Reversible surface structural changes in Pt-based bimetallic nanoparticles during oxidation and reduction cycles

The surface states of supported PtNi nanoparticles treated at alternating O2 and H2 atmosphere were studied by X-ray photoelectron spectroscopy. Reversible structural changes at the surfaces of the supported PtNi nanoparticles in response to reaction gases were observed, showing NiO-rich surface in oxidizing gases and Pt-rich surface in reducing gases. The dynamic behaviors can be attributed to two opposite gas-driven mass transport processes at bimetallic particle surfaces, including surface segregation of Pt at the bimetallic particles in H2 and encapsulation of the particles by NiO in O2. The similar surface structural changes can be observed in other bimetallic catalyst systems, as exemplified in supported PtCu and PtCo nanoparticles.