Subsurface Enrichment in Highly Active Dealloyed Pt-Ni Catalyst Nanoparticles for Oxygen Reduction

Optimization of near surface structure of Pt-bimetallic nanoparticles is an important way to develop highly active fuel cell catalyst. Here, we present the synthesis of homogenous Pt-Ni alloy nanoparticles with different Nirich compositions (PtNi, PtNi3 and PtNi5) by organic solution approach, which showed 3-5 fold increases in Ptmass normalized activity of oxygen reduction reaction (ORR) compared to conventional Pt catalyst after a electrochemical dealloying process. Using aberrationcorrected scanning transmission electron microscopy combined with electron energy loss spectroscopy, we found that there is a strong tendency of subsurface enrichment of Ni in the dealloyed nanoparticles depending on the initial catalyst compositions, which therefore resulted in unusual core-shell structures. Based on this, a correlation of near-surface compositions to the high ORR activities of the dealloyed Pt-Ni catalyst nanoparticles was established.