Despite high theoretical capacity, a Li-O2
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 (Li2
) . Such high potential triggers side reactions such as degradation of electrolyte and carbonaceous electrode, which results in poor cycle-ability . 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 . However, the specific role of promoters in the Li-O2
battery is little known due to complication from accompanying parasitic side reactions . In addition, reasonable comparison of promoters’ activities is not feasible under different performance conditions when various reports were referred . Therefore, to gain a reasonable assessment of their activities in the Li-O2
cell and an understanding of the promoters’ role, it is necessary to examine Li-O2
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 (Co3
), for OER in Li-O2
cells. After preparation of comparable size and mass loading of promoters on carbon nanotube (CNT) electrode, the Li-O2
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.
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