Kinetics of isopropanol oxidation on Pt(111), Pt(110), Pt(100), Pt(610) and Pt(211) single crystal electrodes - Studies of in situ time-resolved FTIR spectroscopy

The electrocatalytic oxidation of isopropanol on three basal planes ((111), (110) and (100)) and two stepped surfaces ((610) and (211)) of platinum single crystals has been studied by using in situ FTIR spectroscopy. The results confirmed that the oxidation of isopropanol obeys the same reaction mechanism on the basal planes (S.-G. Sun, Y. Lin, Electrochim. Acta 41 (1996) 693) as well as on the stepped surfaces. It was determined that acetone (characterized by IR bands around 1698, 1430, 1368, 1238 and 1157 cm(-1)) and carbon dioxide (depicted by an IR band near 2345 cm(-1)) are the main product species involved in isopropanol oxidation. The production rate of acetone (represented by k(C=O)) and carbon dioxide (denoted by k(CO2)) in isopropanol oxidation at different potentials and on different Pt single crystal electrodes has been evaluated quantitatively from in situ time-resolved FTIR spectroscopic data. The different variations of K-C=O and k(CO2) demonstrated that the kinetics of the oxidation varies significantly with the Pt single crystal electrode orientation. It was shown that on all five Pt single crystal electrodes the maximum value of k(C=O) is always larger than that of k(CO2), signifying that the production of acetone is faster than that of carbon dioxide in isopropanol oxidation. From the values of k(C=O) and k(CO2), the activity of Pt single crystal electrodes for producing both acetone and carbon dioxide has been classified. It has been found that Pt(610) is the most active surface for yielding carbon dioxide. The order of activity for producing carbon dioxide of the five electrodes is Pt(610)>Pt(111)>Pt(100)>Pt(211)>Pt(110). Two potential regions are distinguished for the production of acetone in isopropanol oxidation, one between 0.20 and 0.80 V/SCE and the other from 0.80 to 1.20 V. The activity of the five Pt single crystal electrodes in the first potential region is Pt(100)>Pt(610)> Pt(211) > Pt(111) > Pt(110), and in the second potential region it is Pt(110)> Pt(111) > Pt(211)> Pt(100)> Pt(610). The present study provides new data to describe quantitatively the kinetics of isopropanol oxidation on Pt single crystal electrodes, and contributes to the understanding of the structural effects of the Pt surface atomic arrangement in the electrocatalysis of irreversible reactions. (C) 1998 Elsevier Science Ltd. All rights reserved.