Surface diffusion-limited dealloying: A strategy for porosity construction in small-sized alloy nanoparticle electrocatalysts

The formation of porosity within nanoparticles via dealloying is notably constrained by the dimensions of the precursor particles, a limitation stemming from the surface kinetic processes occurring during dealloying. In this study, we present a straightforward methodology, specifically tailored for fabricating diminutive nanoporous alloy nanoparticles, originating from their small-sized precursor counterparts. We initiated our research with precursor PtNi alloy nanoparticles which possess an average diameter of 9 nm. By incorporating an extrinsic metal, Ir, known for its slower surface diffusion on the nanoparticle surface, we successfully modulated the surface migration velocity of Pt during the dealloying process of the PtNi alloy nanoparticles. This precise manipulation led to the formation of an abundantly complex nanoporous structure on diminutive PtNi nanoparticles. Owing to their enhanced high surface area-to-volume ratio and the synergistic alloy effect, electrochemical tests revealed that the Ir-coated diminutive nanoporous PtNi nanoparticles exhibit superior electrocatalytic activities towards oxygen reduction and formic acid oxidation reactions. Furthermore, the presence of Ir on the surface effectively suppresses the surface diffusion rate of Pt, thereby significantly inhibiting the coarsening evolution of the porous metallic structure. This intervention ensures the long-term preservation of both structural integrity and catalytic stability.