Mechanochemical Synthesis of γ‑Fe2O3 Nanoparticles@N-Doped Mesoporous Carbons Derived from Biomass for Oxygen Reduction.

A facile synthesis method via the ball-milling coupled with simultaneous carbonization and activation with KOH at different temperatures was employed to prepare γ-Fe2O3 nanoparticles-supported N-doped mesoporous carbons (denoted as γ-Fe2O3@N-doped CX-T) from a variety of biomass raw materials (sugar cane bagasse, coffee grounds, and luffa) as precursors. The obtained γ-Fe2O3@N-doped CX-T catalysts are characterized by using various spectroscopic measurements (i.e., X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS)) and tested for oxygen reduction reaction (ORR) in an alkaline solution via cyclic and liner sweep voltammetry. As a result, the γ-Fe2O3@N-doped CS-600 catalyst prepared from sugar cane bagasse at 600 °C exhibits the superior catalytic performance toward ORR with positive onset potential (1.01 V vs reversible hydrogen electrode), 4-electron transfer pathway, methanol-resistance, and operation stability, which is comparable to a commercially obtainable Pt/C catalyst. XPS analysis reveals that the nitrogen-doped carbons, i.e., pyridinic-N and graphitic-N, are the active species of catalysts for ORR. XRD and TEM images show that the formation of γ-Fe2O3 on N-doped mesoporous carbons may also be the cocatalysts for boosting ORR performance. This study not only proposes a promising candidate as a nonprecious ORR cathode for alkaline fuel cells but also realizes the purpose of resource recovery and utilization.