Possibility of carbon materials with iron atoms bound to the surface by heat-treatment as cathode catalysts of fuel cells

Abstract

Attention has now been paid to platinum-free catalysts aiming at widespread use of polymer electrolyte fuel cells (PEFCs) after their realization as a power source of electric vehicles and on-site cogeneration systems. In this review, we describe cathode catalysts consisting of iron bound to surfaces of carbon materials through nitrogen atoms, denoted here as FeN_x-C catalysts, which are formed by heat-treatment. Methods for FeN_x-C catalyst formation are classified according to iron-containing compounds and nitrogen sources of the precursors. Difference in the catalysis from conventional Pt-based catalysts, the structure of the active site, the mechanism of oxygen reduction, and long-term durability at the catalysts are discussed. Especially, we mention that the activity of the FeN_x-C catalysts per metal weight is comparable to that of the Pt-based catalysts; a FeN_x-C catalyst electrode whose performance exceeds those of Pt-based electrodes has been already reported, and that stable performance of FeN_x-C catalysts has also been reported. It is reasonable to conclude that the FeN, -C catalysts have the potential to be applied to the cathode of the PEFC. Although the anode still needs the Pt-based catalysts, using FeN_x-C catalysts could lead to significant reduction of the total amount of Pt used in the PEFC.