(617em) Enhanced Electro-Kinetics of CO2 Generation for Ethanol Oxidation Using Catalysts with a Partially Oxidized Pt and Rh Core and a SnO2 Shell

Authors: 
Teng, X., University of New Hampshire

Direct ethanol fuel cell
(DEFC) is a promising technology for generating electricity via the
electro-oxidation of liquid ethanol. Its implementation requires the
development of anode catalysts capable of producing CO2 and yielding 12-electron transfer through
breaking C-C bond of ethanol. To evaluate the capability to break
C-C bond over catalysts, here we designed an electrochemical cell equipped with
a CO2 microelectrode, through which CO2 partial pressure
and current density could be obtained simultaneously. Then CO2
generation rate and selectivity as functions of potential were calculated in
0.5M H2SO4/0.5 M ethanol solution. In this work, the Pt/Rh/Sn catalysts with different Pt
and Rh ratios were synthesized using surfactant free approach. Reduced Pt/Rh/Sn
samples were prepared by reducing the as-made Pt/Rh/Sn catalysts in H2/Ar mixture. Both as-made and reduced samples were
characterized by transmission
electron microscopy (TEM), scanning transmission electron
microscope-electron energy loss spectroscopy (STEM-EELS), X-ray diffraction (XRD), and X-ray absorption
spectroscopy (XAS). We demonstrated that the as-made sample was the tri-phase
PtRhOx-SnO2 catalysts
with a partially oxidized Pt and Rh core and a SnO2 shell, and the reduced sample was the
bi-phase PtRh-SnO2 catalysts
with a metallic PtRh alloy core and a SnO2
shell. The comprehensive kinetics studies showed that PtRhOx-SnO2 catalysts coincided with a 2.5-fold
increase in the CO2 generation
rate towards ethanol oxidation reaction at 0.35V, compared with PtRh-SnO2 and commercial Pt. PtRhOx-SnO2
also exhibited lower onset potential of CO2 generation and
higher CO2 selectivity than PtRh-SnO2.These in situ studies provided insight on the
design of a new genre of electro-catalysts with a partially oxidized noble
metal.