Abstract
<jats:p> Despite extensive research, platinum-group-metal-free electrocatalysts for oxygen reduction reaction (ORR) remain under active development due to their potential largescale application in electrochemical energy conversion and storage devices. Among them, Fe-N-C materials derived from metal-organic frameworks have attracted particular attention owing to their high activity and low cost. In this work, the influence of iron and phosphorus incorporation on ZIF-8-derived catalysts is systematically investigated through a series of materials prepared by post-pyrolysis impregnation using simultaneous and sequential introduction routes. The synthesis procedure strongly akects iron speciation. Simultaneous incorporation of iron and phosphorus at high phosphorus loadings promotes the formation of FePx-containing nanoparticles, whereas sequential incorporation results predominantly in iron species dispersed within the carbon matrix. Electrocatalytic evaluation in near-neutral electrolyte reveals that ORR activity increases upon the initial introduction of iron (~0.5 wt.%) as evidenced by a ~400 mV positive shift in the half-wave potential, while further increase in iron loading provides only limited additional improvement. The catalyst containing FeP <jats:sub>x</jats:sub> nanoparticles and 0.47 wt.% Fe exhibits the highest energy ekiciency and peak power in Zn–air battery tests, suggesting that iron speciation may play a more significant role than total iron content in determining ORR performance in near-neutral media. </jats:p>