热处理对电沉积Ni-W-P合金催化析氢性能的影响

 采用电沉积方法制备了Ni-W-P合金镀层,并在不同温度下进行热处理,通过极化曲线和交流阻抗谱研究了热处理温度对Ni-W-P合金催化析氢性能的影响. 结果表明,经200 ℃热处理的Ni-W-P合金电极析氢过电位最低,在电流密度为8.0 mA/cm2时,其析氢过电位较未经热处理的Ni-W-P合金电极减小约110 mV. 该样品的析氢电化学反应电阻为17.1 Ω·cm2, 交换电流密度约为未经热处理的Ni-W-P合金的5.0倍,析氢反应表观活化能降低. 差示扫描量热法、 X射线衍射和扫描电镜测试结果表明, Ni-W-P合金镀层经200 ℃热处理后发生低温结构弛豫,平均晶粒尺寸由1.1增大到2.8 nm, 合金由非晶结构转变为纳米晶结构,镀层表面形成宽度约为0.2 μm的微裂纹.     

Ni-P-C复合材料的制备及其电催化产氢性能研究

通过化学镀技术制备了亚微米级的Ni-P镀层石墨粉复合粉体新材料(即Ni-PC).采用扫描电子显微镜、X-射线能谱仪、X-射线粉末衍射仪对Ni-P-C复合粉体分别进行表面形貌分析、表面成分分析和物相分析.通过对Ni-P-C材料电极进行电解水析氢、循环伏安和Tafel极化等电化学测试,研究对比了Ni-P-C(石墨)材料与试剂石墨粉体以及纯Ni电极的电化学催化产氢性能.结果表明:利用化学镀技术成功地在石墨粉体表面镀上了一层亚微米级且均匀、致密的非晶态Ni-P合金.Ni-P-C(石墨)复合电极材料析氢能力强,具有良好的电化学活性.     

Ni-P化学镀反应速率及机理研究

通过镀层分析和析氢量测量得到Ni-P镀层的沉积速度和H2PO2的分解速度·以混合电位理论为基础，对Ni－P电极在不同组成饮液中的极化曲线进行分解得到以化学镀电流形式所表示的反应速率·将两种方法所得结果进行对照，确定H2PO2氧化时电子迁移数为1，并用原子红-电化学联合理论解释溶液PH对反应速率及化学镀效率的景响．     

电沉积多孔复合Ni-P/LaNi5电极及其析氢电催化性能

采用复合电沉积制备了Ni-P/(LaNi₅+Al) 复合镀层, 然后将镀层浸泡在浓碱液中除铝, 成功得到多孔复合Ni-P/LaNi₅电极. 通过扫描电镜(SEM)、能谱分析(EDS)和X射线衍射(XRD)仪等技术表征了电极的表面形貌、组成和相结构. 运用电化学线性伏安扫描(LSV)、恒电位电解、电化学阻抗谱(EIS)等手段研究了电极在20%(w) NaOH溶液中的析氢反应(HER)电催化性和稳定性. 结果表明, 与多孔Ni-P 电极相比, 多孔复合Ni-P/LaNi₅电极具有低的析氢过电位、高的比表面积和高的稳定性能; 多孔Ni-P/LaNi₅电极的析氢反应的表观活化自由能为35.44 kJ·mol^-1, 低于多孔Ni-P 的值(50.91 kJ·mol^-1).     

多孔Ni、Ni-Mo合金及其氧化物的制备与析氢性能

采用快速凝固结合脱合金化的方法制备了纳米多孔Ni、Ni-Mo合金及其氧化物电极材料,通过XRD、SEM、TEM、BET等对电极的物相、形貌结构、孔径分布进行表征,通过线性扫描伏安法、Tafel斜率和计时电位等方法测试多孔电极的电催化析氢性能。结果显示,制备的电极材料在10 mA·cm-2电流密度下Ni-Mo合金析氢活性最强,析氢过程由Volmer-Heyrovsky步骤控制,其表观交换电流密度为0.25 mA·cm-2,经10 000 s恒电流密度(100 mA·cm-2)电解后析氢过电位(η)仅增加39 mV,表现出优良的析氢稳定性。Ni-Mo合金电极比表面积的提高和本征催化活性的改善使其获得了更低的析氢过电位。     

镍铜合金立方体纳米晶的脉冲电沉积及电催化析氢性能

以泡沫镍(NF)为基体, 采用常规脉冲伏安法合成了独立分相的金属Ni, Cu为主晶相、 平均粒径为70 nm的规则立方体结构镍铜合金电催化剂(NiCu/NF). 在电催化析氢反应中, NiCu/NF表现出优良的催化活性和优异的催化稳定性, 在电流密度为10 mA/cm ²时, 在1.0 mol/L KOH溶液中需要的析氢过电位仅为86 mV, 催化24 h的电位波动仅为12 mV. 二级复合纳米立方体结构使NiCu/NF展现出15.5倍于空白NF的电化学活性面积(ECSA), 为电催化反应提供了大量催化活性位点, 也为电极表面的电荷传输、 物质传递提供了充足的通道; Cu的引入以及NiO/Ni异质结的形成改善了邻近Ni原子的活性, 使镍基材料本征析氢活性得以改善, 三者协同促进了NiCu/NF电催化活性的提升. NiCu/NF电极在析氢过程中遵循Volmer-Heyrovsky机理, 反应速率由电极表面吸附氢原子的电化学脱附过程决定.     

新型不锈钢基二氧化铅-碳化钨复合电极材料的研制

在不锈钢基上通过复合电沉积的方式制备了二氧化铅 碳化钨（PbO2-WC）电极。 考察了温度、电流、WC颗粒浓度对电极性能的影响;通过析氧曲线、Tafel曲线、扫描电子显微镜能谱、X射线衍射图谱考察了WC颗粒掺杂前后PbO2电极相关性能的变化。 结果表明,在最佳工艺即温度70 ℃、镀液中WC颗粒浓度为40 g/L时,电流密度为0.015～0.025 A/cm2;PbO2-WC共沉积过程中PbO2发生了择优生长,WC颗粒的加入能够细化PbO2晶粒,使镀层变得致密,相对于PbO2电极,PbO2-WC复合电极的耐腐蚀性上升,析氧过电位下降。     

电沉积纳米镍合金在模拟海水溶液中的析氢性能

采用电沉积法获得Ni、Ni-Fe和Ni-Fe-C合金镀层电极,在90℃模拟海水(0.5mol·L-1NaCl,pH=12)的稳态极化曲线表明Ni-Fe-C合金电极具有最好的析氢催化性能.通过扫描电子显微镜(SEM)观察电极表面形貌、X射线衍射(XRD)与高分辨透射电子显微镜(HRTEM)分析合金的成分和晶体结构,发现电极材料的晶粒尺寸影响析氢催化性能,晶粒尺寸越小析氢催化活性越好.用电化学阻抗方法(EIS)研究电极析氢催化性能的本质原因,结果表明电极表面活性点数目和电极的本质电催化活性对合金电极析氢催化活性有重要的影响.     

Ni-Sn电极析氢性能研究

在Fe基底材料上电镀Ni_Sn合金制备低析氢过电位的阴极活性材料 .该材料适用于氯碱工业隔膜型电解槽 ,可达到降低槽压、节能降耗的目的 .在电解槽阴极溶液NaOH 12 0 g/L ,NaCl190 g/L ;温度 90℃ ,阴极极化电流密度i=15 0mA/cm2 的条件下 ,测得其析氢过电位为 88mV .X射线衍射分析表明 ,该种材料与传统装饰用Ni_Sn合金的结构状态有所不同 .采用循环伏安法对Fe电极和Ni_Sn合金电极进行分析 ,可初步判断Ni_Sn合金对氢的吸附较弱 ,有利于析氢反应的进行     

"三明治夹心"型Ni-P@Ni-B/Ni电极的制备及高效全pH下的催化制氢性能

通过化学镀法制备了具有“三明治夹心”结构的Ni-P@Ni-B/Ni催化电极. 该催化材料为直径1 μm左右的微球. 电化学性能测试结果表明, 在电流密度为10 mA/cm ²时, 其在0.5 mol/L PBS缓冲液(pH=7)中的过电位仅为287 mV, 在此电位下连续工作24 h后, 电流密度仅衰减了7.6%. 同时Ni-P@Ni-B/Ni在酸性(0.5 mol/L H₂SO₄)和碱性(1 mol/L KOH)条件下也具有优异的析氢反应催化活性, 达到相同电流密度时过电位分别为199和79 mV. 该工作为全pH环境下高效电解水制氢提供了新思路.     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.