Dynamic dissolution-reorganization of molybdenum triggers synergistic electrocatalysis on copper for efficient nitrate-to-ammonia conversion

Developing highly efficient and robust electrocatalysts to enhance the kinetics of electrochemical nitrate reduction reaction (NO 3 RR) to ammonia is crucial for realizing the conversion and storage of green electrochemical ammonia energy. Herein, we constructed a molybdenum-doped metallic copper electrocatalyst (Cu-Mo 0.2 /NF) and systematically investigated the pivotal role of molybdenum dynamic recombination in enhancing the kinetics of the NO 3 RR. In situ Raman spectroscopy, XPS and ICP-OES reveals that Mo dissolves during the NO 3 RR process and recombines into Mo 2 O 7 2- species, which are adsorbed onto the surface of the electrocatalyst. The experimental results combined with DFT calculations indicates that this dynamic dissolution, reorganization, and adsorption process of Mo significantly activates *NO 3 , thereby greatly enhancing the kinetics of *NO 3 reduction to *NO 2 . Furthermore, Differential electrochemical mass spectrometry (DEMS) and in situ attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) elucidate the NO 3 RR pathway: *NO 3 → *NO 2 → *NO → *NOH → *N → *NH → *NH 2 → *NH 3 . This reaction mechanism, which circumvents high-energy-barrier step (NO → N 2 O), endows the electrocatalyst with superior kinetics and high selectivity. Benefiting from the dynamic dissolution and redeposition of Mo and the advantages of the reaction pathway, the electrocatalyst achieves a record ammonia yield ( 1.55 mmol h -1 cm -2 ) with near-unity Faradaic efficiency ( 98.99% ), and 30 h stability. The Mo-doped metallic copper electrocatalyst supported on nickel foam (Cu-Mo 0.2 /NF) was designed. During the NO 3 RR process in alkaline media, Mo dissolves into the electrolyte and is subsequently transformed into adsorbed Mo 2 O 7 2- species on the electrocatalyst surface. The dynamic reconstruction of Mo 2 O 7 2- accelerates * NO 3 →* NO 2 kinetics for NO 3 RR, achieving a record ammonia yield of 1.55 mmol h -1 cm -2 with 98.99% Faraday efficiency. • The Cu-Mo 0.2 /NF was fabricated via a one-step electrodeposition method. • In situ Raman spectroscopy revealed the dissolution-redeposition mechanism of Mo. • The formed Mo 2 O 7 2- species can accelerate the * NO 3 → * NO 2 kinetics. • The electrocatalyst achieves an NH 3 yield of 1.55 mmol h -1 cm -2 with 98.99% FE. • In situ experiments (DEMS and ATR-FTIR) revealed the NO 3 RR pathway.