Synergy of a hierarchical porous morphology and anionic defects of nanosized Li_(4)Ti_(5)O_(12) toward a high-rate and large-capacity lithium-ion battery

Exploring electrode materials with a high volumetric energy density and high rate capability remains of a great challenge for nanosized-Li_(4)Ti_(5)O_(12)(LTO)batteries.Here,hierarchical porous Ti^(3+)-C-N-Br co-doped LTO(LTOCPB-CC)is synthesized using carboxyl-grafted nanocarbon(CC)and cetylpyridinium bromide(CPB)as combined structure-directing agents.Ti^(4+)-O-CPB/Li^(+)-CC is designed as a new molecular chelate,in which CPB and CC promote the uniform mixing of Li^(+)and Ti^(4+)and control the morphology of TiO_(2) and the final product.The defects(oxygen vacancies and ion dopants)formed during the annealing process increase the electron/hole concentration and reduce the band gap,both of which enhance the n-type electron modification of LTO.As-prepared LTOCPB-CC has a large specific surface area and high tap density,as well as a high electronic conductivity(2.84×10^(-4) S cm^(-1))and ionic conductivity(3.82×10^(-12)cm^(2) s^(-1)),which are responsible for its excellent rate capability(157.7 mA h g^(-1) at 20 C)and stable long-term cycling performance(0.008% fade per cycle after 1000 cycles at 20 C).

Selective conformer detection of short-lived base pair tautomers: A computational study of the unusual guanine-cytosine pairs using ultrafast resonance Raman spectroscopy

Base pair mismatch has been regarded as the main source of DNA point mutations, where minor shortlived tautomers were usually involved. However, the detection and characterization of these unnatural species pose challenges to existing techniques. Here, by using systematic structural and ultrafast resonance Raman(RR) spectral analysis for the four possible conformers of guanine-cytosine base pairs, the prominent marker Raman bands were identified. We found that the hydrogen bonding vibrational region from 2300 cm^(-1) to 3700 cm^(-1) is ideal for the identification of these short live species. The marker bands provide direct evidence for the existence of the tautomer species, thus offering an effective strategy to detect the short-lived minor species. Ultrafast resonance Raman spectroscopy would be a powerful tool to provide direct evidence of critical dynamical details of complex systems involving protonation or tautomerization.

Manipulating hot carrier cooling in silicon phononic crystals opens new application opportunities

Phononic crystals(PnCs)have had a multiple of important and promising applications such as sonic diodes,acoustic cloaking,optomechanic,and thermoelectrics[1–5].Undoubtably,it is of significance to explore new findings for PnCs,which can open new application opportunities.

Computational prediction of Mo_(2)@g-C_(6)N_(6) monolayer as an efficient electrocatalyst for N_(2) reduction

Electrocatalytic nitrogen reduction reaction(NRR)is an environmentally friendly method for sustainable ammonia synthesis under ambient conditions.Searching for efficient NRR electrocatalysts with high activity and selectivity is currently urgent but remains great challenge.Herein,we systematically investigate the NRR catalytic activities of single and double transition metal atoms(TM=Fe,Co,Ni and Mo)anchored on g-C_(6)N_(6) monolayers by performing first-principles calculation.Based on the stability,activity,and selectivity analysis,Mo_(2)@g-C_(6)N_(6) monolayer is screened out as the most promising candidate for NRR.Further exploration of the reaction mechanism demonstrates that the Mo dimer anchored on g-C_(6)N_(6) can sufficiently activate and efficiently reduce the inert nitrogen molecule to ammonia through a preferred distal pathway with a particularly low limiting potential of -0.06 V.In addition,we find that Mo_(2)@g-C_(6)N_(6) has excellent NRR selectivity over the competing hydrogen evolution reaction,with the Faradaic efficiency being 100%.Our work not only predicts a kind of ideal NRR electrocatalyst but also encouraging more experimental and theoretical efforts to develop novel double-atom catalysts(DACs)for NRR.

Structural insights of catalytic intermediates in dialumene based CO_(2) capture: Evidences from theoretical resonance Raman spectra

CO_(2) capture is considered as one of the most ideal strategies for solving the environmental issues and against global warming.Recently,experimental evidence has suggested that aluminum double bond(dialumene) species can capture CO_(2) and further convert it into value-added products.However,the catalytic application of these species is still in its infancy.Both the dynamics mechanism of CO_(2) fixation and the detailed structures of catalytic intermediates are not well understood.In this work,we investigate the structure dependent resonance Raman(RR) signals for different reaction intermediates.Ab-initio simulations of spontaneous resonance Raman(spRR) and time-domain stimulated resonance Raman(stRR) give spectral signatures correlated to the existence of different intermediates during the CO_(2)-dialumene binding process.The unique Raman vibronic feature s contain rich structural information with high temporal resolution,enabling to monitor the transient catalytic intermediates under reaction conditions.Our work shows that RR can be used to monitor intermediates during the dialumene based CO_(2) capture reaction.The spectral features not only provide insight into the structural information of intermediate species,but also allow a deeper understanding of the dynamical details of this kind of catalytic process.

HSH-C_(10):A new quasi-2D carbon allotrope with a honeycomb-star-honeycomb lattice

Two-dimensional(2 D)materials with honeycomb,kagome or star lattice have been intensively studied because electrons in such lattices could give rise to exotic quantum effects.In order to improve structural diversity of 2 D materials to achieve unique properties,here we propose a new quasi-2 D honeycombstar-honeycomb(HSH)lattice based on first-principles calculations.A carbon allotrope named HSH-C_(10) is designed with the HSH lattice,and its mechanical properties have been intensively investigated through total energy,phonon dispersion,ab initio molecular dynamic simulations,as well as elastic constants calculations.Besides the classical covalent bonds,there is an interesting charge-shift bond in this material from the chemical bonding analysis.Additionally,through the analysis of electronic structure,HSH-C_(10) is predicted to be a semiconductor with a direct band gap of 2.89 e V,which could combine the desirable characteristics of honeycomb and star lattice.Importantly,by modulating coupling strength,a flat band near the Fermi level can be obtained in compounds HSH-C_(6)Si_(4) and HSH-C_(6)Ge_(4),which have potential applications in superconductivity.Insight into such mixed lattice would inspire new materials with properties we have yet to imagine.

Highly efficient photocatalytic reduction of nitrogen into ammonia by single Ru atom catalyst supported by BeO monolayer

Ammonia(NH_(3))is one of the most important building blocks of the chemical industry and a promising sustainable energy carrier.Conventional production of NH_(3)via the Haber-Bosch process requires high temperature and high pressure,which is energy demanding and suffers safety issues.Photocatalytic nitrogen reduction reaction(NRR)is a green and sustainable route for NH_(3) production,and has been expected to be an alternative for NH_(3)production under mild conditions.However,solar-driven N_(2)activated has appeared as the bottleneck for photocatalytic NRR.In this work,we propose that single Ru atom supported by BeO monolayer is a promising photocatalytic single atom catalyst(SAC)for efficient N_(2)activation with visible illumination.The high efficiency originates from the enhanced absorption in the visible range,as well as the back-donation mechanism when N_(2)were adsorbed on the SAC.Our results show that N_(2)can be efficiently activated by the Ru/BeO SAC and be reduced to NH_(3) with extremely low limiting potential of-0.41 V.The NRR process also exhibits dominate selectivity respect to hydrogen evolution.

First-principles calculations of stability of graphene-like BC_(3) monolayer and its high-performance potassium storage

With increasing demand for renewable energy,graphene-like BC_(3) monolayer as high performance electrode materials for lithium and sodium batteries are drawing more attention recently.However,its structural stability,potassium storage properties and strain effect on adsorption properties of alkali metal ions have not been reported yet.In this work,phonon spectra,AIMD simulations and elastic constants of graphene-like BC_(3) monolayer are investigated.Our results show that graphene-like BC_(3) monolayer possesses excellent structural stability and the maximum theoretical potassium storage capacity can reach up to 1653 mAh/g with the corresponding open circuit voltages 0.66 V.Due to potassium atom can be effectively adsorbed at the most energetically favorable h-CC site with obvious charge transfer,making adsorbed graphene-like BC_(3) monolayer change from semiconductor to metal which is really good for electrode utilization.Moreover,the migrations potassium atom on the graphene-like BC_(3) monolayer is rather fast with the diffusion barriers as low as 0.12 eV,comparing lithium atom with a relatively large diffusion barrier of 0.46 eV.Additionally,the tensile strains applied on the graphene-like BC3 monolayer have marginal effect on the adsorption and diffusion performances of lithium,sodium and potassium atoms.

Two-dimensional blue-phase CX(X=S,Se)monolayers with high carrier mobility and tunable photocatalytic water splitting capability

Photocatalytic water splitting utilizing solar energy is considered as one of the most ideal strategies for solving the ene rgy and environmental issues.Recently,two-dimensional(2 D)materials with an intrinsic dipole show great chance to achieve excellent photocatalytic performance.In this work,blue-phase monolayer carbon monochalcogenides(CX,X=S,Se)are constructed and systematically studied as photocatalysts for water splitting by performing first-principles calculations based on density functional theory.After confirming the great dynamical,thermal,and mechanical stability of CX monolayers,we observe that they possess moderate band gaps(2.41 eV for CS and 2.46 eV for CSe)and high carrier mobility(3.23×10^(4)cm^(2)V^(^(-1))s^(-1)for CS and 4.27×10^(3)cm^(2)V^(-1)s^(-1)for CSe),comparable to those of many recently reported 2 D photocatalysts.Moreover,these two monolayer materials are found to have large intrinsic dipole(0.43 D for CS and 0.51 D for CSe),thus the build-in internal electric field can be selfintroduced,which can effectively drive the separation of photongenerated carriers.More importantly,the well-aligned band edge as well as rather pronounced optical absorption in the visible-light and ultraviolet regions further ensure that our proposed CX monolayers can be used as high efficient photocatalysts for water splitting.Additionally,the effects of external strain on the electronic,optical and photocatalytic properties of CX monolayers are also evaluated.These theoretical predictions will stimulate further work to open up the energy-related applications of CX monolayers.