Electrochemical oxidation of 2-propanol over platinum and palladium electrodes in alkaline media studied by in situ attenuated total reflection infrared spectroscopy

Abstract

The electrochemical oxidation of 2-propanol over Pt and Pd electrodes was evaluated in alkaline media. Linear sweep voltammograms (LSVs), chronoamperograms (CAs), and simultaneous time-resolved attenuated total reflection infrared (ATR-IR) spectra of both electrodes were obtained in a 0.25 M KOH solution containing 1 M 2-propanol. The onset potential of 2-propanol oxidation for Pt was lower than that for Pd in LSVs while the degree of performance degradation observed for Pd was significantly smaller than that observed for Pt in CAs. The main product of 2-propanol oxidation was acetone over both electrodes and, over Pt only, acetone produced was catalytically oxidized to the enolate ion, which was accumulated on the Pt surface, leading to significant performance degradation. Carbon dioxide and carbonate species (CO3(2-), HCO3(-)) were not observed during 2-propanol oxidation over both electrodes, indicating that the complete oxidation of 2-propanol to CO2 will be a minor reaction.

CO as a Probe Molecule to Study Surface Adsorbates during Electrochemical Oxidation of Propene

“…Attenuated Total Reflection Fourier Transform Infrared Absorption Spectroscopy (ATR-FTIR) is a technique that has previously been employed to characterize intermediates during the electrochemical oxidation of alcohols and hydrocarbons. [8][9][10][11][12] In ATR-FTIR, a catalyst is deposited onto a highly refractive material (e. g., Si) and IR radiation is introduced at an angle higher than the critical angle, such that only the evanescent wave resulting from total reflection probes the surface of the catalyst and the region of the electrolyte in close proximity to the catalyst/electrolyte interface (see SI Figure S1). By using nanostructured electrodes the surface sensitivity is enhanced further, as the nanostructuring increases IR absorption intensity by a factor 10-1000 for species adsorbed to the catalyst.…”

Adsorbed Enolate as the Precursor for the C–C Bond Splitting during Ethanol Electrooxidation on Pt

“…When the reference spectra were taken in background solution (0.1 M HClO 4 ) at each individual potential, two additional bands were clearly observed at ca. 1560 and 1670 cm –1 in the low-potential region (Figure B), which can be assigned to ν­(CC–O) for adsorbed enolate , and ν­(CO) for adsorbed acetaldehyde, respectively.…”

Activity Trends for the Selective Oxidation of 2-Propanol to Acetone on Noble Metal Electrodes in Alkaline Electrolyte

“…This reveals the difficulty in splitting the C−C bond of 2-propanol, which is a secondary alcohol, for any of the surfaces considered as also shown before for platinum electrodes in acid 7,8,10,46 or alkaline conditions. 16,47 Comparing the spectra measured in p-and s-polarization, we find that all spectra show a higher intensity of the carbonyl band in p-polarization than in s-polarization. In addition, the intensity of the bands at 1700 cm −1 , as compared to the bands at 1370 or 1240 cm −1 , is higher in p-polarization than in s-polarization.…”

“…While platinum-based electrodes are also active in alkaline media, − a broader range of electrodes can oxidize 2-propanol compared to acidic media, such as gold, ,, rhodium, palladium, − , and palladium-based alloys. − Here, we study the electrooxidation of 2-propanol in alkaline electrolytes on four noble metal electrodes aiming to establish the activity trends and rationalize them in terms of a simple activity descriptor. We use (a) electrochemical measurements to identify onset potentials and establish current–potential relationships, (b) vibrational spectroscopy and mass spectrometry to determine the reaction selectivity, and (c) computational modeling to elucidate the reaction pathways and justify trends in electrocatalytic activity for the four active metal surfaces.…”