Secondary Alcohols as Rechargeable Electrofuels: Electrooxidation of Isopropyl Alcohol at Pt Electrodes

Abstract

Fuel cells can be operated directly by oxidation of isopropyl alcohol (IPA) to acetone (ACE). If the product ACE is hydrogenated, IPA is formed again. In this way, IPA serves as a rechargeable electrofuel. In this work, we study the oxidation of IPA at Pt electrodes using several complementary experimental methods, including cyclic voltammetry (CV), electrochemical real-time mass spectrometry (EC-RTMS), and electrochemical infrared reflection absorption spectroscopy (EC-IRRAS), in combination with density functional theory (DFT) to assign the vibrational modes of IPA and ACE. Different types of Pt electrodes are investigated, namely single crystalline Pt(111) surfaces, polycrystalline Pt, and nanostructured tubular Pt electrodes. The onset of the IPA oxidation on the Pt electrodes is observed at 0.3 VRHE, yielding ACE with high selectivity. At potentials above 0.9 VRHE, the formation of Pt oxide inhibits the reaction. The only side reaction observed is the formation of small amounts of CO2. We show that adsorbed ACE is formed at the Pt electrodes poisoning the surface. On nanotubular electrodes with high surface area, ACE stays mainly adsorbed on the surface, and only a small fraction desorbs. These observations suggest that poisoning of the Pt electrode by adsorbed ACE limits the oxidation of IPA.

Photoconversion of 2-Propanol on Rutile Titania: A Combined Liquid-Phase and Surface Science Study

“…By irradiation of the rutile substrates, a negative band appears at 1712 cm –1 , which can be assigned to the CO stretching mode of acetone. , This band intensifies with increasing irradiation time. As all spectra are difference spectra, negative bands (downward oriented) indicate species that are formed, while positive bands (upward oriented) correspond to species that are consumed.…”

Mechanistic insight into deep holes from interband transitions in Palladium nanoparticle photocatalysts

“…Under different excitation wavelengths, the product yields were quite close to that of a non-irradiated reaction ( Table S6 ). This result can be explained by the fact that isopropanol is a stronger reducing agent (E o of acetone/isopropanol is around 0.76 V vs SHE) ( Waidhas et al., 2020 ) than Pd (E o of Pd(II)/Pd(0) is around 0.92 V vs SHE) ( Bratsch, 1989 ), and that the holes are quenched by isopropanol before they can catalyze the formation of R-Pd II -X intermediate. To address the concern of homocoupling of phenylboronic acid ( Adamo et al., 2006 ) that could be catalyzed by the hot holes ( Gellé et al., 2020 ) or bromobenzene to the biphenyl, a series of control experiments using only either reactant showed undetected product under various irradiation conditions ( Table S7 ).…”

The 2‐Propanol Fuel Cell: A Review from the Perspective of a Hydrogen Energy Economy

“…[52,53] However, adsorbed CO is not present on platinum during the oxidation of 2-propanol and the reaction is selective to acetone without any dissociation products detected. [36] Given the absence of limitations from adsorbed CO, the beneficial effect of ruthenium in enhancing the 2-propanol oxidation must be of different origin. Indeed, well-controlled rotating disk electrode (RDE) experiments with commercial Pt x Ru 1-x /C catalysts have shown that the presence of ruthenium gives rise to an unusual early oxidation process at potentials around þ0.15 V RHE (i.e., close to the equilibrium potential of the 2-propanol/acetone couple) which determines the OCV in DIFCs using PtRu/C anodes.…”

“…Acetone is the primary product of 2-propanol oxidation with a selectivity of almost 100% with platinum-based catalysts. [32][33][34][35] This originates from the fact that secondary alcohols such as 2-propanol do not adsorb dissociatively, [36][37][38][39] whereas also the product acetone remains molecularly intact when adsorbed, except for Pt(100) terraces. [40] Hence, the difficulty in splitting of the C-C bond of secondary alcohols leads to the absence of adsorbates (such as CO) that would be fully oxidized to CO 2 .…”