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) Fe2Nx decorated on TiOy (Fe2Nx @TiOy) 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 Fe2Nx @TiOy 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 Fe2Nx @TiOy.