The electrochemical oxidation of ethanol on platinum, rhodium, and platinum−rhodium electrodes is studied using on-line differential electrochemical mass spectrometry (DEMS) and in-situ infrared spectroscopy (FTIR). The data were normalized using the oxidation of a CO monolayer in order to compare the activity of the different electrodes. Three products have been detected, namely CO2 and acetaldehyde (detected by DEMS) and acetic acid (detected by in-situ FTIR, since acetic acid is not volatile enough to be detected by DEMS). It is found that rhodium is the far less active electrocatalyst for ethanol electrochemical oxidation. Pure platinum and Pt90Rh10 present similar overall normalized current density, but Pt90Rh10 presents a better CO2 yield than pure platinum. The best CO2 yield is found for the Pt73Rh27 electrodes. The acetaldehyde yield decreases as rhodium is added to the electrode. The ratio CO2/CH3CH2O increases when rhodium is added to the electrode. The possible reasons for the different reactivity for the studied electrodes is discussed in terms of C−H bond activation and C−O bond coupling on the different surfaces.

The particle size effect observed on the performance of Pt/C electrocatalysts toward the methanol oxidation reaction (MOR) has been investigated with differential electrochemical mass spectrometry (DEMS). The investigation has been conducted under both potentiodynamic and potentiostatic conditions as research on methanol electrochemical oxidation is closely related to interest in direct methanol fuel cells. The particle size effect observed on the MOR is commonly regarded as a reflection of different Pt-CO and Pt-OH bond strengths for different particle sizes. This work focuses mainly on the mechanism of methanol dehydrogenation on platinum which is central to the problem of the optimization of the efficiency of methanol electro-oxidation by favoring the CO(2) formation pathway. It was found that the partitioning of the methanol precursor among the end products on supported platinum nanoparticles is strongly dependent on particle size distribution. Also, it is postulated that the coupling among particles of different sizes via soluble products must be considered in order to understand the particle size effects on the observed trends of product formation. An optimum particle size range for efficiently electro-oxidizing methanol to CO(2) was found between 3 and 10 nm, and loss in efficiency is mostly related to the partial oxidation of methanol to formaldehyde on either too small or too large particles. The possible reasons for these observations are also discussed.

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Sum-Frequency Vibrational Spectroscopy (SFVS) has been used to investigate the effect of nitrogen-flow drying on the molecular ordering of Layer-by-Layer (LbL) films of poly(allylamine hydrochloride) (PAH) alternated with poly(styrene sulfonate) (PSS). We find that films dried by spontaneous water evaporation are more ordered and homogeneous than films dried by nitrogen flow. The latter are quite inhomogeneous and may have regions with highly disordered polymer conformation. We propose that drying by spontaneous water evaporation reduces the effect of drag by the drying front, while during nitrogen-flow drying the fast evaporation of water "freezes" the disordered conformation of adsorbed polyelectrolyte molecules. These findings are important for many applications of LbL films, since device performance usually depends on film morphology and its molecular structure.