Enhancing Role of Nickel in the Nickel–Palladium Bilayer for Electrocatalytic Oxidation of Ethanol in Alkaline Media

Direct ethanol fuel cells (DEFCs) have been widely studied because of their potential as a high-energy density and low-toxicity power source of the future. Suitable catalysts for the anode reaction, however, are necessary to fully utilize the advantages of DEFCs. In this paper, we fabricated nickel (Ni)�palladium (Pd) bimetallic catalysts with a bilayer structure, using sputtering deposition on a titanium (Ti) foil substrate, and investigated the activity and stability of the catalysts toward ethanol electro- oxidation in alkaline media. Our results suggest that while Pd is the active component and Ni has negligible activity toward ethanol oxidation, Ni-modified Pd (NiPd/Ti) provides the best activity in comparison to PdNi/Ti and the monometallic catalysts. In fact, optimizing the Ni amount could lead to a highly active and stable bimetallic electrocatalyst because of Ni's ability to increase the active surface area of the Pd layer, provide hydroxyl species to replenish the active sites, and act as a protective layer to the Pd. Overall, these results provide a better understanding on the role of Ni in bimetallic catalysts, especially in a bilayer configuration, to allow the use of an ethanol oxidation reaction (EOR)-active electrocatalyst with a much lower Pd content.