Nanostructured Antireflective Iridium Oxide Coating for Water Oxidation

By Baker, David R.; Graziano, Milena B.; Hanrahan, Brendan M.
Published in The Journal of Physical Chemistry C 2018

Abstract

Iridium oxide (IrOx) is one of the best catalysts for the aqueous oxygen evolution reaction (OER), and its activity is greatly impacted by surface characteristics. By reactively sputtering in a high O2 flow-rate environment, vertically oriented IrOx nanoplatelets grow several hundred nanometers high exhibiting large surface areas and antireflective optical properties across the visible spectrum. The nanoplatelet IrOx surface is electrochemically compared to other morphologies of IrOx surfaces for OER activity. It was found that the nanoplatelet IrOx surface outperforms all other tested morphologies and planar Ir-metal by exhibiting higher currents and lower overpotentials. Longevity testing of catalytic activity shows that the nanoplatelet surface is more stable in a wide pH range. Characterization with X-ray diffraction and X-ray photoelectron spectroscopy shows that the stoichiometry and oxidation states are similar between the different morphologies of IrOx, but the preferred crystallographic orientation of the rutile IrOx film changes at higher O2 flow rates. The change from a (110) to a (101) growth direction corresponds with higher OER activity. Nanoplatelet IrOx films are therefore found to expose active sites preferable for the OER, and when combined with their antireflective properties these surfaces are promising for solar water-splitting applications.

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