The unique Pd@Pt/C core-shell nanoparticles as methanol-tolerant catalysts using sonochemical synthesis

Over the past decades, there were a few reports on the use of sonochemical method to prepare noble metals catalysts for fuel cells. However, the synthetic processes were conducted under high frequency (200 kHz)/long reaction time in most cases. In this work, Pd and PdxPt nanoparticles were prepared by sonochemical method under low frequency (20 kHz) in a shorter time (20-40 mins). In the first time, a sequentialsonochemical synthesis was explored to achieve a core/shell structure of PdxPt nanoparticles. Consequently, the unique core-shell structure was formed with two shells surrounding the Pd core. The Pd core was firstly grown. In the second step, the Pd²⁺ ion existing in the Pd core reduced simultaneously with Pt⁴⁺ ion in the solution as the first layer of PdPt alloy. Further, the Pt layer was formed subsequently. The Pd-based catalysts exhibited a superior ORR selective activity and exceptional methanol-tolerance property compared with the commercial Pt/C catalyst. In 0.5 M CH₃OH + 0.5MH₂SO₄ solution, the best performance was achieved on Pd₃Pt/C catalyst with increased overpotential of 24 mV. However, overpotentials was increased 174 mV on commercial Pt/C catalyst. The excellent performance of the Pd₃Pt/C catalyst is ascribed to its combination of preferable growth of the Pd (1 1 1) plane, small particle size (∼4 nm), unique core/shell structure as well as the electronic effects between Pd and Pt. These results have demonstrated that the sequential ultrasonic synthesis is an effective method for the synthesis of binary/trinary catalysts in a green approach.