METHOD FOR THE TREATMENT OF A METAL SUBSTRATE FOR THE PREPARATION OF ELECTRODES

Abstract

A method for surface treatment of a metal substrate, suitable for use as electrode support in electrochemical processes by: (a) immersion of the metal substrate and of at least one counter electrode in an electrolyte selected from hydrochloric acid, nitric acid, boric acid or sulfuric acid at a weight concentration of between 10-40%; (b) application of an anodic current density to the metal substrate of between 0.1 and 30 A/dm.sup.2 for a time of between 0.5 and 120 minutes. An electrode for gas evolution in electrochemical processes obtained from a correspondingly treated substrate.

Claims

1. A method for surface treatment of a metal substrate selected from nickel or nickel alloy, suitable for use as electrode support in electrochemical processes, comprising the following steps: (a) immersing said metal substrate and at least one counter electrode in an electrolyte selected from hydrochloric acid, nitric acid, boric acid or sulfuric acid at a weight concentration of between 10-40%; (b) applying an anodic current density to said metal substrate between 0.1 and 30 A/dm.sup.2 for a time between 0.5 and 120 minutes.

2. The method according claim 1 wherein said metal substrate is a mesh or a punched or expanded sheet.

3. The method according to claim 1 wherein said metal substrate has a thickness below 1.2 mm.

4. The method according to claim 3 wherein said metal substrate has a thickness equal to or less than 0.5 mm.

5. (canceled)

6. The method according to claim 1 wherein the applied anodic current density is between 5 and 10 A/dm.sup.2.

7. The method according to claim 6 wherein the application time of the anodic current density is between 2 and 10 minutes.

8. The method according to claim 1 wherein the weight concentration of said electrolyte is between 15-30%.

9. The method according to claim 1 wherein the metal substrate is nickel or nickel alloy comprising a further step (c) subsequent to step (b) of nickel electrodeposition comprising the addition to said electrolyte of a nickel salt in a concentration by weight between 150 and 300 g/l and subsequent application of a cathodic current density to said metal substrate between 0.1 and 3 A/dm.sup.2 for a time between 0.5 and 120 minutes at a temperature between 15 and 70° C.

10. A method for manufacturing an electrode for gas evolution in electrochemical processes, comprising the following steps: treating a metal substrate with the method of claim 1, and applying a catalytic coating comprising one or more noble or alloy metals or their oxides and/or one or more metals belonging to the rare earth group or their oxides, to said treated metal substrate.

11. An electrode for gas evolution in electrochemical processes comprising a metal substrate, selected from nickel or nickel alloy, prepared according to the method described in claim 1, said metal substrate having a degree of homogeneity of the roughness profile, expressed as the mean square deviation Ra values, of less than 25%, and a catalytic coating comprising one or more noble or alloy metals or their oxides and/or one or more metals belonging to the rare earth group or their oxides.

12. (canceled)

13. An electrode for gas evolution in electrochemical processes comprising a metal substrate, selected from nickel or nickel alloy, prepared according to the method described in claim 9, comprising a layer of nickel electrodeposited directly on the metal substrate and a catalytic coating comprising one or more metals or alloys or their oxides and/or one or more metals belonging to the group of rare earths or their oxides.

14. A cell for the electrolysis of water or for the electrolysis of alkali chloride solutions comprising an anodic compartment and a cathodic compartment separated by an ion-exchange membrane or by a diaphragm, wherein the cathodic compartment is equipped with an electrode according to claim 11.

Description

EXAMPLE 1

[0057] A nickel mesh with dimensions 100 mm×100 mm×0.89 mm was washed and degreased with acetone according to standard procedure, then subjected to a surface treatment by immersion in a 20% HCl solution at room temperature close to a nickel counter-electrode. An anodic current density equivalent to 10 A/m.sup.2 was applied to the nickel mesh for 1.7 minutes.

[0058] At the end of the treatment, the weight loss was verified and the degree of roughness was measured in different points of the mesh

[0059] The mesh thus obtained was identified as sample E1

EXAMPLE 2

[0060] A nickel mesh with dimensions 100 mm×100 mm×0.89 mm was washed and degreased with acetone according to standard procedure, then subjected to a surface treatment by immersion in a 20% HCl solution at room temperature close to a nickel counter-electrode. An anodic current density equivalent to 5 A/m.sup.2 was applied to the nickel mesh for 3.3 minutes.

[0061] At the end of the treatment, the weight loss was verified and the degree of roughness was measured in different points of the mesh.

[0062] The mesh thus obtained was identified as sample E2.

EXAMPLE 3

[0063] A nickel mesh of dimensions 100 mm×100 mm×0.89 mm was washed and degreased with acetone according to the standard procedure, then subjected to a surface treatment by immersion in a 10% HCl solution at room temperature close to a nickel counter-electrode. An anodic current density equivalent to 12 A/m.sup.2 was applied to the nickel mesh for 1.6 minutes.

[0064] At the end of the treatment, the weight loss was verified and the degree of roughness was measured in different points of the mesh.

[0065] The mesh thus obtained was identified as sample E3.

EXAMPLE 4

[0066] A nickel mesh with dimensions 100 mm×100 mm×0.89 mm was washed and degreased with acetone according to standard procedure, then subjected to a surface treatment by immersion in a 20% HCl solution at room temperature close to a nickel counter-electrode. An anodic current density equivalent to 1.5 A/m.sup.2 was applied to the nickel mesh for 6 minutes.

[0067] It was then coated with 5 coats of an aqueous solution containing Pt, Pr and Pd with a 15-minute heat treatment at 450° C. after each coat until obtaining a coating of 1.90 g/m.sup.2 of Pt, 1.24 g/m.sup.2 of Pd and 3.17 g/m.sup.2 of Pr.

[0068] On the catalytic layer thus obtained 4 coats of a second solution containing Pt, Pr and Pd were applied in a different ratio compared to the first solution with a heat treatment of 15 minutes at 450° C. after each coat until obtaining a coating of 1.77 g/m.sup.2 of Pt, 1.18 g/m.sup.2 of Pd and 1.59 g/m.sup.2 of Pr.

[0069] The electrode thus obtained was identified as sample E4.

EXAMPLE 5

[0070] A nickel mesh with dimensions 100 mm×100 mm×0.89 mm was washed and degreased with acetone according to standard procedure, then subjected to a surface treatment by immersion in a 20% HCl solution at room temperature close to a nickel counter-electrode. An anodic current density equivalent to 1.5 A/m.sup.2 was applied to the nickel mesh for 3 minutes.

[0071] The nickel mesh was subsequently subjected to a nickel electro-deposition treatment after the addition of NiCl.sub.2, at a concentration of 190 g/l, to the HCl solution 20%. A cathodic current density equivalent to 1.5 A/m.sup.2 was applied to the nickel mesh for 13 minutes.

[0072] The nickel mesh thus obtained was coated with 5 coats of an aqueous solution containing Pt, Pr and Pd with a heat treatment of 15 minutes at 450° C. after each coat until obtaining a coating of 1.90 g/m.sup.2 of Pt, 1.24 g/m.sup.2 of Pd and 3.17 g/m.sup.2 of Pr.

[0073] On the catalytic layer thus obtained 4 coats of a second solution containing Pt, Pr and Pd were applied in a different ratio compared to the first solution with a heat treatment of 15 minutes at 450° C. after each coat until obtaining a coating of 1.77 g/m.sup.2 of Pt, 1.18 g/m.sup.2 of Pd and 1.59 g/m.sup.2 of Pr.

[0074] The electrode thus obtained was identified as sample E5.

COUNTEREXAMPLE 1

[0075] A nickel mesh with dimensions 100 mm×100 mm×0.89 mm was washed and degreased with acetone according to a standard procedure, then subjected to a process of sandblasting with corundum and etching in 20% HCl at room temperature for a time of 1100 minutes.

[0076] At the end of the treatment, the weight loss was verified and the degree of roughness was measured in different points of the mesh.

[0077] The mesh thus obtained was identified as sample CE1 sample.

COUNTEREXAMPLE 2

[0078] A nickel mesh with dimensions 100 mm×100 mm×0.89 mm was washed and degreased with acetone according to standard procedure, then subjected to a process of sandblasting with corundum and etching in 20% HCl at a temperature of 60° C. for a period of 40 minutes.

[0079] At the end of the treatment, the weight loss was verified and the degree of roughness was measured in different points of the mesh.

[0080] The mesh thus obtained was identified as sample CE2.

COUNTEREXAMPLE 3

[0081] A nickel mesh with dimensions 100 mm×100 mm×0.89 mm was washed and degreased with acetone according to standard procedure, then subjected to a process of sandblasting with corundum and etching in HNO.sub.3 21% at room temperature for a time of 15 minutes.

[0082] At the end of the treatment, the weight loss was verified and the degree of roughness was measured in different points of the mesh.

[0083] The mesh thus obtained was identified as sample CE3.

COUNTEREXAMPLE 4

[0084] A nickel mesh with dimensions 100 mm×100 mm×0.89 mm was subjected to an etching process in 20% HCl at a temperature of 60° C. for 5 minutes.

[0085] The mesh was then coated with 5 coats of an aqueous solution containing Pt, Pr and Pd with a 15-minute heat treatment at 450° C. after each coat until obtaining a coating of 1.90 g/m.sup.2 of Pt, 1.24 g/m.sup.2 of Pd and 3.17 g/m.sup.2 of Pr.

[0086] On the catalytic layer thus obtained 4 coats of a second solution containing Pt, Pr and Pd were applied in a different ratio compared to the first solution with a heat treatment of 15 minutes at 450° C. after each coat until obtaining a coating of 1.77 g/m.sup.2 of Pt, 1.18 g/m.sup.2 of Pd and 1.59 g/m.sup.2 of Pr.

[0087] The electrode thus obtained was identified as sample CE4.

COUNTEREXAMPLE 5

[0088] A nickel mesh with dimensions of 100 mm×100 mm×0.89 mm was subjected to a process of sandblasting with corundum, etching in 20% HCl at room temperature and stress relieving through heat treatment according to the procedure known in the art. The mesh was then coated with 5 coats of an aqueous solution containing Pt, Pr and Pd with a 15-minute heat treatment at 450° C. after each coat until obtaining a coating of 1.90 g/m.sup.2 of Pt, 1.24 g/m.sup.2 of Pd and 3.17 g/m.sup.2 of Pr.

[0089] On the catalytic layer thus obtained 4 coats of a second solution containing Pt, Pr and Pd were applied in a different ratio compared to the first solution with a heat treatment of 15 minutes at 450° C. after each coat until obtaining a coating of 1.77 g/m.sup.2 of Pt, 1.18 g/m.sup.2 of Pd and 1.59 g/m.sup.2 of Pr.

[0090] The electrode thus obtained was identified as sample CE5.

[0091] Table 1 reports the results of the tests carried out to evaluate the time necessary to achieve a weight loss of between 3 and 6% of a metal substrate; the degree of homogeneity of the roughness profile was also measured, expressed as the mean square deviation in % (% a) of the Ra values measured in different points of the nickel mesh.

TABLE-US-00001 TABLE 1 % Weight loss Minutes % σ E1 4.46% 1.7 <25% E2 4.46% 3.3 <25% E3 4.46% 1.6 <25% CE1 4.46% 1100 >30% CE2 4.46% 40 >40% CE3 4.46% 15 >30%

[0092] The samples of example E5 and counterexample CE5 described above were subjected to performance tests, under hydrogen evolution, in a laboratory cell fed with 32% NaOH at a temperature of 90° C., furthermore they were subsequently subjected to cyclic voltammetry tests in the voltage range from −1 to +0.5 V/NHE with a scan rate of 10 mV/s.

[0093] Table 2 reports the initial cathodic voltage and the one after 25 cycles of cyclic voltammetry (25 CV), index of resistance to inversions and therefore of robustness, measured at a current density of 3 kA/m.sup.2.

TABLE-US-00002 TABLE 2 mV vs NHE mV vs NHE (25 CV) E5 916 934 CE5 922 971

[0094] The previous description does not intend to limit the invention, which can be used according to different embodiments without thereby deviating from the purposes and whose scope is uniquely defined by the attached claims.

[0095] In the description and claims of the present application, the term “comprises” and “contains” and their variants such as “comprising” and “containing” are not intended to exclude the presence of other elements, components or additional process steps.

[0096] Discussion of documents, records, materials, apparatuses, articles and the like is included in the text for the sole purpose of providing context to the present invention; However, it is not to be understood that this matter or part of it constituted general knowledge in the field relating to the invention before the priority date of each of the claims attached to this application.