Pt‐included and Pt‐supported catalysts have been synthesized using graphite and carbon black supports of various specific areas. The graphites are KS6 (20 m2/g), HS100 (110 m2/g), and HS300 (305 m2/g) from Lonza, and the carbon blacks are Vulcan (254 m2/g) and Black Pearls (1475 m2/g) from Cabot. The Pt‐included and Pt‐supported catalysts were used at the cathode of a
H2/O2
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
O2
reduction. Furthermore, the iR‐corrected polarization curves of both HS300‐Pti (with a Pt loading of 0.110 mg/cm2) and Vu‐Pti (with a Pt loading of 0.070 mg/cm2) 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/cm2). 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.
Graphite powders with supported Pt [5 and 20 weight percent (w/o) PtI and Pt inclusions (13 and 17 w/o) in graphite have been bonded with an inorganic polymer LaPO4 and used as cathodes for the hydrogen evolution reaction (HER) in 1 M KOH solution. Pt-supported electrodes [Pt(s)/C/LaPO4] are more active than the electrodes containing Pt inclusions in graphite [Pt(i)/C/LaPO4]. However, in high-current-density conditions (0.25 A/cm2), Pt(i)/C/LaPO4 is stable while Pt(s)/C/LaPO4 disintegrates after 24 h. The ac impedance diagrams display two semicircles on the complex-plane plot for both Pt(s)/C/LaPO4 and Pt(i)/C/LaPO4 electrodes but only one for pure graphite. The same equivalent circuit with two constant-phase elements has been used to explain the behavior of these electrodes. For both materials, the HER proceeds via the Volmer-Heyrovsk mechanism. The difference in the electroactivity of these two materials is related to the effective amount of Pt available. ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 132.236.27.111 Downloaded on 2015-06-22 to IP
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