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 poten tial range, 0.6 to 0.9 V vs. NHE. Both perchlorate and bisulfate anion s were chemisorbed reversibly in the form of unidentate ortridentate c oordination on the surface. Bisulfate and perchlorate ions started to be adsorbed at 300 and 600 mV vs. NHE, respectively, and these potenti als coincided with the onset of hydrogen desorption. The anomalously s harp 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 sh ift of bisulfate anions on a positively charged electrode surface.