α-Fe2O3 spherical nanocrystals supported on CNTs as efficient non-noble electrocatalysts for the oxygen reduction reaction

Abstract

Substitution of low-cost and non-noble-metal catalysts for expensive and scarce Pt to optimize the oxygen reduction reaction (ORR), aimed for applications in producing economical fuel cells, is crucial for solving the world-wide energy crisis in the future. A novel α-Fe₂O₃/CNT nanocatalyst was synthesized via facile nucleation and crystal growth of α-Fe₂O₃ on carbon nanotubes (CNTs) using an annealing process. Characterization by X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) indicated that spherical α-Fe₂O₃ nanocrystals were well dispersed on CNTs, and were also stably stuck in the spatial structure formed by the stacked CNTs. The catalytic activity of α-Fe₂O₃/CNTs for ORR was measured to be almost twice as high as the activity of CNTs and of α-Fe₂O₃ for this reaction. The α-Fe₂O₃ loading on CNTs has a great influence on catalytic performance for ORR, and the special trigonal structure of α-Fe₂O₃ elevates ORR electroactivity. The kinetics studies suggest that the mechanism of the ORR reaction catalyzed by α-Fe₂O₃/CNTs primarily involves a four-electron-transfer pathway. Strong methanol tolerance and long durability are additional advantages of α-Fe₂O₃/CNTs.