Electro-catalytic activity enhancement of Pd-Ni electrocatalysts for the ethanol electro-oxidation in alkaline medium: The promotional effect of CeO ₂ addition

Pd-Ni alloy catalysts with CeO₂ modification are prepared for the ethanol oxidation reaction (EOR) in alkaline electrolyte through the extensively utilized deposition-precipitation route. The structures, morphologies, surface compositions and catalytic activities of the un-modified and Ce-modified Pd-Ni alloy catalysts have been characterized by XRD, TEM, temperature programmed reduction (TPR) and electrochemical measurements, respectively. Physical characterizations show that the 5 wt.% of CeO₂ addition (Ce₅) can not only decrease the particle size of Pd-Ni but also promote the formation of surface Pd-Ni alloy species and amorphous NiO. CO stripping measurements and EOR results confirm that the surface Pd-Ni alloy and NiO species on Ce₅ can modify the adsorption capacity toward ethanol, provide an oxygen source for CO oxidation at low potential, and thus accelerate the decomposition rate toward ethanol. In addition, the long-term durability of Ce₅ is also improved due to its specific surface compositions. On the other hand, the excessive CeO₂ may result in blocking the active sites and alternation in surface conditions in which the Pd-Ni rich surface species gradually converts to only Pd ones, thereby leading to the significant deterioration of EOR activity.