Porous palladium copper nanoparticles for the electrocatalytic oxidation of methanol in direct methanol fuel cells

A facile method has been demonstrated for the preparation of PdCu nanoparticles (NPs) with various morphologies from Pd²⁺ and Cu ²⁺ reduced by ascorbate in the presence of dodecyltrimethylammonium chloride (DTAC) at 95 °C. We have found that DTAC is important to assist the growth of PdCu with high-energy surfaces through the etching and capping of certain surfaces of Pd and PdCu seeds. By varying the Pd²⁺/Cu ²⁺ molar ratio, different morphologies of PdCu NPs have been prepared. Cubic PdCu NPs have a dominant Pd₃Cu composition when prepared at a high Pd²⁺/Cu²⁺ molar ratio (20/1), while porous PdCu NPs have a dominant PdCu₃ composition when prepared at a low Pd²⁺/Cu²⁺ molar ratio (1/10). The copper content not only controls the morphology, but also affects the catalytic activity toward the methanol oxidation reaction (MOR) in alkaline media. Upon increasing the copper content, the catalytic activity toward the MOR increases, mainly due to the advantages of the electroactive surface area, more direct cathodic oxide reduction (lower onset potential for the formation of Pd-OH), and synergistic effects. Porous PdCu NP-modified electrodes provide a higher catalytic activity (363 A g^-1) toward the MOR at a more negative onset potential (-0.62 V vs. Ag/AgCl) on the porous PdCu electrodes than commercial Pd/C-modified ones do (180 A g^-1) at -0.52 V. To the best of our knowledge, this is the first example using porous PdCu NP-modified electrodes as anodes under alkaline conditions in direct methanol fuel cells (DMFCs). With the advantages of high electrochemical activity, stability, and cost effectiveness, the porous PdCu NPs have great potential as anode catalysts for DMFCs.