Highly dense and uniformly dispersed platinum nanoparticles on poly(acrylic acid) modified multi-walled carbon nanotubes for methanol oxidation

Poly(acrylic acid) modified multi-walled carbon nanotubes (PAA-MWNTs) were synthesized through in situ radical polymerization in acetone and the PAA-MWNTs were used as supporting material for platinum nanoparticles. Platinum nanoparticles were deposited on the surface of PAA-MWNTs with high loading and high dispersion through ethylene glycol reduction. The size of Pt nanoparticles on PAA-MWNTs can be tuned by the water content in the reaction system and the loading amount can be adjusted by the mass ratio of H₂PtCl₆ to PAA-MWNTs. The electrocatalytic properties of the Pt/PAA-MWNTs catalyst were evaluated by methanol oxidation. The results of cyclic voltammetry show that the Pt/PAA-MWNTs composite possesses high electrocatalytic activity, good long-term stability and storage property, which can be attributed to the small particle size and high dispersion of Pt nanoparticles as well as the nature of MWNTs.     

Preparation of platinum inverse opals using self-assembled templates and their application in methanol oxidation

Synthetic opals were prepared on indium tin oxide (ITO) glass substrates from a highly monodisperse polystyrene dispersion. Platinum was then electrodeposited through the interstitial space of the opal matrix. The platinum inverse opal (Pt-IOp) was subsequently obtained by the removal of the polystyrene template, leaving a highly ordered three dimensional structure. Both the opal template and platinum (Pt) inverse opal were characterised by scanning electron microscopy, UV–visible spectroscopy and cyclic voltammetry. The results confirmed that the Pt inverse opal (Pt-IOp) has a microporous structure with high surface area and exhibits excellent electrochemical property. The electrocatalytic application of the resulting nanostructured Pt inverse opal electrodes for methanol oxidation was also investigated. The nanostructured Pt-IOp electrode showed a catalytic activity and highly stable electrocatalytic performance in methanol oxidation.     

Pt-TiO2纳米管电极的制备及电催化性能

采用电化学阳极氧化-阴极还原法制备Pt-TiO2纳米管电极.扫描电镜(SEM)结果显示TiO2纳米管平均管径100nm,管长470nm,管壁厚20nm,且其比表面积大,同时纳米Pt微粒分散在TiO2纳米管上,且粒径细小,Pt微粒充分裸露,使得Pt-TiO2纳米管电极活性点多,电催化性能高.对甲醇的电催化性能测试表明:同纯Pt电极和Pt-TiO2电极(Pt微粒固定在TiO2致密膜上)相比,Pt-TiO2纳米管电极对甲醇具有更高的电催化活性,其氧化峰电流密度是在纯Pt片电极上的20倍以上.     

Electrochemical characterization of Pt-Ru-Pd catalysts for methanol oxidation reaction in direct methanol fuel cells

PtRuPd nanoparticles on carbon black were prepared and characterized as electrocatalysts for methanol oxidation reaction in direct methanol fuel cells. Nano-sized Pd (2-4 nm) particles were deposited on Pt/C and PtRu/C (commercial products) by a simple chemical reduction process. The structural and physical information of the PtRuPd/C were confirmed by TEM and XRD, and their electrocatalytic activities were measured by cyclic voltammetry and linear sweep voltammetry. The catalysts containing Pd showed higher electrocatalytic activity for methanol oxidation reaction than the other catalysts. This might be attributed to an increase in the electrochemical surface area of Pt, which is caused by the addition of Pd; this results in increased catalyst utilization.     

Electrochemical fabrication of polyaniline/multi-walled carbon nanotube composite films for electrooxidation of methanol

Polyaniline (PANI)/multi-walled carbon nanotubes (MWNTs) composite films were fabricated by electropolymerization of aniline containing well-dissolved MWNTs. The films can be used as catalyst supports for electro-oxidation of methanol. Cyclic voltammogram and Chronoamperogram results show that platinum particles deposited on PANI/MWNT composite films exhibit higher electrocatalytic activity towards methanol oxidation than that deposited on pure PANI films. The porous structure and electrical conductivity of PANI films has been significantly changed by introduction of MWNTs, higher surface areas of PANI/MWNT composites has been achieved therefore. It favors for platinum particles to be highly dispersed on the PANI/MWNT composite films and the better electrocatalytic activity of Pt/PANI/MWNT electrode is induced consequently.     

Electro-oxidation of methanol on TiO2 nanotube supported platinum electrodes

TiO2 nanotubes have been synthesized using anodic alumina membrane as template. Highly dispersed platinum nanoparticles have been supported on the TiO2 nanotube. The supported system has been characterized by electron microscopy and electrochemical analysis. SEM image shows that the nanotubes are well aligned and the TEM image shows that the Pt particles are uniformly distributed over the TiO2 nanotube support. A homogeneous structure in the composite nanomaterials is indicated by XRD analysis. The electrocatalytic activity of the platinum catalyst supported on TiO2 nanotubes for methanol oxidation is found to be better than that of the standard commercial E-TEK catalyst.     

载铂TiO2纳米管的制备与表征

对在TiO2纳米管表面上沉积铂进行了研究．HRTEM、XPS结果表明：第一步沉积在粉末TiO2表面上的铂粒为纳米尺寸，系由PtO2和Pt(OH)2组成；第二步制成纳米管后，铂粒在纳米管外表面分布均匀．为下一步以TiO2纳米管作为催化剂载体的研究奠定了基础．     

Preparation Ru,Bi monolayer modified Pt nanoparticles as the anode catalyst for methanol oxidation

Platinum nanoparticles were successfully electrodeposited on indium tin oxide (ITO) surface in the solution with hexachloroplatinic acid and copper ion by cyclic voltammogram method. The micrographs and structure of Pt nanoparticles were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. The electrocatalytic properties of Pt nanoparticles/ITO or modified by Ru, Bi underpotential deposition (UPD) for methanol oxidation have been investigated by cyclic voltammetry (CV) and chronoamperometry (CA). High electroactivity and good long-term stability can be observed. These results indicate that Pt nanoparticles modified by UPD may have potential applications in designing noble metal catalysts of fuel cells with low loading and high activity at the atomic level.     

A General Strategy Assisted with Dual Reductants and Dual Protecting Agents for Preparing Pt‐Based Alloys with High‐Index Facets and Excellent Electrocatalytic Performance

Synthesizing noble metallic nanoparticles (NPs) enclosed by high‐index facets (HIFs) is challenged as it involves the tuning of growth kinetics, the selective adsorption of certain chemical species, and the epitaxial growth from HIF enclosed seeds. Herein, a simple and general strategy is reported by using dual reduction agents and dual capping agents to prepare Pt‐based alloy NPs with HIFs, in which both glycine and poly(vinylpyrrolidone) serve as the reductants and capping agents. Due to the facilely tunable growth/nucleation rates and protecting abilities of the reductants and capping agents, Pt concave nanocube (CNC), binary Pt–Ni CNC, ternary Pt–Mn–Cu CNC, and Pt–Mn–Cu ramiform polyhedron alloy NPs terminated by HIFs as well as other NPs with well‐defined morphologies such as Pt–Mn–Cu nanocube and Pt–Mn–Cu nanoflower are obtained with this approach. Owing to the high density of low‐coordinated Pt sites (HIF structure) and the unique electronic effect of Pt–Mn–Cu ternary alloys, the as‐prepared Pt–Mn–Cu NPs show enhanced catalytic activity toward methanol and formic acid electro‐oxidation reactions with excellent stability. This work provides a promising methodology for designing and fabricating Pt‐based alloy NPs as efficient fuel cell catalyst.     

Pt／C催化剂的制备及其对甲醇电催化氧化的研究

首次报道了以乙二胺四乙酸（EDTA）作为螯合剂,采用硼氢化钠还原氯铂酸制备Pt／C（Pt的质量分数为20％）纳米催化剂,TEM分析表明,通过改变反应的pH值可以获得分散度与粒径不同的Pt粒子,当pH=12．5时,Pt的分散度最高,平均粒径最小（3．2nm）。催化剂的退火处理研究表明,经270℃氮气氛围内退火后,其电催化活性有了显著提高。使用循环伏安法在甲醇的溶液中电催化氧化研究结果表明,在pH=12．5时制备的催化剂对甲醇的电催化氧化活性最高。     

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。     

Electrocatalytic activity of surface atoms of platinum supported on silicon

The influence of a carrier matrix on the electrocatalytic activity of platinum nanoparticles with respect to the reaction of methanol oxidation in an acid medium has been studied using a cyclic voltammetry technique. Platinum nanoparticles were formed on the surface of carbon black (commercial E-TEK type catalyst), p-type silicon single-crystals wafers with different resistivities, and mesoporous silicon. It is established that the activity of surface Pt atoms is higher for platinum nanoparticles supported on silicon than on carbon black. An increase in the resistivity of silicon favors growth in the catalytic activity of platinum. The most pronounced carrier effect is produced by the mesoporous silicon matrix.     

Improvement of resistive switching characteristics in ZrO2 film by embedding a thin TiOx layer

The stabilization of the resistive switching characteristics is important to resistive random access memory (RRAM) device development. In this paper, an alternative approach for improving resistive switching characteristics in ZrO(2)-based resistive memory devices has been investigated. Compared with the Cu/ZrO(2)/Pt structure device, by embedding a thin TiO(x) layer between the ZrO(2) and the Cu top electrode, the Cu/TiO(x)-ZrO(2)/Pt structure device exhibits much better resistive switching characteristics. The improvement of the resistive switching characteristics in the Cu/TiO(x)-ZrO(2)/Pt structure device might be attributed to the modulation of the barrier height at the electrode/oxide interfaces.     

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.     

Electrocatalysts for methanol oxidation based on platinum/carbon nanofibers nanocomposite

New carbon nanomaterials, i.e., carbon nanotubes and nanofibers, with special physico-chemical properties, are recently studied as support for methanol oxidation reaction electrocatalysts replacing the most widely used carbon black. Particularly, carbon fibrous structures with high surface area and available open edges are thought to be promising. Platelet type carbon nanofibers, which have the graphene layers oriented perpendicularly to the fiber axis, exhibit a high ratio of edge to basal atoms. Different types of carbon nanofibers (tubular and platelet) were grown by plasma enhanced chemical vapour deposition on carbon paper substrates. The process was controlled and optimised in term of growth pressure and temperature. Carbon nanofibers were characterised by high resolution scanning electron microscopy and X-ray photoelectron spectroscopy to assess the morphological properties. Then carbon nanofibers of both morphologies were used as substrates for Pt electrodeposition. High resolution scanning electron microscopy images showed that the Pt nanoparticles distribution was well controlled and the particles size went down to few nanometers. Pt/carbon nanofibers nanocomposites were tested as electrocatalysts for methanol oxidation reaction. Cyclic voltammetry in H2SO4 revealed a catalyst with a high surface area. Cyclic voltammetry in presence of methanol indicated a high electrochemical activity for methanol oxidation reaction and a good long time stability compared to a carbon black supported Pt catalyst.     

Multi-Layered PtAu Nanoframes and Their Light-Enhanced Electrocatalytic Activity via Plasmonic Hot Spots (Small 17/2023)

Here, the rational design of complex PtAu double nanoframes (DNFs) for plasmon-enhanced electrocatalytic activity toward the methanol oxidation reaction (MOR) is reported. The synthetic strategy for the DNFs consists of on-demand multiple synthetic chemical toolkits, including well-faceted Au growth, rim-on selective Pt deposition, and selective Au etching steps. DNFs are synthesized by utilizing Au truncated octahedrons (TOh) as a starting template. The outer octahedral (Oh) nanoframes (NFs) nest the inner TOh NFs, eventually forming DNFs with a tunable intra-nanogap distance. Residual Au adatoms on Pt skeletons act as light entrappers and produce plasmonic hot spots between inner and outer frames through localized surface plasmon resonance (LSPR) coupling, which promotes enhanced electrocatalytic activity for the MOR. Importantly, the correlation between the gap-induced hot carriers and electrocatalytic activity is evaluated. The highest catalytic activity is achieved when the gap is the narrowest. To further harness their light-trapping capability, hierarchically structured triple NFs (TNFs) are synthesized, wherein three NFs are entangled in a single entity with a high density of hot regions, exhibiting superior electrocatalytic activity toward the MOR with a sixfold larger current density under light irradiation compared to the dark conditions.     

Pt/C doped TiO2/SWNTs as catalyst for methanol oxidation

Platinum/carbon doped titanium dioxide/single-walled carbon nanotubes (Pt/C/TiO2/SWNTs) were successfully prepared by blending method. These composite catalysts were found to exhibit an anatase TiO2 structure with uniform Pt/C and the existence of SWNTs can be confirmed by transmission electron microscopy (TEM). The composite of Pt/C with TiO2/SWNTs could improve an enhancement in catalytic properties upon applying TiO2/SWNTs as catalyst support. The catalytic oxidation of methanol of Pt/C doped TiO2/SWNTs is found to be higher as compared to the undoped and Pt/C doped materials.     

Schottky barrier mediated single-polarity resistive switching in Pt layer-included TiO(x) memory device

A distinct unipolar but single-polarity resistive switching behavior is observed in a TiO(x)/Pt/TiO(x) trilayer structure, formed by thermal oxidation of a Ti/Pt/Ti stack. As a comparison, a memory device with a single TiO(x) active layer (without addition of Pt midlayer) is also fabricated but it cannot perform resistive switching. Energy band diagrams are illustrated to realize the modulation of Schottky barrier junctions and current conduction in TiO(x)-based devices under various biasing polarities. Introduction of the Pt midlayer creates two additional Schottky barriers, which mediate the band bending potential at each metal-oxide interface and attains a rectifying current conduction at the high-resistance state. The rectifying conduction behavior is also observed with an AFM-tip as the top electrode, which implies the rectifying property is still valid when miniaturizing the device to nanometer scale. The current rectification consequently leads to a single-polarity, unipolar resistive switching and electrically rewritable performance for the TiO(x)/Pt/TiO(x) device.     

Fabrication of Supported AuPt Alloy Nanocrystals with Enhanced Electrocatalytic Activity for Formic Acid Oxidation through Conversion Chemistry of Layer‐Deposited Pt2+ on Au Nanocrystals

The exploitation of nanoconfined conversion of Au‐ and Pt‐containing binary nanocrystals for developing a controllable synthesis of surfactant‐free AuPt nanocrystals with enhanced formic acid oxidation (FAO) activity is reported, which can be stably and evenly immobilized on various support materials to diversify and optimize their electrocatalytic performance. In this study, an atomic layer of Pt²⁺ species is discovered to be spontaneously deposited in situ on the Au nanocrystal generated from a reverse‐microemulsion solution. The resulting Au/Pt²⁺ nanocrystal thermally transforms into a reduced AuPt alloy nanocrystal during the subsequent solid‐state conversion process within the SiO₂ nanosphere. The alloy nanocrystals can be isolated from SiO₂ in a surfactant‐free form and then dispersedly loaded on the carbon sphere surface, allowing for the production of a supported electrocatalyst that exhibits much higher FAO activity than commercial Pt/C catalysts. Furthermore, by involving Fe₃O₄ nanocrystals in the conversion process, the AuPt alloy nanocrystals can be grown on the oxide surface, improving the durability of supported metal catalysts, and then uniformly loaded on a reduced graphene oxide (RGO) layer with high electroconductivity. This produces electrocatalytic AuPt/Fe₃O₄/RGO nanocomposites whose catalyst‐oxide‐graphene triple‐junction structure provides improved electrocatalytic properties in terms of both activity and durability in catalyzing FAO.     

Highly efficient fibrous dye-sensitized solar cells based on TiO2 nanotube arrays

The structure of fibrous dye-sensitized solar cells, which were constructed by a TiO(2) nanotube array on Ti wire as the photoanode twisted by a Pt wire counter electrode, has been first systematically investigated by accurately controlling the thread pitch distance of screwed Pt wire. It has been revealed that the thread pitch will strongly influence the photovoltaic performance and kinetic processes in fibrous solar cells. The effect of the length of the TiO(2) nanotube on cell performance has also been discussed. After optimization, a relatively universal optimized thread pitch value of 1 mm for fibrous DSCs has been proved and the light-to-electricity conversion efficiency has been remarkably improved to 5.84%.