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 graphics 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 H-2/O-2 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 O-2 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 cm 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.