A Simple Synthetic Strategy toward Defect‐Rich Porous Monolayer NiFe‐Layered Double Hydroxide Nanosheets for Efficient Electrocatalytic Water Oxidation

In this work, porous monolayer nickel‐iron layered double hydroxide (PM‐LDH) nanosheets with a lateral size of ≈30 nm and a thickness of ≈0.8 nm are successfully synthesized by a facile one‐step strategy. Briefly, an aqueous solution containing Ni²⁺ and Fe³⁺ is added dropwise to an aqueous formamide solution at 80 °C and pH 10, with the PM‐LDH product formed within only 10 min. This fast synthetic strategy introduces an abundance of pores in the monolayer NiFe‐LDH nanosheets, resulting in PM‐LDH containing high concentration of oxygen and cation vacancies, as is confirmed by extended X‐ray absorption fine structure and electron spin resonance measurements. The oxygen and cation vacancies in PM‐LDH act synergistically to increase the electropositivity of the LDH nanosheets, while also enhancing H₂O adsorption and bonding strength of the OH* intermediate formed during water electrooxidation, endowing PM‐LDH with outstanding performance for the oxygen evolution reaction (OER). PM‐LDH offers a very low overpotential (230 mV) for OER at a current density of 10 mA cm^?2, with a Tafel slope of only 47 mV dec^?1, representing one of the best OER performance yet reported for a NiFe‐LDH system. The results encourage the wider utilization of porous monolayer LDH nanosheets in electrocatalysis, catalysis, and solar cells.     

Unraveling the Rapid Redox Behavior of Li‐Excess 3d‐Transition Metal Oxides for High Rate Capability

Li‐excess 3d‐transition metal layered oxides are promising candidates in high‐energy‐density cathode materials for improving the mileage of electric vehicles. However, their low rate capability has hindered their practical application. The lack of understanding about the redox reactions and migration behavior at high C‐rates make it difficult to design Li‐excess materials with high rate capability. In this study, the characteristics of the atomic behavior that is predominant at fast charge/discharge are investigated by comparing cation‐ordered and cation‐disordered materials using X‐ray absorption spectroscopy (XAS). The difference in the atomic arrangement determines the dominance of the transition metal/oxygen redox reaction and the variations in transition metal–oxygen hybridization. In‐depth electrochemical analysis is combined with operando XAS analysis to reveal electronically and structurally preferred atomic behavior when a redox reaction occurs between oxygen and each transition metal under fast charge/discharge conditions. This provides a fundamental insight into the improvement of rate capability. Furthermore, this work provides guidance for identifying high‐energy‐density materials with complex structural properties.     

Insights into the Storage Mechanism of Layered VS2 Cathode in Alkali Metal‐Ion Batteries

VS₂ is one of the attractive layered cathodes for alkali metal‐ion batteries. However, the understanding of the detailed reaction processes and energy storage mechanism is still inadequate. Herein, the Li⁺/Na⁺/K⁺ insertion/extraction mechanisms of VS₂ cathode are elucidated on the basis of experimental analyses and theoretical simulations. It is found that the insertion/extraction behavior of Li⁺ is partially irreversible, while the insertion/extraction behavior of Na⁺/K⁺ is completely reversible. The detailed intermediates and final products (Li_0.33VS₂, LiVS₂, Na_0.5VS₂, NaVS₂, K_0.6VS₂, K_zVS₂, z > 0.6) during the discharging/charging processes are identified, indicating that VS₂ undergoes different phase transitions and solid–solution reactions in different battery systems, which have a great influence on the battery performance. Moreover, the diffusion of Na⁺ in VS₂ cathode is demonstrated to be much slower than that of Li⁺ and K⁺. Such mechanistic research provides a reference for in‐depth understanding of energy storage in layered transition metal sulfides/selenides.     

Understanding the Rate Capability of High‐Energy‐Density Li‐Rich Layered Li1.2Ni0.15Co0.1Mn0.55O2 Cathode Materials

The high‐energy‐density, Li‐rich layered materials, i.e., xLiMO₂(1‐x)Li₂MnO₃, are promising candidate cathode materials for electric energy storage in plug‐in hybrid electric vehicles (PHEVs) and electric vehicles (EVs). The relatively low rate capability is one of the major problems that need to be resolved for these materials. To gain insight into the key factors that limit the rate capability, in situ X‐ray absorption spectroscopy (XAS) and X‐ray diffraction (XRD) studies of the cathode material, Li_1.2Ni_0.15Co_0.1Mn_0.55O₂ [0.5Li(Ni_0.375Co_0.25 Mn_0.375)O₂·0.5Li₂MnO₃], are carried out. The partial capacity contributed by different structural components and transition metal elements is elucidated and correlated with local structure changes. The characteristic reaction kinetics for each element are identified using a novel time‐resolved XAS technique. Direct experimental evidence is obtained showing that Mn sites have much poorer reaction kinetics both before and after the initial activation of Li₂MnO₃, compared to Ni and Co. These results indicate that Li₂MnO₃ may be the key component that limits the rate capability of Li‐rich layered materials and provide guidance for designing Li‐rich layered materials with the desired balance of energy density and rate capability for different applications.     

传统DNA疫苗载体与Semliki森林病毒复制子对HIV-1 Pr55gag表达与体液免疫原性的比较性研究

为探索Semliki森林病毒(SFV)衍生的复制型DNA载体可否用于HIV疫苗的候选载体,对该载体与传统DNA疫苗载体对HIV-1Pr55gag的表达与体液免疫原性进行了系统比较研究.将野生型(wtgag)及密码子改造(syngag)的HIV-1 ⅢB gag基因分别克隆于SFV DNA载体及传统DNA疫苗载体[pCDNA3.1(+)],对其Pr55gag细胞内表达水平、Pr55gag病毒样颗粒释放、以及在BALB/c鼠的体液免疫原性进行了比较.在293T、H1299、C2C12和BHK细胞系中,SFV-wtgag可以Rev非依赖方式有效表达Pr55gag,而pC-wtgag转染的细胞不能有效表达Pr55gag,从而不能诱导小鼠产生免疫反应.虽然SFV质粒的细胞转化效率明显低于pCDNA载体,SFV-wtgag和SFV-syngag在细胞内Pr55gag的表达量与pC-syngag相似,而Pr55gag病毒样颗粒的释放明显低于pC-syngag.在肌内注射免疫的小鼠中,低剂量(0.1和1.0μg)的SFV及pCDNA gag表达质粒均未诱导出GAG特异性免疫反应.在高剂量(10,30,100μg)免疫组中,与SFV gag表达质粒相比,pC-syngag可诱导出较高水平的TH1型GAG特异性抗体.SFV-syngag较SFV-wtgag可诱导出高水平的体液免疫反应.结果提示,SFV衍生的复制子单独使用不能在小鼠诱导出优于传统DNA疫苗载体的HIV-1 GAG特异性体液免疫反应,其原因可能与病毒样颗粒的释放有关.密码子改造的gag基因的优势在SFV载体系统中得到了进一步证实.     

Cyanide Self-Addition,Controlled Adsorption,and Other Processes at Layered Double Hydroxides

Layered double hydroxides (LDH) are anion-exchangingmaterials of the type M(III)-M(II)_x(OH)_(2x+2)Y thatoccur abundantly in nature, and can concentrate, protect, andactivate simple organic anionic species of possible relevance tothe earliest organisms. We now wish to report progress in thefollowing areas:1) Internal vs. external uptake of anions. Ferrocyanidedoes not displace carbonate from synthetic hydrotalcite (Mg:AlLDH carbonate) but is nevertheless taken up on the outside of theparticles. In other cases, anion uptake is controlled byspecific hydrogen bonding requirements rather than by chargedensity alone, a feature that can be used to control whetheruptake will be both internal and external, or external only. These two findings taken together have important implications forspecific catalysis by LDH, since specific hydrogen bonding willaffect the individual and relative conformations of substrateanions, and anions occupying space in the interlayer will beunder tighter constraints than those adsorbed externally.2) Specific reactions catalyzed by LDH. We have found thatthe LDH Mg₂Al(OH)₆Cl catalyzes the self-addition ofcyanide, to give in a one-pot reaction at low concentrations anincreased yield of diaminomaleonitrile and in addition, at higher( 0.05M) concentrations, a purple-pink material that adheres tothe LDH. We are investigating whether this reaction also occurswith hydrotalcite itself, what is the minimum effectiveconcentration of cyanide, and what can be learned about theproducts and how they compare with those reported at high HCNconcentrations in the absence of catalyst.     

Deconvolution of images from 3D printed cells in layers on a chip

Layer‐by‐layer cell printing is useful in mimicking layered tissue structures inside the human body and has great potential for being a promising tool in the field of tissue engineering, regenerative medicine, and drug discovery. However, imaging human cells cultured in multiple hydrogel layers in 3D‐printed tissue constructs is challenging as the cells are not in a single focal plane. Although confocal microscopy could be a potential solution for this issue, it compromises the throughput which is a key factor in rapidly screening drug efficacy and toxicity in pharmaceutical industries. With epifluorescence microscopy, the throughput can be maintained at a cost of blurred cell images from printed tissue constructs. To rapidly acquire in‐focus cell images from bioprinted tissues using an epifluorescence microscope, we created two layers of Hep3B human hepatoma cells by printing green and red fluorescently labeled Hep3B cells encapsulated in two alginate layers in a microwell chip. In‐focus fluorescent cell images were obtained in high throughput using an automated epifluorescence microscopy coupled with image analysis algorithms, including three deconvolution methods in combination with three kernel estimation methods, generating a total of nine deconvolution paths. As a result, a combination of Inter‐Level Intra‐Level Deconvolution (ILILD) algorithm and Richardson‐Lucy (RL) kernel estimation proved to be highly useful in bringing out‐of‐focus cell images into focus, thus rapidly yielding more sensitive and accurate fluorescence reading from the cells in different layers. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 34:445–454, 2018     

NiCoFe‐Layered Double Hydroxides/N‐Doped Graphene Oxide Array Colloid Composite as an Efficient Bifunctional Catalyst for Oxygen Electrocatalytic Reactions

Ternary NiCoFe‐layered double hydroxide (NiCo^IIIFe‐LDH) with Co³⁺ is grafted on nitrogen‐doped graphene oxide (N‐GO) by an in situ growth route. The array‐like colloid composite of NiCo^IIIFe‐LDH/N‐GO is used as a bifunctional catalyst for both oxygen evolution/reduction reactions (OER/ORR). The NiCo^IIIFe‐LDH/N‐GO array has a 3D open structure with less stacking of LDHs and an enlarged specific surface area. The hierarchical structure design and novel material chemistry endow high activity propelling O₂ redox. By exposing more amounts of Ni and Fe active sites, the NiCo^IIIFe‐LDH/N‐GO illustrates a relatively low onset potential (1.41 V vs reversible hydrogen electrode) in 0.1 mol L^?1 KOH solution under the OER process. Furthermore, by introducing high valence Co³⁺, the onset potential of this material in ORR is 0.88 V. The overvoltage difference is 0.769 V between OER and ORR. The key factors for the excellent bifunctional catalytic performance are believed to be the Co with a high valence, the N‐doping of graphene materials, and the highly exposed Ni and Fe active sites in the array‐like colloid composite. This work further demonstrates the possibility to exploit the application potential of LDHs as OER and ORR bifunctional electrochemical catalysts.     

Proton Ion Exchange Reaction in Li3IrO4: A Way to New H3+xIrO4 Phases Electrochemically Active in Both Aqueous and Nonaqueous Electrolytes

Progress over the past decade in Li‐insertion compounds has led to a new class of Li‐rich layered oxide electrodes cumulating both cationic and anionic redox processes. Pertaining to this new class of materials are the Li/Na iridate phases, which present a rich crystal chemistry. This work reports on a new protonic iridate phase H_3+xIrO₄ having a layered structure obtained by room temperature acid‐leaching of Li₃IrO₄. This new phase shows reversible charge storage properties of 1.5 e^? per Ir atom with high rate capabilities in both nonaqueous (vs Li⁺/Li) and aqueous (vs capacitive carbon) media. It is demonstrated that Li‐insertion in carbonate LiPF₆‐based electrolyte occurs through a classical reduction process (Ir⁵⁺ ? Ir³⁺), which is accompanied by a well‐defined structural transition. In concentrated H₂SO₄ electrolyte, this work provides evidence that the overall capacity of 1.7 H⁺ per Ir results from two additive redox processes with the low potential one showing ohmic limitations. Altogether, the room temperature protonation approach, which can be generalized to various Li‐rich phases containing either 3d, 4d or 5d metals, offers great opportunities for the judicious design of attractive electrode materials.