Method of producing an electrocatalyst

Abstract

A method of producing an electrocatalyst, comprising the steps of: a) electrodeposition or electrochemical plating of an alloy comprising nickel and a second metal on a copper, nickel or other metal substrate; and b) electrochemical or chemical dissolution of deposited second metal to obtain a nanoporous structure on the copper, nickel or other metal substrate.

Claims

1. Method of producing an electrocatalyst, comprising: electrodeposition of an alloy comprising nickel, a second metal which is copper, and a third metal which is iron on a metal substrate selected from the group consisting of copper, nickel, iron, cobalt, titanium, zirconium, stainless steel and aluminium, wherein the electrodeposited nickel, copper, and iron are provided as a solution; subjecting the alloy obtained in the electrodeposition of the alloy to a heat treatment comprising a temperature of at least 250° C. for at least 20 minutes; electrochemical or chemical dissolution of deposited second metal to obtain a nanoporous structure on the metal substrate; and deposition of iron on the nanoporous structure.

2. The method of claim 1, wherein an electroplating solution comprising a copper salt and a nickel salt is used in the electrodeposition of the alloy.

3. The method of claim 2, wherein the copper salt is CuSO.sub.4.

4. The method of claim 2, wherein the nickel salt is NiSO.sub.4.

5. The method of claim 2, wherein the electroplating solution has a molar ratio of copper to nickel of between 1:1 and 1:3.

6. The method of claim 1, wherein a voltage of 2-6 V in a two electrodes setup is applied in the electrodeposition of the alloy.

7. The method of claim 1, wherein a solution comprising sulphate ions, an alkaline solution or an acidic solution is used in the electrochemical or chemical dissolution of the deposited second metal.

8. The method of claim 1, wherein a voltage of 1-12 V is applied in a two electrodes setup.

9. The method of claim 1, wherein a pulsed voltage is applied in the electrochemical or chemical dissolution of the deposited second metal.

10. The method of claim 1, further comprising passivating the iron on the nanoporous structure.

11. The method of claim 1, wherein the metal substrate comprises a copper coil.

12. The method of claim 1, wherein the metal substrate is a porous copper or nickel substrate.

Description

DETAILED DESCRIPTION

(1) The present disclosure relates to a method of producing an electrocatalyst and to an electrocatalyst suitable for both oxygen and hydrogen evolution reaction in alkaline water electrolysis. The electrocatalyst may advantageously form part of an electrode for an electrolysis process.

(2) The method of producing an electrocatalyst comprises a step a) of electrodeposition of an alloy comprising nickel and a second metal on a copper substrate.

(3) Step a) of electrodeposition may for example be an electrochemical deposition or a pulse electrodeposition. If pulse electrodeposition is used, i.e. a pulsed voltage is applied, a low pulsed voltage may be used compared to the voltage applied during electrochemical dissolution/dealloying. For example, in a three electrode setup, a low pulsed voltage may be a voltage of −0.92 V for 5 seconds and then −0.005 V for 1 second. These pulses may for example be applied for around 15-30 minutes.

(4) The chemical bath used in step a), i.e. in which the copper substrate is submerged, may for example include an electroplating solution comprising a copper salt, such as CuSO.sub.4, and a nickel salt, such as NiSO.sub.4. The electroplating solution may preferably be aqueous.

(5) In one example, a constant voltage may be applied to the copper substrate during step a) to perform the electrodeposition of the alloy on the copper substrate. The applied voltage may for example be in the range of 2-6 V between the copper substrate and a second electrode in a two-electrode setup.

(6) In one variation, the second metal is copper. In this case, the alloy is a copper-nickel alloy.

(7) In another variation, the second metal is iron. In this case, the alloy is a nickel-iron alloy.

(8) In yet another variation, the alloy also comprises a third metal. In this case the second metal may for example be copper and the third metal may be iron. Thus, in this case, the alloy is a nickel-copper-iron alloy.

(9) In one variation, the copper substrate provided with the alloy obtained in step a) is subjected to a heat treatment. This heat treatment is preferably performed before step b) described below.

(10) Heat treatment before step b) initiates a diffusion mechanism in a nickel-copper alloy, a nickel-copper-iron alloy or nickel-iron alloy on a copper substrate. Heat treatment after step a) significantly reduces the formation of any nano-cracks on the alloy coating in case high pulse voltage electrochemical dealloying is used in step b). It might also improve the stability and activity of the electrocatalyst. A more homogeneous nanoporous surface structure is obtained after step b) if the copper substrate has been subjected to a heat treatment after step a). Heat treatment increases the current density if the copper substrate/electrocatalyst is used as an electrode.

(11) In a step b) the copper substrate is subjected to an electrochemical dissolution of deposited second metal to obtain a nanoporous structure on the copper substrate.

(12) The electrochemical dissolution may involve dealloying. The dealloying may for example be electrochemical dealloying or pulse electrochemical dealloying.

(13) The chemical bath used in step b) may for example include a dealloying solution comprising sulphate ions, such as a potassium sulphate K.sub.2SO.sub.4 solution.

(14) According to one example, in step b) a voltage in the range of 1-12 V, such as 2-3 V, is applied between the copper substrate provided with the deposited alloy and a second electrode in a two-electrode setup.

(15) In one variation, a constant voltage may be used during step b) to perform the electrochemical dissolution of the deposited second metal on the copper substrate. Alternatively, a pulsed voltage may be used during step b) to perform the electrochemical dissolution. In another variation, constant voltage may be combined with a pulsed voltage; for example during one portion of the dealloying, constant voltage may be applied and during another portion a pulsed voltage may be applied.

(16) In the case when the alloy is a copper-nickel alloy, at least a portion of the deposited copper is electrochemically dissolved. Moreover, in this case, in a step c) iron is deposited on the porous structure obtained in step b). The deposition in step c) is preferably electrodeposition.

(17) One variation comprising step c) further comprises a step d) of passivating the deposited iron.

(18) In case the alloy is a nickel-iron alloy, at least a portion of the deposited iron is electrochemically dissolved. In this case, in an optional step c) copper may be deposited on the porous structure obtained in step b). The deposition in step c) is preferably electrodeposition.

(19) In case the alloy is a nickel-copper-iron alloy, at least a portion of the deposited iron and deposited copper is electrochemically dissolved in step b).

EXAMPLE 1

(20) Chemicals and Setup

(21) The following describes the experimental procedure to obtain about 4 cm long high surface area copper wires, with diameter about 1 mm. The copper wires are in this example the copper substrates to be subjected to steps a) and b). The copper wires had a 99.9% degree of purity.

(22) Chemicals: boric acid (H3BO3, 99.97%), sodium sulphate (Na2SO4, 99.99%), copper sulphate pentahydrate (CuSO4.5H2O, analytical grade 99-100.5%), nickel sulphate hexahydrate (NiSO4.6H2O, 98%).

(23) Electrochemical Treatments:

(24) A three-electrode cell was connected to a potentiostat, where a saturated calomel electrode (SCE) is used as a reference electrode and a carbon electrode as a counter electrode. A large volume of electroplating solution containing a source of nickel and a second metal (30 mL) was chosen to ensure complete coverage of the electrodes.

(25) It is to be noted that it is possible to scale down the volume of both for electroplating solution and the dealloying solution and still achieve the same results.

(26) An electrodeposition of an alloy comprising nickel and copper was performed. The deposition of nickel and copper on the copper wires was made from an electroplating solution containing: 0.5 M H3BO3, 0.5 M NiSO4 and 0.005 M CuSO4, resulting in a 1:100 ratio of Cu:Ni. About 3-3.5 cm of the copper wires was immersed in the solution. A constant voltage of −0.92 V (vs. SCE) was applied for 15 minutes.

(27) The copper wires provided with the nickel-copper layer obtained during the electroplating were then rinsed briefly with deionised water before proceeding to the electrochemical dissolution step, which in the present example is a dealloying step. The dealloying solution consisted of 0.5 M H3BO3 and 0.5 M Na2SO4 for a total volume of 30 mL. The copper wires provided with a copper-nickel layer were immersed in the dealloying solution and dealloyed by applying a constant voltage of 2.5 V (vs SCE) for 15 minutes.

EXAMPLE 2

(28) Example 2 is similar to example 1 concerning the chemicals and setup. The electrodeposition step is also the same as in example 1. During the electrochemical dissolution step, also here dealloying, a different voltage profile is however applied.

(29) Instead of a constant voltage, a “low” pulsed voltage or a “high” pulsed voltage was used. The parameters for “low” pulsed voltage were [t1=1 s, V1=0.5 V; t2=5 s, V2=0.005 V] meaning that a voltage of 0.5 V is applied for 1 second, before applying 0.005 V for 5 seconds and repeating the process for a total time of 15 minutes. For a “high” pulse voltage the parameters are [t1=1 s, V1=2.5 V; t2=5 s, V2=0.005 V].

(30) The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.