Surfactant-Free Colloidal Strategies for Highly Dispersed and Active Supported IrO2 Catalysts: Synthesis and Performance Evaluation for the Oxygen Evolution Reaction

Supported Ir oxide catalysts obtained from surfactant-free colloidal Ir nanoparticles (NPs) synthesized in alkaline methanol (MeOH), ethanol (EtOH), and ethylene glycol (EG) are investigated and compared. The comparison of independent techniques such as transition electron microscopy (TEM), small angle X-ray scattering (SAXS), and electrochemistry allows shedding light on the parameters that affect the dispersion of the active phase as well as the catalytic activity. The colloidal dispersions obtained are suitable to develop supported catalysts with little NP agglomeration on a carbon support leading to highly active catalysts with more than 400 A g^-1_Ir reached at 1.5 V_RHE for the OER. While the more common surfactant-free alkaline EG synthesis requires flocculation and re-dispersion leading to Ir loss, the main difference between methanol and ethanol as solvent is related to the dispersibility of the support material. The choice of the suitable monoalcohol determines the maximum achieved Ir loading on the support without detrimental particle agglomeration. This simple consideration on catalyst design can readily lead to significantly improved catalysts.