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

Abstract

The electrocatalytic nitrate reduction reaction (NO3RR) 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 NO3RR, through combined density functional theory calculations and operando spectroscopy. Under reductive potentials, atomically dispersed Cu spontaneously aggregates into nanoclusters that efficiently activate NO3–. Concurrently, Cu clustering induces pronounced structural strain and electronic distortion in adjacent Fe–Nx 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 NO2– conversion to NH3. The synergistic coupling between Cu clusters and spin-modulated Fe establishes a highly effective tandem pathway, yielding superior NO3RR activity and NH3 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.