Method and cell for conversion of dinitrogen into ammonia

Abstract

The invention relates to a method and an electrochemical cell comprising a cathodic working electrode comprising a nanostructured catalyst, a counter electrode and an electrolyte for the reduction of dinitrogen to ammonia. The invention includes introducing dinitrogen and a source of hydrogen to the electrolyte, wherein the dinitrogen is reduced to ammonia at the cathodic working electrode. The electrolyte comprises one or more liquid salts formed from the combination of a specified set of cations and a specified set of anions.

1 . A method for the electrochemical reduction of dinitrogen to ammonia, the method comprising the steps of:
 (1) contacting a cathodic working electrode comprising a nanostructured catalyst and a counter electrode with an electrolyte comprising one or more liquid salts, wherein the liquid salt is formed by a combination of
 (i) a cation selected from the group consisting of PR 1-4 , NR 1-4 , and C 4 H 8 NR 2  wherein each R group is independently linear, branched, or cyclic and comprises from 1 to 18 carbon atoms, optionally partially or completely halogenated, optionally including a heteroatom, optionally including a functional group chosen from ethers, alcohols, carbonyls, thiols, sulphoxides, sulphonates, amines, azos, or nitriles, and wherein two R groups connect to form a monocyclic or heterocyclic ring; and 
 (ii) an anion selected from the group consisting of (RO) x PF 6-x  (RO) x BF 4-x , R′SO 2 NSO 2 R′, R′SO 2 C(SO 2 R′)(SO 2 R′), FSO 2 NSO 2 F, C 2 O 4 BF 2 , C 2 O 4 PF 4 , RC 2 O 4 BF 2 , RC 2 O 4 PF 4 , CF 3 SO 3 , R′SO 3 , R′CO 2 , CF 3 COO, R′ x PF 6-x , and R′ x BF 4-x  wherein each R′ group is independently linear, branched, or cyclic and comprises from 1 to 18 carbon atoms, optionally partially or completely fluorinated and optionally including a functional group, chosen from ethers, alcohols, carbonyls, thiols, sulphoxides, sulphonates, amines, azos, or nitriles, and wherein two R′ groups connect to form a monocyclic or heterocyclic ring; 
   (2) introducing dinitrogen and a source of hydrogen to the electrolyte, wherein the dinitrogen is reduced to ammonia at the cathodic working electrode.   
     
     
         2 . The method according to  claim 1 , wherein the liquid salt is formed by a combination of:
 (i) a cation selected from the group consisting of C 4 mpr, P 6,6,6,14 , and P(C 2 R fn ) 4  where R f  is a perfluoroalkyl moiety; and   (ii) an anion selected from the group consisting of eFAP, NfO, PFO, FSI, NTf 2 , B(otfe) 4 , and CF 3 COO.   
     
     
         3 . The method according to  claim 1 , wherein the liquid salt is selected from the group consisting of [P 6,6,6,14 ][eFAP], [C 4 mpyr][eFAP], [P 6,6,6,14 ][F 9 C 4 SO 3 ], [P 6,6,6,14 ][PFO], [C 4 mpyr][perfluorobutanesulfonate], and [C 4 mpyr][PFO]. 
     
     
         4 .- 8 . (canceled) 
     
     
         9 . The method according to  claim 1 , including the further step of raising the temperature of the electrolyte to between −35° C. and 200° C. 
     
     
         10 . The method according to  claim 1 , including the further step of subjecting the electrolyte to a pressure between 0.7 bar nitrogen to 100 bar nitrogen. 
     
     
         11 . The method according to  claim 10 , wherein the pressure is pulsed. 
     
     
         12 . The method according to  claim 1 , wherein a current passing between the cathodic working electrode and the counter electrode is intermittent. 
     
     
         13 . The method according to  claim 1 , further including the step of applying energy of ultrasonic frequency to the electrolyte. 
     
     
         14 . The method according to  claim 1 , including the further step of humidifying dinitrogen gas, and passing the humidified dinitrogen gas in a stream over the cathodic working electrode. 
     
     
         15 . The method according to  claim 1 , wherein the electrolyte further comprises a membrane chosen from a polymer electrolyte, gelled ionic liquid electrolyte, or porous separator. 
     
     
         16 . (canceled) 
     
     
         17 . A cell for electrochemical reduction of dinitrogen to ammonia, the cell comprising:
 a cathodic working electrode comprising a nanostructured catalyst for reduction of dinitrogen,   a counter electrode, and   an electrolyte comprising one or more liquid salts in contact with the working electrode wherein the liquid salt is formed by a combination of:   (i) a cation selected from the group consisting of PR 1-4 , NR 1-4 , and C 4 H 8 NR 2  wherein each R group is independently linear, branched, or cyclic and comprises from 1 to 18 carbon atoms, optionally partially or completely halogenated, optionally including a heteroatom, optionally including a functional group chosen from ethers, alcohols, carbonyls, thiols, sulphoxides, sulphonates, amines, azos, or nitriles, and wherein two R groups connect to form a monocyclic or heterocyclic ring; and   (ii) an anion selected from the group consisting of (RO) x PF 6-x , (RO) x BF 4-x , R′SO 2 NSO 2 R′, R′SO 2 C(SO 2 R′)(SO 2 R′), FSO 2 NSO 2 F, C 2 O 4 BF 2 , C 2 O 4 PR)RC 2 O 4 BF 2 , RC 2 O 4 PF 4 , CF 3 SO 3 , R′SO 3 , R′CO 2 , CF 3 COO, R′ x PF 6-x  (FAP), and R′ x BF 4-x  wherein each R′ group is independently linear, branched, or cyclic and comprises from 1 to 18 carbon atoms, optionally partially or completely fluorinated and optionally including a functional group, chosen from ethers, alcohols, carbonyls, thiols, sulphoxides, sulphonates, amines, azos, or nitriles and wherein two R′ groups connect to form a monocyclic or heterocyclic ring.   
     
     
         18 . The cell according to  claim 17 , wherein the liquid salt is formed by a combination of:
 (i) a cation selected from the group consisting of C 4 mpyr, P 6,6,6,14 , and P(C 2 R fn ) 4  where R is a perfluoroalkyl moiety; and   (ii) an anion selected from the group consisting of eFAP, NfO, PFO, FSI, NTf 2 , B(otfe) 4 , and CF 3 COO.   
     
     
         19 . The cell according to  claim 17 , wherein the liquid salt is selected from the group consisting of [P 6,6,6,14 ][eFAP], [C 4 mpyr][eFAP], [P 6,6,6,14 ][F 9 C 4 SO 3 ], [P 6,6,6,14 ][PFO], [C 4 mpyr][perfluorobutanesulfonate], and [C 4 mpyr][PFO]. 
     
     
         20 .- 24 . (canceled) 
     
     
         25 . The cell assembly formed by stacking in series two or more cells according to  claim 17 . 
     
     
         26 . The cell according to  claim 17 , further including heating means to maintain the temperature of the electrolyte between −35° C. and 200° C., preferably 0° C. 
     
     
         27 . The cell according to  claim 17 , further including pressurising means to subject the electrolyte to a pressure between 0.7 bar nitrogen to 100 bar nitrogen. 
     
     
         28 . The cell according to  claim 17 , further adapted to pass an intermittent current between the cathodic working electrode and the counter electrode. 
     
     
         29 . The cell according to  claim 17 , which further includes a humidifier for humidifying the dinitrogen gas, and the cell further adapted to pass the humidified dinitrogen gas in a stream over the cathodic working electrode. 
     
     
         30 . The cell according to  claim 17 , wherein the electrolyte comprises a membrane chosen from a polymer electrolyte, gelled ionic liquid electrolyte, or porous separator. 
     
     
         31 . (canceled) 
     
     
         32 . The cell according to  claim 17 , further including an ultrasonic source for applying energy of ultrasonic frequency to the electrolyte. 
     
     
         33 . The cell according to  claim 17 , wherein the reduction of dinitrogen to ammonia occurs principally in a region adjacent a three phase boundary on the working surface of the cathodic working electrode. 
     
     
         34 . The cell according to  claim 17 , wherein the nanostructured electrocatalyst is adjacent an outer surface of the cathodic working electrode and creates a gas/electrolyte/metal three phase boundary region where electrolysis principally takes place. 
     
     
         35 .- 40 . (canceled) 
     
     
         41 . The cell according to  claim 17 , wherein the electrolyte further comprises a molecular liquid present in the liquid salt medium at a level between 90 vol % and 0.1 vol %. 
     
     
         42 . The cell according to  claim 17 , wherein the electrolyte further comprises a molecular liquid chosen from dimethylsulfoxide, tetraglyme and other oligio- and poly-ethers, glutaronitrile and other high boiling point nitriles, and trifluorotoluene present in the liquid salt medium at a level between 90 vol % and 0.1 vol %. 
     
     
         43 .- 45 . (canceled) 
     
     
         46 . An electrolyte membrane comprising a thin layer of material in combination with one or more liquid salts for use in the cell of  claim 1 , wherein the liquid salt is formed by a combination of:
 (i) a cation selected from the group consisting of PR 1-4 , NR 1-4 , and C 4 H 8 NR 2  wherein each R group is independently linear, branched, or cyclic and comprises from 1 to 18 carbon atoms, optionally partially or completely halogenated, optionally including a heteroatom, optionally including a functional group chosen from ethers, alcohols, carbonyls, thiols, sulphoxides, sulphonates, amines, azos, or nitriles, and wherein two R groups connect to form a monocyclic or heterocyclic ring; and   (ii) an anion selected from the group consisting of (RO) x PF 6-x , (RO) x BF 4-x , R′SO 2 NSO 2 R′, R′SO 2 C(SO 2 R′)(SO 2 R′), FSO 2 NSO 2 F, C 2 O 4 BF 2 , C 2 O 4 PF 4 , RC 2 O 4 BF 2 , RC 2 O 4 PF 4 , CF 3 SO 3 , R′SO 3 , R′CO 2 , CF 3 COO, R′ x PF 6-x , and R′ x BF 4-x  wherein each R′ group is independently linear, branched, or cyclic and comprises from 1 to 18 carbon atoms, optionally partially or completely fluorinated and optionally including a functional group, chosen from ethers, alcohols, carbonyls, thiols, sulphoxides, sulphonates, amines, azos, or nitriles and wherein two R′ groups connect to form a monocyclic or heterocyclic ring.   
     
     
         47 . The electrolyte membrane according to  claim 46 , wherein the thin layer of material is chosen from the group comprising a polymer, a gel, or a porous separator material. 
     
     
         48 . The electrolyte membrane according to  claim 46 , wherein the liquid salt is in combination with one of a polymer, a gel, or a porous separator, or a material comprising a polymer, a gel, or a porous separator. 
     
     
         49 .- 50 . (canceled) 
     
     
         51 . The method for the electrochemical reduction of dinitrogen to ammonia according to  claim 1  carried out using:
 an electrochemical cell for electrochemical reduction of dinitrogen to ammonia, the electrochemical cell comprising:
 a cathodic working electrode comprising a nanostructured catalyst for reduction of dinitrogen, 
 a counter electrode, and 
 an electrolyte comprising one or more liquid salts in contact with the working electrode wherein the liquid salt is formed by a combination of:
 (i) a cation selected from the group consisting of PR 1-4 , NR 1-4 , and C 4 H 8 NR 2  wherein each R group is independently linear, branched, or cyclic and comprises from 1 to 18 carbon atoms, optionally partially or completely halogenated, optionally including a heteroatom, optionally including a functional group chosen from ethers, alcohols, carbonyls, thiols, sulphoxides, sulphonates, amines, azos, or nitriles, and wherein two R groups connect to form a monocyclic or heterocyclic ring; and 
 (ii) an anion selected from the group consisting of (RO) x PF 6-x , (RO) x BF 4-x , R′SO 2 NSO 2 R′, R′SO 2 C(SO 2 R′)(SO 2 R′), FSO 2 NSO 2 F, C 2 O 4 BF 2 , C 2 O 4 PF 4 , RC 2 O 4 BF 2 , RC 2 O 4 PF 4 , CF 3 SO 3 , R′SO 3 , R′CO 2 , CF 3 COO, (FAP), and R′ x BF 4-x  wherein each R′ group is independently linear, branched, or cyclic and comprises from 1 to 18 carbon atoms, optionally partially or completely fluorinated and optionally including a functional group, chosen from ethers, alcohols, carbonyls, thiols, sulphoxides, sulphonates, amines, azos, or nitriles and wherein two R′ groups connect to form a monocyclic or heterocyclic ring; 
 
 
 an electrolyte comprising one or more salts having dinitrogen solubility of at least 100 mg/L at the operating temperature and pressure of the electrochemical cell and having water solubility of less than 5 wt % at the operating temperature and pressure of the electrochemical cell; and 
 a nanostructured catalyst for reduction of dinitrogen to ammonia comprising nanoparticles and having a high electrochemical working surface area as indicated by a double layer capacity, measured in an adjacent electrolyte layer of greater than 0.1 mF/cm 2  and preferably greater than 1 mF/cm 2 . 
 
     
     
         52 . The method according to  claim 1 , wherein the electrolyte further comprises a molecular liquid present in the liquid salt medium at a level between 90 vol % and 0.1 vol %. 
     
     
         53 . The method according to  claim 1 , wherein the electrolyte further comprises a molecular liquid chosen from dimethylsulfoxide, tetraglyme and other oligio- and poly-ethers, glutaronitrile and other high boiling point nitriles, and trifluorotoluene present in the liquid salt medium at a level between 90 vol % and 0.1 vol %.