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.

The effect of methanol and ethanol cross-over on the performance of PtRu/C-based anode DAFCs

In the present work, the cross-over rates of methanol and ethanol, respectively, through Nafion(R)-115 membranes at different temperatures and different concentrations have been measured and compared. The changes of Nafion(R)-115 membrane porosity in the presence of methanol or ethanol aqueous solutions were also determined by weighing vacuum-dried and alcohol solution-equilibrated membranes. The techniques of anode polarization and adsorption stripping voltarnmetry were applied to compare the electrochemical activity and adsorption ability, respectively. To investigate the consequences of methanol and ethanol permeation from the anode to the cathode on the performance of direct alcohol fuel cells (DAFCs), single DAFC tests, with methanol or ethanol as the fuel, have been carried out and the corresponding anode and cathode polarizations versus dynamic hydrogen electrode (DHE) were also performed. The effect of alcohol concentration on the performance of PtRu/C anode-based DAFCs was investigated.

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.

Carbon-supported Pd–Ir catalyst as anodic catalyst in direct formic acid fuel cell

It was reported for the first time that the electrocatalytic activity of the Carbon-supported Pd-Ir (Pd-Ir/C) catalyst with the suitable atomic ratio of Pd and Ir for the oxidation of formic acid in the direct formic acid fuel cell (DFAFC) is better than that of the Carbon-supported Pd (Pd/C) catalyst, although Ir has no electrocatalytic activity for the oxidation of formic acid. The potential of the anodic peak of formic acid at the Pd-Ir/C catalyst electrode with the atomic ratio of Pd and Ir = 5:1 is 50 mV more negative than that and the peak current density is 13% higher than that at the Pd/C catalyst electrode.

Platinum-coated gold nanoporous film surface: Electrodeposition and enhanced electrocatalytic activity for methanol oxidation

This report describes the preparation of Pt-nanoparticle-coated gold-nanoporous film (PGNF) on a gold substrate via a simple "green" approach. The gold electrode that has been anodized under a high potential of 5 V is reduced by freshly prepared ascorbic acid (AA) solution to obtain gold nanoporous film electrode. Then the Pt nanoparticle is grown on the electrode by cyclic voltammetry (CV).

Electrostatic layer-by-layer a of platinum-loaded multiwall carbon nanotube multilayer: A tunable catalyst film for anodic methanol oxidation

A simple layer-by-layer (LBL) electrostatic adsorption technique was developed for deposition of films composed of alternating layers of positively charged poly(diallyldimethylammonium chloride) (PDDA) and negatively charged multiwall carbon nanotubes bearing platinum nanoparticles (Pt-CNTs). PDDA/Pt-CNT film structure and morphology up to six layers were characterized by scanning electron microscopy and ultraviolet-visible spectroscopy, showing the Pt-CNT layers to be porous and uniformly deposited within the multilayer films.

Highly active PtRu catalysts supported on carbon nanotubes prepared by modified impregnation method for methanol electro-oxidation

A simple and rapid synthesis method (denoted as modified impregnation method, MI) for PtRu/CNTs (MI) and PtRu/C (MI) was presented. PtRu/CNTs (MI) and PtRu/C (MI) catalysts were characterized by transmission electron microscopy (TEM) and X-ray diffractometry. It was shown that Pt-Ru particles with small average size (2.7 nm) were uniformly dispersed on carbon supports (carbon nanotubes and carbon black) and displayed the characteristic diffraction peaks of Pt face-centered cubic structure.

Electrodeposition of platinum nanoclusters on type I collagen modified electrode and its electrocatalytic activity for methanol oxidation

We firstly reported a novel polymer matrix fabricated by type I collagen and polymers, and this matrix can be used as nanoreactors for electrodepositing platinum nanoclusters (PNCs). The type I collagen film has a significant effect on the growth of PNCs. The size of the platinum nanoparticles could be readily tuned by adjusting deposition time, potential and the concentration of electrolyte, which have been verified by field-emitted scanning electron microscopy (FE-SEM). Furthermore, cyclic voltammetry (CV) has demonstrated that the as-prepared PNCs can catalyze methanol directly with higher activity than that prepared on PSS/PDDA film, and with better tolerance to poisoning than the commercial E-TEK catalyst. The collagen-polymer matrix can be used as a general reactor to electrodeposit other metal nanostructures.

High activity PtRu/C catalysts synthesized by a modified impregnation method for methanol electro-oxidation

A modified impregnation method was used to prepare highly dispersive carbon-supported PtRu catalyst (PtRu/C). Two modifications to the conventional impregnation method were performed: one was to precipitate the precursors ((NH4)(2)PtCl6 and Ru(OH)(3)) on the carbon support before metal reduction: the other was to add a buffer into the synthetic solution to stabilize the pH. The prepared catalyst showed a much higher activity for methanol electro-oxidation than a catalyst prepared by the conventional impregnation method. even higher than that of current commercially available, state-of-the-art catalysts. The morphology of the prepared catalyst was characterized using TEM and XRD measurements to determine particle sizes, alloying degree, and lattice parameters. Electrochemical methods were also used to ascertain the electrochemical active surface area and the specific activity of the catalyst.