first time, the semisacrificial template growth of a self‐supporting metal–organic framework (MOF) nanocomposite electrode composed of ultrasmall iron‐rich ...Fe(Ni)‐MOF cluster‐decorated ultrathin Ni‐rich Ni(Fe)‐MOF nanosheets from the NiFe alloy foam, in which the Fe(Ni)‐MOF clusters are uniform with a particle size of 2–5 nm, while the thickness of the Ni(Fe)‐MOF nanosheets is only about 1.56 nm. When directly used as a self‐supported working electrode for the oxygen evolution reaction (OER), it can afford an impressive electrocatalytic performance with required overpotentials of 227 and 253 mV to achieve current densities of 10 and 100 mA cm−2, respectively, much outperforming the benchmark of RuO2 and most state‐of‐the‐art noble‐metal‐free catalysts. Characterizations demonstrated that the combination of the unique nanostructure of the catalyst and the strong coupling effect between Ni and Fe active sites should be responsible for its excellent OER performance. Remarkably, when coupled with a Pt electrode in an overall water splitting system, they only needed 1.537 V to achieve a current density of 10 mA cm−2. The facile and economical methodology represents a new way to design and prepare high‐performance self‐supporting MOF electrocatalysts for highly efficient electrochemical processes.
A self‐supporting MOF nanocomposite electrode composed of ultrasmall iron‐rich Fe(Ni)‐MOF cluster‐decorated ultrathin Ni‐rich Ni(Fe)‐MOF nanosheets is prepared by a semisacrificial template growth method. The combination of the unique nanostructure and the strong coupling effect between Ni and Fe active sites endow the composite electrode with excellent electrocatalytic oxygen evolution reaction performance.
In basketball game, the traditional motion recognition method is mainly based on video image processing technology, but due to the limited resolution and frame rate of video, as well as the ...interference of light and other factors, there are some limitations. The aim of this study is to explore an intelligent trajectory analysis method based on new spectral imaging technology to improve the accuracy and reliability of action recognition in basketball games. By using spectral imaging technology, players’ movement trajectories and detailed information on key movements can be obtained, enabling more accurate movement analysis. This paper introduces a new type of spectral imaging equipment to acquire basketball match in real time. The device is able to capture the movement of the player and generate high resolution motion images. Then, the spectral image is processed and analyzed by machine learning algorithm to extract the key action features. The experiment proves that the intelligent trajectory analysis method based on the new spectral imaging technology can effectively identify and analyze the key actions in the basketball game. Compared with the traditional method, this method has higher accuracy and reliability, and can provide coaches and players with more accurate and detailed action analysis reports, so as to improve the effect of training and selection.
Individual's decisions, from what product to buy to whether to engage in risky behavior, often depend on the choices, behaviors, or states of other people. People, however, rarely have global ...knowledge of the states of others, but must estimate them from the local observations of their social contacts. Network structure can significantly distort individual's local observations. Under some conditions, a state that is globally rare in a network may be dramatically over-represented in the local neighborhoods of many individuals. This effect, which we call the "majority illusion," leads individuals to systematically overestimate the prevalence of that state, which may accelerate the spread of social contagions. We develop a statistical model that quantifies this effect and validate it with measurements in synthetic and real-world networks. We show that the illusion is exacerbated in networks with a heterogeneous degree distribution and disassortative structure.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
We report a three-dimensional (3D) garnet framework-reinforced solid composite electrolyte with enhanced Li-ion conductivity and excellent thermal, mechanical, and electrochemical stabilities. The 3D ...garnet framework is fabricated via the polymeric sponge method, using low-cost polyurethane foam as the template. The interconnected 3D garnet framework not only reinforces the composite electrolyte but also forms continuous Li-ion transport pathways, thereby increasing the ionic conductivity. The 3D garnet composite electrolyte shows an ionic conductivity of 1.2 × 10–4 S cm–1 at 30 °C, about two times as high as that of the garnet particle-reinforced composite electrolyte. The Li–Li symmetric cell based on the 3D garnet composite electrolyte can be cycled more than 360 h without short circuit, suggesting an improved ability to suppress Li-dendrites. The Li/3D garnet composite electrolyte/LiFePO4 battery demonstrates stable cycling performance at 0.5 C. Owing to the cost-saving characteristics, the 3D garnet-reinforced solid composite electrolyte is promising for mass production.
Electrochemical reduction of CO2 to valuable fuels is appealing for CO2 fixation and energy storage. However, the development of electrocatalysts with high activity and selectivity in a wide ...potential window is challenging. Herein, atomically thin bismuthene (Bi‐ene) is pioneeringly obtained by an in situ electrochemical transformation from ultrathin bismuth‐based metal–organic layers. The few‐layer Bi‐ene, which possesses a great mass of exposed active sites with high intrinsic activity, has a high selectivity (ca. 100 %), large partial current density, and quite good stability in a potential window exceeding 0.35 V toward formate production. It even deliver current densities that exceed 300.0 mA cm−2 without compromising selectivity in a flow‐cell reactor. Using in situ ATR‐IR spectra and DFT analysis, a reaction mechanism involving HCO3− for formate generation was unveiled, which brings new fundamental understanding of CO2 reduction.
Atomically thin bismuthene with excellent electrocatalytic CO2 reduction performance is obtained from ultrathin metal–organic layers by an in situ electrochemical transformation process. A reaction route involving HCO3− for formate production is revealed.
Ligand-to-metal charge transfer (LMCT) can bring about the separation of photogenerated charges. Here we calculate the electronic structures of metal–organic frameworks (MOFs) having the UiO-66 ...architecture and M6O4(OH)4 inorganometallic nodes with M = Zr, Hf, Th, Ti, U, or Ce. We find that LMCT is favorable only in the Ce case, where it is promoted by the low-lying empty 4f orbitals of Ce4+. We therefore propose that incorporating Ce4+ into the node is an effective way to facilitate LMCT in a MOF. In addition, we show that by functionalizing the linker, it should be possible to engineer the electronic structure of the Ce-MOF for a desired reaction (e.g., water splitting) while preserving favorable LMCT. We also find that linker functionalization with electron donating or withdrawing groups allows tuning of the LMCT energy, and increasing the number of functional groups on each linker enhances the tuning; these findings are encouraging for applying Ce-MOFs for visible-response photocatalytic water splitting.
The construction of multi‐stereocenters by a transition metal‐catalyzed cross‐coupling reaction is a major challenge. The catalytic desymmetric functionalization of unactivated alkenes remains ...largely unexplored. Herein, we disclose ‐a desymmetric dicarbofunctionalization of 1,6‐dienes via a nickel‐catalyzed reductive cross‐coupling reaction. The leverage of the underdeveloped chiral 8‐Quinox enables the Ni‐catalyzed desymmetric carbamoylalkylation of both unactivated mono‐ and disubstituted alkenes to form pyrrolidinone bearing two nonadjacent stereogenic centers in high enantio‐ and stereoselectivitives with broad functional‐group tolerance. The synthetic application of pyrrolidinones allows the rapid access to complex chiral fused‐heterocycles.
The desymmetric dicarbofunctionalization of unactivated alkenes by a nickel‐catalyzed reductive cross‐coupling reaction has been developed to access pyrrolidinones bearing multi‐stereocenters with broad functional‐group tolerance. The utilization of the 8‐Quinox ligand is crucial for maintaining high enantio‐ and stereoselectivities.
A novel niobium oxyiodate sulfate, Nb2O3(IO3)2 (SO4), was fabricated by a rational multi‐component design under moderate hydrothermal conditions. This multi‐component design is inspired by an ...interesting niobium oxysulfate reaction, which opens a new door for synthetic method to effectively introduce refractory metals such as Nb into crystal structures by hydrothermal synthesis. Nb2O3(IO3)2(SO4) features a cube‐like topological structure with a large phase‐matching second harmonic generation (SHG) response (6×KDP), a wide transparency window (0.38–8 μm), and a high laser damage threshold (LDT) (20×AgGaS2). It has the highest thermostability (stable up to 580 °C under air) among reported non‐centrosymmetric (NCS) iodates and sulfates and is stable in water and even concentrated H2SO4. Furthermore, Nb2O3(IO3)2(SO4) is a unique nonlinear optical (NLO) material among iodates and sulfates, because its SHG effect is mainly caused by the MO6 units rather than the IO3 or SO4 units, which is demonstrated by density functional theory (DFT) calculations.
Oh my‐obium! The synthesis of crystalline Nb2O3(IO3)2(SO4) under moderate hydrothermal conditions is reported. The highly thermostable crystal features a strong second‐harmonic‐generation response, a wide transparency window, and a high laser damage threshold.
A
bstract
We study the breakdown of diffusive hydrodynamics in holographic systems dual to neutral dilatonic black holes with extremal near horizon geometries conformal to AdS
2
× R
2
. We find that ...at low temperatures by tuning the effective gauge coupling constant in the infra-red, the lowest non-hydrodynamic mode, which collides with the charge diffusive mode and sets the scales at which diffusive hydrodynamics breaks down, could be either an infra-red mode or a slow mode, resulting in different scaling behaviors of the local equilibrium scales. We confirm that the upper bound for the charge diffusion constant is always satisfied using the velocity and timescale of local equilibration from the pole collision. We also examine the breakdown of hydrodynamics at general temperature and find that the convergence radius has nontrivial dependence on temperature, in addition to the effective gauge coupling constant.
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