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

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.

1 - 23 . (canceled) 
     
     
         24 . A process for the catalytic coating of a substrate material which comprises the steps of:
 a) preparing an aqueous solution comprising noble metal nanoparticles embedded in an aqueous solution of a temporary stabilizer which is a polysaccharide;   b) applying said aqueous solution comprising said noble metal nanoparticles to the substrate material; and   c) removing the temporary stabilizer.   
     
     
         25 . The process according to claim  1 , wherein the temporary stabilizer is removed by pyrolysis at temperatures up to 250° C. 
     
     
         26 . The process according to claim  1 , wherein the temporary stabilizer is removed by acidic or alkaline hydrolysis. 
     
     
         27 . The process according to claim  1 , wherein the substrate material is a gas diffusion layer. 
     
     
         28 . The process according to claim  1 , wherein the substrate material is a catalyzed gas diffusion layer or a gas diffusion electrode. 
     
     
         29 . The process according to claim  1  further comprising a washing step. 
     
     
         30 . The process according to claim  1 , wherein said aqueous solution comprising said noble metal nanoparticles is applied to the substrate material by a spray process, by doctor blading, by a brushing process, by an immersing process, by an impregnating process or by a screen printing process. 
     
     
         31 . The process according to  claim 27 , wherein the gas diffusion layer comprises a carbon fleece or a carbon fibre paper. 
     
     
         32 . The process according to  claim 27 , wherein the gas diffusion layer comprises a microlayer, said microlayer comprising a hydrophobic polymer and carbon black. 
     
     
         33 . The process according to  claim 32 , wherein the noble metal nanoparticles are directly deposited onto the microlayer. 
     
     
         34 . The process according to claim  1 , wherein the aqueous solution comprising the noble metal nanoparticles is mixed with additives selected from the group consisting of ionomer, carbon black and further electrocatalysts and mixtures and combinations thereof. 
     
     
         35 . The process according to claim  1 , wherein the noble metal nanoparticles contain at least one noble metal selected from the group consisting of platinum, palladium, rhodium, iridium, ruthenium, osmium, gold and silver and mixtures and combinations thereof. 
     
     
         36 . The process according to claim  1 , wherein the noble metal nanoparticles contain, in addition to the noble metal, at least one base metal selected from the group consisting of iron, cobalt, nickel, copper, titanium, vanadium, chromium, manganese, molybdenum, tungsten and rhenium.