Electrode and method for making the same

Abstract

The present invention relates to an electrode, preferably a gas evolution electrode, which comprises a substrate and a catalytic coating, wherein said catalytic coating comprises praseodymium, iron, nickel and a metal selected from a group consisting of copper, tin and a combination thereof.

Description

[0001] INDUSTRIE DE NORA S.p. A.

[0002] ELECTRODE AND METHOD FOR MAKING THE SAME

[0003] TECHNICAL FIELD

[0004] The present invention relates to an electrode , preferably a gas evolution electrode , method for making the electrode and the use of such electrode in water electrolysis , preferably in alkaline water electrolysis .

[0005] PRIOR ART

[0006] Catalytically active metal-based electrodes such as metal oxide electrodes are widely used in various electrochemical reactions both as anodes and cathodes due to their ef ficacy, stabil ity, and long li fetime . Those electrodes are made of substrates such as plates or meshes coated with one or more catalytically active metal .

[0007] Mixtures of several metals or their oxides can be applied on the substrate to form the catalytic layer . In the catalytic layer, catalytically active metals catalyze targeted electrochemical reactions including electrochlorination or water electrolysis . Some metal can be mixed with the precious metal to provide support or to minimi ze the corrosion during electrolysis .

[0008] Various techniques and modi fications have been adopted by the industry in order to improve the performance of the electrodes including :

[0009] M / 66041-PCT ( 411PCT ) INDUSTRIE DE NORA S.p. A.

[0010] - combining di f ferent metals from the same or di f ferent groups of the periodic table ,

[0011] - doping the catalytic coating with small amounts of speci fic metals ,

[0012] - creating non-stoichiometric defects in the lattice of the catalysts ,

[0013] - increasing the porosity and the surface area of the catalytic coating .

[0014] Noble metals such as ruthenium, iridium and platinum and combinations thereof , alone or in combination of other metals are widely used as active electrocatalysts including in the hydrogen and oxygen evolution reactions .

[0015] The maj or drawback of the use of noble metals as electrocatalysts is the high cost of those metals , which causes an increase in the capital expenses as well as the operational expenses since the catalytic coating erodes over time and the electrode must be recoated periodically .

[0016] Thus , it would be desirable to provide a method for making gas evolution electrodes that can solve the aforementioned drawback without af fecting the performance or the li fetime of the electrodes .

[0017] SUMMARY OF THE INVENTION

[0018] From what is stated above , the present application aims

[0019] M / 66041-PCT ( 411PCT ) INDUSTRIE DE NORA S.p. A.

[0020] - 3 - at providing an electrode for electrochemical reactions , preferably gas evolution electrode , which has high performance properties , without necessarily using noble metals in the catalytic coating .

[0021] This result is achieved using the electrode described in the appended claims , wherein the catalytic coating comprises praseodymium, iron, nickel and a metal selected from a group consisting of copper, tin and a combination thereof .

[0022] These and other obj ects and advantages of the invention will become obvious from the following detailed description .

[0023] DETAILED DESCRIPTION OF THE INVENTION

[0024] In the present patent application, all the operating conditions reported in the text must be understood as preferred conditions even i f not expressly declared .

[0025] For the purposes of the present invention, the term " to comprise" or " to include" also comprises the term " to consist in" or " essentially consisting of" .

[0026] For the purposes of the present invention, the definitions of the ranges always comprise the extreme values unless otherwise speci fied .

[0027] A first obj ect of the invention therefore relates to an

[0028] M / 66041-PCT ( 411PCT ) INDUSTRIE DE NORA S.p. A. electrode , preferably gas evolution electrode , comprising a substrate and a catalytic coating, wherein said catalytic coating comprises praseodymium, iron, nickel and a metal selected from a group consisting of copper, tin and a combination thereof .

[0029] As mentioned, the core of the invention lies in finding a cheaper alternative of the use of noble metals in the catalytic coating . Indeed, each of the aforementioned metals are much cheaper than noble metals . Thus , the present invention provides a promi sing and industrially feasible electrodes for various electrochemical technologies such as water electrolysis .

[0030] Each of said praseodymium, iron, nickel and said metal is present in a form selected from free element , alloy, oxide , sulphide , hydroxide , and mixtures thereof . Preferably, in the form of free element or oxides , even more preferably, in the form of oxides . Oxides are preferable because they generally result in electrodes with higher durability .

[0031] It is not entirely understood why those speci fic combinations lead to a signi ficant improvement in the catalytic performance of the electrode . Without wishing to be limited by any theory, the applicant believes that certain interactions between the atoms of the elements allow to form new catalytic paths that facilitate the electrochemical reactions .

[0032] M / 66041-PCT ( 411PCT ) INDUSTRIE DE NORA S.p. A.

[0033] According to a preferred embodiment , each of said praseodymium, iron, nickel and said metal is present in a percentage compri sed between 5 and 85% by weight with respect to the total weight of said praseodymium, iron, nickel and said metal , wherein the percentages of said praseodymium, iron, nickel and said metal are referred to metals , wherein the sum of the percentages is 100% .

[0034] Preferably, each of said praseodymium, iron, nickel and said metal is present in a percentage comprised between 15 and 55% by weight with respect to the total weight of said praseodymium, iron, nickel and said metal , wherein the percentages of said praseodymium, iron, nickel and said metal are referred to metals , wherein the sum of the percentages is 100% .

[0035] More preferably, each of said praseodymium, iron, nickel and said metal is present in a percentage comprised between 20 and 40% by weight with respect to the total weight of said praseodymium, iron, nickel and said metal , wherein the percentages of said praseodymium, iron, nickel and said metal are referred to metals , wherein the sum of the percentages is 100% .

[0036] In other words , even when the catalytic coating is made in forms that comprises other elements such as oxygen in the oxides and sul fur in the sulphides , the above percentages should be calculated referring to the metals only .

[0037] M / 66041-PCT ( 411PCT ) INDUSTRIE DE NORA S.p. A.

[0038] - 6 -

[0039] Advantageously, the substrate is made of a substrate metal selected from a group consisting of Ni , Fe , alloys thereof and mixtures thereof .

[0040] According to a particularly preferred aspect , the electrode is a cathode , preferably a cathode for electrolysis , more preferably a cathode for alkaline water electrolysis or chlor-alkali reaction .

[0041] A second obj ect of the invention relates to a method for making the electrode according to the present invention, which comprises : a - providing a substrate , b - applying an aqueous solution comprising salts of said praseodymium, iron, nickel and said metal on said substrate , c - baking said substrate of step b at a temperature comprised between 300 and 800 ° C, preferably comprised between 400 and 600 ° C, d - optionally repeating steps b and c to arrive at a predefined metal load .

[0042] Baking can take place under oxygen or air to produce the oxides of the metals or can take place under inert gas such as nitrogen to produce the metals in the free element form .

[0043] A third obj ect of the invention relates to an electrolyzer comprising one or more electrodes according to the present invention .

[0044] M / 66041-PCT ( 411PCT ) INDUSTRIE DE NORA S.p. A.

[0045] A fourth obj ect of the invention relates to the use of the electrode according to the present invention in chlor-alkali reaction, anion exchange membrane water electrolysis , proton exchange membrane electrolysis , or alkaline water electrolysis .

[0046] The following examples are provided for illustrative purposes only of the present invention and must not be understood as limiting the scope o f protection defined by the appended claims .

[0047] EXAMPLES

[0048] Example 1 according to the present invention

[0049] The synthesis of the electrode is done using a nickel mesh (Ni Flynet 40 mesh) as a support .

[0050] Acidic aqueous solution ( 10 % HNO3 ) of nitrates of tin, praseodymium, nickel and iron ( SnPrNiFe ) was prepared . The solution has a Total No Noble Metal concentration of 150 g / L, i . e . total weight of SnPrNiFe referred to metals . The weight percentage of each of SnPrNiFe is reported in table 1 below . The acidity of the solution allows a greater grip on the mesh and thus greater adhesion .

[0051] The solution was applied at a volume of around 80 um per

[0052] M / 66041-PCT ( 411PCT ) INDUSTRIE DE NORA S.p. A. coat on the Ni Flynet 40 mesh by brushing.

[0053] At this point, the Flynet 40 mesh is first dried at a temperature of 80°C and then baked at 500°C under air to produce the oxides of the metals for 10 min.

[0054] The brushing, drying, and backing step is repeated 4 times .

[0055] The resulting electrode is washed by means of DI water and is ready to be used as a cathode.

[0056] Example 2 according to the present invention

[0057] The synthesis of the electrode is done using the same steps of example 1 but using nitrates of cupper, praseodymium, nickel and iron (CuPrNiFe) instead of (SnPrNiFe) , with weight percentages as reported in table 1 referred to metals.

[0058] Comparative examples 1-7

[0059] Comparative examples 1-7 is done using the same steps of example 1 and according to the invention but using nitrates of metals at weight percentages reported in table 1, also referred to metals. The comparative examples aim at demonstrating the synergic effect of the presence of each of the four elements (i.e. PrNiFe with Sn, Cu or a combination thereof) .

[0060] M / 66041-PCT (411PCT) INDUSTRIE DE NORA S.p. A.

[0061] -9-

[0062] Table 1

[0063] Electrochemical characterization

[0064] The activities of the electrodes were tested by means of

[0065] M / 66041-PCT (411PCT) INDUSTRIE DE NORA S.p. A. a classical three electrodes .

[0066] Setup for electrochemical characteri zation :

[0067] A beaker cell was prepared with a solution of KOH at a concentration of 30% by weight and a temperature of 80 ° C . The electrode was welded to a nickel rod and placed in front of a counter electrode into the solution . A cathodic current of 10 kA / m2was applied for at least three hours and up to 60 hours to condition the electrode and successively the hydrogen evolution overpotential at di f ferent current density was determined by means of a reference electrode and a Lugging capillary .

[0068] Table 2 shows the single electrode potential for hydrogen evolution in alkaline media a current density of 4 kA / m2of the electrode of examples 1 and 2 according to the present invention compared and for the electrode of the comparative examples 1 to 7 . The electrodes produced according to the invention showed lower hydrogen evolution overpotential with respect to each of the electrodes of comparative examples 1 to 7 .

[0069] The stability of the electrodes of example 1 and 2 according to the invention and of comparative examples 1 to 7 were tested . As reported in table 2 , several cyclic voltammetry cycles were applied to bring the electrode to anodic potential in order to accelerate its degradation due to potential fluctuations that can be present in an intermittently operated water electrolysis

[0070] M / 66041-PCT ( 411PCT ) INDUSTRIE DE NORA S.p. A.

[0071] - 11 - plant . The hydrogen evolution potential was determined after 25 cycles .

[0072] The electrodes of examples 1 and 2 according to the invention show inferior degradation rates compared to the electrodes of comparative examples 1 to 7 .

[0073] Table 2

[0074] M / 66041-PCT ( 411PCT )

Claims

INDUSTRIE DE NORA S.p. A.- 12 -CLAIMS1 . Electrode comprising a substrate and a catalytic coating, wherein said catalytic coating comprises praseodymium, iron, nickel and a metal selected from a group consisting of copper, tin and a combination thereof .2 . Electrode according to claim 1 , wherein each of said praseodymium, iron, nickel and said metal is present in a form selected from free element , alloy, oxide , sulphide , hydroxide , and mixtures thereof .3 . Electrode according to claim 1 or 2 , wherein each of said praseodymium, iron, nickel and said metal is present in a percentage comprised between 5 and 85% by weight with respect to the total weight of said praseodymium, iron, nickel and said metal , wherein the percentages of said praseodymium, iron, nickel and said metal are referred to metals , wherein the sum of the percentages is 100% .4 . Electrode according to claim 3 , wherein each of said praseodymium, iron, nickel and said metal is present in a percentage comprised between 15 and 55% by weight with respect to the total weight of said praseodymium, iron, nickel and said metal , wherein the percentages of saidM / 66041-PCT ( 411PCT )INDUSTRIE DE NORA S.p. A. praseodymium, iron, nickel and said metal are referred to metals , wherein the sum of the percentages is 100% .5 . Electrode according to claim 4 , wherein each of said praseodymium, iron, nickel and said metal is present in a percentage comprised between 20 and 40% by weight with respect to the total weight of said praseodymium, iron, nickel and said metal , wherein the percentages of said praseodymium, iron, nickel and said metal are referred to metals , wherein the sum of the percentages is 100% .6 . Electrode according to any one of the preceding claims , wherein said substrate is made of a substrate metal selected from a group consisting of Ni , Fe , alloys thereof and mixtures thereof .7 . Electrode according to any one o f the preceding claims , wherein the electrode is a cathode , preferably a cathode for electrolysis , more preferably a cathode for alkaline water electrolysis or chlor-alkali reaction .8 . Method for making electrode according to any one of the preceding claims , which comprises : a- providing a substrate , b- applying an aqueous solution comprising salts of said praseodymium, iron, nickel and saidM / 66041-PCT ( 411PCT )INDUSTRIE DE NORA S.p. A.- 14- metal on said substrate, c- baking said substrate of step b at a temperature comprised between 300 and 800°C, preferably comprised between 400 and 600°C, d- optionally repeating steps b and c to arrive at a predefined metal load.

9. Electrolyzer comprising one or more electrode according to any one of the claims 1 to 7.

10. Use of the electrode according to any one of the claims 1 to 7 in chlor-alkali reaction, anion exchange membrane water electrolysis, proton exchange membrane electrolysis, or alkaline water electrolysis.M / 66041-PCT (411PCT)

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