Method of fabricating a bath of electrolyte for plating a platinum-based metallic underlayer on a metallic substrate

1. A fabrication method for a bath of electrolyte, the method comprising:

a) providing a first system having ligands and amine functional groups, said first system comprising an aqueous solution of an amino ligand comprising:

(i) at least one compound X—(NH 2 ) n , where X is selected from the group consisting of (CH 3 , CH 3 —CH 2 , CH 3 —(CH 2 ) m ;

(ii) NH 3 ; or

(iii) an x P− (NH 4 ) + p salt where x is an acid radical selected from the group consisting of PO 4 3− , HPO 4 2− , H 2 PO 4 − , SO 4 2− , HSO 4 − , and CH 3 COO−, where n, m, and p are non-zero integers;

b) providing a second system forming a buffer system;

c) providing a third system providing a metallic salt, and comprising an aqueous solution of platinum; the metallic salt being at least one salt of platinum of degree of oxidation IV;

d) providing a fourth system suitable for imparting the property of conduction to the bath of electrolyte;

forming a first solution B by grouping the first system, the second system, and the fourth system together in a single solution;

forming a second solution A comprising sodium hydroxide and the least one salt of platinum of degree of oxidation IV of the third system; and

e) mixing together the four systems so as to obtain the electrolyte bath of electrolyte;

wherein

the mixing comprises:

e1) covering the first solution B and raising the first solution B to a temperature of at least 50° C. for at least 1h30 and

e2) adding the second solution A to the first solution B and mixing the second solution A with the first solution B thereby forming a platinum amino complex and thus obtaining said bath of electrolyte.

2. The method according to claim 1 , the first solution B comprises the x p− (NH 4 ) + p salt, where x=HPO 4 2− and p=2, and/or x=H 2 PO 4 − and p=1.

3. The method according to claim 2 , further comprising

f) heating the bath of electrolyte to a temperature of 80° C. to 97° C. for at least two hours; and

g) electroplating a deposit of platinum on a metallic substrate using said heated bath of electrolyte.

4. The method according to claim 3 , wherein prior to e2), the first solution B is raised to a temperature of 60° C.

5. The method according to claim 3 , wherein the molar ratio of sodium hydroxide (NaOH) to the salt of platinum of degree of oxidation IV is 2.

6. The method according to claim 1 , wherein said salt of platinum of degree of oxidation IV is Y 2 PtM 6 with Y═NH 4 + , H + , or K + , and M=Cl − or OH − .

7. The method according to claim 6 , wherein in the second solution A, said salt of platinum of degree of oxidation IV is diammonium hexachloroplatinate of formula (NH 4 ) 2 PtCl 6 .

8. The method according to claim 1 , wherein x of the x p− (NH 4 ) + p salt is an acid radical selected from the group consisting of HPO 4 2− and H 2 PO 4 − ; and wherein the first system comprises diammonium hydrogen phosphate (NH 4 ) 2 HPO 4 , ammonium dihydrogen phosphate NH 4 H 2 PO 4 , or a mixture thereof.

9. The method according to claim 8 , wherein a molar ratio between the ammonium dihydrogen phosphate NH 4 H 2 PO 4 and the diammonium hydrogen phosphate (NH 4 ) 2 HPO 4 is 2.

10. The method according to claim 1 , wherein said second solution A is heated before step e2).