Stability of multifunctional Pd–Rh electrocatalysts supported on Co₃O₄(111) in alkaline environment: impact of the electronic metal–support interaction

The stabilities of monometallic Rh and Pd nanoparticles and bimetallic Pd-Rh core-shell nanoparticles supported on Co₃O₄(111) thin films grown on Ir(100) were investigated with respect to the oxidation state and dissolution in alkaline electrolyte under the conditions relevant for electrochemical ethanol oxidation. Towards this aim, the well-defined model systems were characterized by means of synchrotron radiation photoelectron spectroscopy coupled with an <i>ex situ</i> emersion electrochemical cell (EC-SRPES) and scanning tunneling microscopy (STM). We found that the electronic metal-support interaction (EMSI) has a strong influence on the oxidation state of Rh, resulting in a strong oxidation and anchoring of the oxidized Rh³⁺ species on the surface of Co₃O₄(111). Consequently, the EMSI prevents the dissolution of Rh into the electrolyte regardless of the potential range. In contrast, it has no effect on the oxidation state and dissolution of Pd in the potential range of 0.3-1.1 V_RHE. However, extending the potential range to 0.3-1.5 V_RHE results in a stronger dissolution of Pd due to the reversible oxidation/reduction of Pd, which is enhanced in the presence of the EMSI. Most importantly, the magnitude of the EMSI and, thus, the extent of noble metal oxidation, can be effectively controlled by the nature of the metal/Co₃O₄(111) interface in the bimetallic Pd-Rh core-shell nanoparticles.