Structure and electrochemical properties of PtIrRu, PtIrRhRu and PtIrPdRhRu nanoparticles synthesized by alcohol-mediated reduction methods

Entropy effects are commonly believed to enhance the catalytic properties of metallic alloys due to the tailoring of the binding energy to the catalyst surface. Here, the entropy effect is explored through the synthesis of PtIrRu, PtIrRhRu and PtIrPdRhRu nanoparticles using two different solvothermal methods and by a hot injection precipitation approach at two different pH conditions. A total of 12 samples is studied by high-resolution synchrotron powder X-ray diffraction (PXRD), showing the formation of single-phase alloys in all cases. An improved structural description of the smallest crystallite samples (< 1 nm) is obtained using a decahedral model. Decahedral twinning in those particles was confirmed by transmission electron microscopy (TEM). Elemental distribution maps from scanning transmission electron microscopy coupled with energy dispersive X-ray spectroscopy (STEM-EDX) show that the compositions are close to nominal and that the solvothermal continuous flow method renders the most homogeneous products. The electrocatalytic properties towards the oxygen evolution reaction (OER) are evaluated with a rotating disk electrode (RDE) setup. The measured overpotentials differ significantly between the four sets of samples, indicating a significant influence of the microstructure on the electrocatalytic process. The PtIrRu samples are the most active, although the stability is the largest for PtIrPdRhRu.