Nanoporous silver (NPS) is fabricated by selectively dissolving Al from AgAl alloys in corrosive electrolytes at room temperature. Electron spectroscopy characterizations demonstrate that the NaOH electrolyte is beneficial to the formation of a three‐dimensional bicontinuous porous nanostructure with uniform and tunable pore and ligament dimensions of a few tens of nanometers, while processing in HCl electrolyte easily lead to coarsened porous nanostructures. The high‐surface‐area Ag nanostructures are demonstrated as novel effective template materials to the construction of nanotubular mesoporous Pt/Ag and Pd/Ag alloy structures, which are realized via room temperature galvanic replacement reactions with H2PtCl6 and K2PdCl4 solutions by adding a high concentration of Cl? ions as a coordinating agent. Electrochemical measurements indicate that the resulting hollow and porous bimetallic nanostructures show enhanced electrocatalytic activities and CO‐tolerance with better durability toward methanol and formic acid oxidation due to alloying with Ag.相似文献
An efficient and versatile tandem process of acetalization and cycloisomerization reactions has been developed for the reactions of 1-alkynyl-2-carbonylquinoline substrates. The reaction occurs thanks to Au(I) and Ag(I) catalysis. Silver(I) catalysis has been extensively studied (11 different silver species) on a broad range of quinoline derivatives (variation of alkyne substituent, of carbonyl function and of nucleophiles), leading to a variety of furoquinoline and pyranoquinoline moieties. An insight is given for the presumed mechanism along with DFT-B3 LYP/6-31G** calculations to address the 6-endo and 5-exo regioselectivities observed. 相似文献
The oxygen reduction reaction (ORR) was studied in KOH electrolyte on different manganese oxides, dispersed on a carbon powder (MnOx/C). The oxides were prepared by different methods, for producing MnO, Mn3O4 and MnO2 as major phases dispersed on the Vulcan XC-72 carbon. The oxides were characterized by XRD (X-ray diffraction) and in situ XANES (X-ray absorption near edge structure). The electrochemical measurements were made using cyclic voltammetry and steady state polarization curves carried out in an ultra-thin layer rotating ring/disk electrode. The results have shown lower activity for the ORR on the MnOx/C species compared to that on Pt/C, but higher activity compared to that of pure Vulcan carbon. Formation of involving 2e− per O2 molecule is the main path of the ORR in the studied MnOx/C catalysts but, at low overpotentials and rotation rates the number of electrons is raised to 4 due to the occurrence of a disproportionation reaction. Large differences of electrocatalytic activity were seen for the different oxide species, and these were related to the presence of a Mn(IV) phase and the occurrence of a mediation processes involving the reduction of Mn(IV) to Mn(III), followed by the electron transfer of Mn(III) to oxygen. 相似文献
Journal of Solid State Electrochemistry - In this work, a low-cost, high-performance, and environmentally friendly metal-free electrocatalyst based on N-doped carbon nanosheets (NCNs) was... 相似文献
The nanomaterial industry generates gigantic quantities of metal-based nanomaterials for various technological and biomedical applications; however, concomitantly, it places a massive burden on the environment by utilizing toxic chemicals for the production process and leaving hazardous waste materials behind. Moreover, the employed, often unpleasant chemicals can affect the biocompatibility of the generated particles and severely restrict their application possibilities. On these grounds, green synthetic approaches have emerged, offering eco-friendly, sustainable, nature-derived alternative production methods, thus attenuating the ecological footprint of the nanomaterial industry. In the last decade, a plethora of biological materials has been tested to probe their suitability for nanomaterial synthesis. Although most of these approaches were successful, a large body of evidence indicates that the green material or entity used for the production would substantially define the physical and chemical properties and as a consequence, the biological activities of the obtained nanomaterials. The present review provides a comprehensive collection of the most recent green methodologies, surveys the major nanoparticle characterization techniques and screens the effects triggered by the obtained nanomaterials in various living systems to give an impression on the biomedical potential of green synthesized silver and gold nanoparticles. 相似文献
燃料电池具有较高的能量密度和发电效率,以清洁能源为原料,零污染排放,是一种具有发展前景的能量储存和转化装置.阴极氧还原反应(ORR)在燃料电池中起着关键作用.ORR广泛采用贵金属铂基催化剂,但是它们价格昂贵,电子动力学转移速率慢,碱性条件下易团聚,这些亟需解决的问题阻碍了燃料电池商业化进程.近期,一些非贵金属催化剂被广泛研究,例如氮掺杂碳材料、Fe/N/C和Co/N/C材料等,它们有可能在未来替代铂基催化剂.我们的目标是合成新型高催化活性的Co/N/C及其衍生非贵金属材料,用于ORR催化反应.由于石墨烯具有独特的形貌、较大的比表面积和良好的导电性,其表面含有功能化的官能团,所以我们选择石墨烯作为碳载体.首先,用改性休克尔方法合成了氧化石墨烯(GO),为了提高其催化活性,采用聚吡咯作为氮源对其进行了氮掺杂,制备了聚吡咯/氧化石墨烯(Ppy/GO).通过ORR催化性能测试发现,GO对ORR具有一定的催化活性,它的起始电位和阴极电流电位分别为–0.31 V vs SCE和–0.38 V vs SCE;Ppy/GO的起始电位和阴极电流电位分别为–0.20 V vs SCE和–0.38 V vs SCE,氮掺杂对GO的催化活性有所提高.采用水热法沉积氧化钴合成了Co3O4/聚吡咯/氧化石墨烯(Co3O4/Ppy/GO).其形貌为Co3O4分散在氮掺杂GO表面.在KOH电解质(0.1 mol/L)中测试,Co3O4/Ppy/GO的起始电位和阴极电流电位分别为–0.20 V和–0.38 V vs SCE.经过800℃高温煅烧处理后,Co3O4/Ppy/GO-800的催化活性明显提高,起始电位和阴极电流电位分别达到–0.10 V和–0.18 V vs SCE.ORR电子转移数为3.4,接近于4电子反应途径.Co3O4/Ppy/GO对ORR的催化活性及4电子催化选择性较高,可能是由于纳米形态的Co3O4和Ppy/GO之间具有较强的表面作用力,聚吡咯掺杂的氧化石墨烯具有较强的电子储存及释放能力.综上,我们通过水热法制备了钴、氮共掺杂的GO,并研究了其对ORR的催化活性和电子转移选择性.结果表明Co3O4/Ppy/GO是一种高效的非贵金属电催化剂,在碱性电解质中具有很高的ORR催化活性,在燃料电池阴极催化剂方面很有前景. 相似文献
This work reviews the studies conducted in this laboratory of the oxygen reduction reaction (ORR) on electrocatalysts formed
by Pt-M/C (M = V, Cr, Co) and Ag-Pt/C alloys and on different Mn oxides (MnO/C, Mn3O4/C, MnO2/C) in KOH electrolyte. The physical and electronic properties of the materials are investigated by in situ XAS (x-ray absorption
spectroscopy) in the XANES (x-ray absorption near edge structure) region. The electrocatalytic activity for the ORR on the
different catalysts is compared through mass-transport-corrected Tafel plots. The XANES results for the Pt-M/C and Ag-Pt/C
composites at high electrode potentials show lower vacancy of the Pt 5d band compared to pure Pt/C, while for the results indicate a chance of the Mn oxidation state as a function of the electrode
potential. The electrochemical measurements evidence increased electrocatalytic activity of the Pt alloys compared to pure
Pt and this is attributed to a lowering of the adsorption strength of adsorbed oxygen species caused by the reduced Pt reactivity.
An activity enhancement of the Ag atoms on the Ag-Pt/C alloys compared to pure Ag is ascribed to an electronic effect induced
by the presence of Pt, increasing the Ag-O adsorption strength. In the case of the MnyOx/C materials, the electrochemical results show low activity for MnO/C and higher activity for MnO2/C and Mn3O4/C. This is explained based on the activation for the ORR, which is higher for the material with higher MnO2 contents and the occurrence of a mediation processes involving the reduction of Mn(IV) to Mn(III), followed by the electron
transfer of Mn(III) to oxygen.
Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 12, pp. 1417–1426.
Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22,
2005, Moscow.
The text was submitted by the authors in English. 相似文献
While the reaction of [PW(11)O(39)](7-) with first row transition-metal ions M(n+) under usual bench conditions only leads to monosubstituted {PW(11)O(39)M(H(2)O)} anions, we have shown that the use of this precursor under hydrothermal conditions allows the isolation of a family of novel polynuclear discrete magnetic polyoxometalates (POMs). The hybrid asymmetric [Fe(II)(bpy)(3)][PW(11)O(39)Fe(2) (III)(OH)(bpy)(2)]12 H(2)O (bpy=bipyridine) complex (1) contains the dinuclear {Fe(micro-O(W))(micro-OH)Fe} core in which one iron atom is coordinated to a monovacant POM, while the other is coordinated to two bipyridine ligands. Magnetic measurements indicate that the Fe(III) centers in complex 1 are weakly antiferromagnetically coupled (J=-11.2 cm(-1), H=-JS(1)S(2)) compared to other {Fe(micro-O)(micro-OH)Fe} systems. This is due to the long distances between the iron center embedded in the POM and the oxygen atom of the POM bridging the two magnetic centers, but also, as shown by DFT calculations, to the important mixing of bridging oxygen orbitals with orbitals of the POM tungsten atoms. The complexes [Hdmbpy](2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]14 H(2)O (2) (dmbpy=5,5'-dimethyl-2,2'-bipyridine) and H(2)[Fe(II)(dmbpy)(3)](2)[(PW(11)O(39))(2)Fe(4) (III)O(2)(dmbpy)(4)]10 H(2)O (3) represent the first butterfly-like POM complexes. In these species, a tetranuclear Fe(III) complex is sandwiched between two lacunary polyoxotungstates that are pentacoordinated to two Fe(III) cations, the remaining paramagnetic centers each being coordinated to two dmbpy ligands. The best fit of the chi(M)T=f(T) curve leads to J(wb)=-59.6 cm(-1) and J(bb)=-10.2 cm(-1) (H=-J(wb)(S(1)S(2)+S(1)S(2*)+S(1*)S(2)+S(1*)S(2*))-J(bb)(S(2)S(2*))). While the J(bb) value is within the range of related exchange parameters previously reported for non-POM butterfly systems, the J(wb) constant is significantly lower. As for complex 1, this can be justified considering Fe(w)--O distances. Finally, in the absence of a coordinating ligand, the dimeric complex [N(CH(3))(4)](10)[(PW(11)O(39)Fe(III))(2)O]12 H(2)O (4) has been isolated. In this complex, the two single oxo-bridged Fe(III) centers are very strongly antiferromagnetically coupled (J=-211.7 cm(-1), H=-JS(1)S(2)). The electrochemical behavior of compound 1 both in dimethyl sulfoxide (DMSO) and in the solid state is also presented, while the electrochemical properties of complex 2, which is insoluble in common solvents, have been studied in the solid state. 相似文献
Microwave irradiation (MI) process characteristically enables extremely rapid “in‐core” heating of dipoles and ions, in comparison to conventional thermal (conductance) process of heat transfer. During the process of nanoparticles synthesis, MI both modulates functionality behaviors as well as dynamic of reaction in favorable direction. So, MI providing a facile, favorable and alternative approach during nanoparticles synthesis nanoparticles with enhanced catalytic performances. Although, conventionally used reducing and capping reagents of synthetic origin, are usually environmentally hazardous and toxic for living organism. But, in absence of suitable capping agent; stability, shelf life and catalytic activity of metallic nanoparticles adversely affected. However, polymeric templates which emerged as suitable choice of agent for both reducing and capping purposes; bearing additional advantages in terms of catalyst free one step green synthesis process with high degree of biosafety and efficiency. Another aspect of current works was to understand role of process variables in growth mechanism and catalytic performances of microwave processed metallic nanoparticles, as well as comparison of these parameters with conventional heating method. However, due to poor prediction ability with previously published architect OFAT (One factor at a time) design with these nanoparticles as well as random selection of process variables with their different levels, such comparison couldn't be possible. Hence, using gum Ghatti (Anogeissus latifolia) as a model bio‐template and under simulated reaction conditions; architect of QbD design systems were integrated in microwave processed nanoparticles to establish mechanistic role these variables. Furthermore, in comparison to conventional heating; we reported well validated mathematical modeling of process variables on characteristic of nanoparticles as well as synthesized gold nanoparticles of desired and identical dimensions, in both thermal and microwave‐based processes. Interestingly, despite of identical dimension, MI processed gold nanoparticles bearing higher efficiency (kinetic rate) against remediation of hazardous nitro dye (4‐nitrophenol), into safer amino (4‐aminophenol) analogues. 相似文献
The asymmetric desymmetrization of meso‐2‐alkynylbenzenediols through the use of a combination of axially chiral diphosphine(AuCl)2 precatalysts and silver salt co‐catalysts gave optically active isochromene compounds with high enantioselectivities in good yields. The corresponding dl ‐diol isomers underwent efficient kinetic resolution to give the cyclized isochromenes and recovered diols with high enantioselectivities under similar conditions. The high reactivity and selectivity in the desymmetrization of the meso‐diols is independent of the combination of axially chiral diphosphine(AuCl)2 precatalyst and silver salt co‐catalyst, whereas the corresponding tricarbonylchromium complexes of alkynylbenzenediols were affected by the combination of the diphosphine(AuCl)2 and silver salt. The reactivity was largely dependent on the nature of the gold(I) species. 相似文献
One-dimensional and quasi-one-dimensional semiconductor nanostructures are desirable for dye-sensitized solar cells (DSSCs), since they can provide direct pathways for the rapid collection of photogenerated electrons, which could improve the photovoltaic performance of the device. Quasi-1D single-crystalline anatase TiO(2) nanostructures have been successfully prepared on transparent, conductive fluorine-doped tin oxide (FTO) glass with a growth direction of [101] through a facile hydrothermal approach. The influences of the initial titanium n-butoxide (TBT) concentration, hydrothermal reaction temperature, and time on the length of quasi-1D anatase TiO(2) nanostructures and on the photovoltaic performance of DSSCs have been investigated in detail. A power conversion efficiency of 5.81% has been obtained based on the prepared TiO(2) nanostructure photoelectrode 6.7 μm thick and commercial N719 dye, with a short-circuit current density of 13.3 mA cm(-2) , an open-circuit voltage of 810 mV, and a fill factor of 0.54. 相似文献
Metal (cobalt)/nitrogen codoped carbon was first fabricated by pyrolysis of coordinated “noncarbonizable” polymer as bifunctional catalyst for ORR and HER, which showed better electrocatalytic performances than most bifunctional doped carbon catalysts in alkaline electrolyte. 相似文献
Bimetallic catalysts: The effect of PtRu alloying and the influence of RuO2 species on the methanol oxidation activity of PtRu/C catalysts is studied. Different heat treatments—utilizing either N2 or air—are applied to the bimetallic materials to enhance the degree of alloying or produce RuO2 (see picture). The catalysts with the best performance are characterized by a small particle size, a high degree of PtRu alloying, and the presence of a Pt‐related species on their surface.