EP1984539A2

EP1984539A2 - Catalysts for the production of hydrogen by the electrolysis of water, electrolysers in which they are used, and processes for the production of hydrogen by the electrolysis of water

Info

Publication number: EP1984539A2
Application number: EP07703946A
Authority: EP
Inventors: Paolo Bert; Claudio Bianchini; Stefano Catanorchi; Antonio Filpi; Giuliano Giambastiani; Michele Piana; Serena Santiccioli; Alessandro Tampucci; Francesco Vizza
Original assignee: Acta SpA
Current assignee: Acta SpA
Priority date: 2006-01-18
Filing date: 2007-01-17
Publication date: 2008-10-29
Also published as: WO2007082898A2; ITFI20060018A1; WO2007082898A3

Abstract

Metal catalysts are described which preferably contain manganese, molybdenum, iron, cobalt, nickel, palladium, iridium and their mixtures used for the production of hydrogen by the electrolysis of water in electrolytic apparatus containing solid polymeric anionic exchange membranes.

Description

Catalysts for the production of hydrogen by the electrolysis of water, electrolysers in which they are used, and processes for the production of hydrogen by the electrolysis of water.

Field of the invention

This invention relates to the production of hydrogen by electrolysis of water.

State of the art:

In recent years the technology related to the production of hydrogen by the electrolysis of water is currently of major interest especially in the field of sustainable development. The success of the hydrogen economy will depend upon the sustainability of its infrastructure (i.e. the production, distribution, storage/use etc). The electrolysis of water represents an significant alternative to the production of hydrogen from fossil fuels and is the only system that allows the use of renewable energy sources (photocells, wind, biomass, geothermal etc. (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 ; RJ. 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).

The electrolysis of water is a well defined process: in an electrolyser, a potential difference between the electrodes splits water into hydrogen (at the cathode) and into oxygen (at the anode) (eq. 1):

2 H₂O + electrical energy → 2 H₂ + O₂ (1) The electrolyser is an apparatus consisting of a cell containing: the solution to be electrolysed, two electrodes on which the surface due to the passage of current occur the oxidation/reduction reactions and an ion-exchange membrane between the two electrodes (as explained in more detail as follows). The electrodes normally consist of a metal element or some highly conducting surface onto which is applied a catalyst also usually a metal. The efficiency of an electrolyser depends directly upon the materials in which the electrodes are constructed. In particular the catalysts whose role is that of diminishing the activation energy of both the anodic and cathodic reactions. The electrode materials play an important role in improving the energetic efficiency of an electrolyser in terms of both the energy consumption ( for a particular reaction rate) and the maximum reaction rate of a cell.

There exist three distinct electrolyser technologies, two of which are well established: alkaline electrolysers (AE), solid polymer membrane electrolysers (MPE) and solid oxides electrolysers which are still being developed.

The main difference between AE and MPE is that the electrolyte in the AE case consists of an alkaline solution, generally KOH (25-30%), while in a MPE the electrolyte consists of a polymeric membrane through which pass ions, generally H⁺ to the cathode where they are reduced to make H₂. The other function of the membrane is to separate the gases that are produced at the two electrodes. The advantages of the MPE type are multiple: no moving parts, very low volume of corrosive liquids, high current density obtained, production of pressurised gas, quick response to applied load. The disadvantages include the high cost of the membrane (generally Nafion form DuPont) and the noble metals used in the catalyst (usually platinum and its alloys). Generally the catalysts used are a high percentage of the active phase ((>(10 mg/cm²) to obtain the required output. The high catalyst load is extremely costly especially if noble metals are used and hence limits the potential applications for MPE type electrolysers. The accepted definition for the efficiency of an electrolyser capable of generating hydrogen is expressed in kWh/Nm³ of H₂. A normal m³ di H₂ has a "higher heating value" of 3.54 kWh. An electrolyser operates at 100% efficiency in the conversion of electrical energy into hydrogen when 3.54 kWh is used to produce 1 Nm³ of H₂. Other parameters characteristic for an electrolyser are the voltage applied to the electrolytic cell and the current density (A/cm²). The efficiency of an PME is generally low at high current density (even < 7.5 kWh/Nm³) but can be slightly under 4 kWh/Nm³ at a current density of around 0.2 A/cm². PME type electrolysers using catalysts based upon non-noble metals with anionic exchange solid polymeric membranes are virtually unknown in the sector or in the scientific literature. However, cathode catalysts containing one or more non-noble metals also alloys in AE type electrolysers with liquid electrolytes are well known in the literature. (F. C. Crnkovic, S.A.S. Machado, L.A. Avaca, Int. J. Hydrogen Energy 2004, 29, 249).

Summary of the invention In this invention is described the use of metal catalysts for the production of hydrogen by the electrolysis of water in electrolysers containing anionic exchange solid polymeric membranes. These catalysts are formed from metal complexes obtained from transition metal salts, usually manganese, iron, cobalt, nickel, palladium, iridium or their alloys and polymers (already described in WO2004/036674) obtained by the condensation of a 4-{1-[(fenil-2,4-disubstituted)- hydrazine]-alkyl}-benzene-1 ,3-diol with a 3,5-disubstituted phenol and formaldehyde or para-formaldehyde in the presence of an acid or basic catalysts in water/alcohol mixtures and at a temperature comprised between 20 - 15O⁰C and having a molecular weight comprised between 1000 and 50000.

Description of Figures

Figure 1. Functional design of an electrolyser with an ion exchange solid polymer membrane.

Figure 2. Change in potential of a cell with time during the experiment described in example 5.

Figure 3. Change in potential of a cell at various current densities under the conditions of the experiment described in example 5. Figure 4. Change in potential of a cell with time during the experiment described in example 6.

Figure 5. Change in potential of a cell at various current densities under the conditions of the experiment described in example 6.

Detailed description of the invention

An unexpected discovery, as part of this invention, has been nano-structured electrocatalytic materials which are already utilised to make anodes in fuel cells, are extremely reactive for the cathodic production of hydrogen in electrolysers containing anionic exchange solid polymeric membranes and hence are ideal for the construction of electrodes for use in electrolysers used for the electrolysis of water.

A functional diagram of the electrolyser described in this invention is described in Figure 1. An electrolyser like that shown in Figure can contain anodic catalysts of the state of the art (C-C. Hu, Y.-S. Lee, T.-C. Wen, Materials Chemistry and Physics 1997, 48, 246; C. Bocca, A. Barbucci, M. Delucchi, G. Cerisola, Int. J. Hydrogen Energy, 1998, 23, 1) for AE type electrolysers and for electrolysers with commercial anionic exchange solid polymer membranes. Some cathode catalysts described in this invention are also described for use in fuel cells in WO 2004/036674 (also by the current inventors) in which is reported templating polymers formed form the condensation of an 1 ,3-diol, containing coordinating nitrogen atoms, with phenol or 3,5 disubstituted phenols and formaldehyde or paraformaldehyde which are capable of coordinating metal salts, none of which containing platinum and are preferentially salts or compounds of iron, cobalt and or nickel to give adducts that once reduced using gaseous hydrogen or other reducing agents or pyrolised under inert atmosphere at temperatures above 500 ⁰C, produce catalytic materials for anodes and cathodes in fuel cells fuelled by hydrogen or other compounds containing hydrogen in particular alcohols (methanol, ethanol, ethylene glycol), aldehydes, hydrazine and various hydrocarbons.

Successive studies have demonstrated that the metal particles, containing one or metal metals are extremely small, between 3 and 50 A (10^"1° m). Analogously, other catalysts made according to this invention are described in the Italian patent application FI20040000154 (also by the current inventors) that, using a completely analogous method to that used in the previously mentioned WO 2004/036674, describes the preparation of catalysts based upon platinum or platinum in combination with other transition metals for the production of catalytic materials for anodes and cathodes in fuel cells fuelled by hydrogen or other compounds containing hydrogen. Also in this case, the catalysts are formed from highly dispersed particles of sub-nanometric and nanometric dimentions(10^"9 m). In particular, the catalysts described in this invention are prepared starting from metal complexes formed from metal salts preferably manganese, molybdenum, iron, cobalt, nickel, palladium, iridium and their mixtures, binary, tertiary or quaternary and templating polymers (already described in WO2004/036674) obtained by: The condensation of a 4-{1-[(fenil-2,4-disubstituted)-hydrazine]-alkyl}-benzene- 1 ,3-diol with a 3,5-disubstituted phenol and formaldehyde or para-formaldehyde in the presence of an acid or basic catalyst in water/alcohol mixtures and at a temperature comprised between 20 - 150⁰C and having a molecular weight comprised between 1000 and 50000. Preferably the a 4-{1-[(phenyl-2,4-disubstituted)-hydrazine]-alkyl}-benzene-1 ,3- diol is a compound of formula (A)

Wherein Ri is chosen in the group consisting og: H, a C-M_O hydrocarbon radical, possibly halogenated, R₂ and R₃ independently from each other represent an electron-attractive group chosen in the group consisting of: H, halogen, acyl, ester, carboxylic acid, formyl, nitrile, sulphonic acid, aryl groups or linear or branched alkyl having 1 - 15 carbon atoms, possibly functionalised with halogens or joined to each other in order to form one or more cycles condensed with the phenyl ring, and nitro groups; and the 3,5 disubstituted phenol is a compound of formula (B)

(B)

Wherein R₄ and R₅ independently from each other represent and electro-donating group chosen among H, OH, ether, amine, aryl and linear or branched alkyl groups having 1 - 15 carbon atoms.

The above said polymers can be represented by the formula (C)

(C)

Wherein y is comprised between 2 and 120, x is comprised between 1 and 2, n is comprised between 1 and 3 and R-i, R₂, Rz, R₄ and R₅ are as above defined. The metal salts according to the invention are chosen from the group comprising carboxylates, halogens and pseudohalogens, alcolates, acetylacetonates, formates, oxalates, malonates and analogous organic salts and their mixtures or carbonates and bicarbonates or their mixtures. The metals used are preferably chosen from the group containing: Fe, Ru, Co, Ir, Ni, Pd, Mo, Mn.

The catalysts used in this invention are prepared from either of the following methods 1 , 2 and 3. Method 1 :

A salt or metal compound from the Periodic Table preferably among those described above is dissolved in water and then added to an aqueous suspension containing a templating polymer as described above and in detail in WO 2004/036674, from now on known as the POLYMER. The mixture is adjusted to pH 8-9 by the addition of a solution of 1 M NaOH and then mixed vigorously for 10-15 h at room temperature. The solid product formed known as the MONO- METALLIZED POLYMER, is filtered, washed with water and air dried. The dried solid is added to a suspension in acetone or some other organic solvent of nickel powder (3 micron), or porous conducting carbonaceous material for example Vulcan XC-72R. After 2 hours of mixing the resulting product is treated with a reducing agent of the state of the art (e.g. NaBH₄ or NH₂NH₂), filtered, washed with water and dried.

Alternatively, the solid product obtained by the impregnation of the MONO-METALLIZED POLYMER on the nickel powder support (3 micron) or Vulcan XC-72R, is isolated by evaporation of the solvent under reduced pressure and then is treated with a current of hydrogen at a temperature between 300 e 800 ⁰C.

Method 2: Two salts or metal compounds of the Periodic Table preferably Mn, Fe, Ru, Co, Ir, Ni, Pt, Pd, Mo, Sn, are dissolved in water and the solution is added to an aqueous suspension of the POLYMER. The mixture is adjusted to pH 8-9 using a solution of 1 M of NaOH and then mixed vigorously for 10-15 h at room temperature. The solid product formed known as the BI-METALLIZED POLYMER, is filtered, washed with water and air dried. The dried solid is added to a suspension in acetone or some other organic solvent of nickel powder (3 micron), or a porous conducting carbonaceous material for example Vulcan XC-72R. After 2 hours of mixing the resulting product is treated with a reducing agent of the state of the art (e.g. NaBH₄ or NH₂NH₂), filtered, washed with water and dried. Alternatively, the solid product obtained by the impregnation of the BI-METALLIZED POLYMER on the nickel powder support (3 micron) or Vulcan XC-72R, is isolated by evaporation of the solvent under reduced pressure and then is treated with a current of hydrogen at a temperature between 300 e 800 ⁰C. Method 3:

Three salts or metal compounds of the Periodic Table preferably Mn, Fe, Ru, Co, Ir, Ni, Pt, Pd, Mo, Sn, are dissolved in water and the solution is added to an aqueous suspension of the POLYMER. The mixture is adjusted to pH 8-9 using a solution of 1 M of NaOH and then mixed vigorously for 10-15 h at room temperature. The solid product formed known as the TRI-METALLIZED POLYMER, is filtered, washed with water and air dried. The dried solid is added to a suspension in acetone or some other organic solvent of nickel powder (3 micron), or a porous conducting carbonaceous material for example Vulcan XC- 72R. After 2 hours of mixing the resulting product is treated with a reducing agent of the state of the art (e.g. NaBH₄ or NH₂NH₂), filtered, washed with water and dried. Alternatively, the solid product obtained by the impregnation of the TRI- METALLIZED POLYMER on the nickel powder support (3 micron) or Vulcan XC- 72R, is isolated by evaporation of the solvent under reduced pressure and then is treated with a current of hydrogen at a temperature between 300 e 800 ⁰C. Analogous procedures can be used for the preparation of catalysts with more than three different metals from the Periodic Table deposited on the same support material.

The catalysts prepared according to the methods described above preferably contain the three metals Mn, Co and Ni in various stoichiometric ratios, preferably equimolar, or only Co and Ni, supported on conducting supports such as nickel (3 micron) or porous conducting carbonaceous material for example Vulcan XC-72R and are able to promote the electrolysis of water in alkaline environments. With respect to the common catalysts used for the production of hydrogen from water the advantages are as follows: - the use of non noble metals at low cost - the possibility of synthesising multi-metal catalysts with precise stoichiometric ratio between the metals present.

Based upon these advantages, this invention allows the production of hydrogen with an efficiency greater than 90% and a cost substantially lower with respect to currently used electrolysers, in addition with all the advantages of PME type electrolysers with proton exchange solid polymer membranes. The following examples describe in detail the preparation of several catalysts used for the realisation of cathodes in the electrolyser of this invention. EXAMPLES OF THE PREPARATION OF CATHODE CATALSYTS EXAMPLE 1

Preparation of a trimetallic cathode catalyst based upon Mn, Co and Ni supported on nickel powder or Vulcan XC-72R.

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), 1.59 g of nickel(ll) acetate tetrahydrate (Aldrich) and 1.71 g of manganese(ll) acetate tetrahydrate (Aldrich). The mixture is adjusted to pH 9 by addition of 100 mL of NaOH 1 M and vigorously stirred for 15 h at room temperature. The red precipitate that forms is filtered, washed repeatedly with water and dried under vacuum at 70 ⁰C to constant weight. Yield = 8 g. Co = 4.27 wt.%, Ni = 4.31 wt.%, and Mn = 3.98 wt.%, (ICP-AES). To a sonicated suspension of 0.25 g of the previously obtained compound in 200 mL of acetone, is added 2 g of a suspension sonicated for 20 min. of nickel powder (3 micron) or Vulcan XC-72R. The resulting suspension is vigorously stirred at room temperature for 4 h then cooled to 0⁰C, and 1.8 g of NaBH₄ is added in small portions. The resulting mixture is allowed to return to room temperature and after 2 h the solid residue is isolated by filtration, washed with water (3 x 50 mL) and dried under vacuum at 70 ⁰C to constant weight. Co = 0.51 wt.%, Ni = 0.52 wt.%, and Mn = 0.47 wt.%. (ICP- AES). Atomic ratio percentage Co₃₄Ni₃₄Mn₃₂. Alternatively, the reduction can be effected in a current of hydrogen. In this case 1 g of the solid product POLYMER-Co-Ni-Mn/Ni_powder isolated by evaporation of the solvent under reduced pressure, is introduced into a quartz furnace heated to 360 °C per 1 h under a flow of hydrogen. The product is then conserved under an inert atmosphere of N₂ or Ar. EXAMPLE 2

Preparation of a trimetallic cathode catalyst based upon Co and Ni supported on nickel powder or Vulcan XC-72R.

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), 1.59 g of nickel(ll) acetate tetrahydrate (Aldrich) and (Aldrich). The mixture is adjusted to pH 9 by addition of 100 mL of NaOH 1 M and vigorously stirred for 15 h at room temperature. The red precipitate that forms is filtered, washed repeatedly with water and dried under vacuum at 70 ⁰C to constant weight. Yield = 7.5 g. Co = 4.27 wt.%, Ni = 4.31 wt.%, (ICP-AES). To a sonicated suspension of 0.25 g of the previously obtained compound in 200 mL of acetone, is added 2 g of a suspension sonicated for 20 min. of nickel powder (3 micron) or Vulcan XC-72R.

The resulting suspension is vigorously stirred at room temperature for 4 h then cooled to 0°C, and 1.2 g of NaBH₄ is added in small portions. The resulting mixture is allowed to return to room temperature and after 2 h the solid residue is isolated by filtration, washed with water (3 x 50 mL) and dried under vacuum at 70 ⁰C to constant weight. Co = 0.51 wt.%, Ni = 0.50 wt.% (ICP-AES). Atomic ratio percentage Co₅₀Ni₅O

Alternatively, the reduction can be effected in a current of hydrogen. In this case 1 g of the solid product POLYMER-Co-Ni/Ni_pOwcier isolated by evaporation of the solvent under reduced pressure, is introduced into a quartz furnace heated to 360 °C per 1 h under a flow of hydrogen. The product is then kept under an inert atmosphere of N₂ or Ar. EXAMPLE 3

Preparation of a trimetallic cathode catalyst based upon Ni supported on nickel powder or Vulcan XC-72R. To a suspension containing 7 g of POLYMER in 200 mL of water is added an aqueous solution (150 mL) 1.59 g of nickel(ll) acetate tetrahydrate (Aldrich). The mixture is adjusted to pH 9 by addition of 100 mL of NaOH 1 M and vigorously stirred for 15 h at room temperature. The red precipitate that forms is filtered, washed repeatedly with water and dried under vacuum at 70 ⁰C to constant weight. Yield = 7.5 g. Ni = 4.31 wt.%, (ICP-AES). To a sonicated suspension of 0.25 g of the previously obtained compound in 200 ml_ of acetone, is added 2 g of a suspension sonicated for 20 min. of nickel powder (3 micron) or Vulcan XC-72R. The resulting suspension is vigorously stirred at room temperature for 4 h then cooled to 0⁰C, and 1.2 g of NaBH₄ is added in small portions. The resulting mixture is allowed to return to room temperature and after 2 h the solid residue is isolated by filtration, washed with water (3 x 50 ml_) and dried under vacuum at 70 ⁰C to constant weight. Ni = 0.50 wt.% (ICP-AES).

Alternatively, the reduction can be effected in a current of hydrogen. In this case 1 g of the solid product POLYMER-Ni/Ni_poWder isolated by evaporation of the solvent under reduced pressure, is introduced into a quartz furnace heated to 360 ⁰C per 1 h under a flow of hydrogen. The product is then kept under an inert atmosphere of N₂ Or Ar.

According to this invention the activity of the catalysts is measured in electrolysers of the type EPP illustrated in Figure 1 , by assembling the cathodes of this invention with anodes of the state of the art and commercial anionic exchange membranes. A method for the fabrication of a cathode electrode is described below along with some examples of electrolytic experiments used to evaluate them.

EXAMPLE 4

10 g of the catalyst obtained by the methods 1 , 2, or 3 as described above are dispersed in 100 ml_ of a 1 :1 (v:v) mixture of water/alcohol. To this vigorously stirred suspension are added 2 g of PTFE (polytetrafluoroethylene, ALDRICH) dispersed in water (60 wt%). After 10 min. a flocculent precipitate forms (CF) that is separated by decantation. 200 mg of the mixture (CF) is pasted onto a nickel foam net (Ansheng Wire mesh produco Co., Ltd) and is then pressed to 80 Kg/cm². The electrode thus formed is then sintered at 350 ⁰C under a flow of hydrogen for one hour. EXAMPLE 5 The anode catalyst and the corresponding positive electrode, upon whose surface occurs the oxygen gas evolution reaction, is prepared directly by the cathodic electrodeposition of Co and Ni from a solution of Ni(NOs)2 and Co(NO₃)₂ on a nickel foam electrode of the state of the art (E. B. Castro, S. G. Real, L. F. Pinheiro, Int. J. Hydrogen Energy 2004, 29, 255]. The cathode catalyst and the corresponding negative electrode upon whose surface occurs the evolution of hydrogen gas, is prepared according to the method described in 3 using an alloy of the metals Ni3₄Co3₄Mn32/Ni_poWder- As ionic conductor in the cell is used an alkaline anionic exchange membrane Tokuyama Neosepta^® A-010 produced by ASTOM Corp.

The resulting electrolytic cell is fuelled by a solution of potassium hydroxide at concentrations of 1 moi/dm³, 2 mol/dm³ and 6 mol/dm³ at ambient temperature and pressure (25°C and 1 atm). This allowed the passage of 250 mA/cm² of current at 1.820 V where the electrolyte concentration was 1 mol/dm³, 1.780 V where the electrolyte concentration was 2 mol/dm³ and 1.650 V where the electrolyte concentration was 6 mol/dm³. At the highest electrolyte concentration (6 mol/dm³) an internal resistance of the cell of 30 mOhm was obtained. The faradaic efficiency of the cell is practically equal to 100%; the energetic efficiency of the cell has been calculated using the theoretical value of the Higher Heating Value (HHV) of hydrogen, corresponding to its standard combustion enthalpy (285.8 kJ/mol or 79.39 Wh/mol) and resulted in a value of 93% at 250 mA/cm² of constant current and at 75% at 750 mA/cm² of constant current. EXAMPLE 6 The anode catalyst and the corresponding positive electrode, upon whose surface occurs the oxygen gas evolution reaction, is prepared directly by the cathodic electrodeposition of Co and Ni from a solution of Ni(NO₃)₂ on a nickel foam electrode of the state of the art (E. B. Castro, S. G. Real, L. F. Pinheiro, Int. J. Hydrogen Energy 2004, 29, 255]. The cathode catalyst and the corresponding negative electrode upon whose surface occurs the evolution of hydrogen gas, is prepared according to the method described in 3 using an alloy of the metals Ni3₄Co₃₄Mn32/Nipowder- As ionic conductor in the cell is used an alkaline anionic exchange membrane Solvay ADP 08. The resulting electrolytic cell is fuelled by a solution of potassium hydroxide at concentration of 6 mol/dm³ at ambient temperature and pressure (25°C and 1 atm). This allowed the passage of 250 mA/cm² of current at 1.930 V and 2.180 V at 750 mA/cm² constant current. An internal resistance of the cell of 45 mOhm was obtained. The faradaic efficiency of the cell is practically equal to 100%; the energetic efficiency of the cell has been calculated using the theoretical value of the Higher Heating Value (HHV) of hydrogen, corresponding to its standard combustion enthalpy (285.8 kJ/mol or 79.39 Wh/mol) and resulted in a value of 84% at 250 mA/cm² of constant current and at 70% at 750 mA/cm² of constant current.

EXAMPLE 7

The anode catalyst and the corresponding positive electrode, upon whose surface occurs the oxygen gas evolution reaction is prepared directly by the cathodic electrodeposition of Co and Ni from a solution of Ni(NO₃)₂ and Co(NO₃)₂ on a nickel foam electrode of the state of the art (E. B. Castro, S. G. Real, L. F. Pinheiro, Int. J. Hydrogen Energy 2004, 29, 255]. The cathode catalyst and the corresponding negative electrode upon whose surface occurs the evolution of hydrogen gas, is prepared according to the method described in 3 using an alloy of the metals Ni3₄Cθ3₄Mn₃2/Nip_OWder- As ionic conductor in the cell is used an alkaline anionic exchange membrane Tokuyama Neosepta^® A-010 produced by ASTOM Corp.

The resulting electrolytic cell is fuelled by a solution of potassium hydroxide at concentration of 6 mol/dm³ at ambient temperature and pressure (25°C and 1 atm). This allowed the passage of 250 mA/cm² of current at 2.01 V and 2.20 V at 750 mA/cm² constant current. An internal resistance of the cell of 45 mOhm was obtained. The faradaic efficiency of the cell is practically equal to 100%; the energetic efficiency of the cell has been calculated using the theoretical value of the Higher Heating Value (HHV) of hydrogen, corresponding to its standard combustion enthalpy (285.8 kJ/mol or 79.39 Wh/mol) and resulted in a value of 80% at 250 mA/cm² of constant current and at 69% at 750 mA/cm² of constant current. EXAMPLE 8 The anode catalyst and the corresponding positive electrode, upon whose surface occurs the oxygen gas evolution reaction is prepared directly by the cathodic electrodeposition of Co and Ni from a solution of Ni(NOs)2 and Co(NO3)2 on a nickel foam electrode of the state of the art (E. B. Castro, S. G. Real, L. F. Pinheiro, Int. J. Hydrogen Energy 2004, 29, 255].

The cathode catalyst and the corresponding negative electrode upon whose surface occurs the evolution of hydrogen gas, is prepared according to the method described in method 1 using the catalyst Ni/Ni_powder- As ionic conductor in the cell is used an alkaline anionic exchange membrane Tokuyama Neosepta^® A-010 produced by ASTOM Corp.

The resulting electrolytic cell is fuelled by a solution of potassium hydroxide at concentration of 6 mol/dm³ at ambient temperature and pressure (25°C and 1 atm). This allowed the passage of 250 mA/cm² of current at 2.1 V and 2.52 V at 750 mA/cm² constant current. An internal resistance of the cell of 45 mOhm was obtained. The faradaic efficiency of the cell is practically equal to 100%; the energetic efficiency of the cell has been calculated using the theoretical value of the Higher Heating Value (HHV) of hydrogen, corresponding to it's standard combustion enthalpy (285.8 kJ/mol or 79.39 Wh/mol) and resulted in a value of 80% at 250 mA/cm² of constant current and at 67% at 750 mA/cm² of constant current.

Claims

1. Electrolysers for the hydrolysis of water constructed from a cell, two electrodes and an anionic exchange membrane in which the cathodic electrode contains a catalyst in the form of a nanostructured electrocatalytic material.

2. Electrolysers according to Claim 1 in which the catalysts are prepared from metal complexes formed from salts of manganese, molybdenum, iron, cobalt, nickel, palladium, iridium and their binary, tertiary and quaternary combinations 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 disubstituted phenol and formaldehyde or paraformaldehyde in the presence of either a basic or acidic catalyst in water/alcohol mixtures at a temperature between 20-150⁰C and have an eventual molecular weight from 1000 to 50000.

3. Electrolysers according to Claim 1 in which the 4-{1-[(phenyl-2,4- disubstituted)-hydrazine]-alkyl}-benzene-1 ,3-diol is a compound of the formula (A)

Wherein Ri is chosen in the group consisting og: H, a C-M_O hydrocarbon radical, possibly halogenated,

R₂ and R₃ independently from each other represent an electron-attractive group chosen in the group consisting of: H₁ halogen, acyl, ester, carboxylic acid, formyl, nitrile, sulphonic acid, aryl groups or linear or branched alkyl having 1 - 15 carbon atoms, possibly functionalised with halogens or joined to each other in order to form one or more cycles condensed with the phenyl ring, and nitro groups; and the 3,5 disubstituted phenol is a compound of formula (B)

(B)

4. Electrolysers according to Claims 1-3 in which the polymers have the formula

(C)

(C) Wherein y is comprised between 2 and 120, x is comprised between 1 and 2, n is comprised between 1 and 3 and Ri, R₂, R3, R₄ and R₅ are as above defined. The metal salts according to the invention are chosen from the group comprising carboxylates, halogens and pseudohalogens, alcolates, acetylacetonates, formates, oxalates, malonates and analogous organic salts and their mixtures or carbonates and bicarbonates or their mixtures.

5. Electrolysers according to Claims 1-4 in which the said metals are chosen from the group containing: Fe, Ru, Co, Ir, Ni, Pd, Mo and Mn.

6. The use of nanostructured metal catalysts for the preparation of cathode electrodes for the production of hydrogen gas in electrolysers using anionic exchange solid polymer membranes.

7. The catalysts according to Claim 6 are prepared from metal complexes formed from salts of manganese, molybdenum, iron, cobalt, nickel, palladium, iridium and their binary, tertiary and quaternary combinations 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 disubstituted phenol and formaldehyde or paraformaldehyde in the presence of either a basic or acidic catalyst in water/alcohol mixtures at a temperature between 20-150⁰C and have an eventual molecular weight from 1000 to 50000.

8. The use of catalysts according to Claims 6-7 formed from the three metals Mn, Co, Ni with all possible percentage atomic ratios.

9. The use of catalysts according to Claims 6-7 formed from the three metals Co and Ni with all possible percentage atomic ratios.

10. The use of catalysts according to Claims 6-7 formed from a catalyst based upon nickel.

11. The catalysts described in Claims 8-10 are supported on nickel powder, Vulcan

XC-72R, nickel foam or other metal supports.

12. The metal support described in Claim 11 is nickel or cobalt.

13. A method for the production of hydrogen and oxygen by the electrolysis of water in which are used the electrolysers described in Claims 1-5.

14. A method according to Claim 13 in which:

- The electrolyser is fuelled by an alkaline solution;

A current density of 250 mA/cm² -750 mA/cm² A is applied at a potential of 2.10-2.52 V.

- The hydrogen formed at the cathode and the oxygen that forms at the anode is collected.