One-pot synthesis of Pt/carbon nanotubes by self-regulated reduction for electrocatalysis

This paper describes a method for size-controlled synthesis of Pt nanoparticles and their attachment to the sidewalls of multiwall carbon nanotubes (CNTs) by self-regulated reduction of sodium n-dodecyl sulfate (SDS), without surface pretreatment. The size of the Pt nanoparticles is controlled by adjusting the concentration of SDS. When Pt/CNTs are heated to 500 degrees C in N2 atmosphere, Pt nanochains are formed on the CNTs; some of these nanochains contain small islands. Electrochemical measurements confirm that the electroactivities of the Pt/CNT nanocatalysts increase with a decrease in the size of the Pt nanoparticles. Additionally, comparing with the heated Pt/CNT nanocatalysts containing smooth Pt nanochains, the heated Pt/CNT nanocatalysts containing Pt nanochains with small Pt islands show higher electrocatalysis activities and stability.     

Sphere‐to‐Multipod Transmorphic Change of Nanoconfined Pt Electrocatalyst during Oxygen Reduction Reaction

An oxygen reduction reaction (ORR) catalyst/support system is designed to have Pt nanoparticles nanoconfined in a nanodimensionally limited space. Holey crumpled reduced graphene oxide plates (hCR‐rGO) are used as a carbon support for Pt loading. As expected from interparticular Pt‐to‐Pt distance of Pt‐loaded hCR‐rGO longer than that of Pt/C (Pt‐loaded carbon black as a practical Pt catalyst), the durability of ORR electroactivity along cycles is improved by replacing the widely used carbon black with hCR‐rGO. Unexpected morphological changes of Pt are electrochemically induced during repeated ORR processes. Spherical multifaceted Pt particles are evolved to {110}‐dominant dendritic multipods. Nanoconfinement of a limited number of Pt within a nanodimensionally limited space is responsible for the morphological changes. The improved durability observed from Pt‐loaded hCR‐rGO originates from 1) dendritic pod structure of Pt exposing more active sites to reactants and 2) highly ORR‐active Pt {110} planes dominant on the surface.     

Pt/C催化剂制备及CO催化氧化性能研究

采用大气压介质阻挡放电辅助氢气热还原方法和氢气热还原方法制备Pt/C催化剂,考察了制备方法及Pt负载量对Pt/C催化性能的影响。采用X-射线衍射(XRD)、循环伏安法、CO催化氧化反应研究Pt/C催化剂的晶相结构、电催化性能和CO催化氧化活性。结果表明:大气压介质阻挡放电辅助氢气热还原所制备的样品具有更高的电化学活性和CO催化氧化活性。当Pt负载量在2%到10%之间变化时,Pt/C-PC催化活性随负载量增加而增加。XRD测试结果显示当Pt负载量为2%,5%和10%时,Pt粒径分别为:10.6 nm,9.1 nm和6.4 nm,说明采用等离子体辅助氢气热还原方法制备的Pt/C-PC催化剂,Pt负载量越大,Pt粒径越小,CO催化氧化活性更高。     

Sharp cubic and octahedral morphologies of poly(vinylpyrrolidone)-stabilised platinum nanoparticles by polyol method in ethylene glycol: their nucleation,growth and formation mechanisms

Pt nanoparticles (NPs) were synthesised by a modified polyol method with the addition of silver nitrate. The results showed that the specific shapes of Pt NPs were influenced by the relevant factors, which are the contents of silver nitrate, synthetic time and temperature. A small content of silver nitrate has played an important role in determining their final shapes of platinum NPs. We observed that Pt NPs in the forms of very sharp shapes such as Pt cubes, octahedrons, cuboctahedrons and tetrahedrons have been obtained. In addition, the shape growth mechanisms and formation of Pt NPs have been studied. They exist in both cubic and octahedral shapes. Importantly, Pt nanocrystals can grow into main cubic and octahedral shapes for a short time less than 15?min. Moreover, Pt nanocrystals can also grow into different shapes from cubic and octahedral into spherical ones for several hours. Especially, they exhibited interesting shapes of multiple-branched Pt nanostructures because of their overgrowth and aggregations. Clearly, large cubic and octahedral Pt NPs of 160?nm diameter were observed. The growth and formation of large cubic and octahedral Pt NPs were due to the aggregation of Pt clusters or initial Pt seeds, even small Pt nanocrystals.     

Ultra-thin PtFe-nanowires as durable electrocatalysts for fuel cells

Ultra-thin Pt(x)Fe(y)-nanowires (Pt(x)Fe(y)-NWs) with a diameter of 2-3 nm were successfully prepared through a solution-phase reduction method at Pt-Fe compositions from 1:1 to 2:1. The carbon supported Pt(x)Fe(y)-NWs (Pt(x)Fe(y)-NWs/C) demonstrated higher oxygen reduction reaction (ORR) activity and better electrochemical durability than conventional Pt/C catalyst. After 1000 cycles of 0-1.3 V (versus RHE), the relative electrochemical surface area (ECSA) of Pt(2)Fe(1)-NW/C dropped down to 46%, which was two times better than Pt/C catalyst, and the mass activity at 0.85 V (versus RHE) for Pt(1)Fe(1)-NW/C was 39.9 mA mg(-1)-(Pt), which is twice that for Pt/C (18.6 mA mg(-1)-(Pt)).     

添加Al对燃料电池阴极催化剂(Pt-Fe)/Pt合金微观组织及氧还原催化性能的影响

为提高燃料电池阴极催化剂(Pt-Fe)/Pt合金的氧还原催化活性和稳定性,在Pt-Fe合金体系中引入元素Al,熔炼得到中间合金(Pt-Fe)Al,再经过NaOH溶液定向腐蚀得到(Pt1-xFex)₃Al/Pt合金,用其作为燃料电池氧还原反应的催化剂,并对其结构、催化活性和稳定性进行了研究。结果表明,所制备的催化剂材料(Pt1-xFex)₃Al/Pt合金具有由几个原子层厚的纯Pt外壳和成分为(Pt1-xFex)₃Al的内核构成的双模孔隙且内部互通的包覆式结构。相比于传统燃料电池的氧还原反应催化剂Pt/C材料以及由Pt-Fe体系制备的Pt₄₆Fe₅₄/Pt合金,(Pt1-xFex)₃Al/Pt合金的比活性分别是Pt₄₆Fe₅₄/Pt合金、Pt/C比活性的 1.21倍和2.69倍,其质量活性分别是Pt₄₆Fe₅₄/Pt和Pt/C的1.17倍和5.3倍。在催化稳定性方面,(Pt1-xFex)₃Al/Pt的电化学活性面积在10 000圈伏安循环后衰减到89%,然后趋于稳定,且循环40 000圈后其仍保留80%的电化学活性面积。由此可见,所制备的催化剂材料(Pt1-xFex)₃Al/Pt合金具有较高的催化活性及催化稳定性。     

Pt/AlPO4 nanocomposite thin-film electrodes for ethanol electrooxidation

The enhanced catalytic properties toward ethanol electrooxidation on Pt/AlPO₄ nanocomposite thin-film electrodes were investigated. The Pt/AlPO₄ nanocomposites with various Al/Pt ratios (0.27, 0.57, and 0.96) were fabricated by a co-sputtering method. All of the Pt/AlPO₄ nanocomposites showed a negative shift in the onset potential and a higher current density than those of pure Pt electrode for the electrooxidation of ethanol. Among the various Pt/AlPO₄ nanocomposite thin-film electrodes, the electrode with an atomic ratio of Al to Pt of 0.57 showed the highest electrocatalytic activity for ethanol electrooxidation. The activation enthalpy for the optimum Pt/AlPO₄ nanocomposite was approximately 0.05 eV lower than that of pure Pt. It is believed that the enhancement in catalytic activity is due to the electron-rich Pt resulting from the Fermi-energy difference between Pt and AlPO₄.     

Ultrahigh Mass Activity Pt Entities Consisting of Pt Single atoms,Clusters, and Nanoparticles for Improved Hydrogen Evolution Reaction

Platinum is one of the best-performing catalysts for the hydrogen evolution reaction (HER). However, high cost and scarcity severely hinder the large-scale application of Pt electrocatalysts. Constructing highly dispersed ultrasmall Platinum entities is thereby a very effective strategy to increase Pt utilization and mass activities, and reduce costs. Herein, highly dispersed Pt entities composed of a mixture of Pt single atoms, clusters, and nanoparticles are synthesized on mesoporous N-doped carbon nanospheres. The presence of Pt single atoms, clusters, and nanoparticles is demonstrated by combining among others aberration-corrected annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, and electrochemical CO stripping. The best catalyst exhibits excellent geometric and Pt HER mass activity, respectively ≈4 and 26 times higher than that of a commercial Pt/C reference and a Pt catalyst supported on nonporous N-doped carbon nanofibers with similar Pt loadings. Noteworthily, after optimization of the geometrical Pt electrode loading, the best catalyst exhibits ultrahigh Pt and catalyst mass activities (56 ± 3 A mg⁻¹_Pt and 11.7 ± 0.6 A mg⁻¹_Cat at −50 mV vs. reversible hydrogen electrode), which are respectively ≈1.5 and 58 times higher than the highest Pt and catalyst mass activities for Pt single-atom and cluster-based catalysts reported so far.     

Improved performance of ZnO-based resistive memory by internal diffusion of Ag atoms

An Ag/ZnO/Pt memory device, which has much better resistive switching behaviour than Pt/ZnO/Pt device was demonstrated. The detailed resistive mechanisms for the Pt/ZnO/Pt and the Ag/ZnO/Pt systems are proposed and investigated. Microstructures are observed by transmission electron microscope (TEM), indicating that the formation of conducting path for both systems is different. For the Pt/ZnO/Pt device, the conductive filament path is constructed by the oxygen vacancies from top to bottom electrodes under a larger enough bias at a forming process. For the Ag/ZnO/Pt device, the filament path was grown by oxygen vacancies combined with an internal diffusion of Ag atoms under a large bias and can provide the lowest energy barrier for electrons transported between two electrodes during set and reset processes, which reduces formation of other conducting paths after each switching. Accordingly, the stable switching performance of the Ag/ZnO/Pt device can be achieved over 100 cycles even the thickness of ZnO film <25 nm.     

Gradient-Concentration Design of Stable Core–Shell Nanostructure for Acidic Oxygen Reduction Electrocatalysis

Manipulating the surface structure of electrocatalysts at the atomic level is of primary importance to simultaneously achieve the activity and stability dual-criteria in oxygen reduction reaction (ORR) for proton exchange membrane fuel cells. Here, a durable acidic ORR electrocatalyst with the “defective-armored” structure of Pt shell and Pt–Ni core nanoparticle decorated on graphene (Pt–Ni@Pt_D/G) using a facile and controllable galvanic replacement reaction to generate gradient distribution of Pt–Ni composition from surface to interior, followed by a partial dealloying approach, leaching the minor nickel atoms on the surface to generate defective Pt skeleton shell, is reported. The Pt–Ni@Pt_D/G catalyst shows impressive performance for ORR in acidic (0.1 m HClO₄) electrolyte, with a high mass activity of threefold higher than that of Pt/C catalyst owing to the tuned electronic structure of locally concave Pt surface sites through synergetic contributions of Pt–Ni core and defective Pt shell. More importantly, the electrochemically active surface areas still retain 96% after 20 000 potential cycles, attributing to the Pt atomic shell acting as the protective “armor” to prevent interior Ni atoms from further dissolution during the long-term operation.     

Effective size-controlled synthesis and electrochemical characterization of ordered Pt nanopattern arrays from self-assembling block copolymer template

This work offers an effective size-controlled synthesis of platinum nanoparticle (Pt NP) arrays for electrocatalyst through self-assembled nanopatterns of block copolymers on titanium (Ti) wafers. Size, spacing and uniformity of Pt NP with loading of Pt to a minimum were investigated to be controlled and adjusted in order to improve the electrochemically active surface area (ECSA) and ECSA stability, and Pt concentration in copolymer/chloroplatinic acid (H₂PtCl₆) solution was verified to be one of the most important factors to control the arrays’ structure. In our case, the Pt NPs with predictable size of 5–16.5 nm could be obtained when the Pt concentration is larger than 0.05 mg ml^?1, which the dominant diameter is proved to be proportional to one-third power of the Pt concentration according to the linear relation of templates’ Pt/N mass ratio versus Pt concentration, and the Pt NPs remain highly ordered arrays with predictable spacing when the Pt concentration is larger than 0.125 mg ml^?1. Decrease in Pt concentration from 2 to 0.125 mg ml^?1 is an effective method to improve the ECSA and durability simultaneously. The Pt NP arrays exhibit not only a remarkable initial ECSA value of 106.2 m² g^?1, but also a pseudo-zero particle aggregation possibility during 3000-cycle voltammetry, which is attributed to the high Pt NP dispersion and the ordered arrays that improve the Pt utilization and lower the possibility of aggregation.     

Magnetic properties and microstructures of sputtered epitaxial Co-rich Co-Pt films

Co₃Pt films of various thicknesses were deposited on Pt underlayers by conventional sputtering in order to investigate the effects of Pt underlayers and annealing temperatures on their microstructure and the magnetic properties. XRD and HRTEM analyses reveal perpendicular magnetic anisotropy in films of good epitaxial growth of Co₃Pt (002) on the Pt (111) underlayer when annealed at 300 °C. However, Pt atoms in the Pt underlayer will diffuse seriously into the Co₃Pt layer when the annealing temperature is increased to 375 °C. This changes the compositions to approach equiatomic CoPt, and shows in-plane magnetic anisotropy with soft magnetic properties.     

Interface architecture determined electrocatalytic activity of Pt on vertically oriented TiO(2) nanotubes

The surface atomic structure and chemical state of Pt is consequential in a variety of surface-intensive devices. Herein we present the direct interrelationship between the growth scheme of Pt films, the resulting atomic and electronic structure of Pt species, and the consequent activity for methanol electro-oxidation in Pt/TiO(2) nanotube hybrid electrodes. X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) measurements were performed to relate the observed electrocatalytic activity to the oxidation state and the atomic structure of the deposited Pt species. The atomic structure as well as the oxidation state of the deposited Pt was found to depend on the pretreatment of the TiO(2) nanotube surfaces with electrodeposited Cu. Pt growth through Cu replacement increases Pt dispersion, and a separation of surface Pt atoms beyond a threshold distance from the TiO(2) substrate renders them metallic, rather than cationic. The increased dispersion and the metallic character of Pt results in strongly enhanced electrocatalytic activity toward methanol oxidation. This study points to a general phenomenon whereby the growth scheme and the substrate-to-surface-Pt distance dictates the chemical state of the surface Pt atoms, and thereby, the performance of Pt-based surface-intensive devices.     

Microwave-assisted synthesis of high-loading, highly dispersed Pt/carbon aerogel catalyst for direct methanol fuel cell

A Pt supported on carbon aerogel catalyst has been synthesized by the microwave-assisted polyol process. The Pt supported on carbon aerogel catalyst was characterized by high resolution transmission electron microscopy and X-ray diffraction. The results show a uniform dispersion of spherical Pt nanoparticles 2·5–3·0 nm in diameter. Cyclic voltammetry and chronoamperometry were used to evaluate the electrocatalytic activity of the Pt/carbon aerogel catalyst for methanol oxidation at room temperature. The Pt/carbon aerogel catalyst shows higher electrochemical catalytic activity and stability for methanol oxidation than a commercial Pt/C catalyst of the same Pt loading.     

介孔碳化钨负载铂催化剂对甲醇氧化的电催化性能

采用硬模板法制备了介孔碳化钨(m-WC), 进一步还原铂的前驱体(H2PtCl6)得到Pt/m-WC催化剂。采用X射线粉末衍射(XRD)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等测试手段对样品的物相、结构和形貌进行了表征。结果表明, 所制得的m-WC载体为单一的碳化钨相, 孔径为10~20 nm, Pt/m-WC催化剂中Pt的粒径约为3.4 nm, 主要以金属态形式存在, 相对比较均一的Pt纳米粒子均匀地分散在载体的表面和孔道中。电化学测试结果表明, 与普通WC载Pt催化剂(Pt/c-WC)相比, Pt/m-WC催化剂具有较大的电化学活性表面积, 对甲醇呈现出更高的电催化氧化活性和更好的稳定性。     

Nano-scaled Pt/Ag/Ni/Au contacts on p-type GaN for low contact resistance and high reflectivity

We synthesized the vertical-structured LED (VLED) using nano-scaled Pt between p-type GaN and Ag-based reflector. The metallization scheme on p-type GaN for high reflectance and low was the nano-scaled Pt/Ag/Ni/Au. Nano-scaled Pt (5 A) on Ag/Ni/Au exhibited reasonably high reflectance of 86.2% at the wavelength of 460 nm due to high transmittance of light through nano-scaled Pt (5 A) onto Ag layer. Ohmic behavior of contact metal, Pt/Ag/Ni/Au, to p-type GaN was achieved using surface treatments of p-type GaN prior to the deposition of contact metals and the specific contact resistance was observed with decreasing Pt thickness of 5 A, resulting in 1.5 x 10(-4) ohms cm2. Forward voltages of Pt (5 A)/Ag/Ni contact to p-type GaN showed 4.19 V with the current injection of 350 mA. Output voltages with various thickness of Pt showed the highest value at the smallest thickness of Pt due to its high transmittance of light onto Ag, leading to high reflectance. Our results propose that nano-scaled Pt/Ag/Ni could act as a promising contact metal to p-type GaN for improving the performance of VLEDs.     

Corrosion‐Activated Chemotherapeutic Function of Nanoparticulate Platinum as a Cisplatin Resistance‐Overcoming Prodrug with Limited Autophagy Induction

Despite nanoparticulate platinum (nano‐Pt) has been validated to be acting as a platinum‐based prodrug for anticancer therapy, the key factor in controlling its cytotoxicity remains to be clarified. In this study, it is found that the corrosion susceptibility of nano‐Pt can be triggered by inducing the oxidization of superficial Pt atoms, which can kill both cisplatin‐sensitive/resistance cancer cells. Direct evidence in the oxidization of superficial Pt atoms is validated to observe the formation of platinum oxides by X‐ray absorption spectroscopy. The cytotoxicity is originated from the dissolution of nano‐Pt followed by the release of highly toxic Pt ions during the corrosion process. Additionally, the limiting autophagy induction by nano‐Pt might prevent cancer cells from acquiring autophagy‐related drug resistance. With such advantages, the possibility of further autophagy‐related drug resistance could be substantially reduced or even eliminated in cancer cells treated with nano‐Pt. Moreover, nano‐Pt is demonstrated to kill cisplatin‐resistant cancer cells not only by inducing apoptosis but also by inducing necrosis for pro‐inflammatory/inflammatory responses. Thus, nano‐Pt treatment might bring additional therapeutic benefits by regulating immunological responses in tumor microenvironment. These findings support the idea that utilizing nano‐Pt for its cytotoxic effects might potentially benefit patients with cisplatin resistance in clinical chemotherapy.     

Catalytic properties of Pt cluster-decorated CeO2 nanostructures

Uniform clusters of Pt have been deposited on the surface of capping-agent-free CeO₂ nanooctahedra and nanorods using electron beam (e-beam) evaporation. The coverage of the Pt nanocluster layer can be controlled by adjusting the e-beam evaporation time. The resulting e-beam evaporated Pt nanocluster layers on the CeO₂ surfaces have a clean surface and clean interface between Pt and CeO₂. Different growth behaviors of Pt on the two types of CeO₂ nanocrystals were observed, with epitaxial growth of Pt on CeO₂ nanooctahedra and random growth of Pt on CeO₂ nanorods. The structures of the Pt clusters on the two different types of CeO₂ nanocrystals have been studied and compared by using them as catalysts for model reactions. The results of hydrogenation reactions clearly showed the clean and similar chemical surface of the Pt clusters in both catalysts. The support-dependent activity of these catalysts was demonstrated by CO oxidation. The Pt/CeO₂ nanorods showed much higher activity compared with Pt/CeO₂ nanooctahedra because of the higher concentration of oxygen vacancies in the CeO₂ nanorods. The structure-dependent selectivity of dehydrogenation reactions indicates that the structures of the Pt on CeO₂ nanorods and nanooctahedra are different. Thes differences arise because the metal deposition behaviors are modulated by the strong metal-metal oxide interactions.     

Deposition of platinum nanoparticles on organic functionalized carbon nanotubes grown in situ on carbon paper for fuel cells

Deposition of small Pt nanoparticles of the order of 2-2.5?nm on carbon nanotubes (CNTs) grown directly on carbon paper is demonstrated in this work. Sulfonic acid functionalization of CNTs is used as a means to facilitate the uniform deposition of Pt on the CNT surface. The organic molecules attached covalently to the CNT surface via electrochemical reduction of corresponding diazonium salts are treated with concentrated sulfuric acid and the sulfonic acid sites thus attached are used as molecular sites for Pt ion adsorption, which are subsequently reduced to yield the small Pt nanoparticles. Cyclic voltammograms reveal that, after removal of the organic groups during high temperature reduction, these Pt nanoparticles are in electrical contact with the carbon paper backing. A typical Pt loading of 0.09?mg?cm(-2) is achieved, that shows higher specific surface area of Pt than an E-TEK electrode with Pt loading of 0.075?mg?cm(-2). A membrane and electrode assembly (MEA) is prepared with a Pt/CNT electrode as cathode and an E-TEK electrode as anode, and it offers better performance than a conventional E-TEK MEA.     

Pt nanowire electrodes electrodeposited in PVP for methanol electrooxidation

We report Pt nanowire electrodes fabricated by means of electrodeposition method as a function of molecular weight of polyvinylpyrrolidone (PVP-L and PVP-H). The higher molecular weight of PVP results in a smaller grain size of Pt nanophases in the electrode. The Pt nanowire array electrode electrodeposited with PVP-H shows the smallest gain size of Pt and an excellent catalytic activity for methanol electrooxidation in comparison with pure Pt nanowire array electrodes electrodeposited without PVP and with PVP-L.