Confinement-Induced Enrichment in Hollow Multishelled Structure for High-Efficiency Ammonia Electrosynthesis

Electrochemical nitrate reduction represents a sustainable route for ammonia synthesis, yet its advancement is hampered by two bottlenecks: the fundamental limitation on conversion efficiency stems from inadequate in situ nitrate enrichment and the elusive dynamic evolution of catalytic mechanisms under operational conditions. Here, we report a CuO hollow multishelled structure (CuO-HoMS) that functions as a spontaneous pre-enrichment micronanoreactor capable of enriching, confining, and converting nitrate with exceptional efficiency. The CuO-HoMS with triple shells (3s-CuO-HoMS) achieves a champion Faradaic efficiency of 96.4 ± 0.9%, and an ammonia yield of 6316.3 ± 96.1 mmol·g_cat^-1·h^-1 at -0.4 V versus RHE among various catalysts. In situ confocal laser scanning microscopy directly visualized the rapid and sustained enrichment of NO₃^- within the stratified three-cavity reactor, with this enhanced anionic accessibility significantly reducing the overpotential and boosting efficient ammonia production. In situ XAS, Raman, FTIR, and DEMS collectively uncovered the dynamic evolution of 3s-CuO-HoMS, captured N-containing intermediates, and deduced a convincing reaction pathway validated by ¹⁵N isotopic tracing of the nitrogen source. This work offers guidance for designing anion-rich micronanoreactors under specific conditions and for elucidating the dynamic evolution mechanisms of nitrate reduction under operational conditions.