Method for generating hydrogen and oxygen by steam electrolysis

Abstract

The present invention relates to a method for generating hydrogen and oxygen adsorbates by steam electrolysis at 200 to 800° C. using an electrolysis cell ( 30 ) comprising a solid electrolyte ( 31 ) which is made of a proton-conducting ceramic and which is arranged between an anode ( 32 ) and a cathode ( 33 ), each of which comprises a proton-conducting ceramic, and the ratio of the electroactive surface to the geometric surface of each of which is equal to at least 10, said method comprising the following steps: circulating a current between the anode ( 32 ) and the cathode ( 33 ), wherein the density of the current is no less than 500 mA/cm 2 ; inserting water in the form of steam, which is fed under pressure to the anode ( 32 ); oxidizing said water in the form of steam at the anode ( 32 ), and generating highly reactive oxygen at the anode ( 32 ) after said oxidation; generating protonated species in the electrolyte ( 31 ) after said oxidation and migrating said protonated species in the electrolyte ( 31 ); and reducing said protonated species at the surface of the cathode ( 33 ) in the form of reactive hydrogen atoms.

1 . Method for generating hydrogen and oxygen adsorbates by steam electrolysis at 200° C. to 800° C. using an electrolysis cell comprising a solid electrolyte which is made of a proton-conducting ceramic, said electrolyte being arranged between an anode and a cathode, said anode and cathode each comprising a proton-conducting ceramic and the ratio of the electroactive surface to the geometric surface of each of which is equal to at least 10, said method comprising the following steps:
 circulating a current between the anode and the cathode, wherein the density of the current is no less than 500 mA/cm 2 ; 
 inserting water in the form of steam, which is fed under pressure to the anode; 
 oxidizing said water in the form of steam at the anode; 
 generating highly reactive oxygen at the anode after said oxidation; 
 generating protonated species in the electrolyte after said oxidation; 
 migrating said protonated species in the electrolyte; 
 reducing said protonated species at the surface of the cathode in the form of reactive hydrogen atoms. 
 
     
     
         2 . Method according to  claim 1 , wherein said ratio between the electroactive surface and the geometric surface of said cathode and anode is no less than 100. 
     
     
         3 . Method according to  claim 1 , wherein said density of the current is no less than 1 A/cm 2 . 
     
     
         4 . Method according to  claim 1 , wherein the partial and relative pressure of the steam is advantageously no less than 1 bar and preferentially no less than 10 bars. 
     
     
         5 . Method according to  claim 1 , wherein the circulation of the current takes place between an anode and a cathode each made of a cermet constituted of a mixture of a proton-conducting ceramic and a conducting material. 
     
     
         6 . Method according to  claim 1 , wherein said conducting material is a passivable material with high melting point being able to contain at least 40% of chromium. 
     
     
         7 . Method according to  claim 1 , wherein the circulation of the current takes place between an anode and a cathode each comprising a proton-conducting ceramic formed of a perovskite doped with a lanthanide with one or more degrees of oxidation. 
     
     
         8 . Method according to  claim 1 , wherein it comprises the following steps:
 introducing carbon dioxide CO 2  and/or carbon monoxide CO at the cathode of the electrolysis cell;   reducing the CO 2  and/or CO introduced at the cathode from said generated reactive hydrogen atoms;   forming compounds of C X H y O Z  type, where x≧1, 0<y≦(2x+2) and 0≦z≦2x after the reduction of the CO 2  and/or CO.   
     
     
         9 . Method according to  claim 1 , wherein it comprises the following steps:
 introducing nitrogen containing compounds at the cathode of the electrolysis cell;   reducing said nitrogen containing compounds introduced at the cathode from said generated reactive hydrogen atoms.   
     
     
         10 . Method according to  claim 1 , wherein said nitrogen containing compounds are compounds of the NO x  type where x≧1, said method comprising a step of forming compounds of N t O y H z  type, where t is no less than 1, y no less than 0 and z no less than zero, after the reduction of the NO x . 
     
     
         11 . Method according to  claim 9  wherein said nitrogen containing compounds are N 2  compounds, said method comprising a step of forming compounds of N x H y  type where x≧1 and y≧0 to result in the formation of NH 3  after the reduction of N 2 . 
     
     
         12 . Method according to  claim 1 , wherein said reactive hydrogen atoms are used to carry out a step of hydrocracking at the cathode. 
     
     
         13 . Method according to  claim 1 , wherein said reactive hydrogen atoms are used to convert aromatic compounds at the cathode. 
     
     
         14 . Method according to  claim 1 , further comprising a step consisting in making said highly reactive oxygen react with a compound introduced at the anode such that the latter undergoes oxygenation. 
     
     
         15 . Electrolysis cell for the implementation of the method according to  claim 1  comprising:
 a solid electrolyte, which is made of a proton-conducting ceramic; 
 an anode comprising a proton-conducting ceramic, said anode and cathode each having a ratio between the electroactive surface and the geometric surface equal to at least 10; 
 a cathode comprising a proton-conducting ceramic, said electrolyte being arranged between said anode and said cathode; 
 means for inserting water in the form of steam which is fed under pressure at the anode; 
 means for inducing a current circulating between the anode and the cathode, wherein the density of the current is no less than 500 mA/cm 2 .