Exploring the Surface Segregation of Rh Dopants in PtNi Nanoparticles through Atom Probe Tomography Analysis

Proton-exchange membrane fuel cells hold promise as energy conversion devices for hydrogen-based power generation and storage. However, the slow kinetics of oxygen reduction at the cathode imposes the need for highly active catalysts, typically Pt or Pt based, with a large available area. The scarcity of Pt increases the deployment and operational cost, driving the development of novel highly active material systems. As an alternative, a Rh-doped PtNi nanoparticle has been suggested as a promising oxygen reduction catalyst, but the three-dimensional distributions of constituent elements in the nanoparticles have remained unclear, making it difficult to guide property optimization. Here, a combination of advanced microscopy and microanalysis techniques is used to study the Rh distribution in the PtNi nanoparticles, and Rh surface segregation is revealed, even with an overall Rh content below 2 at. %. Our findings suggest that doping and surface chemistry must be carefully investigated to establish a clear link with catalytic activity that can truly be established.