Electrocatalytic reduction of nitrate to ammonia over activated carbon-supported copper-iron bimetallic catalyst synthesized by hydrothermal co-precipitation method

Abstract

Ammonia synthesis via electrocatalytic reduction of nitrate is a promising approach for green ammonia production. However, this process limited by multiple reaction pathways and NO3− adsorption over electrocatalyst surface. Herein, copper-iron bimetallic catalysts with different atom ratios of Cu/Fe (Cu/Fe = 10/0, 7/3, 5/5, 3/7 and 0/10) and activated carbon as supporter (CuFeOx/AC) were synthesized through hydrothermal co-precipitation method for catalytic reduction of nitrate. Synergistic effects between the Cu and Fe were observed in the copper-iron bimetallic catalysts and an appropriate atom proportion of Cu/Fe was benefit to accelerate the adsorption and electrocatalytic kinetics of nitrate reduction to *NO2 and *NO2 hydrogenation to·NH3 through electron redistribution. The catalyst of 7Cu3FeOx/AC presented the best catalytic performance in nitrogen electroreduction reaction for ammonia synthesis, with an NH3 yield rate of 2091 μg h−1 mgcat−1 and a faradaic efficiency of 76 % at −0.8 V vs. reversible hydrogen electrode. The 7Cu3FeOx/AC also exhibited excellent cycle ability and long-term durability whose NH3 yield rates maintained as high as 1476 and 2326 μg h−1 mgcat−1 after 9 cycles and 10 h durability measurement, respectively. The nitrate reduction behavior over 7Cu3FeOx/AC proceeded with a series of deoxygenation reactions as follows: NO3− → *NO3 → *NO2 → *NO → *NOH → *NH2OH →·NH3. With the above excellent properties, the 7Cu3FeOx/AC may prove to be a promising electrocatalyst for ammonia synthesis via nitrogen electroreduction reaction.