Salt-splitting electrolysis system comprising flow electrodes and methods of operating such systems

Abstract

Described herein are salt-splitting electrolysis systems, which comprise flow electrodes, and methods of operating such systems. Specifically, the flow electrodes comprise active particles (suspended in a solvent) with catalysts. These catalysts are configured to react with either cations or anions, provided in a feed stream. The flow electrodes allow using the same system for different feed streams, e.g., by flowing different types of electrodes through the system. Furthermore, the flow electrodes allow in-situ catalyst reconditioning. For example, the active particles can be flown from the current collectors to respective recovery devices where the particles are discharged or subjected to a reverse potential. The active particles can be conductive and provide more desirable electrical field distribution between the current collectors resulting in greater ionic mobility. Finally, the active particles concentrate ions around the particles thereby providing a higher concentration gradient through separating structures, which enclose the feed stream.

1 . A salt-splitting electrolysis system comprising:
 a feed stream, comprising a solvent and a salt, dissolved in the solvent and comprising cations and anions;   a negative current collector;   a negative flow electrode, comprising the solvent and negative active particles, suspended in the solvent and comprising a negative catalyst configured to react with the cations;   a negative separating structure, disposed between and in contact with the feed stream and the negative flow electrode, wherein the negative separating structure is configured to selectively pass the cations from the feed stream to the negative flow electrode;   a positive current collector;   a positive flow electrode, comprising the solvent and positive active particles, suspended in the solvent and comprising a positive catalyst configured to react with the anions; and   a positive separating structure, disposed between and in contact with the feed stream and the positive flow electrode, wherein the positive separating structure is configured to selectively pass the anions from the feed stream to the positive flow electrode.   
     
     
         2 . The salt-splitting electrolysis system of  claim 1 , wherein:
 each of the negative active particles comprises a negative base structure, comprising supporting the negative catalyst , and   each of the positive active particles comprises a positive base structure, comprising supporting the positive catalyst.   
     
     
         3 . The salt-splitting electrolysis system of  claim 2 , wherein at least one of the negative base structure and the positive base structure comprises an electronically conductive material. 
     
     
         4 . The salt-splitting electrolysis system of  claim 3 , wherein the electronically conductive material is one or more of graphitic carbon, glassy carbon, graphene, carbon nanotubes, a transition metal carbide, iron oxide, platinum, and, iridium. 
     
     
         5 . The salt-splitting electrolysis system of  claim 1 , wherein:
 the negative catalyst comprises one or more of graphitic carbon, carbon-nitride, graphene, carbon nanotubes, transition metal carbides, platinum, palladium, rhodium, and iridium, and   the positive catalyst comprises one or more of graphitic carbon, carbon-nitride, graphene, carbon nanotubes, a transition metal carbide, platinum, palladium, rhodium, iridium, metal oxide, and a perovskite oxide.   
     
     
         6 . The salt-splitting electrolysis system of  claim 1 , wherein:
 the negative separating structure is one of a cation-exchange membrane or a first size-exclusion porous separator, and   the positive separating structure is one of an anion-exchange membrane or a second size-exclusion porous separator.   
     
     
         7 . A method of operating a salt-splitting electrolysis system, the method comprising:
 flowing a feed stream into a feed channel of the salt-splitting electrolysis system, wherein:
 the feed stream comprises cations and anions, 
 the cations are selectively transferred to a negative flow electrode comprising negative active particles, 
 the anions are selectively transferred to a positive flow electrode comprising positive active particles, 
 the negative active particles comprise a negative catalyst configured to react with the cations in the feed stream; 
 the positive active particles comprise a positive catalyst configured to react with the anions; and 
   applying a voltage between a negative current collector and a positive current collector of the salt-splitting electrolysis system thereby causing the cations in the feed stream to react with the negative catalyst and further causing the anions in the feed stream to react with the positive catalyst.   
     
     
         8 . The method of  claim 7 , wherein:
 the negative active particles are suspended in a solvent and flow through a negative chamber of the salt-splitting electrolysis system, and   the positive active particles are suspended in the solvent and flow through a positive chamber of the salt-splitting electrolysis system.   
     
     
         9 . The method of  claim 8 , wherein:
 the negative active particles are uniformly distributed through the negative flow electrode, and   the positive active particles are uniformly distributed through the positive flow electrode.   
     
     
         10 . The method of  claim 7 , wherein:
 the negative active particles are contained within a set portion of a negative chamber of the salt-splitting electrolysis system such that a remaining portion of the negative flow electrode flows through the negative active particles, and   the positive active particles are contained within a set portion of a positive chamber of the salt-splitting electrolysis system such that a remaining portion of the positive flow electrode flows through the positive active particles.   
     
     
         11 . The method of  claim 7 , further comprising:
 pumping at least a portion of the negative flow electrode into a negative electrode recovery device, recovering at least the portion of the negative flow electrode using the negative electrode recovery device, and pumping at least the portion of the negative flow electrode back to the negative current collector; and   pumping at least a portion of the positive flow electrode into a positive electrode recovery device, recovering at least the portion of the positive flow electrode using the positive electrode recovery device, and pumping at least the portion of the positive flow electrode back to the positive current collector.   
     
     
         12 . The method of  claim 11 , wherein:
 recovering at least the portion of the negative flow electrode using the negative electrode recovery device comprises discharging the negative active particles of the negative flow electrode, and   recovering at least the portion of the positive flow electrode using the positive electrode recovery device comprises discharging the positive active particles of the positive flow electrode.   
     
     
         13 . The method of  claim 11 , wherein:
 discharging the negative active particles of the negative flow electrode comprises flowing the negative active particles past a ground connection within the negative electrode recovery device or applying a reverse potential to the negative flow electrode, and   discharging the positive active particles of the positive flow electrode comprises flowing the positive active particles past a ground connection within the positive electrode recovery device or applying a reverse potential to the positive flow electrode.   
     
     
         14 . The method of  claim 7 , wherein the voltage applied between the negative current collector and the positive current collector is between 1.5 V and 10 V per cell. 
     
     
         15 . The method of  claim 7 , wherein applying the voltage between the negative current collector and the positive current collector causes a current density between 2000 A/m 2 and 8000 A/m 2  (based on the membrane area) between the negative current collector and the positive current collector. 
     
     
         16 . The method of  claim 7 , further comprising pretreating the feed stream before flowing the feed stream into the feed channel. 
     
     
         17 . The method of  claim 16 , wherein pretreating the feed stream comprises flowing the feed stream through one or more ion-exchange columns, configured to selectively capture one or more of calcium (Ca), magnesium (Mg), iron (Fe), boron (B), sodium (Na), potassium (K), chloride (Cl), and sulfate (SO 4 ).