Sulfur doped iron-nitrogen-hard carbon nanosheets as efficient and robust noble metal-free catalysts for oxygen reduction reaction in PEMFC

Transition metal-nitrogen-carbon(M-N-C)as a promising substitute for the conventional noble metalbased catalyst still suffers from low activity and durability for oxygen reduction reaction(ORR)in proton exchange membrane fuel cells(PEMFCs).To tackle the issue,herein,a new type of sulfur-doped ironnitrogen-hard carbon(S-Fe-N-HC)nanosheets with high activity and durability in acid media were developed by using a newly synthesized precursor of amide-based polymer with Fe ions based on copolymerizing two monomers of 2,5-thiophene dicarboxylic acid(TDA)as S source and 1,8-diaminonaphthalene(DAN)as N source via an amination reaction.The as-synthesized S-Fe-N-HC features highly dispersed atomic Fe Nxmoieties embedded into rich thiophene-S doped hard carbon nanosheets filled with highly twisted graphite-like microcrystals,which is distinguished from the majority of M-N-C with soft or graphitic carbon structures.These unique characteristics endow S-Fe-N-HC with high ORR activity and outstanding durability in 0.5 M H_(2)SO_(4).Its initial half-wave potential is 0.80 V and the corresponding loss is only 21 m V after 30,000 cycles.Meanwhile,its practical PEMFC performance is a maximum power output of 628.0 mW cm^(-2)and a slight power density loss is 83.0 m W cm^(-2)after 200-cycle practical operation.Additionally,theoretical calculation shows that the activity of Fe Nxmoieties on ORR can be further enhanced by sulfur doping at meta-site near FeN_(4)C.These results evidently demonstrate that the dual effect of hard carbon substrate and S doping derived from the precursor platform of amid-polymers can effectively enhance the activity and durability of Fe-N-C catalysts,providing a new guidance for developing advanced M-N-C catalysts for ORR.

Gel time of calcium acrylate grouting material

Calcium acrylate is a polymerized grout, and can polymerize in an aqueous solution. The polymerization reaction utilizes ammonium persulfate as a catalyst and sodium thiosulfate as the activator. Based on the theory of reaction kinetics, this study on the relation between gel time and concentration of activator and catalyst showed that gel time of calcium acrylate is inversely proportional to activator and catalyst concentration. A formula of gel time is proposed, and an example is provided to verify the proposed formula.

Temperature-dependent Hydrothermal Synthesis of Two Distinct Three-dimensional Copper Complexes

Two distinct copper coordination polymers, namely [Cu^Ⅱ2（2,5-pydc）2（bpp）2]·H2O（1） and Cu2^ⅠCu^Ⅱ（2,5-pydc）2（bpp）2（2）（2,5-pydc = pyridine-2,5-dicarboxylic acid, bpp = 1,3-bi（4-pyridyl）propane）, have been successfully synthesized through hydrothermal conditions under different temperatures. Single-crystal X-ray structural analysis revealed that both complexes 1 and 2 are 3D frameworks. Complex 1 is an 8-connected 2-fold interpenetrating network based on [Cu（2,5-pydc）]4 molecular building block（MBB）, and also can be simplified as a 4-connected net if the Cu（Ⅱ） ion is regarded as an independent node, whereas 2 shows a（4,4）-connected non-interpenetrated framework which contains mixed valence Cu（Ⅰ/Ⅱ） centers. The results demonstrate that temperature plays a significant role in the final structures of the complexes.

Syntheses,Structures and Photoluminescent Properties of Cd(Ⅱ)Polymeric Complexes Based on 5-Aminoisophthalic Acid and Bipyridine Co-ligands

Two novel complexes, namely {[Cd（AIP）（4,4＇-bpy）]·1.3DMF}n（1） and [Cd（AIP）（2,2＇- bpy）]n（2）, have been synthesized through solvothermal reaction（H2AIP = 5-aminoisophthalic acid, 2,2＇-bpy = 2,2＇-bipyridine, 4,4＇-bpy = 4,4＇-bipyridine, and DMF = N,N＇-dimethylformamide） and structurally determined by single-crystal X-ray diffraction. Complex 1 shows a three-dimensional（3D） layer-pillar framework with rectangular channels, while complex 2 displays a two-dimensional（2D） wave net architecture. Furthermore, 1 and 2 were characterized by elemental analysis, infrared spectra（IR）, thermal gravimetric analyses（TGA） and fluorescence measurements. The luminescent properties of 1 dispersed in various organic solvents have been investigated systematically, demonstrating high selectivity for acetone via the fluorescence quenching effect.

Grafting modification on the surface of titanium dioxide by polystyrene

Based on the technology of titanium dioxide grafting modification withpolystyrene (PS), the modification mechanisms are studied and the polystyrene-grafting states on thesurface of titanium dioxide have been set up. Under the synergistic actions of mechanical force,chemistry and heat, macromolecular free radicals of PS are created, at the same time, the O-O bondsof titanium dioxide are broken and the oxide free radicals produced, and the numbers of oxygen atomare increased and crystal lattice defects rich electrons are formed on the surface of titaniumdioxide. The radical polymerization is the main reaction between PS and titanium dioxide and C-Obonds form in the process of modification. Multi-sites chemical adsorption also exists besidesgrafting between PS and titanium dioxide.

The amount effect of catalyst on the urethane reaction of o-hydroxybenzyl alcohol

The urethane reaction of o-hydroxybenzyl alcohol with phenyl isocyanate was monitored with in situ FT-IR.Dibutyltin dilaurate was used as catalyst and its amount effect was investigated.It was found that there was an obvious induction period before reaction began.It was interesting that the time of induction period climbed up and then declined with the increase of dibutyltin dilaurate. When the concentration of dibutyltin dilaurate reached 9.58×10^（-5） mol/L,the induction period disappeared completely and hereafter did not appear any more.Furthermore,the urethane reaction kinetics was studied.When the concentration of dibutyltin dilaurate increased,the reaction rate of phenolic group（k_1） increased sharply,but the reaction rate of alcoholic group（k_2） appeared of little change on the whole.k_1 increased about 20-fold,yet k_2 increased about 2-fold when the concentration of dibutyltin dilaurate varied from 9.58×10^（-6） mol/L to 1.92×10~4 mol/L,which made the value of k_1/k_2 enlarge.

New Penta-ether as the Internal Donor in the MgCl2-supported ZieglerNatta Catalysts for Propylene Polymerization

The penta-ether compound was synthesized by the reaction of di（trimethylolpropane） with sodium hydride as the strong base and methyl iodide as the alkyl halide. This compound was characterized by NMR, FTIR, and GC techniques. The MgCl_2-supported titanium catalysts were incorporated with varying amounts of penta-ether compound as the internal donor and also the catalysts without the internal donor were synthesized. The synthesized catalysts and the conventional ZieglerNatta catalyst were characterized. The titanium contents were determined by spectrophotometry, magnesium by complexometric titration and chloride by argentometric titration. The effects of the new internal donor on propylene polymerization with the prepared MgCl_2-supported Ziegler-Natta catalysts were investigated and then these results were compared to the results obtained using the conventional diisobutyl phthalate-besed-Ziegler-Natta catalyst. The highest crystallinity degree, melting temperature, and isotacticity of polypropylene were obtained using the catalyst with a pentaether/Mg molar ratio equal to 0.21.