Electrocatalytic Conversion of Nitrate Into Ammonia Through Heterogeneous Catalysis of NiMoO4 and Cu/Cu2O

Abstract

AbstractFacilitating equilibrium in the nitrogen cycle, electrochemical nitrate reduction (NitRR) to ammonia stands as a carbon‐free method for ammonia synthesis. Copper‐based catalysts, renowned for NitRR, face a hurdle in supplying sufficient hydrogen radicals (*H) for efficient hydrogenation of NitRR intermediates. Addressing this, NiMoO4 is leveraged as an excellent *H donor, synergistically coupling it with a copper‐based catalyst. The work introduces a high‐performance NiMoO4/CuO nanowire (NW)/Copper foam (CF) catalyst for NitRR, achieving a remarkable Faraday efficiency (FE) of 98.8% and a yield of 0.8221 mmol cm−2 h−1. Operating at −0.2 V versus reversible hydrogen electrode (vs RHE) in an H‐type electrolytic cell, the catalyst demonstrates exceptional stability over 20 h. Additionally, coupling NitRR with an air stripping process enables efficient collection of NH4Cl products, offering a practical avenue for converting waste nitrates into valuable ammonia products. In‐depth in situ electrochemistry and density‐functional theory (DFT) calculations affirm the transformation of CuO into Cu/Cu2O during the electrocatalytic reduction process. Cu/Cu2O catalyzes nitrate conversion to nitrite, while NiMoO4, serving as a *H donor, facilitates deoxidation and hydrogenation of other N intermediates on the Cu/Cu2O surface, effectively driving the reduction of nitrate to ammonia.