Electrocatalysts, preparation thereof, and using the same for ammonia synthesis

Abstract

Electrocatalysts comprising transition metal oxide are disclosed. Uses the electrocatalyst as a working electrode are further disclosed. Electrochemical cells containing the working electrode and use thereof in the process of synthesizing ammonia is further disclosed.

1 . An electrochemical cell comprising a first chamber in liquid communication with a second chamber, wherein:
 the first chamber comprises an anode and is configured to contain a liquid electrolyte pressurized with a gas comprising nitrogen;   the second chamber comprises a cathode;   the anode comprises an electrocatalyst characterized by Nitrate Oxidation Reaction (NOR) activity to convert the nitrogen to nitrate;   the electrochemical cell is configured for transferring the nitrate from the first chamber to the second chamber; and wherein the cathode comprises an electrocatalyst characterized by Nitrogen Reduction Reaction (NO3RR) activity to convert the nitrate in the second chamber to ammonia.   
     
     
         2 . The electrochemical cell of  claim 1 , wherein each of the cathode and the anode has an electrocatalytically effective loading of the electrocatalyst of between 0.5 and 10 mg/cm 2 ; wherein the cathode and the anode are connectable to a power source configured to provide the predefined voltage; and wherein the transferring is by a pump configured to generate a flow of the liquid electrolyte from the first chamber into the second chamber; and wherein the electrochemical cell is operable at a predefined voltage of between 1.5 and 2.5V. 
     
     
         3 . (canceled) 
     
     
         4 . (canceled) 
     
     
         5 . The electrochemical cell of claim lany one of  claims 1 , wherein the electrocatalyst characterized by NOR activity and the electrocatalyst characterized by NO3RR activity is present in a form of a coating in contact with an outer surface of the anode and of the cathode, respectively; wherein the coating further comprises an electrically conductive material; and wherein the electrically conductive material comprises a conductive carbon material, a conductive ceramic material a conductive polymer, a conductive metal oxide, or any combination thereof. 
     
     
         6 . (canceled) 
     
     
         7 . (canceled) 
     
     
         8 . The electrochemical cell of  claim 1 , wherein the electrocatalyst characterized by NOR activity comprises Rh dopped carbon material (Rh/C); and wherein the electrocatalyst characterized by NO3RR activity comprises any one of: (i) RuO2, (ii) Ce-oxide Fe-oxide composite and (iii) a transition metal chalcogenide. 
     
     
         9 . (canceled) 
     
     
         10 . The electrochemical cell of  claim 8 , wherein the transition metal chalcogenide comprises any one of: NiCo 2 S 4 , copper sulfide and nickel sulfide; and wherein a molar ratio between Ce and Fe within the Ce-oxide Fe-oxide composite is about 1:1. 
     
     
         11 . (canceled) 
     
     
         12 . The electrochemical cell of  claim 1 , wherein the first chamber comprises a first gas inlet configured for directing gas into the liquid electrolyte; wherein the electrochemical cell further comprises a unidirectional flow element selected from a pump and a valve and located downstream the first chamber and upstream the second chamber. 
     
     
         13 . A working electrode comprising an electrocatalyst bound to a surface of an electrode, wherein:
 the electrocatalyst comprises any of: (a) a transition metal oxide; (b) transition metal chalcogenide and (c) Rh dopped carbon material (Rh/C);   the electrocatalyst is characterized by an electrocatalytic activity selected from: (i) nitrogen to ammonia reduction (NRR) activity; (ii) NO3RR activity and (iii) NOR activity, or any combination of (i) to (ii); and wherein said transition metal oxide is devoid of Ti-oxide, an elemental state metal, or a salt thereof.   
     
     
         14 . The working electrode of  claim 13 , wherein said transition metal oxide comprises a transition metal selected from (i) Ru, Ce, Co, Ni, Fe, Pd, Sc, V, Cr, Mn, Cu, Zn, Y, Zr, Nb, Mo, Tc, Rh, Ag, Cd, W, Re, Os, Ir, Au and Pt; and (ii) a combination of iron oxide and the transition metal oxide. 
     
     
         15 . The working electrode of  claim 13 , wherein the transition metal oxide comprises any one of: RuO 2 , CeFeO3 and PdO; and wherein the transition metal chalcogenide comprises any one of: NiCo 2 S 4 , copper sulfide and nickel sulfide. 
     
     
         16 . The working electrode of  claim 13 , wherein the electrocatalyst is (i) a RuO2 co-catalyst composite, wherein the co-catalyst is characterized by oxygen to peroxide reduction activity; and wherein the electrode is a cathode; or (ii) wherein the electrocatalyst is Rh/C; wherein a weight content of Rh within said Rh/C is between 3 and 20%, wherein said carbon material is in a form of microparticles, and wherein said Rh is in a form of nanoparticles. 
     
     
         17 . The working electrode of  claim 16 , wherein the co-catalyst is a metal-phthalocyanine complex. 
     
     
         18 . The working electrode of  claim 13 , wherein the electrocatalyst is any one of:
 (i) an electrocatalyst characterized by NOR activity consisting essentially of: Rh/C, the RuO2 co-catalyst, iron oxide-TiO 2  composite, Ni oxide, Co oxide, or mixed spinel Ni-Co oxide; and   (ii) an electrocatalyst characterized by NO3RR activity consisting essentially of: RuO2, Ce-oxide Fe-oxide composite or the transition metal chalcogenide.   
     
     
         19 . The working electrode of  claim 13 , wherein said electrocatalyst is in a form of a coating further comprising a conductive material; and wherein a concentration of said electrocatalyst within said coating is between 50 and 90% w/w; wherein said conductive material is a particulate matter comprising carbon particles, elemental metal particles conductive metal oxide particles, or any combination thereof. 
     
     
         20 . (canceled) 
     
     
         21 . The working electrode of  claim 13 , being: (i) an anode, and wherein the electrocatalyst bound to a surface of the anode comprises Rh/C; or (ii) a cathode, and wherein the electrocatalyst bound to a surface of the cathode comprises any one of: RuO2, Ce-oxide Fe-oxide composite or the transition metal chalcogenide. 
     
     
         22 . An electrochemical cell comprises the working electrode of  claim 13  and a counter electrode in contact with a liquid electrolyte; wherein said electrochemical cell is configured to perform a reaction selected from NRR, NOR and NO3RR. 
     
     
         23 . The electrochemical cell of  claim 22 , wherein the working electrode comprises Rh/C and the electrochemical cell is configured to perform NOR upon application of an anodic potential in a range between about 1.5 and about 1.7V relative to RHE; wherein the working electrode comprises the RuO2 co-catalyst composite and the electrochemical cell is configured to perform NOR upon application of a cathodic potential in a range between 0 and 0.3V relative to RHE. 
     
     
         24 . (canceled) 
     
     
         25 . The electrochemical cell of  claim 22 , wherein the working electrode comprises any one of: RuO2, RuO2 co-catalyst composite, Ce-oxide Fe-oxide composite or the transition metal chalcogenide and the electrochemical cell is configured to perform NO3RR upon application of a negative cathodic potential; wherein the negative cathodic potential is between −0.05V and −0.6V relative to RHE; wherein said electrolyte solution is saturated with nitrogen. 
     
     
         26 . (canceled) 
     
     
         27 . (canceled) 
     
     
         28 . (canceled) 
     
     
         29 . (canceled) 
     
     
         30 . A method of synthesizing ammonia, comprising:
 (i) generating a flow of a gas comprising nitrogen into the first chamber of the electrochemical cell of  claim 1 , wherein the electrochemical cell is in contact with the liquid electrolyte, and   (ii) applying electrical current to the electrochemical cell, thereby inducing NOR at the anode to obtain nitrate within the first chamber; and   (iii) generating a flow of nitrate from the first chamber into the second chamber to reduce said nitrate at the cathode, thereby generating the ammonia.   
     
     
         31 . The method of  claim 30 , wherein the gas further comprises between 10 and 30% v/v of oxygen; and wherein said electrical current comprises a potential between 1.5 and 2.5V wherein the gas enters the first chamber via the first gas inlet, and wherein the flow of the gas is sufficient for saturating the liquid electrolyte in the first chamber with the gas; wherein the flow of nitrate is generated via the unidirectional flow element; optionally wherein the first gas inlet is in fluid communication with the anode, wherein the anode is configured to support gas flow. 
     
     
         32 . (canceled) 
     
     
         33 . (canceled) 
     
     
         34 . The method of  claim 30 , wherein the flow of nitrate is at a rate of between 0.1 and 3 ml/min; and wherein said method is performed at a temperature between 5° C. and 100° C.; and wherein the liquid electrolyte comprises between 0.01 and 2M of one or more ions selected from chloride hydroxide and sulfate. 
     
     
         35 . (canceled) 
     
     
         36 . (canceled)