Transition‐metal alloys are currently drawing increasing attention as promising electrocatalysts for the alkaline hydrogen evolution reaction (HER). However, traditional ...density‐functional‐theory‐derived d‐band theory fails to describe the hydrogen adsorption energy (ΔGH) on hollow sites. Herein, by studying the ΔGH for a series of Ni−M (M=Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mo, W) bimetallic alloys, an improved d‐band center was provided and a potential NiCu electrocatalyst with a near‐optimal ΔGH was discovered. Moreover, oxygen atoms were introduced into Ni−M (O−NiM) to balance the adsorption/desorption of hydroxyl species. The tailored electrocatalytic sites for water dissociation can synergistically accelerate the multi‐step alkaline HER. The prepared O−NiCu shows the optimum HER activity with a low overpotential of 23 mV at 10 mA cm−2. This work not only broadens the applicability of d‐band theory, but also provides crucial understanding for designing efficient HER electrocatalysts.
An improved d‐band model is presented as a valid descriptor to reflect hollow‐site adsorption and hydrogen evolution reaction (HER) activity for multi‐elemental alloy catalysts. NiCu was found to have a near‐optimal ΔGH value and the introduction of O atoms into the Ni−Cu surface could accelerate water dissociation. Tailoring electrocatalytic sites for water dissociation can synergistically complete the multi‐step reactions of alkaline HER.
This paper studies the real effects of losing political capital by exploiting exogenous shocks from the sudden deaths of politically connected independent directors in Chinese firms. Using ...difference-in-differences estimation, we find that upon losing political capital, a firm boosts its physical capital expenditures by 28%, or 2.93 percentage points, which is an order of magnitude larger than estimates from the United States. The loss of political capital leads to a decrease in the economic benefits a firm can obtain, in terms of bank loans, tax benefits, and government subsidies, and an increase in its production costs. Our evidence suggests that private firms use physical capital investment as a substitute for political capital.
•This paper studies how losing political capital affects private firms' investment.•We exploit sudden deaths of politically connected independent directors as shocks.•A loss of political capital causes a firm to increase its investment considerably.•A loss of political capital decreases the economic benefits private firms can obtain.•Private firms use physical capital investment as a substitute for political capital.
Cysteine is a commercially important sulfur-containing amino acid widely used as a supplement in the agricultural and food industries. It is extremely desirable to achieve a high sulfur conversion ...rate in the fermentation-based cysteine production. Here, the metabolic engineering of Escherichia coli was performed to enhance the sulfur conversion rate in cysteine biosynthesis. Accordingly, the reduction of sulfur loss by the regulator decR and its yhaOM operons were deleted. serACB was integrated into chromosome with constitutive promoter to coordinately increase sulfur utilization. The sulfur assimilation pathways and sulfur transcriptional regulator cysB were overexpressed to regulate sulfur metabolism and enhance sulfur conversion significantly. After the process optimization in fed-batch fermentation, LH16 SLH02 ΔyhaM Ptrc1-serACB-cysM-nrdH-(pLH03, pTrc99a-cysB) produced 7.5 g/L of cysteine with a sulfur conversion rate of 90.11%. These results indicate that cysteine production by LH16 is a valuable process in the agricultural and food industries.
Abstract
We report the synthesis and crystal structure of a nanocluster composed of 23 silver atoms capped by 8 phosphine and 18 phenylethanethiolate ligands. X-ray crystallographic analysis reveals ...that the kernel of the Ag nanocluster adopts a helical face-centered cubic structure with
C
2
symmetry. The thiolate ligands show two binding patterns with the surface Ag atoms: tri- and tetra-podal types. The tetra-coordination mode of thiolate has not been found in previous Ag nanoclusters. No counter ion (e.g., Na
+
and NO
3
−
) is found in the single-crystal and the absence of such ions is also confirmed by X-ray photoelectron spectroscopy analysis, indicating electrical neutrality of the nanocluster. Interestingly, the nanocluster has an open shell electronic structure (i.e., 23(Ag 5
s
1
)–18(SR) = 5e), as confirmed by electron paramagnetic resonance spectroscopy. Time-dependent density functional theory calculations are performed to correlate the structure and optical absorption/emission spectra of the Ag nanocluster.
The development of highly active, eco-friendly, and structurely fine-tunable organic luminophores is currently desirable for electrochemiluminescence (ECL). Tetraphenylethene (TPE) derivatives are ...the most representative aggregation-induced emission characteristic (AIEgens). In contrast, their aggregation-induced ECLs have not been detail studied. Herein, we report the bright cathodic aggregated state ECL of TPE derivatives by a coreactant approach. In this system, the substituents profoundly affect ECL emissions by changing the relative intensities of R and B band intensity ratios in their UV–vis spectra as well as the HOMO and LUMO energies. It was discovered that electron-withdrawing nitro-substituted TPE-(NO2)4 with a smaller LUMO/HOMO band gap and stronger R band featured the strongest ECL emissions and became the best luminophore for the highly efficient detection of iodide (I–) in the aqueous phase. This work not only reveals the influence of R and B bands in TPE derivative UV–vis spectra on their optical properties but also constructs a novel aggregation-induced ECL sensing.
The heterogeneous stacking of a thin two-dimensional (2D) perovskite layer over the three-dimensional (3D) perovskite film creates a sophisticated architecture for perovskite solar cells (PSCs). It ...combines the remarkable thermal and environmental stabilities of 2D perovskites with the superior optoelectronic properties of 3D materials which resolves the chronic stability issue with no compromise on efficiency. Herein, we propose the vapor-assisted growth strategy to fabricate high-quality 2D/3D heterostructured perovskite films by introducing long-chain organoamine gases in which the 2D layers have a uniform and tunable thickness. The 3D to 2D transformation of the widely adopted MAPbI3 (MA = methylammonium) film is initiated by the butylamine vapor and monitored through the in situ grazing-incidence X-ray diffraction technique. A variety of 2D species are observed and rationalized by the different collapsing and reconstruction models of the Pb–I octahedra. The PSC devices based on the optimized 2D/3D heterostructures show significant improvements in photovoltaic performances, owing to better energy level alignments, longer carrier lifetimes, and less defects as compared to their 3D analogues. In addition, both the butylamine vapor-treated perovskite films and the derived PSC devices demonstrate exceptional long-term stabilities.
plays an important role in the mineralization of many metal ions, but it is unclear whether this fungus is involved in the mineralization of calcium carbonate. In this study,
was cultured under ...various conditions to explore its ability to perform microbially induced calcium carbonate precipitation (MICP). Organic acids, yeast extract, and low-carbon conditions were the factors influencing the biomineralization of calcium carbonate caused by
, and biomolecules secreted by the fungus under different conditions could change the morphology, size, and crystal form of the biosynthesized mineral. In addition, transcriptome analysis showed that the oxidation of organic acids enhanced the respiration process of yeast. This implied that
played a role in the formation of calcium carbonate through the mechanism of creating an alkaline environment by the respiratory metabolism of organic acids, which could provide sufficient dissolved inorganic carbon for calcium carbonate formation. These results provide new insights into the role of
in biomineralization and extend the potential applications of this fungus in the future.
The manipulation of crystal orientation from the thermodynamic equilibrium states is desired in layered hybrid perovskite films to direct charge transport and enhance the perovskite devices ...performance. Here we report a templated growth mechanism of layered perovskites from 3D-like perovskites which can be a general design rule to align layered perovskites along the out-of-plane direction in films made by both spin-coating and scalable blading process. The method involves suppressing the nucleation of both layered and 3D perovskites inside the perovskite solution using additional ammonium halide salts, which forces the film formation starts from solution surface. The fast drying of solvent at liquid surface leaves 3D-like perovskites which surprisingly templates the growth of layered perovskites, enabled by the periodic corner-sharing octahedra networks on the surface of 3D-like perovskites. This discovery provides deep insights into the nucleation behavior of octahedra-array-based perovskite materials, representing a general strategy to manipulate the orientation of layered perovskites.
Three dimensional (3D) tolerance analysis is an innovative method which represents and transfers tolerance in 3D space. The advantage of 3D method is taking both dimensional and geometric tolerances ...into consideration, compared with traditional 1/2D tolerance methods considering dimensional tolerances only. This paper reviews four major methods of 3D tolerance analysis and compares them based on the literature published over the last three decades or so. The methods studied are Tolerance-Map (T-Map), matrix model, unified Jacobian–Torsor model and direct linearization method (DLM). Each of them has its advantages and disadvantages. The T-Map method can model all of tolerances and their interaction while the mathematic theory and operation may be challenging for users. The matrix model based on the homogeneous matrix which is classical and concise has been the foundation of some successful computer aided tolerancing software (CATs), but the solution of constraint relations composed of inequalities is complicated. The unified Jacobian–Torsor model combines the advantages of the torsor model which is suitable for tolerance representation and the Jacobian matrix which is suitable for tolerance propagation. It is computationally efficient, but the constraint relations between components of torsor need to be considered to improve its accuracy and validity. The DLM is based on the first order Taylor’s series expansion of vector-loop-based assembly models which use vectors to represent either component dimensions or assembly dimensions. Geometric tolerances are operated as dimensional tolerances in DLM, which is not fully consistent with tolerancing standards. The results of four models with respect to an example are also listed to make a comparison. Finally, a perspective overview of the future research about 3D tolerance analysis is presented.
•Introduce four major 3D tolerance analysis models briefly.•Make a comprehensive comparison and discussion between them.•Expound the connotation of 3D tolerance analysis.•Present a perspective overview of the future research about 3D tolerance analysis.
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