Electrocatalytic Conversion of Nitrates and Nitrites to Ammonia

Abstract

Electrocatalytic reduction of waste nitrates (NO 3 − ) enables the synthesis of ammonia (NH 3 ) in a carbon neutral and decentralized manner. The present invention uses atomically dispersed transition metal-nitrogen-carbon (M-N—C) catalysts with varying metal centers to uniquely favor mono-nitrogen products (e.g., NH 3 ) via the electrochemical nitrate reduction reaction (NO 3 RR).

We claim: 
     
         1 . A method for the electrocatalytic conversion of nitrates and nitrites to ammonia, comprising:
 providing an electrochemical H-cell, comprising
 a working electrode comprising an atomically dispersed transition metal-nitrogen-carbon (M-N—C) catalyst, 
 a counter electrode, 
 a hydrogen-permeable membrane between the working electrode and the counter electrode, and 
 an electrolyte comprising an aqueous solution of nitrate and/or nitrite; and 
   applying a cathodic potential between the working electrode and the counter electrode sufficient to electrocatalytically reduce the nitrate and/or nitrite to ammonia at the working electrode.   
     
     
         2 . The method of  claim 1 , wherein the transition metal comprises Fe, Mo, Cr, Mn, Co, Ni, Cu, Ru, Rh, Pd, W, La, or Ce, or a combination thereof. 
     
     
         3 . The method of  claim 1 , wherein the M-N—C catalyst comprises a monometallic catalyst. 
     
     
         4 . The method of  claim 1 , wherein the M-N—C catalyst comprises a bimetallic catalyst. 
     
     
         5 . The method of  claim 1 , wherein the nitrate comprises potassium nitrate. 
     
     
         6 . The method of  claim 1 , wherein the nitrite comprises potassium nitrite. 
     
     
         7 . The method of  claim 1 , wherein the electrolyte comprises a concentration of greater than 0.01 M nitrate or nitrite. 
     
     
         8 . The method of  claim 1 , wherein the electrolyte is alkaline. 
     
     
         9 . The method of  claim 1 , wherein the electrolyte is neutral or acidic. 
     
     
         10 . The method of  claim 1 , wherein the cathodic potential is more negative than −0.1 V.