Spinel CoFe2O4 supported by three dimensional graphene as high-performance bi-functional electrocatalysts for oxygen reduction and evolution reaction

Spinel CoFe₂O₄ supported on three dimensional graphene (3DG) is prepared by hydrothermal reaction, which is denoted as CoFe₂O₄/3DG. The 3DG is prepared by the templated method, where coal tar pitch (CTP) and MgO are used as the carbon source and the template, respectively. The microstructure and composition of the resultant have been investigated by X-ray diffraction as well as X-ray photoelectron spectroscopy indicating the formation of spinel CoFe₂O₄ and composite of CoFe₂O₄/3DG. The multilayer structure of 3DG and CoFe₂O₄/3DG is also examined by the Raman spectra. Electrochemically, CoFe₂O₄/3DG shows high-performance half-wave potential is 0.80 V vs. RHE in O₂-saturated 0.1 M KOH, which is compared to 20 wt% Pt/C. When evaluated for OER activity, CoFe₂O₄/3DG obtains a low overpotential 1.63 V vs. RHE (at j = 10 mA cm⁻²), which is 180 mV better than 20 wt% Pt/C. Moreover, it possesses excellent durability superior to 20 wt% Pt/C.     

Development of shape-engineered α-MnO2 materials as bi-functional catalysts for oxygen evolution reaction and oxygen reduction reaction in alkaline medium

In this work, three kinds of α-MnO₂ nano shapes, namely, nano-wires, nano-tubes and nano-particles have been prepared with a fine control over α-crystallographic form by employing hydrothermal procedure. The materials have been thoroughly characterized by X-ray diffraction (XRD), thermo-gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) spectrometry, field-emission scanning electron microscopy (FE-SEM), energy dispersive spectroscopy (EDS), transmission electron microscopy (TEM), electron paramagnetic resonance (EPR) spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques. The MnO₂ nano shapes are used as a model system for examining the shape-influenced bi-functional electrocatalytic activity towards oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in alkaline medium. The bi-functional role has been investigated by cyclic voltammetry and linear sweep voltammetry with rotating ring disc electrode (RRDE) techniques. It is found that α-MnO₂ nano-wires possess enhanced electrocatalytic activity compared to other two shapes namely nano-tubes and nano-particles despite the nano-tubes having a much higher specific surface area. The insight of bi-functional electrocatalytic activity is analysed in terms of catalyst surface with the help of first principles density functional theory (DFT) calculations based on the fact of surface energies and adsorption of water on the surface for a facile reaction.     

基于蒽酰亚胺基团的新型Fe~(3+)和Hg~(2+)化学敏感器

含蒽酰亚胺基团的化合物N-(2-(6-氨基吡啶))-9-蒽酰亚胺(L1)对Fe3+表现出灵敏的荧光增强响应.L1的衍生物N,N-′(2,6-吡啶基)-二(9-蒽酰亚胺)(L2)对Hg2+在紫外-可见吸收光谱和荧光光谱上显示了良好的识别性.即使在其它金属阳离子存在下,L1和L2分别对于Fe3+和Hg2+仍然表现出较好的选择性.     

High purity H2 production from sorption enhanced bio-ethanol reforming via sol-gel-derived Ni–CaO–Al2O3 bi-functional materials

Catalytic steam reforming of renewable bio-oxygenates coupled with in-situ CO₂ capture is a promising option for sustainable H₂ production. The current work focuses on high purity H₂ production over Ni–CaO–Al₂O₃ bi-functional materials via sorption enhanced steam reforming of ethanol (SEESR). To ensure the uniform distribution of catalytic sites (Ni), adsorptive sites (CaO) and stabilizer (Al₂O₃) in the bi-functional materials, a citrate sol-gel synthetic route was employed. These materials were characterized by XRD, N₂ physical adsorption, SEM, TG and TPR techniques. It was revealed that the existence of CaO in bi-functional materials could not only in-situ remove CO₂, but also play the role of inhibiting the formation of harmful spinel phase. The stabilizing role of Al component against capacity decay was confirmed, whereas the presence of Ni ions had a negative effect on the cycle CO₂ uptake. The sample of Ni/Al/Ca-85.5 possessed large specific surface area, abundant porosity with fluffy morphology, and thereby, exhibited the best CO₂ sorption capacity during 20 carbonation/calcination cycles. The highest H₂ concentration of 96% was obtained through the SEESR during the pre-breakthrough period when the Ni/Al/Ca-85.5 was employed. Over the optimized bi-functional material, the effect of operating conditions on the SEESR was investigated and the results indicated that temperature of 600 °C, reaction liquid space velocity of 0.05 ml/min and steam/ethanol ratio of 4 were the suitable conditions. After 10 cycles, the bi-functional material of Ni/Al/Ca-85.5 also showed the best performance, with a H₂ purity of about 90% and pre-breakthrough time of 18 min, conforming the high potential of this material for SEESR process.     

A bipyridine-containing water-soluble conjugated polymer: Highly efficient fluorescence chemosensor for convenient transition metal ion detection in aqueous solution

A novel sulfonato-functionalized water-soluble conjugated polymer (WSCP), which containing 2′2-bipyridine units as receptors for transition metal ions in the main chain was successfully synthesized by Sonogashira-coupling reaction for the first time. This polymer could easily dissolve in water (5 mg/mL) and some polar organic solvents such as methanol. Its fluorescence in aqueous solution can be completely quenched upon addition of transition metal ions. The K_sv of different transition metal ions in aqueous solution were much higher than previous reports in organic solutions and showed highest selectivity to Ni²⁺. These results opened opportunities for developing novel chemosensors by introducing selective fluorescent chromophore into the water-soluble conjugated backbone.     

基于萘二酰胺衍生物的氟离子荧光传感器

设计合成了一个以萘酰胺衍生物为荧光团,硫脲基团为键合基团的荧光化学传感器1。化学传感器1对氟离子表现出了较好的荧光响应性。随着氟离子浓度的增加,荧光强度先表现为增强,这是由于氟离子加入后可以和化学传感器1中硫脲基团上的氢原子形成氢键,从而增强了萘酰胺4-位取代基的给电子能力。随着氟离子浓度的继续增加,化学传感器1表现为荧光强度的降低。在对磷酸二氢根离子的实验中,化学传感器1则没有表现出较明显的荧光变化。     

Hydrogen production by steam reforming of dimethyl ether over ZnO–Al2O3 bi-functional catalyst

A series of ZnO–Al₂O₃ catalysts with various ZnO/(ZnO + Al₂O₃) molar ratios have been developed for hydrogen production by dimethyl ether (DME) steam reforming within microchannel reactor. The catalysts were characterized by N₂ adsorption-desorption, X-ray diffraction and temperature programmed desorption of NH₃. It was found that the catalytic activity was strongly dependent on the catalyst composition. The overall DME reforming rate was maximized over the catalyst with ZnO/(ZnO + Al₂O₃) molar ratio of 0.4, and the highest H₂ space time yield was 315 mol h⁻¹·kg_cat⁻¹ at 460 °C. A bi-functional mechanism involving catalytic active site coupling has been proposed to account for the phenomena observed. An optimized bi-functional DME reforming catalyst should accommodate the acid sites and methanol steam reforming sites with a proper balance to promote DME steam reforming, whereas all undesired reactions should be impeded without sacrificing activity. This work suggests that an appropriate catalyst composition is mandatory for preparing good-performance and inexpensive ZnO–Al₂O₃ catalysts for the sustainable conversion of DME into H₂-rich reformate.     

Ru@Pt core–shell nanoparticles for methanol fuel cell catalyst: Control and effects of shell composition

The present work presents a method to encapsulate pre-synthesised Ru nanoparticles (NPs) by Pt using a polyol method without capping agents at various pH values (6, 7, 8 and 10). The structural and surface properties of the catalysts were characterised using X-ray diffraction, transmission electron microscopy, CO stripping, and energy-dispersive X-ray spectroscopy. The studies suggest that the pH during encapsulation of Ru by Pt plays an important role in controlling of shell composition. A core–shell catalyst with an alloy shell was obtained at a pH of 6, whereas a monometallic Pt shell was obtained at a pH of 10. The core–shell catalysts gave higher steady-state current for methanol oxidation: 10-fold higher for alloy shells and 5-fold higher for Pt-enriched shells compared to the pure Pt catalyst. It is suggested that the highest catalytic enhancement of the core–shell catalysts is obtained through the bi-functional character that dominates the alloy shells rather than the ligand-effect-promoted Pt-enriched shells.     

Statistical analysis of the performance of a bi-functional catalyst under operating conditions of LPDME process

Liquid phase direct synthesis of dimethyl ether (LPDME™) under various operating conditions (temperature, H₂/CO molar ratio of feed) was conducted in a mechanically agitated slurry reactor system. Each run was monitored for 60 h time on stream (TOS) in order to confirm the high activity and long-term stability of a bi-functional catalytic system (CuO–ZnO–Al₂O₃/H-MFI-90). Statistical experimental design was applied for determining the optimum operating conditions under which the catalytic system shows the highest performance. A significant improvement in the performance of the bi-functional catalyst was observed when the temperature and H₂/CO molar ratio of feed were increased from 200 to 240 °C and 1 to 2, respectively at a constant pressure of 35 bar and GHSV equal to 1100 mLn/(g-cat h). CO conversion was increased from 9.1 mol% at T = 200 °C and H₂/CO = 1 to 79.6 mol% at T = 240 °C and H₂/CO = 2 and the yield and selectivity of DME also increased from 7.11% to 47.05% and 41.57% to 59.96%, (molar basis) respectively. No significant deactivation has been observed during 60 h TOS at different operating conditions. Furthermore, from the main effect plots and response table results, it was concluded that the most effective factor on activity and stability of bi-functional catalytic system is temperature.