Efficient electrocatalytic properties of transition metal (Mn, Co, Cu) doped LaFeO3 for ammonia synthesis via nitrate reduction

Abstract

Electrochemical reduction of nitrate in wastewater to synthesize high-value energy, ammonia, is a promising technology to deal with the energy crisis and environmental pollution. It is an urgent task for this technology to find efficient, stable and environmental-friendly catalysts. This work innovatively applied transition metal (Mn, Co, Cu) doped LaFeO3 as the electrocatalyst to reduce nitrate to ammonia. Cu-doped LaFeO3 exhibited the optimum activity, achieving the ammonia yield of 1005.0 μg h−1cm−2 at − 1.1 V (vs. RHE) and the Faradaic efficiency of 71.9% at − 1.0 V (vs. RHE). The highly efficient electrocatalytic activity could be mainly attributed to the oxygen vacancies on the surface of the catalyst generated from Cu-doping. The oxygen atoms in the nitrate tended to fill in the oxygen vacancies, which promoted the adsorption of NO3- and weakened the N-O bonds. Besides, the oxygen vacancies and Cu sites could combine easily with the intermediate in the reaction, and their existence could also enhance the conductivity of the catalyst. Moreover, the catalyst showed outstanding stability and performed even enhanced activity during recycling, which was arised from the ferroelectricity of the catalyst. The ammonia yield was as high as 1250.5 μg h−1cm−2 in the third cycle, and the Faradaic efficiency was 74.5% in the fifth cycle at − 1.0 V (vs. RHE). This work presents a good paradigm of catalysts for the electrochemical synthesis of ammonia.