Joule Heating Synthesis of Cobalt Molybdate with Unsaturated Mo4+ Coordination for Greatly Enhanced Electrocatalytic Nitrate Reduction to Ammonia

Electrocatalytic conversion of nitrates to produce high-value-added NH3 exhibited promise as a replacement for the Haber-Bosch process due to the involvement of an eight-electron and nine-proton transfer in the electrocatalytic nitrate reduction reaction (NO3RR), which exhibits low Faradaic efficiency and selectivity toward NH3. Herein, a cobalt molybdate catalyst was in situ grown on nickel foam with abundant oxygen vacancies and a rich unsaturated coordination Mo4+ environment by a rapid Joule heating method. The synergistic optimization of these features modulated the overall catalyst electronic structure, achieving both high activity and high selectivity in NO3RR. Specifically, in an electrolyte of 0.1 M K2SO4 and 1000 mg(NO3)(-)/L, a Faradaic efficiency of 94.6% and a NH3 yield rate of 1.32 mg h(-1) cm(-2) were achieved at -0.35 V vs RHE. Meanwhile, the selectivity of NH3 reached 97% after the 12 h test. In six consecutive cycles and during a 12 h extended stability assessment, the CMO/NF-800 catalyst consistently exhibited exceptional chemical stability. DFT results demonstrated that nitrate adsorption and ammonia desorption were more readily achieved on the surface of the CMO/NF-800 and that there was a lower energy barrier that needed to be overcome for RDS. This work provided a reservable approach to the preparation of catalysts with abundant unsaturated coordination environments on the highly selective electroreduction of nitrate into ammonia.