Pt deposited Pt-Pd/C electrocatalysts with the enhanced oxygen reduction activity

Reducing the cost of state-of-the-art Pt electrocatalysts while maintaining their oxygen reduction performance is always a hotspot in fuel cell research owing to their significant economic benefit for the commercialization of polymer electrolyte membrane fuel cells. Herein, we report a simple and cost-effective synthesis of Pt-Pd catalysts and a systematic study of their characteristics and catalytic performances for the oxygen reduction reaction (ORR). Pt-Pd bimetallic catalysts were prepared by a simple chemical deposition of Pt on the surface of Pd particles using a commercial Pd/C catalyst. During the synthesis, Pt precursor was reduced, and Pt layers were preferentially overgrown on the surface of the preexisting Pd particles resulting in Pd at Pt core-shell particles, which are favorable for ORR. By varying Pt precursors and the amount of Pt deposited, the physicochemical and electrochemical properties of the Pt-Pd catalysts were optimized. The formation of a thin Pt layer on Pd surface is more favorable, when using Pt(NH₃)₄Cl₂·xH₂O rather than H₂PtCl₆·xH₂O. As the amount of Pt increased from 0 to 10%, the surface properties of metal particles changed to similar to that of Pt, and the resulting catalysts mainly consist of a Pt-rich layer with a Pd core such as the Pd at Pt core-shell configuration. Pt(10%)Pd/C catalyst prepared by using Pt(NH₃)₄Cl₂·xH₂O exhibited a significant improvement in the ORR with the mass activities of 221 and 53 mA/mg_PGM at 0.85 and 0.9 V, respectively, which are beatable values compared to those (219 and 59 mA/mg_Pt at 0.85 and 0.9 V) of commercial Pt/C catalysts. The performance improvement of our bimetallic Pt-Pd/C catalysts mainly originate from the formation of an active Pt surface on the Pd core. In addition, considering that Pd is generally less expensive than Pt, these catalysts should have much better ORR performance and more feasibility of decreasing the total cost of fuel cells. In this study, the characteristics, electrochemical behaviors, and ORR performance improvements of the simply prepared Pt(x)-Pd/C core-shell catalysts were systemically investigated and are discussed.