Interfacial tandem catalysis in Co/WC heterojunctions for efficient nitrate-to-ammonia electrosynthesis

Electrocatalytic nitrate reduction to ammonia offers a sustainable route to couple nitrate remediation with NH₃ production under ambient conditions. However, its overall efficiency is often constrained by sluggish hydrogenation of NO_x intermediates and the insufficient supply of active hydrogen under cathodic polarization. Herein, we construct a Co/WC heterojunction embedded in an N-doped carbon framework (Co/WC@NC) as an efficient tandem electrocatalyst for nitrate-to-ammonia conversion. In this heterostructure, Co sites preferentially mediate nitrate adsorption, activation and stepwise deoxygenation, while WC sites accelerate water dissociation to continuously provide reaction hydrogen for subsequent hydrogenation of nitrogen-containing intermediates. The intimate Co-WC interfacial coupling spatially integrates these complementary elementary steps, thereby accelerating intermediate conversion and overall nitrate reduction kinetics. As a result, Co/WC@NC delivers an NH₃ yield rate of 12.02 mg h^-1 cm^-2 with a Faradaic efficiency of 87.94% at -0.4 V versus the reversible hydrogen electrode. Operando differential electrochemical mass spectrometry further reveals that NH₃ formation predominantly proceeds via an N-dominated pathway. In addition, a rechargeable Zn-NO₃^- battery assembled with Co/WC@NC demonstrates its promise for nitrate utilization and energy conversion. This work highlights heterointerface-enabled tandem catalysis as an effective strategy for promoting electrocatalytic nitrate-to-ammonia conversion.