Accelerated electrochemical nitrate-to-ammonia conversion over bimetallic Ni2Mo3N with mechanistic insights

Abstract

In this study, bimetallic nickel molybdenum nitride supported on nickel foam (Ni₂Mo₃N/NF) was developed as a highly efficient electrocatalyst for electrochemical nitrate reduction to ammonia (NO₃⁻RR). Ni₂Mo₃N/NF delivered a remarkable faradaic efficiency (FE) of 97.72% and a maximum ammonia yield of 5.55 mg h⁻¹ cm⁻², significantly outperforming bare nickel foam. Moreover, Ni₂Mo₃N/NF maintained a high FE of NH₃ during consecutive cycling tests, accompanied by the formation of an amorphous Ni(OH)₂ layer through surface reconstruction. Mechanistic investigations revealed that Ni components in Ni₂Mo₃N/NF accelerate the conversion of NO₃⁻ to NO₂⁻ during the NO₃⁻RR by forming an amorphous Ni(OH)₂ layer on the catalyst surface, and Mo–N species facilitate the subsequent reduction of NO₂⁻ to NH₃. Furthermore, online differential electrochemical mass spectrometry (DEMS) analysis confirmed the reaction pathway of sequential deoxygenation (*NO₃⁻ → *NO₂⁻ → *NO), followed by hydrogenation (*NO → *NH₂OH → *NH₃). These findings highlight the synergistic roles of Ni and Mo in boosting the NO₃⁻RR, offering mechanistic insights for the rational design of high-performance bimetallic catalysts for sustainable NH₃ production.