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

Abstract

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/CuxO 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 VRHE). 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, in situ 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.