Insights into Electrochemical Oxidation of NaO2 in Na–O2 Batteries via Rotating Ring Disk and Spectroscopic Measurements

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• 作者：Robert Morasch ; David G. Kwabi ; Michal Tulodziecki ; Marcel RischShiyu Zhang ; Yang Shao-Horn
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2017
• 出版时间：February 8, 2017
• 年：2017
• 卷：9
• 期：5
• 页码：4374-4381
• 全文大小：497K
• ISSN：1944-8252

文摘

O₂ reduction in aprotic Na–O₂ batteries results in the formation of NaO₂, which can be oxidized at small overpotentials (<200 mV) on charge. In this study, we investigated the NaO₂ oxidation mechanism using rotating ring disk electrode (RRDE) measurements of Na−O₂ reaction products and by tracking the morphological evolution of the NaO₂ discharge product at different states of charge using scanning electron microscopy (SEM). The results show that negligible soluble species are formed during NaO₂ oxidation, and that the oxidation occurs predominantly via charge transfer at the interface between NaO₂ and carbon electrode fibers rather than uniformly from all NaO₂ surfaces. X-ray absorption near edge structure (XANES), and X-ray photoelectron spectroscopy (XPS) measurements show that the band gap of NaO₂ is smaller than that of Li₂O₂ formed in Li–O₂ batteries, in which charging overpotentials are much higher (∼1000 mV). These results emphasize the importance of discharge product electronic structure for rationalizing metal–air battery mechanisms and performance.