In Situ Synthesized MEMS Compatible Energetic Arrays Based on Energetic Coordination Polymer and Nano-Al with Tunable Properties.

Integrating energetic materials with a microelectromechanical system (MEMS) to achieve miniaturized integrated smart energetic microchips is promising. The potential applications include actuation in lab-on-a-chip devices, ignition in automobile airbags, propulsion and attitude control of micro-/nano-satellites, and miniaturized electro-explosive devices. In this work, a new type of MEMS-compatible energetic arrays was in situ realized on a copper substrate, which comprised a new energetic coordination polymer (ECP; Cu1.5C2N8O2·H2O) with tunable nanostructures and a nano-aluminum (nano-Al) covering layer. The composition, morphology, and energetic characteristics of the energetic arrays can be easily tuned by adjusting the reaction time. The maximum heat release of 1850.2 J/g in thermal analysis and the intense flame in open burning experiment proved its excellent exothermic and combustion performance. A closed-bomb experiment further revealed that the ECP@nano-Al energetic arrays supported on Cu(OH)2 nanorods had a peak pressure (5.5 MPa) and a pressure duration (0.5 s) more than twice those of nanoscale Al/CuO powder because of the introduction of gas elements (e.g., C, H, and N). A preliminary impulse experiment was also conducted through the torsion pendulum method. The displacement of the torsion pendulum in the micrometer scale proved the potential application of the energetic arrays in micropropulsion systems. Overall, this work can serve as a reference for the synthesis and applications of ECPs.

Triple-Layered Carbon-SiO2 Composite Membrane for High Energy Density and Long Cycling Li-S Batteries.

Here we report a highly scalable yet flexible triple-layer structured porous C/SiO2 membrane via a facile phase inversion method for advancing Li-sulfur battery technology. As a multifunctional current-collector-free cathode, the conductive dense layer of the C/SiO2 membrane offers hierarchical macropores as an ideal sulfur host to alleviate the volume expansion of sulfur species and facilitate ion/electrolyte transport for fast kinetics, as well as spongelike pores to enable high sulfur loading. The triple-layer structured membrane cathode enables the filling of most sulfur species in the macropores and additional loading of a thin sulfur slurry on the membrane surface, which facilitates ion/electrolyte transport with faster kinetics than the conventional S/C slurry-based cathode. Furthermore, density functional theory simulations and visual adsorption measurements confirm the critical role of the doped SiO2 nanoparticles (∼10 nm) in the asymmetric C membrane in suppressing the shuttle effect of polysulfides via chemisorption and electrocatalysis. The rationally designed C/SiO2 membrane cathodes demonstrate long-term cycling stability of 300 cycles at a high sulfur loading of 2.8 mg cm-2 with a sulfur content of ∼75%. This scalable yet flexible self-supporting cathode design presents a useful strategy for realizing practical applications of high-performance Li-S batteries.

Converting Corncob to Activated Porous Carbon for Supercapacitor Application.

Carbon materials derived from biomass are promising electrode materials for supercapacitor application due to their specific porosity, low cost and electrochemical stability. Herein, a hierarchical porous carbon derived from corncob was developed for use as electrodes. Benefitting from its hierarchical porosity, inherited from the natural structure of corncob, high BET surface area (1471.4 m²·g-1) and excellent electrical conductivity, the novel carbon material exhibited a specific capacitance of 293 F·g-1 at 1 A·g-1 in 6 M KOH electrolyte and maintained at 195 F·g-1 at 5 A·g-1. In addition, a two-electrode device was assembled and delivered an energy density of 20.15 Wh·kg-1 at a power density of 500 W·kg-1 and an outstanding stability of 99.9% capacitance retention after 4000 cycles.

Lithiophilic Cu-CuO-Ni Hybrid Structure: Advanced Current Collectors Toward Stable Lithium Metal Anodes.

Metallic lithium (Li) is a promising anode material for next-generation rechargeable batteries. However, the dendrite growth of Li and repeated formation of solid electrolyte interface during Li plating and stripping result in low Coulombic efficiency, internal short circuits, and capacity decay, hampering its practical application. In the development of stable Li metal anode, the current collector is recognized as a critical component to regulate Li plating. In this work, a lithiophilic Cu-CuO-Ni hybrid structure is synthesized as a current collector for Li metal anodes. The low overpotential of CuO for Li nucleation and the uniform Li+ ion flux induced by the formation of Cu nanowire arrays enable effective suppression of the growth of Li dendrites. Moreover, the surface Cu layer can act as a protective layer to enhance structural durability of the hybrid structure in long-term running. As a result, the Cu-CuO-Ni hybrid structure achieves a Coulombic efficiency above 95% for more than 250 cycles at a current density of 1 mA cm-2 and 580 h (290 cycles) stable repeated Li plating and stripping in a symmetric cell.

Templated and Catalytic Fabrication of N-Doped Hierarchical Porous Carbon-Carbon Nanotube Hybrids as Host for Lithium-Sulfur Batteries.

Nitrogen-doped hierarchical porous carbon and carbon nanotube hybrids (N-HPC-CNTs) are fabricated by simple pyrolysis of the N-rich raw material melamine-formaldehyde (MF) resin in the presence of nano-CaCO3 and a bimetallic combination of Fe-Co catalyst. During carbonization, nano-CaCO3 acts as a template for creating a hierarchical porous carbon, and the N atoms originated from MF resin are in situ doped into the carbon matrix simultaneously. Meanwhile, volatile gases generated by the thermal decomposition of MF resin could serve as carbon and nitrogen sources to grow nitrogen-doped CNTs on HPC. The growth mechanism is the same as that for conventional chemical vapor deposition (CVD) growth of CNTs on the metal catalysts, but the technological requirements are obviously not as harsh as those for the CVD method. Low-cost raw materials and simple equipment are sufficient for the growth. Moreover, the density and length of the CNTs are tunable, which can be simply adjusted via applying different amounts of Fe-Co catalysts. Such an N-doped hybrid structured carbon with mesopores can not only effectively prompt the physical and chemical adsorption of polysulfides but also ensures a fast electron transfer because of the incorporation of CNTs, which provides sufficient conducting pathways and effective connections between the CNTs and HPC. Furthermore, CNTs grown on HPC can act as physical barriers to block the large pores on HPC, thereby reducing the polysulfide loss. Benefiting from the advantages, the N-HPC-CNT hybrids are a desirable host prospect for Li-S batteries.

Activated Microporous Carbon Derived from Almond Shells for High Energy Density Asymmetric Supercapacitors.

Via the activation treatment of carbonized almond shells with HNO3 and KOH, activated microporous carbon (AMC-3 and AMC-2) was successfully synthesized. These two AMC electrodes demonstrate remarkable electrochemical behaviors such as high rate capability, high specific capacitance, and excellent cycle stability when serving as electrodes for supercapacitors. More importantly, through the use of a Zn-Ni-Co ternary oxide (ZNCO) positive electrode and the AMC negative electrode, asymmetric supercapacitors (ASC) were assembled that deliver superior energy density (53.3 Wh kg(-1) at a power density of 1126.1 W kg(-1) for ASC-2 and 53.6 Wh kg(-1) at a power density of 1124.5 W kg(-1) for ASC-3) and excellent stability (82.7% and 83.4% specific capacitance retention for ZNCO//AMC ASC-2 and ZNCO//AMC ASC-3, respectively, after 5000 cycles). Through these two methods, low-cost, renewable, and environmentally friendly electrode materials can be provided for high energy density supercapacitors.

Magnetic titania-silica composite-polypyrrole core-shell spheres and their high sensitivity toward hydrogen peroxide as electrochemical sensor.

A novel core-shell sphere with controlled shell thickness was synthesized by in situ chemical oxidative polymerization of pyrrole on FTS (Fe(2)O(3)/TiO(2)/SiO(2) composite) surface. The dual porosity of 2-3 nm and 40-50 nm in FTS core particle provides the hybrids with a high surface area to volume ratio, which enormously facilitates the molecule diffusion process. Furthermore, the porous FTS particle encapsulate Fe(2)O(3) and TiO(2) leading to its synergetic interaction with the PPy coating based on FTIR analysis. The unique structure and composition of the hybrid spheres result in new sensing property that is not available from their single counterparts. Cyclic voltammetry results demonstrate that the spheres with appropriate concentration of PPy exhibit enhanced electrocatalytic activity toward the reduction of H(2)O(2) in 0.1 M phosphate buffer solution. The sensing performance tests show that the hybrids possess good linear response in wide H(2)O(2) concentration range (10-4000 µM) and high sensitivity to H(2)O(2) (0.653 AM(-1) cm(-2)) at room temperature. The formation mechanism of the spheres was proposed based on the fact that the FTS core was coated firstly by a smooth PPy layer and then PPy nanoparticles. The work reported here provides an alternative concept for preparation of functional materials with new nanostructures and properties.