Synthesis of noble metal, sulphide catalysts in a sulfide ion-free aqueous environment
A noble metal sulfide catalyst obtained by reaction of a precursor of at least one noble metal with a thionic species in an aqueous environment essentially free of sulfide ions useful as an electrocatalyst in the depolarized electrolysis of hydrochloric acid.
1. A method for producing a noble metal sulfide catalyst comprising reacting a solution of a precursor of the at least one noble metal, optionally a chloride, with an aqueous solution containing a thionic species in an essentially sulfide-free environment.
2. The method of claim 1 wherein the pH of said solution of a precursor of at least one noble metal and said aqueous solution containing a thionic species is between 0.1 and 4.
3. The method of claim 2 wherein said solution of a precursor of at least one noble metal further contains carbon particles, optionally a carbon black with a surface area exceeding 50 m 2 /g.
4. The method of claim 1 wherein said thionic species is selected from the group of thiosulfates, dithionates, trithionates, tetrathionates, pentathionates, heptathionates and noble or non-noble metal thionates, optionally as sodium or ammonium salts.
5. The method of claim 1 wherein said aqueous solution containing a thionic species is added to said solution of a precursor of a noble metal in descrete aliquots, optionally 2 to 10 equivalent aliquots at a time interval of 15 seconds to ten minutes.
6. The method of claim 5 wherein said completion of the reaction is determined by detection of a color change.
7. The method of claim 5 further comprising isolating the resulting noble metal sulfide catalyst and subjecting the same to a thermal treatment at a temperature between 150° and 700° C.
8. The method of claim 1 wherein said aqueous solution containing a thionic species is added to said solution of a precursor of a noble metal and the resulting solution is brought to boiling temperature for 5 to 120 minutes until completion of the reaction.
9. The method of claim 1 wherein said at least one noble metal is selected from the group consisting of ruthenium, rhodium, platinum, iridium and palladium.