氮掺杂活性炭及其载铂催化剂氧还原催化活性

采用化学原位聚合法制备聚吡咯/活性炭(AC)复合物,在惰性气氛进行热处理,制备了氮掺杂活性炭(NAC)。利用化学浸渍还原法制备AC和NAC载铂催化剂,并对比分析他们的氧还原催化性能。氮掺杂处理明显降低了活性炭的比表面积,但因其改善了活性炭水分散性和表面活性,铂在NAC表面沉积和分布较在AC载体表面更均匀。尤其经900℃炭化处理获得的氮掺杂活性炭NAC900,源于其微孔的高比表面积和含氮官能团共同作用,使铂粒子多以尺寸小于5 nm的粒子均匀沉积分布于载体表面,且铂担载量高。循环伏安曲线分析表明,与活性炭载铂催化剂(Pt-AC)相比,氮掺杂活性炭载铂催化剂(Pt-NAC900)的氧还原峰电位更正,氧还原峰电流为前者两倍,且峰电流随循环次数的衰减更低。结果表明,通过对传统炭材料活性炭进行氮掺杂处理,能够增强其载铂催化剂氧还原催化性能。     

从催化剂废料中再生提纯铂

铂是贵重的铂族金属之一,由于稀缺和价格昂贵,我国目前使用的铂大部分仍靠进口。国内各行业中,每年产出几十吨含铂族金属的催化剂废料,进行再生回收其中有价值的铂族金属具有极大的经济意义。对于含贵金属废料——铂石棉再生回收铂的工艺研究或工业生产国内目前尚未见报道,国外再生回收催化剂废料中的铂族金属的技术历来是严格保密的。从专利文献得知以下方     

还原氧化石墨烯-柱[5]芳烃-铂纳米粒子复合材料的制备及其应用

将带胺基的双亲柱[5]芳烃(AP5)修饰在还原氧化石墨烯(RGO)表面,得到水分散性RGO-AP5。用AP5做桥联剂,将预先制备的铂纳米粒子(PtNPs:Platinum Nanoparticles)自组装到RGO-AP5表面后得到三元纳米复合材料RGO-AP5-PtNPs。采用TEM、SEM、XRD等手段表征了复合材料的结构和形貌。考查了RGO-AP5-PtNPs中的三组分对客体分子在其修饰电极上的电化学响应的协同促进作用。     

用绿矾去除海绵铂中的金

众所周知,铂具有特殊的优良性能而广泛应用于各个领域中。由于资源关系,铂的再生回收利用实有重要意义。废料的来源主要是产品经使用后报废及生产加工过程中的边角废料等。当前,贵金属加工工场是以加工铂及铂铑合金为主,也包括钯、铱、金、银等合金材料,在铂废料再生回收的过程中,采用经典的溴酸盐水解-氯化铵沉淀法可将铑、钯、铱、银等贵金属去除,收到满意的效果。但除金则较为困难,往往生成类似铂的铵盐-氯金酸铵[NH_4AuCl_4]与氯铂酸铵[(NH_4)_2PtCl_6[一道沉淀下来,经煅烧分解后,而残留于海绵铂中,不利于铂的优越性能的发挥。某单位要求我们将一批含金在0.012—0.12％的海绵铂,     

铂2003年供应量增至690万盎司

据COM Group在其2003年铂族金属综述一文中所述，供应市场铂总供应量在2003年及2004年都将有显著增加，主要归功于南非原矿铂产量及回收废料的作用。     

催化苯乙烯与三乙氧基硅烷的硅氢加成反应研究

研究了聚乙二醇(PEG)作为络合剂的负载型铂催化剂的制备及其催化苯乙烯与三乙氧基硅烷硅氢加成反应的反应规律,考察了温度、催化剂用量、载体粒度等因素对催化活性的影响.结果表明,该催化反应在50℃、投料比为1:1、催化剂铂含量为2.6×10-5mol·g-1时,三乙氧基硅烷的转化率可达90%,反应无明显诱导期,催化剂性能稳定,回收使用3次无明显失活.     

碳纳米管沉积铂和钌对PEMFC抗CO中毒能力的影响

通过催化裂解法制备了碳纳米管,对其进行氧化处理后,在其表面沉积了分布均匀、尺寸呈纳米级的铂和铂/钌颗粒.实验结果表明,当采用碳纳米管沉积铂为催化剂时,质子交换膜燃料电池的催化剂铂很容易受CO的毒化而失去活性,从而使电池的电压随电流密度的降低而迅速降低;当采用碳纳米管沉积铂/钌为催化剂时,钌能够使铂表面吸附的CO被氧化为CO₂,增加催化剂对CO的抵抗能力,使燃料电池的性能提高.     

还原氧化石墨烯-贵金属纳米复合物的制备及表征

以氧化石墨和氯铂酸为前驱体,在油胺中简便地合成了还原氧化石墨烯-铂(Reduced graphene oxide-platinum,rGOPt)纳米复合物,并对其进行了表征。透射电子显微镜和光谱测试结果表明,铂纳米颗粒均匀分布在石墨烯表面,尺寸约为30nm,铂纳米粒子为多孔隙结构,结晶性能良好,氧化石墨在高温下转变为还原氧化石墨烯。用此方法也可以制备还原氧化石墨烯-金(rGO-Au)或还原氧化石墨烯-银(rGO-Ag)的纳米复合物,金、银纳米颗粒呈球状,对可见光具有明显的表面等离子吸收。同时,油胺作为溶剂、贵金属盐的还原剂和表面活性剂,使制备过程简单、快捷。     

用于电刺激的植入式铂黑微电极

传统的植入式电刺激微电极表面积小,电极／组织界面阻抗高,并且电荷存储容量（CSC）小,这些都会增加植入式系统的功耗并影响电刺激效果．提出了一种在电极点电镀铂黑的方法来增加微电极的有效面积（ESA）．通过在超声波浴下使用脉冲电流电镀的方法,可以极大地增加微电极的ESA,降低界面阻抗并增加CSC和电荷注入容量．铂黑微电极的几何特性和电学特性分别由扫描电子显微镜（SEM）和电化学分析仪测定,并与未镀铂黑的电极特性进行了对比,对铂黑镀层的机械稳定性也做了相应的测试．实验结果表明,铂黑镀层的纳米结构使铂黑电极相比普通铂电极界面阻抗降低了1／16,CSC扩大13倍．在5min的室温超声波衰减实验中,阴极电荷存储容量（CSCc）仅减小20％．     

载铂钴酸镧的制备与电化学性能

采用乙二醇还原法在钴酸镧表面上沉积铂,制备了载铂20%的载铂钴酸镧复合材料Pt-LCO/C。采用X射线粉末衍射、透射电子显微镜研究了载铂钴酸镧的结构与形貌,发现铂在钴酸镧中的分散性好,获得的铂金属颗粒仅2nm,且颗粒大小均匀。采用循环伏安法研究了载铂钴酸镧复合材料的电化学性能和对甲醇的电化学氧化行为。研究表明,载铂钴酸镧复合材料具有很好的扩散性能,具有优良的电催化氧化甲醇的性能。     

Auger electron spectroscopy study of the sputtering effect on platinum silicide surfaces

Modifications of platinum silicides in the composition range between Pt₃Si and PtSi induced by argon ion beams were studied by angle-integrated Auger electron spectroscopy (AES). A platinum surface enrichment, which was stronger at low sputtering energies and in silicon-rich silicides, was found in the 1–5 keV ion energy range. In all silicides sputtering yield ratios Y_Si/Y_Pt of about 2.9 and 2.1 were estimated for the 1 keV and 5 keV steady state regimes respectively. Simultaneous analysis of low and high energy platinum and silicon Auger lines indicated that the platinum enrichment extended over a range of a few tens of ångströms and was slightly higher at the surface than in the subsurface region. The platinum enrichment, its energy dependence and the in-depth graded composition of the altered layer are discussed in terms of silicon preferential sputtering, recoil implantation and surface segregation. Dynamic surface composition changes were also studied, and a model which accounts for the various “shapes” of the transient regimes and their dependence on the height of the steps in the sputtering energy is shown schematically. Shape analysis of the core-valence-valence Auger lines suggests that changes in the chemical bonding in platinum silicides are induced by ion bombardment so that enrichment with platinum results in the formation of compounds which are richer in platinum.     

Deposition of platinum nanoparticles on carbon nanotubes by supercritical fluid method

Carbon nanotube-supported platinum nanoparticles with a 5-15 nm diameter size range can be synthesized by hydrogen reduction of platinum(ll) acetylacetonate in methanol modified supercritical carbon dioxide. X-ray photoelectron spectroscopy and X-ray diffraction spectra indicate that the carbon nanotubes contain zero-valent platinum metal and high-resolution transmission electron microscopy images show that the visible lattice fringes of platinum nanoparticles are crystallites. Carbon nanotubes synthesized with 25% by weight of platinum nanoparticles exhibit a higher activity for hydrogenation of benzene compared with a commercial carbon black platinum catalyst. The carbon nanotube-supported platinum nanocatalyst can be reused at least six times for the hydrogenation reaction without losing activity. The carbon nanotube-supported platinum nanoparticles are also highly active for electrochemical oxidation of methanol and for reduction of oxygen suggesting their potential use as a new electrocatalyst for proton exchange membrane fuel cell applications.     

The catalytic nanodiode: gas phase catalytic reaction generated electron flow using nanoscale platinum titanium oxide Schottky diodes

Forty microampere current was generated on a platinum-titanium dioxide Schottky diode during the platinum catalyzed steady-state oxidation of carbon monoxide at 80 degrees C. For reaction events that produced four CO(2) molecules, three injected electrons were collected in a diode comprising a 5 nm thick platinum and a 150 nm titanium dioxide film. The electron injection flux depends on the thickness of the platinum and the titanium dioxide diode properties as well as the conditions of the catalytic reactions.     

Room temperature amorphous to nanocrystalline transformation in ultra-thin films under tensile stress: an in situ TEM study

The amorphous to crystalline phase transformation process is typically known to take place at very high temperatures and facilitated by very high compressive stresses. In this study, we demonstrate crystallization of amorphous ultra-thin platinum films at room temperature under tensile stresses. Using a micro-electro-mechanical device, we applied up to 3% uniaxial tensile strain in 3-5 nm thick focused ion beam deposited platinum films supported by another 3-5 nm thick amorphous carbon film. The experiments were performed in situ inside a transmission electron microscope to acquire the bright field and selected area diffraction patterns. The platinum films were observed to crystallize irreversibly from an amorphous phase to face-centered cubic nanocrystals with average grain size of about 10 nm. Measurement of crystal spacing from electron diffraction patterns confirms large tensile residual stress in the platinum specimens. We propose that addition of the externally applied stress provides the activation energy needed to nucleate crystallization, while subsequent grain growth takes place through enhanced atomic and vacancy diffusion as an energetically favorable route towards stress relaxation at the nanoscale.     

Synthesis and electrocatalytic activity of platinum nanoparticle/carbon nanotube composites

Pt/CNT nanocomposite materials with an average platinum particle size of 3–5 nm and platinum content of 13–28 wt % have been prepared by reducing chloroplatinic acid, H₂PtCl₆, in the presence of conical carbon nanotubes. The effect of synthesis conditions on the average platinum particle size, total platinum content, and surface composition of the nanocomposites has been studied using X-ray photoelectron spectroscopy, IR spectroscopy, electron microscopy, X-ray diffraction, and thermogravimetry. The materials have been tested as catalysts for hydrogen oxidation and oxygen reduction. Their performance has been assessed by cyclic and steady-state voltammetric techniques. The structure and composition effects on the electrocatalytic properties of the nanocomposites are discussed.     

Uranium-Platinum System

The phase diagram of the uranium-platinum system was constructed from data obtained by thermal analysis, metallographic examination, and X-ray diffraction. The system is characterized by four intermetallic compounds: UPt, formed peritectoidally at 961° C; UPt₂, formed peritectically at 1,370° C; UPt₃, melting congruently at 1,700° C; and UPt₅, formed peritectically at 1,460° C. One eutectic occurs at 1,005° C and 12 a/o platinum, and a second at 1,345° C and 87.5 a/o platinum. The maximum solubilities are 4.5 a/o uranium in platinum and 5 a/o platinum in gamma-uranium. Platinum lowers the gamma-beta uranium transformation to 705° C and the beta-alpha transformation to 589° C.     

Room temperature synthesis of colloidal platinum nanoparticles

Efficient preparation of stable dispersions of platinum nanoparticles from platinous chloride (K₂PtCl₄) was achieved by simultaneous addition of capping polymer material. The size of platinum nanoparticles was controlled by changing the ratio of concentration of capping polymer material to the concentration of platinum cation used. The morphology of colloidal particles were studied by means of UV-visible spectrophotometry and transmission electron microscopy (TEM). Particle size increased with low reagent concentration. The change in absorption spectra with the particle size was observed, i.e. blue shift attributed to decrease in particle size Paper presented at the 5th IUMRS ICA98, October 1998, Bangalore.     

Characterization of the growth of sol-gel derived Ba---Ti---O thin films by laser Raman spectroscopy

The isothermal growth kinetics of sol-gel derived BaTi₅O₁₁ thin films has been studied by laser Raman spectroscopy. Thin films of the precursors were spin coated on silicon wafers with platinum or gold overlayers. The films were then annealed isothermally, and Raman spectra were recorded in situ. The time-dependent intensity changes of the Raman bands could be analyzed in terms of Avrami models. The interaction of the BaTi₅O₁₁ film with the platinum or gold overlayers during heat treatment apparently increased the Raman intensity by a factor of about 100.     

Non-destructive evaluation of nano-sized structure of thin film devices by using small angle neutron scattering

Nano-sized multi-layers copper-doped SrZrO3, platinum (Pt) and silicon oxide (SiO2) on silicon substrates were prepared by dense plasma focus (DPF) device with the high purity copper anode tip and analyzed by using small angle neutron scattering (SANS) to establish a reliable method for the non-destructive evaluation of the under-layer structure. Thin film was well formed at the time-to-dip of 5 microsec with stable plasma of DPF. Several smooth intensity peaks were periodically observed when neutron beam penetrates the thin film with multi-layers perpendicularly. The platinum layer is dominant to intensity peaks, where the copper-doped SrZnO3 layer next to the platinum layer causes peak broadening. The silicon oxide layer has less effect on the SANS spectra due to its relative thick thickness. The SANS spectra shows thicknesses of platinum and copper-doped SrZnO3 layers as 53 and 25 nm, respectively, which are well agreement with microstructure observation.     

Supported and unsupported platinum catalysts prepared by a one-step dry deposition method and their oxygen reduction reactivity in acidic media

The present study examines the physical and electrochemical properties of platinum particles generated by a combustion method for use in oxygen reduction on the cathode side of a proton exchange fuel cell (PEMFC). This method employs a one-step, open-atmosphere, and dry deposition technique called reactive spray deposition technology (RSDT). The objective of this study is to characterize the intrinsic activity of the platinum produced for incorporation into low-loading cathode electrodes in high performing membrane electrode assemblies (MEA). The process allows for independent real-time control of the carbon, platinum, and ionomer ratios in the final electrode. In this research work we examine the oxygen reduction reaction via a rotating disk three electrode set-up to understand the intrinsic activity of the as-sprayed platinum as well as platinum condensed onto a carbon support. The mass and specific activities were measured in a 0.1 M perchloric acid electrolyte under different deposition conditions and loading was verified by atomic emission spectroscopy inductively coupled plasma (AES-ICP). Microscopy results indicate that the platinum particle sizes are 5 nm (σ = 2.8 nm) in diameter while TEM and XRD show that the platinum generated by the process is pure and crystalline without bulk oxides or precursor material present. The initial rotating disk electrode result shows that the RSDT technique is capable of producing catalysts with an oxygen reduction mass activity at 0.9 V of 200 mA/mg_Pt rotating at 1600 rpm and 30 °C. The electrochemically active surface area approaches 120 m²/g for the platinum, carbon, and ionomer samples and the unsupported sample with only platinum has an active area of 92 m²/g. The rather larger surface area of the unsupported sample exists when the platinum is deposited as a highly porous nanostructured layer that allows for high penetration of reactant.