Electrochemical tuning of Pd100−xAux bimetallics towards ethanol oxidation: effect of an induced d-band center shift and oxophilicity

This study presents the influence of the Au content on the catalytic activity of Pd100−xAux catalysts for ethanol electrooxidation in alkaline media. Potentiostatic electrochemical synthesis of the catalysts is adopted to reduce the resistance at the catalyst support interface and ensure minimal precursor wastage. Characterization of the Pd100−xAux bimetallic catalysts has been done using field-emission scanning electron microscopy (FESEM), energy dispersive X-ray analysis (EDAX), EDAX elemental mapping, high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) studies. Cyclic voltammetry and chronoamperometry studies imply superior electrocatalytic activity of the Pd100−xAux compositions with at least 50% Au to Pd. The Pd70Au30 bimetallic demonstrates the lowest onset potential of 0.475 V vs. RHE and highest mass activity with excellent stability. The combined effects of increased hydroxyl coverage on the Au and a d-band center shift, due to the induced compressive strain, are correlated with the excellent catalytic activity of the Pd70Au30 bimetallic catalyst. This claim is verified by evaluating the catalytic activity and the d-band centers of the Pd100−xAux catalysts obtained from their valence band spectra. On the basis of experimental UPS data, the authors report a downward shift of the d-band center for the Pd70Au30 bimetallic, which ensures ‘optimal chemisorption’, leading to enhanced oxidation.