THE STRUCTURE OF BISULFATE AND PERCHLORATE ON A PT(111) ELECTRODE SURFACE STUDIED BY INFRARED-SPECTROSCOPY AND AB-INITIO MOLECULAR-ORBITAL CALCULATION

In situ infrared reflection absorption spectroscopy yielded the first spectroscopic evidence that perchlorate anion is adsorbed on a Pt(111) electrode surface in a 0.1 M perchlorate acid solution over the potential range, 0.6 to 0.9 V vs. NHE. Both perchlorate and bisulfate anions were chemisorbed reversibly in the form of unidentate ortridentate coordination on the surface. Bisulfate and perchlorate ions started to be adsorbed at 300 and 600 mV vs. NHE, respectively, and these potentials coincided with the onset of hydrogen desorption. The anomalously sharp spike peaks seen in the cyclic voltammetry of the Pt(111)in acid solutions were associated with the structure change of both anions. Ab-initio molecular orbital calculation supported the large frequency shift of bisulfate anions on a positively charged electrode surface.