We report an investigation of the formation mechanism of a gold (Au) thin-film electrode made by electroless deposition for in situ electrochemical (EC) attenuated-total-reflection surface enhanced infrared adsorption spectroscopy (ATR-SEIRAS). The Au thin film was generated via galvanic electroless deposition from [Au(S2O3)(2)](3-) precursor and consisted of similar to 46 nm Au nanoparticles (NPs) deposited on Si infrared window. The observation of v(Au-S) (263 cm(-1)) and v(S-S) (454 cm(-1)) on the freshly deposited Au film using surface enhanced Raman spectroscopy (SERS) confirmed that the initial adsorbed sulfur species was S2O32-. Subsequent acid-treatment broke the S-S bond and yielded Au surface-bound atomic sulfur species. EC stripping of them led to the formation of (bi) sulfate identifiable by in situ EC ATR-SEIRAS. A sulfur coverage of 0.5 was estimated. We also discovered that square-wave treatment of the Au film led to significant surface reconstruction and much enhanced oxygen reduction reaction (ORR) activity. We attribute the latter to the reconstruction-caused new sites that could stabilize better the adsorbed ORR intermediates for facilitating the subsequent reaction step(s). (C) 2011 Elsevier B.V. All rights reserved.