Selective Dissolution of Pt–Co Binary Alloys and Surface Enrichment of Platinum in Sulfuric Acid Solution

Abstract

The selective dissolution of cobalt and the consequent surface enrichment of platinum in Pt–Co binary alloys immersed in 0.5 mmol·m⁻³ H₂SO₄ at 298 K were investigated. Four different Pt–Co alloy thin films with various Pt contents, deposited on glassy carbon sheets by physical vapor deposition, were investigated: 51 at% Pt (Pt₅₁–Co₄₉), 43 at% Pt (Pt₄₃–Co₅₇), 28 at% Pt (Pt₂₈–Co₇₂), and 24 at% Pt (Pt₂₄–Co₇₆). When the thin films were immersed for 24 h in a 0.5 mmol·m⁻³ H₂SO₄ solution, a Pt-enriched layer was formed on the surface of all the alloys due to Co-selective dissolution. The enriched layer formed in the higher-Pt alloys (Pt₅₁–Co₄₉ and Pt₄₃–Co₅₇) significantly suppressed further dissolution, whereas the lower-Pt alloys (Pt₂₈–Co₇₂ and Pt₂₄–Co₇₆) exhibited more extensive selective dissolution and roughened surfaces. In this study, the selective dissolution and surface morphology of the Pt–Co alloys are discussed on the basis of these experimental results.