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

Abstract

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 (Fe₃O₄-xGO) possess a hierarchical porous architecture (coral-like morphology), thereby endowed with outstanding structural properties (329.1 cm² 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 Fe₃O₄–10GO achieved a high Faradaic efficiency of 28 % and an NH₃ production rate of 30.45 μg h⁻¹ mg_cat⁻¹ at −0.3 V vs. RHE in a 0.1 M Na₂SO₄, 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.