Multiple active components synergistically driven heteroatom-doped porous carbon as high-performance counter electrode in dye-sensitized solar cells

A facile template-free in situ self-activation approach for the multiple active components synergistically driven porous carbon was presented via a feasible annealing process.The biomass-derived carbon without additional activation reagents was fabricated using K-rich pomelo peel(PP)as the carbon source,which possesses a high electric conductivity where abundant functional hetero-metal atoms are doped into the carbon framework that playing the role of catalytic graphitization.The K^+that exists within the biomass can induce self-activation during pyrolysis apart from the activating gases during the pyrolysis process.The resulting electrocatalyst of PP-850(PP was pyrolyzed at 850°C in an N_2atmosphere)with abundant heteroatoms possesses a higher power conversion efficiency(PCE)of 7.81%as the counter electrode(CE)of dye-sensitized solar cells(DSCs)compared with the CEs calcinated at other temperatures and a similar PCE with Pt counterpart(8.24%)based on the liquid I_3^-/I^-electrolyte.The better electrocatalytic performance is attributed to the synergistic effect between self-activation and the co-doping of nitrogen,sulfur and phosphorus all together in a carbon matrix.Due to the feasibility of large-scale production,rich heteroatom doping,the PP-derived carbon,which simplifies the procedure and decreases the cost,has a potential application for an alternative electrocatalyst for high-performance photovoltaic devices.

Competing reduction induced homogeneous oxygen doping to unlock MoS_(2)basal planes for faster polysulfides conversion

The parasitic polysulfides shuttle effect greatly hinders the practical application of lithium sulfur batteries,and this issue can be addressed by promoting polysulfides conversion with catalytic materials such as Mo S_(2).However,the catalytic activity of Mo S_(2)mainly relies on edge sites,but is limited by inert basal planes.We herein report a novel,facile,ethylene glycol enabled competing reduction strategy to dope Mo S_(2)homogeneously with oxygen atoms so that its inert basal planes can be unlocked.Ethylene glycol works as a reducing agent and competes with thiourea to react with ammonium molybdate,leading to insufficient sulfuration of Mo,and consequent formation of O-Mo S_(2).Our theoretical and experimental investigations indicate that the homogeneously distributed O dopants can create abundant adsorption/-catalytic sites in the Mo S_(2)basal planes,enlarge the inter-plane distance to promote ion transport,and thus enhance the catalytic conversion of polysulfides.The oxygen doped Mo S_(2)(O-Mo S_(2))is supported on carbon nanosheets(CNS)and the composite(O-Mo S_(2)/CNS)is employed to modify the separator of Li-S battery.It gives the battery an initial discharge capacity of 1537 m Ah g-1at 0.2 C,and the battery retains a discharge capacity of 545 m Ah g-1after ultra-long 2000 cycles at 1 C,corresponding to a very small cyclic decay rate of 0.0237%.Even under a raising sulfur loading of 8.2 mg cm^(-2),the Li-S battery also delivers a high discharge capacity(554 m Ah g^(-1))with outstanding cycle stability(84.6%capacity retention)after 100 cycles at 0.5 C.Our work provides a novel,facile approach to fabricate highly catalytically active oxygen-doped Mo S_(2)for advanced Li-S batteries.

Polyaniline-based electrocatalysts through emulsion polymerization:Electrochemical and electrocatalytic performances

One of the major challenges associated with fuel cells is the design of highly efficient electrocatalysts to reduce the high overpotential of the oxygen reduction reaction (ORR). Here we report Polyaniline (PANI) based micro/nanomaterials with or without transition metals, prepared by the emulsion polymerization and subsequent heat treatment. PANI microspheres with the diameter of about 0.7 mu m have been prepared in basic (NH3 solution) condition, using two different types of surfactant (CTAB, SDS) as the stabilizer, ammonium persulphate (APS) as oxidant with aniline/surfactants molar ratio at 1/1 under the hydrothermal treatment. PANI nanorods, Fe-PANI, and Fe-Co-PANI have been synthesized in acidic (HCI) medium with aniline/surfactants molar ratio at 1/2 and polymerization carried out without stirring for 24 h. Products mainly Fe-Co-PANI have shown high current density with increasing sweep rate and excellent specific capacitance 1753 F/g at the scan rate of 1 mV/s. Additionally, it has shown high thermal stability by thermogravimetric analysis (TGA). Fe-PANI has been investigated for excellent performance toward ORR with four electron selectivity in the basic electrolyte. The PANI-based catalysts from emulsion polymerization demonstrate that the method is valuable for making non-precious metal heterogeneous electrocatalysts for ORR or energy storage and conversion technology. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

Theoretical design and experimental synthesis of counter electrode for dye-sensitized solar cells: Amino-functionalized graphene

For some specific catalytic reaction, how to construct active sites on two dimensional materials is of great scientific significance. Dye-sensitized solar cells（DSCs） can be viewed as one representative photovoltaics because in which liquid electrolyte with triiodide/iodide（I;/I;） as redox couples are involved. In this study, amino-functionalized graphene（AFG） has been designed according to theoretically analyzing iodine reduction reaction（IRR） processes and rationally screening the volcanic plot. Then, such AFG has been successfully synthesized by a simple hydrothermal method and shows high electrocatalytic activity towards IRR when serving as counter electrode in DSCs. Finally, a high conversion efficiency of 7.39% by AFG-based DSCs was obtained, which is close to that using Pt as counter electrode.

光系统Ⅱ光驱动CO_(2)同化的光合作用

光合作用作为地球上最重要的化学反应,是一切生命活动赖以生存的基础.光合作用分为光反应和暗反应两个阶段.通常认为,光反应阶段产生O2,暗反应阶段CO_(2)被还原(也称“CO_(2)同化”).尽管这一观点已被公众所熟知,但也存在诸多疑点,一些科学家(包括1931年的诺贝尔生理学或医学奖得主OttoWarburg)认为,CO_(2)也可能在光反应阶段作为反应底物参与了产氧并被还原.然而,该观点至今没有在实验上获得充足的证据支持.那么,在光反应阶段是否能够进行CO_(2)同化?如果能够发生,产物和机理是什么?毫无疑问,这些科学问题具有十分重要的研究价值,对这些问题的探索能帮助我们更加充分认识光合作用机制.然而,自上世纪十年代以来,相关研究已陷入停滞状态.为了解开光合作用领域的这个重要科学谜团,即在光合作用中CO_(2)是否能通过光反应被还原,本文选取三类不同层次的光合作用体系(小球藻、叶绿体、PSII中心复合体)为研究对象,结合原位质谱、气相色谱和同位素标记等手段,设计了一系列实验,排除了呼吸作用和其它因素干扰,实验发现在光反应阶段PSII中心复合体不但产生O2,还能产生C1化合物CH_(3)OH.^(13)CO_(2)和C^(18)O2标记实验结果表明,CH_(3)OH来源于CO_(2)光还原,排除了CH_(3)OH来自于光呼吸或细胞壁果胶脱甲基分解的可能.说明光合作用光反应阶段能够进行CO_(2)还原,反应场所是PSII中心复合体,这与CO_(2)的同化只能发生在暗反应阶段的传统观点相矛盾.因此,除了非光依赖性CO_(2)同化这一已知路径外,还有一条未知的光驱动CO_(2)同化路径.进一步推测,这种CO_(2)光还原路径可能与暗反应下的CO_(2)同化同时进行.目前,对这种光驱动下CO_(2)同化机制仍需进一步深入研究.综上,本文丰富了人们对光合作用机理以及CO_(2)同化路径的认知,并为长期以来存在争议的CH_(3)OH来源问题提供了新解释.

Quaternary-ammonium-immobilized polystyrenes as efficient and reusable heterogeneous catalysts for synthesis of cyclic carbonate:Effects of linking chains and pendent hydroxyl group

Spherical polystyrene‐supported ammonium salts containing different linking chains between the support and ammonium groups were prepared as efficient and easily reusable heterogeneous catalysts for the cycloadditions of CO2and epoxides.The effects of the length of the linking chains and a hydroxyl group pendent on the linking chain on the catalytic performance of ionic liquid immobilized catalysts and their mechanisms were studied through experiments and density functional theory calculations.It was found that,compared with a short linking chain,a long chain can make the halogen anion more negative and provide a larger contact area of the catalysts with the reactants,thus enhancing the reaction kinetics.The hydroxyl group can stretch the C-O bonds of the epoxides,promoting the reaction thermodynamics.As a result,for the cycloaddition of propylene oxide,the yield of propylene carbonate is much higher for the catalyst with a long linking chain(yield:91.4%)compared with the yield for that with a short chain(yield:70.9%),and is further increased in the presence of pendent hydroxyl groups(yield:98.5%).The catalyst also shows a high catalytic activity even at mild temperature and good reusability(yield:≥96%for10cycles),and the selectivity is always above99%.

Molten salt as ultrastrong polar solvent enables the most straightforward pyrolysis towards highly efficient and stable single-atom electrocatalyst

Currently,pyrolysis as the most widely used method still has some key issues not well resolved for synthesis of carbon-supported single-atom catalysts(C-SACs),e.g.,the sintering of metal atoms at high temperature as well as the high cost and complicated preparations of precursors.In this report,molten salts are demonstrated to be marvellous medium for preparation of C-SACs by pyrolysis of small molecular precursors(ionic liquid).The ultrastrong polarity on one hand establishes robust interaction with precursor and enables better carbonization,resulting in largely enhanced yield.On the other hand,the aggregation of metal atoms is effectively refrained while no nanoparticle or cluster is formed.By this strategy,a C-SAC with atomically dispersed Fe-N_(4) sites and a high specific area over 2000 m^(2) g^(-1) is obtained,which illustrates high ORR activity in both acid and alkaline media.Moreover,this SAC exhibits superior methanol tolerance and stability after acid soaking at 85℃ for 48 h.It is believed that the molten-salts-assisted pyrolysis can be developed into a routine strategy as it not only can largely simply the synthesis of C-SACs,but also can be extended to prepare other types of SACs.

Insight into the CO2 photoreduction mechanism over 9-hydroxyphenal-1-one(HPHN) carbon quantum dots

Converting CO2 to carbon-containing fuels is an effective approach to relieving energy shortages.Carbon quantum dots(CQDs) have shown distinct properties and attracted tremendous interest in CO2 reduction.Herein,we report a joint experimental-computational mechanistic study of photoreduction CO2 to CO on the model catalyst 9-hydroxyphenal-1-one(HPHN) CQDs with known structure.Our theoretical calculations reveal that the rate-determining step is COOH·formation,which is closely related to the proton and electron transfer induced by hydrogen bonding in the excited state.According to the calculated volcano plot,the solution we proposed is addition Zn^(2+) ions.The active center changed from the hydroxyl oxygen atom to the Zn atom and the barrier of the COOH·formation step is noticeably decreased when Zn^(2+) ions are added.It is further confirmed by the experimental data that the activity of CO2 reduction increases 2.9 times when Zn^(2+) ions are added.

New insight into the ultra-long lifetime of excitons in organic-inorganic perovskite： Reverse intersystem crossing

Recently, an effective exciton diffusion length L exceeding 100μm has been reported for organic- inorganic halide perovskites owing to both the high mobility and ultra-long lifetime of the excitons; however, the origin of ultra-long L is still unclear in nature. In some photoelectric materials, reverse intersystem crossing （RISC） from the triplet to the singlet state can enhance the quantum yield of pho- toluminescence greatly. In this study, our theoretical investigation indicated that the energy difference △E_st between the singlet state and the triplet state of CH_3NH_3Pbl_3 was less than 0.1 eV, which represents one crucial prerequisite for the occurrence of RISC. Meanwhile, the experimental results showed that the photoluminescence lifetime increased with the increasing temperature, a typical feature of RISC. Based on this study, we put forward the hypothesis that the ultra-long lifetime of excitons in organic-inorganic halide perovskite might be caused by the RISC process. This may provide a new insight into the important photophysical properties of such novel photovoltaic materials.

Simulation and experimental analysis of melt pool evolution in laser engineered net shaping

In this work,the evolution of melt pool under single-point and single-line printing in the laser engineered net shaping(LENS)process is analyzed.Firstly,the basic structure of the melt pool model of the LENS process is established and the necessary assumptions are made.Then,the establishment process of the multi-physical field model of the melt pool is introduced in detail.It is concluded that the simulation model results are highly consistent with the online measurement experiment results in terms of melt pool profile,space temperature gradient,and time temperature gradient.Meanwhile,some parameters,such as the 3D morphology and surface fluid field of the melt pool,which are not obtained in the online measurement experiment,are analyzed.Finally,the influence of changing the scanning speed on the profile,peak temperature,and temperature gradient of the single-line melt pool is also analyzed,and the following conclusions are obtained:With the increase in scanning speed,the profile of the melt pool gradually becomes slender;The relationship between peak temperature and scanning speed is approximately linear in a certain speed range;The space temperature gradient at the tail of the melt pool under different scanning speeds hardly changes with the scanning speed,and the time temperature gradient at the tail of the melt pool is in direct proportion to the scanning speed.

Insights into atomically dispersed reactive centers on g-C_(3)N_(4)photocatalysts for water splitting

Co-catalysts decorations provide unique opportunity in promoting the photocatalytic water splitting performance of graphite carbon nitride(g-C_(3)N_(4))system,while mechanistic understanding of this complex catalytic network remains elusive.Here,taking the single-atom-based photocatalysts(M1-g-C_(3)N_(4))as an unprecedented simplified model system,we theoretically tracked the photocatalytic kinetics for a comprehensive understanding of the photocatalytic process and afforded the descriptorαS1-T1/αT1-S0(ratio of the extent of S1-T1 and T1-S0 state mixing)andΔGH^(*)(hydrogen adsorpti on free energy)for rational screening of photocatalysts.The targeted Fe1-g-C_(3)N_(4)yields an excellent H_(2)evolution rate(ca.3.2⋅mmol⋅gcat^(-1)⋅h^(-1)under full arc),two order of magnitude improvement relative to pristine g-C_(3)N_(4)counterpart and also outperforms other representative 3d-transition-metal-based photocatalysts.This work presents a comprehensive understanding of the essential role of isolated atomic sites in the photocatalytic course and sheds light on the design of photocatalysts from both photophysical and photochemical aspects.

The Tianwen-1 Guidance, Navigation, and Control for Mars Entry, Descent, and Landing

Tianwen-1,the first mission of China’s planetary exploration program,accomplished its goals of orbiting,landing,and roving on the Mars.The entry,descent,and landing(EDL)phase directly determines the success of the entire mission,of which the guidance,navigation,and control(GNC)system is crucial.This paper outlines the Tianwen-1 EDL GNC system design by introducing the GNC requirements followed by presenting the GNC system architecture and algorithms to meet such requirements.The actual flight results for the whole EDL phase are also provided in this paper.

Corrigendum to “The Tianwen-1 Guidance, Navigation, and Control for Mars Entry, Descent, and Landing”

In the article titled“The Tianwen-1 Guidance,Navigation,and Control for Mars Entry,Descent,and Landing”[1],there was an error in Figure 9(b).On the y-axis,the data read q1,q2,and q1.It should have read q1,q2,and q3.This is updated as shown in Figure 1 below.

Selective Insertion in Copolymerization of Ethylene and Styrene Catalyzed by Half-Titanocene System Bearing Ketimide Ligand： A Theoretical Study

The copolymerization of ethylene and styrene can be efficiently carried out by using Cp＊TiCl2（N=CtBu2）/ MAO （Cp＊=η5-C5Me5） system, yielding the poly（ethylene-co-styrene）s with isolated styrene units. In order to in- vestigate the reasons for formation of the structure, the mechanism of copolymerization, especially the selective in- sertion of ethylene and styrene, is studied in detail by density functional theory （DFT） method. At the initiation stage, insertion of ethylene is kinetically more favorable than insertion of styrene, and insertion of styrene kinet- ically and thermodynamically prefers 2,1-insertion. That is different from the conventional half-titanocene system, in which the 1,2-insertion is favorable. At chain propagation stage, the computational results suggest that the con- tinuous insertion of styrene is hard to occur at room temperature due to the high free energy barriers （28.90 and 35.04 kcal/mol for 1,2-insertion, and 29.15 and 34.00 kcal/mol for 2,1-insertion） and thermodynamically unfavora- ble factors in two different conditions. That is mainly attributed to the steric hindrance between the coming styrene and chain-end styrene or ketimide ligand. The computational results are in good agreement with the experimental data.

Tuned single atom coordination structures mediated by polarization force and sulfur anions for photovoltaics

Impeding high temperature sintering is challengeable for synthesis of carbon-supported single-atom catalysts (C-SACs), which requires high-cost precursor and strictly-controlled procedures. Herein, by virtue of the ultrastrong polarity of salt melts, sintering of metal atoms is effectively suppressed. Meanwhile, doping with inorganic sulfur anions not only produces sufficient anchoring sites to achieve high loading of atomically dispersed Co up to 13.85 wt.%, but also enables their electronic and geometric structures to be well tuned. When served as a cathode catalyst in dye-sensitized solar cells, the C-SAC with Co-N4-S2 moieties exhibits high activity towards the iodide reduction reaction (IRR), achieving a higher power conversion efficiency than that of conventional Pt counterpart. Density function theory (DFT) calculations revealed that the superior IRR activity was ascribed to the unique structure of Co-N4-S2 moieties with lower reaction barriers and moderate binding energy of iodine on the Co center, which was beneficial to I2 dissociation.

Benzimidazolium Functionalized Polysulfone-based Anion Exchange Membranes with Improved Alkaline Stability

The stability of anion exchange membranes(AEMs)is an important feature of alkaline exchange membrane fuel cells(AEMFCs),which has been extensively studied.However it remains a real challenge due to the harsh working condition.Herein,we developed a novel type of polysulfone-based AEMs with three modified 1,2-dimethylbenzimidazoliums containing different substitutes at C4-and C7-position.The results showed that the introduction of the substitutes could obviously improve the dimensional and alkaline stabilities of the corresponding membranes.The swelling ratios of resultant AEMs were all lower than 10%after water immersion.The membrane with 4,7-dimethoxy-1,2-dimethylbenzimidazolium group exhibited the highest alkaline stability.Only 9.2%loss of hydroxide conductivity was observed after treating the membrane in 1 mol·L^(-1)KOH solution at 80°C for 336 h.Furthermore,the density functional theory(DFT)study on the three functional group models showed that the substitutes at C4-and C7-position affected the lowest unoccupied molecular orbital(LUMO)energies of the different 1,2-dimethylbenzimidazolium groups.

Quantum chemical investigation on photodegradation mechanisms of sulfamethoxypyridazine with dissolved inorganic matter and hydroxyl radical

Sulfamethoxypyridazine（SMP） is one of the commonly used sulfonamide antibiotics（SAs）.SAs are mainly studied to undergo triplet-sensitized photodegradation in water under natural sunlight with other coexisting aquatic environmental organic pollutants.In this work,SMP was selected as a representative of SAs.We studied the mechanisms of triplet-sensitized photodegradation of SMP and the influence of selected dissolved inorganic matter,i.e.,anions（Br^-,Cl^-,and NO^-_3） and cations ions（Ca^（2＋）,Mg^（2＋）,and Zn^（2＋）） on SMP photodegradation mechanism by quantum chemical methods.In addition,the degradation mechanisms of SMP by hydroxyl radical（OH·） were also investigated.The creation of SO_2 extrusion product was accessed with two different energy pathways（pathway-1 and pathway-2） by following two steps（step-I and step-II） in the tripletsensitized photodegradation of SMP.Due to low activation energy,the pathway-1 was considered as the main pathway to obtain SO_2 extrusion product.Step-II of pathway-1 was measured to be the rate-limiting step（RLS） of SMP photodegradation mechanism and the effect of the selected anions and cations was estimated for this step.All selected anions and cations promoted photodegradation of SMP by dropping the activation energy of pathway-1.The estimated low activation energies of different degradation pathways of SMP with OH·radical indicate that OH·radical is a very powerful oxidizing agent for SMP degradation via attack through benzene derivative and pyridazine derivative ring.

Carrier dynamics in CsPbI_3 perovskite microcrystals synthesized in solution phase

All-inorganic cesium lead halide perovskites （CsPbX3, X=CF, Br-, I-） could provide comparableoptoelectronic properties as a promising class of materials for photovoltaic cell （PV）, photodetector andlight-emitting diode （LED） with enhanced thermal and moisture stabilities compared to organic-inorganic lead halide species. However, fabrication of CsPbI3 perovskite via facile solution process hasbeen difficult due to instability of CsPbl3 in the perovskite cubic phase in ambient air. Herein, we reportthe synthesis of CsPbl3 perovskite microcrystals by low-temperature, catalyst-free, solution-phasemethod. By applying the time-resolve spectroscopic technique, we determine the carrier diffusioncoefficient of 0.6-1.2 cm2/s, the intrinsic carrier lifetimes of 200-1300 ns and diffusion length of4-10 μm in different individual CsPbl3 perovskite microcrystals. Our results suggest the CsPbl3 perovskitemicrocrystals synthesized by solution process exhibit high quality feature and are suitable forapplications in optoelectronic devices.