Enhanced Ammonia Electrosynthesis via In-Plane Integration of Fe₂O₃ Dual-Phase Nanodomains

Iron oxides are notable among oxide semiconductors for their abundance and environmental friendliness, positioning Fe₂O₃ as a promising candidate for industrial nanotechnology. However, polymorphic Fe₂O₃ presents up to four phases, posing significant challenges in customizing them for nanocatalysis, including tasking a single phase with complex catalytic reactions, harnessing synergistic advantages during phase integration, and achieving selective reactivity amidst competing side reactions. Here, we developed a 2D-templated Z-direction-confining strategy combined with dual-phase nanocrystallization to synthesize thin-layered Fe₂O₃ with an in-plane nanoscale integration of α- and γ-phases. The resulting dual-phase Fe₂O₃ achieved superior electrochemical nitrate reduction to ammonia, yielding 4329.8 μg/mg_cat/h at -0.8 V vs a reversible hydrogen electrode with high faradaic efficiency (∼95.7%) and outstanding selectivity (99.9%). Combined computational and experimental studies revealed that the enhanced performance arises from the synergistic integration of electron transport through the γ phase and active sites within the α phase, facilitated by ultrafine nanophase domains. Electrons reaching the α phase selectively drive nitrate reduction over proton reduction. The electrocatalyst exhibited exceptional stability across 28 cycles. This catalyst, with its high yield, faradaic efficiency, selectivity, stability, and low cost, outperforms previous catalysts under comparable conditions, highlighting the potential of nanophase manipulation for sustainable ammonia electrosynthesis from nitrate waste.