Finite-time boundedness of uncertain Hamiltonian systems via sliding mode control approach

Nonlinear Dynamics - This paper seeks to address the problem of finite-time stabilization for a class of uncertain Hamiltonian systems via sliding mode control approach. A novel sliding function in...     

Kinetics of hydrogen peroxide decomposition catalyzed by Cu-buserite over a well-sealed and thermostated kinetics assembly

Herein a well-sealed and thermostated kinetics assembly is designed and built, which can run stirred at different reaction temperatures. With the reaction assembly above and the volumetric method together, the hydrogen peroxide (H₂O₂) decomposition reaction kinetics is systematically investigated under a variety of reaction conditions over a copper-doped buserite-type layer manganese oxide (referred to as Cu-buserite) as a heterogeneous catalyst. The overall second-order rate law is fitted out by the linear regression analysis, with the reaction orders with respect to both H₂O₂ and Cu-buserite determined to each be equal to 1, and then explicitly explained by the proposed Michaelis-Menten like mechanism. The apparent activation energy E_a is estimated as 33.5 ± 2.5 kJ mol⁻¹.     

Sulfonated poly(ether ether ketone) composite membranes based on amino-modified halloysite nanotubes that effectively immobilize phosphotungstic acid

In this work, we prepared amino-modified halloysite nanotubes (PEI-DHNTs) via the co-deposition of self-polymerized dopamine and polyethylenimine (PEI) on the surface of nanotubes, which was confirmed by X-ray photoelectron spectroscopy (XPS) and Thermogravimetric analysis (TGA). A series of composite proton exchange membranes (PEMs) were prepared by incorporating PEI-DHNTs and phosphotungstic acid (HPW) into sulfonated poly(ether ether ketone) (SPEEK). It was found that both PEI-DHNTs and HPW were well dispersed in the polymer matrix, exhibiting excellent filler-matrix compatibility. The composite membranes demonstrated enhanced proton conductivity, reaching as high as 0.078 S cm⁻¹ with 33.3 wt.% HPW loading, which was ~90% higher than that of SPEEK control membrane. Such improvement was mainly attributed to the strong acid–base pairs formed by PEI-DHNT with both SPEEK and HPW, which shortened proton hopping distance and created more continuous proton conduction pathways. Furthermore, the membrane conductivity remained almost constant after 1 year's immersion in liquid water, indicating the successful immobilization of HPW in the composite membranes.     

FeNi Alloy Nanoparticles Encapsulated in Carbon Shells Supported on N-Doped Graphene-Like Carbon as Efficient and Stable Bifunctional Oxygen Electrocatalysts

The development of cost-effective and durable oxygen electrocatalysts remains highly critical but challenging for energy conversion and storage devices. Herein, a novel FeNi alloy nanoparticle core encapsulated in carbon shells supported on a N-enriched graphene-like carbon matrix (denoted as FeNi@C/NG) was constructed by facile pyrolyzing the mixture of metal salts, glucose, and dicyandiamide. The in situ pyrolysis of dicyandiamide in the presence of glucose plays a significant effect on the fabrication of the porous FeNi@C/NG with a high content of doped N and large specific surface area. The optimized FeNi@C/NG catalyst displays not only a superior catalytic performance for the oxygen reduction reaction (ORR, with an onset potential of 1.0 V and half-wave potential of 0.84 V) and oxygen evolution reaction (OER, the potential at 10 mA cm⁻² is 1.66 V) simultaneously in alkaline, but also outstanding long-term cycling durability. The excellent bifunctional ORR/OER electrocatalytic performance is ascribed to the synergism of the carbon shell and FeNi alloy core together with the high-content of nitrogen doped on the large specific surface area graphene-like carbon.     

Lithium–Lanthanide Bimetallic Metal–Organic Frameworks towards Negative Electrode Materials for Lithium-Ion Batteries

Novel lithium–lanthanide (Ln: cerium and praseodymium) bimetallic coordination polymers with formulas C₁₀H₂LnLiO₈ (Ln: Ce (CeLipma) and Pr (PrLipma)) and C₁₀H₃CeO₈ (Cepma) were prepared through a simple hydrothermal method. The three compounds were characterized by means of FTIR spectroscopy, X-ray diffraction, single-crystal X-ray diffraction, SEM, TEM, and X-ray photoelectron spectroscopy. The results of structural refinement show that they belong to triclinic symmetry and P space group with cerium (or praseodymium) and lithium cations, forming coordination bonds to oxygen atoms from different pyromellitic acid molecules, and leading to the construction of 3D structures. It is interesting to note that the frameworks exclude any coordination water and lattice water. As an electrode material for lithium-ion batteries, CeLipma exhibits a maximum capacity of 800.5 mAh g⁻¹ and a retention of 91.4 % after 50 cycles at a current density of 100 mA g⁻¹. The favorable electrochemical properties of the lanthanide coordination polymers show potential application prospects in the field of electrode materials.     

Sustained and Controlled Release of Volatile Precursors for Chemical Vapor Deposition of Graphene at Atmospheric Pressure

Precursors and catalysts play vital roles in chemical reactions. Considerable efforts have been devoted to the investigation of catalysts for graphene growth by chemical vapor deposition in recent years. However, there has been little research on precursors because of a lack of innovation in term of creating a controllable feeding method. Herein, we present a novel sustained and controlled release approach, and develop a convenient, safe, and potentially scalable feeding system with the assistance of matrix materials and a simple portable feeder. As a result, a highly volatile liquid precursor can be fed accurately to grow large-area, uniform graphene films with optimal properties. This feeding approach will further benefit the synthesis of other two-dimensional materials from various precursors.     

Pitch-Based Laminated Carbon Formed by Pressure Driving at Low Temperature as High-Capacity Anodes for Lithium Energy Storage Systems

Pitch has been used to prepare electrodes by high-temperature heat treatments for supercapacitors, lithium-ion batteries, on account of its rich aromatic ring structure. Here, the toluene-soluble component of pitch is used to prepare a kind of laminated carbon. This was realized by a template-free synthesis at low temperature with the addition of pressure. The toluene-soluble component has a small molecular weight, which makes the thermal deformation ability stronger and then enhances the orientation of the carbon layer with the help of pressure. The prepared anode exhibits a splendid electrochemical performance compared with the traditional graphite anode. A high stable capacity of approximately 550 mAh g⁻¹ at 50 mA g⁻¹, which is much higher than graphite (372 mAh g⁻¹), is obtained. Also, when the current density is up to 2 A g⁻¹, the capacity is about 150 mAh g⁻¹. Surprisingly, it also delivers a superior cycling performance. And when used as the anode/cathode electrode for lithium-ion capacitors, a high energy density can be obtained. The present work offers an opportunity to utilize the pitch source in lithium energy storage with promising cycle life, high energy/power density, and low cost.