Attenuated Total Reflection−Fourier Transform Infrared Study of Methanol Oxidation on Sputtered Pt Film Electrode

Abstract

Methanol oxidation has been investigated at a sputtered Pt film electrode by using in situ Fourier transform infrared spectroscopy with the attenuated total reflection technique, which can identify directly adsorbed species on the electrode surface. Linear CO, bridged CO, formyl species, and formic acid-related species have been clearly identified during the electro-oxidation of methanol in the intact cyclic voltammogram between 0.05 and 1.0 V, where the initial potential is applied at 0.05 or 1.0 V. The formyl species, linear CO, and bridged CO adsorb on the Pt surface at a low potential, for example, 0.05 V. A potential-induced conversion between the linear CO, the bridged CO, and the formic acid-related species is observed during the methanol oxidation. It was clear that an oxidation via formic acid, at least up to formic acid, is the predominant route for the methanol oxidation in a potential range from 0.2 V to ca. 0.6 V and the oxidation is prohibited by the high coverage of Pt sites with CO. In a higher potential region than that, the CO and HCOOH parallel routes are opened for the complete methanol oxidation. The correlation between the methanol oxidation and the oxides formed on Pt surface is also discussed, which affects the reactivity of the electrode and the reaction mechanism.

Catalysts for the electro‐oxidation of small molecules

“…Thus, it is indicated that the rapid increase in the MOR current strongly corresponds to the oxidation of the poisoning intermediate CO. Figure 2 shows the ATR-IRAS simultaneously acquired with the LSV for the MOR at the Pt 50 Ru 50 electrode. At the low-potential region less positive than the E onset in Figure 1, strong bipolar-shaped bands and some positive bands are observed at 2050-1700 cm −1 , which can be assigned to the stretching mode of linearly bonded CO (CO L ) at the Pt site (2050 cm −1 ), [23][24][25][26] CO L adsorbed at Ru sites (1940-2000 cm −1 ), [28,29] and the stretching mode of bridge-type CO (CO B , 1700-1900 cm −1 ). [25,26,30] These results indicate that methanol is dehydrogenated to CO ad predominantly while keeping the potential at 0.10 V on the Pt-Ru electrode.…”

“…[25][26][27][28] We prepared thin-film Pt or Pt alloy (about 10 nm thick) electrodes on the flat plane of a silicon semicylindrical prism by Ar-sputtering Pt and the second metal targets simultaneously. The resulting alloy composition was determined by energy-dispersive X-ray fluorescence spectroscopy (EDXRF).…”

“…Because such sharp bands were also clearly observed at the pure Ru electrode but not at pure Pt, [28] water molecules were probably adsorbed at Ru sites. The bands at 1315 and 1390 cm −1 (very weak) can be assigned to COO − , COOH, [23,26] or HCOO − (adsorbed formate [33] ). The decrease of the height in the negative bands with increasing potential implies that the concentrations of these species increase with the potential, i.e., they are the reaction intermediates generated at a highpotential region.…”

Attenuated Total Reflection Surface-Enhanced Infrared Absorption Spectroscopy: a Powerful Technique for Bioanalysis

“…Physical methods, normally referring to vacuum evaporation [10,21,29] and vacuum sputtering [43][44][45], are the first and extensively used approaches. With physical methods, metal films containing island nanoparticles can be directly deposited on the prism.…”

Pathways for the Non‐CO‐Involved Oxidation of Methanol on Pt(111)

“…[18,19] However, there is no consensus on the nature of the reactive intermediates in the non-CO pathway. By using in situ IR reflection-absorption spectroscopy or surface-enhanced IR absorption spectroscopy in the Kretschmann (attenuated total reflectance, ATR) configuration, various adsorbates, such as formyl (-HCO) ad , [20] carboxy (-COOH) ad , [20] a dimer of formic acid (HCOOH) 2ad , [21] and formate (HCOO-ad ), [2] were identified as reactive intermediates for methanol electro-oxidation. Similar to CO ad , formate was also argued to be a catalystpoisoning intermediate.…”