A comparative study of activity toward ethanol oxidation was carried out for catalysts having the same loading of identical Pd nanoparticles supported on carbon-oxide hybrids containing antimony tin oxide (Sb 2 O 5 /SnO 2-ATO) in different amounts (20, 30 and 40 wt.%). Enhanced catalytic activity was observed for Pd nanoparticles supported on C-ATO hybrids. X-ray absorption spectroscopy experiments carried out around the Pd L 3 edge evidenced an increase in the electronic occupancy of the Pd 4d band indicating an electronic transfer from the hybrid supports to the Pd particles. A strong correlation between ethanol oxidation currents and X-ray absorption data reveals the importance of electronic effects in the electrocatalysis of ethanol oxidation on Pd. In addition, FTIR data show that C-ATO hybrid supports promote a decrease in the onset potential and an increase in carbonate/CO 2 production.

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A B S T R A C TOperando assessment of electronic properties near the Fermi level is essential to gain new insights into the mechanisms of electrochemical reactions as well as for the development of more efficient electrocatalysts. However, the high vacuum ambient needed for X-ray absorption measurements at low energies has made studies under electrochemical conditions quite challenging. Here, we describe an out-of-chamber setup with a new electrochemical cell that allowed us to performed operando X-ray absorption studies at the low energy of the Pd L3 edge. Using the new electrochemical cell, we were able to probe, for the first time, the changes in electronic properties of carbon-supported Pd nanoparticles induced by the electrochemical oxidation of the Pd surface. Our results demonstrate that the oxidation process produces an increase in the Pd 4d band vacancy, which indicates that charge is transferred from the metal to the adsorbed oxygenated species.

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