The high theoretical energy density

The high theoretical energy density of lithium−oxygen batteries brings
the promise of higher performance than existing batteries, but several technological
problems must be addressed before actual applications are made possible. Among the
difficulties to be faced is the slow oxygen reduction reaction (ORR), which requires a
suitable choice of catalysts and electrolytic solution. This can only be achieved if the
kinetics and mechanism of this reaction are known in detail. In this study, we
determined the rate constants for each elementary step of ORR for a platinum electrode
in 0.1 mol·L−1 LiClO4/1,2-dimethoxyethane (DME), using a kinetic model in the
frequency domain. We found that the energy storage capacity of lithium−air batteries
can be increased by converting a large amount of lithium superoxide into lithium
peroxide during the electrochemical step in comparison with chemical disproportionation.
The mechanisms for ORR were supported by data from an electrochemical quartz
crystal microbalance (EQCM): ORR could be distinguished from parasitic reactions
induced by solvent degradation, and agglomerates of LixO2 (1 ≤ x ≤ 2) were adsorbed on the electrode. The rate-limiting step
for ORR was the electron transfer to the oxygen molecules strongly adsorbed onto platinum sites, particularly as a large amount
of reaction product (Li2O2) adsorbed onto the electrode. Even though Pt sheets are likely to be impracticable for real
applications due to their low surface area, they were useful in making it possible to determine the kinetics of ORR steps. This can
now be employed to devise more involved electrodes, such as those containing dispersed Pt nanoparticles.