Selective Electrosynthesis of Ammonia via Sequential Electron-Proton Transfer

The proton-coupled electron transfer (PCET) process is central to sustainable electrochemical energy conversion (e.g., electrocatalytic nitrate reduction (NO₃RR) to ammonia). Decoupling electron transfer (ET) and proton transfer (PT) could suppress the *H dimerization that happens in the Volmer-Tafel process, thereby enhancing activity and product selectivity. Herein, we demonstrate that π-conjugated cyanamide (NCN^2-) groups featuring a flexible structure ([N═C═N]^2- ⇔ [N≡C─N]^2-) function as an electron accelerator and proton relay in NO₃RR, leading to a decoupled ETPT process. The electron-withdrawing [N═C═N]^2- induces the polarization of [Bi₂O₂] catalytic layers, with more σ holes and an enhanced surface electrostatic potential (V_S(r)), which facilitates ET and forms high-valence NO₃^(1+δ)- (δ > 1) traps. Simultaneously, switchable [N≡C─N]^2- serves as a proton relay that accelerates PT in the hydrogenation of NO_x intermediates. This sequential ETPT is validated by various in situ experimental characterizations and molecular dynamic modeling. The ETPT-dominant NO₃RR process achieves 95.3% Faradaic efficiency for NH₃ and stably works for over 500 h at an industrial current density (500 mA cm^-2) in a paired electro-refinery system. This work establishes sequential ETPT regulation as a general strategy for optimizing PCET-mediated sustainable energy conversion systems.