Formation of Pt Skin Layer on Ordered and Disordered Pt-Co Alloys and Corrosion Resistance in Sulfuric Acid

Abstract

The formation of the Pt-enriched layer (Pt skin layer) formed at the surface of the ordered and disordered Pt-Co alloy specimens by a dealloying treatment and its corrosion resistance under potential cycling in sulfuric acid were examined to clarify the dissolution behavior of the Pt skin layer in polymer electrolyte fuel cell-operating conditions. The ordered and disordered Pt-Co specimens were obtained by heat treatment at 1073 and 1473 K, respectively. Co at the alloy surfaces dramatically dissolved in an early phase of the dealloying treatment in naturally aerated 0.5 M H2SO4 at 298 K, and Pt skin layers were formed. Pt skin layers ca. 2 monolayer in thickness were formed on the Pt-Co alloy specimens by the dealloying treatment in 0.5 M H2SO4. The cyclic voltammetry measurements of the Pt-Co specimens showed the existence of Pt skin layers after the dealloying treatment and the inhibition of the Pt oxide formation on the Pt skin layers. The Pt oxide formation for ordered Pt-Co was more suppressed than that for the disordered Pt-Co. The Pt skin layers on the Pt-Co specimens exhibited a higher corrosion resistance than pure Pt, and the dissolution of the Pt skin layer for ordered Pt-Co was more inhibited than that for disordered Pt-Co under potential cycling in the potential range of 0.6–1.4 V in 0.5 M H2SO4 (dissolution test). A thin, continuous Pt skin layer remained at the surface of the ordered Pt-Co specimen after the dissolution test. The formation of a uniform Pt skin layer seems to provide high oxidation resistance to the surface, leading to high corrosion resistance.Graphical The dissolution of Pt skin layer for the ordered Pt-Co was highly suppressed compared with that for the disordered Pt-Co and pure Pt. The suppression of Pt-O formation seems to be the main reason for the high corrosion resistance. The formation of a thin and continuous Pt skin layer is important to prevent the dissolution of Pt.