A Simple Preheating-Pyrolysis Strategy Leading to Superior Oxygen Reduction Reaction Activity in Fe-N/Carbon Black.

Abstract

Maintaining the high catalytic activity of the oxygen reduction reaction (ORR) while reducing costs is a long-standing effort to promote the application of polymer electrolyte fuel cells. Here, the binding of nitrogen-containing ligands and carbon black is enhanced by controlling the pyrolysis conditions of a FeSO₄ , 1,10-phenanthroline (phen), carbon black mixture, which significantly improves the ORR catalytic activity of the pyrolysis products. Preheating is proposed as a process improvement method using a heat treatment at a temperature between the melting and boiling points of phen before high-temperature pyrolysis, which achieves an effective combination of phen and carbon black, and enhances the interaction between phen and ferrous ions. This method substantially increases the number of FeN_x active centers in the pyrolysis product, resulting in an impressive Fe-N/C catalyst with half-wave potential (E_1/2 ) up to 0.93 V and a diffusion-limited current density (j_L ) of 5.9 mA cm^-2 and no obvious decay after 20 000 cyclic voltammetry cycles in 0.1 m KOH, which are all among the best-reported data known to date. The interaction between the ratio of Fe/phen and the pyrolysis conditions is also investigated. Under the right conditions, cheap raw materials can also generate highly catalytically active sites.