硼、磷共掺杂铁钴双金属材料的制备及其电催化析氧性能

采用一步水热法合成了硼、磷共掺杂铁钴材料(Fe-Co-B-P)。借助扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、傅里叶变换红外光谱(FT-IR)等技术对所合成材料的形貌、结构和组成进行表征。利用线性扫描伏安(LSV)、循环伏安(CV)、电化学阻抗谱(EIS)等技术研究材料电化学析氧反应(OER)性能。结果表明,Fe-Co-B-P表面疏松且粗糙,颗粒间有许多空隙。在电流密度为10和100 mA·cm^-2时,其过电势分别为278和309 mV,Tafel斜率为24 mV·dec^-1,说明该材料具有较优的电催化析氧性能。其在连续进行10 h的计时电位测试过程中,电势基本保持在1.55 V(vs RHE),表明该催化剂具有较好的电化学稳定性。这是由于铁钴双金属与硼、磷非金属之间的协同作用促进了电子的传递。     

Comparison of LaFeO3, La0.8Sr0.2FeO3, and La0.8Sr0.2Fe0.9Co0.1O3 perovskite oxides as oxygen carrier for partial oxidation of methane

Comparison of LaFeO3, La0.8Sr0.2FeO3, and La0.8Sr0.2Fe0.9Co0.1O3 perovskite oxides as oxygen cartier for partial oxidation of methane in the absence of gaseous oxygen was investigated by continuous flow reaction and sequential redox reaction. Methane was oxidized to syngas with high selectivity by oxygen species of perovskite oxides in the absence of gaseous oxygen. The sequential redox reaction revealed that the structural stability and continuous oxygen supply in redox re-action decreased over La0.8Sr0.2Fe0.9Co0.1O3 oxide, while LaFeO3 and Lao.sSro.2FeO3 exhibited excellent structural stability and continuous oxygen supply.     

Preparation and photoactivity of thermosensitive polymer supported metallophthalocyanine

A novel reactive metallophthalocyanine derivative,zinc tetra(2,4-dichloro-1,3,5-triazine)aminophthalo-cyanine(Zn-TDTAPc),was prepared and immobilized on poly(N-isopropylacrylamide)(PNIPAAm) by covalent bonding to obtain a thermosensitive polymer(Zn-TDTAPc-g-PNIPAAm).Compared with zinc tetraaminophthalocyanine(Zn-TAPc),Zn-TDTAPc-g-PNIPAAm exhibits excellent solubility in water and in most organic solvents.Furthermore,it has a special thermosensitive property in water and the lower critical solution temperature(LCST) is 34.1℃.It was found that both dissolved and precipitated Zn-TDTAPc-g-PNIPAAm present high photoactivity evidenced by the experiment of photocatalytic degra-dation of 1,3-diphenylisobenzofuran(DPBF) in the presence of Zn-TDTAPc-g-PNIPAAm.These proper-ties suggest that it can be used potentially in photodynamic therapy(PDT).     

Studies on the preparation of active oxygen-deficient copper ferrite and its application for hydrogen production through thermal chemical water splitting

Hydrogen generation through thermal chemical water splitting technology has recently received in- creasingly international interest in the nuclear hydrogen production field. Besides the main known sulfur-iodine (S-I) cycle developed by the General Atomics Company and the UT3 cycle (iron, calcium, and bromine) developed at the University of Tokyo, the thermal cycle based on metal oxide two-step water splitting methods is also receiving research and development attention worldwide. In this work, copper ferrite was prepared by the co-precipitation method and oxygen-deficient copper ferrite was synthesized through first and second calcination steps for the application of hydrogen production by a two-step water splitting process. The crystal structure, properties, chemical composition and δ were investigated in detail by utilizing X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), atomic absorption spectrometer (AAS), ultraviolet spectrophotometry (UV), gas chro- matography (GC), and so on. The experimental two-step thermal chemical cycle reactor for hydrogen generation was designed and developed in this lab. The hydrogen generation process of water splitting through CuFe2O4-δ and the cycle performance of copper ferrite regeneration were firstly studied and discussed.     

Study on the electroreduction process of oxygen to superoxide ion by using acetylene black powder microelectrode

In this paper, the powder microelectrode technique was employed in studying the voltametric response of the O₂/₂⁻ couple, which demonstrated a nearly reversible redox process at an acetylene black powder microelectrode in N,N-dimethylformamide (DMF). A well-developed steady state current plateau for the electrochemical reduction of oxygen was obtained in this system. The electron transfer number (n) and heterogeneous electron transfer rate constant k _s were measured by steady-state voltametric response, and the results were 1.08, 3.4 × 10⁻³ cm s⁻¹, respectively. Additionally, the scavenging activity of O₂⁻ with biological antioxidant (ascorbic acid) was evaluated by cyclic voltammetry; IC₅₀ came to 5 × 10⁻⁴ mol/l. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 8, pp. 1040–1044. The text was submitted by the authors in English.     

Electrocatalysis of oxygen reduction by lanthanum-strontium manganate

The electrocatalysis of the oxygen reduction reaction by lanthanum-strontium manganate La_0.5Sr_0.5MnO₃ (LSM) has been studied by cyclic voltammetry using the rotating ring-disc electrode technique (RRDE) in alkaline medium. From the ring-disc data and other kinetic parameters it was concluded that the oxygen reduction occurs by dissociative chemisorption at low overpotentials. At higher overpotentials, the formation of hydrogen peroxide (HO₂⁻ in this case) on the electrocatalyst has been observed. The apparent exchange current density for oxygen reduction on LSM has been found to be 2 × 10⁻⁷ A cm⁻², while the corresponding Tafel slope is 0.100 V per decade. The possible reaction mechanism for electroreduction of oxygen on this oxide catalyst has been discussed. Published in Russian in Elektrokhimiya, 2008, Vol. 44, No. 7, pp. 919–923. The text was submitted by the authors in English.     

How often are two permutations comparable?

Two permutations of are comparable in the Bruhat order if one is closer, in a natural way, to the identity permutation, , than the other. We show that the number of comparable pairs is of order at most, and at least. For the related weak order, the corresponding bounds are and , where . In light of numerical experiments, we conjecture that for each order the upper bound is qualitatively close to the actual number of comparable pairs.

     

Instantaneous Free Radical Scavenging by CeO2 Nanoparticles Adjacent to the Fe−N4 Active Sites for Durable Fuel Cells

To achieve the Fe−N−C materials with both high activity and durability in proton exchange membrane fuel cells, the attack of free radicals on Fe−N₄ sites must be overcome. Herein, we report a strategy to effectively eliminate radicals at the source to mitigate the degradation by anchoring CeO₂ nanoparticles as radicals scavengers adjacent (Sca^ad-CeO2) to the Fe−N₄ sites. Radicals such as ⋅OH and HO₂⋅ that form at Fe−N₄ sites can be instantaneously eliminated by adjacent CeO₂, which shortens the survival time of radicals and the regional space of their damage. As a result, the CeO₂ scavengers in Fe−NC/Sca^ad-CeO2 achieved ∼80 % elimination of the radicals generated at the Fe−N₄ sites. A fuel cell prepared with the Fe−NC/Sca^ad-CeO2 showed a smaller peak power density decay after 30,000 cycles determined with US DOE PGM-relevant AST, increasing the decay of Fe−NC_Phen from 69 % to 28 % decay.     

Syntheses of octasubstituted zinc azaphthalocyanines with thiophene or thiophene combined with sulfanyl,amino or imido substituents: Influence of the substituents on photochemical and photophysical properties

Several octasubstituted zinc azaphthalocyanines (ZnAzaPcs) of the tetrapyrazinoporphyrazine type have been synthesized as potential sensitizers for photodynamic therapy (PDT). Octasubstituted complexes, with thiophen-2-yl, thiophen-3-yl or benzo[b]thiophen-3-yl peripheral groups, were synthesized and characterized. Octa(thiophen-2-yl) ZnAzaPc is a better singlet oxygen producer and has a red shifted UV absorption Q-band compared to both thiophen-3-yl and benzo[b]thiophen-3-yl substituted ZnAzaPcs. Thus, the thiophen-2-yl substituent is better suited for our purpose. Unsymmetrically substituted ZnAzaPcs were synthesized by cyclotetramerisations of pyrazine-2,3-dicarbonitriles attached to one thiophen-2-yl group and one alkylsulfanyl, thiomorpholinyl or imide group. Constitutional isomers were detected by NMR spectroscopy for some of these complexes. Compared to unsubstituted ZnAzaPc, red shifted Q-bands were observed for all these complexes, due to the presence of thiophen-2-yl groups. The least promising complexes are ZnAzaPcs with thiomorpholine or imide peripheral substituents, i.e. where the peripheral substituents are attached to the macrocycle through nitrogen atoms. Low singlet oxygen quantum yields (Φ_Δ) and also low fluorescence quantum yields (Φ_F) were observed for these ZnAzaPcs. In the case of combined thiophen-2-yl and alkylsulfanyl substituents, the values of Φ_Δ were the highest and reached values of approximately 0.69.     

Poly(N,N-dimethylaminoethyl methacrylate)–poly(ethylene oxide) copolymer membranes for selective separation of CO2

A series of copolymers containing ether oxygen groups and amino groups were prepared based on N,N-dimethylaminoethyl methacrylate (DMEMA) and polyethylene glycol methyl ether methyl acrylate (PEGMEMA). The effect of PEGMEMA content in the copolymer on density, free volume, mechanical performance, and H₂, CO₂, N₂ and CH₄ gas transport properties of the copolymer was determined. Free volume was characterized using the polymer density and group contribution theory. The permeability of the copolymer to CO₂ is high, and both the CO₂/N₂ and CO₂/H₂ selectivities are high. For example, the permeability coefficient of PDMAEMA–PEGMEMA-90 (“90” represents the weight percent of PEGMEMA) to CO₂ is 112 Barrer and the CO₂/N₂ and CO₂/H₂ selectivity coefficients are 31 and 7, respectively. The effect of the temperature on gas transport properties was also determined. Finally, the potential application of the copolymer membranes for CO₂/light gases separation was explored.