Mingyuan Zhu

Two-dimensional SnS2@PANI nanoplates with high capacity and excellent stability for lithium-ion batteries

Nanostructured electrode materials have been extensively studied with the aim of enhancing lithium ion and electron transport and lowering the stress caused by their volume changes during the charge–discharge processes of electrodes in lithium-ion batteries. In this work, novel two-dimensional nanocomposite, polyaniline-coated SnS2 (SnS2@PANI) nanoplates have been prepared by an in situ oxidative polymerization of aniline on the surface of ultrasonic exfoliated SnS2 nanoplates. The SnS2@PANI nanoplates present a lamellar sandwich nanostructure, which can provide a good conductive network between neighboring nanoplates, shorten the path for ion transport in the active material, and alleviate the expansion and contraction of the electrode material during charge–discharge processes, leading to improved electrochemical performance. As an anode material for lithium-ion batteries, SnS2@PANI nanoplates have a high initial reversible capacity (968.7 mA h g−1), excellent cyclability (730.8 mA h g−1 after 80 cycles, corresponding to 75.4% of the initial reversible capacity), and an extraordinary rate capability (356.1 mA h g−1 at the rate of 5000 mA g−1). This study not only provides a simple and efficient synthesis strategy for various inorganic–organic composites obtained by the exfoliation of layered inorganic materials, but can also help in the design of novel, high performance electrode materials.

Nitrogen-Doped Banana Peel-Derived Porous Carbon Foam as Binder-Free Electrode for Supercapacitors

Nitrogen-doped banana peel–derived porous carbon foam (N-BPPCF) successfully prepared from banana peels is used as a binder-free electrode for supercapacitors. The N-BPPCF exhibits superior performance including high specific surface areas of 1357.6 m2/g, large pore volume of 0.77 cm3/g, suitable mesopore size distributions around 3.9 nm, and super hydrophilicity with nitrogen-containing functional groups. It can easily be brought into contact with an electrolyte to facilitate electron and ion diffusion. A comparative analysis on the electrochemical properties of BPPCF electrodes is also conducted under similar conditions. The N-BPPCF electrode offers high specific capacitance of 185.8 F/g at 5 mV/s and 210.6 F/g at 0.5 A/g in 6 M KOH aqueous electrolyte versus 125.5 F/g at 5 mV/s and 173.1 F/g at 0.5 A/g for the BPPCF electrode. The results indicate that the N-BPPCF is a binder-free electrode that can be used for high performance supercapacitors.

Mechanism studies of LiFePO4 cathode material: lithiation/delithiation process, electrochemical modification and synthetic reaction

Olivine-structured lithium ion phosphate (LiFePO4) is one of the most competitive candidates for fabricating energy-driven cathode material for sustainable lithium ion battery (LIB) systems. However, the high electrochemical performance is significantly limited by the slow diffusivity of Li-ion in LiFePO4 (ca. 10−14 cm2 s−1) together with the low electronic conductivity (ca. 10−9 S cm−1), which is the big challenge currently faced by us. To resolve the challenge, many efforts have been directed to the dynamics of the lithiation/delithiation process in LixFePO4 (0 ≤ x ≤ 1), mechanism of electrochemical modification, and synthetic reaction process, which are crucial for the development of high electrochemical performance for LiFePO4 material. In this review, in order to reflect the recent progress ranging from the very fundamental to practical applications, we specifically focus on the mechanism studies of LiFePO4 including the lithiation/delithiation process, electrochemical modification and synthetic reaction. Firstly, we highlight the Li-ion diffusion pathway in LixFePO4 and phase translation of LixFePO4. Then, we summarize the modification mechanism of LiFePO4 with high-rated capability, excellent low-temperature performance and high energy density. Finally, we discuss the synthetic reaction mechanism of high-temperature carbothermal reaction route and low-temperature hydrothermal/solvothermal reaction route.

Novel catalyst by immobilizing a phosphotungstic acid on polymer brushes and its application in oxidative desulfurization

In the study, an HPW–PDMAEMA–SiO2 (phosphotungstic acid (HPW); poly-N,N-dimethylaminoethyl methacrylate (PDMAEAM)) catalyst was successfully synthesized. The synthesized HPW–PDMAEMA–SiO2 catalyst was characterized via XRD, TEM, FT-IR, TGA, and ICP-AES. The results show that the HPW active species retained its Keggin structure after immobilizing into polymer brushes. At optimal reaction conditions, the oxidative desulfurization conversion of dibenzothiophene reached 100%, and there was no significant catalytic performance decrease after six recycles. The excellent recoverability of the catalyst was attributed to the decreased leaching of the HPW active species caused by the strong interaction between the negative [PW12O40]3− ions and positive ammonium ions in the PDMAEMA polymer brushes.

C-doped boron nitride fullerene as a novel catalyst for acetylene hydrochlorination: a DFT study

Density functional theory calculations were used to investigate the mechanism of acetylene hydrochlorination separately catalyzed by un-doped B12N12 and carbon-doped BN fullerene (B12−nN11+nC (n = 0, 1)). We have discovered that carbon-doped BN clusters displayed extraordinary catalyst performance for acetylene hydrochlorination compared with un-doped B12N12 clusters. C2H2 was adsorbed onto B12−nN11+nC (n = 0, 1) clusters prior to HCl and then formed three adsorption states. The first two states were in a trans configuration, in which the two H atoms of C2H2 were on opposite sides of the CC bond; the third state was a cis configuration, in which the two H atoms were on the same side of the CC bond. Afterwards, we illustrated three possible pathways with corresponding transition states. In particular, the minimum energy pathway R1 based on the B11N12C catalyst had an energy barrier as low as 36.08 kcal mol−1, with only one transition state.

Mesoporous carbon with controllable pore sizes as a support of the AuCl3 catalyst for acetylene hydrochlorination

Mesoporous carbon materials with controllable pore sizes within the range of 5.6–40.5 nm were successfully synthesized using colloidal silica as hard templates and boric acid as the pore expanding agent. The catalytic properties of the 0.5% AuCl3 loaded mesoporous carbon catalysts towards acetylene hydrochlorination were tested in a fixed-bed reactor. Under reaction conditions of 180 °C, C2H2 hourly space velocity = 720 h−1 and HCl/C2H2 feed volume ratio = 1.15, it was found that larger mesoporous carbon supports could accelerate the reaction rate, resulting in higher acetylene conversion. The AuCl3 catalyst supported on mesoporous carbon with a pore size of about 40.5 nm displayed excellent catalytic activity (acetylene conversion was above 83%). The dependence of regular catalytic performance on pore size is important for acetylene hydrochlorination because large pore sizes enable fast molecular diffusion, thus suppressing coke formation.

Neutral Aun (n = 3–10) clusters catalyze acetylene hydrochlorination: a density functional theory study

The mechanisms of acetylene hydrochlorination to vinyl chloride catalyzed by neutral Au3–10 clusters were systematically investigated using density functional theory with the B3LYP/LANL2DZ function. In this reaction, the gold cluster functions as a bridge of electron transfer: the electrons transfer from C2H2 to the gold cluster then from the gold cluster to HCl. HCl and C2H2 are simultaneously activated by the gold cluster, which presents a synergistic effect in co-adsorption. In the size range of Au3 to Au10, all gold clusters undergo the same catalytic cycle. The whole process of the acetylene hydrochlorination on the gold cluster consists of two transition states and one intermediate, and the dissociation of hydrogen chloride is the rate-controlling step. Overall, small-sized gold clusters perform better than large-sized clusters, and the odd-number atom clusters are better than even-number atom clusters.

Nitrogen functional groups on an activated carbon surface to effect the ruthenium catalysts in acetylene hydrochlorination

To improve the activity and stability of Ru-based catalysts with a carbon support for acetylene hydrochlorination, activated carbon (AC) was consecutively modified by nitration, amination and pyridine, and the effect of the different carbon supports on the Ru-based catalysts for acetylene hydrochlorination was investigated. The results of the FT-IR studies confirmed that –NO2, –NH2 and –N–H–N groups were separately grafted onto the surface of the AC. Under the same reaction conditions, the modified catalysts exhibited better catalytic activity compared with the original Ru/AC catalyst. Moreover, the catalyst Ru/AC-NHN showed the best catalytic performance with a slight decrease after 48 h from 93.2% to 91.8%. The increase in catalytic activity indicates that the modification with nitrogen functional groups is beneficial for acetylene hydrochlorination.

Nickel catalysts supported on amino-functionalized MCM-41 for syngas methanation

MCM-41 was functionalized with amino groups using (3-aminopropyl) triethoxysilane (APTES) as a precursor, and then Ni was chemically immobilized to synthesize the Ni/NH2-MCM-41 catalyst. The obtained catalysts were characterized using various physicochemical techniques. The catalyst activity of Ni/NH2-MCM-41 catalyst was superior to that of Ni/MCM-41 at low temperatures for synthetic gas methanation. Almost no CO conversion decrease was observed even after a 200 h run, indicating that the catalytic performance of the Ni/NH2-MCM-41 catalyst was very stable. It was proposed that the amino groups and carbon skeleton of APTES on the surface of the MCM-41 support could inhibit the aggregation of Ni nanoparticles, thereby improving catalyst activity and stability for synthetic gas methanation.

Effect of Au nano-particle aggregation on the deactivation of the AuCl3/AC catalyst for acetylene hydrochlorination.

A detailed study of the valence state and distribution of the AuCl3/AC catalyst during the acetylene hydrochlorination deactivation process is described and discussed. Temperature-programmed reduction and X-ray photoelectron spectral analysis indicate that the active Au3+ reduction to metallic Au0 is one reason for the deactivation of AuCl3/AC catalyst. Transmission electron microscopy characterization demonstrated that the particle size of Au nano-particles increases with increasing reaction time. The results indicated that metallic Au0 exhibits considerable catalytic activity and that Au nano-particle aggregation may be another reason for the AuCl3/AC catalytic activity in acetylene hydrochlorination.