Magnetically Induced Reversible Transition between Cassie and Wenzel States of Superparamagnetic Microdroplets on Highly Hydrophobic Silicon Surface

In this work, we report a magnetic technique for reversible wetting–dewetting transitions of microdroplets on highly hydrophobic surfaces. A superparamagnetic microdroplet can be reversibly switched between the Cassie state and the Wenzel state on a highly hydrophobic microstructured silicon substrate by the application of the magnetic field. The transition can be controlled by both the intensity of the magnetic field and the concentration of the superparamagnetic Fe₃O₄ nanoparticles in the microdroplet. The magnetic force needed during the transition from the Cassie state to the Wenzel state was found to be apparently smaller than that needed in the reverse process. Such asymmetry is ascribed to the higher energy of the Cassie state compared with the Wenzel state, the change of the gravitational potential energy, and the adhesion hysteresis. This report provides a novel method of dynamically controlling liquid/solid interactions, which can not only help us to understand further the transition between the Cassie state and the Wenzel state but also potentially be used in some important applications, such as lab-on-a-chip devices and chemical microreactors

An In Situ Ionic-Liquid-Assisted Synthetic Approach to Iron Fluoride/Graphene Hybrid Nanostructures as Superior Cathode Materials for Lithium Ion Batteries

A tactful ionic-liquid (IL)-assisted approach to <i>in situ</i> synthesis of iron fluoride/graphene nanosheet (GNS) hybrid nanostructures is developed. To ensure uniform dispersion and tight anchoring of the iron fluoride on graphene, we employ an IL which serves not only as a green fluoride source for the crystallization of iron fluoride nanoparticles but also as a dispersant of GNSs. Owing to the electron transfer highways created between the nanoparticles and the GNSs, the iron fluoride/GNS hybrid cathodes exhibit a remarkable improvement in both capacity and rate performance (230 mAh g^–1 at 0.1 C and 74 mAh g^–1 at 40 C). The stable adhesion of iron fluoride nanoparticles on GNSs also introduces a significant improvement in long-term cyclic performance (115 mAh g^–1 after 250 cycles even at 10 C). The superior electrochemical performance of these iron fluoride/GNS hybrids as lithium ion battery cathodes is ascribed to the robust structure of the hybrid and the synergies between iron fluoride nanoparticles and graphene

Probing Zr Substituting Effects on the Oxygen Reduction Reaction of Fe-Based Double Perovskite Cathodes for Solid Oxide Fuel Cells

The mixed ionic and electronic conductor (MIEC), as a classical family of high-performance cathode materials, is essential for ensuring the low-temperature operation performance and high efficiency of solid oxide fuel cells. The Fe-based double perovskites get the advantages of low cost, good thermal compatibility with the electrolyte, and good high-temperature stability, showing good application promise. However, due to the unsatisfactory electrochemical properties, Fe-based double perovskite MIECs are generally not sufficiently active for the oxygen reduction reaction. Herein, the consequences indicate that Zr-substitution of the Fe sites in the NdBaFe2O6‑δ(NBF) lattice can obtain a higher oxygen vacancy concentration and a more high-lying position of the O p-band center simultaneously. Then, the Zr-doped NBF cathode obtains a higher oxygen-ion diffusion and oxygen surface exchange coefficients. The lower polarization resistance for NdBaFe1.9Zr0.1O6‑δmeasured at 700 °C is 0.066 Ω·cm2 compared to 0.104 Ω·cm2 for NBF

pH-Controllable Water Permeation through a Nanostructured Copper Mesh Film

Water permeation is an important issue in both fundamental research and industrial applications. In this work, we report a novel strategy to realize the controllable water permeation on the mixed thiol (containing both alkyl and carboxylic acid groups) modified nanostructured copper mesh films. For acidic and neutral water, the film is superhydrophobic, and the water cannot permeate the film because of the large negative capillary effect resulting from the nanostructures. For basic water, the film shows superhydrophilic property, and thus the water can permeate the film easily. The permeation process of water can be controlled just by simply altering the water pH. A detailed investigation indicates that nanostructures on the substrate and the appropriate size of the microscale mesh pores can enhance not only the static wettability but also the dynamic properties. The excellent controllability of water permeation is ascribed to the combined effect of the chemical variation of the carboxylic acid group and the microstructures on the substrate. This work may provide interesting insight into the new applications that are relevant to the surface wettability, such as filtration, microfluidic device, and some separation systems

Titanium–Oxygen Clusters Brazing Li with Li_6.5La₃Zr_1.5Ta_0.5O₁₂ for High-Performance All-Solid-State Li Batteries

Garnet-based solid-state electrolytes are considered crucial candidates for solid-state Li batteries due to their high Li+ conductivity and nonflammability; however, poor interfacial contact with the Li anode and growth of Li dendrites limit their application. Herein, a high-activity titanium–oxygen cluster is used as a brazing filler to braze the Li6.5La3Zr1.5Ta0.5O12 (LLZTO) with an Li anode into the whole unit. The brazing layer leads to a significantly lower interfacial impedance of 8.32 Ω cm2. Furthermore, the brazing layer is an isotropic amorphous ion-electron hybrid conductive layer, which significantly promotes Li+ transport and regulates the distribution of the electric field, therefore inhibiting the growth of Li dendrites. The cell exhibits an ultrahigh critical current density of 2.3 mA cm–2 and stable cycling of over 4000 h at 0.5 mA cm–2 (25 °C)

In Situ Synthesis of CuCo₂S₄@N/S-Doped Graphene Composites with Pseudocapacitive Properties for High-Performance Lithium-Ion Batteries

To satisfy the demand of high power application, lithium-ion batteries (LIBs) with high power density have gained extensive research effort. The pseudocapacitive storage of LIBs is considered to offer high power density through fast faradic surface redox reactions rather than the slow diffusion-controlled intercalation process. In this work, CuCo₂S₄ anchored on N/S-doped graphene is in situ synthesized and a typical pseudocapacitive storage behavior is demonstrated when applied in the LIB anode. The pseudocapacitive storage and N/S-doped graphene enable the composite to display a capacity of 453 mA h g^–1 after 500 cycles at 2 A g^–1 and a ultrahigh rate capability of 328 mA h g^–1 at 20 A g^–1. We believe that this work could further promote the research on pseudocapacitive storage in transition-metal sulfides for LIBs

Underwater Superoleophilic to Superoleophobic Wetting Control on the Nanostructured Copper Substrates

Surfaces with controlled underwater oil wettability would offer great promise in the design and fabrication of novel materials for advanced applications. Herein, we propose a new approach based on self-assembly of mixed thiols (containing both HS­(CH₂)₉CH₃ and HS­(CH₂)₁₁OH) on nanostructured copper substrates for the fabrication of surfaces with controlled underwater oil wettability. By simply changing the concentration of HS­(CH₂)₁₁OH in the solution, surfaces with controlled oil wettability from the underwater superoleophilicity to superoleophobicity can be achieved. The tunable effect can be due to the synergistic effect of the surface chemistry variation and the nanostructures on the surfaces. Noticeably, the amplified effect of the nanostructures can provide better control of the underwater oil wettability between the two extremes: superoleophilicity and superoleophobicity. Moreover, we also extended the strategy to the copper mesh substrates and realized the selective oil/water separation on the as-prepared copper mesh films. This report offers a flexible approach of fabricating surfaces with controlled oil wettability, which can be further applied to other ordinary materials, and open up new perspectives in manipulation of the surface oil wettability in water

Designing Heterogeneous Chemical Composition on Hierarchical Structured Copper Substrates for the Fabrication of Superhydrophobic Surfaces with Controlled Adhesion

Controlling water adhesion is important for superhydrophobic surfaces in many applications. Compared with numerous researches about the effect of microstructures on the surface adhesion, research relating to the influence of surface chemical composition on the surface adhesion is extremely rare. Herein, a new strategy for preparation of tunable adhesive superhydrophobic surfaces through designing heterogeneous chemical composition (hydrophobic/hydrophilic) on the rough substrate is reported, and the influence of surface chemical composition on the surface adhesion are examined. The surfaces were prepared through self-assembling of mixed thiol (containing both HS­(CH2)9CH3 and HS­(CH2)11OH) on the hierarchical structured copper substrates. By simply controlling the concentration of HS­(CH2)11OH in the modified solution, tunable adhesive superhydrophobic surfaces can be obtained. The adhesive force of the surfaces can be increased from extreme low (about 8 μN) to very high (about 65 μN). The following two reasons can be used to explain the tunable effect: one is the number of hydrogen bond for the variation of surface chemical composition; and the other is the variation of contact area between the water droplet and surface because of the capillary effect that results from the combined effect of hydrophilic hydroxyl groups and microstructures on the surface. Noticeably, water droplets with different pH (2–12) have similar contact angles and adhesive forces on the surfaces, indicating that these surfaces are chemical resistant to acid and alkali. Moreover, the as-prepared surfaces were also used as the reaction substrates and applied in the droplet-based microreactor for the detection of vitamin C. This report provides a new method for preparation of superhydrophobic surfaces with tunable adhesion, which could not only help us further understand the principle for the fabrication of tunable adhesive superhydrophobic surfaces, but also potentially be used in many important applications, such as microfluidic devices and chemical microreactors

Blocking Polysulfide with Co₂B@CNT via “Synergetic Adsorptive Effect” toward Ultrahigh-Rate Capability and Robust Lithium–Sulfur Battery

Li–S batteries have attracted great interest as the next-generation secondary batteries due to their high energy density, being environmentally friendly, and low price. However, the road to commercialization of lithium–sulfur batteries remains limited owing to the “shuttle effect” of soluble polysulfides, which results in the inferior cycle stability. Herein, a potent functional separator is developed to restrain the “shuttle effect” by coating Co2B@carbon nanotube layer on the commercialized polypropylene separator. In merits of the coadsorption of Co sites and B sites, such Co2B shows highly efficient polysulfides block (11.67 mg/m2 for Li2S6). Besides, the composite also exhibits obviously catalysis from Li2S8 to Li2S. By combining the fast electron transportation along the carbon nanotube, a superior rate performance is achieved with the modified separator and common carbon–sulfur cathode. Typically, the cell with Co2B@CNT shows prominent cycling life with a capacity degradation of 0.0072% per cycle (3000 cycles) and ultrahigh-rate capability at 5 C current (1172.8 mAh/g), which outstands the previously reported polysulfides barrier layer. The cell with Co2B@CNT can exhibit electrochemical performance at areal capacity of 5.5 mAh/cm2 (0.5 C) when the sulfur loading increased to 5.8 mg/cm2. This work defines an efficacious strategy to restrain the “shuttle effect” of polysulfides and shed light on the great potential of borides in Li–S battery

pH-Induced Reversible Wetting Transition between the Underwater Superoleophilicity and Superoleophobicity

Surfaces with controlled oil wettability in water have great potential for numerous underwater applications. In this work, we report a smart surface with pH-responsive oil wettability. The surface shows superoleophilicity in acidic water and superoleophobicity in basic water. Reversible transition between the two states can be achieved through alteration of the water pH. Such smart ability of the surface is due to the cooperation between the surface chemistry variation and hierarchical structures on the surface. Furthermore, we also extended this strategy to the copper mesh substrate and realized the selective oil/water separation on the as-prepared film. This paper reports a new surface with excellently controllable underwater oil wettability, and we believe such a surface has a lot of applications, for instance, microfluidic devices, bioadhesion, and antifouling materials