Noble metal nanoparticles, a process for preparing these and their use

Inactive Publication Date: 2002-03-21
DMC2 DEGUSSA METALS CATALYSTS CERDEC +1
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

0016] Furthermore it was found that the water based solution of the polysaccharide has to be preferably in the pH neutral form. A pH range of 5 to 8 , preferably 5.5 to 7.5 and most preferably 6 to 7 is required to ensure stability of the polysaccharide. At a lower, more acidic pH, as well as at higher alkaline pH values, the glycosidic bonds of the polysaccharide are broken up and the macromolecule is destroyed. This effect is used in turn to remove traces of the stabilizer after the colloidal noble metal particles have been deposited on the suitable substrate material (ionomer membranes, gas diffusion electrodes or carbon black supports) as described further below in this invention.
0017] When properly selected, the stabilizers mentioned are able to keep the colloidal preparation of nanoparticles, even in high concentrations, stable for a long time. For this purpose, it has proven advantageous

Problems solved by technology

The process is complicated and expensive and provides only electrocatalysts which are contaminated with sulfur due to using sulfur-containing precursor compounds for the platinum.
It has been shown that these stabilizers adhere firmly to the noble metal surface, due to their long polymethylene main chains, and thus contaminate the catalytically active catalyst surfaces.
For this reason, these nanoparticles are not very suitable as catalytically active species for membrane electrode assem

Method used

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  • Noble metal nanoparticles, a process for preparing these and their use
  • Noble metal nanoparticles, a process for preparing these and their use
  • Noble metal nanoparticles, a process for preparing these and their use

Examples

Experimental program
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example 1

[0051] a) Preparing Pt Nanoparticles

[0052] 11.1 g of a solution of bis(ethanolammonium) hexahydroxoplatinate (Pt content 9 wt. %; total chlorine content <100 ppm; from dmc.sup.2, Hanau) were added dropwise to 1.5 l of fully deionized water in which 1.0 g of gum arabic (Merck) had previously been dissolved. Then, 1 l of ethanol was added with stirring and the resulting mixture was heated, wherein the mixture turned black. The solution was kept under reflux for one hour at 85.degree. C. and then concentrated to a volume of 100 ml by evaporation. The colloidal solution prepared in this way had a pH value of 5.9 and contained 10 g Pt / l (1 wt.% Pt) and 10 g / l (1 wt. %) of the stabilizer gum arabic. The ratio of Pt nanoparticles to stabilizer was thus 1:1. The total chlorine content of the solution was less than 10 ppm. The average size of the Pt particles was determined using TEM (transmission electron microscopy) and was 2 nm.

[0053] b) Catalyzing Ionomer Membranes

[0054] 5.6 g of the col...

example 2

[0058] a) Preparation of Pt / Ru Nanoparticles

[0059] 7.28 g of a solution of bis(ethanolammonium) hexahydroxoplatinate (Pt content 9 wt. %; total chlorine content <100 ppm; from dmc.sup.2, Hanau) and 2.265 g of a solution of ruthenium nitrosylnitrate (Ru content 15 wt. %, total chlorine content <200 ppm; from dmc.sup.2, Hanau) were added dropwise to 1.5 1 of fully deionized water, in which 1.0 g of gum arabic (Merck) had been dissolved. Then 1 l of ethanol was added with stirring and the resulting mixture was heated, wherein it turned black. The solution was held under reflux for one hour at 85.degree. C. and then concentrated by evaporation to a volume of 100 ml. The colloidal solution obtained in this way had a pH value of 5.7 and contained 10 g PtRu / l (1 wt. % PtRu, atomic ratio 1:1) and 10 g / l (1 wt. %) of the stabiliser gum arabic. The ratio of PtRu nanoparticles to stabilizer was thus 1:1. The total chlorine content of the solution was less than 50 ppm. The average size of the P...

example 3

[0062] 2.22 g of a solution of bis(ethanolammonium) hexahydroxoplatinate (Pt content 9 wt. %; total chlorine content <100 ppm; from dmc.sup.2, Hanau) were added dropwise to 1.5 l of fully deionized water in which 0.2 g of Kelzan (xanthan gum, Lubrizol-Langer, Bremen) had previously been dissolved. Then 1 l of isopropanol was added with stirring and the resulting mixture was heated, wherein it turned black. The solution was held under reflux for one hour at 85 .degree. C. and then concentrated by evaporation to a volume of 100 ml. The colloidal solution obtained in this way had a pH value of 5.6 and contained 2 g Pt / l (0.2 wt. % Pt) and 2 g / l (0.2 wt. %) of the stabilizer Kelzan. The ratio of Pt nanoparticles to stabilizer was thus 1:1. The total chlorine content of the solution was less than 30 ppm. The average size of the Pt particles was determined by TEM and was 2.5 nm.

[0063] An ionomer membrane was catalyzed in the same way as described in example 1 and a membrane with a total p...

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Abstract

Nanoparticles which contain noble metals alone or noble metals in combination with base metals. The nanoparticles are embedded in an aqueous solution of a temporary stabilizer based on a polysaccharide.

Description

INTRODUCTION AND BACKGROUND[0001] The present invention provides noble metal-containing nanoparticles for producing membrane electrode assemblies (MEAS) for fuel cells, in particular for low temperature fuel cells, for example polymer electrolyte membrane fuel cells (PEM fuel cells) and direct methanol fuel cells (DMFC). New types of colloidal solutions which contain the noble metal alone or in association with other metals are described, wherein the metals are in the form of nanoparticles embedded in a temporary stabilizer. The nanoparticles are used to produce electrocatalysts and catalysed components for fuel cells. Using these nanoparticles, catalyzed ionomer membranes, catalyzed gas diffusion electrodes (so-called "backings") and membrane electrode assemblies can be produced.[0002] Fuel cells convert a fuel and an oxidizing agent which are spatially separated from each other at two electrodes into electricity, heat and water. Hydrogen or a hydrogen-rich gas may be used as the f...

Claims

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Application Information

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IPC IPC(8): B82B1/00B01J13/00B01J23/42B01J23/46B01J23/652B01J35/00B01J35/02B22F1/054B22F1/0545B22F1/10B22F5/00C09C1/62C09C3/10H01M4/86H01M4/88H01M4/90H01M4/92H01M8/1004
CPCB01J13/0043B01J23/462B01J35/0013B22F1/0018B22F1/0022B22F1/0059B22F2998/00B82Y30/00H01M4/8605H01M4/92H01M4/926H01M8/1004Y02E60/521Y02P70/50Y02E60/50B22F1/0545B22F1/054B22F1/10B82B1/00B82B3/00
Inventor STARZ, KARL-ANTONGOIA, DANKOEHLER, JOACHIMBANISCH, VOLKER
Owner DMC2 DEGUSSA METALS CATALYSTS CERDEC
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