It is an effective strategy to develop novel electrocatalysts with controllable defects to enhance their electrocatalytic activity and stability. However, how to precisely design these catalysts on ...the atom scale remains very difficult. Herein, several vacancy‐dependent CoZnxMn2–xO4 catalysts are prepared through tailoring the concentration of Zn ions. The in situ activation of the obtained products accelerates the surface reconstruction. The superior electrocatalytic performance can be ascribed to the formations of MOOH (Mn, Co) active species and abundant oxygen vacancies, which are comparable to noble IrO2 and Pt/C catalysts. Zn‐CoMn2O4‐1.5 catalyst delivers a cell voltage of 1.63 V and long durability. Density functional theory calculations demonstrate that the appropriate Zn ion doping can improve the density states of p electron on the surface of catalysts significantly and benefit the d‐band center closing to Fermi level, suggesting their high charge carrier density and low adsorption energy.
In this work, several vacancy‐dependent CoZnxMn2–xO4 catalysts are prepared by tailoring the concentration of Zn ions. The in situ activation can accelerate the surface reconstruction. The excellent electrocatalytic performance can be attributed to the formations of active species and abundant oxygen vacancies, which are comparable to noble IrO2 and Pt/C catalysts.
Rational design and exploration of robust and low‐cost bifunctional oxygen reduction/evolution electrocatalysts are greatly desired for metal–air batteries. Herein, a novel high‐performance oxygen ...electrode catalyst is developed based on bimetal FeCo nanoparticles encapsulated in in situ grown nitrogen‐doped graphitic carbon nanotubes with bamboo‐like structure. The obtained catalyst exhibits a positive half‐wave potential of 0.92 V (vs the reversible hydrogen electrode, RHE) for oxygen reduction reaction, and a low operating potential of 1.73 V to achieve a 10 mA cm−2 current density for oxygen evolution reaction. The reversible oxygen electrode index is 0.81 V, surpassing that of most highly active bifunctional catalysts reported to date. By combining experimental and simulation studies, a strong synergetic coupling between FeCo alloy and N‐doped carbon nanotubes is proposed in producing a favorable local coordination environment and electronic structure, which affords the pyridinic N‐rich catalyst surface promoting the reversible oxygen reactions. Impressively, the assembled zinc–air batteries using liquid electrolytes and the all‐solid‐state batteries with the synthesized bifunctional catalyst as the air electrode demonstrate superior charging–discharging performance, long lifetime, and high flexibility, holding great potential in practical implementation of new‐generation powerful rechargeable batteries with portable or even wearable characteristic.
Bamboo‐like FeCo alloy encapsulated in nitrogen‐doped carbon nanotubes exhibits superior catalytic oxygen reduction and oxygen evolution performance than that of noble metal benchmarks, which benefits from the nitrogen‐rich and defect‐rich catalyst surface. The all‐solid‐state zinc–air batteries equipped by the synthesized materials show low charging/discharging overpotentials, long lifetime, and high flexibility, suitable for practical application.
Herein we report two new TPE‐based 3D MOFs, that is, Sr‐ETTB and Co‐ETTB (TPE=Tetraphenylethylene, H8ETTB=4′,4′′′,4′′′′′,4′′′′′′′‐(ethene‐1,1,2,2‐tetrayl)tetrakis((1,1′‐biphenyl‐3,5‐dicarboxylic ...acid))). Through tailoring outer shell electron configurations of SrII and CoII cations, the fluorescence intensity of the MOFs is tuned from high emission to complete non‐emission. Sr‐ETTB with strong blue fluorescence shows reversible fluorescence variations in response to pressure and temperature, which is directly related to the reversible deformation of the crystal structure. In addition, non‐emissive Co‐ETTB counterpart exhibits a turn‐on fluorescent enhancement under the stimulation of analyte histidine. In the process, TPE‐cored linkers in the MOFs are released through competitive coordination substitution and subsequently reassembled to perform aggregation‐induced luminescence behavior originated from the organic linkers.
Two new tetraphenylethylene‐based 3D MOFs are obtained. Sr‐ETTB performs uncommon reversible thermo/piezofluorochromism and thermo/piezochromic behaviors which are driven by its characteristic crystalline framework flexibility. Non‐emissive Co‐ETTB exhibits a turn‐on fluorescent enhancement under the stimulation of analyte histidine.
Aromatic-fluorinated sumanene derivatives have been designed and studied systematically using DFT and TDDFT methods. The geometric structures, frontier molecular orbitals, ionization potentials, ...electron affinities, reorganization energies, absorption spectra, fluorescence emission spectra, radiative decay rates, non-radiative decay rates and fluorescence quantum yields of the molecules have been discussed by comparison. The results show that 2,5,8-trifluorosumanene (
8
) should be especially beneficial to charge transport rather than fluorescence emission. Besides, 3,5-difluorosumanene (
5
), 2,3,6-trifluorosumanene (
7
) and 2,3,6,8-tetrafluorosumanene (
13
) should be more beneficial to charge transport and fluorescence emission than their respective isomers. In addition, the mono-substituted sumanenes could be designed as good optoelectronic materials more easily than other sumanene derivatives. In a word, the relationship between the molecular structures and optoelectronic properties of aromatic-fluorinated sumanene derivatives has been established by calculation, which can provide a theoretical reference for the experimental design of novel bowl-shaped organic optoelectronic materials based on aromatic-substituted sumanene derivatives.
The relationship between the structures and optoelectronic properties of sumanene and its aromatic-fluorinated derivatives has been systematically studied in depth.
Computational analyses of the solid-state properties of triazasumanene (TAS), a
C
3
-symmetric nitrogen-doped sumanene derivative, were carried out in this work. The present studies are mainly ...divided into two parts. In the first part, we demonstrated the differences in the interactions of the crystal packing between the racemic and the homochiral structures: the former having perpendicular columnar packing and the latter forming slipped helical packing. Two geometries of the TAS monomer, a theoretically optimized structure under vacuum and an X-ray crystal structure in experiment, were compared. It can be found that it is not the total interaction energy, but the local interactions (mainly the electrostatic interactions) of the molecular dimer that dominate the columnar stacking conformation. The second part involves the investigation of the potential charge transport properties of the crystals according to the semiclassical Marcus theory with the hopping mechanism using the simple dimer model. The charge transfer integrals of the two sets of dimers, racemic and homochiral dimer models, were compared as well. The calculation results show that the TAS racemic crystal was predicted to have an advantage of hole transport properties. The perpendicular columnar stacking of the homochiral conformation should essentially have better charge transport properties than the racemic conformation. It is reasonable to employ the simple dimer model built using optimized monomers under vacuum for the purpose of the prediction of the molecular packing conformation by IES calculation and the charge transport properties of the perpendicular columnar-stacking crystal. Our work provides a simple approach to the deep understanding of the structure-property relationship of bowl-shaped molecular systems in theory. It can help to facilitate the design and preparation of heteroatom-doped sumanene derivatives with perpendicular columnar stacking crystals as novel organic semiconductor materials.
Different molecular interactions in triazasumanene racemic and homochiral crystals were investigated by a simple dimer model.
The high crystalline covalent triazine framework-1 (CTF-1), composed of alternating triazine and phenylene, has emerged as an efficient photocatalyst for solar-driven hydrogen evolution reaction ...(HER). However, it is of great challenge to further improve photocatalytic HER performance via increasing crystallinity due to its near-perfect crystallization. Herein, an alternative strategy of scaffold functionalization is employed to optimize the energy band structure of crystalline CTF-1 for boosting hydrogen-evolving activity. Guided by the computational predictions, versatile CTF-based polymer photocatalysts are prepared with different functional groups (OH, NH
, COOH) using binary polymerization for practical hydrogen production. Experiment evidence verifies that the introduction of a limited number of electron-donating groups is sufficient to maintain high crystallinity in CTF, modulate the band structure, broaden visible light absorption, and consequently enhance its photophysical properties. Notably, the functionalization with OH exhibits the most positive effect on CTF-1, delivering a photocatalytic activity with a hydrogen-producing rate exceeding 100 µmol h
.
A series of reported Pt(II) carbene complexes possibly have the ability to serve as the new generation of blue emitters in luminescent devices because of their narrow emission spectra, high ...photoluminescence quantum yields (PLQYs), and rigid molecular skeleton. However, the combination of all carbene ligands with different multidentate structures will affect the overall planarity and horizontal dipole ratio to varying degrees, but the specific extent of this effect has not previously been analyzed in detail. In this work, density functional computation is used to study a class of platinum tetracarbene bidentate complexes with similar absorption and emission band characteristics, which is the main reason for the remarkable difference in quantum efficiency due to subtle differences in electronic states caused by different ligands. From the calculation results, the major reason, which results in significantly decrease in quantum efficiency for Pt(cyim)
, is that Pt(cyim)
can reach the non-radiative deactivation metal-centered d-d excited state through an easier pathway compared with Pt(meim)
. The result, based on changes in the dihedral angle between ligands, can achieve the goal of improving and designing materials by adjusting the degree of the dihedral angle. (meim: bis(1,1'-dimethyl-3,3'-methylene-diimidazoline-2,2'-diylidene); cyim: bis(1,1'-dicyclohexyl-3,3'-methylene-diimidazoline-2,2'-diylidene).
We present a time-domain ab initio study of electron–hole recombination in pristine MAPbI3, and compare it to the trap mediated recombination in MAPbI3 with the iodine interstitial defect. ...Nonadiabatic molecular dynamics combined with time-domain density functional theory show that the iodine interstitial defect creates a subgap state capable of trapping both electrons and holes. Hole trapping occurs much faster than electron trapping or electron–hole recombination. The trapped hole survives for hundreds of nanoseconds, because, rather surprisingly, recombination of electrons with the trapped hole takes several times longer than recombination of electrons with holes in the valence band. Because the hole trap is relatively shallow, the hole can escape into the valence band prior to recombining with the electron. The differences are rationalized by variation in nonadiabatic electron–phonon couplings, phonon-induced pure-dephasing times and electronic energy gaps. The time-domain atomistic simulations contribute to understanding of the experimentally known defect-tolerance of perovskite solar cells, which is of great importance to the solar cell performance.
Dye sensitizers play an important role in dye-sensitized solar cells (DSSCs). As a promising strategy for the design of novel porphyrin sensitizers, the asymmetric modification of the porphyrin ring ...to meso-link porphyrin sensitizer has emerged in recent years, which can improve the light-harvesting properties and enhance the electron distribution. In this work, in order to reveal the essence of the effect of unsymmetrical substitution on the performance of β-link porphyrin dyes in DSSCs, four kinds of common β-link porphyrin dyes with different structures are calculated by using density functional theory (DFT) and time-dependent density functional theory (TD-DFT). The electronic structures and optical properties of these studied dyes in dimethylformamide (DMF) are also investigated. The key parameters of the short-circuit current density (J
), including light harvesting efficiency (LHE), electron injection driving force (ΔG
), and intra-molecular charge transfer (ICT) are discussed in detail. In addition, the periodic DFT calculations in the dye-TiO
systems are also employed to investigate the geometrical and electronic injection process of the different connection types of these studied dyes adsorbed on the periodic TiO
model with an exposed anatase (101) surface. We expect the present study would deepen the understanding of the alternative function of unsymmetrical substitution and may contribute to future DSSC design.
Tetrabutylammonium hydroxide (TBAH) and other quaternary ammonium hydroxides catalyzed the cycloaddition of CO 2 to epoxides under solvent-free conditions to give cyclic carbonates. When TBAH was ...exposed to CO 2 , TBAH was converted into tetrabutylammonium bicarbonate (TBABC), which was a catalytically active species. A D-labeled epoxide and an optically active epoxide were used to study the reaction mechanism, which invoked three plausible pathways. Among them, path A seemed to be predominant; the bicarbonate ion of TBABC attacks the less hindered C atom of the epoxide to generate a ring-opened alkoxide intermediate, which adds to CO 2 to give a carbonate ion, and the subsequent cyclization yields a cyclic carbonate. Density functional theory (DFT) calculations successfully delineated the potential energy profile for each reaction pathway, among which path A was the lowest-energy pathway in accordance with the experimental results. The tetrabutylammonium (TBA) cation carries the positive charges on the H atoms, but not on the central N atom, and the positively charged H atoms close to the central N atom form an anion-binding site capable of stabilizing various anionic transition states and intermediates.
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