In Situ Electrochemical Construction of CoCu₂O Nanoclusters for Efficient Nitrate-to-Ammonia Electroreduction.

Abstract

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 (H_ad), 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 (FE_NH3). 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% FE_NH3, which demonstrated an exceptional catalytic stability and practical application potential.