Preparation of PtSnSb/C by an alcohol reduction process for direct ethanol fuel cell (DEFC)

PtSn/C and PtSnSb/C electrocatalysts (20 wt.% metal loading) were prepared by an alcohol reduction process using H₂PtCl₆.6H₂O, SnCl₂.2H₂O, and Sb(OOCCH3) as metal sources, ethylene glycol as solvent and reducing agent, and Vulcan XC72 as carbon support. The electrocatalysts were characterized by energy dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy, while that the performance for ethanol oxidation was investigated by cyclic voltammetry and chronoamperommetry (chrono) at room temperature. The diffractograms of the PtSn/C and PtSnSb/C electrocatalysts showed four peaks associated to Pt face-centered cubic structure and two peaks that were related to a SnO₂ phase. For PtSb/C and PtSnSb/C electrocatalysts, no Sb (antimony) peaks corresponding to a metallic antimony or antimony oxide phases were observed. Transmission electron microscopy images showed that the metal particles were homogeneously distributed over the support. The PtSnSb/C (50:45:05) electrocatalyst showed an increase of performance for ethanol oxidation in relation to PtSn/C electrocatalyst at room temperature. In the tests at 100 °C on a single cell of a direct ethanol fuel cell, the maximum power density of PtSnSb/C (50:45:05) electrocatalyst was slightly higher than that of PtSn/C electrocatalyst.     

Electro-oxidation of ethanol using PtSnRh/C electrocatalysts prepared by an alcohol-reduction process

PtRh/C (90:10), PtRh/C (50:50), PtSn/C (50:50), and PtSnRh/C (50:40:10) electrocatalysts were prepared by an alcohol-reduction process using ethylene glycol as solvent and reduction agent and Vulcan Carbon XC72 as supports. The electrocatalysts were characterized by energy-dispersive X-ray analysis, X-ray diffraction, and transmission electron microscopy. The electro-oxidation of ethanol was studied by cyclic voltammetry chronoamperometry at room temperature and on a single cell of a direct ethanol fuel cell at 100 °C. Cyclic voltammetry and chronoamperometry experiments showed that PtSnRh/C and PtSn/C electrocatalysts have similar performance for ethanol oxidation at room temperature, while the activity of PtRh/C electrocatalysts was very low. At 100 °C on a single cell, PtSnRh/C showed superior performance compared to PtSn/C and PtRh/C electrocatalysts.     

Preparation of PtSnRh/C-Sb2O5·SnO2 electrocatalysts by an alcohol reduction process for direct ethanol fuel cell

PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts with different Pt/Sn/Rh atomic ratios (90:05:05, 70:25:05, and 50:45:05) were prepared by an alcohol reduction process using H₂PtCl₆·6H₂O, SnCl₂·2H₂O, RhCl₃·xH₂O as metal sources, ethylene glycol as solvent and reducing agent, and a physical mixture of Vulcan XC72 (85?wt%) and Sb₂O₅·SnO₂ (15?wt%) as support. The electrocatalysts were characterized by X-ray diffraction and transmission electron microscopy. The electro-oxidation of ethanol was studied by cyclic voltammetry and chronoamperometry at 25 and 50?°C and in single direct ethanol fuel cell (DEFC) at 100?°C. The diffractograms of PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts showed the peaks characteristic of Pt face-centered cubic structure and several others peaks associated with ·SnO₂ and Sb₂O₅·SnO₂. Transmission electron micrographs of PtSnRh/C-Sb₂O₅·SnO₂ electrocatalysts showed the metal nanoparticles distributed on the supports with particle sizes of about 2?C3?nm. The electrochemical measurements and the experiments in a single DEFC showed that PtSnRh/C-Sb₂O₅·SnO₂ (90:05:05) and PtSnRh/C-Sb₂O₅·SnO₂ (70:25:05) electrocatalysts exhibited higher performance for ethanol oxidation in comparison with PtSnRh/C electrocatalyst.     

Electro-oxidation of ethanol using PtRuBi/C electrocatalyst prepared by borohydride reduction

Pt/C, PtRu/C, PtBi/C, and PtRuBi/C electrocatalysts (20 wt.% metal loading) were prepared by borohydride reduction using H₂PtCl₆·6H₂O, RuCl₃·xH₂O, and Bi(NO₃)₃·5H₂O as metal sources and Vulcan XC 72 as support. The electrocatalysts were characterized by energy-dispersive X-ray analysis, X-ray diffraction, and thermogravimetric analysis. The electro-oxidation of ethanol was studied in sulfuric acid solution by cyclic voltammetry and chronoamperometry. The electrochemical studies showed that PtRuBi/C (50:40:10) electrocatalyst has superior performance for ethanol electro-oxidation at room temperature compared to the other electrocatalysts. Preliminary tests at 100 °C on a single direct ethanol fuel cell also confirm the results obtained by electrochemical techniques.     

Electro-oxidation of ethylene glycol on PtSn/C and PtSnNi/C electrocatalysts

A PtSn/C electrocatalyst with a Pt–Sn molar ratio of 50:50 and A PtSnNi/C electrocatalyst with a Pt–Sn–Ni molar ratio of 50:40:10 were prepared by alcohol-reduction process using ethylene glycol as solvent and reducing agent. The electrocatalysts were characterized by energy dispersive X-ray, X-ray diffraction, and cyclic voltammetry. The electro-oxidation of ethylene glycol was studied by cyclic voltammetry and chronoamperometry using the thin porous coating technique. PtSnNi/C electrocatalyst showed a superior performance compared to PtSn/C electrocatalysts in the potential range of interest for a direct ethylene glycol fuel cell.     

Effect of Ni proportion on the performance of proton exchange membrane fuel cells using PtNi/C electrocatalysts

PtNi/C electrocatalysts were synthesised by borohydride method on functionalised carbon support. Energy-dispersive X-ray spectroscopy, X-ray diffraction, transmission electron microscopy and both cyclic and linear voltammetry were employed to characterise the composition, crystalline structure, morphology and catalytic properties of the PtNi/C electrocatalysts. Different Ni proportions in the PtNi/C electrocatalysts were evaluated in the cathode or anode in a H₂/air proton exchange membrane fuel cells (PEMFC) by polarisation curves. PtNi particles uniformly dispersed with different proportions of metals obtained. The increase of Ni proportion in the electrocatalyst led to materials with higher mass activity values toward the oxygen reduction reaction and a greater electrochemical-active surface area. PtNi/C electrocatalysts in the cathode presented higher mass activity values at high potential in the PEMFC. The best PEMFC performance was obtained with PtNi 13 at.% Ni (cathode) and Pt/C (anode) relative to the Pt/C (cathode and anode) with identical Pt loadings. PtNi/C electrocatalysts in PEMFC may be used as an alternative to Pt/C electrocatalyst.     

Fuel cell and electrochemical studies of the ethanol electro-oxidation in alkaline media using PtAuIr/C as anodes

Ethanol electro-oxidation reaction was investigated considering conventional electrochemical experiments in alkaline media, direct ethanol fuel cell (DEFC), and in situ ATR-FTIR. The working electrode/anodes were composed of monometallic Pt/C, Au/C, Ir/C, and trimetallic PtAuIr/C nanoparticles with atomic Pt/Au/Ir ratios of 40:50:10, 50:40:10, 60:30:10, 70:20:10, and 80:10:10. X-ray diffraction (XRD) suggests PtAuIr/C alloy formation, and according to transmission electron micrographs, the mean particle sizes are from 4 to 6 nm for all catalyst compositions. PtAuIr/C 40:50:10 showed the highest catalytic activity for ethanol electro-oxidation in the electrochemical experiments; using this material, the peak current density from ethanol electro-oxidation on cyclic voltammetry experiment was 50 mA per g of Pt, 3.5 times higher than that observed with Pt/C. The fuel cell performance was superior using all PtAuIr/C compositions than using Pt/C. Au/C and Ir/C presented very poor catalytic activity toward ethanol electro-oxidation. The improved results obtained using PtAuIr/C might be related to the OH_ads species formed at low overpotential on Ir and to the decrease on adsorption energy of poisoning intermediates on Pt sites, promoted by Au.     

Novel synthesis and characterization of nanocomposite Pt-WO3-TiO2/C electrocatalyst for PEMFC

In this study, an effective preparation of Pt-WO₃-TiO₂/C electrocatalysts has been developed for polymer electrolyte membrane fuel cell (PEMFC) application. The single cell performance of Vulcan XC-72R carbon-supported Pt-WO₃-TiO₂ electrocatalysts with various compositions (as weight percentage Pt-W-Ti 0:5:5, 2:4:4, 4:3:3, 6:2:2, and 8:1:1) as anode materials are investigated in PEMFC. These catalysts are compared with 10 % Pt/C on the same Vulcan XC-72R carbon support and 10 % Pt/C (commercial) electrocatalyst. The physical and morphological characterization of the optimized Pt-WO₃-TiO₂/C, 10 % Pt/C, and 10 % Pt/C (commercial) electrocatalysts are further investigated by X-ray diffraction (XRD), cyclic voltammetry, scanning electron microscopy with energy-dispersive X-ray analysis, and transmission electron microscopy (TEM) techniques. Among all the molar ratio of the catalysts, the Pt-W-Ti (4:3:3) molar ratio catalyst exhibited the larger electrochemical active surface area. The electrochemical performance of Pt-WO₃-TiO₂/C (with a weight percentage of Pt-W-Ti 4:3:3) as anode material is better than those of other compositions of Pt-WO₃-TiO₂/C catalysts. The amount of platinum was also reduced from 1.76 to 0.704 mg cm^?2 which exhibited higher performance in single cell tests. Platinum shows a smaller-sized crystalline structure in XRD and TEM analysis. High performance indicates that enhanced proton transport occurs through the use of this catalyst.     

Preparation and characterization of PtRu/C-rare earth using an alcohol-reduction process for ethanol electro-oxidation

PtRu/C (100% C) and PtRu/C-CeO₂, PtRu/C-La₂O₃, PtRu/C-Nd₂O₃, and PtRu/C-Er₂O₃ (85% C and 15% rare earth) electrocatalysts were prepared in a single step by an alcohol-reduction process using H₂PtCl₆ 6H₂O and RuCl₃ xH₂O as metal sources, ethylene glycol as solvent and reducing agent, Vulcan XC72 and rare earth (RE) as support. The electrocatalysts were characterized by energy dispersive X-ray, X-ray diffraction, and transmission electron microscopy. The performance for ethanol oxidation was investigated by cyclic voltammetry and chronoamperommetry at room temperature, and studies on the direct ethanol fuel cell were carried at 100 °C. The Pt:Ru atomic ratios were similar to the nominal used in preparation, and the average particle sizes were in the range of 2.0–3.0 nm. All PtRu/C-RE electrocatalysts showed an increase of performance for ethanol oxidation at room temperature and also on a single direct ethanol fuel cell tests in relation to PtRu/C electrocatalyst at 100 °C.     

Electrochemical characterization of platinum-based anode catalysts for membraneless fuel cells

In the present work, carbon-supported Pt–Sn, Pt–Ru, and Pt–Sn–Ru electrocatalysts with different atomic ratios were prepared by alcohol-reduction method to study the electro-oxidation of ethanol in membraneless fuel cells. The synthesized electrocatalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD) analyses. The prepared catalysts had similar particle morphology, and their particle sizes were 2–5 nm. The electrocatalytic activities were characterized by cyclic voltammetry (CV) and chronoamperometry (CA). The electrochemical results obtained at room temperature showed that the addition of Sn and Ru to the pure Pt electrocatalyst significantly improved its performance in ethanol electro-oxidation. The onset potential for ethanol electro-oxidation was 0.2 V vs. Ag/AgCl, in the case of the ternary Pt–Sn–Ru/C catalysts, which was lower than that obtained for the pure Pt catalyst (0.4 V vs. Ag/AgCl). During the experiments performed on single membraneless fuel cells, Pt ? Sn ? Ru/C (70:10:20) performed better among all the catalysts prepared with power density of 36 mW/cm². The better performance of ternary Pt–Sn–Ru/C catalysts may be due to the formation of a ternary alloy and the smaller particle size.     

Investigation of a Pt–Fe/C catalyst for oxygen reduction reaction in direct ethanol fuel cells

Three cathode catalysts (60% Pt/C, 30% Pt/C and 60% Pt–Fe/C), with a particle size of about 2–3 nm, were prepared to investigate the effect of ethanol cross-over on cathode surfaces. All samples were studied in terms of structure and morphology by using X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. Their electrocatalytic behavior in terms of oxygen reduction reaction (ORR) was investigated and compared using a rotating disk electrode (RDE). The tolerance of cathode catalysts in the presence of ethanol was evaluated. The Pt–Fe/C catalyst showed both higher ORR activity and tolerance to ethanol cross-over than Pt/C catalysts. Moreover, the more promising catalysts were tested in 5 cm² DEFC single cells at 60 and 80 °C. An improvement in single cell performance was observed in the presence of the Pt–Fe catalyst, due to an enhancement in the oxygen reduction kinetics. The maximum power density was 53 mW cm⁻² at 2 bar rel. cathode pressure and 80 °C.     

Exploration of bimetallic Pt-Pd/C nanoparticles as an electrocatalyst for oxygen reduction reaction

In this study, carbon supported Pt and Pt-Pd were synthesized as oxygen reduction reaction electrocatalysts for polymer electrolyte membrane fuel cells (PEMFCs). Pt and Pt-Pd nanoparticles have been synthesized by reduction of metal precursors in presence of NaBH₄. Various techniques such as X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and scanning electron microscopy (SEM) were utilized to study the prepared samples. Furthermore, electrochemical properties of the prepared samples were evaluated from cyclic voltammetry (CV), linear sweep voltammetry (LSV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed, the crystallite size of electrocatalysts (Pt and Pt-Pd) is below 10 nm. The higher catalytic activity was detected for Pt-Pd/C electrocatalyst for oxygen reduction reaction (ORR). In addition, it is believed that the better performance of electrocatalyst is related to the synergic effect between Pt and Pd nanoparticles, weakening of the OO bond on Pd-modified Pt nanoparticles in ORR, uniform dispersion of Pd and Pt on the carbon support and higher electrochemical active surface area (EAS) of Pt-Pd/C electrocatalyst.     

Auger spectroscopic study of the surface composition of Pt/Sn alloys in ultrahigh vacuum and in the presence of oxygen and hydrogen

The surface composition of two Pt/Sn alloys, viz. PtSn and Pt₃Sn, has been followed by means of AES, as a function of annealing in ultrahigh vacuum, oxygen chemisorption and reduction with hydrogen.The results, which were quantitatively interpreted with the aid of a novel calibration technique, reveal the following features: - The surface of PtSn and Pt₃Sn becomes enriched with tin by annealing in vacuum. Ultimate values of 68±5 at% Sn for PtSn and 41±5 at% Sn for Pt₃Sn were attained after annealing at 500°C. - The adsorption of oxygen on the annealed surface of PtSn and Pt₃Sn causes a further enrichment with tin, while severe oxidation of PtSn at 500°C leads to complete disappearance of Pt from the surface. - Oxygen is more strongly and differently bound on a surface containing about 40 at% Sn than on a surface containing about 70 at% Sn. Activated adsorption of oxygen takes place only on the latter. The results suggest the formation of SnO₂ surface complexes on the exposed surface of Pt₃Sn. - Reduction of the alloys at 500°C carries the excess of tin into the bulk and reduces its surface concentration to 35±5 at% for Pt₃Sn and 64±5 at% for PtSn, which is an enrichment of the surface with platinum relative to the annealed state.     

Structural and optical properties of Bi<Subscript>3.25</Subscript>La<Subscript>0.75</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> ferroelectric thin films prepared by chemical solution methods

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films have been grown on Pt/Ti/SiO₂/Si substrates by chemical solution methods. X-ray diffraction analysis shows that BLT thin films are polycrystalline with (171)-preferential orientation. Atomic force microscopy investigation shows that they have large grains about 120 nm in size. A Pt/BLT/Pt capacitor has been fabricated and showed excellent ferroelectricity, with a remnant polarization and coercive field of 24 μC/cm² and 116 kV/cm, respectively. The capacitor shows no polarization fatigue up to 10⁹ switching cycles. The optical constants (n,k) of the BLT thin films in the wavelength range 0.35–1.7 μm were obtained by spectroscopic ellipsometry measurements, and the band-gap energy was found to be about 3.25 eV. Received: 16 October 2001 / Accepted: 6 January 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +86-21/65830-734, E-mail: gswang@mail.sitp.ac.cn     

Ordered intermediate compound PtBi-modified Pt/C catalyst for 2-propanol electrooxidation in alkaline medium

The PtBi-modified Pt/C catalyst was prepared by liquid chemical reduction method. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) were used to characterize PtBi-modified Pt/C catalyst. The electrochemical behaviors for the 2-propanol electrooxidation reaction in alkaline medium were measured by cyclic voltammetry, line sweep voltammetry, and electrochemical impedance spectra (EIS). The results showed that the prepared PtBi is ordered intermediate compound. Compared with the spectrum obtained from Pt/C catalyst, the XPS peak of PtBi-modified Pt/C catalyst is obviously moving toward the low Pt 4f biding energy. The Bi⁰ and Bi₂O₃ coexist on the surface of PtBi/C catalyst. In alkaline medium, the electrochemical activity of 2-propanol electrooxidation of PtBi/C catalyst is higher than that of commercial Pt/C catalyst. EIS result shows that the reaction mechanism of 2-propanol electrooxidation for both catalysts is similar.     

Glycerol oxidation reaction using PdAu/C electrocatalysts

Glycerol oxidation reactions were evaluated using PdAu/C electrocatalysts under alkaline conditions. These electrocatalysts were synthesized in different ratios (100:0, 75:25, 50:50, 25:75, and 0:100), using the borohydride reduction method. The materials were characterized with X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrochemical techniques associated by in situ attenuated total reflectance Fourier transformed infrared spectroscopy (ATR-FTIR). According to the XRD diffractograms, the presence of Pd and Au (face-centered cubic (fcc)) phases and Pd-Au (fcc) alloys were detected. Cyclic voltammetry assisted by ATR-FTIR in situ and chronoamperometry experiments revealed that the addition of Au remarkably enhances the electrocatalytic activity, due to the action of bifunctional effect, with addition of the interactions of alcohoxide with hydroxylate species in gold surface, and the stability of Pd/C catalysts. Highest current density (≈4 mA mg_metal ^?1) was achieved for the catalyst Pd₅₀Au₅₀/C and Pd₇₅Au₂₅/C, which is two times higher than that achieved by Pd/C (2 mA mg_metal ^?1), demonstrating the beneficial effect of the PdAu alloy.     

Ion-beam formation of electrocatalysts for fuel cells with polymer membrane electrolyte

Active layers of electrocatalysts are prepared by the ion-beam assisted deposition (IBAD) of platinum onto carbon-based AVCarb® Carbon Fiber Paper P50 and Toray Carbon Fiber Paper TGP-H-060 T supports and Nafion® N 115 polymer membrane electrolyte in the mode where the deposited metal ions are used as ions assisting the deposition process. Metal deposition and mixing of the deposited layer with the substrate under an accelerating voltage of 10 kV by the same metal ions are carried out from a neutral fraction of metal vapor and the ionized plasma of a pulsed vacuum-arc discharge, respectively. The composition and microstructure of the surface layers obtained are studied by Rutherford backscattering spectrometry (RBS), scanning electron microscopy (SEM), electron-probe microanalysis (EPMA), and X-ray fluorescence (XRF) analysis. The platinum concentration in the layers is (0.5–1.5) × 10¹⁶ at/cm². The prepared electrocatalysts exhibit activity in the process of the electrochemical oxidation of methanol and ethanol, which form the basis for the principle of operation of low temperature fuel cells (direct methanol fuel cells (DMFC) and direct ethanol fuel cells (DEFC)).     

Improved catalytic activity of Pt/rGO counter electrode in In2O3-based DSSC

A platinum/reduced graphene oxide (Pt/rGO) nanocomposite acting as a counter electrode (CE) was fabricated using a chemical bath deposition method for In₂O₃-based dye-sensitized solar cell (DSSC) via sol-gel technique. The report analyzes the morphological and electrochemical impedance spectroscopy of the annealing Pt/rGO films at 350, 400, and 450 °C. Micrograph images obtained from field emission scanning electron microscopy demonstrated the annealed films are highly porous. The energy-dispersive X-ray results show that the carbon atoms were homogeneously distributed on the film annealed at 400 °C. A good photovoltaic performance was exhibited with high photocurrent density of 8.1 mA cm⁻² and power conversion efficiency (η) of 1.68 % at the Pt/rGO CE annealed at 400 °C. The employed electrochemical impedance spectroscopy analysis quantifies that the Pt/rGO films annealed at 400 °C provide more efficient charge transfer with the lowest effective recombination rate and high electron life time, hence improving the performance of Pt/rGO CE.

     

Preparation of PdAu/C-Sb2O5·SnO2 electrocatalysts by borohydride reduction process for direct formic acid fuel cell

Pd/C-Sb₂O₅·SnO₂ and PdAu/C-Sb₂O₅·SnO₂ electrocatalysts with different PdAu atomic ratio (90:10, 70:30, and 50:50) were prepared by borohydride reduction method, and characterized by X-ray diffraction, transmission electron microscopy, cyclic voltammetry, chronoamperommetry, and performance test on direct formic acid fuel cell at 100 °C. X-ray diffraction showed for Pd/C-Sb₂O₅·SnO₂ the presence of Pd face-centered cubic (fcc) system, while for PdAu/C-Sb₂O₅·SnO₂ it showed the presence of Pd fcc phase, PdAu fcc alloys and a segregated phases fcc Pd-rich and Au-rich phases. TEM micrographs and histograms for all electrocatalysts showed that the nanoparticles where not well dispersed on the support and some agglomerates were present. The electrochemical studies showed that PdAu/C-Sb₂O₅·SnO₂ (70:30) had superior performance for formic acid electro-oxidation at 25 °C compared to others electrocatalysts prepared while PdAu/C-Sb₂O₅·SnO₂ (90:10) showed superior performance in direct formic acidic fuel cell at 100 °C. These results indicated that the addition of 10–30 % Au to Pd favor the electro-oxidation of formic acid. This effect could be attributed to the synergy between the constituents of the electrocatalyst (metallic Pd and Au, SnO₂, and Sb₂O₅·SnO₂).     

Structure, dielectric and ferroelectric properties of highly (1 0 0)-oriented BaTiO3 grown under low-temperature conditions

The highly (1 0 0)-oriented BaTiO₃ thin films were fabricated on LaNiO₃(1 0 0)/Pt/Ti/SiO₂/Si substrates under low-temperature conditions. Substrate temperatures throughout the fabrication process remained at or below 400 °C, which allows this process to be compatible with many materials commonly used in integrated circuit manufacturing. X-ray diffraction data provided the evidence for single BaTiO₃ phase. Field-emission scanning electron microscopy was used to study the columnar structure of the films. The dielectric properties as a function of frequency in the range of 1 kHz to 1 MHz was obtained. The room temperature remanent polarization (2P_r) and coercive field were found to be ∼5 μC/cm² and 50 kV/cm, respectively. The BTO film maintains an excellent fatigue-free character even after 10⁹ switching cycles.