Co-Assembly of Nanoparticles in Evaporating Aerosol Droplets: Preparation of Nanoporous Pt/TiO2 Composite Particles

Nanoporous Pt/TiO₂ micro-particles were synthesized via an aerosol assisted co-assembly (AACA) route. Aerosol droplets were produced from a colloidal mixture of 5 nm Pt and 20 nm TiO₂ nanoparticles, which formed spherical micro-aggregates of Pt and TiO₂ with average diameter of around 1.2 μm. The resulting composite micro-particles have very open structure with pore sizes ranging from 20 to 200 nm. Pt nanoparticles were found to be well dispersed on the surface of the supporting TiO₂ particles. Electrocatalytic application of the nanoporous Pt/TiO₂ composites was examined through methanol oxidation reaction. The performance of 20 wt% Pt/TiO₂ particles was found to be comparable to that of commercial 20 wt% Pt/carbon black catalyst.     

A study of TiO2/carbon black composition as counter electrode materials for dye-sensitized solar cells

This study describes a systematic approach of TiO₂/carbon black nanoparticles with respect to the loading amount in order to optimize the catalytic ability of triiodide reduction for dye-sensitized solar cells. In particular, the cell using an optimized TiO₂ and carbon black electrode presents an energy conversion efficiency of 7.4% with a 5:1 ratio of a 40-nm TiO₂ to carbon black. Based on the electrochemical analysis, the charge-transfer resistance of the carbon counter electrode changed based on the carbon black powder content. Electrochemical impedance spectroscopy and cyclic voltammetry study show lower resistance compared to the Pt counter electrode. The obtained nanostructures and photo electrochemical study were characterized.     

Platinum Nanoparticles Anchored on TiO2/C Nanowires as a High Performance Catalyst for Hydrogen Peroxide Eletroreduction

In this paper, we employed the as‐prepared TiO₂/C core/shell nanoarrays (TiO₂/C) obtained by a facile thermal evaporation method as a three‐dimensional (3D) architecture to support Pt nanoparticles through an optimized electrodeposition process. The morphology and structure of the as‐prepared electrode are characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Its catalytic performance towards H₂O₂ electroreduction in basic medium is evaluated by linear sweep voltammetry (LSV) and chronoamperometry (CV). Results revealed that the electrode exhibits significantly high catalytic activity. The current density reached –0.172 A cm⁻² in 1 mol dm⁻³ NaOH and 0.5 mol dm⁻³ H₂O₂ at –1.1 V (vs. Ag/AgCl). This high performance might be due to the 3D electrode architecture inheriting the high electronic conductivity from carbon shell and providing a short pathway for the ion diffusion, and the using of Pt owning an excellent catalytic activity.     

Monodispersed hard carbon spherules as a catalyst support for the electrooxidation of methanol

Hard carbon spherules (HCS) were used as support of Pt nanoparticles as electrocatalyst for direct methanol fuel cells (DMFCs). Scanning electron microscopy (SEM) images show that the size of the Pt particles on HCS by reduction of K₂PtCl₆ with ethylene glycol is 4-5 nm. High-resolution transmission electron microscopy (HRTEM) study reveals that the Pt particles on the HCS surface have faceted crystalline structures. The size and aggregation of the Pt particles depend on the surface properties of the carbon support and the medium of the reduction reaction. Cyclic voltammetry and galvanostatic polarization experiments show that the Pt/HCS catalyst exhibits a higher catalytic activity in the electrooxidation of methanol than either the Pt/MCMB or the commercial Pt/Vulcan XC-72 catalyst does.     

The effect of plasma pre-treatment of carbon used as a Pt catalyst support for methanol electrooxidation

Vulcan XC-72 carbon black for use as a catalyst support was treated in three different plasma atmospheres, H₂, Ar and O₂. The results showed that the microstructure and surface functional groups were significantly changed after plasma treatment. Pt/C catalysts were prepared by chemical reduction of H₂PtCl₆ with HCHO and those with untreated and plasma treated carbon black supports were characterized and tested for methanol electrooxidation. TEM showed that the platinum nanoparticles on H₂ and Ar plasma treated carbon were uniform and well distributed. Those on untreated carbon were uniform in most regions but coalesced in others. On O₂ plasma treated carbon agglomeration of the platinum nanoparticles was significant. XRD showed that the catalysts were composed of face-centered cubic Pt nanoparticles and XPS showed that they were metallic with no oxides present. Cyclic voltammetry and chronoamperometry were used to study methanol electrooxidation on the Pt/C catalysts in a solution of 0.5 M H₂SO₄ + 0.5 M CH₃OH, and showed that the catalytic activity those using H₂ and Ar plasma treated carbon was higher than for the untreated one. Catalysts supported by O₂ plasma treated carbon showed no catalytic activity. The treatment atmosphere of carbon therefore had a large effect on the catalyst performance, with the H₂ plasma being the best.     

Multi-walled carbon nanotubes modified by sulfated TiO2 - A promising support for Pt catalyst in a direct ethanol fuel cell

We report the synthesis of multi-walled carbon nanotubes coated with sulfated TiO₂ (S-TiO₂/MWCNTs) as a promising support for Pt catalyst in a direct ethanol fuel cell. Highly dispersed Pt nanoparticles were supported on the S-TiO₂/MWCNT composites by NaBH₄ reduction procedure (Pt-S-TiO₂/MWCNTs). The presence and nature of the catalyst were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy. The size of the sulfated TiO₂ product was about 8 nm, and that of the Pt nanoparticle on the S-TiO₂/MWCNT composites was about 5 nm. The Pt-S-TiO₂/MWCNTs were used to study the electrochemical ethanol oxidation reaction using cyclic voltammetry, chronoamperometry and impedance spectroscopy. The results show that Pt-S-TiO₂/MWCNT catalysts show higher catalytic activity for ethanol oxidation compared with Pt supported on non-sulfated TiO₂/MWCNT composites and commercial Pt/C catalysts.     

Synthesis of hybrid Pt/TiO2 (anatase)/MWCNTs nanomaterials by a combined sol–gel and polyol process

In the present study, hybrid Pt/TiO₂/MWCNTs nanomaterials are prepared successfully by a combined sol–gel and polyol process. The as-prepared nanomaterials are characterized by X-ray diffraction, high resolution transmission electron microscopy, and thermogravimetry analysis. In addition, its catalytic performance by converting CO into CO₂ is also evaluated. Experimental results show that the hybrid Pt/TiO₂/MWCNTs nanomaterials exhibit a mixture of anatase TiO₂ and Pt phases. Multi-wall carbon nanotubes serve as an excellent supporting material where anatase TiO₂ nanoparticles are decorated with well-distributed Pt nanoparticles. Excellent catalytic performance can be revealed for the hybrid Pt/TiO₂/MWCNTs nanomaterials. When compared with its Pt/TiO₂ counterparts where ～ 100% CO conversion occurred at 150 °C, almost 100% conversion of CO into CO₂ can be observed at a temperature ranged from 30 °C to 100 °C.     

Nb–TiO2 supported platinum nanocatalyst for oxygen reduction reaction in alkaline solutions

Platinum based nanocatalyst at home made Nb–TiO₂ support was synthesized and characterized as the catalyst for oxygen reduction reaction in 0.1 mol dm⁻³ NaOH, at 25 °C. Nb doped TiO₂ catalyst support, containing 5% of Nb, has been synthesized by modified acid-catalyzed sol–gel procedure in non-aqueous medium. BET and X-ray diffraction (XRD) techniques were applied for characterization of synthesized supporting material. XRD analysis revealed only presence of anatase TiO₂ phase in synthesized support powder. Existence of any peaks belonging to Nb compounds has not been observed, indicating Nb incorporated into the lattice.Nb–TiO₂ supported Pt nanocatalyst synthesized, using borohydride reduction method, was characterized by TEM and HRTEM techniques. Platinum nanoparticles distribution, over Nb doped TiO₂ support, was quite homogenous. Mean particle size of about 4 nm was found with no pronounced particle agglomeration. Electrochemical techniques: cyclic voltammetry and linear sweep voltammetry at rotating disc electrode were applied in order to study kinetics and estimate catalytic activity of this new catalyst for the oxygen reduction reaction in alkaline solution. Two different Tafel slopes were found: one close to −90 mV dec⁻¹ in low current density region and other approximately −200 mV dec⁻¹ in high current density region, which is in good accordance with literature results for oxygen reduction at Pt single crystals, as well as Pt nanocatalysts in alkaline solutions. Similar specific catalytic activity (expressed in term of kinetic current density per real surface area) of Nb(5%)–TiO₂/Pt catalyst for oxygen reduction reaction in comparison with the carbon supported platinum (Vulcan/Pt) nanocatalyst, was found.     

Formation of carbon nanotubes through ethylene decomposition over supported Pt catalysts and silica-coated Pt catalysts

Ethylene decomposition was performed over supported Pt catalysts to fabricate composites of Pt metal nanoparticles and carbon nanotubes (CNTs). All supported Pt catalysts (Pt/carbon black, Pt/CNT, Pt/MgO, Pt/Al₂O₃ and Pt/SiO₂) showed catalytic activity for ethylene decomposition at 973 K to form CNTs. Pt metal particles were found at tips of CNTs. These results indicate that Pt metal particles have catalytic activity for growth of CNTs through hydrocarbon decomposition. A broad range (5-50 nm) of CNT diameters were formed from the use of supported Pt metal catalysts although Pt metal particles in the catalysts before ethylene decomposition were relatively uniform in size (2-5 nm). These results imply that Pt metal particles in the catalysts aggregated during ethylene decomposition at 973 K. Aggregation of Pt metal particles in catalysts during ethylene decomposition could be suppressed by covering catalysts with silica layers that were a few nanometers thick. Silica-coated Pt catalysts showed high activity for ethylene decomposition to form CNTs with uniform diameters (8-10 nm) despite the uniform coverage of Pt metal particles with silica layers.     

The preparation and characterization of Au@TiO2 nanoparticles and their catalytic activity for CO oxidation

Au@TiO₂ core/shell nanoparticles were synthesized by a simple and efficient one-step method using tetrabutyl titanate as TiO₂ precursor. The samples were characterized by TEM, XRD, UV–vis and XPS. The experiments demonstrated that the average particles size of Au was 10–15 nm, and the thickness of TiO₂ shell was 1–3 nm. TiO₂ shell induced a red-shift of the absorption peak of Au. This material exhibited catalytic activity for CO oxidation. This study offered an approach for CO oxidation by using Au@TiO₂ model catalysts.     

Electrocatalytic activity of Pt nanoparticles deposited on porous TiO2 supports toward methanol oxidation

Porous TiO₂ thin films were prepared on the Si substrate by hydrothermal method, and used as the Pt electrocatalyst support for methanol oxidation study. Well-dispersed Pt nanoparticles with a particle size of 5–7 nm were pulse-electrodeposited on the porous TiO₂ support, which was mainly composed of the anatase phase after an annealing at 600 °C in vacuum. Cyclic voltammetry (CV) and CO stripping measurements showed that the Pt/TiO₂ electrode had a high electrocatalytic activity toward methanol oxidation and an excellent CO tolerance. The excellent electrocatalytic performance of the electrode is ascribed to the synergistic effect of Pt nanoparticles and the porous TiO₂ support on CO oxidation. The strong electronic interaction between Pt and the TiO₂ support may modify CO chemisorption properties on Pt nanoparticles, thereby facilitating CO oxidation on Pt nanoparticles via the bifunctional mechanism and thus improving the electrocatalytic activity of the Pt catalyst toward methanol oxidation.     

Core-shell-type Fe3O4@carbon nanoparticles and their fabrication using silanic/polymeric amino functionalization

A facile strategy for the fabrication of a carbon shell on Fe₃O₄ nanoparticles with a cluster structure has been proposed. Unlike the conventional solvothermal process using an autoclave, the proposed synthesis method could yield core-shell structured Fe₃O₄@C nanoparticles at low temperature and atmospheric pressure. This synthesis method was based on the chemical bonding among the terminal amine groups, introduced on the Fe₃O₄ surface, and carbonization by the catalytic reaction of glucose (carbon source) with sulfuric acid. The properties of the Fe₃O₄@C nanoparticles so obtained depended on the terminal amine groups that modified the iron oxide surface. The effects of the silane- and polymer-based amination on the fabrication of the carbon shell were investigated.     

Preparation of acid-resistant core/shell Fe3O4@C materials and their use as catalyst supports

Core/shell materials with a movable Fe₃O₄ core and a carbon shell were prepared using polypyrrole as carbon precursor. They are good candidates as metal catalyst supports due to their magnetic property and large surface area. The outer carbon shell thickness could be well-controlled. In addition, the Fe₃O₄@C materials displayed good resistance to acids, which would greatly extend their range of use. Because nitrogen atoms originating from pyrrole rings still remained in the carbon shell after calcination, Pd nanoparticles could be anchored on the surface without aggregation. The Fe₃O₄@C/Pd materials showed excellent catalytic performance in the reduction of methylene blue with sodium borohydride as reducing agent. The catalysts could be easily recycled by an external magnetic field and reused without obvious activity loss.     

A novel nanocomposite catalytic cathode for direct methanol fuel cells

We report a new nanocomposite catalytic cathode composed of iron phthalocyanine, platinum, carbon black and Nafion^® (FePc-Pt/C-Nafion^®) which exhibited enhanced catalytic activity for the oxygen reduction reaction (ORR) in the presence of methanol compared with usual Pt/C based electrodes. The catalytic cathode was prepared by depositing Pt colloidal nanoparticles (d_av = 2.2 nm) on a FePc/C support to form a FePc-Pt/C powder and ultrasonically treating a mixture of Nafion^® and the FePc-Pt/C powder in ethanol, followed by loading the mixture on a glassy carbon electrode and drying at 120 °C. In an O₂-saturated H₂SO₄ solution (0.5 M) with methanol (0.5 M), the onset potential (0.92 V vs RHE) over the FePc-Pt/C-Nafion^® electrode shifted by more than 240 mV toward positive relative to that over an electrode prepared with a commercial Pt/C catalyst and Nafion^®. A new kind of catalytic sites constructed by FePc nanocrystals and Pt nanoparticles was found in the FePc-Pt/C-Nafion^® electrode for the first time, which exhibited higher specific activity for ORR than Pt as calculated based on the hydrogen desorption charge.     

Synthesis and characterization of methanol tolerant Pt/TiOx/C nanocomposites for oxygen reduction in direct methanol fuel Cells

Pt/TiO_x/C nanocomposites have been synthesized by depositing hydrated titanium oxide on carbon-supported Pt (Pt/C), reducing H₂PtCl₆ with sodium formate on carbon-supported hydrated titanium oxide (TiO₂/C), and simultaneously depositing hydrated titanium oxide and reducing H₂PtCl₆ with formate on carbon support, followed by heat treatment at 500 and 900 °C in 90% Ar-10% H₂ mixture. The catalytic activity for oxygen reduction was evaluated in half cells with sulfuric acid electrolyte and in single direct methanol fuel cells (DMFC). Tolerance to methanol was studied with half cells containing sulfuric acid mixed with methanol. Charge transfer resistance and electrochemical active surface area of the Pt/TiO_x/C catalysts were studied with impedance and cyclic voltammetry measurements. Both the synthesis methods and heat treatments influence the catalytic activity, and some of the Pt/TiO_x/C composites exhibit higher catalytic activity than Pt/C. The Pt/TiO_x/C catalysts also exhibit better methanol tolerance than Pt/C. The mechanism for the enhanced catalytic activity of Pt/TiO_x/C is discussed.     

Morphological Control of Carbon Carrier in Pt–Carbon Nanocomposites Derived from Photocatalytic Reactions on Titanium(IV) Oxide Powders

Photodeposition of Pt nanoparticle and phenolic polymer on TiO₂ in a deaerated aqueous system containing hexachloroplatinic acid and phenol were investigated. We observed that reductive deposition of Pt nanoparticles with electrons proceeded rapidly, while the oxidative deposition of a phenolic polymer with positive holes was relatively slow. The difference ensured the encapsulation of Pt nanoparticles between the polymer layer and TiO₂. Carbonization of the polymer components followed by removing TiO₂ resulted in the formation of two types of Pt–carbon nanocomposites with different morphologies of carbons, depending on photoirradiation duration. These composites exhibited high levels of catalytic activity and reusability for aqueous oxidation of 1-phenylethanol with molecular oxygen.     

Support Dependence of MeOH Decomposition Over Size-Selected Pt Nanoparticles

We present here the decomposition of methanol over Pt nanoparticles supported on a series of oxide powders. The samples tested may be roughly grouped in two categories consisting of large (∼15–18 nm) and small (∼8–9 nm) Pt particles deposited on reducible (CeO₂, TiO₂) and non-reducible (SiO₂, ZrO₂, Al₂O₃) supports. The smallest particles (∼8 nm), deposited on ZrO₂, were found to be cationic and the most active for the decomposition of methanol. Furthermore, the stability of metallic Pt and its oxides was observed to be dependent on the choice of support. In all Pt containing samples the reaction proceeds via he direct decomposition of methanol, as no significant amounts of by-products were detected in the experimental range of 100–300 °C.     

Synergistic effect of RE2O3 (RE = Sm, Eu and Gd) on Pt/mesoporous carbon catalyst for methanol electro-oxidation

This work aims at developing the synergetic catalysis of rare earth oxides, which can serve as the anchoring sites for Pt and in turn as the active sites for the methanol electro-oxidation. Ordered mesoporous carbon has been modified with RE₂O₃ (RE = Sm, Eu and Gd) and subsequently deposited with Pt nanoparticles by a microwave heating process. The catalytic activities for methanol electro-oxidation are evaluated by cyclic voltammogram, chronoamperometry and electrochemical impedance spectroscopy. Pt/C-Sm₂O₃ exhibits an improvement on dispersion and electrocatalytic performance, with the highest mass activity (145.1 mA mg⁻¹) as well as good stability. A possible mechanism is proposed for the effect of RE₂O₃ on Pt nanoparticles. The adsorbed hydroxyl species supplied by RE₂O₃ in the support are contributed to the release of Pt active sites through CO removal and therefore promote the catalytic activity spontaneously.     

Nanowires embedded porous TiO2@C nanocomposite anodes for enhanced stable lithium and sodium ion battery performance

A porous carbon nanocomposite with embedded TiO₂ nanowires (NWs) was synthesized using a two-step synthetic method in which carbon matrix was obtained by carbonizing a vacuum dried gel. This unique structure in which TiO₂ nanowires uniformly distributed in and tightly bonded to the carbon matrix shortened the electron transport path and reduced the transmission resistance. Nanoporous structure ensured continuous transfer of Li⁺/Na⁺ and supplied a large specific surface area of 280.82 m² g⁻¹ to provide more active sites. Different from other existing works on TiO₂@C anode materials with TiO₂ loading higher than 60 wt%, the obtained very small amount of TiO₂ (~12 wt%) improved the electrochemical and long-cycle performance of carbon substrate with TiO₂ NWs embedded significantly, due to uniformly distributed TiO₂ NWs throughout the carbon matrix. These TiO₂@C composite anodes could deliver a specific capacity of 286 mA h g⁻¹ at 0.3 C, 197 mA h g⁻¹ at 0.15 C for lithium and sodium ion batteries, respectively. It maintained remarkably stable reversible capacities of 128 and 125 mA h g⁻¹ for lithium and sodium ion batteries at 3 C during 2500 cycles, respectively. Smaller fluctuations and smoother curves demonstrated that sodium ion storage was more stable than lithium ion storage for the TiO₂@C composite anode. In addition, the capacitive contributions of TiO₂@C in both systems are quantified by kinetics analysis.     

Electrochemical oxidation of ammonia on carbon-supported bi-metallic PtM (M = Ir, Pd, SnOx) nanoparticles

Ammonia electro-oxidation was studied in alkaline solution on carbon-supported Pt and bimetallic Pt_yM_1−y (M = Pd, Ir, SnO_x and y = 70, 50 at.%) nanoparticles. Catalysts were synthesized using the modified polyol method and deposited on carbon, resulting in 20 wt.% of metal loading. Particle size, structure and surface composition of the particles were investigated using TEM, XRD and XPS. Mean size of PtM bi-metallic nanoparticles varied between 2.0 and 4.7 nm, depending on the second metal (M). XRD revealed the structure of all bi-metallic particles to be face-centered cubic and confirmed alloy formation for Pt_yPd_1−y (y = 70, 50 at.%) and Pt₇Ir₃nanoparticles, as well as partial alloying between Pt and SnO_x. Electrochemical behaviour of ammonia on Pt and PtM nanoparticles is comparable to that expected for bulk Pt and PtM alloys. Addition of Pd to Pt at the nanoscale decreased the onset potential of ammonia oxidation if compared to pure platinum nanoparticles; however stability of the catalyst was poor. For Pt₇(SnO_x)₃, current densities were similar to Pt, whereas catalyst stability against deactivation was improved. It is found that carbon supported Pt₇Ir₃ nanoparticles combine good catalytic activity with enhanced stability for ammonia electro-oxidation. Electronic effect generated between two metals in the bimetallic nanoparticles might be responsible for increase in the catalytic activity of Pd- and Ir-containing catalysts, causing weakening of the adsorption strength of poisonous N_ads intermediate.