Co–O–Si interface engineering for sustainable ammonia synthesis with nearly 100% faradaic efficiency

Abstract

Electrocatalytic nitrate reduction to ammonia (NO₃RR) under ambient conditions offers a sustainable alternative to the traditional Haber–Bosch process. Herein, we develop a silica-templated strategy to construct nanoflower-like CoSiO_x catalysts composed of ultrathin, self-assembled nanosheets enriched with oxygen vacancies and Co–O–Si interfacial sites. The optimized catalyst, Co_1.0SiO_x-140, achieves a remarkable ammonia yield of 66.95 mg h⁻¹ mg_cat.⁻¹ and a faradaic efficiency approaching 100% at −1.5 V vs. RHE in 0.1 M KOH + 0.1 M KNO₃ electrolyte. Comprehensive spectroscopic characterization and density functional theory (DFT) calculations reveal that the synergistic effect between structural oxygen vacancies and Co–O–Si interfaces enhances NO₃⁻ adsorption and reduces the energy barrier for NH₃ desorption. The catalyst also demonstrates excellent long-term stability over 35 hours without morphological degradation. This work highlights a robust design principle for nitrate-to-ammonia electrocatalysts through rational defect and interface engineering enabled by templated nanostructure synthesis.