WO2008061975A2

WO2008061975A2 - Electrodes for the production of hydrogen by the electrolysis of aqueous solutions of ammonia, electrolyser containing them and their use

Info

Publication number: WO2008061975A2
Application number: PCT/EP2007/062555
Authority: WO
Inventors: Paolo Bert; Claudio Bianchini; Stefano Catanorchi; Antonio Filpi; David Nugent; Marina Ragnoli; Alessandro Tampucci; Francesco Vizza; Xiaoming Ren
Original assignee: Acta S.P.A.
Priority date: 2006-11-21
Filing date: 2007-11-20
Publication date: 2008-05-29
Also published as: WO2008061975A3; ITFI20060287A1

Abstract

Described herein is the preparation and use of electrodes containing metal catalysts, preferably based upon cobalt, nickel, iridium, ruthenium, rhodium, platinum and their combinations used for the production of hydrogen by the electrolysis of aqueous solutions of ammonia in electrolytic apparatus using anionic exchange solid polymer membranes.

Description

ELECTRODES FOR THE PRODUCTION OF HYDROGEN BY THE ELECTROLYSIS OF AQUEOUS SOLUTIONS OF AMMONIA, ELECTROLYSER CONTAINING THEM AND THEIR USE Field of the invention This invention is related to the field of production of hydrogen by the electrolysis of aqueous solutions of ammonia. State of the art

In recent years, technologies related to the production of hydrogen are receiving more and more interest in the field of sustainable development. The success of the hydrogen economy depends in part upon the sustainability of the choices adopted for the production, distribution, storage and release of the hydrogen it self.

Current thermo-chemical technologies produce hydrogen at a price of between 4 and 5 €/kg, mostly due to the high temperature and pressure required and the cost of separation and purification.

In addition, environmentally unfriendly by-products are produced: NO_x e CO_x. The DOE, like other European organisations has fixed the cost for the production of 1 Kg of hydrogen at 2 $ (1.5 €). The electrochemical reduction of water represents a significant alternative to the production of hydrogen from fossil fuels and the only route that permits the use of renewable energy sources (photovoltaic, wind, bio-mass, geothermal etc). It also allows the production of hydrogen 99.999% pure.

The electrolysis of water is a known and consolidated process that occurs in devices called electrolysers (M. Kauffmann, Electrolytic Hydrogen Production, United States Department of Energy, Energy Efficiency & Renewable Energy; R.J Friedland, T.M. Maloney, F. Mitlitsky, Hydrogen fuel through PEM electrolysis, Warrendale, Society of Automotive Engineers, 2001 ; R.J. Friedland, A.J. Speranza (Proton Energy Systems Inc), Hydrogen Production through Electrolysis, Proceedings of the 2001 DOE Hydrogen Program Review, NREL/CP-570-30535, May 2001 ; Development of large scale water electrolyser using solid polymer electrolyte in WENET project, Takahiro Nakanori & Osamu Yamamoto, Fuji Electric Corporate, Ltd., Japan, 2002; T.G. Coker, A.B. LaConti, LJ. Nuttall, General Electric Company, Industrial and Government applications of SPE fuel cell and electrolysers', Proceeding of the Case Western Symposium on Membranes & Ionic & Electronic Conducting Polymers', Cleveland, Ohio, May 1982). An electrolyser is essentially a device comprised of a cell containing the solution to be electrolysed, two electrodes upon the surface of which, with the passage of current, occur the reduction and oxidation reactions and the concentrated solution of an electrolyte (e.g. KOH) or an ionic exchange membrane placed between the two electrodes (as described in more detail below). The electrodes consist of a metal or a highly conductive material upon the surface of which is applied a metal catalyst. The efficiency of an electrolyser is directly related to the electrode materials, in particular of the catalysts deposited onto the surface of the electrode whose role is that of reducing the activation energy for both the anode (oxygen production) and cathode (hydrogen production) reactions. Therefore, a crucial role for the improvement of the effective energetic efficiency of an electrolyser is played by the electrode materials, given that they determine both the energy consumption (for a given reaction rate) and the maximum reaction rate in the cell. There exists three distinct electrolyser technologies for hydrogen production: two of which are well established: alkaline electrolyser (AE), solid polymeric membrane electrolyser (PME) and the solid oxide electrolyser (EOS). The EOS technology is at present experimental and is designed for use in large reactors at high temperatures, while PME devices are more adapted for the production of hydrogen in small devices, also being able to be used in portable devices at temperatures below 100 °C.

The principle difference between EA and PME technologies is due to the fact that the electrolyte in the former is an alkaline solution, generally KOH (25-30%), while in PME devices the electrolyte consists of a polymeric membrane (ionomer) through which pass the H⁺ or OH^" ions depending upon the type of ionomer used, that move from the anode to the cathode (H⁺) or from the cathode to the anode (OH^"). The solid membrane is also used to separate the gases that develop at the two electrodes. The advantages of the PME electrolysers are many: no moving parts, very low volume of corrosive liquid, high current density used, production of gas at high pressure, rapid response to applied current and minimal carbonatation of the electrolyte. PME type electrolysers are particularly adaptable to the delocalised production of hydrogen even in portable devices.

Generally, the catalysts used have a high percentage of active phase >(10 mg/cm²) in order to obtain the performance necessary when used. A high percentage of active phase makes a catalyst very expensive especially if it contains noble metals.

The principle characteristics of PME type electrolysers can be summarised as follows:

- No circulating electrolyte

- Can work at high current densities (1 -2 A/cm²) - Are adaptable to variations in electricity (compatible with power generated by renewable resources: wind or solar)

- Can work at high pressure, up to 200 bar (including the pressure difference between the compartments where the gas is produced).

In a traditional electrolytic device, a difference in potential between the electrodes splits water into hydrogen (at the cathode) and oxygen (at the anode): 2 H₂O + electrical energy → 2 H₂ + O₂

According to the following anodic and cathodic semi-reactions: Acid conditions 2 H₂O → O₂ + 4 H⁺ + 4 e^" anode E°_{1 =} 1.23 V (1 ) 4 H⁺ + 4 e^" → 2 H₂ cathode E°₂ = O V (2) Basic conditions 4 OH^" → O₂ + 2 H₂O + 4 e^" anode E°i = 0.40 V (3)

4 H₂O + 4 e^" → 2 H₂ + 4 OH^" cathode E°₂ = -0.83 V (4)

Of increasing academic and industrial interest and also the object of this patent application is the sustainable production of hydrogen by the electrolysis of aqueous solutions of ammonia with PME type electrolysers in which ammonia is oxidised at the anode and water is reduced at the cathode (F. M. Vitse, M. Cooper, G. Botte J. Power Sources 2005, 142, 18; M. Cooper, G. Botte J. Electrochem. Soc. 2006, 153, 1894; US 2005/021 1569). Ammonia-water electrolysers function in alkaline conditions with the following semi-cell reactions:

2 NH₃ (aq) + 6 OH^" → N₂(g) + 6 H₂O + 6 e^" anode (E^ = -0.77 V) (5) 6 H₂O + 6 e^" → H₂(g) + 6 OH^" cathode (E°₂ = -0.83 V) (6) 2 NH₃ (aq) → N₂(g) + 3 H₂(g) overall (E^o _Cθn = 0.06 V) (7)

The thermodynamic values of the process are evidently in favour of the production of hydrogen coupled to the oxidation of ammonia with respect to the oxidation of water where the reversible potential is 1.223 V. Given the low energy consumption, this type of electrolytic cell can operate with renewable energy sources such as PEMFC. That is to say this type of device can operate producing hydrogen without the need for its subsequent storage.

The theoretical consumption of energy in an electrolytic ammonia cell (under reversible thermodynamic conditions), calculated at the standard potential of the cell is 1.55 Wh g-1 , much lower that the analogous consumption of a traditional water electrolyser (33 Wh g^"1). This means that an ammonia electrolyser consumes 95% less energy than a water electrolyser to produce the same amount of hydrogen. The efficiency of an electrolytic cell can be defined by the following equation:

ε =. ΔE^C ΔE^C ΔE ΔE° + η_a + η_c + η_ifi

Where ΔE° represents the cell reversible voltage and ΔE represents the actual measured cell voltage (sum of the reversible voltage and the anodic, cathodic and ohmic overvoltages). By convention, the efficiency of an electrolyser capable of generating hydrogen can be expressed in kWh/Nm³ of H₂. A normal m³ of H₂ (Nm^) has a higher heating value of 3.54 kWh, so an electrolyser is considered to have 100% efficiency in conversion of electricity into hydrogen when the production of 1 Nm³ of hydrogen requires 3.54 kWh. Other characteristic parameters of an electrolyser are the applied voltage to each electrolyte and the current density (A/cm²). Considering an efficiency of an electrolyser of this invention of slightly higher than 20%, assuming the production of electricity by using solar energy (€ 0.17/kWh) and a fixed cost of ammonia at € 119/ton, a kg of hydrogen can be produced with 7.4 kWh at a cost of € 1.9. Close to the limit required by the Department of Energy USA (DOE) and the UE (1.5 €).

From many points of view the production of hydrogen by the electrolytic reduction of water combined with the electro-oxidation of ammonia presents numerous advantages:

- Ammonia is easily condensed and hence adapted to storage and transport: A cylinder of ammonia contains the equivalent of 9-10 cylinders of compressed hydrogen. - The decomposition of ammonia per electro-oxidation under alkaline conditions produces exclusively nitrogen and water as by-products, in other words without toxic side products.

- The characteristic odour of ammonia can be detected even in tiny concentrations so will help control any loss to the environment. - The purity of the hydrogen produced is practically unaltered (studies have shown the presence of 0.5 ppm of ammonia in the hydrogen produced that can be easily recovered using an acid trap).

- Flexibility of the fuel (ammonia can also be used directly in a PEM type fuel cell in which many components of a EPM type electrolyser are adaptable e.g. MEA).

- The capacity to function at a range of temperatures (from room temperature to as high a temperature at which the anionic exchange polymeric membrane is stable (at present 60-80 °C).

The fact that there do not exist commercially electrolysers which function by the electro-oxidation of ammonia seems to be due to the poor reversibility of the oxidation process (anodic catalyst poisoning) that inhibits the ability to obtain for sufficient time the high current densities that the oxidation of ammonia can theoretically offer.

The anodic overpotentials can in fact reach values up to 0.5 V (e.g. platinum black) at current densities of only 50 mA/cm² at room temperature.

The electrode passivation is usual reversed by the use of inverse potential cycling that reduces the amount of adsorbed species on the anode. In both the scientific and patent literature there does not exist to date data on PME type electrolysers for the production of hydrogen by the electro-oxidation of ammonia with nanostructured electrocatalysts. Also in the case of EA type electrolysers there do not exist studies using nanostructured catalysts that have given rise to large advances in the preparation of efficient anode catalysts for fuel cells.

Brief description of the figures

Figure 1. Functional design of an electrolyser used for the electrolysis of aqueous solutions of ammonia with an anionic exchange solid polymeric membrane. Figure 2. Polarisation curve for the ammonia electrolysis cell described in example 9.

Figure 3. Durability test at constant potential (0.6 V) with potential inversion every 5 min at -0.6 V for 20 seconds, for the cell described in example 9. Figure 4. Charge capacity derived from the durability test at constant potential (0.6 V) with potential inversion every 5 min at -0.6 V for 20 seconds, for the cell described in example 9. Summary of the invention

Described herein are the preparation and use of anodic and cathodic electrodes upon the surface of which are placed state of the art nanostructured metallic catalysts which are based upon transition metals, preferably cobalt and nickel, together with noble metals, preferably ruthenium, platinum, rhodium and iridium. The noble metals are deposited either electrochemically or by spontaneous deposition. These electrodes are used for the production of hydrogen through the electrolysis of aqueous solutions of ammonia in electrolysers using solid polymer anionic exchange membranes. The state of the art nanostructured catalysts formed from transition metal salts, preferably cobalt, nickel, palladium, iridium, rhodium, ruthenium or their combinations and polymers (already described in WO 2004/036674) obtained by the condensation of an 4-{1 -[(phenyl-2,4-disubstituted)- hydrazine]-alkyl}-benzene-1 ,3-diol with phenol or a phenol 3,5 substituted and formaldehyde or paraformaldehyde in the presence of an acid or basic catalyst in alcohol/water and at temperatures between 20 and 150°C and with a resulting molecular weight from 1000 to 50000.

With the catalysts of this invention it is possible to oxidise ammonia in PME type electrolysers, equipped with polymeric anionic exchange membranes, at potentials of 0.6-0.5 V with currents of 100 mA and with faradic efficiencies around 99%. The energetic efficiency, estimated from overvoltage calculations, is around 20. Detailed description of the invention

The object of this invention is the surprising discovery that state of the art nanostructured electrocatalysts, based upon transition metals and already used in fuel cells, can be used, combined with other electrodeposited metals, for the electro-oxidation of ammonia to nitrogen and the reduction of water to hydrogen in electrolysers containing solid polymeric anionic exchange membranes according to reactions 5 and 6. In addition state of the art electrochemical materials (PT FI2006A000180, 2006), obtained by the spontaneous deposition of metals onto the preformed catalysts is already used in fuel cells, can be used in electrolysers as described above. The electrodes of this invention are perfectly usable in electrolysers of aqueous solutions of ammonia, hydrazine and hydroxylamine. The function of an electrolyser described in this invention is shown in Figure 1. Some of the catalysts described in this invention have been already reported as anodic catalysts for fuel cells (WO 2004/036674 by the same applicant as this present patent applications), in which it is described that a templating polymer formed by the condensation of a 1 ,3-diol containing a coordinating nitrogen, with phenol or a phenol 3,5 substituted and formaldehyde or paraformaldehyde is capable of coordinating metal salts to give adducts that once reduced with gaseous hydrogen or other reducing agents, produce materials for anodic or cathodic electrodes in fuels cells fed by hydrogen or various compounds containing combined hydrogen, in particular alcohols (methanol, ethanol, ethylene glycol), aldehydes, hydrazine and also hydrocarbons. Successive studies have demonstrated that the metal particles formed, containing one or more metals, have very small dimensions, from 3-50 A (10^"1° m). Additionally, other catalysts described in this invention have been reported in the Italian patent application FI20040000154 (by the same applicant as this present patent application) that, through an analogous method to that written in the above application WO 2004/036674, describes the preparation of catalysts based upon platinum or platinum in combination with other transition metals used for the production of catalytic materials for cathodic and anodic electrodes of fuel cells fed with hydrogen or other compounds containing combined hydrogen. Also in this case, the catalysts consist of highly dispersed particles of nano or sub-nanometric dimensions (10^"9 m). In particular the nanostructured catalysts described in this invention are prepared from a metal salt, preferably cobalt or nickel, in binary combinations and templating polymers (already described in WO 2004/036674) obtained by the condensation of an 4-{1 -[(phenyl-2,4-disubstituted)-hydrazine]-alkyl}-benzene-1 ,3- diol with phenol or a phenol 3,5 substituted and formaldehyde or paraformaldehyde in the presence of an acid or basic catalyst in alcohol/water and at temperatures between 20 and 150°C and with a resulting molecular weight from 1000 to 50000.

Preferably, the 4-{1 -[(phenyl-2,4-disubstituted)-hydrazine]-alkyl}-benzene-1 ,3-diol is a compound of formula (A)

R₁ is chosen in the group consisting of: H or a radical hydrocarbon having from 1 to 10 carbon atoms, possibly halogenated; R₂ e R₃ independently from each other represent an electron-attracting group chosen from the following; hydrogen, halogen, acyl, ester, carboxylic acid, formyl, nitrile, sulfonic acid, aryl groups or alkyl groups linear or branched having 1 to 15 carbon atoms possibly functional ised with halogens or joined to each other in order to form one or more condensed cycles with the phenyl ring and nitro groups. The phenolic reagent is a compound of formula (B):

(B)

In which R₄ and R₅ independently from each other represent electrodonating groups chosen from a group consisting of H, OH, ether, amine, aryl groups and linear or branched groups, having from 1 to 15 carbon atoms. Additionally, the said polymeric resins are polymers that may be represented by the formula (C).

(C) in which y can vary from 2 to 120, x can vary from 1 to 2, n can vary from 1 to 3 and R-i, R₂, R3,R4 and R₅ are defined above.

The metal salts according to this invention are chosen from the group of carboxylates, halogens and pseudohalogens, alcholates, acetylacetonates, formates, oxalates, malonates, and analogous organic salts and their mixtures or carbonates and bicarbonates or their mixtures. The metals utilised are preferably chosen from the group consisting of Ru, Co, Ir, Ni, Pd, Rh, Pt. The electrodes of this invention for the production of hydrogen through the electrolysis of aqueous solutions of ammonia, of hydrazine, of hydroxylamine and in general compounds containing NH groups, are made by the electrodeposition of metals from example Pt, Ir, Ru and Rh, alone or in binary or ternary mixtures, onto supports of nickel or titanium onto which had been previously supported state of the art catalysts known as HYP E RM EC™.

This invention also refers to the use of electrodes already used as electrodes for fuel cells made with state of the art catalysts known as HYPERMEC™ (PT FI2006A000180, 2006) produced by the spontaneous deposition of metals like Pt, Ir, Ru and Rh as binary or ternary mixtures onto catalysts based upon Co and Ni supported on nickel powder and also their preparation.

For the preparation of the electrodes described in this invention both methods 1 and 2 can be used. Method 1 Two salts or metal compounds from the periodic table, chosen preferably from cobalt or nickel, are dissolved in water and the resulting solution is added to an aqueous suspension containing a state of the art templating polymer as described above and described in WO 2004/036674, from now on known as POLYMER. The mixture is then adjusted to pH 8-9 by the addition of 1 M NaOH and the mixture is stirred vigorously for 10-15 h at room temperature. The solid product that forms, known as POLYMER Co-Ni, is filtered, washed with water and air-dried. A suspension of POLYMER Co-Ni as described in WO 2004/036674, is deposited onto a conductive porous support such as titanium or nickel mesh, and is then treated with a state of the art reducing agent for example an aqueous solution of NaBH₄ Or NH₂NH₂.

The titanium or nickel mesh treated with the reducing agent, is immersed in an aqueous solution containing a salt or alternatively a binary or ternary mixture of noble metals preferably chosen from the group containing Ru, Rh, Pt, Ir and in this solution is immersed a platinum counter electrode. The electrodeposition of the noble metals mentioned above, is performed galvanostatically with a current density of 0.5 mA/cm². The quantity of POLYMER Co-Ni deposited on the support, the successive reduction and electrodeposition of noble metals, determines the quantity of metal per cm² present in the electrode. Method 2

A nickel salt, preferably nickel sulfate, is treated with a state of the art reducing agent such as aqueous solutions of NaBH₄ or NH₂NH₂. The product that forms is filtered, washed with water and then suspended in water. To this vigorously stirred mixture is added a suspension of POLYMER Co-Ni above defined and known. After 1 h, an aqueous solution of NaBH₄ is added and after 2 h the solid product that forms is filtered, washed with an aqueous solution of KOH, and then washed repeatedly with distilled water until the pH of the wash water is neutral. This compound is then suspended in water and to which is added an aqueous solution containing two or three metal salts chosen from the group of Ru Pt, Ir and Rh. The resulting suspension is filtered, washed with water and dried. The above isolated compound is suspended in a water/ethanol mixture (1 :1 , v:v). To this suspension, stirred vigorously, is added PTFE (polytetrafluoroethylene) and the flocculent solid obtained is separated and then spread onto a conductive support like nickel mesh. The electrode is then heated to 350 °C under a flow of inert gas (Ar, N₂). To better understand the invention the following examples are provided for the preparation of electrodes.

EXAMPLES OF ELECTRODE PREPARATION

Example 1

Preparation of an electrode based on Co, Ni and Ru on a titanium support

To a suspension containing 7 g of POLYMER in 200 mL of water is added an aqueous solution (150 mL) containing 1.59 g of cobalt(ll) acetate tetrahydrate (Aldrich) and 1.59 g of nickel(ll) acetate tetrahydrate (Aldrich). The mixture is adjusted to pH 9 through the addition of 100 mL of NaOH 1 M and is vigorously stirred for 15 h at room temperature. A dark red precipitate forms, which is then filtered, washed several times with water and then dried under vacuum at 70 °C to constant weight. Yield Polymer Co-Ni = 7.5 g. Content of Co = 4.27 wt.%, Ni = 4.31 wt.% (ICP-AES). A sonicated suspension of 0.04 g of the above product in 3 mL of acetone, is slowly deposited onto titanium mesh (microgrid foils, Dexmet) 4 cm² previously washed several times with acetone, dried and successively immersed in a solution of aqua regia (100 ml_) for 30 minutes and then washed with distilled water. This procedure which described the deposition of polymer Co- Ni onto a titanium mesh and successive reduction with NaBH₄ is repeated 5 times. 0.1 g of ruthenium(lll) trichloride hydrate is dissolved in an aqueous solution 1 M of NaCI. In this solution is immersed the titanium sheet treated as described above with an counter platinum electrode. The electrodeposition of Ru is undertaken galvanostatically with a current density of 0.5 mA/cm² for 10 minutes. Electrodes thus obtained are washed various times with distilled water. Co content 1.45 mg/cm², Ni = 1.28 mg/cm², Ru = 0.16 mg/cm² (Analysis EDX). Example 2

Preparation of an electrode based on Co₁ Ni and Rh on a titanium support A sonicated suspension of 0.04 g of Polymer Co-Ni (described in example 1 ) in 3 ml_ of acetone, is slowly deposited onto titanium mesh (microgrid foils, Dexmet) 4 cm² previously washed several times with acetone, dried and successively immersed in a solution of aqua regia (100 ml_) for 30 min. and then washed with distilled water. The titanium mesh impregnated with polymer Co-Ni is immersed in an aqueous solution of NaBH₄ (0.5 g) heated to 50 °C for 10 minutes and then washed several times with distilled water. This procedure which described the deposition of polymer Co-Ni onto a titanium mesh and successive reduction with NaBH₄ is repeated 5 times.

0.1 g of rhodium(lll) trichloride hydrate is dissolved in an aqueous solution 1 M of NaCI. In this solution is immersed the titanium sheet treated as described above an a counter platinum electrode. The electrodeposition of Rh is undertaken galvanostatically with a current density of 0.5 mA/cm² for 10 minutes. Electrodes thus obtained are washed various times with distilled water. Co content 1.47 mg/cm², Ni = 1.32 mg/cm², Rh = 0.2 mg/cm² (Analysis EDX). Example 3 Preparation of an electrode based on Co, Ni and Ir on a titanium support A sonicated suspension of 0.04 g of Polymer Co-Ni (described in example 1 ) in 3 ml_ of acetone, is slowly deposited onto titanium mesh (microgrid foils, Dexmet) 4 cm² previously washed several times with acetone, dried and successively immersed in a solution of aqua regia (100 ml_) for 30 minutes and then washed with distilled water. The titanium mesh impregnated with polymer Co-Ni is immersed in an aqueous solution of NaBH₄ (0.5 g) heated to 50 °C for 10 minutes and then washed several times with distilled water. This procedure which described the deposition of polymer Co-Ni onto a titanium mesh and successive reduction with NaBH₄ is repeated 5 times.

0.1 g di lrCI₃.xH₂O is dissolved in an aqueous solution 1 M of NaCI. In this solution is immersed the titanium sheet treated as described above an a counter platinum electrode. The electrodeposition of Ir is undertaken galvanostatically with a current density of 0.5 mA/cm² for 10 minutes. Electrodes thus obtained are washed various times with distilled water. Co content 1.61 mg/cm², Ni = 1.33 mg/cm², Ir = 0.2 mg/cm² (Analysis EDX). Example 4 Preparation of an electrode based on Co₁ Ni and Pt on a titanium support A sonicated suspension of 0.04 g of Polymer Co-Ni (described in example 1 ) in 3 ml_ of acetone, is slowly deposited onto titanium mesh (microgrid foils, Dexmet) 4 cm² previously washed several times with acetone, dried and successively immersed in a solution of aqua regia (100 ml_) for 30 minutes and then washed with distilled water. The titanium mesh impregnated with polymer Co-Ni is immersed in an aqueous solution of NaBH₄ (0.5 g) heated to 50 °C for 10 minutes and then washed several times with distilled water. This procedure which described the deposition of polymer Co-Ni onto a titanium mesh and successive reduction with NaBH₄ is repeated 5 times. 0.1 g of H₂PtCI₆ is dissolved in an aqueous solution 1 M of NaCI. In this solution is immersed the titanium sheet treated as described above an a counter platinum electrode. The electrodeposition of Pt is undertaken galvanostatically with a current density of 0.5 mA/cm² for 10 minutes. Electrodes thus obtained are washed various times with distilled water. Co content 1.35 mg/cm², Ni = 1.18 mg/cm², Pt = 0.3 mg/cm² (Analysis EDX). Example 5

Preparation of an electrode based on Co, Ni, Pt, Rh and Ir on a titanium support A sonicated suspension of 0.04 g of Polymer Co-Ni (described in example 1 ) in 3 ml_ of acetone, is slowly deposited onto titanium mesh (microgrid foils, Dexmet) 4 cm² previously washed several times with acetone, dried and successively immersed in a solution of aqua regia (100 ml_) for 30 minutes and then washed with distilled water. The titanium mesh impregnated with polymer Co-Ni is immersed in an aqueous solution of NaBH₄ (0.5 g) heated to 50 °C for 10 minutes and then washed several times with distilled water. This procedure which described the deposition of polymer Co-Ni onto a titanium mesh and successive reduction with NaBH₄ is repeated 5 times. 0.1 g of H₂PtCI_6, 0.1 g of RhCI₃ XH₂O and 0.1 g of IrCI₃ xH20 are dissolved in an aqueous solution 1 M of NaCI. In this solution is immersed the titanium sheet treated as described above an a counter platinum electrode. The electrodeposition of the metals is undertaken galvanostatically with a current density of 0.5 mA/cm² for 10 minutes. Electrodes thus obtained are washed various times with distilled water. Co content = 1.35 mg/cm², Ni = 1.18 mg/cm², Rh = 0.22 mg/cm², Ir = 0.1 1 mg/cm² Pt = 0.31 mg/cm² (Analysis EDX). Example 6

Preparation of an electrode based on Co, Ni, Pt and Ir on a nickel support 25 g of NiSO₄6H₂O are dissolved in 400 ml_ of water and to this vigorously stirred solution cooled to 0 °C, is added in small portions 5 g of NaBH₄. The mixture is left to warm to room temperature and is stirred vigorously for 30 minutes. The residue solid that forms is filtered and washed several times with distilled water (5 x 100 ml_). The wet solid is then suspended in 200 ml_ of distilled water and to the resulting suspension is added a sonicated suspension of 5 g of Polymer Co-Ni (described in example 1 ) in 50 ml_ of water. To the mixture obtained, sonicated for 20 min and under vigorous stirring is heated 50 °C, is slowly added an aqueous solution of (100 ml_) containing 5 g of NaBH₄. The reaction mixture is left under vigorous stirring for 1 h and is then filtered, washed with 200 ml_ of an aqueous solution of KOH 0.1 M and then washed with distilled water until the wash water is neutral. The residual black solid, still wet, is suspended in distilled water (200 ml_) and to the resulting suspension, stirred vigorously, is slowly added 300 ml_ of water containing 0.5 g of H₂PtCI₆6H₂O and 0.5 g of lrCI₃.xH₂O. Once added the suspension is stirred vigorously for one hour and then filtered, washed with water (3 x 50 ml_). The solid residue obtained is dried under vacuum at 40 °C to constant weight. Yield 5 g. Co content 0.88 wt.% Ir = 2.02 wt.% e Pt = 4.9 wt.% Ni = 92.2 wt.%. (Analysis ICP-AES). Electrode preparation:

5 g of this solid residue is dispersed in water. To this vigorously stirred suspension, is added 1 g of PTFE (polytetrafluoroethylene, Aldrich) dispersed in water (60 wt%). After 5 minutes, a floccules precipitate (CF) forms that is separated by decantation. 100 mg of the compound (CF) is spread onto nickel mesh (Ansheng Wire mesh produco Co., Ltd) which is then pressed at 80 Kg/cm². The thus formed electrode is then sintered by heating in an oven to 350 °C under a flow of hydrogen for 1 h. Example 7 Preparation of an electrode based on Co, Ni, Pt and Rh on a nickel support 25 g of NiSO₄6H₂O are dissolved in 400 ml_ of water and to this vigorously stirred solution cooled to 0 °C, is added in small portions 5 g of NaBH₄. The mixture is left to warm to room temperature and is stirred vigorously for 30 min. The residue solid that forms is filtered and washed several times with distilled water (5 x 100 ml_). The wet solid is then suspended in 200 ml_ of distilled water and to the resulting suspension is added a sonicated suspension of 5 g of Polymer Co-Ni (described in example 1 ) in 50 ml_ of water. To the mixture obtained, sonicated fro 20 minutes and under vigorous stirring is heated 50 °C, is slowly added an aqueous solution of (100 ml_) containing 5 g of NaBH₄. The reaction mixture is left under vigorous stirring for 1 h and is then filtered, washed with 200 ml_ of an aqueous solution of KOH 0.1 M and then washed with distilled water until the wash water is neutral. The residual black solid, still wet, is suspended in distilled water (200 ml_) and to the resulting suspension, stirred vigorously, is slowly added 300 ml_ of water containing 0.5 g of H₂PtCI₆6H₂O and 0.5 g of RhCI₃ XH₂O. Once added the suspension is stirred vigorously for one hour and then filtered, washed with water (3 x 50 ml_). The solid residue obtained is dried under vacuum at 40 °C to constant weight. Yield 5.5 g. Co= 0.81 wt.%, Rh = 2.03 wt.% and Pt = 4.8 wt.%, Ni = 92.36 wt.%. (Analysis ICP-AES) Electrode preparation is described in example 6. Example 8

Preparation of an electrode based on Co₁ Ni₁ Pt and Ru on a nickel support 25 g of NiSO₄6H₂O are dissolved in 400 ml_ of water and to this vigorously stirred solution cooled to 0 °C, is added in small portions 5 g of NaBH₄. The mixture is left to warm to room temperature and is stirred vigorously for 30 minutes. The residue solid that forms is filtered and washed several times with distilled water (5 x 100 ml_). The wet solid is then suspended in 200 ml_ of distilled water and to the resulting suspension is added a sonicated suspension of 5 g of Polymer Co-Ni (described in example 1 ) in 50 ml_ of water. To the mixture obtained, sonicated fro 20 min and under vigorous stirring is heated 50 °C, is slowly added an aqueous solution of (100 ml_) containing 5 g of NaBH₄. The reaction mixture is left under vigorous stirring for 1 h and is then filtered, washed with 200 ml_ of an aqueous solution of KOH 0.1 M and then washed with distilled water until the wash water is neutral. The residual black solid, still wet, is suspended in distilled water (200 ml_) and to the resulting suspension, stirred vigorously, is slowly added 300 ml_ of water containing 0.5 g of H₂PtCI₆6H₂O and 0.5 g of RuCI₃.xH₂O. Once added the suspension is stirred vigorously for one hour and then filtered, washed with water (3 x 50 ml_). The solid residue obtained is dried under vacuum at 40 °C to constant weight. Yield 5.5 g. Co= 0.78 wt.%, Ru = 1.88 wt.% e Pt = 4.9 wt.% Ni = 92.44 wt.%. (Analysis ICP-AES) Electrode preparation is described in example 6. EXAMPLES OF ELECTROLYTIC CELL PREPARATION Example 9 The anode catalyst and the corresponding positive electrode, on the surface of which occur the evolution of nitrogen gas from ammonia, is prepared directly by the electrodeposition of a mixture of metals chosen from Pt, Ir, Ru and Rh on Ti mesh containing Co and Ni, according to the method 1 and in example 5. The cathode catalyst and the corresponding negative electrode, on the surface of which occurs the evolution of gaseous hydrogen, is prepared by the electrodeposition of Pt on Ti mesh containing Co and Ni, according to the method described in example 4. The ionic conductor in the cell is an alkaline exchange membrane (4 cm²) Tokuyama Neosepta^® A-006 produced by ASTOM Corp. The resulting electrolytic cell was fuelled on the cathode side with a solution of potassium hydroxide of 5 mol/dm³ and on the anode side by a solution of potassium hydroxide of 5 mol/dm³ and ammonium hydroxide at a concentration of 1 mol/dm³ at both room temperature and ambient pressure (25 °C and 1 atm). This allows the passage of 25 mA/cm² of current at 0.6 V. The internal resistance of the cell was 30 mOhm. From measurements of the hydrogen produced the faradaic efficiency was 99%. The energy efficiency was estimated from overvoltage measurements as 19%

The polarisation curve relative to the electrolysis cell shown in Figure 2 was run with an open cell voltage of 0.7 V with a scan speed of 10 mV/s. Successively, the same cell was subjected to a duration test (Figure 3) that consists of many consecutive load cycles at constant potential of 0.6 V for 5 minutes followed by a potential inversion at -0.6 V for 20 seconds, with the purpose of regenerating the optimum function of the catalyst. From the measurement of duration the load capacity can be obtained for every cycle of 5 minutes (Figure 4). Example 10 The anode catalyst and the corresponding positive electrode, on the surface of which occur the evolution of nitrogen gas from ammonia, is prepared according to the method 2 and in example 6.

The cathode catalyst and the corresponding negative electrode, on the surface of which occurs the evolution of gaseous hydrogen, is prepared by the electrodeposition of Pt on Ni mesh according to a state of the art method. The ionic conductor in the cell is an alkaline exchange membrane (4 cm²) Tokuyama Neosepta^® A-006 produced by ASTOM Corp.

The resulting electrolytic cell was fuelled on the cathode side with a solution of potassium hydroxide of 5 mol/dm³ and on the anode side by a solution of potassium hydroxide of 5 mol/dm³ and ammonium hydroxide at a concentration of 1 mol/dm³ at both room temperature and ambient pressure (25 °C and 1 atm). This allows the passage of 25 mA/cm² of current at 0.6 V.

Claims

1. Electrodes for electrolysers with a solid polymer anionic exchange electrolyte comprising a nickel or titanium support on which it is deposited a nanostructured catalyst based on transition metals modified by the electrochemical or spontaneous deposition of metals chosen from the group: Pt, Ir, Ru and Rh, alone or in binary or ternary mixtures.

2. Electrodes according to claim 1 in which the said nanostructured catalysts are prepared starting from metal complexes formed from a transition metal salt, in binary combination and templating polymers obtained by the condensation of a 4- {1 -[(phenyl-2,4-disubstituted)-hydrazine]-alkyl}-benzene-1 ,3-diol with phenol or a 3,5 substituted phenol and formaldehyde or paraformaldehyde in the presence of an acidic or basic catalyst in alcohol/water and at temperatures between 20 and 150 °C and with a resulting molecular weight from 1000 to 50000.

3. Electrodes according to claim 2 in which the said transition metal salts are salts of Co, Ni, Pt, Ir, Rh, Ru or their combinations.

4. Electrodes according to claims 1 and 2 in which the said support is made of titanium or nickel mesh.

5. Electrodes according to the claims 1 -4 containing:

Co = 1.45 mg/cm², Ni = 1.28 mg/cm², Ru = 0.16 mg/cm²; Co = 1.47 mg/cm², Ni = 1.32 mg/cm², Rh = 0.2 mg/cm²;

Co = 1.61 mg/cm², Ni = 1.33 mg/cm², Ir = 0.2 mg/cm²;

Co = 1.35 mg/cm², Ni = 1.18 mg/cm², Pt = 0.3 mg/cm²;

Co = 1.35 mg/cm², Ni = 1.18, Rh = 0.22 mg/cm², Ir = 0.1 1 mg/cm², Pt = 0.31 mg/cm²; Co= 0.88 wt.%, Ir = 2.02 wt.% e Pt = 4.9 wt.% Ni = 92.2 wt.%;

Co= 0.81 wt.%, Rh = 2.03 wt.% e Pt = 4.8 wt.%, Ni = 92.36 wt.%;

Co= 0.78 wt.%, Ru = 1.88 wt.% e Pt = 4.9 wt.% , Ni = 92.44 wt.%.

6. Methods for the preparation of electrodes according to the claims 1 -5 in which: - two different metal salts are dissolved in water and to the resulting solution is added an aqueous suspension containing the templating polymer. - the mixture is adjusted to pH 8-9 through the addition of a basic solution and vigorously stirred for 10-15 h at room temperature and the solid product that forms is filtered, washed with water and air-dried.

- a suspension in acetone of the polymer obtained by the above procedure is deposited onto a porous and conducting support made of titanium or nickel mesh, which is then successively treated with a reducing agent and then immersed in an aqueous solution containing a salt or alternatively a binary or ternary mixture of noble metal salts and in the same solution is immersed a platinum counter electrode. - the electrodeposition of the noble metals cited above proceeds galvanostatically with a current density of 0.5 mA/cm2.

7. The use of the electrodes described in claims 1 -5 for the production of gaseous hydrogen through the electrolysis of aqueous solutions of ammonia, of hydrazine, of hydroxylamine and in general compounds containing NH groups.

8. Electrolysers of the type described in claim 1 containing electrodes according to claims 1 -5.

9. Use of electrodes, containing a nanostructured catalyst formed from transition metal salts, in binary combination, and templating polymers as reported in claim 2 onto which are deposited by the spontaneous deposition of noble metal salts, for the production of gaseous hydrogen through the electrolysis of aqueous solutions of ammonia, of hydrazine, of hydroxylamine and in general compounds containing NH groups.

10. The use according to claim 9 in which the said transition metals are Co and Ni and the said noble metals are Pt, Ir, Ru and Rh.

1 1 . Method for the preparation of the electrodes as reported in claim 9 in which:

- a nickel salt is treated with a state of the art reducing agent and the product that forms is filtered, washed with water and suspended in water.

- to this solution is added a suspension of the complex formed from the transition metal salts and templating polymer according to claim 2 and then is added a hot aqueous solution of NaBH₄ . - the remaining solid product is filtered, washed with an aqueous solution of KOH, followed by washing with distilled water until the wash water is a neutral pH, the compound obtained is suspended in water and to this suspension is added an aqueous solution containing two or three noble metal salts and the suspension is filtered, washed with water and dried; the above isolated compound, is suspended in a mixture of water/ethanol to which is added polytetrafluoroethylene and the flocculous compound that forms is separated and then spread onto conductive supports;

- the electrode is finally heated to 350 °C under a flow of inert gas.