Short O-O separation in layered oxide Na<sub>0.67</sub>CoO<sub>2</sub> enables an ultrafast oxygen evolution reaction.
basic_science · Level V
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- Record sourced from PubMed, PMID 31685612.
- Also identified by DOI 10.1073/pnas.1901046116 and PMC identifier 6876228.
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Abstract
The layered oxide Na<sub>0.67</sub>CoO<sub>2</sub> with Na<sup>+</sup> occupying trigonal prismatic sites between CoO<sub>2</sub> layers exhibits a remarkably high room temperature oxygen evolution reaction (OER) activity in alkaline solution. The high activity is attributed to an unusually short O-O separation that favors formation of peroxide ions by O<sup>-</sup>-O<sup>-</sup> interactions followed by O<sub>2</sub> evolution in preference to the conventional route through surface O-OH<sup>-</sup> species. The dependence of the onset potential on the pH of the alkaline solution was found to be consistent with the loss of H<sup>+</sup> ions from the surface oxygen to provide surface O<sup>-</sup> that may either be attacked by solution OH<sup>-</sup> or react with another O<sup>-</sup>; a short O-O separation favors the latter route. The role of a strong hybridization of the O-2<i>p</i> and low-spin Co<sup>III</sup>/Co<sup>IV</sup> π-bonding <i>d</i> states is also important; the OER on other Co<sup>III</sup>/Co<sup>IV</sup> oxides is compared with that on Na<sub>0.67</sub>CoO<sub>2</sub> as well as that on IrO<sub>2</sub>.