Effect of Ti addition to Pt/C catalyst on methanol electro-oxidation and oxygen electro-reduction reactions

Carbon supported binary Pt-Ti alloys were investigated for application in methanol electro-oxidation (MOR) and oxygen electro-reduction reactions (ORR). Various compositions of Pt_100−xTi_x/C (x = 0, 25, 50, and 75) catalysts were synthesized by sequential impregnation of Pt and Ti followed by annealing at 900 °C for 30 min under H₂/Ar flow. X-ray diffraction results showed formation of the Pt₃Ti intermetallic phase in Pt₅₀Ti₅₀ and Pt₂₅Ti₇₅ catalysts after annealing at 900 °C. The Pt₅₀Ti₅₀/C-900 and Pt₂₅Ti₇₅/C-900 catalysts (the ‘-900’ designation indicates the catalyst was annealed at 900 °C) exhibited 103% () and 198% () higher MOR activity, respectively, than in the Pt/C-900 catalyst () at 0.7 V (vs. reversible hydrogen electrode (RHE)). These two catalysts also showed high ORR activity. From a specific activity basis, the Pt₅₀Ti₅₀/C-900 and Pt₂₅Ti₇₅/C-900 catalysts exhibited , respectively, which were 171 and 154% higher than the value of the Pt/C catalyst at 0.8 V (vs. RHE). Methanol-tolerant ORR activity was also investigated, but in the presence of methanol, the Pt₅₀Ti₅₀/C-900 and Pt₂₅Ti₇₅/C-900 catalysts both exhibited poor ORR activity.     

Dye-sensitized solar cell using natural dyes extracted from rosella and blue pea flowers

Dye-sensitized solar cells (DSSCs) were fabricated using natural dyes extracted from rosella, blue pea and a mixture of the extracts. The light absorption spectrum of the mixed extract contained peaks corresponding to the contributions from both rosella and blue pea extracts. However, the mixed extract adsorbed on TiO₂ does not show synergistic light absorption and photosensitization compared to the individual extracts. Instead, the cell sensitized by the rosella extract alone showed the best sensitization, which was in agreement with the broadest spectrum of the extract adsorbed on TiO₂ film. In case that the dyes were extracted at , using water as extracting solvent, the energy conversion efficiency (η) of the cells consisting of rosella extract alone, blue pea extract alone and mixed extract was 0.37%, 0.05% and 0.15%, respectively. The sensitization performance related to interaction between the dye and TiO₂ surface is discussed. The explanations are supported by the light absorption of the extract solution compared to extracts adsorbed on TiO₂ and also dye structures. The effects of changing extracting temperature, extracting solvent and pH of the extract solution are also reported. The efficiency of rosella extract sensitized DSSC was improved from 0.37% to 0.70% when the aqueous dye was extracted at instead of and pH of the dye was adjusted from 3.2 to 1.0. Moreover, DSSC stability was also improved by the changes in conditions. However, the efficiency of a DSSC using ethanol as extracting solvent was found to be diminished after being exposed to the simulated sunlight for a short period.     

Fabrication of multilayer TiO2 thin films for dye-sensitized solar cells with high conversion efficiency by electrophoresis deposition

This research coats a commercial TiO₂ nanoparticle Degussa P25 with good roundness and size uniformity on an indium tin oxide (ITO) glass substrate and to be photoelectrical electrode by electrophoresis deposition. It combined with dye N719, electrolyte I^-/ and counter-electrode of Pt layer to produce dye-sensitized solar cells (DSSCs). Through the electrophoretic technique, a multilayer film of an appropriate thickness is deposited in the suspension containing TiO₂ nanoparticles and isopropanol. In this process, electric current, voltage, and the number of deposition cycles are well controlled to obtain a single TiO₂ film of around 3.3 μm thick. Stacking is then performed to obtain a multilayer-typed TiO₂ film of around 12 μm thick. As the sintering temperature reaches 400 °C, the prepared multilayer TiO₂ film with a good compactness can increase the dye adsorption capability of the thin film and enhance its adsorption percentage. In addition, the heat treatment will transfer a portion of the rutile crystalline into the anatase crystalline, resulting in better material properties for DSSCs application. DSSCs produced are exposed to metal halide lamp and their energy conversion efficiency is measured. The I-V curve of the produced DSSCs shows that it has an excellent energy conversion efficiency of 6.9%.     

Fatty acid methyl ester synthesis catalyzed by solid superacid catalyst /ZrO2–TiO2/La

A new type of solid superacid catalyst with the composition of /ZrO₂–TiO₂ loaded with lanthanum was prepared by precipitation and impregnation. The catalytic performance for the synthesis of fatty acid methyl ester from fatty acid and methanol was investigated. The influences of preparation conditions on catalyst performance were studied, the optimum results of which showed that amount of La(NO₃)₃ was 0.1 wt.%, the concentration of H₂SO₄ for impregnation was 0.5 mol l⁻¹ and calcination temperature was 550 °C. In addition, the effects of reaction parameters on esterification efficiency were also studied. With the catalyst amount of 5 wt.%, methanol amount of 1 ml/g fatty acid (FA) and reaction duration of 5 h at 60 °C, the conversion ratio could reach above 95%. The catalyst recycled without any treatments could exhibit high activity with the conversion efficiency of above 90% after being reused five times.     

Enhanced long-term durability of proton exchange membrane fuel cell cathode by employing Pt/TiO2/C catalysts

Pt/TiO₂/C catalysts are employed as the cathode catalysts for proton exchange membrane fuel cell (PEMFC). The comparative studies on the Pt/C and Pt/TiO₂/C catalysts are conducted with the physical and electrochemical techniques.After the accelerating aging test (AAT), the remaining electrochemical active surface area (EAS) of the Pt/TiO₂/C catalysts is 75.6%, which is larger than that of the Pt/C catalysts (42.6%). The apparent exchange current density () of the oxygen reduction reaction (ORR) at the Pt/C catalysts decreases from 3.02 × 10⁻⁹ to 1.32 × 10⁻¹¹ A cm⁻² after the AAT. And the value of of the ORR at the Pt/TiO₂/C catalysts is 2.88 × 10⁻⁹ A cm⁻² before the AAT and 2.51 × 10⁻⁹ A cm⁻² after the AAT. Furthermore, the output performance degradation of the PEMFC using the Pt/TiO₂/C cathode catalysts is also less than that using the Pt/C catalysts. The particle size of the Pt/C catalysts increases significantly from 5.3 to 26.5 nm after the AAT. The mean particle size of the Pt/TiO₂/C catalysts is 7.3 nm before the AAT and 9.2 nm after the AAT. It can be concluded that the long-term durability of the Pt/TiO₂/C catalysts in a PEMFC is much better than that of the Pt/C catalysts.     

Improved dye-sensitized solar cells by composite ionic liquid electrolyte incorporating layered titanium phosphate

We reported a composite electrolyte prepared by incorporating layered α-titanium phosphate (α-TiP) into a binary ionic liquid of 1-propyl-3-methylimidazolium iodide (PMII) and 1-ethyl-3-methylimidazolium tetrafluoroborate (EmimBF₄) (volume ratio, 13:7) electrolyte. The addition of α-TiP markedly improved the photovoltaic properties of dye-sensitized solar cells (DSSCs) compared to that without α-TiP. The enhancement was explained by improved diffusion of tri-iodide ions, suppressed electron recombination with in the electrolyte and increased lifetime of electrons in mesoscopic TiO₂ film.     

Photocatalytic degradation of oil industry hydrocarbons models at laboratory and at pilot-plant scale

Photodegradation/mineralization (TiO₂/UV Light) of the hydrocarbons: p-nitrophenol (PNP), naphthalene (NP) and dibenzothiophene (DBT) at three different reactors: batch bench reactor (BBR), tubular bench reactor (TBR) and tubular pilot-plant (TPP) were kinetically monitored at pH = 3, 6 and 10, and the results compared using normalized UV light exposition times. The results fit the Langmuir-Hinshelwood (LH) model; therefore, LH adsorption equilibrium constants (K) and apparent rate constants (k) are reported as well as the apparent pseudo-first-order rate constants,  = kK/(1 + Kc_r). The batch bench reactor is the most selective reactor toward compound and pH changes in which the reactivity order is: NP > DBT > PNP, however, the catalyst adsorption (K) order is: DBT > NP > PNP at the three pH used but NP has the highest k values. The tubular pilot-plant (TPP) is the most efficient of the three reactors tested. Compound and pH photodegradation/mineralization selectivity is partially lost at the pilot plant where DBT and NP reaches ca. 90% mineralization at the pH used, meanwhile, PNP reaches only 40%. The real time, in which these mineralization occur are: 180 min for PNP and 60 min for NP and DBT. The mineralization results at the TPP indicate that for the three compounds, the rate limiting step is the same as the degradation one. So that, there is not any stable intermediate that may accumulate during the photocatalytic treatment.     

Cathode reaction models and performance analysis of Sm0.5Sr0.5CoO3−δ-BaCe0.8Sm0.2O3−δ composite cathode for solid oxide fuel cells with proton conducting electrolyte

Cathode reaction models for solid oxide fuel cells with proton conducting electrolyte (H-SOFC) are proposed, and the reacting orders for each elementary step with respect to oxygen and water vapor partial pressure are calculated. The limiting steps of cathode reactions are investigated with Sm_0.5Sr_0.5CoO_3−δ (SSC)-BaCe_0.8Sm_0.2O_3−δ (BCS) composite cathodes. The results suggest that the migration of protons to TPBs and the surface diffusion of might be the limiting reactions for SSC-BCS composite cathodes in wet atmosphere, while the oxygen ions transferring into electrolyte, the reducing of O_ad to , and surface diffusion of might be the limiting reactions for SSC-BCS composite cathode in dry atmosphere.     

Landfill leachate treatment by solar-driven AOPs

Sanitary landfill leachate resulting from the rainwater percolation through the landfill layers and waste material decomposition is a complex mixture of high-strength organic and inorganic compounds which constitutes serious environmental problems. In this study, different heterogeneous (TiO₂/UV, TiO₂/H₂O₂/UV) and homogenous (H₂O₂/UV, Fe²⁺/H₂O₂/UV) photocatalytic processes were investigated as an alternative for the treatment of a mature landfill leachate. The addition of H₂O₂ to TiO₂/UV system increased the reduction of the aromatic compounds from 15% to 61%, although mineralization was almost the same. The DOC and aromatic content abatement is similar for the H₂O₂/UV and TiO₂/H₂O₂/UV processes, although the H₂O₂ consumption is three times higher in the H₂O₂/UV system. The low efficiency of TiO₂/H₂O₂/UV system is presumably due to the alkaline leachate solution, for which the H₂O₂ becomes highly unstable and self-decomposition of H₂O₂ occurs. The efficiency of the TiO₂/H₂O₂/UV system increased 10 times after a preliminary pH correction to 4. The photo-Fenton process is much more efficient than heterogeneous (TiO₂, TiO₂/H₂O₂/UV) or homogeneous (H₂O₂/UV) photocatalysis, showing an initial reaction rate more than 20 times higher, and leading to almost complete mineralization of the wastewater. However, when compared with TiO₂/H₂O₂/UV with acidification, the photo-Fenton reaction is only two times faster.The optimal initial iron dose for the photo-Fenton treatment of the leachate is 60 mg Fe²⁺ L⁻¹, which is in agreement with path length of 5 cm in the photoreactor. The kinetic behaviour of the process (60 mg Fe²⁺ L⁻¹) comprises a slow initial reaction, followed by a first-order kinetics (k = 0.020 , r₀ = 12.5 mg ), with H₂O₂ consumption rate of k_H2O2 = 3.0 mmol H₂O₂, and finally, the third reaction period, characterized by a lower DOC degradation and H₂O₂ consumption until the end of the experiment, presumably due to the formation of low-molecular-weight carboxylic groups. A total of 306 mM of H₂O₂ was consumed for achieving 86% mineralization (DOC_final = 134 mg L⁻¹) and 94% aromatic content reduction after 110 kJ_UV L⁻¹, using an initial iron concentration of 60 mg Fe²⁺ L⁻¹.