Stable blue suspensions of 2 nm diameter iridium oxide (IrO x·nH2O) nanoparticles were obtained by hydrolyzing IrCl62- in base at 90 °C to produce [Ir(OH) 6]2- and then treating with HNO3 at 0 °C. UV-visible spectra show that acid condensation of [Ir(OH)6] 2- results in quantitative conversion to stable, ligand-free IrO x·nH2O nanoparticles, which have an extinction coefficient of 630 ± 50 M-1cm-1 at 580 nm. In contrast, alkaline hydrolysis alone converts only 30% of the sample to IrO x·nH2O at 2 mM concentration. The acidified nanoparticles are stable for at least one month at 2 °C and can be used to make colloidal solutions between pH 1 and 13. At pH 7 and above, some hydrolysis to form [Ir(OH)6]2- occurs. Uniform IrOx ·nH2O electrode films were grown anodically from pH 1 solutions, and were found to be highly active for water oxidation between pH 1 and 13.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Physical and Theoretical Chemistry