Thermally Induced Strains on the Catalytic Activity and Stability of Pt–M₂O₃/C (M=Y or Gd) Catalysts towards Oxygen Reduction Reaction

Yttrium oxide and gadolinium oxide modified platinum nanoparticles supported on carbon (Vulcan XC‐72), noted as Pt–M 2 O 3 /C (M=Y and Gd), were synthesized by water‐in‐oil nanoemulsion chemical route, followed by heat treatment at 100 and 300 °C under hydrogen/nitrogen (H 2 /N 2 ) atmosphere and tested as electrocatalysts for the oxygen reduction reaction (ORR). As revealed by powder X‐ray diffraction analysis, all obtained catalysts showed solely Pt face‐centered‐cubic structure, and absence of a secondary phase before and after heat treatments, indicating that Y 2 O 3 and Gd 2 O 3 are highly disordered (amorphous) and dispersed clusters. The surface Pt:M ratio (M=Y and Gd), as revealed by X‐ray photoelectron spectroscopy, increased after heat treatment with respect to the value of as‐prepared samples, for which the ratio was 1:1. Microstrain data extracted from Williamson–Hall plots for Pt–M 2 O 3 /C (M=Y and Gd) catalysts surprisingly increased after heat treatment at 100 °C, remaining nearly constant after heat treatment at 300 °C, whereas the value of pure Pt nanoparticles, noted as Pt/C, decreased after heat treatments. The mean particle size derived from TEM images for Pt–M 2 O 3 /C (M=Y and Gd) was almost unchanged after heat treatments, at variance with the Pt/C case where a clear increase is observed. Surface specific activity and mass activity towards ORR obtained with as‐prepared Pt–M 2 O 3 /C (M=Y and Gd) catalysts were higher than those of as‐prepared Pt/C catalyst. After heat treatment, the ORR activity of Pt–M 2 O 3 /C (M=Y and Gd) augmented, whereas that of Pt/C diminished. Moreover, after 6000 cycles between 0.5 and 0.95 V versus reversible hydrogen electrode (vs. RHE), Pt–M 2 O 3 /C (M=Y and Gd) catalysts retained a large active surface area and a high kinetic current density at 0.9 V vs. RHE in comparison with Pt/C samples. These facts assess a positive effect of the interaction between M 2 O 3 (M=Y and Gd) and Pt catalytic centers both on the catalytic activity of the material towards ORR and on its durability.