Electrochemical nitrate reduction to ammonia with cation shuttling in a solid electrolyte reactor

Abstract

While electrochemical nitrate reduction to ammonia represents a promising route for water treatment and ammonia generation, one critical challenge in the field is the need for high-concentration supporting electrolytes in this electrochemical system. Here we report a three-chamber porous solid electrolyte reactor design coupled with cation shielding effects for efficient nitrate reduction reaction without supporting electrolytes. By feeding treated water from the cathode chamber to the middle porous solid electrolyte layer, we can realize an alkali metal cation shuttling loop from the middle layer back into the cathode chamber to boost the nitrate reduction selectivity and suppress the hydrogen evolution side reaction. This reactor system can deliver high ammonia Faradaic efficiencies (>90%) at practical current densities (>100 mA cm−2) under a typical wastewater nitrate concentration of 2,000 ppm, enabling a high-purity water effluent and NH3(g) as products with no need for electrolyte recovery processes. Electrocatalysis offers a route to improving the treatment of wastewater, yet the need for supporting electrolytes complicates the purification of products. Here a cell is designed based on a porous solid electrolyte layer with a cation shuttling strategy that allows direct conversion of nitrate-containing wastewater into NH3(g) and purified water.