Operando Cu Aggregation-Induced Spin State Modulation in Fe–Cu Single Atom Catalyst for Enhanced Tandem Electrochemical Nitrate Reduction Reaction

High Resolution Image Download MS PowerPoint Slide The electrocatalytic nitrate reduction reaction (NO 3 RR) provides a sustainable pathway to convert excess nitrate into ammonia, yet realizing high selectivity requires a fundamental understanding of dynamic structural changes occuring at active sites during reactions. Here, we investigate how in situ Cu clustering dynamically activates dual catalytic sites in Fe–Cu bimetallic single-atom catalysts (FeCu–N–C) during NO 3 RR, through combined density functional theory calculations and operando spectroscopy. Under reductive potentials, atomically dispersed Cu spontaneously aggregates into nanoclusters that efficiently activate NO 3 – . Concurrently, Cu clustering induces pronounced structural strain and electronic distortion in adjacent Fe–N x moieties, triggering a spin-state transition in the Fe active site from low-spin to high-spin configuration. This spin modulation dramatically enhances the activity for subsequent NO 2 – conversion to NH 3 . The synergistic coupling between Cu clusters and spin-modulated Fe establishes a highly effective tandem pathway, yielding superior NO 3 RR activity and NH 3 selectivity, compared to Cu–N–C and Fe–N–C counterparts. These findings provide new insights into the rational design of advanced multicomponent electrocatalysts with dynamically tunable active site properties.