Upgrading of nitrate to hydrazine through cascading electrocatalytic ammonia production with controllable N-N coupling

Nitrogen oxides (NOx) play important roles in the nitrogen cycle system and serve as renewable nitrogen sources for the synthesis of value-added chemicals driven by clean electricity. However, it is challenging to achieve selective conversion of NOx to multi-nitrogen products (e.g., N2H4) via precise construction of a single N-N bond. Herein, we propose a strategy for NOx-to-N2H4 under ambient conditions, involving electrochemical NOx upgrading to NH3, followed by ketone-mediated NH3 to N2H4. It can achieve an impressive overall NOx-to-N2H4 selectivity of 88.7%. We elucidate mechanistic insights into the ketone-mediated N-N coupling process. Diphenyl ketone (DPK) emerges as an optimal mediator, facilitating controlled N-N coupling, owing to its steric and conjugation effects. The acetonitrile solvent stabilizes and activates key imine intermediates through hydrogen bonding. Experimental results reveal that Ph2CN* intermediates formed on WO3 catalysts acted as pivotal monomers to drive controlled N-N coupling with high selectivity, facilitated by lattice-oxygen-mediated dehydrogenation. Additionally, both WO3 catalysts and DPK mediators exhibit favorable reusability, offering promise for green N2H4 synthesis. Nitrogen oxides are vital in the nitrogen cycle and renewable chemical synthesis, but selective conversion to multi-nitrogen products via precise N-N bond formation is challenging. Here, the authors report a two-step electrochemical process that achieves an impressive 88.7% selectivity for hydrazine production using a WO3 catalyst with diphenyl ketone as a mediator.