Hollandite Structure K(x≈0.25)IrO2 Catalyst with Highly Efficient Oxygen Evolution Reaction.

Oxygen evolution reaction (OER) catalysts with high activity are of particular importance for renewable energy production and storage. Here, we prepare Kx≈0.25IrO2 catalyst that exhibits an excellent OER activity compared to IrO2, which is univerally acknoweledged as a state-of-the-art OER catalyst. The prepared catalyst reflects a small overpotential 0.35 V at a current density of 10 mA cm(-2) and a lower Tafel slope (65 mV dec(-1)) compared to that for IrO2 (74 mV dec(-1)). The performed X-ray photoelectron spectroscopy (XPS) and X-ray adsorption (XAS) experiments indicate that the Ir-site of Kx≈0.25IrO2 has a lower valence and more Ir-5d occupied states, suggesting more electrons on the Ir site. The extra electrons located on the Ir site and distorted IrO6 octahedral symmetry have a significant effect on the 5d orbital energy distribution which is verified by our DOS calculation. The performed DFT calculations state that the Kx≈0.25IrO2 essentially obtains good OER performance because it has a lower theoretical overpotential (0.50 V) compared to IrO2 (0.61 V).