High‐Performance, Low Pt Content Catalysts for the Electroreduction of Oxygen in Polymer‐Electrolyte Fuel Cells

Pt‐included and Pt‐supported catalysts have been synthesized using graphite and carbon black supports of various specific areas. The graphites are KS6 (20 m 2 /g), HS100 (110 m 2 /g), and HS300 (305 m 2 /g) from Lonza, and the carbon blacks are Vulcan (254 m 2 /g) and Black Pearls (1475 m 2 /g) from Cabot. The Pt‐included and Pt‐supported catalysts were used at the cathode of a fuel cell, and their polarization curves were compared to each other and to those of various Pt‐supported catalysts from E‐TEK. In the high current region of interest to fuel cell developers, it is shown that Pt‐supported catalysts perform better than Pt‐included ones when the specific area of the support is small. The contrary is true when the specific area of the support is large. The best catalysts are HS300‐Pti [8.3 weight percent (w/o) Pt included in HS300 graphite] and Vu‐Pti (6.1 w/o Pt included in Vulcan XC‐72R). These catalysts display very high mass and specific activities for reduction. Furthermore, the iR‐corrected polarization curves of both HS300‐Pti (with a Pt loading of 0.110 mg/cm 2 ) and Vu‐Pti (with a Pt loading of 0.070 mg/cm 2 ) cross at high current the polarization curve of the electrode prepared with E‐TEK20 (20 w/o of supported Pt, with a Pt loading of 0.287 mg/cm 2 ). Pt inclusion in graphite or carbon black is therefore an interesting way of reducing the Pt loading of fuel cell cathodes without lowering electrochemical performance. HS300‐Pti and Vu‐Pti have been characterized by x‐ray diffraction, transmission electron microscopy, and x‐ray photoelectron spectroscopy. These analyses indicate that they both contain metallic Pt and Pt(II and IV) oxides and/or hydroxides.