Insights into interfacial water and key intermediates on Cu95Co5 aerogels for electrocatalytic nitrate-to-ammonia conversion

Abstract

Electrocatalytic nitrate reduction (NO₃RR) to ammonia presents a sustainable route for pollutant remediation and green synthesis, yet challenges persist in achieving high efficiency and selectivity. Herein, we report a cobalt-doped copper aerogel (Cu₉₅Co₅) synthesized via one-step co-reduction, demonstrating exceptional NO₃RR performance with 94.91% faradaic efficiency at −0.6 V and 31.15 mg per mg_cat per cm² per h NH₃ yield at −0.7 V vs. RHE. The system achieves an impressive energy efficiency of 31.03% and enables a record-low ammonia production cost of $0.53 per kg. Multiscale characterization reveals that Co doping induces lattice contraction, optimizes d-band positioning, and enhances interfacial K⁺·H₂O interactions, collectively promoting water dissociation and *H generation. The combination of operando spectroscopies (SERS, ATR-FTIR, DEMS) and density functional theory (DFT) calculations elucidates a stepwise hydrogenation pathway: *NO₃ → *NO₂ → *NO → *NH₂OH → *NH₃, with the rate-determining step (RDS) identified as *NO hydrogenation to *NHO. The hierarchical porosity of the aerogel facilitates mass transport while Cu–Co synergy suppresses hydrogen evolution reactions via electronic modulation. Practical viability is demonstrated through stable 12 hour operation in a Zn–NO₃⁻ battery. This work provides insights into Cu–Co catalysis and establishes design principles for high-performance NO₃RR systems.