Ordered mesoporous Fe2Nx electrocatalysts with regulated nitrogen vacancy for oxygen reduction reaction and Zn-air battery.

Highly efficient transition-metal electrocatalysts hold great promise for overcoming the sluggish kinetics of the oxygen reduction reaction (ORR), while the dense stacking of active sites within bulk materials constrains electrocatalytic behaviors. Therefore, nano-structure engineering to obtain hierarchal morphology is crucial to enrich the active sites and facilitate the corresponding mass transfer. Here, the three-dimensional interconnected and ordered mesoporous (3DOM) Fe 2 N x decorated on TiO y (Fe 2 N x @TiO y) is constructed. By introducing nitrogen vacancies, the increased surface area, and active sites boost ORR kinetics, including a high half-wave potential (0.88 V vs reversible hydrogen electrode) and high current density (71 mA cm⁻² at 0.8 V) have been reached. The zinc-air battery assembled with Fe 2 N x @TiO y catalysts presents a high specific capacity of 809 mAh g⁻¹. Density functional theory analysis and X-ray absorption spectroscopy further confirm the promoter effects of nitrogen vacancies on modulating electronic structure of Fe, through regulating intermediates adsorption/desorption. The shift of its d -band center is also found toward the Fermi energy level, strengthening the adsorbate-substrate interaction. This allows oxygen species to be favorably stabilized onto active sites of Fe 2 N x @TiO y. [Display omitted] • The three-dimensional interconnected and ordered mesoporous Fe 2 N x embedded on TiO y (Fe 2 N x @TiO y) is fabricated. • The coordination environment of Fe sites is regulated through introducing nitrogen vacancies. • Nitrogen vacancies upshift the d band level of Fe active sites to the Fermi level, result in binding energy increases of the adsorbents. • Fe 2 N x @TiO y shows outstanding performance to power oxygen reduction reactions and zinc-air batteries. [ABSTRACT FROM AUTHOR]