Herein we investigate the effect of irreversibly adsorbed bismuth on polycrystalline platinum (Pt p) on the electrooxidation of glycerol in alkaline media by combining electrochemical, spectroscopic (in situ FTIR) and analytical (HPLC on line) techniques. We found that the activity of Pt p increases by about fivefold when the optimal quantity of Bi ions is added to the solution. Besides, the adatom strongly impacts the reaction products by suppressing the pathways with CC bond breaking, hindering the formation of CO (and other unknown intermediates) and enhancing the production of Glycerate. Different to the results in acid media for Pt p-Bi systems where Bi block the oxidation pathway through the primary carbon, glycerate is the main product in alkaline media and dihydroxyacetone is either produced in extremely low quantities or not produced. Besides, comparing our results with those in acid media, the peak current recorded at 1 mV.s-1 in this work was one order of magnitude higher. These results show the strong impact of the pH in the reaction rate and selectivity.

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.

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Herein we investigated the effect of the adsorption of Bi and Pb on polycrystalline platinum (Pt p ) on the electrooxidation of glycerol (EOG) in alkaline media by combining electrochemical, spectroscopic (in situ FTIR), and analytical (online HPLC) techniques. Besides, we used single crystal Pt electrodes to understand the effect of the modification of Pt p in terms of the atomic arrangements on its surface. We found that the activity of Pt p increases in the presence of Pb (Pt p −Pb), which acts by suppressing the pathways with complete CC bond breaking (to produce carbonate) and enhancing the production of glycerate, formate, tartronate, and glycolate. We also found that Pt(100) and Pt(111) are affected by the adsorption of both adatoms. However, the modification of Pt(110) explains the results obtained with Pt p . This basal plane is highly activated by Bi and Pb and its behavior is similar to those of Pt p −Bi and Pt p −Pb, respectively. These results permit the conclusion that the adatoms acts mainly by activating Pt atoms with low coordination, which generally binds the adsorbates more strongly and, in consequence, suffers more from poisoning. The adatoms act by preventing the formation of multiple bonded intermediates, likely through a combination of a third body effect and also to a change in the electronic configuration at the surface of the catalyst. We propose in this work that the higher promotion of the EOG by the adatoms in alkaline media is due to a stabilization of the negatively charged intermediates by the Coulombic interaction with the positively charged adatoms.

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