The Electrochemical Stability and Calculated Free Energies of PtCr Alloys
In this investigation the calculated free energies and electrochemical stability of the PtCr system are presented as well as the calculated free energies of the PtZr, PtTi, and the PtV systems. These alloy systems are currently of interest as fuel cell electrodes providing dealloying does not occur and cause degradation of performance. The calculations indicate that the PtZr and PtCr systems are the most stable with respect to their elements, followed by PtTi and finally by the PtV system. These results are consistent with the experimental data of previous investigations involving the compositional stability in a fuel cell environment for Pt4Zr, Pt3Ti, and Pt3V. The PtCr calculations are compared with the experimental electrochemical results of this investigation and are found to support the experimental findings in the low chromium concentration samples but do not support the findings for the higher chromium concentration alloys. Experimental results indicated that the samples of 0–35 atom percent (a/o) Cr were electrochemically very stable although the 25 a/o disordered specimen did undergo some minor changes during cycling. The 50 and 80 a/o Cr samples were quite unstable during cycling, yielding a large surface area increase and a depleted Cr layer. The Cr sample was also quite unstable as seen by the surface pitting which occurred. © 1988, The Electrochemical Society, Inc. All rights reserved.
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