In situ X-ray absorption spectroscopy of Sn species adsorbed on platinized platinum electrode in perchloric acid solution containing stannous ions

Abstract

In situ X-ray absorption spectroscopy (XAS) was applied to investigate the Sn adlayer on platinized (pl-) Pt electrode in deaerated 0.2 M HClO4 solution containing 10−3 M Sn2+ in relation to the effect of Sn addition on electrocatalysis of Pt. A periodical emersion method under potentiostatic polarization, using pl-Pt plate (roughness factor Sr = 770) as a working electrode was employed to detect sensitively the sub-monolayer coverage of Sn on Pt. The Sn K-edge absorption spectra in a scanning XAS mode were measured by monitoring the Sn Kα1 fluorescence line. The Sn K-edge absorption near-edge structure (XANES) has indicated that the Sn species adsorbed on the pl-Pt electrode is partly oxygenated in the Sn-underpotential (UPD) region between − 0.05 and 0.25 V (RHE) which is overlapped with the UPD region of hydrogen. The extended X-ray absorption fine structure (EXAFS) analysis has supported a Sn overlayer model in which Sn atom occupies the hollow site of the nearest neighbor Pt atoms and is further bound with oxygen atoms in the Sn-UPD region. The coordination number of the Sn–Pt bond or Sn–Sn bond decreases with increasing potential, while the coordination number of the Sn–O bond increases reversely. In the potential region between 0.45 and 0.85 V (RHE), the EXAFS analysis has suggested that two-dimensional surface Sn oxide forms on the pl-Pt electrode, which is supported from the potential-pH equilibrium diagram of the Sn/H2O system.