Development of high performance carbon composite catalyst for oxygen reduction reaction in PEM Proton Exchange Membrane fuel cells

Abstract

Highly active and stable carbon composite catalysts for oxygen reduction in PEM fuel cells were developed through the high-temperature pyrolysis of Co–Fe–N chelate complex, followed by the chemical post-treatment. A metal-free carbon catalyst was used as the support. The carbon composite catalyst showed an onset potential for oxygen reduction as high as 0.87 V (NHE) in H 2SO 4 solution, and generated less than 1% H 2O 2. The PEM fuel cell exhibited a current density as high as 0.27 A cm −2 at 0.6 V and 2.3 A cm −2 at 0.2 V for a catalyst loading of 6.0 mg cm −2. No significant performance degradation was observed over 480 h of continuous fuel cell operation with 2 mg cm −2 catalyst under a load of 200 mA cm −2 as evidenced by a resulting cell voltage of 0.32 V with a voltage decay rate of 80 μV h −1. Materials characterization studies indicated that the metal–nitrogen chelate complexes decompose at high pyrolysis temperatures above 800 °C, resulting in the formation of the metallic species. During the pyrolysis, the transition metals facilitate the incorporation of pyridinic and graphitic nitrogen groups into the carbon matrix, and the carbon surface doped with nitrogen groups is catalytically active for oxygen reduction.