E-TEK Catalyst Research Articles

High Methanol Tolerance of Carbon-Supported Pt-Cr Alloy Nanoparticle Electrocatalysts for Oxygen Reduction

The electrocatalytic reduction of oxygen on carbon-supported Pt-Cr (1:1) alloy nanoparticle catalysts with two different metal loadings prepared via a carbonyl route was investigated based on the porous thin-film rotating disk-ring electrode technique and compared with that on E-TEK catalyst in pure and methanol-containing electrolytes. The as-prepared Pt-Cr alloy nanoparticles, which have single-phase disordered structures, are well dispersed on the surface of carbon with a narrow size distribution even at metal loading. Such catalysts are stable in air up to . As compared to the catalyst, the alloy catalysts showed slightly enhanced activity for the oxygen reduction reaction in pure acid electrolyte and significantly enhanced activity in the presence of methanol, and the ring-current measurements on the homemade catalysts showed a reduction in peroxide yield in pure acid solution. The enhanced activity could be ascribed to the effect of alloying on the initiation and extent of surface oxide formation. Oxygen reduction kinetic analysis indicated a potential dependence of the apparent number of electrons transferred per oxygen molecule during the reduction in methanol-containing solution. High methanol tolerance of Pt-Cr alloy catalysts during the oxygen reduction could be explained well by the lower reactivity of methanol oxidation, which may originate from the composition effect and the disordered structure of the alloy catalysts.

Chloride free Pt‐ and PtRu‐ Nanoparticles Stabilised by “Armand's Ligand” as Precursors for Fuel Cell Catalysts

AbstractChloride residues on the surface of fuel cell catalysts are known to decrease the catalytic activity, especially for O2 reduction. Using Armand's ligand, which contains the chloride free DCTA anion, for the colloidal stabilisation of nanoscopic Pt and PtRu catalysts precursors (< 2 nm size) leads to PEMFC and DMFC catalysts with improved activity compared to commercial E‐TEK catalysts as evidenced by both methanol oxidation and CO‐stripping voltametric studies.

Preparation and the physical/electrochemical properties of a Pt/C nanocatalyst stabilized by citric acid for polymer electrolyte fuel cells

Pt/C nanocatalysts were prepared by the reduction of chloroplatinic acid with sodium borohydride, with citric acid as a stabilizing agent in ammonium hydroxide solution. These nanocatalysts were obtained by altering the molar ratio of citric acid to chloroplatinic acid (CA/Pt) from 1:1, 2:1, 3:1 to 4:1. Transmission electron microscopy and X-ray diffraction analyses indicated that the well-dispersed Pt nanoparticles of around 3.82 nm in size were obtained when the CA/Pt ratio was maintained at 2:1. X-ray photoelectron spectroscopy measurements revealed that the 2:1, 3:1 and 4:1 molar ratio catalysts had a relatively higher amount of Pt in their metallic state than did the 1:1 molar ratio catalyst. Cyclic voltammetry results demonstrated that the Pt/C nanocatalysts annealed at 400 °C in an N 2 atm provided higher electrocatalytic activity. Among all the molar ratio catalysts, the 2:1 molar ratio catalyst exhibited the largest electrochemical active surface (EAS) area, and its methanol oxidation reaction current was superior to the E-TEK catalyst. The oxygen reduction reaction of the catalysts studied by linear sweep voltammetry and tested in a fuel cell indicated that the catalytic activity of the 2:1 molar ratio catalyst was comparable to that of an E-TEK catalyst.

Effects of membrane electrode assembly preparation on the polymer electrolyte membrane fuel cell performance

This paper presents results of recent investigations to develop an optimized in-house membrane electrode assembly (MEA) preparation technique combining catalyst ink spraying and assembly hot pressing. Only easy steps were chosen in this preparation technique in order to simplify the method, aiming at cost reduction. The influence of MEA fabrication parameters like electrode pressing or annealing on the performance of hydrogen fuel cells was studied by single cell measurements with H 2/O 2 operation. Toray paper and carbon cloth as gas diffusion layer (GDL) materials were compared and the composition of electrode inks was optimized with regard to most favorable fuel cell performance. Commercial E-TEK catalyst was used on the anode and cathode with Pt loadings of 0.4 and 0.6 mg/cm 2, respectively. The MEA with best performance delivered approximately 0.58 W/cm 2, at 65 °C cell temperature, 80 °C anode humidification, dry cathode and ambient pressure on both electrodes. The results show, that changing electrode compositions or the use of different materials with same functionality (e.g. different GDLs), have a larger effect on fuel cell performance than changing preparation parameters like hot pressing or spraying conditions, studied in previous work.

Synthesis and physical/electrochemical characterization of Pt/C nanocatalyst for polymer electrolyte fuel cells

Abstract In the present study, 20 wt.% Pt/C nanocatalyst has been synthesized by the simple formic acid reduction method (FARM) in the organic solvent tetrahyrofuran (THF). Transmission electron microscope (TEM) and X-ray diffraction (XRD) analyses indicate the formation of well-dispersed Pt nanoparticles having sizes of around 3–4 nm on the Vulcan XC-72 carbon support. A comparison between two different synthetic approaches by using the FARM shows that the formation and dispersion of the Pt nanoparticles can be facilitated by the THF solvent and high surface area Vulcan XC-72 carbon support. The surface characterization of the Pt/C by X-ray photoelectron spectroscopy (XPS) reveals that 60.3% of Pt is present in its metallic state. Furthermore, the electrochemical characterization by the cyclic voltammetry (CV) demonstrates that the electrochemical active surface (EAS) area and methanol oxidation reaction of the Pt/C is respectively almost similar and slightly higher than that of the 20 wt.% Pt/C E-TEK catalyst.

Synthesis and physical/electrochemical characterization of Pt/C nanocatalyst for polymer electrolyte fuel cells

In the present study, 20 wt.% Pt/C nanocatalyst has been synthesized by the simple formic acid reduction method (FARM) in the organic solvent tetrahyrofuran (THF). Transmission electron microscope (TEM) and X-ray diffraction (XRD) analyses indicate the formation of well-dispersed Pt nanoparticles having sizes of around 3–4 nm on the Vulcan XC-72 carbon support. A comparison between two different synthetic approaches by using the FARM shows that the formation and dispersion of the Pt nanoparticles can be facilitated by the THF solvent and high surface area Vulcan XC-72 carbon support. The surface characterization of the Pt/C by X-ray photoelectron spectroscopy (XPS) reveals that 60.3% of Pt is present in its metallic state. Furthermore, the electrochemical characterization by the cyclic voltammetry (CV) demonstrates that the electrochemical active surface (EAS) area and methanol oxidation reaction of the Pt/C is respectively almost similar and slightly higher than that of the 20 wt.% Pt/C E-TEK catalyst.

Spherical carbon capsules with hollow macroporous core and mesoporous shell structures as a highly efficient catalyst support in the direct methanol fuel cell

Carbon capsules with hollow core and mesoporous shell (HCMS) structures were used as a support material for Pt(50)-Ru(50) catalyst, and the catalytic performance of the HCMS supported catalyst in the direct methanol fuel cell was described; the HCMS carbon supported catalysts exhibited much higher specific activity for methanol oxidation than the commonly used E-TEK catalyst by about 80%, proving that the HCMS carbon capsules are an excellent support for electrode catalysts in DMFC.

Synthesis and Characterization of Surfactant-Stabilized Pt/C Nanocatalysts for Fuel Cell Applications

Platinum nanocatalysts supported on Vulcan XC-72 carbon have been synthesized through the reduction of chloroplatinic acid with formic acid, using surfactant tetraoctylammonium bromide (TOAB) as the stabilizer in the solvent tetrahydrofuran (THF). These nanocatalysts are synthesized by changing the molar ratio of TOAB to chloroplatinic acid, i.e., N/Pt ratio of 0.76, 0.38, and 0.19. A control catalyst that does not contain TOAB is also synthesized by this method for comparison purposes. Comparison of the morphological properties of these catalysts by transmission electron microscopy (TEM) reveals that the N/Pt ratio of 0.76 catalyst has well-separated smaller particles (2.2 nm) than the other lower molar ratio and control catalysts. X-ray diffraction (XRD) analysis indicates the presence of platinum in the fcc phase and the average size of the particles calculated from the XRD peak widths agreed well with the TEM results. X-ray photoelectron spectroscopic (XPS) measurement of the 0.76 ratio catalyst reveals that a higher amount of Pt exists in its metallic state (73.64% of Pt(O) and 26.36% Pt(II)) and the data are on par with that of the E-TEK catalyst. Stabilization effect of the TOAB on the surface of platinum particles has been discussed with respect to the different N/Pt molar ratios. The XPS technique has been exploited to prove the presence of coverage of TOAB and its subsequent removal from the surface of the Pt particles, which is considered to be the crucial step prior to the electrochemical measurements. Electrochemical measurements have demonstrated that the surface area of the 0.76 ratio catalyst is higher than that of the lower molar ratios (0.38 and 0.19).

CO-tolerance of low-loaded Pt/Ru anodes for PEM fuel cells

Anodes with various Pt/Ru loadings were prepared using three different anode catalysts: E-TEK 40% Pt-Ru/Vulcan XC-72 and Engelhard 40 and 50% Pt-Ru/C. These anodes were tested for their CO-tolerance at a cell temperature of 70 °C in the presence of 10 and 50 ppm CO, respectively. The performance declined with CO concentration for all the anodes. However, Engelhard catalysts showed better performance than E-TEK catalyst under our experimental conditions. A minimum Pt/Ru loading of 0.43, 0.22 and 0.30 mg/cm 2 was needed to achieve the maximum performance for E-TEK 40% Pt-Ru/C, Engelhard 40 and 50% Pt-Ru/C, respectively, when 10 ppm CO/70% H 2/30% CO 2 was used at a cell current density of 0.20 A/cm 2. Using 50 ppm CO/70% H 2/30% CO 2 and at a cell current density of 0.20 A/cm 2, a minimum Pt/Ru loading of 0.60, 0.32 and 0.36 mg/cm 2 was needed to achieve the highest performance for E-TEK 40% Pt-Ru/C, Engelhard 40 and 50% Pt-Ru/C, respectively.

Requirement for metals of electric vehicle batteries

Anodes with various Pt/Ru loadings were prepared using three different anode catalysts: E-TEK 40% Pt-Ru/Vulcan XC-72 and Engelhard 40 and 50% Pt-Ru/C. These anodes were tested for their CO-tolerance at a cell temperature of 70 °C in the presence of 10 and 50 ppm CO, respectively. The performance declined with CO concentration for all the anodes. However, Engelhard catalysts showed better performance than E-TEK catalyst under our experimental conditions. A minimum Pt/Ru loading of 0.43, 0.22 and 0.30 mg/cm2 was needed to achieve the maximum performance for E-TEK 40% Pt-Ru/C, Engelhard 40 and 50% Pt-Ru/C, respectively, when 10 ppm CO/70% H2/30% CO2 was used at a cell current density of 0.20 A/cm2. Using 50 ppm CO/70% H2/30% CO2 and at a cell current density of 0.20 A/cm2, a minimum Pt/Ru loading of 0.60, 0.32 and 0.36 mg/cm2 was needed to achieve the highest performance for E-TEK 40% Pt-Ru/C, Engelhard 40 and 50% Pt-Ru/C, respectively.

Effect of thermal treatment on the performance of CO-tolerant anodes for polymer electrolyte fuel cells

In this work, carbon-supported Pt:Ru electrocatalysts, mainly for application in polymer electrolyte fuel cells, have been prepared by different methods. The materials were tested in single cells with respect to the hydrogen–oxidation reaction in the presence of CO, and the performances, before and after thermal treatments, compared to that of state-of-the-art, commercial E-TEK catalysts. In most cases, it was found that the performance of the anode improves substantially after the thermal treatment of the material. Of the several methods considered, the preparation of the catalyst via the formation of a sulfite complex, followed by a thermal treatment, gave the best results, comparable to those obtained with the state-of-the-art catalyst.