Kinetic study of oxygen reduction reaction and PEM fuel cell performance of Pt/TiO2-C electrocatalyst

The electrochemical activity and thermal stability of the Pt/TiO₂-C were evaluated in the oxygen reduction reaction (ORR) in acid medium at different temperatures. The platinum was selectively deposited onto the TiO₂ (E_bg = 2.3 eV) by the photo-irradiation of platinum precursor (Pt⁴⁺→Pt⁰). The Pt/TiO₂-C electrocatalyst prepared was characterized by XRD, TEM/EDS, cyclic and lineal voltammetry techniques. TEM images indicated that platinum nanoparticles (<5 nm) were deposited in agglomerates form around the oxide sites. EDS and XRD results confirm the composition and crystalline structure of Pt/TiO₂-C. The thermal stability and electrochemical activity of the Pt/TiO₂-C for ORR at different temperatures (298–343 K) is higher than Pt/C commercial sample (Pt-Etek). A more favorable apparent enthalpy of activation for Pt/TiO₂-C was greatly influenced by addition of oxide in the catalyst compare to Pt-Etek. Single H₂/O₂ fuel cell performance results of Pt/TiO₂-C show an improvement of the power density with the increase of the temperature.     

High quantum efficiency Pt/TiO2 catalyst for sacrificial water reduction

Platinum photodeposition on TiO₂ from methanolic solution of chloroplatinic acid (CPA) is investigated to determine the conditions that give optimum photocatalytic activity towards dehydrogenation of methanol. Conditions favoring nucleation of Pt islets rather than their autocatalytic growth enhance the catalytic activity. Photoplatinization from idoplatinic acid, adsorbing more strongly on TiO₂ than CPA produced more active Pt/TiO₂ catalysts. The best catalyst prepared from CPA yielded H₂ from 12.5% methanol solution at a quantum efficiency of 23.9% whereas for idoplatinic acid based catalysts, the quantum efficiency increased to 42.5%.     

A dye sensitized TiO2 photovoltaic cell constructed with an elastomeric electrolyte

A photovoltaic solar cell employing an elastomeric electrolyte and using a dye-sensitized nanoporous TiO₂ electrode has been assembled. The polymeric electrolyte is poly(epichlorohydrin-co-ethylene oxide) filled with NaI/I₂. This cell exhibits an open-circuit voltage of 0.71 V and a short-circuit current of 0.46 mA cm⁻² under 120 mW cm⁻² of white-light illumination. The overall conversion efficiency of the cell is 0.22%. The polymeric electrolyte behavior under different conditions of external resistance and intensity of light as well as the performance of this photoelectrochemical cell are discussed.     

TiO2 nanotubes promoting Pt/C catalysts for ethanol electro-oxidation in acidic media

In this paper, TiO₂ nanotubes/Pt/C (TNT/Pt/C) catalysts for ethanol electro-oxidation were prepared by co-mixing method in solution. TEM and XRD showed that uniform anatase TiO₂ nanotubes were about 100 nm in length and 8 nm in diameter and the TGA results indicated that the amount of H₂O contained in TiO₂ nanotubes was much more than that in anatase TiO₂. The composite catalysts activities were measured by cyclic voltammetry (CV), chronoamperometry and CO stripping voltammetry at 25 °C in acidic solutions. The results demonstrated that the TNT can greatly enhance the catalytic activity of Pt for ethanol oxidation and increase the utilization rate of platinum. The CO stripping test showed that the TNT can shift the CO oxidation potential to lower direction than TiO₂ does, which is helpful for ethanol oxidation.     

A highly stable TiB2-supported Pt catalyst for polymer electrolyte membrane fuel cells

Pt nanoparticles supported on TiB₂ conductive ceramics (Pt/TiB₂) have been prepared through a liquid reduction method, where the TiB₂ surfaces are stabilized with perfluorosulfonic acid. The prepared Pt/TiB₂ catalyst is characterized with X-ray diffraction (XRD) and TEM techniques, and a rotating disk electrode (RDE) apparatus. The Pt nanoparticles are found to uniformly disperse on the surface of the TiB₂ particles with narrow size distribution. The electrochemical stability of Pt/TiB₂ is evaluated and found highly electrochemically stable compared to a commercial Pt/C catalyst. Meanwhile, the catalyst also shows comparable performance for oxygen reduction reaction (ORR) to the Pt/C. The mechanism of the remarkable stability and comparable activity for ORR on Pt/TiB₂ is also proposed and discussed.     

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.     

Activity of dealloyed PtCo3 and PtCu3 nanoparticle electrocatalyst for oxygen reduction reaction in polymer electrolyte membrane fuel cell

We report a comparative study of the alloy formation and electrochemical activity of dealloyed PtCo₃ and PtCu₃ nanoparticle electrocatalysts for the oxygen reduction reaction (ORR). For the Pt-Co system the maximum annealing temperatures were 650 °C, 800 °C and 900 °C for 7 h to drive the Pt-Co alloy formation and the particle growth. EDS and XRD were employed for the characterization of catalyst powders. The RDE and RRDE experiments were conducted in 0.1 M HClO₄ at room temperature.We demonstrate that the mass and surface area specific ORR activities of Pt-Co and Pt-Cu alloys after voltammetric activation exhibit a considerable improvement compared to those of pure Pt/C. The dealloyed PtCo₃ (800 °C/7 h) electrocatalyst performs 3 times higher in terms of Pt-based mass activity and 4-5 times higher in terms of ECSA-based specific activity than a 28.2 wt.% Pt/C. Dealloyed Pt-Co catalysts (800 °C/7 h) show the most favorable balance between mass and specific ORR activity with a particle size of 2.2 ± 0.1 nm. We hypothesize that geometric strain effects of the dealloyed Pt-Co nanoparticles, similar to those found in dealloyed PtCu₃ nanoparticles, are responsible for the improvement in ORR activity [1].     

Dye-sensitized, nano-porous TiO2 solar cell with poly(acrylonitrile): MgI2 plasticized electrolyte

Dye-sensitized solar cells are promising candidates as supplementary power sources; the dominance in the photovoltaic field of inorganic solid-state junction devices is in fact now being challenged by the third generation of solar cells based on dye-sensitized, nano-porous photo-electrodes and polymer electrolytes. Polymer electrolytes are actually very favorable for photo-electrochemical solar cells and in this study poly(acrylonitrile)-MgI₂ based complexes are used. As ambient temperature conductivity of poly(acrylonitrile)-salt complexes are in general low, a conductivity enhancement is attained by blending with the plasticizers ethylene carbonate and propylene carbonate. At 20 °C the optimum ionic conductivity of 1.9 × 10⁻³ S cm⁻¹ is obtained for the (PAN)₁₀(MgI₂)_n(I₂)_n/10(EC)₂₀(PC)₂₀ electrolyte where n = 1.5. The predominantly ionic nature of the electrolyte is seen from the DC polarization data. Differential scanning calorimetric thermograms of electrolyte samples with different MgI₂ concentrations were studied and glass transition temperatures were determined. Further, in this study, a dye-sensitized solar cell structure was fabricated with the configuration Glass/FTO/TiO₂/Dye/Electrolyte/Pt/FTO/Glass and an overall energy conversion efficiency of 2.5% was achieved under solar irradiation of 600 W m⁻². The I-V characteristics curves revealed that the short-circuit current, open-circuit voltage and fill factor of the cell are 3.87 mA, 659 mV and 59.0%, respectively.     

New materials for polymer electrolyte membrane fuel cell current collectors

Polymer Electrolyte Membrane Fuel cells for automotive applications need to have high power density, and be inexpensive and robust to compete effectively with the internal combustion engine. Development of membranes and new electrodes and catalysts have increased power significantly, but further improvements may be achieved by the use of new materials and construction techniques in the manufacture of the bipolar plates. To show this, a variety of materials have been fabricated into flow field plates, both metallic and graphitic, and single fuel cell tests were conducted to determine the performance of each material. Maximum power was obtained with materials which had lowest contact resistance and good electrical conductivity. The performance of the best material was characterised as a function of cell compression and flow field geometry.     

A novel TiO2/PVC layer for use in a photoelectrochemical cell

Titanium dioxide (TiO₂) has been widely used with UV light to degrade organic waste contaminants. Immobilised layers of TiO₂ on electrode surfaces have shown enhanced activity when appropriate potentials have been applied. In this work, it is shown that a novel immobilised layer of TiO₂ on an electrode, a TiO₂/poly(vinylchloride) composite cast from THF, mineralises acetone or starch when exposed to a xenon arc light only if the electrode is connected to a Pt electrode where concomitant reduction of oxygen occurs. When an isolated electrode with an immobilised TiO₂ layer is exposed to UV light in a solution of starch or acetone, no decrease in acetone or starch concentration is observed.     

Study on surface states of Pt/TiO2 thin film in different atmospheres

In this paper, the surface states of Pt/TiO₂ thin film were tested in air, H₂ and N₂ flows. Pt/TiO₂ was prepared by means of photoreduction of on anatase nano-TiO₂ powders and was coated on the microscopy glass using powder–sol technique. Powder conductivity method was applied in the analysis of surface states. The experimental results show that a new surface state was formed in air flow; which was 0.43 eV lower than the conduction band edge of TiO₂. In N₂ flow, three surface states, with the energy levels of 0.42, 0.62 and 0.90 eV, respectively, were detected. Compared with that tested in airflow, 0.42 and 0.62 eV could be attributed to Pt and floating bond of TiO₂ respectively, while 0.90 eV might have resulted from the Ti³⁺ formed at high temperature in N₂ flow. The conductivity of the sample tested in H₂ flow increased significantly and was almost unchanged with temperature, which could be interpreted by the dissociative adsorption of H₂ on Pt.     

Photocatalytic properties of redox-treated Pt/TiO2 photocatalysts for H2 production from an aqueous methanol solution

The influence of redox-treated Pt/TiO₂ photocatalysts on H₂ production is investigated. Catalyst characterizations are performed by TEM, XPS, XRD, BET, and UV–vis/DR spectroscopy techniques. In terms of production rate, the oxidation treatment shows higher reactivity than the reduction treatment. The reduction treatment allows the formation of metallic Pt(0), which more easily catalyzes the transition of TiO₂ from the anatase to the rutile phases. Reduction-treated Pt/TiO₂ photocatalysts have lower S_BET values than oxidation-treated Pt/TiO₂ photocatalysts due to the higher percentage of TiO₂ in the rutile phase. Combining the results of XPS and optical analyses, PtO/TiO₂ shows a higher energy band gap than metallic Pt(0)/TiO₂, indicating that oxidation-treated Pt/TiO₂ is more capable of achieving water splitting for H₂ production. According to the results of this study, the oxidation treatment of Pt/TiO₂ photocatalysts can significantly enhance the reactivity of photocatalytic H₂ production because of their homogenous distribution, lower phase transition, higher S_BET, and higher energy band gap.     

Comparative studies of polymer electrolyte membrane fuel cell stack and single cell

The polymer electrolyte membrane fuel cell (PEMFC) was investigated comparatively as a single cell and a 30-cell stack. Various types of Nafion membranes, such as Nafion 117, 115, 112 and 105, were tested as electrolyte within the single cell and at different temperatures, among which Nafion 112 gave the optimal result. The 30-cell stack was evaluated at different humidities and temperatures. The potential–current and power–current curves, both for single cell and the stack, were analyzed by computer simulation, whereby the kinetic and mass-transfer parameters were calculated. The long-term performance of the stack and the water production during long-term operation were also measured.     

Water-gas shift reaction over magnesia-modified Pt/CeO2 catalysts

Fuel cells have risen as a clean technology for power generation and much effort has been done for converting renewable feedstock in hydrogen. The water-gas shift reaction (WGS) can be applied aiming at reducing the CO concentration in the reformate. As Pt/CeO₂ catalysts have been pointed out as an alternative to the industrial WGS catalysts, the modification of such systems with magnesium was investigated in this work. It was shown that the addition of MgO to Pt/CeO₂ increased the activity and stability of the catalyst irrespective of the preparation method used, either impregnation or co-precipitation. Based on TPR and IR spectroscopy experiments, it was seen that the presence of magnesium improved ceria reduction favoring the creation of OH groups, which are considered the active sites for the WGS reaction. The evolution of the surface species formed under reaction conditions (CO, H₂O, H₂) observed by DRIFTS evidenced that the formation of formate species and the generation of CO₂ is closely attached to each other; under a reaction stream containing hydrogen the presence of formate species showed to be more relevant while the CO₂ formation was hindered. It is suggested that the addition of MgO favors the formate decomposition and lower the carbonate concentration on the catalyst surface during WGS reaction.     

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.     

Nitrogen-doped carbon coated ZrO2 as a support for Pt nanoparticles in the oxygen reduction reaction

A new nitrogen-doped carbon (CN_x) support for Pt electrocatalysts was prepared by carbonizing polypyrrole on the surface of ZrO₂ (ZrO₂@CN_x) at high temperature. Well-dispersed Pt nanoparticles were easily formed on the ZrO₂@CN_x. The electrocatalyst was characterized by FT-IR, XRD, TEM, XPS. The electrochemical performances indicate that the presence of ZrO₂ modified the electro-structure of Pt on the catalyst surface and that ZrO₂@CN_x had superior oxygen reduction activity compared to a nitrogen-doped carbon coated carbon (C@CN_x).     

Preparation and photocatalytic properties of HLaNb2O7/(Pt,TiO2) perovskite intercalated nanomaterial

A novel perovskite intercalated nanomaterial HLaNb₂O₇/(Pt, TiO₂) is fabricated by successive intercalated reaction of HLaNb₂O₇ with [Pt(NH₃)₄]Cl₂ aqueous solution, n-C₆H₁₃NH₂/C₂H₅OH organic solution and acidic TiO₂ colloid solution, followed by ultraviolet light irradiation. The gallery height and the band gap energy of HLaNb₂O₇/(Pt, TiO₂) is less than 0.6 nm and 3.14 eV, respectively. The photocatalytic activity of HLaNb₂O₇/TiO₂ is superior to that of unsupported TiO₂ and is enhanced by the co-incorporation of Pt. The photocatalytic hydrogen evolution based on HLaNb₂O₇/(Pt, TiO₂) is 240 cm³ h⁻¹ g⁻¹ using methanol as a sacrificial agent under irradiation with wavelength more than 290 nm from a 100-W mercury lamp. High photocatalytic activity of HLaNb₂O₇/(Pt, TiO₂) may be due to the host with rare earth La element and perovskite structure, the quantum size effect of intercalated semiconductor and the coupling effect between host and guest.     

Electrospun Pt/TiO2 hybrid nanofibers for visible-light-driven H2 evolution

One-dimensional (1D) Pt/TiO₂ hybrid nanofibers (HNFs) with different concentrations of Pt were fabricated by a facile two-step synthesis route combining an electrospinning technique and calcination process. X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM) results showed that the Pt nanoparticles (NPs) with the size of 5–10 nm were well dispersed in the TiO₂ nanofibers (NFs). Further investigations from the UV–Vis diffuse reflectance (DR) and X-ray photoelectron spectroscopy (XPS) analysis revealed that some Pt ions were incorporated into the TiO₂ lattice as Pt⁴⁺ state, which contributed to the visible light absorption of TiO₂ NFs. Meanwhile, the Pt²⁺ ions existing on the surface of Pt NPs resulted in the formation of Pt–O–Ti bond at Pt NPs/TiO₂ NFs interfaces that might serve as an effective channel for improving the charge transfer. The as-electrospun Pt/TiO₂ HNFs exhibited remarkable activities for photocatalytic H₂ evolution under visible light irradiation in the presence of l-ascorbic acid as the sacrificial agent. In particular, the optimal HNFs containing 1.0 at% Pt showed the H₂ evolution rate of 2.91 μmol h⁻¹ and apparent quantum efficiency of 0.04% at 420 nm by using only 5 mg of photocatalysts. The higher photocatalytic activity could be ascribed to the appropriate amount of Pt ions doping and excellent electron-sink effect of Pt NPs co-catalysts.     

Effect of uniformity and surface morphology of Pt nanoparticles to enhance oxygen reduction reaction in polymer electrolyte membrane fuel cells

Platinum (Pt)-based electrocatalysts supported by reduced graphene oxide (rGO) is fabricated under microwave-assisted polyol method with various nucleation and growth conditions. The surface morphologies of the Pt nanoparticles (NPs) under various reaction conditions owing to different Pt NP sizes and inter-particle spacings are investigated by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, thermogravimetric analysis, cyclic and linear sweep voltammetry, and electrochemical impedance spectroscopy. The synthesized Pt/rGO catalyst under nucleation and growth times of 10 s and 50 s, respectively, exhibits excellent catalytic activity with increased electrochemical surface area, high density, good uniformity and surface morphology with a particle size and inter-particle spacing of 2.16 nm and 17.2 nm, respectively. These results elucidate the relationship between the Pt NP morphology distribution and oxygen reduction reaction of catalysts in polymer electrolyte membrane fuel cell systems. We also highlight the important role of size and inter-particle spacing on the Pt electrochemical catalystic performance.     

Synthesis and characterization of Cu@Pt/C core-shell structured catalysts for proton exchange membrane fuel cell

A Cu@Pt/C catalyst was synthesized by a two-step reduction method using Vulcan XC-72R as the supporting material. Physical and electrochemical techniques were applied to investigate the structure and performance of the catalyst. X-ray diffraction (XRD) and transmission electron microscopy (TEM) examinations showed that the catalyst has a core-shell structure, the distribution of the catalyst particles is quite uniform, and the particle size ranges from 5 to 6 nm. Cyclic voltammetry (CV) and rotating disk electrode (RDE) tests confirmed the high performance of the Cu@Pt/C catalyst with the atom ratio Cu: Pt of 2.73: 1, making it a promising low-Pt catalyst for proton exchange membrane fuel cell (PEMFC).