Apparatus and method for the synthesis and treatment of metal monolayer electrocatalyst particles in batch or continuous fashion

Abstract

An apparatus and method for the synthesis and treatment of electrocatalyst particles in batch or continuous fashion is provided. In one embodiment, the apparatus is comprised of a three-electrode cell which includes a reference electrode, a counter electrode, and a working electrode. The working electrode is preferably a cylindrical vessel having an electrically conductive region. The electrode assembly is introduced into a slurry containing metal ions and a plurality of particles. During operation an electrical potential is applied and the working electrode is rotated at a predetermined speed. When particles in the slurry collide with the electrically conductive region the transferred charge facilitates deposition of an ad-layer of the desired metal. In this manner film growth can commence on a large number of particles simultaneously. This process is especially suitable as a commercial thin film deposition process for forming catalytically active layers on nanoparticles for use in energy conversion devices.

1 . An apparatus for depositing ultrathin films on a plurality of microparticles or nanoparticles comprising:
 a cell for holding a slurry containing the plurality of microparticles or nanoparticles,   a first electrode having a cylindrical body comprising:   a first electrically insulating section provided with a hollow channel through its interior, and   an electrically conductive section which is connected to an external power source by means of a conducting medium which passes through the hollow channel,   wherein the first electrode is configured to rotate about a longitudinal axis; and   a second electrode comprising a good electrical conductor.   
     
     
         2 . The apparatus of  claim 1  further comprising a third electrode which has a known reduction potential. 
     
     
         3 . The apparatus of  claim 2  wherein the third electrode is a normal hydrogen electrode or a silver-silver chloride reference electrode. 
     
     
         4 . The apparatus of  claim 1  wherein the electrically insulating section comprises polytetrafluoroethylene. 
     
     
         5 . The apparatus of  claim 1  wherein the electrically conductive section comprises a material selected from the group consisting of titanium activated by a ruthenium coating, stainless steel, and glassy carbon. 
     
     
         6 . The apparatus of  claim 1  wherein the second electrode comprises a platinum wire. 
     
     
         7 . The apparatus of  claim 1  wherein the first electrode has a circular, oval, hexagonal, or octagonal cross-section. 
     
     
         8 . The apparatus of  claim 1  wherein the first electrode is screw-shaped. 
     
     
         9 . The apparatus of  claim 1  wherein the first electrode further comprises a second insulating section which is provided at an end of the first electrode such that the electrically conductive section is located between the first and second insulating sections. 
     
     
         10 . The apparatus of  claim 1  wherein the cell comprises a glass container. 
     
     
         11 . The apparatus of  claim 1  further comprising a power supply configured to supply an applied potential to the electrically conductive section of the first electrode. 
     
     
         12 . The apparatus of  claim 11  wherein the power supply is operable to supply a voltage in the range of −1 to +1 Volts. 
     
     
         13 . The apparatus of  claim 1  further comprising a rotational controller configured to rotate the first electrode at a predetermined rotational speed. 
     
     
         14 . The apparatus of  claim 13  wherein the rotational speed is 0 to 500 rotations per minute. 
     
     
         15 . The apparatus of  claim 14  wherein the rotational speed is 10 to 200 rotations per minute. 
     
     
         16 . A method of forming a film on a plurality of microparticles or nanoparticles by electrodeposition, the method comprising:
 (a) preparing a slurry comprising the plurality of microparticles or nanoparticles and an electrolyte having a predetermined concentration of ions of a material to be deposited as an adlayer;   (b) contacting with the slurry the apparatus according to  claim 1 ;   (c) rotating the first electrode at a predetermined rotational speed; and   (d) applying a predetermined potential to the electrically conductive section of the first electrode for a predetermined duration.   
     
     
         17 . The method of  claim 16  wherein the first electrode is rotated at a rotational speed of 100 rotations per minute. 
     
     
         18 . The method of  claim 16  wherein the applied potential is between −1 and +1 Volts. 
     
     
         19 . The method of  claim 18  wherein the predetermined duration is between 10 minutes and 2 hours. 
     
     
         20 . The method of  claim 16  wherein an adlayer of up to one monolayer is deposited on the surface of the microparticles or nanoparticles. 
     
     
         21 . The method of  claim 16  wherein the slurry is prepared using one to twenty grams of microparticles or nanoparticles in 200 ml to 2000 ml of electrolyte solution. 
     
     
         22 . The method of  claim 16  wherein the ions are selected from the group consisting of Cu, Pb, Bi, Sn, Ce, Ag, Sb, and Tl. 
     
     
         23 . The method of  claim 16  further comprising removing excess ions from the slurry after a predetermined potential has been applied to the first electrode. 
     
     
         24 . The method of  claim 23  further comprising adding ions of a metal which is more noble than the material deposited as an adlayer to the slurry to facilitate deposition of the more noble metal by galvanic displacement, and whereby the process of galvanic displacement results in deposition of the more noble metal. 
     
     
         25 . The method of  claim 24  wherein ions of a more noble metal are produced by adding a salt of one or more of PdCl 2 , K 2 PtCl 4 , AuCl 3 , IrCl 3 , RuCl 3 , OsCl 3 , and ReCl 3 , and whereby addition of the salt results in galvanic displacement of the material deposited as an adlayer by the more noble metal contained within the salt. 
     
     
         26 . The method of  claim 16  wherein the slurry is processed as a batch. 
     
     
         27 . The method of  claim 16  wherein the slurry is continuously fed to the apparatus for depositing ultrathin films using a predetermined flow rate.