(561b) Enhancing Complete Oxidation of Ethanol during the Electrochemical Reforming Process for Hydrogen Production (Invited)

Energy demands coupled with concerns over environmental pollution have created a great need for clean and efficient power sources. Ethanol, recognized as a substantial energy source in the green technologies, has many advantages as a fuel in energy conversion process. We have been developing a highly energy-efficient process for hydrogen production via the ethanol electrochemical reforming (EER, C2H5OH + 3H2O = 6H2 + 2CO2) in a proton exchange membrane (PEM) cell, where the hydrogen evolution reaction (HER) happens at the cathode and ethanol oxidation reaction (EOR) happens at the anode. Our objective is to develop catalysts for the high reactivity and selectivity to H2 formation via complete oxidation of ethanol into CO2 at the anode (the bottleneck of EER process). Ethanol is the simplest molecule containing C-C, C-H, C-O and O-H bonds, and the selective cleavage of these bonds determines reaction pathways and relative selectivity of products. For example, EOR via C-C bond-cleavage pathway leads to the production of CO₂ through a complete oxidation of ethanol with a twelve-electron transfer, while cleavage of C-H, O-H and/or C-O bonds without C-C bond lead to incomplete oxidation with production of acetaldehyde (two-electron transfer) or acetic acid (four-electron transfer).

In this talk, I will present our recent studies of electro-kinetics of the CO₂ generation on Pt/SnO2 binary catalysts and Pt/Rh/Sn ternary catalysts. Our studies showed that several special catalyst structures were able to enhance the electro-kinetics of the CO₂ generation by C-C splitting of the ethanol molecule. For example, in Pt/SnO₂ core shell structure, a thin SnO₂ shell were able to increase the reactivity and selectivity of CO₂ generation especially in high overpotential range. In Pt/Rh/Sn ternary structure, the tri–phase PtRhO_x-SnO₂ catalysts with a partially oxidized Pt and Rh core and a SnO₂ shell, coincided with a 2.5-fold increase in the CO₂ generation rate towards ethanol oxidation reaction, compared with the bi-phase PtRh-SnO₂ catalysts with a metallic PtRh alloy core and commercial Pt. These interesting results provided insight on the design of a new genre of electro-catalysts with a partially oxidized noble metal.