Search

High-/medium-entropy materials have been explored as promising electrocatalysts for water splitting due to their unique physical and chemical properties. Unfortunately, state-of-the-art materials face the dilemma of explaining the enhancement mechanism, which is now limited to theoretical models or an unclear cocktail effect. Herein, a medium-entropy NiCoFeMnP with an advanced hierarchical particle-nanosheet-tumbleweed nanostructure has been synthesized via simple precursor preparation and subsequent phosphorization. Evaluated as the electrocatalyst for oxygen evolution reaction (OER), the medium-entropy NiCoFeMnP displays a lower overpotential of 272 mV at a current density of 10 mA cm -2 , and more favorable kinetics than the binary NiFeP, ternary NiCoFeP, quaternary NiCoFeCuP and NiCoFeCrP counterparts, and other reported high-/medium-entropy electrocatalysts. Careful experimental analyses reveal that the incorporation of Mn can significantly regulate the electronic structure of Ni, Co, and Fe sites. More importantly, the Mn introduction and entropy stabilization effect in the reconstructed metal (oxy)hydroxide simultaneously promote the lattice oxygen mechanism, improving the activity. This work sheds new light on the design of high-/medium-entropy materials from an in-depth understanding of the underlying mechanism for improving energy conversion efficiency.

The pursuit of highly efficient electrocatalysts for the alkaline hydrogen evolution reaction (HER) is of paramount importance for water splitting. However, it is still a formidable task in Mo 2 C-based materials because of the agglomeration and strong Mo-H binding of Mo 2 C units. Herein, a novel CeOCl-CeO 2 /Mo 2 C heterostructure nesting within a three-dimensional porous nitrogen-doped carbon matrix has been designed and used for catalyzing HER via simultaneous morphology and heterointerface engineering. As expected, the optimal CeOCl-CeO 2 (0.2)/Mo 2 C@3DNC exhibits impressive HER activity, with a low overpotential of 156 mV at a current density of 10 mA cm -2 coupled with a slight Tafel slope of 62.20 mV dec -1 . Introducing a Ce promoter, that is CeOCl and CeO 2 , would endow the interface with an internal electric field and electron redistribution between CeOCl-CeO 2 and Mo 2 C induced by the heterogeneous work function difference. Moreover, experimental investigation and density functional calculations confirm that the CeOCl-CeO 2 /Mo 2 C heterointerface can downshift the d-band center of the active Mo center, weakening the strength of the Mo-H coupling. This proposed concept, engineering Ce-based promoters into active entities involved in the heterostructure to modulate intermediate adsorption, offers a great opportunity for the design of superior electrocatalysts for energy conversion.

Lung cancer poses a serious threat to people's lives and health due to its high incidence rate and high mortality rate, making it necessary to effectively conduct early screening. As an important biomarker for lung cancer, the detection of n -propanol gas suffers from a low response value and a high detection limit. In this paper, flower-like Ho-doped ZnO was fabricated by the coprecipitation method for n -propanol detection at subppm concentrations. The gas sensor based on the 3% Ho-doped ZnO showed selectivity to n -propanol gas. Its response value to 100 ppm n -propanol was 341 at 140 °C, and its limit of detection (LOD) was about 25.6 ppb, which is lower than that of n -propanol in the breath of a healthy person (150 ppb). The calculation results show that the adsorption of n -propanol on a Ho-doped ZnO surface releases more energy than isopropanol, ethanol, formaldehyde, acetone, and ammonia. The enhanced gas-sensing properties of the Ho-doped ZnO material can be attributed to the fact that the Ho-doping distorts the crystal lattice of the ZnO, increases the specific surface area, and generates a large amount of oxygen defects. In addition, the doped Ho partially forms a Ho 2 O 3 /ZnO heterojunction in the material and improves the gas-sensing properties. The 3% Ho-doped ZnO material is expected to be a promising candidate for the trace detection of n -propanol gas.

It is a challenging task to utilize efficient electrocatalytic metal hydroxide-based materials for the oxygen evolution reaction (OER) in order to produce clean hydrogen energy through water splitting, primarily due to the restricted availability of active sites and the undesirably high adsorption energies of oxygenated species. To address these challenges simultaneously, we intentionally engineer a hollow star-shaped Ag/CoMo-LDH heterostructure as a highly efficient electrocatalytic system. This design incorporates a considerable number of heterointerfaces between evenly dispersed Ag nanoparticles and CoMo-LDH nanosheets. The heterojunction materials have been prepared using self-assembly, in situ transformation, and spontaneous redox processes. The nanosheet-integrated hollow architecture can prevent active entities from agglomeration and facilitate mass transportation, enabling the constant exposure of active sites. Specifically, the powerful electronic interaction within the heterojunction can successfully regulate the Co 3+ /Co 2+ ratio and the d-band center, resulting in rational optimization of the adsorption and desorption of the intermediates on the site. Benefiting from its well-defined multifunctional structures, the Ag0.4/CoMo-LDH with optimal Ag loading exhibits impressive OER activity, the overpotential being 290 mV to reach a 10 mA cm -2 current density. The present study sheds some new insights into the electron structure modulation of hollow heterostructures toward rationally designing electrocatalytic materials for the OER.

Accomplishing a green hydrogen economy in reality through water spitting ultimately relies upon earth-abundant efficient electrocatalysts that can simultaneously accelerate the oxygen and hydrogen evolution reactions (OER and HER). The perspective of electronic structure modulation via interface engineering is of great significance to optimize electrocatalytic output but remains a tremendous challenge. Herein, an efficient tactic has been explored to prepare nanosheet-assembly tumbleweed-like CoFeCe-containing precursors with time-/energy-saving and easy-operating features. Subsequently, the final metal phosphide materials containing multiple interfaces, denoted CoP/FeP/CeO x , have been synthesized via the phosphorization process. Through the optimization of the Co/Fe ratio and the content of the rare-earth Ce element, the electrocatalytic activity has been regulated. As a result, bifunctional Co3Fe/Ce0.025 reaches the top of the volcano for both OER and HER simultaneously, with the smallest overpotentials of 285 mV (OER) and 178 mV (HER) at 10 mA cm -2 current density in an alkaline environment. Multicomponent heterostructure interface engineering would lead to more exposed active sites, feasible charge transport, and strong interfacial electronic interaction. More importantly, the appropriate Co/Fe ratio and Ce content can synergistically tailor the d-band center with a downshift to enhance the per-site intrinsic activity. This work would provide valuable insights to regulate the electronic structure of superior electrocatalysts toward water splitting by constructing rare-earth compounds containing multiple heterointerfaces.

Electrochemical N 2 reduction reaction (NRR) emerges as a highly attractive alternative to the Haber-Bosch process for producing ammonia (NH 3 ) under ambient circumstances. Currently, this technology still faces tremendous challenges due to the low ammonia production rate and low Faradaic efficiency, urgently prompting researchers to explore highly efficient electrocatalysts. Inspired by the Fe-Mo cofactor in nitrogenase, we report Mo-doped hematite (Fe 2 O 3 ) porous nanospheres containing Fe-O-Mo subunits for enhanced activity and selectivity in the electrochemical reduction from N 2 to NH 3 . Mo-doping induces the morphology change from a solid sphere to a porous sphere and enriches lattice defects, creating more active sites. It also regulates the electronic structures of Fe 2 O 3 to accelerate charge transfer and enhance the intrinsic activity. As a consequence, Mo-doped Fe 2 O 3 achieves effective N 2 fixation with a high ammonia production rate of 21.3 ± 1.1 μg h -1 mg cat. -1 as well as a prominent Faradaic efficiency (FE) of 11.2 ± 0.6%, superior to the undoped Fe 2 O 3 and other iron oxide catalysts. Density functional theory (DFT) calculations further unravel that the Mo-doping in Fe 2 O 3 (110) narrows the band gap, promotes the N 2 activation on the Mo site with an elongated N≡N bond length of 1.132 Å in the end-on configuration, and optimizes an associative distal pathway with a decreased energy barrier. Our results may pave the way toward enhancing the electrocatalytic NRR performance of iron-based materials by atomic-scale heteroatom doping.

The modulation of the electronic structure is the effective access to achieve highly active electrocatalysts for the hydrogen evolution reaction (HER). Transition-metal phosphide-based heterostructures are very promising in enhancing HER performance but the facile fabrication and an in-depth study of the catalytic mechanisms still remain a challenge. In this work, the catalytically inactive n-type CeO x is successfully combined with p-type CoP to form the CoP/CeO x heterojunction. The crystalline-amorphous CoP/CeO x heterojunction is fabricated by the phosphorization of predesigned Co(OH) 2 /CeO x via the as-developed reduction-hydrolysis strategy. The p-n CoP/CeO x heterojunction with a strong built-in potential of 1.38 V enables the regulation of the electronic structure of active CoP within the space-charge region to enhance its intrinsic activity and facilitate the electron transfer. The functional CeO x entity and the negatively charged CoP can promote the water dissociation and optimize H adsorption, synergistically boosting the electrocatalytic HER output. As expected, the heterostructured CoP/CeO x -20:1 with the optimal ratio of Co/Ce shows significantly improved HER activity and favorable kinetics (overpotential of 118 mV at a current density of 10 mA cm -2 and Tafel slope of 77.26 mV dec -1 ). The present study may provide new insight into the integration of crystalline and amorphous entities into the p-n heterojunction as a highly efficient electrocatalyst for energy storage and conversion.

Controllable and scalable fabrication is the precondition for realizing the large number of superior electronic and catalytic applications of MoS 2 . Here, we report a new type of synergistic additives, ammonium salts, for chemical vapor deposition (CVD) growth of MoS 2 . On the basis of the catalysis of ammonium salts, we can achieve layer and shape-controlled MoS 2 domains and centimeter-scale MoS 2 films. Compared to frequently used alkali metal ions as the catalysts, ammonium salts are decomposed completely at low temperature (below 513 °C), resulting in clean and nondestructive as-grown substrates. Thus, MoS 2 electronic devices can be directly fabricated on them, and the redundant transfer step is no longer needed. This method can also promote the direct growth of MoS 2 on the conductive substrate and boost the improvement of hydrogen evolution reaction (HER) performance. The ammonium salt-mediated CVD method will pave a new way for MoS 2 toward real applications in modern electronics and catalysis.

Because of its unique electronic band structure, molybdenum disulfide (MoS 2 ) has been regarded as a star semiconducting material. However, direct growth of continuous and high-quality MoS 2 films on SiO 2 /Si substrates is still very challenging. Here, we report a facile chemical vapor deposition (CVD) method based on synergistic modulation of precursor and Na 2 SO 4 catalysis, realizing the centimeter scale growth of a continuous MoS 2 film on SiO 2 /Si substrates. The as-grown MoS 2 film had an excellent spatial homogeneity and crystal quality, with an edge length of the composite domain as large as 632 μm. Both experimental and theoretical results proved that Na tended to bond with SiO 2 substrates rather than to interfere with as-grown MoS 2 . Thus, they showed decent and uniform electrical performance, with electron mobilities as high as 5.9 cm 2 V -1 s -1 . We believe our method will pave a new way for MoS 2 toward real application in modern electronics.

The Chinese mitten crab ( Eriocheir sinensis ) is a commercially important crab in China and is usually managed at high stocking densities. Agonistic behavior directly impacts crab integrity, survival, and growth and results in economic losses. In the present study, we evaluated the modulatory effects of serotonin (5-HT) and dopamine (DA) though the 5-HT2 and DA2 receptor-cyclic adenosine monophosphate (cAMP)-protein kinase A (PKA) pathway on agonistic behavior. The results showed that injection of either 10 -6 mol/crab 5-HT or DA reduced the agonistic behavior of E. sinensis ( P < 0.05), as did 10 -10 mol/crab DA and 10 -8 mol/crab 5-HT and DA ( P < 0.05); however, a dose of 10 -10 mol/crab 5-HT promoted agonistic behavior. 5-HT significantly increased the mRNA expression level of 5-HT7 receptor and reduced that of the DA2 receptor in the cerebral ganglion ( P < 0.05). In contrast to 5-HT, DA significantly decreased 5-HT2B mRNA levels and increased 5-HT7 and DA2 receptor levels in the thoracic ganglia ( P < 0.05). In addition, injections of either 5-HT or DA increased the cAMP and PKA levels in hemolymph ( P < 0.05). By using in vitro culture of the thoracic ganglia, the current study showed that ketanserin (5-HT2 antagonist) and [R(-)-TNPA] (DA2 agonist) had obvious effects on the expression levels of the two receptors ( P < 0.05). In vivo experiments further demonstrated that ketanserin and [R(-)-TNPA] could both significantly reduce the agonistic behavior of the crabs ( P < 0.05). Furthermore, both ketanserin and [R(-)-TNPA] promoted the cAMP and PKA levels ( P < 0.05). The injection of CPT-cAMP (cAMP analogue) elevated the PKA levels and inhibited agonistic behavior. In summary, this study showed that 5HT-2B and DA2 receptors were involved in the agonistic behavior that 5-HT/DA induced through the cAMP-PKA pathway in E. sinensis .

A novel thermally activated delayed fluorescent (TADF) compound, 9-(3-((4,6-diphenyl-1,3,5-triazin-2-yl)oxy)phenyl)-3,6-diphenyl-9 H-carbazole (PhCz- o-Trz), with a donor-σ-acceptor (D-σ-A) motif is developed. A flexible small space σ-junction is adopted to partly suppress the intramolecular charge transfer (intra-CT) while inversely enhancing the intermolecular charge transfer (inter-CT) between D/A moieties, realizing the coexistence of both intra-CT and inter-CT in an amorphous aggregate. The coexistence of dual CTs increases the complexity of the singlet and triplet state mixing, enhancing the triplet-to-singlet spin-flip transition and thereby the TADF emission. Additionally, PhCz- o-Trz is evaluated not only as an emitter but also as a sensitizing host for fluorescent and phosphorescent dopants, all exhibiting high efficiencies with alleviated efficiency roll-offs. These results shed light on the development of new TADF materials with dual CTs and may further deepen our understanding about TADF mechanisms.

Herein, through a morphology-inherited annealing treatment of a hollow Fe-doped MOF-5 octahedron as the self-sacrificing template, we report the synthesis of concave ZnFe 2 O 4 hollow octahedral nanocages as sensing materials, which exhibited high performance, including unprecedented excellent sensitivity, good selectivity, and cyclic stability at ultralow working temperature (120 °C).

Fluorescent energy transfer measurements of dansyl-C6-choline binding to the nicotinic acetylcholine receptor (AChR) from Torpedo californica were used to determine binding characteristics of the alpha gamma and alpha delta binding sites. Equilibrium binding measurements show that the alpha gamma site has a lower fluorescence than the alpha delta site; the emission difference is due to differences in the intrinsic fluorescence of the bound fluorophores rather than differences in energy transfer at the two sites. Stopped-flow fluorescence kinetics showed that dissociation of dansyl-C6-choline from the AChR in the desensitized conformation occurs 5-10-fold faster from the alpha gamma site than from the alpha delta site. The dissociation rates are robust for distinct protein preparations, in the presence of noncompetitive antagonists, and over a broad range of ionic strengths. Equilibrium fluorescent binding measurements show that dansyl-C6-choline binds with higher affinity to the alpha delta site (K = 3 nM) than to the alpha gamma site (K = 9 nM) when the AChR is desensitized. Similar affinity differences were observed for acetylcholine itself. The distinct dissociation rates permit the extent of desensitization to be measured at each site during the time course of binding. This sequential mixing method of measuring the desensitized state population at each agonist site can be applied to study the mechanism of AChR activation and subsequent desensitization in detail.

Axial ligation of nickel(II) 5,10,15,20-tetraphenylporphyrin (NiTPP) with pyrrolidine or piperidine has been investigated using X-ray crystallography, UV-visible spectroscopy, resonance Raman spectroscopy, and molecular mechanics (MM) calculations. By varying the pyrrolidine concentration in dichloromethane, distinct nu(4) Raman lines are found for the four-, five-, and six-coordinate species of NiTPP. The equilibrium constants for addition of the first and second pyrrolidine axial ligands are 1.1 and 3.8 M(-)(1), respectively. The axial ligands and their orientations influence the type and magnitude of the calculated nonplanar distortion. The differences in the calculated energies of the conformers having different ligand rotational angles are small so they may coexist in solution. Because of the similarity in macrocyclic structural parameters of these conformers and the free rotation of the axial ligands, narrow and symmetric nu(2) and nu(8) Raman lines are observed. Nonetheless, the normal-coordinate structural-decomposition analysis of the nonplanar distortions of the calculated structures and the crystal structure of the bis(piperidine) complex reveals a relationship between the orientations of axial ligand(s) and the macrocyclic distortions. For the five-coordinate complex with the plane of the axial ligand bisecting the Ni-N(pyrrole) bonds, a primarily ruffled deformation results. With the ligand plane eclipsing the Ni-N(pyrrole) bonds, a mainly saddled deformation occurs. With the addition of the second axial ligand, the small doming of the five-coordinate complexes disappears, and ruffling or saddling deformations change depending on the relative orientation of the two axial ligands. The crystal structure of the NiTPP bis(piperidine) complex shows a macrocycle distortion composed of wav(x) and wav(y) symmetric deformations, but no ruffling, saddling, or doming. The difference in the calculated and observed distortions results partly from the phenyl group orientation imposed by crystal packing forces. MM calculations predict three stable conformers (ruf, sad, and planar) for four-coordinate NiTPP, and resonance Raman evidence for these conformers was given previously.

The out-of-plane and in-plane distortions of a series of nickel(II) meso-substituted porphyrins with 0, 1, 2, or 4 tert-butyl groups [nickel(II) porphine (NiP), nickel(II) mono-tert-butylporphyrin (NiMtBuP), nickel(II) di-tert-butylporphyrin (NiDtBuP), and nickel(II) tetra-tert-butylporphyrin (NiTtBuP)] are investigated using molecular mechanics (MM) calculations, X-ray crystallography, UV-visible absorption spectroscopy, and resonance Raman spectroscopy. MM calculations are used to predict the stable conformations for this series of porphyrins. The out-of-plane distortions are then analyzed in terms of displacements along the normal coordinates of the porphyrin macrocycle using a new normal-coordinate structural decomposition method. As expected, the distortions are found to occur primarily along the lowest-frequency normal coordinate of each symmetry type and the distortions could be adequately simulated using only the lowest-frequency normal coordinates as a basis (the minimal basis). However, the distortions could be simulated significantly more accurately by extending the minimal basis by including the second-lowest-frequency normal coordinate of all symmetries. Using the extended basis is most important for the in-plane distortions. Detailed analysis of the types of distortion revealed that both the out-of-plane and the in-plane distortions depend on the perturbation symmetry of the peripheral substituents. The symmetry primarily depends on the pattern of substitution (number and positions of substituents) and the orientations of substituents. Often the perturbation symmetry can be predicted for a given porphyrin simply from the possible orientations of the substituents. Then, the main type(s) of symmetric deformation occurring for each possible molecular symmetry can be readily predicted from a D(4)(h)() correlation table. The stable conformers predicted by MM for the series of tert-butyl-substituted porphyrins confirm this simple but informative approach. Experimental verification of the calculated contributions of the symmetric deformations is provided by normal-coordinate structural decomposition of the available X-ray crystal structures of NiP, NiMtBuP, and NiDtBuP. The solid-state results are also supported by the resonance Raman and UV-visible absorption spectroscopic characterization of the porphyrins in solutions. The X-ray crystal structure of NiMtBuP is reported here for the first time.

The influence of the protein on the nonplanarity of the macrocycle for nickel(II)-reconstituted cytochrome c (NiCyt-c) has been investigated with pH-dependent resonance Raman and UV-visible absorption spectroscopy and molecular mechanics calculations. The spectra reveal that NiCyt-c near neutral pH has axially coordinated Ni, but below pH 3 and above pH 12, four-coordinate species predominate. The shape of the structure-sensitive Raman line nu10 of NiCyt-c is asymmetric and broad and it changes with pH. This broad line can be decomposed well into at least two sublines, a low-frequency line that results from a nonplanar conformer and a high-frequency line that arises from a nearly planar conformer. Upon lowering the pH from 3.0 to 1.0, the amount of the nonplanar conformer decreases relative to that of the planar conformer. The decreased nonplanarity can be accounted for in terms of the disruption of a hydrogen-bonding network in the peptide backbone upon lowering the pH. Molecular mechanics (MM) calculations on iron(III) and nickel(II) microperoxidase 5 (MP-5) as well as some model heme derivatives have been carried out in order to locate the part of the protein that causes the heme distortion observed in the X-ray crystal structures of cytochromes c. The energy-optimized structures of MP-5 and the model compounds were analyzed using the normal-coordinate structural decomposition method to specify and quantify the out-of-plane macrocyclic distortions. MM calculations for MP-5 show that two hydrogen bonds formed between the amide groups in the peptide backbone are important in maintaining the ruffled deformation of the macrocycle. All evidence presented supports the hypothesis that the nonplanar distortion of the porphyrin of cytochromes c is largely maintained by a relatively small protein segment including the cysteines, the amino acids between the cysteines, and the adjacent histidine ligand. Hydrogen bonding within the backbone of this segment is important in maintaining the conformation of the peptide that induces the porphyrin distortion.