Phase-Controlled Synthesis of Pd-Se Nanocrystals for Phase-Dependent Oxygen Reduction Catalysis.

Searching for highly efficient oxygen reduction reaction (ORR) electrocatalysts for fuel cell technology, in which the crystal structure plays a powerful role in regulating the electrocatalysis, is urgent yet challenging. Herein, we have explored the active and stable Pd-Se alloy electrocatalysts with controlled phase toward alkaline ORR. The phase-controlled Pd-Se nanoparticles (NPs) show interesting phase-dependent electrocatalytic performance, in which the Pd17Se15 NPs/C exhibits much better ORR performance than its counterpart, Pd7Se4 NPs/C, and the commercial Pd/C and Pt/C. Based on the detailed analysis, Pd in Pd17Se15 possesses more Se atom coordination and a higher valence state, thus providing a stronger capacity for the absorption of oxygenated species. DFT further reveals more charge transfer from the Pd17Se15 surface to the *OOH intermediate, which is the reason for the activity enhancement.