(Invited) Towards Solving the Long Standing Mystery of the Chemical State of Co in Pt_xCo_1-X to Boost HOR and ORR

Recently, Pt-based core-shell nanoparticles (NPs) have emerged as highly active catalyst materials to accelerate the sluggish oxygen reduction reaction (ORR) in acidic media as well as the hydrogen oxidation reaction (HOR) in alkaline. Less attention has been payed to the chemical state of the less noble metal after forming core-shell NPs. Intuitively; a metallic state of the less noble metal inside the particles has been suggested from many research groups. In this talk, we will show a new catalyst concept for Pt-Co nanoparticles by manipulating the surface arrangement and composition induced by the reaction conditions. More precisely, our catalysts exhibit superior Pt surface area-based specific activities (up to 10-fold) and Pt mass-based activities (up to 5-fold) towards the ORR compared to commercial Pt/C at 0.95 VRHE. In addition, we will show the influence of the chemical state and surface enrichment of the cobalt on the HOR activity in alkaline media. Altogether, we will solve the long standing mystery of the chemical state of the cobalt and its distribution for PtxCo1-x nanoparticles and its remarkable effect on the catalytic performance for HOR and ORR.