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Electrocatalytic Oxidation of Glycerol on Platinum

Liu, Yifan, Yu, Wenjian, Raciti, David, Gracias, David H., Wang, Chao
Journal of physical chemistry 2018 v.123 no.1 pp. 426-432
biodiesel, byproducts, carbon, carbon dioxide, carbon monoxide, catalysts, chemical bonding, cleavage (chemistry), dissociation, electrodes, energy, fuel cells, fuel production, glycerol, hydrogen, oxidation, platinum
Glycerol, a surplus byproduct of biodiesel production, is a promising energy source for fuel cells. However, the low selectivity toward the complete-oxidation product, carbon dioxide (CO₂), hinders the electro-oxidation of glycerol. In this work, we combine spectro-electrochemical studies of extended surfaces using sum frequency generation and product-resolved electrocatalytic measurements on high-surface-area catalysts under potentiostatic conditions to investigate the glycerol oxidation reaction on platinum (Pt). We observed adsorbing carbon monoxide (CO) as the reaction intermediate at potentials as low as 0.05 V (vs the reversible hydrogen electrode; the same potential scale is used throughout this discussion unless otherwise specified) on polycrystalline Pt electrode, indicating that cleavage of the C–C bond in glycerol is feasible on Pt. This observation is in contradiction to the low selectivity toward CO₂ (with a faradaic efficiency of <4%) measured by the electrocatalytic studies on Pt/C. The discrepancy is ascribed to the rather feasible cleavage of one terminal carbon to form *CO, but kinetically hindered oxidation of *CO and further dissociation of the remaining C₂ fragments at low potentials, whereas at high potentials partial oxidation pathways become more favorable due to suppressed C–C bond cleavage.