Nano-Structured Pd-Sn Catalysts for Alcohol Electro-Oxidation in Alkaline Medium

The study of alcohols electrooxidation is of paramount importance not only for direct fuel cell and/or electrolysis cell applications, but also in order to gain the fundamental knowledge on reaction mechanisms for electrosynthesis applications.

Tin is known to be a high performance co-catalyst of noble metal for alcohol oxidation, particularly concerning the ethanol electrooxidation reaction in acidic medium.  This property of tin in association with palladium was recently confirmed for the electrooxidation of methanol, ethanol, and ethylene glycol in alkaline medium.

Here, the electrocatalytic behavior of Pd₁Sn_xcatalysts towards the electrooxidation of different C1, C2 and C3 alcohols is compared and discussed in terms of activity and reaction pathways: methanol and ethylene glycol since they are the simplest alcohol and polyol, respectively, ethanol and glycerol because they can both be produced from biomass, and isopropanol which only bears a secondary alcohol function, because it can be interesting for the development of “rechargeable” direct fuel cells.  

Particularly, the occurrence of two possible mechanisms, a base-catalyzed one and a mechanism based on the ability of the catalytic surface to favor the adsorption and desorption of species at low potentials, is discussed, as well as the difference in activity comparing isopropanol and glycerol oxidation reactions.

For this purpose, active self-supported Pd₁Sn_x catalysts are synthesized by the Sacrificial Support Method (SSM). Their catalytic activity towards the oxidation of C1 to C3 alcohols was determined in alkaline medium. The comparison of the activity allowed discarding a first base catalyzed deprotonation reaction of alcohols as rate determining step (rds), and spoke up for a mechanism involving a C-adsorption of carbon bearing an alcohol function. By comparing isopropanol and glycerol oxidation voltammograms, and on the basis of in situFTIR spectroscopy measurements, it has been shown that desorption of dihydroxyacetone could be the limiting step for glycerol oxidation at low potentials.

Acknowledgement: Anna Zalineeva thanks the Center for Emerging Energy Technologies, Farris Engineering Center (UNM) for assistance and technical support, and the County Council of Poitou-Charentes (France) for financial support.