Enhanced water photolysis with Pt metal nanoparticles on single crystal TiO2 surfaces

Two novel deposition methods were used to synthesize Pt-TiO(2) composite photoelectrodes: a tilt-target room temperature sputtering method and aerosol-chemical vapor deposition (ACVD). Pt nanoparticles (NPs) were sequentially deposited by the tilt-target room temperature sputtering method onto the as-synthesized nanostructured columnar TiO(2) films by ACVD. By varying the sputtering time of Pt deposition, the size of deposited Pt NPs on the TiO(2) film could be precisely controlled. The as-synthesized composite photoelectrodes with different sizes of Pt NPs were characterized by various methods, such as SEM, EDS, TEM, XRD, and UV-vis. The photocurrent measurements revealed that the modification of the TiO(2) surface with Pt NPs improved the photoelectrochemical properties of electrodes. Performance of the Pt-TiO(2) composite photoelectrodes with sparsely deposited 1.15 nm Pt NPs was compared to the pristine TiO(2) photoelectrode with higher saturated photocurrents (7.92 mA/cm(2) to 9.49 mA/cm(2)), enhanced photoconversion efficiency (16.2% to 21.2%), and increased fill factor (0.66 to 0.70). For larger size Pt NPs of 3.45 nm, the composite photoelectrode produced a lower photocurrent and reduced conversion efficiency compared to the pristine TiO(2) electrode. However, the surface modification by Pt NPs helped the composite electrode maintain higher fill factor values.     

Synthesis of CuCorePtShell Nanoparticles as Model Structures for Core–Shell Electrocatalysts by Direct Platinum Electrodeposition on Copper

The synthesis of Cu(core)Pt(shell) model catalysts by the direct electrochemical deposition of Pt on Cu particles is presented. Cu particles with an average diameter of 200 nm have been deposited on glassy‐carbon electrodes by double pulse electrodeposition from a copper sulfate solution. Subsequent deposition from a platinum nitrate solution under potential control allows for a high selectivity of the Pt deposition towards Cu. Using a combination of cyclic voltammetry, XPS and sputtering, the structure of the generated particles has been analyzed and their core–shell configuration proven. It is shown that the electrocatalytic activity for the oxygen reduction is similar to that of other PtCu catalyst systems. The synthesized structures could allow for the analysis of structure–activity relations of core–shell catalysts on the way to the simple and controlled synthesis of supported Cu(core)Pt(shell) nanoparticles as oxygen reduction catalysts.     

Polyaniline/gallium doped ZnO heterostructure device via plasma enhanced polymerization technique: Preparation, characterization and electrical properties

The ZnO and gallium-doped ZnO nanoparticles (NPs) were synthesized by simple chemical method and used for the fabrication of p-polyaniline/n-ZnO heterostructures devices in which polyaniline was deposited by plasma-enhanced polymerization. The increment in the crystallite sizes of gallium doped ZnO nanoparticles from ~21.85 nm to ~32.39 nm indicated the incorporation of gallium ion into the ZnO nanoparticles. The surface and structural studies investigated the participation of protonated N atom for the bond formation between polyaniline and gallium-ZnO through partial hydrogen bonding. Compared to a Pt/polyaniline/ZnO diode, the fabricated Pt/polyaniline/gallium-ZnO heterostructure diode exhibited good rectifying behavior with Current–Voltage characteristics of improved saturation current, low ideality factor, and a high barrier height might due to the efficient charge conduction via gallium ion at the junction of the polyaniline/gallium doped-ZnO interface.

Monolithic integration of three-material microelectrodes for electrochemical detection on PMMA substrates

Monolithic integration of three-material microelectrodes for electrochemical detection on poly (methyl methacrylate) (PMMA) substrates is presented. Au–Ag–Pt three-material electrodes were all fabricated based on polymer compatible photolithography processes, and the fabrication sequence of the electrodes was optimized. The C–Ag–Pt three-electrode system was also demonstrated. To reduce the electrical resistance, the carbon electrode was made on a silver intermediate layer which was simultaneously fabricated with Ag electrodes. A PMMA/poly(dimethylsiloxane) electrochemical sensing microchip with the Au–Ag–Pt three-electrode systems was constructed. The reproducibility of the three-electrode system from single and different microchips was characterized. The performance of the microchip was evaluated by two kinds of electrochemical probes (Ru(bpy)₃Cl₂ and dopamine).     

Electrochemical properties of stoichiometric RuN film prepared by rf-magnetron sputtering: A preliminary study

The electrochemical properties and stability of ruthenium mononitride (RuN) thin films were studied. Coatings of RuN were synthesized on electropolished titanium supports by rf-magnetron sputtering. RuN electrodes appear rather stable against dissolution, independently of pH, but show to possess the greatest stability only in alkaline environment. Under hydrogen evolution conditions the films show relevant catalytic properties, comparable with Pt, Pd and Ru/Ir derivatives; a significant coverage by adsorbed reaction intermediates is involved. These electrodes are of potential application in energetics and sensoring.     

One-step synthesis of Pt nanoparticles/reduced graphene oxide composite with enhanced electrochemical catalytic activity

A one-step electrochemical approach for synthesis of Pt nanoparticles/reduced graphene oxide(Pt/RGO) was demonstrated.Graphene oxide(GO) and chloroplatinic acid were reduced to RGO and Pt nanoparticles(Pt NPs) simultaneously,and Pt/RGO composite was deposited on the fluorine doped SnO 2 glass during the electrochemical reduction.The Pt/RGO composite was characterized by field emission-scanning electron microscopy,Raman spectroscopy and X-ray photoelectron spectroscopy,which confirmed the reduction of GO and chloroplatinic acid and the formation of Pt/RGO composite.In comparison with Pt NPs and RGO electrodes obtained by the same method,results of cyclic voltammetry and electrochemical impedance spectroscopy measurements showed that the composite electrode had higher catalytic activity and charge transfer rate.In addition,the composite electrode had proved to have better performance in DSSCs than the Pt NPs electrode,which showed the potential application in energy conversion.     

Graphene Paper Decorated with a 2D Array of Dendritic Platinum Nanoparticles for Ultrasensitive Electrochemical Detection of Dopamine Secreted by Live Cells

To circumvent the bottlenecks of non‐flexibility, low sensitivity, and narrow workable detection range of conventional biosensors for biological molecule detection (e.g., dopamine (DA) secreted by living cells), a new hybrid flexible electrochemical biosensor has been created by decorating closely packed dendritic Pt nanoparticles (NPs) on freestanding graphene paper. This innovative structural integration of ultrathin graphene paper and uniform 2D arrays of dendritic NPs by tailored wet chemical synthesis has been achieved by a modular strategy through a facile and delicately controlled oil–water interfacial assembly method, whereby the uniform distribution of catalytic dendritic NPs on the graphene paper is maximized. In this way, the performance is improved by several orders of magnitude. The developed hybrid electrode shows a high sensitivity of 2 μA cm^?2 μm ^?1, up to about 33 times higher than those of conventional sensors, a low detection limit of 5 nm, and a wide linear range of 87 nm to 100 μm . These combined features enable the ultrasensitive detection of DA released from pheochromocytoma (PC 12) cells. The unique features of this flexible sensor can be attributed to the well‐tailored uniform 2D array of dendritic Pt NPs and the modular electrode assembly at the oil–water interface. Its excellent performance holds much promise for the future development of optimized flexible electrochemical sensors for a diverse range of electroactive molecules to better serve society.     

Ordered Mesoporous Silica Incorporating Platinum Nanoparticles as Electrode Material for Paracetamol Detection

High ordered mesoporous materials (SBA-15) modified with Al and/or B and Pt nanoparticles (Pt NPs) were used for preparing modified graphite paste electrodes (Pt/M−SBA-15-GPE, where M=Al−, B− or Al−B−) and applied for paracetamol (PA) detection. The electrodes were investigated by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Square wave voltammetry (SWV) technique was used to obtain the analytical parameters for PA detection. The acquired values of electrochemical and analytical parameters recommend the mesoporous compound containing Pt NPs to be used as composite electrode material for PA detection in real samples.     

Fast and Controlled Decorating of Metallic Nanoparticles Using Wall‐jet Configuration

A new method to decorate metallic nanoparticles (NPs) based on the wall‐jet configuration was developed. A homemade wall‐jet amperometric cell coupled to an electronic micropipette was used to decorate Pt NPs with Sb and Sn hydrodynamically through the injection of metallic precursor solutions onto an electrode modified with NPs under applied potential. The method allows the control of the coverage degree (θ) by changing easy handling parameters such as injection flow rate, injected volume and concentration of precursors. The decoration procedure is fast, reproducible, simple and economic, since it only uses a few microlitres of precursors to prepare each electrode composition. It is possible to prepare an average of 1000 electrodes using the same amount of precursors for each one prepared by a conventional method using a typical three‐electrode cell. Sb‐ and Sn‐decorated Pt/C NPs were first evaluated towards diluted glucose electrooxidation in buffer solution. These first insights reveal that the output current density increases with θ_Sb and θ_Sn; Sb‐decorated Pt/C shows the greatest improvement.     

Fabrication and characterisation of nanometre-sized platinum electrodes for voltammetric analysis and imaging

A simple procedure is described for the fabrication of micrometre to nanometre scale Pt electrodes. These electrodes are prepared by etching a fine Pt wire, which is subsequently coated with an electrophoretic paint, deposited anodically or cathodically. The electrodes are characterised by scanning electron microscopy and steady-state linear sweep voltammetry. Voltammetric measurements of the oxidation of aqueous ferrocyanide at electrodes with effective radii varying from 1 μm to 10 nm show the expected increase in irreversibility with increasing mass transport rate. The electrodes are shown to be particularly promising as imaging probes for scanning electrochemical microscopy.     

Designed Synthesis of Well‐Defined Pd@Pt Core–Shell Nanoparticles with Controlled Shell Thickness as Efficient Oxygen Reduction Electrocatalysts

Improving the electrocatalytic activity and durability of Pt‐based catalysts with low Pt content toward the oxygen reduction reaction (ORR) is one of the main challenges in advancing the performance of polymer electrolyte membrane fuel cells (PEMFCs). Herein, a designed synthesis of well‐defined Pd@Pt core–shell nanoparticles (NPs) with a controlled Pt shell thickness of 0.4–1.2 nm by a facile wet chemical method and their electrocatalytic performances for ORR as a function of shell thickness are reported. Pd@Pt NPs with predetermined structural parameters were prepared by in situ heteroepitaxial growth of Pt on as‐synthesized 6 nm Pd NPs without any sacrificial layers and intermediate workup processes, and thus the synthetic procedure for the production of Pd@Pt NPs with well‐defined sizes and shell thicknesses is greatly simplified. The Pt shell thickness could be precisely controlled by adjusting the molar ratio of Pt to Pd. The ORR performance of the Pd@Pt NPs strongly depended on the thickness of their Pt shells. The Pd@Pt NPs with 0.94 nm Pt shells exhibited enhanced specific activity and higher durability compared to other Pd@Pt NPs and commercial Pt/C catalysts. Testing Pd@Pt NPs with 0.94 nm Pt shells in a membrane electrode assembly revealed a single‐cell performance comparable with that of the Pt/C catalyst despite their lower Pt content, that is the present NP catalysts can facilitate low‐cost and high‐efficient applications of PEMFCs.     

Preparation of Co/Pd alloy particles dispersed multiwalled carbon nanotube supported nanocatalysts via gamma irradiation

New multiwalled carbon nanotube/silica supported cobalt-palladium bimetallic nanocatalysts (MWNT@silica/Co–Pd NPs) were prepared by a simple one step gamma irradiation method. The method involves the in-situ surface modification of MWNT with silica (MWNT@silica) and simultaneous formation of Co–Pd bimetallic NPs using gamma irradiation. The bimetallic NPs were stabilized by silica particles formed over the surface of MWNT. Extensive characterization studies have been performed on structural, morphological, and electrochemical, aspects of MWNT@silica/Co–Pd NPs. MWNT@silica/Co–Pd NPs were characterized by field emission scanning microscopy (FESEM), UV–visible spectroscopy, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Raman spectroscopy. The influence of irradiation dosage levels on the stabilizing effect of silica particles has been studied. The electrolytic activities of the MWNT@silica/Co–Pd NPs were investigated by cyclic voltammetry.     

Ensemble size estimation in formic acid oxidation on Bi-modified Pt(111)

The physical dimensions of ensemble structures formed by adsorbed Bi on Pt(111) were estimated and correlations were established between ensemble size and oxidation activity. Measurements were made by examining electrochemical scanning tunneling microscopy (EC-STM) images of Bi irreversibly adsorbed on Pt(111). Percentage coverages of Bi, CO, poison, and ensemble were determined by both EC-STM and cyclic voltammetry. As the fractional Bi coverage increased, from 0.03 to 0.21, the ensemble size decreased, from approximately 9 to 1 nm. Poison formation was inhibited at ensemble sizes less than 2 nm and the turnover frequency of formic acid was enhanced by a factor of 100–200. Bi is hypothesized to not only physically produce the ensembles, but may also chemically alter their electronic properties.     

Electrochemical detection on electrowetting-on-dielectric digital microfluidic chip

In this work, the use of three-electrode electrochemical sensing system with an electrowetting-on-dielectric (EWOD) digital microfluidic device is reported for quantitative analysis of iodide. T-junction EWOD mixer device was designed using arrays of 50-μm spaced square electrodes for mixing buffer reagent and analyte droplets. For fabrication of EWOD chips, 5-μm thick silver EWOD electrodes were formed on a glass substrate by means of sputtering and lift-off process. PDMS and Teflon thin films were then coated on the electrodes by spin coating to yield hydrophobic surface. An external three-electrode system consisting of Au working, Ag reference and Pt auxiliary wires were installed over EWOD electrodes at the end of T-junction mixer. In experiment, a few-microliter droplets of Tris buffer and iodide solutions were moved toward the mixing junction and transported toward electrochemical electrodes by EWOD process. A short processing time within seconds was achieved at EWOD applied voltage of 300 V. The analyte droplets mixed with different concentrations were successfully analyzed by cyclic voltametry. Therefore, the combination of EWOD digital microfluidic and electrochemical sensing system has successfully been demonstrated for rapid chemical analysis with minimal reagent consumption.     

Optimization of Nanohybrid Biosensors Based on Electro-Crosslinked Tannic Acid Capped Nanoparticles/Enzyme

Enzymes/Nanoparticles (NPs) bioconjugates are massively used nowadays to develop thin films for optical and electrochemical biosensors. Nevertheless, their full characterization as a thin coating onto electrodes remains little discussed, in particular the influence of NPs size and enzyme/NPs ratio used in the electrodeposition solution. In this study, GOx (160 kDa) and HRP (44 kDa) were used in association with tannic acid capped gold NPs (a series with sizes from 7 to 40 nm) to electrodeposit biosensor coatings, sensitive towards glucose and H₂O₂, respectively. The electrodeposition process was based on a mussel-inspired electro-crosslinking between gallol moieties of tannic acid (at the surface of NPs) and amine moieties of the enzymes. On one hand, the sensitivity of the GOx/NPs coatings depends strongly on the NP size and the enzyme/NPs molar ratio of the electrodeposition solution. An optimal sensitivity was obtained by electrodeposition of 11 nm NPs at a GOx/NPs molar ratio close to the theoretical value of the enzyme monolayer. On the other hand, a modest influence of the NPs size was found on the sensitivity in the case of the electrodeposited HRP/NPs coatings, reaching a plateau at the HRP/NPs molar ratio close to the value of the theoretical enzyme monolayer. In both cases, the enzyme/NPs molar ratio played a role in the sensitivity. To fully understand the parameters driving the biosensor sensitivity, a comprehensive evaluation of the colloidal state of the bioconjugates is proposed here.     

Sonochemical synthesis of graphene oxide supported Pt–Pd alloy nanocrystals as efficient electrocatalysts for methanol oxidation

Pt–Pd bimetallic nanoparticles supported on graphene oxide (GO) nanosheets were prepared by a sonochemical reduction method in the presence of polyethylene glycol as a stabilizing agent. The synthetic method allowed for a fine tuning of the particle composition without significant changes in their size and degree of aggregation. Detailed characterization of GO-supported Pt–Pd catalysts was carried out by transmission electron microscopy (TEM), AFM, XPS, and electrochemical techniques. Uniform deposition of Pt–Pd nanoparticles with an average diameter of 3 nm was achieved on graphene nanosheets using a novel dual-frequency sonication approach. GO-supported bimetallic catalyst showed significant electrocatalytic activity for methanol oxidation. The influence of different molar compositions of Pt and Pd (1:1, 2:1, and 3:1) on the methanol oxidation efficiency was also evaluated. Among the different Pt/Pd ratios, the 1:1 ratio material showed the lowest onset potential and generated the highest peak current density. The effect of catalyst loading on carbon paper (working electrode) was also studied. Increasing the catalyst loading beyond a certain amount lowered the catalytic activity due to the aggregation of metal particle-loaded GO nanosheets.     

Electrochemical properties of carbon nanotube-supported metallic catalysts prepared by changing a sweep- or step-applied potential

The electrochemical deposition of Pt nanoparticles on carbon nanotube (CNTs) supports and their catalytic activities for an electro-oxidation were investigated. Pt catalysts of 4–12 nm average crystalline size were grown on supports by changing applied potential methods such as sweep-potential or step-potential. Electroplating of 24-min time by a step-applied potential was enough to obtain small crystalline-size 4.6-nm particles, resulting in good electrochemical activity. The catalysts’ loading contents could be controlled by increasing the deposition time. The crystalline sizes and structures of the Pt/support catalysts were analyzed using X-ray diffraction (XRD). The electrochemical properties of the Pt/support catalysts were studied according to their characteristic current–potential curves in a methanol solution. As a result, the electrochemical activity was increased by enlarging the plating time. The activity reached the maximum at 24 min and then decreased. The enhanced electroactivity for catalysts by step-potential methods could be explained by the changes of the crystalline size and crystalline structures of the catalysts.     

Silica veils-conductive diamond powder composite as a new propitious substrate for platinum electrocatalysts

An innovative composite was obtained by a straightforward sol-gel procedure, involving boron-doped diamond powder (BDDP) incorporation into a SiO₂ veil (SiO₂V) matrix. Composite-coated glassy carbon plates were used as substrate for Pt electrochemical deposition, and the electrodes thus obtained (Pt/BDDP–SiO₂V) were compared on a relative basis with those prepared in the absence of the silica matrix (Pt/BDDP). SEM measurements have shown that a BDDP substrate promotes Pt cluster formation, whereas on BDDP–SiO₂V, particles are much smaller (ca. 45 nm to ca. 140 nm). The activity for CH₃OH oxidation was checked by cyclic voltammetry, and it was found that at Pt/BDDP–SiO₂V, the main anodic peak is shifted with ca. 0.35 V toward lower potentials, indicating a considerable improvement in the overall process kinetics. Stripping experiments together with long-term polarization measurements demonstrated that when deposited on the BDDP–SiO₂V support, Pt particles are less susceptible to CO poisoning and this behavior was tentatively ascribed to the presence of a higher relative surface concentration of more stable, oxidized platinum species, as evidenced by XPS.     

Influence of lanthanum on morphology and electrochemical performance of nano-platinum-based catalytic membrane electrode

The current research of platinum (Pt)–based catalysts focuses on reducing Pt loading in the catalysts while enhancing the catalytic activity. As a rare-earth element, lanthanum (La) has demonstrated good synergistic effect with Pt-based catalysts, because of its catalytic promoting capability and high dispersibility. Here, we fabricated La-doped nano-Pt-based catalytic membrane electrode using ion beam sputtering method. The effect of La on the morphology and electrochemical performance of the catalytic membrane electrode was investigated by scanning electron microscope, X-ray photoelectron spectroscopy, and electrochemical measurements. Compared with pure Pt-based sample, the electrochemical activity specific area of the La-doped sample increases by 74.59%, with 63.95% increase in exchange current density. The results also show that La₂O₃ enhances oxygen enrichment of the membrane electrode and reduces interfacial energy among Pt grains while pinning the grain boundaries. In addition, the inductively coupled plasma atomic emission spectroscopy (ICP-AES) measurement shows that the Pt loading in the membrane electrodes is below 0.1 mg/cm². Thus, enhanced catalytic performance is achieved in catalysts with lower Pt loading.     

Pt/Co3O4/3DOM Al2O3：甲苯燃烧的高效催化剂

与硫氧化物、氮氧化物、一氧化碳以及悬浮颗粒一样,大部分挥发性有机物(VOCs)污染大气环境.控制 VOCs排放有多种方法,其中催化氧化法是一种有效技术,关键在于获得高效催化剂.
　　近年来,负载过渡金属和贵金属催化剂因具有比单纯负载贵金属和单纯负载过渡金属氧化物更好的催化性能而备受关注.在负载贵金属催化剂中,高比表面积载体负载 Pt, Pd或 Rh催化剂得到广泛而深入的研究,尽管这些催化剂成本较高,但是其对 VOCs氧化反应显示了很高的低温催化活性.众所周知,催化活性取决于贵金属和 VOCs的种类,不同负载贵金属催化剂对特定反应会表现出不同的催化活性.负载 Pt催化剂对长链碳氢化合物和芳香族化合物氧化反应表现出更高的活性.相对于负载贵金属催化剂,负载过渡金属氧化物催化剂不仅具有良好的氧化活性,而且价格低廉.迄今已发现许多过渡金属氧化物(如 Co3O4, Cr2O3和 MnO2等)对典型 VOCs氧化反应具有催化活性,其中 Co3O4的催化活性尤为突出.研究表明, Co3O4的性质和分散度是决定其性能的关键因素,制备方法、载体性质和过渡金属氧化物负载量对 Co3O4的物化性质具有重要影响,而且在负载 Pt催化剂中添加金属氧化物能改善其催化性能.尽管多孔氧化铝是一种常用的载体材料,但目前尚无文献报道三维有序大孔-介孔氧化铝负载 Co3O4和 Pt纳米粒子催化剂的制备及其对甲苯氧化反应的催化性能.
　　本文采用聚甲基丙烯酸甲酯微球胶晶模板法、等体积浸渍法和聚乙烯醇保护的硼氢化钠还原法制备了三维有序大孔-介孔(3DOM Al2O3)负载 Co3O4和 Pt (xPt/yCo3O4/3DOM Al2O3, Pt的质量分数(x%)为0-1.4%, Co3O4的质量分数(y%)为0-9.2%)纳米催化剂.通过电感耦合等离子体原子发射光谱、X射线衍射、氮气吸附-脱附、扫描电子显微镜、透射电子显微镜、选区电子衍射、X射线光电子能谱及氢气程序升温还原等技术表征了催化剂的物化性质,利用固定床微型石英反应器评价了催化剂对甲苯氧化反应的催化活性.结果表明,xPt/yCo3O4/3DOMAl2O3催化剂具有多级孔结构(大孔孔径为180–200 nm,介孔孔径为4–6 nm),比表面积为94?102 m2/g.粒径为18.3 nm的 Co3O4纳米粒子和粒径为2.3?2.5 nm的 Pt纳米粒子均匀分散在3DOM Al2O3表面.在xPt/yCo3O4/3DOM Al2O3催化剂中,1.3Pt/8.9Co3O4/3DOM Al2O3拥有最高的 Oads浓度、最好的低温还原性和最高的甲苯氧化反应催化活性(当空速为20000mL g–1 h–1时,甲苯转化率达90%的反应温度为160oC).基于催化剂的活性数据和结构表征,我们认为,1.3Pt/8.9Co3O4/3DOM Al2O3优异的催化性能与其高分散的 Pt纳米粒子、高的 Oads浓度、好的低温还原性、Pt和 Co3O4纳米粒子间的强相互作用以及多级孔结构相关.