C. Yang (Byon Initiative Research Unit, RIKEN, Japan), R. A. Wong (RIKEN, Tokyo Institute of Technology), A. Dutta, M. O (RIKEN), M. Hong (Byon Initiative Research Unit, RIKEN, Japan), K. Yamanaka (SR center, Ritsumeikan University, Shiga 525-8577, Japan), T. Ohta (Ritsumeikan University), and H. R. Byon (RIKEN)
Despite high theoretical capacity, a Li-O
2 cell has suffered from huge oxidation potential polarization on carbon-based positive electrode for charge (>4.2 V vs. Li/Li
+), due to sluggish decomposition of non-conductive discharge product, lithium peroxide (Li
2O
2 ↔ 2Li
+ + O
2 + 2e
-) [1]. Such high potential triggers side reactions such as degradation of electrolyte and carbonaceous electrode, which results in poor cycle-ability [1]. To mitigate this problem during oxygen evolution reaction (OER), solid-state metal or metal oxide nanoparticles (indicated as promoters), which have been widely employed as catalysts in aqueous media, were introduced to the electrode [2]. However, the specific role of promoters in the Li-O
2 battery is little known due to complication from accompanying parasitic side reactions [3]. In addition, reasonable comparison of promoters’ activities is not feasible under different performance conditions when various reports were referred [2]. Therefore, to gain a reasonable assessment of their activities in the Li-O
2 cell and an understanding of the promoters’ role, it is necessary to examine Li-O
2 cells with these promoters under the same condition and analyze their reaction processes in detail. Here I present diagnosis of the true role of promoters, representative of platinum (Pt), gold (Au), palladium (Pd) and cobalt oxide (Co
3O
4), for OER in Li-O
2 cells. After preparation of comparable size and mass loading of promoters on carbon nanotube (CNT) electrode, the Li-O
2 cells containing these promoter/CNT combinations were examined using galvanostatic mode under the same operating conditions. The promoter/CNT electrodes show reasonably lower charge potentials than the promoter-free electrode for the 1st charge. Through in situ gas analysis of online electrochemical mass spectroscopy (OEMS) and ex situ chemical analysis of X-ray near-edge fine structure (XANES) spectroscopy, the evolved gas amount and remaining product after charge could be correlated, which accounted for the true reaction occurring for each promoter.
References
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[2] (a) Y. –C. Lu, H. A. Gasteiger and Y. Shao-Horn, J. Am. Chem. Soc., 2011, 133, 19048-19051; (b) Z. Peng, S. A. Freunberger, Y. Chen and P. G. Bruce, Science, 2012, 337, 563-566; (c) F. Li, D. –M. Tang, Y. Chen, D. Golberg, H. Kitaura, T. Zhang, A. Yamada and H. Zhou, Nano Lett., 2013, 13, 4702-4707; (d) R. Black, J.-H. Lee, B. Adams, C. A. Mims and L. F. Nazar, Angew. Chem. Int. Ed., 2013, 52, 392–396;
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