We present a detailed characterization of the pyrochloreBi2Ir2O7prepared by a one-step hydrothermalsynthesis route from aqueous sodium hydroxide solution of NaBiO3·2H2O and IrCl3·5H2O in the presence of Na2O2at 240 °C.Using 5 M NaOH solution as the reaction medium, a fine powder of polycrystallineBi2Ir2O7with an average crystalsize of 10 nm and surface area of ∼46 m2g–1is produced. Structure refinement against powder neutron diffractionreveals a stoichiometric pyrochlore with no evidence for significantoxide-ion defects. X-ray absorption near-edge structure (XANES) spectrarecorded at both metal LIII-edges show that, although Biis present solely as Bi3+, there is evidence for the oxidationof iridium slightly beyond +4. This would suggest some surface oxidationof iridium, which is also shown by X-ray photoelectron spectroscopy(XPS) measurements. Magnetization data, as a function of temperature,show that the system is paramagnetic down to a temperature of 2 K,while the electrical conductivity shows hydrothermal Bi2Ir2O7to be a metallic conductor. In electrochemicaltests, performed on rotating disk electrodes fabricated from the powderediridate and Nafion solution, the material shows oxygen evolution activityin acidic solution, comparable to the most active precious-metal oxidematerials, with reproducibility over >1000 cycles, demonstratingtheformation of robust electrodes. [ABSTRACT FROM AUTHOR]