Pulse-Driven Active-Site Switching on Bromine-Modified Cu Enables Sequential 2e – + 6e – Nitrate-to-Ammonia Conversion

Steady active-site electronic states commonly lead to product decentralization and energy consumption increase when overcoming the kinetic mismatch within 8-electron transfer inherent in the electrocatalytic nitrate reduction reaction (NO3RR) to NH3. Here, we first report a reversible and self-adaptive regulation of Cu active sites by Br modification in pulsed electroreduction electrolysis (PE) to match distinct reaction kinetics steps of the (2 + 6)-electron pathway for the NO3RR on trace-Br-modified Cu/Cu2O catalysts (Br–Cu). Mechanistic investigations integrating in situ spectroscopy and DFT calculations reveal that Br-mediated electronic modulation and d-band center downshift strengthen Cu active sites to possess a reversibly tunable Cuδ+ (0 < δ < 1) state under PE, which selectively favor the first 2-electron (*NO3 → *NO2, δ close to 1) and the latter 6-electron (*NO2 → *NH3, δ close to 0) steps, delivering 94% Faradaic efficiency. The continuous-flow electrochemical cell employing Br–Cu maintains high NO3– conversion, NH3 Faradaic efficiency, and NH3 selectivity in approximately 700-h electrolysis while enabling efficient NH3 recovery from real aquaculture tailwater. This work presents a robust strategy for programmable self-adaptive electronic modulation toward sustainable NH3 electrosynthesis.