Intermediate-Mediated Selectivity in Electrocatalytic Nitrate Reduction for Nitrogen Product Synthesis.

Electrocatalytic nitrate (NO3 -) reduction reaction (eNO3RR) has emerged as a promising strategy for waste NO3 - valorization, offering opportunities for environmental remediation. However, its complex proton-coupled electron transfer processes involve multiple competing pathways, in which the fate of key intermediates governs reaction activity and product selectivity. In this review, we provide an intermediate-centered perspective on eNO3RR, covering the reaction pathways from NO3 - activation to the selective synthesis of NH3, N2, and NH2OH. We then summarize current techniques for probing N-containing intermediates and active hydrogen (*H). On this basis, we discuss how catalyst design and microenvironment engineering regulate key processes in eNO3RR, including intermediate adsorption, retention and desorption, N─O bond cleavage, hydrogenation, and N─N coupling. We also examine the emerging role of data-driven approaches in optimizing eNO3RR systems. Drawing these discussions together, we distill principles for selective product synthesis. Finally, we discuss remaining challenges in achieving a deeper mechanistic understanding, regulating the interfacial microenvironment, and applying eNO3RR to real wastewater.