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

Facilitating 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.