Modulating d‑Band center of iron oxide via interfacial oxygen vacancies engineering for boosting electrocatalytic nitrogen reduction

• Interfacial oxygen vacancies modified coral-like Fe 3 O 4 were obtained by self-assembly Fe-base gels with ultrafast heating strategy. • The d -band center of Fe in Fe 3 O 4 can be shifted to higher energy level by decreasing the interfacial oxygen vacancies . • The obtained electrocatalytic e-NRR activity outperforms most- reported e-NRR catalysts. • Fe 3 O 4 –10GO exhibited 24 h electrochemical stability and practical potential in e-NRR application. The electrochemical nitrogen reduction reaction (e-NRR) is a promising energy-efficient and low-emission alternative to the traditional Haber–Bosch process, but the sluggish kinetic and difficult activation of nitrogen impede the reaction activity. In particular, addressing the weak interaction of nitrogen with catalysts is very challenging in this field. Here, a surface oxygen vacancies tailored method was proposed to shift the d -band center of iron-based electrocatalysts to Femi energy level, by leveraging molecule self-assembly strategy to obtain Fe-base gels followed by ultrafast calcined process. The optimal electrocatalysts (Fe 3 O 4 -xGO) possess a hierarchical porous architecture (coral-like morphology), thereby endowed with outstanding structural properties (329.1 cm 2 g⁻ 1 ). Meanwhile, interfacial oxygen vacancies could be constructed during the ultrafast heat-pyrolysis process, and their concentration could be tailored with the assistance of graphene oxide (GO). Benefiting from these structure characters, the d -band center of Fe in coral-like iron oxide can be shifted to a higher energy level, which is conducive to trapping and activating the intermediate in the e-NRR process. The results of the electrocatalytic NRR test, as anticipated, indicated that Fe 3 O 4 –10GO achieved a high Faradaic efficiency of 28 % and an NH 3 production rate of 30.45 μg h⁻¹ mg cat ⁻¹ at −0.3 V vs. RHE in a 0.1 M Na 2 SO 4 , positioning it comparably to most iron-based electrocatalytic materials used in e-NRR applications. This work could provide new insight for moldering the d band center of the electrocatalyst. The d band center of Fe in iron oxide (Fe 3 O 4 –10GO) can be up shifted by decreasing its interfacial oxygen vacancies, which results in the enhanced adsorption of intermediates for e-NRR. These effects give a greatly improved e-NRR performance, 30.45 μg h⁻¹ mg cat ⁻¹ NH 3 yield rate, 28 % Faradaic efficiency and 24 h electrochemical stability.