Electrochemical determination of the degree of atomic surface roughness in Pt-Ni alloy nanocatalysts for oxygen reduction reaction

Abstract

Pt-Ni alloy nanocrystals with Pt-enriched shells were prepared by selective etching of surface Ni using sulfuric acid and hydroquinone. The changes in the electronic and geometric structure of the alloy nanoparticles at the surface were elucidated from the electrochemical surface area, the potential of zero total charge (PZTC), and relative surface roughness, which were determined from CO- and CO2-displacement experiments before and after 3000 potential cycles under oxygen reduction reaction conditions. While the highest activity and durability were achieved in hydroquinone-treated Pt-Ni, sulfuric acid-treated one showed the lower activity and durability despite its higher surface Pt concentration and alloying level. Both PZTC and Q CO 2 /Q (CO) ratio (desorption charge of reductively adsorbed CO2 normalized by COad-stripping charge) depend on surface roughness. In particular, Q CO 2 /Q (CO) ratio change better reflects the roughness on an atomic scale, and PZTC is also affected by the electronic modification of Pt atoms in surface layers. In this study, a comparative study is presented to find a relationship between surface structure and electrochemical properties, which reveals that surface roughness plays a critical role to improve the electrochemical performance of Pt-Ni alloy catalysts with Pt-rich surfaces.