Glycerol (GlOH) accumulation and its very low price constitute a real problem for the biodiesel industry. To overcome these problems, it is imperative to find new GlOH applications. In this context, electrochemistry arises as an important alternative to the production of energy or fine chemicals using GlOH as a reactant. To make these opportunities a reality, it is fundamentally necessary to understand how the glycerol electro-oxidation reaction (GEOR) occurs on catalysts used in real systems. Thus, research using model surfaces generates the first insight into the electrochemistry of extremely complex real catalysts. Accordingly, in this work, we generate Pt(100) disturbed surfaces in a reproducible manner, carefully controlling the surface defect density. Then, GEOR is studied on well-ordered Pt(100) and on the disturbed Pt(100) surfaces in 0.5 M H 2 SO 4 using cyclic voltammetry (CV) and in-situ Fourier transform infrared spectroscopy (FTIR). The CV profile of GEOR consists of a single peak in the positive scan. The onset reaction displays the influence of defects present on the surface. On a surface with a high degree of disorder, the main GlOH oxidation process begins at 0.8 V vs. RHE, whereas for well-ordered Pt(100), it starts 0.1 V earlier. FTIR experiments show the presence of carbon monoxide and carbonyl absorption bands. The electrochemical and spectroelectrochemical results are supported by computational calculations (DFT) showing that both CO and GlOH bind more strongly on disturbed than well-ordered surfaces. Thus, our experiments show that Pt-CO (or other GlOH residue) bond breaking may be the GEOR rate determining step.

The glycerol electrooxidation reaction (GEOR) has attracted huge interest in the last decade due to the very low price and availability of this polyol. In this work, we studied the GEOR on Pt(111) electrodes by introducing different densities of random defects. Our results showed that the generation of defects on Pt(111) slightly modified the GEOR onset potential, however it generates changes in the voltammetric oxidation charges and also in the relative production of CO to carbonyl containing compounds, C[double bond, length as m-dash]O. The voltammetric profiles in the forward scan show two oxidation peaks. FTIR data show that the first one is connected with the GlOH dissociative adsorption to form CO (and others intermediates) while the second one, at higher potentials, matches the onsets of the CO oxidation to CO and the C[double bond, length as m-dash]O production. FTIR also confirms that the lower activity of defected electrodes at lower potentials is connected to a higher CO poisoning. DFT calculations show that the presence of CO molecules on a Pt defected surface keeps water and GlOH molecules far from the surface and linked by H bonds. This paper is the last of a series of three works where we explore the GEOR on an important number of different Pt surfaces. These works show that it is difficult to oxidize GlOH at potentials lower than 0.6 V (under our experimental conditions) without suffering an important electrode poisoning (mainly by CO). Since the structure of nanoparticles might be mimicked by defected single crystals, these sets of reports provide a considerable amount of information concerning the influence of such surfaces towards GlOH reaction in acidic media. Therefore, if the well-known "nano"-effect does not produce substantial changes in the activity of Pt materials, they are not useful to be applied in a Direct Glycerol Fuel Cell (DGFC). On the other hand, it is very interesting that the density of electrode defects permits us to tune the relative production of CO to C[double bond, length as m-dash]O.

We investigate the electrooxidation of glycerol (GlOH) on polycrystalline Pt. The results obtained in the presence of GlOH were compared with those of fresh and disturbed low‐index Pt single crystals [(111), (100) and (110)]. Monitoring of the oxidation currents of GlOH by cyclic voltammetry on the different surfaces revealed that the electrooxidation of GlOH is highly sensitive to the order of the polycrystalline Pt atoms. Interestingly, after being disturbed by the application of voltammetric cycles, the combined responses of the disordered single crystals become similar to that of polycrystalline Pt. The changes in the current values associated with the specific potentials at which each oxidation peak takes place suggest that different ordered domains of Pt oxidize GlOH independently. This simple approach can clearly assist in our understanding of the effect of the order of surface atoms in a given reaction, not only in electrochemical reactions.

Glycerol electrooxidation reaction (GEOR) in alkaline media was studied on the Pt(111) electrode with in situ FTIR and electrochemical methods. Cyclic voltammogram profiles display strong electrode deactivation after the first potential scan. Chronoamperometric pulses demonstrate that the deactivation is a result of the reaction intermediates yielded during the faradaic process. In situ FTIR shows evidence that the strongly adsorbed intermediate formed during GEOR is an acyl species which remains present on the surface within the potential window studied.

CO oxidation curves on the Pt(111) electrode in the presence and the absence of CO are simulated using a mean field Langmuir-Hinselwood mechanism, in which the rate-determining step is an electrochemical reaction between adsorbed CO and adsorbed OH. The OH adsorption process has been modeled using a Frumkin isotherm that reproduces the experimental OH adsorption behavior on the clean Pt(111) electrode. From the results of the simulation, the rate constants of the different steps in the mechanism are determined. Although the model reproduces quite well the main characteristics of the chronoamperometric and voltammetric curves, some deviations are observed due to factors that cannot be included in the model. These factors are the existence of a nonhomogeneous distribution of defects on the surface of a real Pt(111) electrode, the CO-CO and OH-CO interactions in the adsorbed adlayer, and the nonhomogeneous flux of the CO from the bulk to the electrode surface. Using the model, the effective Tafel slope that would have been obtained experimentally is calculated and compared to the literature values in order to understand the wide range of different values reported. Those differences can be easily justified maintaining the same mechanism, but with a different OH adsorption behavior.

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The electrooxidation of small organic molecules on platinum surfaces usually involves different structure-dependent steps that include adsorption and desorption of various species and multiple reaction pathways. Because temperature plays a decisive role on each individual step, understanding its global influence on the reaction mechanism is often a difficult task, especially when the system is studied under far from equilibrium conditions in the presence of kinetic instabilities. Aiming at contributing to unravel this problem, herein, we report an experimental study of the role played by temperature on the electrooxidation of formic acid on a Pt(100) electrode. The system was investigated under both close and far from equilibrium conditions, and apparent activation energies were estimated using different strategies. Overall, comparable activation energies were estimated under oscillatory and quasi-stationary conditions, at high potentials. At low potentials, the poisoning process associated with the formic acid dehydration step presented a negligible dependence with temperature and, therefore, zero activation energy. On the basis of our experimental findings, we suggest that formic acid dehydration is the main, but maybe not the unique, step that differentiates the temperature dependence of the oscillatory electrooxidation of formic acid on Pt(100) with that on polycrystalline platinum.