Preparation and electrochemical behaviors of platinum nanoparticles impregnated on binary carbon supports as catalyst electrodes of direct methanol fuel cells

Binary carbon-supported platinum (Pt) nanoparticles were prepared by a chemical reduction method of Pt precursor on two types of carbon materials such as carbon blacks (CBs) and graphite nanofibers (GNFs). Average sizes and loading levels of Pt metal particles were dependent on a mixing ratio of two carbon materials. The highest electroactivity for methanol oxidation was obtained by preparing the binary carbon supports consisting of GNFs and CBs with a weight ratio of 30:70. Furthermore, with an increase of GNFs content from 0% to 30%, a charge-transfer resistance changed from 19 Ohm cm² to 11 Ohm cm². The change of electroactivity or the resistance of catalyst electrodes was attributed to the changes of specific surface area and morphological changes of carbon-supported catalyst electrodes by controlling the mixing ratio of GNFs and CBs.     

Platinum Nanoparticles Supported on Graphite Nanofibers Prepared by Microwave Irradiation and Its Electrocatalytic Activity

Platinum nanoparticles supported on graphite nanofibers (GNFs) were prepared by microwave assistant heating polyol process. TEM images showed that microwave prepared Pt nanoparticles supported on GNFs were small and uniform, and the average diameter was about 3.4 nm. Cyclic voltammetric test showed that Pt/GNFs exhibited very high electrocatalytic activity for methanol oxidation.     

Epoxy polymer coating to prevent the corrosion of aluminum nanoparticles

Aluminum nanoparticles were coated by epoxy polymer in order to prevent the corrosion reaction. The coverage of the epoxy polymer film was controlled from 0% to 100%, which changed the corrosion rate of nanoparticles quantitatively. The surface of the polymer coating was investigated by transmission electron microscopy (TEM) and atomic force microscopy (AFM), and the corrosion resistance of these nanoparticles was estimated by the wet/dry corrosion test on platinum (Pt) plate with a NaCl solution. From a TEM analysis, 10 mass% polymer‐coated Al particles in the synthesis were almost 100% covered on the surface by a polymer film of 10 nm thick. On the other hand, 3 mass% polymer‐coated Al was partially covered by a film. In the AFM–Kelvin force microscopy, the potential around the Al particles had a relatively low value by the polymer coating, which indicated that the conductivity of the Al was isolated from Pt plate by the polymer. Both the corrosion and H₂ evolution reaction rates were quantitatively reduced by the mass% of polymer coating. In the case of 10 mass% coated sample, there was very little corrosion of Al nanoparticles. This fact suggested that the electrochemical reaction was suppressed by the polymer coating. Thus, it was found that the corrosion reaction rate of Al nanoparticles could be quantitatively suppressed by the mass% of epoxy coating. Copyright © 2015 John Wiley & Sons, Ltd.     

Hydrogen Storage Mediated by Pd and Pt Nanoparticles

The hydrogen storage properties of metal nanoparticles change with particle size. For example, in a palladium–hydrogen system, the hydrogen solubility and equilibrium pressure for the formation of palladium hydride decrease with a decrease in the particle size, whereas hydrogen solubility in nanoparticles of platinum, in which hydrogen cannot be stored in the bulk state, increases. Systematic studies of hydrogen storage in Pd and Pt nanoparticles have clarified the origins of these nanosize effects. We found a novel hydrogen absorption site in the hetero‐interface that forms between the Pd core and Pt shell of the Pd/Pt core/shell‐type bimetallic nanoparticles. It is proposed that the potential formed in the hetero‐interface stabilizes hydrogen atoms rather than interstitials in the Pd core and Pt shells. These results suggest that metal nanoparticles a few nanometers in size can act as a new type of hydrogen storage medium. Based on knowledge of the nanosize effects, we discuss how hydrogen storage media can be designed for improvement of the conditions of hydrogen storage.     

CeO2修饰的Pt/Ni催化剂在碱性溶液中对乙醇电催化氧化性能的增强

有机小分子直接燃料电池具有高能量密度和转换效率、易贮存及运输方便等优点.在过去几十年,有机小分子化合物尤其是乙醇的电催化氧化引起了研究者的关注,高活性和稳定性及低价格的电催化剂的设计和制备一直是乙醇燃料电池的研究热点.本文采用复合电沉积方法制备了Ni和CeO2复合镀层,然后利用Ni置换铂前驱体中Pt的方法制备了纳米CeO2修饰的Pt/Ni电催化剂(Pt/Ni-CeO2).采用X射线衍射(XRD)、扫描电子显微镜(SEM)及能谱仪(EDS)等手段表征了所制样品的组成和相结构、表面形貌及组成成份.XRD结果表明,所制Pt/Ni催化剂主要是PtNi合金相结构.与Pt/Ni相比,Pt/Ni-CeO2催化剂的XRD峰强明显变弱,表明纳米CeO2修饰的Pt/Ni电催化剂的结晶性较差或者其晶体颗粒较小.这可能是由于CeO2的共沉积阻止了Ni纳米颗粒的进一步生长或团聚.当电镀液中CeO2含量为50和100 mg/L时,所制Pt/Ni-CeO2催化剂样品Pt/NiCe1和Pt/NiCe2的XRD谱上未观察到CeO2相关的衍射峰,这主要可归因于催化剂中沉积的CeO2量少或其高度分散.随着电镀液中CeO2浓度进一步增大到200 mg/L时,在Pt/Ni-CeO2催化剂(Pt/NiCe4)的XRD谱上出现了CeO2相关的衍射峰.这表明采用复合电沉积-化学还原法可以成功制备CeO2修饰的Pt/Ni电催化剂.SEM结果显示,所制催化剂都是由团聚状态的纳米颗粒组成,并且Pt/NiCe2表现出比Pt/Ni更开放的微结构,从而有利于反应物扩散至催化剂内部.该结果进一步表明共沉积的CeO2对所制Pt/Ni催化剂微结构的影响.此外,EDS结果也证实成功制备了CeO2修饰的Pt/Ni电催化剂.采用多次循环伏安、电流时间曲线和电化学阻抗谱(EIS)等手段研究了所制电催化剂的电化学性能.与Pt/Ni相比,Pt/Ni-CeO2催化剂表现出更好的电催化氧化乙醇活性和稳定性,这可能与CeO2的贮氧特性及其共沉积增大了电极的粗糙度有关.红外光谱测试结果表明,在CeO2修饰的Pt/Ni电催化剂催化氧化乙醇过程中,CH3COO?可能是乙醇氧化的主要产物.在所制催化剂中,CeO2含量影响其电催化氧化乙醇性能.循环伏安和电流时间曲线测试结果表明,随着催化剂中CeO2含量增大,催化剂活性先增加后减弱.电化学阻抗谱结果表明,随着CeO2含量增大,CeO2修饰的Pt/Ni电催化剂的接触电阻先增大后变小再变大;而电荷转移电阻不断变小.在电解液中含有100 mg/L CeO2时所制电催化剂(Pt/NiCe2)具有最佳的电催化氧化乙醇活性和稳定性.这主要与CeO2的贮氧功能、Pt与CeO2/Ni间的相互作用和其较小的接触电阻和电荷转移电阻有关.该结果可为设计和制备低价格、高活性乙醇燃料电池中的催化剂提供思路.     

Photoassisted charge behavior of hydrogen storage alloy-TiO2/Pt electrodes

The photoassisted charge behavior of hydrogen storage alloy modified with TiO2/Pt nanocomposites (HSA-TiO2/Pt electrode) was investigated. The HSA-TiO2/Pt electrode can be photocharged under current. The mechanism of photoassisted behavior of the HSA-TiO2/Pt electrode was explained through the results of cyclic voltammogram and impedance measurements of the HSA-TiO2/Pt electrode. Upon illumination, the photogenerated electrons can charge the electrode, but the photogenerated holes may oxidize the hydrogen storage alloy to form a layer of metal oxide. Because the current could keep the electrode active, the H atoms produced by photogenerated electrons diffused to the hydrogen storage alloy and a metal hydride formed. The electrode delivered a higher discharge capacity due to the assistance of photocharge.     

氢化燃烧法合成La1.5Ni0.5Mg17的工艺优化

采用正交实验设计方法安排实验，运用L9(3^4)优化氢化燃烧法合成La1.5Ni0.5Mg17的工艺，考察了施压制饼时间、合成保温时间、合成起始氢气压力、保温温度4个因素对储氢材料的储放氢容量和速率的影响，通过直观分析和方差分析得出优化的工艺为：保温温度903K，制饼施压时间40min，合成起始氢气压力为1MPa，合成保温时间1800min。此条件下合成储氢材料La1.5M0.5Mg17在573K的储放氢容量分别为：5．40和5．15％H(质量分数)；储放氢速率分别为：0．734和0.681％H／min。用XRD分析了材料吸氢和脱氢后的物相结构发现：用Ni适量取代La2Mg17中的La没有导致结构变化，存在的LaNi5，LaH3和La改善了材料的吸放氢速率。     

Influence of surface treatments on micropore structure and hydrogen adsorption behavior of nanoporous carbons

The scope of this work was to control the pore sizes of porous carbons by various surface treatments and to investigate the relation between pore structures and hydrogen adsorption capacity. The effects of various surface treatments (i.e., gas-phase ozone, anodic oxidation, fluorination, and oxygen plasma) on the micropore structures of porous carbons were investigated by N(2)/77 K isothermal adsorption. The hydrogen adsorption capacity was measured by H(2) isothermal adsorption at 77 K. In the result, the specific surface area and micropore volume of all of the treated samples were slightly decreased due to the micropore filling or pore collapsing behaviors. It was also found that in F(2)-treated carbons the center of the pore size distribution was shifted to left side, meaning that the average size of the micropores decreased. The F(2)- and plasma-treated samples showed higher hydrogen storage capacities than did the other samples, the F(2)-treated one being the best, indicating that the micropore size of the porous carbons played a key role in the hydrogen adsorption at 77 K.     

Remarkable hydrogen storage properties for nanocrystalline MgH2 synthesised by the hydrogenolysis of Grignard reagents

The possibility of generating MgH(2) nanoparticles from Grignard reagents was investigated. To this aim, five Grignard compounds, i.e. di-n-butylmagnesium, tert-butylmagnesium chloride, allylmagnesium bromide, m-tolylmagnesium chloride, and methylmagnesium bromide were selected for the potential inductive effect of their hydrocarbon group in leading to various magnesium nanostructures at low temperatures. The thermolysis of these Grignard reagents was characterised in order to determine the optimal conditions for the formation of MgH(2). In particular, the use of di-n-butylmagnesium was found to lead to self-assembled and stabilized nanocrystalline MgH(2) structures with an impressive hydrogen storage capacity, i.e. 6.8 mass%, and remarkable hydrogen kinetics far superior to that of milled or nanoconfined magnesium. Hence, it was possible to achieve hydrogen desorption without any catalyst at 250 °C in less than 2 h, while at 300 °C, hydrogen desorption took only 15 min. These superior performances are believed to result from the unique physical properties of the MgH(2) nanocrystalline architecture obtained after hydrogenolysis of di-n-butylmagnesium.     

Pt@Au/Al2O3核壳纳米粒子的制备和表征及其在催化氧化甲苯中的应用

Customizing core-shell nanostructures is considered to be an efficient approach to improve the catalytic activity of metal nanoparticles. Various physiochemical and green methods have been developed for the synthesis of core-shell structures. In this study, a novel liquid-phase hydrogen reduction method was employed to form core-shell Pt@Au nanoparticles with intimate contact between the Pt and Au particles, without the use of any protective or structure-directing agents. The Pt@Au core-shell nanoparticles were prepared by depositing Au metal onto the Pt core; AuCl⁴⁻ was reduced to Au(0) by H₂ in the presence of Pt nanoparticles. The obtained Pt@Au core-shell structured nanoparticles were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution TEM, fast Fourier transform, powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and H₂-temperature programmed reduction (H₂-TPR) analyses. The EDX mapping results for the nanoparticles, as obtained from their scanning transmission electron microscopy images in the high-angle annular dark-field mode, revealed a Pt core with Au particles grown on its surface. Fourier transform measurements were carried out on the high-resolution structure to characterize the Pt@Au nanoparticles. The lattice plane at the center of the nanoparticles corresponded to Pt, while the edge of the particles corresponded to Au. With an increase in the Au content, the intensity of the peak corresponding to Pt in the FTIR spectrum decreased slowly, indicating that the Pt nanoparticles were surrounded by Au nanoparticles, and thus confirming the core-shell structure of the nanoparticles. The XRD results showed that the peak corresponding to Pt shifted gradually toward the Au peak with an increase in the Au content, indicating that the Au particles grew on the Pt seeds; this trend was consistent with the FTIR results. Hence, it can be stated that the Pt@Au core-shell structure was successfully prepared using the liquid-phase hydrogen reduction method. The catalytic activity of the nanoparticles for the oxidation of toluene was evaluated using a fixed-bed reactor under atmospheric pressure. The XPS and H₂-TPR results showed that the Pt₁@Au₁/Al₂O₃ catalyst had the best toluene oxidation activity owing to its lowest reduction temperature, lowest Au 4d & 4f and Pt 4d & 4f binding energies, and highest Au⁰/Au^δ+ and Pt⁰/Pt²⁺ proportions. The Pt₁@Au₂Al₂O₃ catalyst showed high stability under dry and humid conditions. The good catalytic performance and high selectivity of Pt@Au/Al₂O₃ for toluene oxidation could be attributed to the high concentration of adsorbed oxygen species, good low-temperature reducibility, and strong interaction.     

On the role of TiO<Subscript>2</Subscript> nanoparticles on thermal behavior of flexible polyurethane foam sandwich panels

A series of flexible polyurethane foam (FPUF) and monolithic polyurethane (PU) sandwich panels reinforced with different contents of TiO₂ nanoparticles (0, 0.5 and 1 mass%) have been successfully prepared by compression molding process at room temperature. The influence of TiO₂ nanoparticles on the thermal properties of PU matrix has been investigated by thermogravimetric and dynamic mechanical thermal analysis (DMTA). The morphology of porous structure of FPUF sandwich panels has been characterized by scanning electron microscopy. The presence of TiO₂ nanoparticles as reinforcement has improved the thermal properties of the FPUF and PU sandwich panel samples. It has been observed that FPUF and PU sandwich panel reinforced with 1 mass% of TiO₂ nanoparticles possessed the highest enhancement in thermal properties in all accomplished thermal tests. The DMTA results for the FPUF and PU sandwich panel reinforced with 1 mass% of TiO₂ nanoparticles indicated that the storage modulus and loss modulus have increased about 1.22 and 1.25 times, 1.5 and 1.55 times, respectively, compared to pure samples. Furthermore, the glass transition (T _g) obtained from the damping factor (tanδ) curves has increased 2 and 1 °C for FPUF and PU sandwich panels, respectively.     

Effect of activated graphite nanofibers on electrochemical activities of Pt–Ru nanoparticles for fuel cells

In this work, graphite nanofibers (GNFs) were chemically activated for high specific surface area, small pore diameter, and high oxygen-containing groups with different KOH/GNFs ratios and used as carbon supports of Pt–Ru nanoparticles for fuel cells. As a result, the oxygen functional groups and specific surface area of carbon supports were increased with increasing the ratios of KOH/GNFs up to 4:1, while the average of Pt–Ru nanoparticle size was decreased owing to the improvement of dispersibility of the Pt–Ru/K–GNFs catalysts. The electrochemical activity of the Pt–Ru/K–GNFs catalysts was improved by the larger available active surface area due to the increase of oxygen functional groups and specific surface area. Therefore, it was found that chemical activation using KOH could influence the surface characteristic of carbon supports, resulting in enhanced electrochemical activity of the Pt–Ru/K–GNFs catalysts of fuel cells.     

Hydrogen spillover in Pt-single-walled carbon nanotube composites: formation of stable C-H bonds

Using in situ electrical conductivity and ex situ X-ray photoelectron spectroscopy (XPS) measurements, we have examined how the hydrogen uptake of single-walled carbon nanotubes (SWNTs) is influenced by the addition of Pt nanoparticles. The conductivity of platinum-sputtered single-walled carbon nanotubes (Pt-SWNTs) during molecular hydrogen exposure decreased more rapidly than that of the corresponding pure SWNTs, which supports a hydrogenation mechanism facilitated by "spillover" of dissociated hydrogen from the Pt nanoparticles. C 1s XPS spectra indicate that the Pt-SWNTs store hydrogen by means of chemisorption, that is, covalent C-H bond formation: molecular hydrogen charging at elevated pressure (8.27 bar) and room temperature yielded Pt-SWNTs with up to 16 ± 1.5 at. % sp(3)-hybridized carbon atoms, which corresponds to a hydrogen-storage capacity of 1.2 wt % (excluding the weight of Pt nanoparticles). Pt-SWNTs prepared by the Langmuir-Blodgett (LB) technique exhibited the highest Pt/SWNT ratio and also the best hydrogen uptake.     

Ordered porous carbon with tailored pore size for electrochemical hydrogen storage application

Ordered porous carbon with tailored pore size represents an innovative concept in electrochemical hydrogen storage. This work deals with physical characteristics and electrochemical hydrogen storage behavior of the ordered porous carbons with well-tailored pore size, synthesized by a replica technique using hexagonal mesoporous silica as templates. By using a mixture of two surfactants (HTAB and C16EO8) at different ratios, it is possible to control the wall thickness of silica and, consequently, the pore diameter of carbons within a narrow range of 2.1-2.8 nm. In addition, highly developed ultramicroporosity (pore size smaller than 0.7 nm), which plays a predominant role in hydrogen storage, can be produced in the ordered porous carbons. A discharge capacity of up to 527 mAh/g (corresponding to 1.95 wt % hydrogen storage) has been achieved in 6 M KOH for the ordered porous carbon. Furthermore, the ordered porous carbons also possess excellent capacity retainability after charge-discharge cycles and rate capability.     

Synthesis of flower-like gold nanoparticles and their electrocatalytic activity towards the oxidation of methanol and the reduction of oxygen

This article describes the synthesis of branched flower-like gold (Au) nanocrystals and their electrocatalytic activity toward the oxidation of methanol and the reduction of oxygen. Gold nanoflowers (GNFs) were obtained by a one-pot synthesis using N-2-hydroxyethylpiperazine-N-2-ethanesulphonic acid (HEPES) as a reducing/stabilizing agent. The GNFs have been characterized by UV-visible spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and electrochemical measurements. The UV-visible spectra show two bands corresponding to the transverse and longitudinal surface plasmon (SP) absorption at 532 and 720 nm, respectively, for the colloidal GNFs. The GNFs were self-assembled on a sol-gel-derived silicate network, which was preassembled on a polycrystalline Au electrode and used for electrocatalytic applications. The GNFs retain their morphology on the silicate network; the UV-visible diffuse reflectance spectra (DRS) of GNFs on the silicate network show longitudinal and transverse bands as in the case of colloidal GNFs. The GNFs show excellent electrocatalytic activity toward the oxidation of methanol and the reduction of oxygen. Oxidation of methanol in alkaline solution was observed at approximately 0.245 V, which is much less positive than that on an unmodified polycrystalline gold electrode. Reduction of oxygen to H2O2 and the further reduction of H2O2 to water in neutral pH were observed at less negative potentials on the GNFs electrode. The electrocatalytic activity of GNFs is significantly higher than that of the spherically shaped citrate-stabilized Au nanoparticles (SGNs).     

Design and preparation of poly(lactic acid) hydroxyapatite nanocomposites reinforced with phosphorus‐based organic additive: Thermal,combustion, and mechanical properties studies

A new phosphorus‐based organic additive (PDA) was designed and successfully synthesized using a three‐component reaction for improvement of the thermal and combustion resistance of polylactic acid (PLA). For compensate for mechanical properties of PLA, hydroxyapatite nanoparticles was modified via in situ surface modification with PDA and was used for preparation of PLA nanocomposites. The structure and morphology as well as thermal, combustion, and mechanical properties of the all PLA systems were investigated. The X‐ray diffraction (XRD) and field‐emission scanning electron microscopy (FE‐SEM) results indicated that the presence of PDA as surface modifier has been necessary for a desirable dispersion of hydroxyapatite (HA) nanoparticles in the PLA matrix. The thermal, combustion, and mechanical properties of the PLA system films were investigated using thermogravimetric analysis (TGA), microscale combustion calorimeter (MCC), and tensile test, respectively. The initial decomposition temperature and char residue of PLA containing 6 mass% of PDA along with 2 mass% HA nanoparticles were increased 20°C and 12% respectively, compared with that of the neat PLA. The peak of heat release rate was decreased from 566 W/g for the neat PLA to 412 W/g for PLA containing 2 mass% of PDA along with 6 mass% HA nanoparticles. By incorporation of only 2 mass% HA nanoparticles and 6 mass% of PDA, the tensile strength was obtained 51 MPa higher than that of the neat PLA.     

General synthesis of Pt and Ni co-doped porous carbon nanofibers to boost HER performance in both acidic and alkaline solutions

It is essential to develop efficient electrocatalysts to generate hydrogen from water electrolysis for hydrogen economy. In this work, platinum(Pt) and nickel(Ni) co-doped porous carbon nanofibers(Pt/NiPCNFs) with low Pt content were prepared via an electrospinning, carbonization and galvanic replacement reaction. Because of the high electrical conductivity, abundant electrochemical active sites and synergistic effect between Pt and Ni nanoparticles, the optimized Pt/Ni-PCNFs catalyst shows an e...     

Pt纳米粒子修饰的多孔硅电极的制备及其电催化性能

通过循环伏安法电沉积使直径约为7 nm的Pt纳米粒子均匀地分散于多孔硅表面, 拟用作微型质子交换膜燃料电池的催化电极. 与刷涂法相比较, 电沉积Pt纳米粒子的多孔硅电极(Pt/Si)呈现出高的Pt利用率和增强的电催化活性. 当Pt载量为0.38 mg•cm−2时, 其电化学活性比表面积高达148 cm2•mg−1, 是刷涂相近质量的纳米Pt/C催化剂的多孔硅电极Pt-C/Si的2倍多；该修饰电极对甲醇氧化也呈现了增强的催化性能和好的稳定性, 在0.5 V(vs SCE)极化1 h后电流密度为4.52 mA•cm−2, 而刷涂了相近Pt量的Pt-C/Si电极的电流密度只有0.36 mA•cm−2.     

多孔氮化钛载体上铂催化剂的原子层沉积制备及其催化氧气还原性能

为有效解决铂(Pt)催化剂用于氧气还原反应(ORR)面临的催化活性及稳定性问题,本文首先合成了具有良好导电性、电化学稳定以及耐腐蚀等优点的一维多孔氮化钛(Ti N)纳米管载体材料,然后使用原子层沉积技术(ALD)在Ti N载体上沉积制备了Pt催化剂(ALD-Pt/Ti N),所得的Pt纳米颗粒尺寸均匀、高度分散且与Ti N载体之间存在着较强的相互作用。催化氧气还原活性和稳定性测试表明,所得的ALD-Pt/Ti N对ORR具有较高的催化活性,同时兼具良好的稳定性和耐久性。相比商用Pt/C,ALD-Pt/Ti N的起始电位和稳态极限电流密度与其相近,半波电位则高出了20 m V,表现出优异的电催化性能。其优良的电催化性能主要归因于ALD沉积Pt纳米颗粒的高分散性,一维多孔结构Ti N载体的高比表面积、良好导电性和抗腐蚀性能以及ALD-Pt与Ti N载体间较强的相互作用等综合影响。本工作为设计新型高催化活性、高稳定性的Pt基催化剂提供了有益借鉴。     

Direct synthesis of platelet graphitic-nanofibres as a highly porous counter-electrode in dye-sensitized solar cells

We synthesized platelet graphitic-nanofibres (GNFs) directly onto FTO glass and applied this forest of platelet GNFs as a highly porous structural counter-electrode in dye-sensitized solar cells (DSSCs). We investigated the electrochemical properties of counter-electrodes made from the highly porous structural GNFs and the photoconversion performance of the cells made with these electrodes.