In Situ Electrochemical Construction of CoCu 2 O Nanoclusters for Efficient Nitrate-to-Ammonia Electroreduction

Designing highly efficient and synergistic electrocatalysts for the electrochemical nitrate reduction reaction (NO3RR) toward ammonia (NH3) is crucial for developing green, sustainable, and scalable pathways for NH3 synthesis. This study used a in situ electrochemical reduction strategy to construct CoCu2O nanoparticles on a CoCuHHTP substrate, successfully fabricating a CoCu2O@CoCuHHTP catalyst. The characterization techniques, including TEM, XRD, XPS, and FTIR, revealed that the CoCuHHTP surface was uniformly decorated with 2-5 nm CoCu2O nanoparticles. Moreover, the partially reduced substrate exposed abundant noncoordi-nated hydroxyl groups, which provided an ideal microenvironment for the adsorption of reaction intermediates and a stable proton transfer. A combination of electrochemical measurements, in situ spectroscopic/mass spectrometric analyses, and DFT calculations was used to elucidate the synergistic catalytic mechanism. CoCu2O acted as an efficient water dissociation center to continuously supply abundant hydrogen adatoms (Had), while the numerous hydroxyl groups in the partially reduced CoCuHHTP substrate stabilized various key nitrogen-containing intermediates (e.g., *NO3, *NO2, *NO, and *NOH) via hydrogen bonding. Consequently, this effectively suppressed the byproduct formation, which significantly reduced the reaction energy barrier and synergistically promoted efficient NH3 generation with high selectivity. DFT calculations further confirmed, at the atomic level, the NO3- adsorption and *NO hydrogenation step, is identified as the rate-determining step, that on the HHTP-modified CoCu2O(111) surface were only 0.54 and 0.55 eV, respectively, which were significantly lower than those on CoCuHHTP (0.98 and 1.16 eV) and pure CoCu2O (0.80 and 0.68 eV). This highlighted the critical role of hydrogen bonding in optimizing the reaction pathway and enhancing the intrinsic activity. Electrochemical performance tests demonstrated that CoCu2O@CoCuHHTP achieved a 1200 μmol h-1 cm-2 NH3 production rate at - 0.6 V (vs RHE), which was 3.5 times higher than that of pristine CoCuHHTP, with up to 97.9% faradaic efficiency for NH3 (FENH3). In a flow electrolyzer coupled with the oxygen evolution reaction, the catalyst operated stably for 1800 h (30 cycles) at 100 mA cm-2 while maintaining an above 80% FENH3, which demonstrated an exceptional catalytic stability and practical application potential.