Enhanced Performance of IrOx-Modified Copi Electrodes and the Characterization

The CoPi electrode films supported on ITO glass plates were modified with iridium oxide nano nanoparticles. This IrO_x-modified CoPi electrodes showed Tafel slopes of ~30 mV per decade during OER at the pH between 4.5 and 13.9. The overpotentials were less than 0.2 V and the turnover frequency (TOF) was 68,631 h^-1 (based on the Ir atom) at 1.3 V vs. Ag/AgCl at pH 7. The TOF is the highest value ever observed from IrO₂ catalysts tested for electrochemical water oxidation. The mechanism during water oxidation was studied by an in-situ X-ray absorption spectroscopy to explain the unusually high catalytic activity. In the fully oxidized state the amounts of edge-sharing CoO₆ octahedra bond and extended planes of CoO₆ octahedra increased whereas those of IrO₆ octahedra bond and extended planes of IrO₆ octahedra decreased. These results demonstrate that the water oxidation occurred by transferring oxygen from Ir-O to Co-O generating O₂ molecules. The details of the mechanism and the related research results obtained from our lab will be presented.