Breaking Long-Range Order in Iridium Oxide by Alkali Ion for Efficient Water Oxidation
Journal
Journal of the American Chemical Society
Journal Volume
141
Journal Issue
7
Pages
3014-3023
Date Issued
2019
Author(s)
Abstract
Oxygen electrochemistry plays a critical role in clean energy technologies such as fuel cells and electrolyzers, but the oxygen evolution reaction (OER) severely restricts the efficiency of these devices due to its slow kinetics. Here, we show that via incorporation of lithium ion into iridium oxide, the thus obtained amorphous iridium oxide (Li-IrOx) demonstrates outstanding water oxidation activity with an OER current density of 10 mA/cm2 at 270 mV overpotential for 10 h of continuous operation in acidic electrolyte. DFT calculations show that lithium incorporation into iridium oxide is able to lower the activation barrier for OER. X-ray absorption characterizations indicate that both amorphous Li-IrOx and rutile IrO2 own similar [IrO6] octahedron units but have different [IrO6] octahedron connection modes. Oxidation of iridium to higher oxidation states along with shrinkage in the Ir-O bond was observed by in situ X-ray absorption spectroscopy on amorphous Li-IrOx, but not on rutile IrO2 under OER operando conditions. The much more "flexible" disordered [IrO6] octahedrons with higher oxidation states in amorphous Li-IrOx as compared to the periodically interconnected "rigid" [IrO6] octahedrons in crystalline IrO2 are able to act as more electrophilic centers and thus effectively promote the fast turnover of water oxidation. © 2019 American Chemical Society.
SDGs
Other Subjects
Electrolytes; Fuel cells; Lithium compounds; Oxidation; Oxide minerals; Oxygen; Reaction kinetics; Titanium dioxide; X ray absorption spectroscopy; Acidic electrolytes; Activation barriers; Clean energy technology; Continuous operation; In-situ X-ray absorption spectroscopy; Long range orders; Oxidation state; Oxygen evolution reaction; Iridium compounds; alkali; electrolyte; iridium; iridium oxide; lithium ion; oxide; unclassified drug; water; Article; chemical bond; chemical reaction; chemical structure; crystal structure; density functional theory; electrochemical analysis; oxidation; oxygen evolution; X ray absorption spectroscopy
Type
journal article