The present invention relates to a process for the preparation of an electrode or a precursor thereof comprising sulfurizing a metal layer deposited on an electrode substrate, said metal layer comprising nickel, iron or a mixture of iron with nickel or cobalt. The invention also relates to the electrode or a precursor thereof obtainable by said process, the use thereof in electrocatalysis, for instance in alkaline water electrolysis, and to a device comprising said electrode.
CLAIMS 1. Process for making a precursor of an electrode for alkaline water electrolysis, said electrode comprising a precursor of an electrocatalytically active material comprising a compound of formula M<1>x(i-y)M<2>(i-<X>)(i-y)S and/or a compound of formula M<1>X M<2>(1-<X>)S2 wherein y is higher than 0 and equal to or lower than 0.2; said process comprising the steps of: (i) in a first alternative of step (i) providing a substrate for electrode comprising an outer layer which comprises a compound of formula M<1>X M<2>(1.<X>) wherein: M<1>is Fe and M<2>is Co; x is higher than 0 and equal to or lower than 1 ; or, in a second alternative of step (i), (a) providing a mixture of powders of M<1>and M<2>such that the molar ratio of M<1>to M<2>is x:(1-x) wherein M<1>is selected from the group consisting of Fe and Ni; M<2>is selected from the group consisting of Ni and Co; when M<1>is Fe, x is higher than 0 and lower than 1 ; and when M<1>is Ni, x is 1 ; (b) providing a substrate for electrode; (c) evaporating the mixture of powders provided in step (a), thus producing a gaseous metal mixture, (d) depositing the gaseous metal mixture produced in step (c) on the substrate provided in step (b); thereby producing a substrate for electrode comprising an outer layer which comprises a compound of formula M<1>X M<2>(1.<X>); (ii) contacting the substrate provided in (i) with an atmosphere comprising gaseous sulphur in conditions allowing for sulfurizing at least partially one metal comprised in said coating. 2. The process according to claim 1 wherein the first alternative of step (i) comprises providing a substrate for electrode comprising an outer layer which comprises a compound of formula M<1>X M<2>(1.<X>) that is substantially free of nickel. 3. The process according to any one of claims 1 to 2 wherein the first alternative of step (i) comprises providing a substrate for electrode comprising an outer layer which comprises a compound of formula M<1>X M<2>(1.<X>) wherein M<1>is Fe and x is 1 ; preferably said substrate is iron foam. 4. The process according to claim 1 wherein M<1>is selected from the group consisting of Fe and Ni and; M<2>is selected from the group consisting of Ni and Co; when M<1>is Fe, x is higher than 0 and lower than 1 ; when M<1>is Ni, x is 1 ; y is higher than 0 and equal to or lower than 0.2; and wherein step (i) comprises: (a) providing a mixture of powders of M<1>and M<2>such that the molar ratio of M<1>to M<2>is x:(1-x); (b) providing a substrate for electrode; (c) evaporating the mixture of powders provided in step (a), thus producing a gaseous metal mixture, (d) depositing the gaseous metal mixture produced in step (c) on the substrate provided in step (b). 5. The process according to claim 4 wherein x is equal to or higher than 0.50 and lower than 1 when M<1>is Fe; preferably x is selected from 0.55 and 0.85 when M<1>is Fe. 6. The process according to any one of claims 4 to 5 wherein the mixture of powders provided in step (a) is selected from the group consisting of: Ni powder; a mixture of Fe powder and Ni powder whereby the molar ratio of Fe to Ni is 55:45; a mixture of Fe powder and Ni powder whereby the molar ratio of Fe to Ni is 85:15; and a mixture of Fe powder and Co powder whereby the molar ratio of Fe to Co is 55:45. 7. The process according to any one of claims 4 to 6 wherein the substrate for electrode of step (b) is selected from the group consisting of metal mesh, metal foam, metal foil, metal felt, metal disk, carbon paper, carbon felt, transparent conducting oxides, glassy carbon and carbon cloth; preferably, the substrate for electrode is selected from the group consisting of glassy carbon, steel and iron disk; more preferably, the substrate for electrode is selected from the group consisting of glassy carbon and iron disk. 8. The process according to any one of claims 4 to 7 wherein step (c) comprises heating said mixture of powders by means of an electric current. 9. The process according to any one of claims 4 to 8 wherein step (d) comprises condensing the gaseous mixture produced in step (c) on the surface of the substrate; thereby producing a substrate coated with an outer layer comprising M<1>and further comprising M<2>when x is not 1 , said layer having preferably a thickness of between 50 nm and 10 .m; more preferably of 100 nm. 10. The process according to any one of claims 8 to 9 wherein steps (c) and (d) are carried out under vacuum; preferably at a pressure of equal to or less than 10'<4>mbar. 11. The process according to any one of claims 1 to 10 wherein step (ii) comprises heating at a temperature of between 180 °C and 300 °C for a period of time of between 1 hour and 20 hours and under vacuum the substrate provided in (i) in the presence of solid sulphur; preferably at a temperature of 200 °C and/or at a pressure prior to sulphur vaporization of between 10'<5>and 10'<6>mbar and/or for a period of time of 4 hours. 12. Electrode precursor obtainable by the method according to any of claims 1 to 11. 13. Electrode precursor according to claim 12 wherein the at least partially sulfurized coating material does not essentially comprise particles or flakes of said material. 14. Process of activating an electrode precursor as defined in claim 12 comprising the circulation of a current through said precursor electrode placed in a basic medium at an electrode potential equal to or higher than 1.30 V vs RHE; said basic medium being preferably an aqueous solution of alkaline hydroxide salt, such as potassium hydroxide, with a preferred concentration equal to or higher than 0.1 M. 15. Electrode obtainable by the method of claim 14. 16. Use of the electrode precursor according to any one of claims 12 to 13 or the electrode of claim 15 as electrode in an electrocatalytic process; preferably alkaline water electrolysis. 17. Device, such as an alkaline water electrolyser, comprising one or more electrodes selected from the electrodes according to any one of claims 12 to 13 and the electrode of claim 15.