Fe-based catalysts for oxygen reduction in PEM fuel cells - Pretreatment of the carbon support

Fe-based catalysts for O-2 reduction have been prepared on four carbon supports (Vulcan, Black Pearl, Norit, and a developmental carbon, RC2, from Sid Richardson Carbon Corp.). Four preparation procedures have been used with each carbon support and the catalytic activities for the reduction of oxygen in H2SO4, pH 1, and in polymer electrolyte membrane fuel cell tests are compared for all the catalysts, which are nominally loaded with 0.2 wt % Fe, using iron(II) acetate as Fe precursor. The catalytic activity of these Fe-based catalysts greatly depends upon the chosen carbon support and also upon the preparation procedure used. The results are rationalized in terms of N content at the surface of the catalysts; the larger the N content, the better the catalytic activity. The best catalysts are obtained after refluxing either RC2 or Norit in HNO3 before adsorbing iron acetate on the oxidized carbon supports and heat-treating the resulting materials at 900degreesC in an atmosphere containing NH3. The surface nitrogen content of these catalysts, measured by XPS, is 2.5 and 4.1 atom %, respectively. For the Fe-based catalyst prepared on Norit and tested in fuel cell, the mass activity at low current regime, expressed in A/mg Fe, is only slightly lower than the A/mg Pt recorded for a state-of-the-art, Pt-based membrane electrode assembly. (C) 2004 The Electrochemical Society.