Highly Efficient Oxygen Evolution Activity of Ca(2)IrO(4) in an Acidic Environment due to Its Crystal Configuration

[Image: see text] We systematically characterized the perovskite-like oxides Ca(2)IrO(4) and CaIrO(3) as the oxygen evolution reaction (OER) catalysts. Compared with IrO(2), universally accepted as the current state-of-the-art OER catalyst, Ca(2)IrO(4) showed an excellent OER catalytic activity in an acidic environment, whereas CaIrO(3) did not. X-ray photoelectron spectroscopy (XPS) spectra showed that the oxidation of iridium in Ca(2)IrO(4) and CaIrO(3) was slightly beyond +4. X-ray absorption near-edge structure (XANES) spectra illustrated that the IrO(6) octahedral geometric structure in Ca(2)IrO(4) and CaIrO(3) showed differences. The IrO(6) octahedral is asymmetrically distorted and uniformly compressed in Ca(2)IrO(4) and CaIrO(3). Therefore, we propose that the IrO(6) octahedral distortion plays an important role in the OER activities.