太阳能光催化分解水制氢※

利用太阳能光催化分解水制氢是解决能源环境问题并实现太阳能有效转化和储存最有前途的技术之一, 这一“圣杯”式反应经过几十年不懈努力取得了诸多重要研究进展. 本文将综述光催化分解水制氢体系的基本概念、活性测试方法与注意事项、光催化材料种类等; 并从光催化分解水制氢的光吸收、光生电荷分离和表面催化反应等基本过程和关键科学问题的角度总结其重要研究进展, 最后对于太阳能光催化分解水制氢的挑战和潜在的发展方向进行分析和展望. 希望通过本综述的简要介绍能让刚从事光催化分解水制氢研究的青年科技人员清晰地了解掌握该领域的一些基本概念、操作规范、研究总体进展和现状等.     

Reversible Photoinduced Conversion of Unprecedented Norbornadiene-Based Photoswitches with Redox-Active Naphthalene Diimide Functionalities

An unprecedented compound class of functional organic hybrids consisting of a photoswitchable norbornadiene building block and a redoxactive chromophore, namely naphthalene diimide, were designed and synthesized. Within these structures the capability of rylene chromophores to function as a redox active catalyst upon their photoexcitation was utilized to initiate the oxidative back-conversion of the in situ formed quadricyclane unit to its norbornadiene analogue. In this way successive photoexcitation at two different wavelengths enabled a controlled photoswitching between the two isomerical states of the hybrids. Beyond this prove of concept, the dependency of the reaction rate to the intramolecular distance of the two functional molecular building blocks as well as the concentration of the photoexcited sample was monitored. The experimental findings and interpretations were furthermore supported by quantum chemical investigations.     

Competitive Photoisomerization and Energy Transfer Processes in Fluorescent Multichromophoric Systems

Multichromophoric systems showing both fluorescence and photoisomerization are fascinating, with complex interchromophoric interactions. The experimental and theoretical study of a series of compounds, bearing a variable number of 4-dicyanomethylene-2-tert-butyl-6-(p-(N-(2-azidoethyl)-N-methyl)aminostyryl)-4H-pyran (DCM) units are reported. The photophysical properties of multi-DCM derivatives, namely 2DCM and 3DCM , were compared to the single model azido-functionalized DCM , in the E and Z isomers. The (EE)- 2DCM and (EEE)- 3DCM were synthesized via the click reaction. Steady-state spectroscopy and photokinetics experiments under UV or visible irradiation indicated the presence of intramolecular energy transfer processes among the DCM units. Homo- and hetero-energy transfer processes between adjacent chromophores were confirmed by fluorescence anisotropy and decays. Molecular dynamics simulations for 2DCM were carried out and analyzed using a Markov state model, providing geometrical parameters (orientation and distance between chromophores) and energy transfer efficiency. This work contributes to a better understanding and rationalization of multiple energy transfer processes occuring within multichromophoric systems.     

表面限域掺杂提升高比能正极材料稳定性

Lithium ion batteries (LIBs) have broad applications in a wide variety of a fields pertaining to energy storage devices. In line with the increasing demand in emerging areas such as long-range electric vehicles and smart grids, there is a continuous effort to achieve high energy by maximizing the reversible capacity of electrode materials, particularly cathode materials. However, in recent years, with the continuous enhancement of battery energy density, safety issues have increasingly attracted the attention of researchers, becoming a non-negligible factor in determining whether the electric vehicle industry has a foothold. The key issue in the development of battery systems with high specific energies is the intrinsic instability of the cathode, with the accompanying question of safety. The failure mechanism and stability of high-specific-capacity cathode materials for the next generation of LIBs, including nickel-rich cathodes, high-voltage spinel cathodes, and lithium-rich layered cathodes, have attracted extensive research attention. Systematic studies related to the intrinsic physical and chemical properties of different cathodes are crucial to elucidate the instability mechanisms of positive active materials. Factors that these studies must address include the stability under extended electrochemical cycles with respect to dissolution of metal ions in LiPF₆-based electrolytes due to HF corrosion of the electrode; cation mixing due to the similarity in radius between Li⁺ and Ni²⁺; oxygen evolution when the cathode is charged to a high voltage; the origin of cracks generated during repeated charge/discharge processes arising from the anisotropy of the cell parameters; and electrolyte decomposition when traces of water are present. Regulating the surface nanostructure and bulk crystal lattice of electrode materials is an effective way to meet the demand for cathode materials with high energy density and outstanding stability. Surface modification treatment of positive active materials can slow side reactions and the loss of active material, thereby extending the life of the cathode material and improving the safety of the battery. This review is targeted at the failure mechanisms related to the electrochemical cycle, and a synthetic strategy to ameliorate the properties of cathode surface locations, with the electrochemical performance optimized by accurate surface control. From the perspective of the main stability and safety issues of high-energy cathode materials during the electrochemical cycle, a detailed discussion is presented on the current understanding of the mechanism of performance failure. It is crucial to seek out favorable strategies in response to the failures. Considering the surface structure of the cathode in relation to the stability issue, a newly developed protocol, known as surface-localized doping, which can exist in different states to modify the surface properties of high-energy cathodes, is discussed as a means of ensuring significantly improved stability and safety. Finally, we envision the future challenges and possible research directions related to the stability control of next-generation high-energy cathode materials.     

Facile hydrothermal synthesis of zinc sulfide nanowires for high-performance asymmetric supercapacitor

A facile, single-step hydrothermal route is followed to prepare ZnS nanowires with large aspect ratios. The obtained ZnS nanowires deposited on nickel foam (ZnS/Ni-foam) exhibit a specific capacitance of 781 F/g at a current density of 0.5 A/g. An asymmetric supercapacitor fabricated from ZnS/Ni-foam as a positive electrode and jute derived activated carbon coated on Ni-foam (JAC/Ni-foam) as a negative electrode attains a high specific capacitance of 573 F/g at a current density of 0.5 A/g, with an accompanying high energy density of 51 Wh/kg at a power density of 200 W/kg in an extensive operating potential window of 1.2 V. In addition, the ZnS//JAC asymmetric supercapacitor reveals long-term cyclic stability, after 10,000 GCD cycles the device sustain around ～87 % of the initial specific capacitance. These results shed enlighten a new opportunity for promising electrode materials in supercapacitors.     

Chemistry-Performance Relationships of Polymer Gel-Electrolytes for Mg−S and Li−S Batteries: Influence of Network Cation Solvation Capacity on Polymer-Polysulfide Interactions

Metal-sulfur batteries are a promising next-generation energy storage technology, offering high theoretical energy densities with low cost and good sustainability. An active area of research is the development of electrolytes that address unwanted migration of sulfur and intermediate species known as polysulfides during operation of metal-sulfur batteries, a phenomenon that leads to low energy efficiency and short life-spans. A particular class of electrolytes, gel polymer electrolytes, are especially attractive for their ability to repel polysulfides on the basis of structure, electrostatics, and other polymer properties. Herein, within the context of magnesium- and lithium-sulfur batteries, we investigate the impact of gel polymer electrolyte cation solvation capacity, a property related to network dielectric constant and chemistry, on sulfur/polysulfide-polymer interactions, an understudied property-performance relationship. Polymers with lower cation solvation capacity are found to permanently absorb less polysulfide active material, which increases sulfur utilization for Li−S batteries and significantly increases charge efficiency and life-span for Li−S and Mg−S batteries.     

Semiclassical Trajectory Studies of Reactive and Nonreactive Scattering of OH(A 2Σ+) by H2 Based on an Improved Full-Dimensional Ab Initio Diabatic Potential Energy Matrix

We present a new full-dimensional diabatic potential energy matrix (DPEM) for electronically nonadiabatic collisions of OH(A ²Σ⁺) with H₂, and we calculate the probabilities of electronically adiabatic inelastic collisions, nonreactive quenching, and reactive quenching to form H₂O+H. The DPEM was fitted using a many-body expansion with permutationally invariant polynomials in bond-order functions to represent the many-body part. The dynamics calculations were carried out with the fewest-switches with time uncertainty and stochastic decoherence (FSTU/SD) semiclassical trajectory method. We present results both for head-on collisions (impact parameter b equal to zero) and for a full range of impact parameters. The results are compared to experiment and to earlier FSTU/SD and quantum dynamics calculations with a previously published DPEM. The various theoretical results all agree that nonreactive quenching dominates reactive quenching, but there are quantitative differences between the two DPEMs and between the b=0 results and the all-b results, especially for the probability of reactive quenching.     

Optimizing the Photovoltaic Performance of Organic Solar Cells for Indoor Light Harvesting

Organic solar cells (OSCs) harvesting indoor light are highly promising for emerging technologies, such as internet of things. Herein, the photovoltaic performance of PTB7-Th:PC₇₁BM solar cells constructed using “optimized (with 1,8-diiodooctane (DIO))” and “non-optimized (without DIO)” processing conditions are compared for indoor and outdoor applications. We find that in comparison to the “optimized” solar cell, the “non-optimized” solar cell is less efficient under simulated solar light illumination (100 mW cm⁻², spectral range 350–1100 nm), owing to significant bimolecular charge carrier recombination losses. However, under simulated indoor illumination (3.28 mW cm⁻², spectral range 400–700 nm), bimolecular recombination losses are effective suppressed, thus the power conversion efficiency of the solar cell without DIO was increased to 14.7 %, higher than that of the solar cell with DIO (14.2 %). These results suggest that the common strategy used to optimize the OSCs could be undesired for indoor OSCs. We demonstrate that the efforts for realizing the desired “morphology” of the active layer for the outdoor OSCs may be unnecessary for indoor OSCs, allowing us to realize high-efficiency indoor OSCs using a non-halogenated solvent.     

Insights and Activation Energy Surface of the Dehydrogenation of C2HxO Species in Ethanol Oxidation Reaction on Ir(100)

Dehydrogenation of an organic compound is the first and the most fundamental elementary reaction in many organic reactions. In ethanol oxidation reaction (EOR) to form CO₂, there are a total of 46 pathways in C₂H_xO (x=1–6) species leading to the removal of all six hydrogen atoms in five C−H bonds and one O−H bond. To investigate the degree of dehydrogenation in EOR under operando conditions, we performed density function theory (DFT) calculations to study 28 dehydrogenation steps of C₂H_xO on Ir(100). An activation energy surface was then constructed and compared with that of the C−C bond cleavages to understand the importance of the degree of dehydrogenation in EOR. The results show that there are likely 28 dehydrogenations in EOR under fuel cell temperatures and the last two hydrogens in C₂H₂O are less likely cleaved. On the other hand, deep dehydrogenation including 45 dehydrogenations can occur under ethanol steam reforming conditions.     

双金属MOFs及其衍生物在电化学储能领域中的应用

双金属有机骨架及其衍生物一方面具有单金属有机骨架孔道丰富、比表面积大、结构可调、活性位点丰富等特点,另一方面具有双组分与多孔结构之间的协同效应,因而受到了研究人员的密切关注,在储能、催化、分离、传感器、医药、气体存储等领域广泛应用。和单金属MOFs类似,双金属MOFs的导电性不佳、结构易坍塌,这极大地限制了其在电化学储能中的应用。通过对双金属MOFs进行热处理,易得到分布均匀的多孔碳@双金属氧化物/硫化物/磷化物/硒化物等衍生物,不仅保持了独特的多孔结构,而且提高了材料的导电性和结构稳定性,有利于在电化学储能中的应用。因此,本文从双金属MOFs中的主要金属离子入手,综述了双金属MOFs及其衍生物用于超级电容器、锂离子电池、钠离子电池、金属空气电池等电化学储能器件的最新应用进展。在此基础上,总结了双金属MOFs在电化学储能应用中的优势,并对其制备、作用机理和后处理研究提出了建议。