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Cobalt-based spinel oxides (i.e., Co3O4) are emerging as low-cost and selective electrocatalysts for the electrochemical nitrate reduction reaction (NO3–RR) to ammonia (NH3), although their activity is still unsatisfactory and the genuine active site is unclear. Here, we discover that the NO3–RR activity of Co3O4is highly dependent on the geometric location of the Co site, and the NO3–RR prefers to occur at octahedral Co (CoOh) rather than tetrahedral Co (CoTd) sites. Moreover, CoOhO6is electrochemically transformed to CoOhO5along with the formation of O vacancies (Ov) during the process of NO3–RR. Both experimental and theoretic results reveal that in situ generated CoOhO5–Ovconfiguration is the genuine active site for the NO3–RR. To further enhance the activity of CoOhsites, we replace inert CoTdwith different contents of Cu2+cations, and a volcano-shape correlation between NO3–RR activity and electronic structures of CoOhis observed. Impressively, in 1.0 M KOH, (Cu0.6Co0.4)Co2O4with optimized CoOhsites achieves a maximum NH3Faradaic efficiency of 96.5% with an ultrahigh NH3rate of 1.09 mmol h–1cm–2at −0.45 V vs reversible hydrogen electrode, outperforming most of other reported nonprecious metal-based electrocatalysts. Clearly, this work paves new pathways for boosting the NO3–RR activity of Co-based spinels by tuning local electronic structures of CoOhsites.

Ordered intermetallic pallium-zinc (PdZn) electrocatalyst comprising a high density of PdZn pairs is synthesized for achieving co-adsorption and co-activation carbon dioxide and nitrate.Both operando measurements and theoretical calculations reveal that the PdZn pairs provide a dual-site geometric structure conducive to the key C–N coupling with a low kinetical barrier.The intermetallic PdZn displays excellent performance for the co-reduction of nitrate (NO3–) and carbon dioxide (CO2) toward urea, with a maximum FEureaof 62.78% at a small potential of – 0.4 V versus RHE.