Comparative study of catalytic activities among transition metal-doped IrO2 nanoparticles

Abstract

Abstract Catalytic activities of transition metal-doped IrO 2 nanoparticles (TM-IrO 2 NPs; TM = Cr, Mn, Fe, Co, or Ni) are compared for various oxidation reactions such as electrochemical oxygen evolution reaction (OER), gas-phase photo-oxidation of thiol function group, and CO oxidative conversion. Here, we discovered a series of TM-IrO 2 catalysts have a common activity trend for these oxidation reactions, and their activities are closely related with modified electronic states of IrO 2 , strongly affected by the types of the transition metal across the periodic table. For all oxidation reactions, Cr- and Mn-IrO 2 achieved the highest oxidation catalytic activity, and sequentially decreased activities were obtained with Fe, Co, and Ni doped IrO 2 . For instance, the highest OER activity was achieved by Cr or Mn doping exhibiting the smallest overpotential η = 275~230 mV at 10 mA/cm 2 , while Ni-IrO 2 showed rather larger overpotential (η = 347 mV) even compared with non-doped IrO 2 (η = 314 mV). Scanning transmission X-ray microscopy and high-resolution photoemission spectra of TM-IrO 2 indicated dopant metals modified the Ir-O interaction and thus increasing oxygen vacancy defects in IrO 2 . Strongly positive correlation was observed between the catalytic activities and vacancy states. The amount of defect related signals was observed the most for Cr- or Mn-IrO 2 , less so for Fe- or Co-IrO 2 , and unnoted for Ni-IrO 2 compared with bare IrO 2 . Based on these catalytic activities and surface spectroscopic analysis results, vacancy defects induced by doping in TM-IrO 2 NPs are proposed to contribute to enhance the oxidation activities.