One-Pot Synthesis of Fe–N–C Species-Modified Carbon Nanotubes for ORR Electrocatalyst with Overall Enhanced Performance Superior to Pt/C

Abstract

Novel synthesis of efficient noble-metal-free electrocatalysts for both oxygen reduction/evolution reaction (ORR/OER) in energy conversion devices (e.g., fuel cells, metal–air batteries) is of essential significance for further sustainable development. This paper reports a facile synthesis of Fe–N–C species-modified carbon nanotubes (F/N-CNTs) for ORR application by directly pyrolyzing a fluffy hybrid precursor at a moderate temperature ([Formula: see text]C) in Ar. The fluffy hybrid precursors consisting of nitro-hydrochloric-acid-treated CNTs, melamine and Fe[Formula: see text] species are prepared via a freeze-drying method. On account of the synergistic effect of various active sites, including pyridine–N, Fe–Nx and Fe3C, and the high conductivity of the CNTs matrix, the as-obtained F/N-CNT electrocatalysts exhibit excellent ORR activities, comparable to commercial Pt/C. The addition of N heteroatoms, the dosage of Fe and the pyrolysis temperature highly influence the ORR properties of the F/N-CNT samples. The typical F/N-CNT sample obtained at the optimized parameters shows an onset potential of 1.06[Formula: see text]V and a half-wave potential of 0.91[Formula: see text]V versus reversible hydrogen electrode (RHE) in an alkaline condition, more positive than those (1.01[Formula: see text]V and 0.88[Formula: see text]V versus RHE) of Pt/C. The F/N-CNT exhibits outstanding bifunctional ORR/OER activity and excellent methanol tolerance, and the F/N-CNT-based Zn–air battery (ZAB) with an open-circuit voltage (OCV) of 1.405[Formula: see text]V presents a current density of 125[Formula: see text]mA[Formula: see text]cm[Formula: see text] and a power density of 76.5[Formula: see text]mW[Formula: see text]cm[Formula: see text]; these electrocatalytic properties are highly superior to Pt/C. The direct pyrolysis of fluffy hybrid precursors provides a concise but robust technical platform to achieve high-performance noble-metal-free electrocatalysts with ORR/OER activities superior to Pt/C.