High electrocatalytic activity and stability of PtAg supported on rutile TiO2 for methanol oxidation

Rutile TiO₂ is used as a support for the PtAg nanoparticles, and the catalytic activity and stability of PtAg/TiO₂ for the electrooxidation of methanol are investigated. The PtAg nanoparticles with a Pt:Ag atomic ratio of 1:1 are prepared by the chemical co-reduction of the precursors of Pt and Ag, and physical characterizations reveal that the PtAg nanoparticles are evenly dispersed on TiO₂. PtAg/TiO₂ shows significantly higher catalytic activity and stability than PtAg/C, Pt/TiO₂ and Pt/C for methanol oxidation in both alkaline and acidic solutions, indicating that rutile TiO₂ is superior to carbon black as supports and PtAg is superior to Pt in achieving high catalytic activity. Rutile TiO₂ is also shown to be superior to anatase TiO₂ as supports for the PtAg nanoparticles. The results of this study suggest high potential of rutile TiO₂ as a support material for electrocatalysts.     

PtRu nanoalloys loaded on graphene and TiO2 nanotubes co-modified Ti wire as an active and stable methanol oxidation electrocatalyst

Highly active, durable and scalable fuel cell electrocatalysts are highly desirable but challenging. Herein, we first develop a novel catalyst of PtRu nanoalloys loaded on graphene modified anodic TiO₂ nanotubes arrays (TNTs) grown on flexible Ti wires (denoted as PtRu/RGO/TNTs). Electrodeposited reduced graphene oxide (RGO) is used to improve the electric conductivity and facilitate the dispersion of PtRu nanoparticles. TiO₂ nanotubes arrays could guarantee the large surface area, and PtRu nanoalloys are well-dispersed on the inner and external walls of the TNTs as well as the RGO surface, which could facilitate the fast mass transport and enhanced electrocatalytic activity. PtRu nanoalloys with intimate contact between the two metals is conductive to remove the harmful CO-like byproduct, resulting in superior tolerance to CO poisoning. In addition, this work first design and use the spirally flexible Ti wire electrode configuration in direct methanol fuel cell, which shows a highly efficient catalytic performance. Moreover, this kind of catalytic support is a strong candidate for other electrochemical energy conversion devices.     

Construction of CdSe@TiO2 core‐shell nanorod arrays by electrochemical deposition for efficient visible light photoelectrochemical performance

The CdSe@TiO₂ core‐shell nanorod arrays for photoelectrochemical (PEC) application were designed and constructed by a facile electrochemical deposition strategy. The CdSe@TiO₂ photoanodes exhibit highly efficient PEC performance under visible light irradiation, among which the CdSe shell layer thickness can be precisely adjusted by different electrodeposition time. In comparison with nude TiO₂ nanorods, the optimized CdSe@TiO₂ photoanode (TC‐500) shows a significant saturated photocurrent density of 2.1 mA/cm² at 0 V (vs Ag/AgCl), which is attributed to the good distribution of CdSe nanoparticles on TiO₂ nanorod arrays, the favorable band alignment, and the intimate interfacial interaction between CdSe nanoparticles and TiO₂ nanorods. The introduction of CdSe shell layer does not only improve light absorption ability but also enhances photogenerated charge carrier's transfer and separation. This current work systematically studies the accurate adjustment of CdSe shell layer thickness on TiO₂ nanorod arrays by electrochemical deposition strategy and provides a paradigm to design and fabricate heterostructure composite for PEC application.     

Surface treated TiO2 nanorod arrays for the improvement of water splitting

Water splitting is widely employed for the hydrogen production for its abundant sources of water and sunlight. The TiO₂ nanostructures are the most promising materials because of their properties of the non-toxicity and relatively low cost. Surface treatments with TiCl₄ solution and titanium butoxide solution are applied on the TiO₂ nanorod arrays respectively. On the surface of the TiO₂ nanorods, TiO₂ nanoparticles are prepared through hydrolysis of TiCl₄ and homogeneous phase of TiO₂ synthesized with assist of second hydrothermal synthesis in titanium butoxide, resulting in the increase of the surface area of the TiO₂. Comparing with that of the original TiO₂ nanorod arrays, the incident photon-to-electron conversion efficiency (IPCE) of the TiO₂–TiCl₄ and TiO₂–H₂O samples is greatly enhanced by 25% and 250% in the ultraviolet region, respectively. The obviously enhanced activity is due to the larger surface structure after treatments, which could contribute to the improved performance in the water splitting. These surface treatments provide an efficient way to regulate the properties of the TiO₂ nanorod arrays for their extensive applications in the solar device for the hydrogen production.     

Synthesis of Pd/TiO2 nanotubes/Ti for oxygen reduction reaction in acidic solution

Highly ordered and uniformly distributed TiO₂ nanotubes on a pure titanium substrate (TNTs/Ti) are successfully fabricated by a pulse anodic oxidation method as the support for Pd electrocatalyst. Pd is electrochemically deposited onto TNTs/Ti support. The sensitization with SnCl₂ and activation with PdCl₂ are critical for the formation of highly dispersed Pd nanoparticles on the TNTs/Ti support. It has been found that both Pd/TNTs/Ti and Pt electrodes show the similar electrochemical behavior in H₂SO₄, implying the possibility to develop the Pt-free alternative electrocatalyst based on the Pd/TNTs/Ti system in acid medium. The preliminary results in this work show that the Pd/TNTs/Ti catalysts have an acceptable catalytic activity for the oxygen reduction reaction (ORR) in acid medium. The factors influencing the structure of TNTs and the catalytic activity of Pd/TNTs/Ti for the ORR are also studied in detail.     

Influence of Pt deposition on water-splitting hydrogen generation by highly-ordered TiO2 nanotube arrays

Highly-ordered TiO₂ nanotube arrays (TNTAs) were fabricated on Ti sheets by electrochemical anodization. Uniform Pt nanoparticles with an average diameter of 3 nm could be successfully located on the TiO₂ nanotubes on only one side (Pt/TNTAs) or both sides of the Ti sheet (Pt/TNTAs/Pt). Pt/TNTAs, the single-sided Pt deposited TNTAs, could be directly used to split water without a counter electrode. The hydrogen evolution rate can reach 120 μmol h⁻¹ cm⁻² in a mixed solution of 0.5 M Na₂SO₄ and 0.5 M ethylene glycol without any applied bias, which is six times of that by the pure TNTAs. In comparison to the traditional three electrode system, this single-sided Pt deposited TNTAs is a much more simple and efficient water splitting system. Meanwhile, the photoelectrical conversion mechanism has been investigated in detail.     

Pt catalyst supported on titanium suboxide for formic acid electrooxidation reaction

Pt catalysts supported on titanium suboxide (Ti₄O₇), commercial TiO₂ and carbon black were prepared by a borohydride reduction method, respectively, and used as electrocatalysts for direct formic acid fuel cells (DFAFCs). Transmission electron microscopy (TEM) images show that Pt nanoparticles have a poorer dispersion on Ti₄O₇ compared to that on TiO₂ and carbon black due to the hydrophobicity and high density of Ti₄O₇. Nevertheless, according to cyclic voltammetry (CV) and chronoamperometry (CA) results, it is found that the Pt/Ti₄O₇ catalyst possesses better catalytic activity and stability. Besides the high electrical conductivity, it is suggested from X-ray photoelectron spectroscopy (XPS) analyses that the higher content of metallic Pt caused by the Ti₄O₇ support material also contributes to the better catalytic performance of Pt/Ti₄O₇.     

An excellent room-temperature hydrogen sensor based on titania nanotube-arrays

Hydrogen sensors have been fabricated from highly ordered TiO₂ nanotube arrays through anodization of a Ti substrate in an ethylene glycol solution containing NH₄F. The vertically oriented TiO₂ nanotube arrays containing Pt electrodes exhibit an ability to detect a wide-range of hydrogen concentrations at room temperature. On exposure to 2000 ppm (parts per million) hydrogen, the sensors exhibit seven orders of magnitude change in resistance with a response time of 13 s at room temperature. The TiO₂ nanotube arrays sensor equipped with Pt electrodes exhibited a diode-type current–voltage (I–V) characteristic in air, but nearly ohmic behavior in hydrogen balanced with argon. A significant response to hydrogen was observed without the presence of oxygen in the base atmosphere. The response of two kinds of sensors with either Pt or Pt/Ti electrodes to 500 ppm hydrogen was measured and the results suggested that the excellent hydrogen sensing properties in air resulted primarily from the variation of the Schottky barrier height at the Pt/TiO₂ interface.     

Hydrogen production by photocatalytic membranes fabricated by supersonic cluster beam deposition on glass fiber filters

Photoactive membranes coated with TiO₂ and Pt/TiO₂ nanostructured thin films were produced by one-step deposition of gas phase nanoparticles on glass fiber filters. Pt/TiO₂ nanoparticles (0–1.5 wt.% Pt content) were produced by flame spray pyrolysis, starting from liquid solutions of the Ti and Pt precursors, and then expanded in a supersonic beam to be deposited on the filters. The nanostructured coatings were composed of crystalline nanoparticles (mainly anatase phase), without any need of post-deposition annealing. The so obtained photocatalytic membranes were tested in hydrogen production by photo-steam reforming of ethanol in an expressly set-up diffusive photoreactor. The reaction rate was found to increase with increasing the Pt content in the photoactive material, up to 1.5 wt.% Pt. The use of these membranes allowed a significant increase of the hydrogen production rate compared to that obtained with the same photoactive Pt/TiO₂ films deposited on a quartz substrate.     

Titanium dioxide as support material for Pt1Pd3 toward methanol oxidation

The electrocatalytic oxidation of methanol on the Pt₁Pd₃ nanoparticles supported on rutile TiO₂ in alkaline solution is investigated. The Pt₁Pd₃ nanoparticles are prepared by the chemical co-reduction of the precursors of Pt and Pd and then loaded on TiO₂. The Pt₁Pd₃ nanoparticles with sizes of about 2–4 nm and a certain degree of aggregation are dispersed on TiO₂. The position and shape of the methanol oxidation peak on Pt₁Pd₃/TiO₂ are more similar to those on Pt/TiO₂ than those on Pd/TiO₂, while Pt₁Pd₃/TiO₂ exhibits higher catalytic activity, e.g., a significantly higher peak intensity, than Pt₁Pd₃/C, Pt/TiO₂ and Pd/TiO₂. This indicates the advantage of TiO₂ as a support material and the strong synergy between the Pt₁Pd₃ and TiO₂ and between the Pt and Pd. Moreover, Pt₁Pd₃/TiO₂ has a high tolerance for the poisoning caused by CO. Rutile TiO₂ is shown to be suitable as a support material for the Pt₁Pd₃ to achieve enhanced catalytic activity and stability.     

Pt modified TiO2 nanotubes electrode: Preparation and electrocatalytic application for methanol oxidation

Pt nanoparticles decorated TiO₂ nanotubes (Pt/TiO₂NTs) modified electrode has been successfully synthesized by depositing Pt in TiO₂NTs, which were prepared by anodization of the Ti foil. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and electrochemical methods were adopted to characterize their structures and properties. The Pt/TiO₂NTs electrode shows excellent electrocatalytic activity toward methanol oxidation reaction (MOR) in alkaline electrolyte without UV irradiation.     

Pt hierarchical structure catalysts on BaTiO3/Ti electrode for methanol and ethanol electrooxidations

Electrooxidations of methanol and ethanol have been investigated on different Pt catalytic titanium-supported electrodes in both acidic and alkaline media using cyclic voltammetry. BaTiO₃ is used for the first time to make a nanoscaled roughness on the surface of Ti foil in order to effectively deposit Pt hierarchical structure and block foulness in solution reactions. The morphology of BaTiO₃ nanocube on Ti foil, Pt catalysts deposited on BaTiO₃/Ti and Ti foil electrodes are characterized by field emission scanning electron microscopy. The results indicate that Pt nanoflowers can be effectively grown on the Ti foil covered with 1 μm layer of BaTiO₃ nanocubes and the catalytic oxidation behaviors to methanol and ethanol are much better than those of the Pt/Ti electrode as Pt nanoparticles can hardly be deposited on the smooth surface of the Ti foil. The Pt/BaTiO₃/Ti electrode could be adopted as excellent catalytic anode in fuel cells.     

Fabrication of TiO2 nanorod array/semiconductor nanocrystal hybrid structure for photovoltaic applications

We present all-inorganic solar cells fabricated from TiO₂ nanorod array and semiconductor nanocrystals. CdSe or CdTe nanocrystals are drop-casted on TiO₂ nanorod arrays to form TiO₂ nanorod array/semiconductor nanocrystal hybrid structure. Thermal annealing is used to remove the organic molecules on the surface of the nanocrystals which could suppress electron transport, resulting in the morphological and structural change of the nanocrystals. For CdSe nanocrystals, p-type transparent semiconductor CuSCN is introduced as solid-state electrolyte to collect holes and TiO₂/CdSe/CuSCN trilayer structure is adopted. While for CdTe nanocrystals, simpler TiO₂/CdTe bilayer structure is adopted. Conversion efficiency of the two solar cells reaches to 0.21% and 0.07%, respectively. The results are a step towards development of high efficiency all-inorganic TiO₂ nanorod array-based solar cells.     

Bimetallic platinum–ruthenium nanoparticles immobilized on reduced graphene oxide-TiO2 (RGO-TiO2) support for ethanol electro oxidation in acidic media

The present work addresses the potentialities of Pt–Ru nanoparticles deposited on a graphene oxide (RGO) and TiO₂ composite support towards electrochemical oxidation of ethanol in acidic media relevant for fuel cell applications. To immobilize platinum–ruthenium bimetallic nanoparticles on to an RGO-TiO₂ nanohybrid support a simple solution-phase chemical reduction method is utilized. An examination using electron microscopy and energy dispersive X-ray spectroscopy (EDS) indicated that Pt–Ru particles of 4–8 nm in diameter are dispersed on RGO-TiO₂ composite support. The corresponding Pt–Ru/RGO-TiO₂ nanocomposite electrocatalyst was studied for the electrochemical oxidation of ethanol in acidic media. Compared to the commercial Pt–Ru/C and Pt/C catalysts, Pt–Ru/RGO-TiO₂ nanocomposite yields higher mass-specific activity of about 1.4 and 3.2 times, respectively towards ethanol oxidation reaction (EOR). The synergistic boosting provided by RGO-TiO₂ composite support and Pt–Ru ensemble together contributed to the observed higher EOR activity and stability to Pt–Ru/RGO-TiO₂ nanocomposite compared with other in-house synthesized Pt–Ru/RGO, Pt/RGO and commercial Pt–Ru/C and Pt/C electrocatalysts. Further optimization of RGO-TiO₂ composite support provides opportunity to deposit many other types of metallic nanoparticles onto it for fuel cell electrocatalysis applications.     

Design and preparation of highly active carbon nanotube-supported sulfated TiO2 and platinum catalysts for methanol electrooxidation

A novel electrocatalyst structure of carbon nanotube-supported sulfated TiO₂ and Pt (Pt-S-TiO₂/CNT) is reported. The Pt-S-TiO₂/CNT catalysts are prepared by a combination of improved sol-gel and ethylene glycol reduction methods. Transmission electron microscopy and X-ray diffraction show that the sulfated TiO₂ is amorphous and is coated uniformly on the surface of the CNTs. Pt nanoparticles of about 3.6 nm in size are homogenously dispersed on the sulfated TiO₂ surface. Fourier transform infrared spectroscopy analysis proves that the CNT surfaces are modified with sulfated TiO₂ and a high concentration of SO_x, and adsorbed OH species exist on the surface of the sulfated TiO₂. Electrochemical studies are carried out using chronoamperometry, cyclic voltammetry, CO stripping voltammetry and impedance spectroscopy. The results indicate that Pt-S-TiO₂/CNT catalysts have much higher catalytic activity and CO tolerance for methanol electrooxidation than Pt/TiO₂/CNTs, Pt/CNTs and commercial Pt/C.     

Pt/ZrO2 catalyst for a single-stage water-gas shift reaction: Ti addition effect

Ti modified Pt/ZrO₂ catalysts were prepared to improve the catalytic activity of Pt/ZrO₂ catalyst for a single-stage WGS reaction and the Ti addition effect on ZrO₂ was discussed based on its characterization and WGS reaction test. Ti impregnation into ZrO₂ increased the surface area of the support and the Pt dispersion. The reducibility of the catalyst was enhanced in the controlled Ti impregnation (∼20 wt.%) over Pt/ZrO₂ by the Pt-catalysed reduction of supports, particularly, at the interface between ZrO₂ and TiO₂. The significant CO₂ gas band in the DRIFTS results of Pt/Ti[20]/ZrO₂ indicated that the Ti addition made the formate decomposition rate faster than the Pt/ZrO₂ catalyst, linked with the enhanced Pt dispersion and reducibility of the catalyst. Consequently, Ti impregnation over the ZrO₂ support led to a remarkably enhanced CO conversion and the reaction rate of Pt/Ti[20]/ZrO₂ increased by a factor of about 3 from the bare Pt/ZrO₂ catalyst.     

Photodeposition of Pt nanoparticles onto TiO2@CNT as high-performance electrocatalyst for oxygen reduction reaction

The commonly used Pt/C catalyst has low durability for oxygen reduction reaction (ORR). In this work, CNT-supported TiO₂ nanoparticles, which synergistically combines the merits of TiO₂ (high stability and strong interactions with the supported Pt nanoparticles) and CNT (high specific surface area and large electrical conductivity), are prepared by a sol-gel process coupled with an annealing process and used as the support for Pt nanoparticles, which are anchored around TiO₂ nanoparticles by a photodeposition technique. The as-synthesized Pt/TiO₂@CNT catalyst exhibits a mass activity 5.3 times as large as that of the commercial Pt/C catalyst (0.358 A mg_Pt⁻¹ vs. 0.067 A mg_Pt⁻¹ at 0.9 V) and an excellent stability (no activity loss after 10000 potential cycles) for ORR, which can be mainly attributed to the lower oxygen adsorption energy of Pt, resulting from the strong metal-support interaction induced by the deposition of Pt nanoparticles around the well-dispersed TiO₂ nanoparticles on CNT.     

Tuning the surface structure and phase structure of PtCu3 nanoparticle for highly efficient electrocatalysts

Significantly improving the catalytic activity and durability of platinum (Pt) based electrocatalysts is crucial for commercial application of fuel cells by tuning structure of Pt alloy nanoparticles. Here, we report a method of tuning structure of PtCu₃ alloy nanoparticle by annealing in different atmospheres. The detailed analyses showed that evolution of surface structure and phase structure of PtCu₃ alloy nanoparticles heat-treated in N₂ atmosphere and N₂/H₂ mixed atmosphere are mainly as follows: (1) when heat-treated in N₂, the crystal phase of PtCu₃ has undergone a transformation from disordered PtCu₃ alloy to ordered PtCu₃ alloy and then to disordered PtCu₃ alloy with the increase of holding time from 30 min to 90 min; (2) when heat-treated in H₂/N₂, a Pt-rich surface is formed on the Pt–Cu nanoparticles due to Pt segregation induced by H₂ adsorption. Electrochemical measurements demonstrated that both PtCu₃/C_-N2 electrocatalysts prepared in N₂ and PtCu₃/C_-N2/H2 electrocatalysts prepared in H₂/N₂ exhibit enhanced mass activities toward the oxygen reduction reaction (ORR) relative to Pt/C electrocatalyst in acidic media. In particular, when the holding time is 90 min, the obtained PtCu₃/C_-N2/H2 electrocatalysts with Pt-rich surface showed highest mass activity of 435 mA/mg_Pt (at 0.9 V vs. RHE), which is four times greater than that of Pt/C catalyst (20 wt.% Pt, 115 mA/mg_Pt). This study provides a promising method for the reasonable design and preparation of low cost and high performance Pt-based electrocatalysts.     

Pt–rGO–TiO2 nanocomposite by UV-photoreduction method as promising electrocatalyst for methanol oxidation

Pt/TiO₂-decorated reduced graphene oxide composite as catalyst for methanol electro-oxidation with three phase junction structure has been synthesized by UV-photoreduction (denoted as p-Pt/rGO@TiO₂). The obtained p-Pt/rGO@TiO₂ has been detailedly characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and chronoamperometry (CA). XRD and TEM characterizations indicate that photoreduction is favorable to anchoring Pt nanoparticles (NPs) (ca. 2.2 nm) at the interface between TiO₂ and reduced graphene oxide (rGO), and forming the Pt, TiO₂ and rGO three phase junction structure. P-Pt/rGO@TiO₂ exhibits a higher activity for methanol electro-oxidation than m-Pt/rGO and m-Pt/rGO@TiO₂ (prepared by microwave-assisted polyol process). Lifetime tests demonstrate that the electrochemical durability of p-Pt/rGO@TiO₂ is improved by a factor of 2 or more as compared with m-Pt/rGO and m-Pt/rGO@TiO₂. XPS characterizations of p-Pt/rGO@TiO₂ reveal stronger interaction between Pt and support hybrid compared with m-Pt/rGO@TiO₂, which facilitates poisoning species removal and prevents Pt nanoparticles from migrating/agglomerating on or detaching from carbon support. This provides a facile and promising strategy to improve both the activity and durability of electrocatalysts for DMFCs.     

Thermally stable Pt/Ti mesh catalyst for catalytic hydrogen combustion

In this study, platinum (Pt) supported on titanium (Ti) mesh catalysts for catalytic hydrogen combustion were prepared by depositing Pt as a thin-layer on metallic or calcined Ti mesh. The Pt thin-layer could be stabilized as uniformly distributed, near nano-sized particles on the surface of calcined Ti mesh by exposing the freshly sputtered Pt to hydrogen. Temperatures between 478 and 525 °C were reached during hydrogen combustion and could be maintained at a hydrogen flow rate of 0.4 normal liter (Nl)/min for several hrs. It was determined that Ti mesh calcination at ≥900 °C formed an oxide layer on the surface of Ti wires, which prevented significant Pt aggregation. X-ray photoelectron spectroscopy revealed that the surface of Ti mesh was fully converted to TiO₂ at ≥900 °C. Raman spectroscopy showed that the majority of TiO₂ was present in the rutile phase, with some minor contribution from anatase-TiO₂. The calcined Ti support was stable through all investigations and did not indicate any signs of degradation.