Tailoring Reconstruction of Co/Cu Mixed Oxide-Derived Tandem Electrocatalysts via <i>In Situ</i> Electrochemical Dissolution–Redeposition for Enhanced Nitrate-to-Ammonia Conversion

Cobalt- and copper-based oxides have emerged as cost-effective electrocatalysts for the electrochemical nitrate reduction reaction (NO₃RR) to ammonia. However, the cathodic potentials required for NO₃RR induce irreversible structural transformations that often compromise catalyst stability and selectivity, depending on the applied electrochemical protocol. To understand the resulting dynamic structure-performance relationships and improve nitrate-to-ammonia conversion, a tandem Co₃O₄/Cu _<i>x</i> O electrocatalyst was prepared by electrodeposition followed by thermal treatment, and two surface activation strategies were employed: by cycles of cyclic voltammetry (CV) or by holding at a constant potential by chronoamperometry (CA). The CA-reconstructed Co/Cu mixed oxide-derived electrocatalyst exhibited a higher faradaic efficiency (FE) toward ammonia across the entire potential window studied (0.00 to -0.40 V_RHE). The reconstruction effects induced by both electrochemical protocols were systematically investigated, revealing morphological, structural, and compositional changes that underpin the improved nitrate-to-ammonia conversion. Furthermore, <i>in situ</i> and online electrochemical techniques were employed to identify intermediates and active sites, providing new mechanistic insights into the electrochemical nitrate-to-ammonia conversion pathway. These findings contribute to understanding dynamic reconstruction phenomena and offer design guidelines for more stable and selective mixed oxide electrocatalysts for sustainable ammonia production.