Glycerol electrochemical oxidation

Alkaline glycerol electrochemical oxidation on Pt-Pd alloys is dependant on the surface composition of the alloys. Compared with the pure metals, enhanced activity is found when the alloy contains about 33% Pd, leading to a synergetic effect [63]. 

Fuels cells are of interest both from energetic and environmental considerations. When methanol is fed directly to an anode, as in Direct Methanol Fuel Cells , electric power is generated, making the devices suitable for small and lightweight uses [53], Alternative fuels such as polyhydric alcohols like ethylene glycol and glycerol are much less volatile and toxic, on the one hand, and electrochemically oxidizable on the other [54]. Therefore, the electrochemical oxidation of various polyhydric alcohols has been investigated in acidic as well as in alkaline conditions. 

The electrochemical oxidation of polyhydric alcohols, viz. ethylene glycol, glycerol, meso-erythritol, xilitol, on a platinum electrode show high reactivity in alkaline solutions of KOH and K2C03 [53]. This electro-oxidation shows structural effects, Pt(lll) being the most active orientation. This results from different adsorption interactions of glycerol with the crystal planes [59]. 

A. Nirmala Grace and K. Pandian, Pt, Pt-Pd and Pt-Pd/Ru nanoparticles entrapped polyaniUne electrodes - a potent electrocatalyst towards the oxidation of glycerol, Electrochem. Commun., 8,1340 1348 (2006). 

If, rather than with hydrogen or syngas, the MCFC system is fed with hydrocarbons or oxygenated compounds such as glycerol [16] or other alcohols [17-20], the fuel must typically undergo water steam reforming to be converted to mainly H2 prior to being introduced into the FC and electrochemically oxidized. 

The indirect electrochemical process for the regeneration of NAD" from NADH is very fast, which is indicated by a strong catalytic current in the presence of glycerol dehydrogenase, the oxidized cofactor, and 7e.so-l,2-cyclohexanediol as substrate [109]. 

According to the reaction scheme given in Fig. 26, the anaerobic oxidation of l-glycerol 3-phosphate was performed under the conditions of an indirect electrochemical process using a water-soluble ferrocene derivative as mediator in the presence of o-fruc-tose-1,6-diphosphate aldolase from rabbit muscle for the in situ generation of the carbohydrate product. With a mediator concentration fo 1.5 mM using about 80 U of immobilized enzyme, after 25 h a 75% turnover of the substrate L-glycerol phosphate... 

This paper will discuss the characteristics of this detector with respect to the above applications. Stable oxides are formed at potentials in excess of 200 mV vs. SUE. A chrono-coulorometric experiment has been used to follow the formation of the oxide layer, loss of silver due to the formation of soluble hydroxy species, and reduction of the oxide to metallic silver. With respect to carbohydrate oxidation, several factors are important including hydroxide concentration, temperature and potential. The long term stability has been considered and is analyte dependent. Many carbohydrates (i.e. glucose, fructose, galactose) do not cause any observable dimunition while some analytes (cytidine, glycerol) cause a noticable loss of sensitivity. In all cases the sensitivity can be restored by electrochemical treatment in which the oxide is reduced and regenerated. 

Previous studies about the glycerol oxidation in heterogeneous liquid phase [34-39] as well as in electrochemical environment [13, 40-42] show that glycerol react on metal surfaces through a complex mechanism that lead to the formation of a large variety of final reaction products, including compounds with one, two and three carbon atoms. There are evidences that the pH [13, 40, 41, 43], the nature of... 

Fernandez PS, Martins ME, Martins CA, Camara GA (2012) The electro-oxidation of isotopi-cally labelled glycerol on platinum new information on C-C bond cleavage and CO2 production. Electrochem Commun 15 14-17... 

On the other hand, the Pd/MWCNT electrode is electrochemically stable only for the oxidation of ethanol as the oxidation reactions of methanol and glycerol are featured by a fast increase of the overpotential (Fig. 13). 

Bianchini, Serp and cowoikers have also observed a remarkable effect of the MWCNTs on the alcohol diffusion. As shown in Figure 14a, a linear Sap/(V s ) relationship, typical of an electrochemical reaction under diffusion control, features the oxidation of ethanol on PD/MWCNT at scan rates lower than 350 mV s (Sap = specific peak current density). Above this scan rate, the slope decreases tending to a plateau, which has been ascribed to a reaction limited by other factors than substrate diffusion, for example the very low density of catalytic centers due to the extremely low Pd loading (17 pg cm ) as well as the slow desorption of the acetate product. A much narrower window of diffusion-controlled kinetics was observed for the oxidation of glycerol (Fig. 14b), the independence of the peak current density on the voltage scanning frequency being attained already at scan rates above 50 mV s and ascribed to the concomitant action of... 

Unlike ethanol oxidation, chronopotentiometric experiments of methanol and glycerol oxidation on Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C electrodes show a remarkable increase of the overpotential with time, the oxygen discharge potential being attained after 2.5 and 1.5 h with methanol and glycerol, respectively. In addition to decreasing the electrochemical stability of the electrodes, the oxidation of methanol and glycerol on Pd-(Ni-Zn)/C and Pd-(Ni-Zn-P)/C is also much slower tlm that of ethanol under comparable experimental conditions as shown by the CVs illustrated in Fig. 23. 

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