Electrochemical corrosion of Pt electrode in concentrated sulfuric acid

Abstract

Pt electrode corrosion in concentrated sulfuric acid has been studied by a series of electrochemical measurements in combination with instrumental analyses. It has been found that the cathodic polarization of Pt in 16 ∼ 18 mol dm-3 H2SO4 generates sulfur deposition on the Pt electrode. The following anodic polarization induces sulfur dissolution and Pt corrosion. SEM-EDS, XPS and EQCM results well-supported that the electrochemical behaviors occurred at the Pt electrode. The sulfur deposition was proven to take place by H2SO4 reduction at -0.08 ∼ +0.02 V vs. SHE and sulfur dissolution at +1.32 ∼ +1.52 V vs. SHE, which indirectly causes Pt corrosion. The RRDE result con.rmed that Pt corrosion takes place via a two-step electrode reaction at +1.62 ∼ +1.92 V vs. SHE and +1.12 ∼ +1.32 V vs. SHE. As a result of Pt corrosion, no Pt was detected in the electrolytic solution, but was found to yield a Pt-S composite accumulated on the electrode. The Pt corrosion mechanism in the concentrated sulfuric acid was thus found to be complicated, which is far from the simple Pt ionization predicted in the Pourbaix's diagram. © 2008 The Japan Society for Analytical Chemistry.