Relay Catalysis on Phase‐Separated Janus–CuCo Alloys for Efficient Electrochemical Nitrate Reduction at Industrial Low Concentration

ABSTRACT Earth‐abundant Cu and Co are attractive electrocatalysts for nitrate reduction to ammonia (NO 3 − RR); however, conventional solid‐solution alloys with single‐phase active sites lack effective intermediate spillover, impeding the hydrogenation of multiple reaction intermediates and limiting NH 3 selectivity under dilute nitrate conditions. Here we report phase‐separated yet electronically coupled Janus–CuCo alloys synthesized via a time–charge regulated electrochemical reduction strategy, forming metallic Cu/Co domains with a well‐defined interphase electronic structure. This Janus architecture enables relay catalysis, in which Cu domains activate NO 3 − , intermediates migrate to Cu−Co interfaces for hydrogenation, and adjacent Co domains promote subsequent NH 3 formation. In situ characterizations reveal pronounced Cu–Co synergy, where Co sites regulate *H‐mediated hydrogenation while the balanced surface coverage of *H and *NO 3 − optimizes NH 3 selectivity and yield. Consequently, the optimized Janus Cu−Co catalyst, Janus–Cu 70 Co 30 /NOMC, achieves a peak NH 3 Faradaic efficiency (FE NH3 ) of 95.5% at −500 mA cm −2 and delivers a FE NH3 of 93.1% with an NH 3 yield rate of 4.2 mg h −1 mg cat −1 at −0.4 V vs RHE in an MEA flow cell under low nitrate concentrations. These findings establish phase separation with electronic coupling, enabled by electrochemical time–charge control, as an effective design principle for efficient multistep NO 3 − RR electrocatalysis.