Pt-based anode catalysts for direct ethanol fuel cells

In the present work, several carbon supported PtSn and PtSnRu catalysts were prepared with different atomic ratios and tested in direct ethanol fuel cells (DEFC) operated at lower temperature (T=90 degreesC). XRD and TEM results indicate that all of these catalysts consist of uniform nano-sized particles of narrow distribution and the average particle sizes are always less than 3.0 nm. As the content of Sn increases, the Pt lattice parameter becomes longer. Single direct ethanol fuel cell tests were used to evaluate the performance of carbon supported PtSn catalysts for ethanol electro-oxidation. It was found that the addition of Sn can enhance the activity towards ethanol electro-oxidation. It is also found that a single DEFC of Pt/Sn atomic ratioless than or equal to2, "Pt1Sn1/C, Pt3Sn2/C, and Pt2Sn1/C" shows better performance than those with Pt3Sn1/C and Pt4Sn1/C. But even adopting the least active PtSn catalyst, Pt4Sn1/C, the DEFC also exhibits higher performance than that with the commercial Pt1Ru1/C, which is dominatingly used in PEMFC at present as anode catalyst for both methanol electro-oxidation and CO-tolerance. At 90 degreesC, the DEFC exhibits the best performance when Pt2Sn1/C is adopted as anode catalysts. This distinct difference in DEFC performance between the catalysts examined here is attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and Sn. It is thought that -OHads, Surface Pt active sites and the ohmic effect of PtSn/C catalyst determines the electro-oxidation activity of PtSn catalysts with different Pt/Sn ratios. (C) 2004 Elsevier B.V. All rights reserved.

Pt based anode catalysts for direct ethanol fuel cells

In the present work several Pt-based anode catalysts supported on carbon XC-72R were prepared with a novel method and characterized by means of XRD, TEM and XPS analysis. It was found that all these catalysts are consisted of uniform nanosized particles with sharp distribution and Pt lattice parameter decreases with the addition of Ru or Pd and increases with the addition of Sn or W. Cyclic voltammetry (CV) measurements and single direct ethanol fuel cell (DEFC) tests jointly showed that the presence of Sn, Ru and W enhances the activity of Pt towards ethanol electro-oxidation in the following order: Pt1Sn1/C > Pt1Ru1/C > Pt1W1/C > Pt1Pd1/C > Pt/C. Moreover, Pt1Ru1/C further modified by W and Mo showed improved ethanol electro-oxidation activity, but its DEFC performance was found to be inferior to that measured for Pt1Sn1/C. Under this respect, several PtSn/C catalysts with different Pt/Sn atomic ratio were also identically prepared and characterized and their direct ethanol fuel cell performances were evaluated. It was found that the single direct ethanol fuel cell having Pt1Sn1/C or Pt3Sn2/C or Pt2Sn1/C as anode catalyst showed better performances than those with Pt3Sn1/C or Pt4Sn1/C. It was also found that the latter two cells exhibited higher performances than the single cell using Pt1Ru1/C, which is exclusively used in PEMFC as anode catalyst for both methanol electro-oxidation and CO-tolerance. This distinct difference in DEFC performance between the catalysts examined here would be attributed to the so-called bifunctional mechanism and to the electronic interaction between Pt and additives. It is thought that an amount of -OHads, an amount of surface Pt active sites and the conductivity effect of PtSn/C catalysts would determine the activity of PtSn/C with different Pt/Sn ratios. At lower temperature values or at low current density regions where the electro-oxidation of ethanol is considered not so fast and its chemisorption is not the rate-determining step, the Pt3Sn2/C seems to be more suitable for the direct ethanol fuel cell. At 75 degreesC, the single ethanol fuel cell with Pt3Sn2/C as anode catalyst showed a comparable performance to that with Pt2Sn1/C, but at higher temperature of 90 degreesC, the latter presented much better performance. It is thought from a practical point of view that Pt2Sn1/C, supplying sufficient -OHads and having adequate active Pt sites and acceptable ohmic effect, could be the appropriate anode catalyst for DEFC. (C) 2003 Elsevier B.V. All rights reserved.

PtSnIr/C anode electrocatalysts: Promoting effect in direct ethanol fuel cells

This study investigates the promoting effect of PtSnIr/C (1:1:1) electrocatalyst anode, prepared by polymeric precursor method, on the ethanol oxidation reaction in a direct ethanol fuel cell (DEFC). All of the materials used were 20% metal m/m on carbon. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of Pt, PtOH 2, PtO 2, SnO 2 and IrO 2 at the electrocatalyst surface, indicating a possible decorated particle structure. X-ray diffractometry (XRD) analysis indicated metallic Pt and Ir as well as the formation of an alloy with Sn. Using the PtSnIr/C electrocatalyst prepared here with two times lower loading of Pt than PtSn/C E-tek electrocatalyst, it was possible to obtain the same maximum power density found for the commercial material. The main reaction product was acetic acid probably due to the presence of oxides, in this point the bifunctional mechanism is predominant, but an electronic effect should not be discarded. © 2012 Sociedade Brasileira de Química.

PtSnIr/C Anode Electrocatalysts: Promoting Effect in Direct Ethanol Fuel Cells

This study investigates the promoting effect of PtSnIr/C (1:1:1) electrocatalyst anode, prepared by polymeric precursor method, on the ethanol oxidation reaction in a direct ethanol fuel cell (DEFC). All of the materials used were 20% metal m/m on carbon. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of Pt, PtOH2, PtO2, SnO2 and IrO2 at the electrocatalyst surface, indicating a possible decorated particle structure. X-ray diffractometry (XRD) analysis indicated metallic Pt and Ir as well as the formation of an alloy with Sn. Using the PtSnIr/C electrocatalyst prepared here with two times lower loading of Pt than PtSn/C E-tek electrocatalyst, it was possible to obtain the same maximum power density found for the commercial material. The main reaction product was acetic acid probably due to the presence of oxides, in this point the bifunctional mechanism is predominant, but an electronic effect should not be discarded.

PtSnIr/C anode electrocatalysts: promoting effect in direct ethanol fuel cells

This study investigates the promoting effect of PtSnIr/C (1:1:1) electrocatalyst anode, prepared by polymeric precursor method, on the ethanol oxidation reaction in a direct ethanol fuel cell (DEFC). All of the materials used were 20% metal m/m on carbon. X-ray photoelectron spectroscopy (XPS) analysis showed the presence of Pt, PtOH2, PtO2, SnO2 and IrO2 at the electrocatalyst surface, indicating a possible decorated particle structure. X-ray diffractometry (XRD) analysis indicated metallic Pt and Ir as well as the formation of an alloy with Sn. Using the PtSnIr/C electrocatalyst prepared here with two times lower loading of Pt than PtSn/C E-tek electrocatalyst, it was possible to obtain the same maximum power density found for the commercial material. The main reaction product was acetic acid probably due to the presence of oxides, in this point the bifunctional mechanism is predominant, but an electronic effect should not be discarded.

Perspectives on the design and use of direct alcohol fuel cells fed by alcohol blends

The fast-growing power demand by portable electronic devices has promoted the increase of global production of portable PEM fuel cell, a quarter of them consist of direct methanol fuel cell (DMFC) units. These present the advantage of being fuelled directly with a liquid fuel, as well as direct ethanol fuel cells (DEFC) do.

Performance comparison of low-temperature direct alcohol fuel cells with different anode catalysts

Low-temperature polymer electrolyte membrane fuel cells directly fed by methanol and ethanol were investigated employing carbon supported Pt, PtSn and PtRu as anode catalysts, respectively. Employing Pt/C as anode catalyst, both direct methanol fuel cell (DMFC) and direct ethanol fuel cell (DEFC) showed poor performances even in presence of high Pt loading on anode. It was found that the addition of Ru or Sn to the Pt dramatically enhances the electro-oxidation of both methanol and ethanol. It was also found that the single cell adopting PtRu/C as anode shows better DMFC performance, while PtSn/C catalyst shows better DEFC performance. The single fuel cell using PtSn/C as anode catalyst at 90degreesC shows similar power densities whenever fueled by methanol or ethanol. The cyclic voltammetry (CV) and single fuel cell tests indicated that PtRu is more suitable for DMFC while PtSn is more suitable for DEFC. (C) 2003 Elsevier B.V. All rights reserved.

Preparation and characterization of PtSn/C anode electrocatalysts for direct ethanol fuel cell

Highly active PtSn/C catalyst was prepared by a polyol method. The catalyst was reduced in H-2/Ar atmosphere at 600 degreesC for 2 h in order to obtain different metallic phase. TEM images show uniform dispersion of spherical metal nanoparticles with average diameters of 1.8 and 3.9 nm for the as-prepared and treated catalysts, respectively. UV-vis spectrophotometry is employed to monitor the preparation process and the results indicate that Pt-Sn complex formed once the precursors of Pt and Sn were mixed together. The structure properties of the samples were characterized using X-ray diffraction. The results show that after reduction, the catalyst tends to form PtSn alloy. TPR experiment results show that Sn exists in multivalent state in the as-prepared sample while only zero-valence Sn was detected in the treated sample, while it could not be excluded that the multivalent tin existed in the treated sample. Cyclic voltammetry (CV) technique and single direct ethanol fuel cell (DEFC) tests indicate that the as-prepared catalyst possesses superior catalytic activity for ethanol oxidation to the treated sample. The results suggest that Pt and multivalent Sn are the active species for ethanol oxidation. (C) 2004 Elsevier B.V. All rights reserved.

Electrode catalysts behavior during direct ethanol fuel cell life-time test

In the present paper, a 60 h life-time test of a direct ethanol fuel cell (DEFC) at a current density of 20 mA cm(-2) (the beginning 38 h) and 40 mA cm(-2) (the last 22 h) was carried out. After the life-time test, the MEA could not achieve the former performance. X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX) were employed to characterize the anode and cathode catalyst before and after the life-time test. The XRD and TEM results showed that the particle size of the anode catalyst increased from 2.3 to 3.3 nm and the cathode from 3.0 to 4.6 nm. The EDX results of PtSn/C anode catalysts before and after the life-time test indicated that the content of the oxygen and tin, especially the content of the platinum, decreased prominently after the life-time test. The results suggest that the agglomeration of electrocatalysts, the destruction of the anode catalyst together with the fuel/water crossover from anode to cathode concurrently contribute to the performance degradation of the DEFC. (C) 2005 Elsevier B.V. All rights reserved.

Acetaldehyde Production in the Direct Ethanol Fuel Cell: Mechanistic Elucidation by Density Functional Theory

This study employs density functional theory (DFT) calculations to examine the mechanism by which acetaldehyde is formed on platinum in a typical direct ethanol fuel cell (DEFC). A pathway is found involving the formation of a strongly hydrogen-bonded complex between adsorbed ethanol and the surface hydroxyl (OH) species, followed by the facile alpha-dehydrogenation of ethanol, with spontaneous weakening of the hydrogen bond in favor of adsorbed acetaldehyde and water. This mechanism is found to be comparably viable on both the close-packed surface and the monatomic steps. Comparison of further reactions on these two sites strongly indicates that the steps act as net removers of acetaldehyde from the product stream, while the flat surface acts as a net producer.

Investigation of a Pt3Sn/C Electro-Catalyst in a Direct Ethanol Fuel Cell Operating at Low Temperatures for Portable Applications

A 20% Pt3Sn/C catalyst was prepared by reduction with formic acid and used in a direct ethanol fuel cell at low temperatures. The electro-catalytic activity of this bimetallic catalyst was compared to that of a commercial 20% Pt/C catalyst. The PtSn catalyst showed better results in the investigated temperature range (30 degrees-70 degrees C). Generally, Sn promotes ethanol oxidation by adsorption of OH species at considerably lower potentials compared to Pt, allowing the occurrence of a bifunctional mechanism. The bimetallic catalyst was physico-chemically characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses. The presence of SnO2 in the bulk and surface of the catalyst was observed. It appears that SnO2 can enhance the ethanol electro-oxidation activity at low potentials due to the supply of oxygen-containing species for the oxidative removal of CO and CH3CO species adsorbed on adjacent Pt active sites.